BR112019013389B1 - VARIABLE PRESSURE INVENTORY CONTROL METHODS OF A CLOSED CYCLE SYSTEM WITH A HIGH PRESSURE TANK AND AN INTERMEDIATE PRESSURE TANK - Google Patents

Abstract

Systems and methods for variable pressure inventory control of a closed thermodynamic cycle power generation system or energy storage system, such as a Brayton reversible cycle system, with at least one high pressure tank and one intermediate pressure tank are disclosed. System operating parameters, such as working fluid pressure, turbine torque, turbine RPM, torque generator, generator RPM, and current, voltage, phase, frequency, and/or amount of electrical energy generated and/or distributed by the generator can be the basis for controlling an amount of working fluid circulating through a closed-loop fluid path of the system.

Description

CROSS REFERENCE TO RELATED ORDER

[001] This application claims priority to US Patent Application No. 15/392,927, filed on December 28, 2016.

FUNDAMENTALS

[002] In a heat engine or heat pump, a heat exchanger can be employed to transfer heat between a thermal storage material and a working fluid for use with turbomachinery. The heat engine can be reversible, that is, it is also a heat pump, and the working fluid and heat exchanger can be used to transfer heat or cold to a plurality of thermal reserves. Thermal energy within a given system can be stored in a variety of forms and in a variety of containers, including pressure vessels and/or insulated containers.

SUMMARY

[003] A closed thermodynamic cycle power generation system or energy storage system, such as a reversible Brayton cycle system, may include at least one working fluid circulated through a closed cycle fluid path including at least least two heat exchangers, a turbine and a compressor. In some systems, one or more recuperative heat exchangers may also be included. At least two temperature reservoirs may contain thermal fluids that can be pumped through the heat exchangers, providing and/or extracting thermal energy from the working fluid. A motor/generator can be used to obtain work from the thermal energy in the system, preferably generating electricity from the mechanical energy received from the turbine.

[004] The system may further include a high pressure tank and an intermediate pressure tank and the fluid connections between the tanks and the closed cycle fluid path may be controlled to vary an amount of working fluid circulating through the path. of closed cycle fluid. Fluid connections can be controlled based on one or more system operating parameters. Beneficially, varying the amount of working fluid circulating through the closed-loop fluid path can be used to control system energy.

[005] Examples of methods may include in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and an exchanger cold-side heat, wherein the closed-loop fluid path comprises a high-pressure leg and a low-pressure leg; remove a first quantity of working fluid from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank such that the working fluid pressure in the high pressure decreases and the pressure of the working fluid in the high pressure tank increases; closing the first fluid connection when the working fluid pressure in the high pressure tank reaches a first threshold pressure value; and removing a second amount of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and an intermediate-pressure tank such that the pressure of the working fluid in the leg high pressure tank decreases and the pressure of the working fluid in the intermediate pressure tank increases.

[006] Examples of methods may include in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and an exchanger cold-side heat, wherein the closed-loop fluid path comprises a high-pressure leg and a low-pressure leg; remove a first quantity of working fluid from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank such that the working fluid pressure in the high pressure decreases and the pressure of the working fluid in the high pressure tank increases; closing the first fluid connection when the working fluid pressure reaches a first threshold pressure value; and removing a second amount of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and an intermediate-pressure tank such that the pressure of the working fluid in the leg high pressure tank decreases and the pressure of the working fluid in the intermediate pressure tank increases.

[007] Examples of methods may include in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and an exchanger cold-side heat, wherein the closed-loop fluid path comprises a high-pressure leg and a low-pressure leg; adding a first amount of working fluid to the closed-loop fluid path by opening a first fluid connection between the low pressure leg and an intermediate pressure tank, wherein the intermediate pressure tank contains working fluid at a pressure of storing greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the intermediate pressure tank decreases; closing the first fluid connection when the working fluid pressure in the intermediate pressure tank reaches a first threshold pressure value; and adding a second amount of working fluid to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg and a high-pressure tank, wherein the high-pressure tank contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the high pressure tank decreases.

[008] Examples of methods may include in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and an exchanger cold-side heat, wherein the closed-loop fluid path comprises a high-pressure leg and a low-pressure leg; adding a first amount of working fluid to the closed-loop fluid path by opening a first fluid connection between the low pressure leg and an intermediate pressure tank, wherein the intermediate pressure tank contains working fluid at a pressure of storing greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the intermediate pressure tank decreases; closing the first fluid connection when the working fluid pressure reaches a first threshold pressure value; and adding a second amount of working fluid to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg and a high-pressure tank, wherein the high-pressure tank contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the high pressure tank decreases.

[009] Example of non-transitory computer readable medium may include instructions stored thereon executable by a computing device to cause the computing device to perform functions, the functions include in a closed loop system, circulating a working fluid through of a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg; remove a first quantity of working fluid from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank such that the working fluid pressure in the high pressure decreases and the pressure of the working fluid in the high pressure tank increases; closing the first fluid connection when the working fluid pressure in the high pressure tank reaches a first threshold pressure value; and removing a second amount of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and an intermediate-pressure tank such that the pressure of the working fluid in the leg high pressure tank decreases and the pressure of the working fluid in the intermediate pressure tank increases.

[0010] Example of non-transitory computer readable medium may include instructions stored thereon executable by a computing device to cause the computing device to perform functions, the functions include in a closed loop system, circulating a working fluid through of a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg; remove a first quantity of working fluid from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank such that the working fluid pressure in the high pressure decreases and the pressure of the working fluid in the high pressure tank increases; closing the first fluid connection when the working fluid pressure reaches a first threshold pressure value; and removing a second amount of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and an intermediate-pressure tank such that the pressure of the working fluid in the leg high pressure tank decreases and the pressure of the working fluid in the intermediate pressure tank increases.

[0011] Example of non-transitory computer readable medium may include instructions stored thereon executable by a computing device to cause the computing device to perform functions, the functions include in a closed loop system, circulating a working fluid through of a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg; adding a first amount of working fluid to the closed-loop fluid path by opening a first fluid connection between the low pressure leg and an intermediate pressure tank, wherein the intermediate pressure tank contains working fluid at a pressure of storing greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the intermediate pressure tank decreases; closing the first fluid connection when the working fluid pressure in the intermediate pressure tank reaches a first threshold pressure value; and adding a second amount of working fluid to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg and a high-pressure tank, wherein the high-pressure tank contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the high pressure tank decreases.

[0012] Example of non-transitory computer readable medium may include instructions stored thereon executable by a computing device to cause the computing device to perform functions, the functions include in a closed loop system, circulating a working fluid through of a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg; adding a first amount of working fluid to the closed-loop fluid path by opening a first fluid connection between the low pressure leg and an intermediate pressure tank, wherein the intermediate pressure tank contains working fluid at a pressure of storing greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the intermediate pressure tank decreases; closing the first fluid connection when the working fluid pressure reaches a first threshold pressure value; and adding a second amount of working fluid to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg and a high-pressure tank, wherein the high-pressure tank contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the high pressure tank decreases.

[0013] Example systems may include in a closed cycle system, means for circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold-side heat exchanger, wherein the closed-loop fluid path comprises a high-pressure leg and a low-pressure leg; means for removing a first quantity of working fluid from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank such that the pressure of the working fluid in the high pressure leg decreases and the working fluid pressure in the high pressure tank increases; means for closing the first fluid connection when the working fluid pressure in the high pressure tank reaches a first threshold pressure value; and means for removing a second quantity of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and an intermediate pressure tank such that the pressure of the working fluid in the high pressure leg it decreases and working fluid pressure in the intermediate pressure tank increases.

[0014] Exemplary systems may include in a closed cycle system means for circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg; means for removing a first quantity of working fluid from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank such that the pressure of the working fluid in the high pressure leg decreases and the working fluid pressure in the high pressure tank increases; means for closing the first fluid connection when the working fluid pressure reaches a first threshold pressure value; and means for removing a second quantity of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and an intermediate pressure tank such that the pressure of the working fluid in the high pressure leg it decreases and working fluid pressure in the intermediate pressure tank increases.

[0015] Exemplary systems may include in a closed cycle system means for circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg; means for adding a first amount of working fluid to the closed-loop fluid path by opening a first fluid connection between the low pressure leg and an intermediate pressure tank, wherein the intermediate pressure tank contains working fluid at a storage pressure greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the intermediate pressure tank decreases; means for closing the first fluid connection when the working fluid pressure in the intermediate pressure tank reaches a first threshold pressure value; and means for adding a second amount of working fluid to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg and a high-pressure tank, wherein the high-pressure tank contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the high pressure tank decreases.

[0016] Example systems may include in a closed cycle system means for circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg; means for adding a first amount of working fluid to the closed-loop fluid path by opening a first fluid connection between the low pressure leg and an intermediate pressure tank, wherein the intermediate pressure tank contains working fluid at a storage pressure greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the intermediate pressure tank decreases; means for closing the first fluid connection when the working fluid pressure reaches a first threshold pressure value; and means for adding a second amount of working fluid to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg and a high-pressure tank, wherein the high-pressure tank contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the high pressure tank decreases.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 schematically illustrates the operation of a pumped thermal electrical storage system.

[0018] Figure 2 is a schematic flowchart of working fluid and heat storage medium of a pumped thermal system in a load/heat pump mode.

[0019] Figure 3 is a schematic flowchart of working fluid and heat storage medium of a pumped thermal system in a discharge/heat engine mode.

[0020] Figure 4 is a schematic diagram of pressure and temperature of the working fluid as it undergoes the load cycle in Figure 2.

[0021] Figure 5 is a schematic diagram of pressure and temperature of the working fluid as it undergoes the discharge cycle in Figure 3.

[0022] Figure 6 is a schematic perspective view of a working fluid system closed in the pumped thermal system in Figures 2-3.

[0023] Figure 7 is a schematic perspective view of the pumped thermal system in Figures 2-3 with hot side and cold side storage tanks and a closed cycle working fluid system.

[0024] Figure 8 shows a heat storage load cycle for a molten salt/water system nc = 0.9 and nt = 0.95. The dashed lines correspond to nc = nt = 1.

[0025] Figure 9 shows a heat storage discharge (extraction) cycle for the molten salt/water system in Figure 8 with nc = 0.9 and nt = 0.95. The dashed lines correspond to nc = nt = 1.

[0026] Figure 10 shows a heat storage cycle in a pumped thermal system with variable compression rates between charge and discharge cycles.

[0027] Figure 11 shows the round-trip efficiency contours for a water/salt system. The symbols © and © represent an approximate range of the adiabatic efficiency values of current turbomachinery. The dashed arrows represent the direction of efficiency increase.

[0028] Figure 12 shows round-trip efficiency contours for a colder salt/storage system. The symbols © and © represent an approximate range of the adiabatic efficiency values of current turbomachinery.

[0029] Figure 13 is a schematic flowchart of working fluid and heat storage medium of a pumped thermal system with a gas-gas heat exchanger for the working fluid in a load/heat pump mode.

[0030] Figure 14 is a schematic flowchart of working fluid and heat storage medium from a pumped thermal system with a gas-gas heat exchanger to the working fluid in a discharge/heat engine mode.

[0031] Figure 15 is a schematic flowchart of working fluid and heat storage medium from a pumped thermal system with a gas-gas heat exchanger to the working fluid in a charge/heat pump mode with heat rejection. indirect heat to the environment.

[0032] Figure 16 is a schematic flowchart of working fluid and heat storage medium from a pumped thermal system with a gas-gas heat exchanger to the working fluid in a discharge/heat engine mode with heat rejection. indirect heat to the environment.

[0033] Figure 17 shows a heat storage charge cycle for a storage system with a gas-to-gas heat exchanger, a cold-side storage medium capable of descending to temperatures significantly below ambient temperature and nc = 0 .9 and nt = 0.95.

[0034] Figure 18 shows a heat storage discharge cycle for a storage system with a gas-to-gas heat exchanger, a cold-side storage medium capable of descending to temperatures significantly below ambient temperature and nc = 0 .9 and nt = 0.95.

[0035] Figure 19 is a schematic flowchart of hot side recharging in a pumped heat cycle in solar mode with heating of a solar salt by solar energy alone.

[0036] Figure 20 is a schematic flowchart of a discharge cycle of a pumped thermal system with heat rejection to the environment.

[0037] Figure 21 is a schematic flowchart of a discharge cycle of a pumped thermal system with heat rejection for an intermediate fluid circulated in a thermal bath at room temperature.

[0038] Figures 22 and 23 are pumped thermal systems with separate compressor/turbine pairs for charging and discharging modes.

[0039] Figures 24 and 25 show pumped thermal systems configured in a combustion heat input generation mode.

[0040] Figure 26 is a schematic flowchart of hot side recharging in a pumped heat cycle through heating by a combustion heat source or a waste heat source.

[0041] Figure 27 shows an example of a pumped thermal system with pressure-regulated power control.

[0042] Figure 28 shows an example of a thermal system pumped with an encapsulated pressure generator.

[0043] Figure 29 is an example of variable stators in a compressor/turbine pair.

[0044] Figure 30 shows a computer system that is programmed to implement various methods and/or regulate various systems of the present disclosure.

[0045] Figure 31 illustrates a variable pressure inventory control system, according to an example embodiment.

[0046] Figure 32 illustrates a variable pressure inventory control system, according to an example embodiment.

[0047] Figure 33 illustrates a variable pressure inventory control method, according to an example embodiment.

[0048] Figure 34 illustrates a variable pressure inventory control method, according to an example embodiment.

[0049] Figure 35 illustrates a variable pressure inventory control method, according to an example embodiment.

[0050] Figure 36 illustrates a variable pressure inventory control method, according to an example embodiment.

DETAILED DESCRIPTION

[0051] Although various embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed. It should be understood that different aspects of the invention can be appreciated individually, collectively or in combination with each other.

[0052] It should be understood that the terminology used here is used for the purpose of describing specific embodiments, and is not intended to limit the scope of the present invention. It should be noted that, as used here, the singular forms of “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Furthermore, unless otherwise indicated, all technical and scientific terms used herein have the same meaning as is normally understood by one skilled in the art to which this invention belongs.

[0053] Although preferred embodiments of the present invention are shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in the practice of the invention. The following claims are intended to define the scope of the invention and the methods and structures within the scope of these claims and their equivalents are hereby encompassed.

[0054] The term “reversible”, as used herein, generally refers to a process or operation that can be reversed through infinitesimal changes in some property of the process or operation without substantial production of entropy (e.g., energy dissipation). A reversible process can be approximated by a process that is in thermodynamic equilibrium. In some examples, in a reversible process, the direction of energy flow is reversible. Alternatively, or in addition, the general direction of operation of a reversible process (e.g., the direction of fluid flow) may be reversed, such as from clockwise to counterclockwise, and vice versa.

[0055] The term “sequence”, as used here, generally refers to elements (e.g., unit operations) in order. Such order may refer to process order, such as the order in which a fluid flows from one element to another. In one example, a compressor, heat storage unit and turbine in sequence include the compressor upstream of the heat exchange unit, and the heat exchange unit upstream of the turbine. In this case, a fluid can flow from the compressor to the heat exchange unit and from the heat exchange unit to the turbine. A fluid that flows through unit operations sequentially can flow through unit operations sequentially. A sequence of elements may include one or more intervening elements. For example, a system comprising a compressor, heat storage unit and turbine in sequence may include an auxiliary tank between the compressor and the heat storage unit. A sequence of elements can be cyclic.

I. Overview

[0056] An example of a heat engine in which variable pressure inventory control methods and systems can be implemented is a closed thermodynamic cycle power generation system or energy storage system, such as a reversible Brayton cycle system . The system may be a closed reversible system and may include a recuperative heat exchanger. A Brayton cycle system may use a generator/engine connected to a turbine and a compressor that act on a working fluid circulating in the system. Examples of working fluids include air, argon, carbon dioxide or gas mixtures. A Brayton cycle system can have a hot side and/or a cold side. Each side may include a heat exchanger coupled to one or more cold storage containers and/or one or more hot storage containers. Preferably, the heat exchangers can be arranged as counterflow heat exchangers for greater thermal efficiency. Liquid thermal storage media may be used and may include, for example, liquids that are stable at high temperatures, such as molten nitrate salt or solar salt, or liquids that are stable at low temperatures, such as glycols or alkanes such as hexane. For an example molten salt and hexane system, the hot-side molten salt may include hot storage at approximately 565°C and cold storage at approximately 290°C and the cold-side hexane may include hot storage at approximately 35°C. °C and cold storage at approximately -60 °C.

[0057] In the Brayton cycle system, the working fluid may circulate through a closed cycle fluid path and the closed cycle fluid path may include a high pressure leg and a low pressure leg. An exemplary embodiment of variable pressure inventory control may involve removing a first quantity of working fluid from a closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank, such so that the working fluid pressure in the closed cycle fluid path decreases and the pressure in the high pressure tank increases; close the first fluid connection; and removing a second quantity of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and an intermediate pressure tank such that the pressure of the working fluid in the path of closed cycle fluid decreases and the pressure in the intermediate pressure tank increases.

[0058] Another example of variable pressure inventory control embodiment may involve adding a first quantity of working fluid to the closed cycle fluid path by opening a first fluid connection between the low pressure leg and a pressure tank. intermediate, such that the pressure of the working fluid in the closed cycle fluid path increases and the pressure in the intermediate pressure tank decreases; close the first fluid connection; and adding a second amount of working fluid to the closed cycle by opening a second fluid connection between the closed cycle fluid path and a high pressure tank such that the pressure of the working fluid in the closed cycle fluid path closed increases and the pressure in the high pressure tank decreases.

[0059] The fluid connections between the closed cycle fluid path and the tanks can be closed based on the pressure of the working fluid. In some embodiments, the first fluid connection between the high pressure leg and the high pressure tank may be closed when the working fluid pressure in the high pressure tank reaches a threshold pressure value. Furthermore, in some embodiments, the first fluid connection between the high pressure leg and the intermediate pressure tank may be closed when the pressure of the working fluid in the intermediate pressure tank reaches a threshold pressure value.

[0060] In some embodiments, the threshold pressure value related to closing the first fluid connection between the high pressure leg and the intermediate pressure tank may be different from the threshold pressure value related to closing the first fluid connection between the high pressure leg and the intermediate pressure tank.

II. Illustrative reversible heat engine A. Pumped thermal systems

[0061] The disclosure provides pumped thermal systems capable of storing electrical energy and/or heat and releasing energy (e.g., producing electricity) at a later time. The pumped thermal systems of the disclosure may include a heat engine and a heat pump (or chiller). In some cases, the heat engine can be operated in reverse as a heat pump. In some cases, the heat engine can be operated in reverse as a refrigerator. Any description of heat pump/heat engine systems or refrigerator/heat engine systems capable of reversing operation herein may also be applied to systems that include heat engine system(s), heat pump system(s), separate and/or reversible heat and/or refrigerator system(s). Furthermore, because heat pumps and refrigerators share the same operating principles (albeit with different purposes), any description of heat pump settings or operation here can also be applied to refrigerator settings or operation, and vice versa.

[0062] The systems of the present disclosure can operate as heat engines or heat pumps (or refrigerators). In some situations, disclosure systems may function alternately as heat engines and heat pumps. In some examples, a system may operate as a heat engine to generate energy and subsequently operate as a heat pump to store energy, or vice versa. Such systems can operate alternately and sequentially as heat engines and as heat pumps. In some cases, such systems operate reversibly or substantially reversibly as heat engines such as heat pumps.

[0063] Reference will now be made to the Figures, where like numerals refer to like parts throughout. It will be appreciated that the Figures and features therein are not necessarily drawn to scale.

[0064] Figure 1 schematically illustrates the operating principles of pumped thermal electrical storage using a heat pump/heat engine electricity storage system. Electricity can be stored in the form of thermal energy from two materials or media at different temperatures (e.g. thermal energy reservoirs comprising heat storage fluids or thermal storage media) using a combined heat pump/heat engine system . In a load or heat pump mode, the system may consume work to transfer heat from a cold material or medium to a hot material or medium, thereby decreasing the temperature (e.g., sensible energy) of the cold material and increasing the temperature (e.g., sensible energy) of the cold material or medium. i.e. sensible energy) of the hot material. In a discharge or heat engine mode, work can be produced by the system by transferring heat from the hot material to the cold material, thereby decreasing the temperature (i.e., sensible energy) of the hot material and increasing the temperature (i.e. , sensible energy) of the cold material. The system can be configured to ensure that the work produced by the system on discharge is a favorable fraction of the energy consumed under load. The system can be configured to achieve high round-trip efficiency, defined here as the work produced by the system at discharge divided by the work consumed by the system under load. Furthermore, the system can be configured to achieve high round-trip efficiency using components of a desired cost (e.g., a reasonably low cost). Arrows H and W in Figure 1 represent directions of heat flow and work, respectively.

[0065] Heat engines, heat pumps, and refrigerators of the disclosure may involve a working fluid to and from which heat is transferred during a thermodynamic cycle. Disclosure's heat engines, heat pumps, and refrigerators can operate in a closed cycle. Closed cycles allow, for example, a wider selection of working fluids, operation at high cold-side pressures, operation at lower cold-side temperatures, greater efficiency and a lower risk of turbine damage. One or more aspects of the disclosure described in relation to systems with working fluids subjected to closed cycles may also be applied to systems with working fluids subjected to open cycles.

[0066] In one example, heat engines may operate on a Brayton cycle and heat pumps/refrigerators may operate on a reverse Brayton cycle (also known as a gas refrigeration cycle). Other examples of thermodynamic cycles that the working fluid may undergo or approximate include the Rankine cycle, the ideal vapor compression refrigeration cycle, the Stirling cycle, the Ericsson cycle, or any other cycle advantageously employed in conjunction with temperature exchange. heat with disclosure heat storage fluids.

[0067] The working fluid can undergo a thermodynamic cycle operating at one, two or more pressure levels. For example, the working fluid may operate in a closed cycle between a low pressure limit on a cold side of the system and a high pressure limit on a hot side of the system. In some implementations, a low pressure limit of about 10 atmospheres (atm) (1.01325 MPa) or greater may be used. In some cases, the low pressure limit may be at least about 1 atm (0.101325 MPa), at least about 2 atm (0.20265 MPa), at least about 5 atm (0.506625 MPa), at least about 10 atm (1.01325 MPa), at least about 15 atm (1.51988 MPa), at least about 20 atm (2.0265 MPa), at least about 30 atm (3.03975 MPa ), at least about 40 atm (4.053 MPa), at least about 60 atm (6.0795 MPa), at least about 80 atm (8.106 MPa), at least about 100 atm (10.1325 MPa), at least about 120 atm (12.159 MPa), at least about 160 atm (16.212 MPa), or at least about 200 atm (20.265 MPa), 500 atm (50.6625 MPa), 1000 atm (101.325 MPa), or more. In some cases, a low subatmospheric pressure limit may be used. For example, the low pressure limit may be less than about 0.1 atm (0.0101325 MPa), less than about 0.2 atm (0.020265 MPa), less than about 0.5 atm (0 .0506625 MPa) or less than about 1 atm (0.101325 MPa). In some cases, the low pressure limit may be about 1 atmosphere (atm) (0.101325 MPa). In the case of a working fluid operating in an open cycle, the low pressure limit may be about 1 atm (0.101325 MPa) or equal to ambient pressure.

[0068] In some cases, the low pressure limit value may be selected based on the desired energy output and/or energy input requirements of the thermodynamic cycle. For example, a pumped thermal system with a low pressure limit of about 10 atm (1.01325 MPa) may be capable of providing power output comparable to an industrial gas turbine with ambient air input (1 atm) ( 0.101325 MPa). The value of the low pressure limit may also be subject to cost/safety tradeoffs. Furthermore, the value of the low pressure limit may be limited by the value of the high pressure limit, the hot side and heat storage medium operating ranges (e.g., pressure and temperature ranges over which the heat storage media heat storage are stable), pressure rates and operating conditions (e.g. operating limits, optimum operating conditions, pressure drop) achieved by turbomachinery and/or other system components, or any combination thereof. The high pressure limit can be determined according to these system constraints. In some cases, higher values of the high pressure limit can lead to better heat transfer between the working fluid and the hot-side storage medium.

[0069] Working fluids used in pumped thermal systems may include air, argon, other noble gases, carbon dioxide, hydrogen, oxygen, or any combination thereof, and/or other fluids in a gaseous, liquid, critical, or critical state. supercritical (e.g. supercritical CO2). The working fluid can be a gas or a low viscosity liquid (e.g. viscosity below about 500x10-6 Poise at 1 atm), satisfying the requirement that the flow be continuous. In some implementations, a gas with a high specific heat rate can be used to achieve greater cycle efficiency than a gas with a low specific heat rate. For example, argon (e.g. specific heat ratio of about 1.66) can be used to replace air (e.g. specific heat ratio of about 1.4). In some cases, the working fluid may be a mixture of one, two, three or more fluids. In one example, helium (with high thermal conductivity and high specific heat) can be added to the working fluid (e.g., argon) to improve heat transfer rates in heat exchangers.

[0070] Here, pumped thermal systems may utilize heat storage media or materials, such as one or more heat storage fluids. The heat storage media can be gases or low viscosity liquids, satisfying the requirement that the flow be continuous. Systems may utilize a first heat storage medium on a hot side of the system (“hot side thermal storage (HTS) medium” or “HTS” here) and a second heat storage medium on a cold side of the system. (“cold-side thermal storage (CTS) medium” or “CTS” here). Thermal storage media (e.g. low viscosity liquids) can have high heat capacities per unit volume (e.g. heat capacities above 1400 Joule (kilogram Kelvin)-1) and high thermal conductivities (e.g. thermal conductivity above 0.7 Watt Kelvin)-1). In some implementations, several different thermal storage media (also "heat storage medium" here) either hot side, cold side, or hot side and cold side may be used.

[0071] The operating temperatures of the hot-side thermal storage medium may be in the net range of the hot-side thermal storage medium, and the operating temperatures of the cold-side thermal storage medium may be in the net range of the hot-side thermal storage medium. cold side thermal storage. In some examples, liquids may allow faster exchange of large amounts of heat by convective counterflow than solids or gases. Thus, in some cases, liquid HTS and CTS media may be used with advantage. Pumped thermal systems using thermal storage means here can advantageously provide a safe, non-toxic and geography-independent energy storage alternative (e.g. electricity).

[0072] In some implementations, the hot-side thermal storage medium may be a molten salt or a mixture of molten salts. Any salt or salt mixture that is liquid over the operating temperature range of the hot-side thermal storage medium may be employed. Molten salts can provide numerous advantages as a means of storing thermal energy, such as low vapor pressure, lack of toxicity, chemical stability, low chemical reactivity with typical steels (e.g., melting point below the creep temperature of steels, low corrosivity, low capacity for dissolving iron and nickel) and low cost. In one example, HTS is a mixture of sodium nitrate and potassium nitrate. In some examples, HTS is a eutectic mixture of sodium nitrate and potassium nitrate. In some examples, HTS is a mixture of sodium nitrate and potassium nitrate with a lower melting point than the individual constituents, a higher boiling point than the individual constituents, or a combination thereof. Other examples include potassium nitrate, calcium nitrate, sodium nitrate, sodium nitrite, lithium nitrate, mineral oil, or any combination thereof. Additional examples include any gaseous (including compressed gases), liquid, or solid (e.g., powdered solids) media with adequate (e.g., high) thermal storage capabilities and/or capable of achieving adequate heat transfer rates (e.g., , high) with the working fluid. For example, a mixture of 60% sodium nitrate and 40% potassium nitrate (also known as solar salt in some situations) may have a heat capacity of approximately 1500 Joule (mol Kelvin)-1 and a thermal conductivity of approximately 0.75 Watt (meter Kelvin)-1 within a temperature range of interest. The hot-side thermal storage medium can be operated in a temperature range that structural steels can handle.

[0073] In some cases, liquid water at temperatures of about 0 °C to 100 °C (about 273 K-373 K) and a pressure of about 1 atm (0.101325 MPa) can be used as a medium cold side thermal storage. Due to a possible explosion hazard associated with the presence of steam at or near the boiling point of water, the operating temperature may be maintained below 100°C or less while maintaining an operating pressure of 1 atm (0.101325 MPa ) (without pressurization). In some cases, the operating temperature range of the cold-side thermal storage medium can be extended (e.g., to -30°C to 100°C at 1 atm) (0.101325 MPa) using a mixture of water and a or more antifreeze compounds (e.g. ethylene glycol, propylene glycol or glycerol).

[0074] As described in greater detail elsewhere in this document, improved storage efficiency can be achieved by increasing the temperature difference at which the system operates, for example, by utilizing a cold-side heat storage fluid capable of operating at lower temperatures. In some examples, the cold-side thermal storage medium may comprise hydrocarbons such as, for example, alkanes (e.g., hexane or heptane), alkenes, alkynes, aldehydes, ketones, carboxylic acids (e.g., HCOOH), ethers , cycloalkanes, aromatic hydrocarbons, alcohols (e.g., butanol), other type(s) of hydrocarbon molecules, or any combinations thereof. In some cases, the cold-side thermal storage medium may be hexane (e.g., n-hexane). Hexane has a wide liquid range and can remain fluid (i.e. liquid) throughout its liquid range (-94°C to 68°C at 1 atm (0.101325 MPa)). Low temperature properties of hexanes are aided by their immiscibility with water. Other liquids, such as, for example, ethanol or methanol, may become viscous at the low temperature ends of their liquid ranges due to pre-crystallization of water absorbed from the air. In some cases, the cold-side thermal storage medium may be heptane (e.g., n-heptane). Heptane has a wide liquid range and can remain fluid (i.e., liquid) throughout its liquid range (-91°C to 98°C at 1 atm (0.101325 MPa)). Heptane's low temperature properties are aided by its immiscibility with water. At even lower temperatures, other heat storage media can be used, such as isohexane (2-methylpentane). In some examples, cryogenic liquids with boiling points below -150 °C (123 K) or about -180 °C (93.15 K) may be used as a cold-side thermal storage medium (e.g., propane, butane, pentane, nitrogen, helium, neon, argon and krypton, air, hydrogen, methane or liquefied natural gas). In some implementations, the choice of cold-side thermal storage medium may be limited by the choice of working fluid. For example, when a gaseous working fluid is used, a liquid cold-side thermal storage means having a liquid temperature range at least partially or substantially above the boiling point of the working fluid may be required.

[0075] In some cases, the operating temperature range of the CTS and/or HTS means can be changed by pressurizing (i.e., increasing pressure) or evacuating (i.e., decreasing pressure) the tanks and thereby changing the temperature at which storage media undergo phase transitions (e.g., going from liquid to solid, or from liquid to gas).

[0076] In some cases, the hot-side and cold-side heat storage fluids of pumped thermal systems are in a liquid state in at least a portion of the operating temperature range of the energy storage device. The hot-side heat storage fluid can be liquid within a certain temperature range. Likewise, the cold-side heat storage fluid can be liquid within a certain temperature range. Heat storage fluids can be heated, cooled, or maintained to reach a suitable operating temperature before, during, or after operation.

[0077] Pumped thermal systems of the disclosure can cycle between charged and discharged modes. In some examples, pumped thermal systems may be fully charged, partially charged or partially discharged, or fully discharged. In some cases, cold-side heat storage can be charged (also "recharged" here) independently of hot-side heat storage. Furthermore, in some implementations, charging (or part thereof) and discharging (or part thereof) may occur simultaneously. For example, a first portion of a hot-side heat storage may be recharged while a second portion of the hot-side heat storage together with a cold-side heat storage are being discharged.

[0078] Pumped thermal systems may be capable of storing energy for a certain period of time. In some cases, a given amount of energy may be stored for at least about 1 second, at least about 30 seconds, at least about 1 minute, at least about 5 minutes, at least about 30 minutes, at least about 1 hour, at least about 2 hours, at least about 3 hours, at least about 4 hours, at least about 5 hours, at least about 6 hours, at least about 7 hours, at least about 8 hours, at least about 9 hours 10 hours, at least about 12 hours at least about 14 hours, at least about 16 hours, at least about 18 hours, at least about 20 hours, at least about 22 hours, at least about 24 hours (1 day), at least about 2 days, at least about 4 days, at least about 6 days, at least about 8 days, at least about 10 days, 20 days, 30 days, 60 days, 100 days, 1 year or more.

[0079] The pumped thermal systems of the disclosure may be capable of storing/receiving input from, and/or extracting/providing output of, a substantially large amount of energy and/or power for use with power generation systems (e.g., systems intermittent power generation systems such as wind or solar power), power distribution systems (e.g., electrical grid), and/or other loads or uses in grid-scale or stand-alone configurations. During a load mode of a pumped thermal system, electrical energy received from an external energy source (e.g., a wind energy system, a solar photovoltaic energy system, an electrical grid, etc.) can be used to operate the thermal system pumped in a heat pump mode (i.e. transferring heat from a low-temperature reservoir to a high-temperature reservoir, thus storing energy). During a pumped thermal system discharge mode, the system may supply electrical energy to an external power system or load (e.g., one or more electrical grids connected to one or more loads, a load such as a factory or a manufacturing process). energy intensive, etc.) operating in heat engine mode (i.e. transferring heat from a high temperature reservoir to a low temperature reservoir, thus extracting energy). As described herein, during charging and/or discharging, the system may receive or reject thermal energy, including, but not limited to, electromagnetic energy (e.g., solar radiation) and thermal energy (e.g., sensible energy from a medium heated by solar radiation, combustion heat, etc.).

[0080] In some implementations, the pumped thermal systems are synchronous to the grid. Synchronization can be achieved by combining the speed and frequency of a system's motors/generators and/or turbomachinery with the frequency of one or more grid networks with which the system exchanges energy. For example, a compressor and turbine may rotate at a certain fixed speed (e.g., 3600 revolutions per minute (rpm)) that is a multiple of the grid frequency (e.g., 60 hertz (Hz)). In some cases, this configuration can eliminate the need for additional power electronics. In some implementations, the turbomachinery and/or motors/generators are not synchronized to the grid. In such cases, frequency matching can be accomplished through the use of power electronics. In some implementations, the turbomachinery and/or motors/generators are not directly synchronous to the grid, but can be combined through the use of gears and/or a mechanical gearbox. As described in greater detail elsewhere, pumped thermal systems can also be rampable. Such capabilities could enable these grid-scale energy storage systems to operate as peaking power plants and/or as load after power plants. In some cases, the systems of the disclosure may be capable of operating as baseload power plants.

[0081] Pumped thermal systems can have a certain energy capacity. In some cases, the energy capacity during charging may differ from the energy capacity during discharge. For example, each system may have a charging and/or discharging capacity of less than 1 megawatt (MW), at least about 1 megawatt, at least about 2 MW, at least about 3 MW, at least about 4 MW, at least about 5 MW, at least about 6 MW, at least about 7 MW, at least about 8 MW, at least about 9 MW, at least about 10 MW, at least 20 MW, at least at least about 30 MW, at least about 40 MW, at least about 50 MW, at least about 75 MW, at least about 100 MW, at least about 200 MW, at least about 500 MW, at least 1 gigawatt (GW), at least about 2 GW, at least about 5 GW, at least about 10 GW, at least about 20 GW, at least about 30 GW, at least about 40 GW, at least about 50 GW , at least about 75 GW, at least about 100 GW, or more.

[0082] Pumped thermal systems can have a certain energy storage capacity. In one example, a pumped thermal system is configured as a 100 MW unit operating for 10 hours. In another example, a pumped thermal system is configured as a 1 GW plant operating for 12 hours. In some cases, the energy storage capacity may be less than 1 megawatt-hour (MWh), at least about 1 megawatt-hour, at least about 10 MWh, at least about 100 MWh, at least 1 gigawatt-hour (GWh) at least about 5 GWh, at least about 10 GWh, at least about 20 GWh, at least about 50 GWh, at least about 100 GWh, at least about 200 GWh, at least about 500 GWh, at least around 700 GWh, at least GWh or more.

[0083] In some cases, a given energy capacity can be obtained with a certain size, configuration and/or operating conditions of the heat engine/heat pump cycle. For example, size of turbomachinery, ducts, heat exchangers or other system components may correspond to a certain energy capacity.

[0084] In some implementations, a given energy storage capacity can be achieved with a certain size and/or number of hot-side thermal storage tanks and/or cold-side thermal storage tanks. For example, the heat engine/heat pump cycle may operate at a certain energy capacity for a certain period of time defined by the heat storage capacity of the system or plant. The number and/or heat storage capacity of hot side thermal storage tanks may be different from the number and/or heat storage capacity of cold side thermal storage tanks. The number of tanks may depend on the size of the individual tanks. The size of hot side storage tanks may differ from the size of cold side thermal storage tanks. In some cases, the hot-side thermal storage tanks, the hot-side heat exchanger, and the hot-side thermal storage medium may be referred to as a hot-side (thermal) heat storage unit. In some cases, the cold-side thermal storage tanks, the cold-side heat exchanger, and the cold-side thermal storage medium may be referred to as a cold-side (thermal) heat storage unit.

[0085] A pumped thermal storage facility may include any suitable number of hot-side storage tanks, such as at least about 2, at least about 4, at least about 10, at least about 50, at least about 100, at least about 500 about 1,000, at least about 5,000, at least about 10,000, and so on. In some examples, a pumped thermal storage facility includes 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200 , 300, 400, 500, 600, 700, 800, 900, 1,000 or more hot side tanks.

[0086] A pumped thermal storage facility may also include any suitable number of cold-side storage tanks, such as at least about 2, at least about 4, at least about 10, at least about 50, at least about at least about 100, at least about 500, at least about 1,000, at least about 5,000, at least about 10,000, and so on. In some examples, a pumped thermal storage facility includes 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200 , 300, 400, 500, 600, 700, 800, 900, 1,000 or more cold side tanks.

B. Pumped thermal storage cycles

[0087] One aspect of the disclosure relates to pumped thermal systems that operate in pumped thermal storage cycles. In some examples, cycles allow electricity to be stored as heat (for example, in the form of a temperature differential) and then converted back to electricity through the use of at least two turbomachinery components, a compressor and a turbine. The compressor consumes work and increases the temperature and pressure of a working fluid (WF). The turbine produces work and reduces the temperature and pressure of the working fluid. In some examples, more than one compressor and more than one turbine are used. In some cases, the system may include at least 1, at least 2, at least 3, at least 4, or at least 5 compressors. In some cases, the system may include at least 1, at least 2, at least 3, at least 4, or at least 5 turbines. Compressors can be arranged in series or in parallel. The turbines can be arranged in series or in parallel.

[0088] Figures 2 and 3 are schematic flowcharts of working fluid and heat storage medium of an exemplary pumped thermal system in a load/heat pump mode and in a discharge/heat engine mode, respectively. The system can be designed to simplify the explanation so that there are no losses (i.e., entropy generation) either in the turbomachinery or in the heat exchangers. The system may include a working fluid 20 (e.g., argon gas) flowing in a closed cycle between a compressor 1, a hot-side heat exchanger 2, a turbine 3, and a cold-side heat exchanger 4. Paths/ fluid flow directions for the working fluid 20 (e.g., a gas), a hot-side thermal storage medium (HTS) 21 (e.g., a low-viscosity liquid), and a cold-side thermal storage medium (CTS) 22 (e.g. a low viscosity liquid) are indicated by arrows.

[0089] Figures 4 and 5 are schematic diagrams of pressure and temperature of the working fluid 20 as it passes through the load cycles in Figures 2 and 3, respectively, once again simplified to the approximation of entropy-free generation. Normalized pressure is shown on the y-axis and temperature is shown on the x-axis. The direction of processes occurring during the cycles is indicated with arrows, and the individual processes occurring in compressor 1, hot-side CFX 2, turbine 3, and cold-side CFX 4 are indicated on the diagram with their respective numerals.

[0090] Heat exchangers 2 and 4 can be configured as counterflow heat exchangers (CFXs), where the working fluid flows in one direction and the substance with which it is exchanging heat is flowing in the opposite direction. In an ideal counterflow heat exchanger with correctly matched flows (i.e., balanced capacities or capacity flow rates), the temperatures of the working fluid and thermal storage medium are reversed (i.e., the counterflow heat exchanger may have unit effectiveness).

[0091] Counterflow heat exchangers 2 and 4 can be designed and/or operated to reduce entropy generation in the heat exchangers to negligible levels compared to entropy generation associated with other system components and/or processes (e.g. example, compressor and/or turbine entropy generation). In some cases, the system can be operated in such a way that the generation of entropy in the system is minimized. For example, the system can be operated in such a way that the generation of entropy associated with heat storage units is minimized. In some cases, a temperature difference between the fluid elements exchanging heat can be controlled during operation, such that the generation of entropy in the hot-side and cold-side heat storage units is minimized. In some cases, the entropy generated in the hot-side and cold-side heat storage units is insignificant when compared to the entropy generated by the compressor, the turbine, or both the compressor and the turbine. In some cases, entropy generation associated with heat transfer in heat exchangers 2 and 4 and/or entropy generation associated with the operation of the hot-side storage unit, the cold-side storage unit, or both storage units hot and cold side may be less than about 50%, less than about 25%, less than about 20%, less than about 15%, less than about 10%, less than about 5%, less to about 4%, less than about 3%, less than about 2%, or less than about 1% of the total entropy generated within the system (e.g., entropy generated by compressor 1, the side heat exchanger hot side 2, the turbine 3, the cold side heat exchanger 4 and/or other described components such as, for example, a recuperator). For example, entropy generation can be reduced or minimized if the two substances exchanging heat do so at a local temperature differential ΔT^0 (i.e., when the temperature difference between any two fluid elements that are in thermal contact next to the heat exchanger is small). In some examples, the temperature differential ΔT between any two fluid elements that are in close thermal contact may be less than about 300 Kelvin (K), less than about 200 K, less than about 100 K, less than about 75K, less than about 50K, less than about 40K, less than about 30K, less than about 20K, less than about 10K, less than about 5K, less than about 3 K, less than about 2 K, or less than about 1 K. In another example, the entropy generation associated with pressure drop can be reduced or minimized by proper design. In some examples, the heat exchange process may occur at constant or near-constant pressure. Alternatively, a non-negligible pressure drop may be experienced by the working fluid and/or one or more thermal storage means during passage through a heat exchanger. Pressure drop across heat exchangers can be controlled (e.g., reduced or minimized) through proper heat exchanger design. In some examples, the pressure drop across each heat exchanger may be less than about 20% of the inlet pressure, less than about 10% of the inlet pressure, less than about 5% of the inlet pressure, less than about about 3% of inlet pressure, less than about 2% of inlet pressure, less than about 1% of inlet pressure, less than about 0.5% of inlet pressure, less than about 0, 25% of inlet pressure or less than about 0.1% of inlet pressure.

[0092] Upon entering heat exchanger 2, the temperature of the working fluid can either increase (taking heat from the HTS medium 21, corresponding to the discharge mode in Figures 3 and 5) or decrease (giving heat to the HTS medium 21 , corresponding to the charging mode in Figures 2 and 4), depending on the temperature of the HTS medium in the heat exchanger relative to the temperature of the working fluid. Likewise, upon entering heat exchanger 4, the temperature of the working fluid can either increase (taking heat from the CTS medium 22, corresponding to the charging mode in Figures 2 and 4) or decrease (giving heat to the CTS medium 22, corresponding to the discharge mode in Figures 3 and 5), depending on the temperature of the CTS medium in the heat exchanger relative to the temperature of the working fluid.

[0093] As described in more detail with reference to the charging mode in Figures 2 and 4, the heat addition process in the cold side CFX 4 can occur in a different temperature range from the heat removal process in the cold side CFX 4. Similarly, in the discharge mode in Figures 3 and 5, the heat rejection process in cold-side CFX 4 may occur in a different temperature range than the heat addition process in hot-side CFX 2. At least a portion of the temperature ranges of the hot-side and cold-side heat exchange processes may overlap during charging, during discharging, or during charging and discharging.

[0094] As used herein, the temperatures T0, T1, T0+ and T1+ are so called because T0+, T1+ are the temperatures reached with the outlet of a compressor with a given compression ratio r, adiabatic efficiency nc and inlet temperatures of T0, T1 respectively. The examples in Figures 2, 3, 4 and 5 may be idealized examples where nc = 1 and where the adiabatic efficiency of the turbine also has the value nt = 1.

[0095] With reference to the charging mode shown in Figures 2 and 4, the working fluid 20 can enter the compressor 1 at position 30 at a pressure P and a temperature T (e.g., at T1, P2). As the working fluid passes through the compressor, work W1 is consumed by the compressor to increase the pressure and temperature of the working fluid (e.g., for T1+, P1), as indicated by Pt and Tf at position 31. charge mode, the temperature T1+ of the working fluid leaving the compressor and entering the hot side CFX 2 at position 31 is greater than the temperature of the medium of HTS 21 entering the hot side CFX 2 at position 32 from one second hot side thermal storage tank 7 at a temperature T0+ (i.e. T0+ < T1+). As these two liquids pass into thermal contact with each other in the heat exchanger, the temperature of the working fluid decreases as it moves from position 31 to position 34, releasing heat Q1 to the HTS medium, while the temperature The medium's HTS in turn increases as it moves from position 32 to position 33, absorbing heat Q1 from the working fluid. In one example, the working fluid leaves the hot-side CFX 2 at position 34 at temperature T0+ and the HTS medium leaves the hot-side CFX 2 at position 33 to a first hot-side thermal storage tank 6 at temperature T1+ . The heat exchange process can occur at a constant or nearly constant pressure, so that the working fluid leaves CFX hot side 2 at position 34 at a lower temperature but at the same pressure P1, as indicated by P and Tj at position 34. Similarly, the temperature of the medium of HTS 21 increases in hot-side CFX 2, while its pressure may remain constant or nearly constant.

[0096] Upon exiting the hot-side CFX 2 at position 34 (e.g., at T0+, P1), the working fluid 20 undergoes expansion in turbine 3 before exiting the turbine at position 35. During expansion, the pressure and the working fluid turbine temperature decreases (e.g., to T0, P2), as indicated by Pj and Tj at position 35. The magnitude of work W2 generated by the turbine depends on the enthalpy of the working fluid entering the turbine and the degree of expansion. In charge mode, heat is removed from the working fluid between positions 31 and 34 (in hot-side CFX 2) and the working fluid is expanded back to the pressure at which it initially entered the compressor at position 30 (for example, P2). The compression ratio (e.g. P1/P2) in compressor 1 is equal to the expansion ratio in turbine 3, and the enthalpy of the gas entering the turbine is less than the enthalpy of the gas leaving the compressor, the work W2 generated by turbine 3 is less than the work W1 consumed by compressor 1 (i.e., W2 < W1).

[0097] Because heat has been removed from the working fluid in hot-side CFX 2, the temperature T0 at which the working fluid leaves the turbine at position 35 is lower than the temperature T1 at which the working fluid initially entered in the compressor at position 30. To close the cycle (i.e., to return the pressure and temperature of the working fluid to their initial values T1, P2 at position 30), heat Q2 is added to the working fluid from the medium of CTS 22 on cold side CFX 4 between positions 35 and 30 (i.e. between turbine 3 and compressor 1). In one example, the CTS medium 22 enters the cold-side CFX 4 at position 36 from a first cold-side thermal storage tank 8 at temperature T1 and exits the cold-side CFX 4 at position 37 in a second tank. of cold-side thermal storage 9 at temperature T0, while the working fluid 20 enters the cold-side CFX 4 at position 35 at temperature T0 and leaves the cold-side CFX 4 at position 30 at temperature T1. Again, the heat exchange process can occur at a constant or nearly constant pressure, so that the working fluid leaves CFX cold side 2 at position 30 at a higher temperature but same pressure P2, as indicated by P and T? at position 30. Similarly, the temperature of the medium of CTS 22 decreases in cold-side CFX 2, while its pressure may remain constant or nearly constant.

[0098] During charging, heat Q2 is removed from the CTS medium and heat Q1 is added to the HTS medium, where Q1 > Q2. A net amount of work W1 - W2 is consumed, since the work W1 used by the compressor is greater than the work W2 generated by the turbine. A device that consumes work while moving heat from a cold body or thermal storage medium to a hot body or thermal storage medium is a heat pump; thus, the pumped thermal system in load mode operates as a heat pump.

[0099] In one example, the discharge mode shown in Figures 3 and 5 may differ from the charge mode shown in Figures 2 and 4 in the temperatures of the thermal storage medium being introduced into the heat exchangers. The temperature at which the HTS medium enters the hot-side CFX 2 at position 32 is T1+ instead of T0+, and the temperature of the CTS medium entering the cold-side CFX 4 at position 36 is T0 instead of T1. During discharge, the working fluid enters the compressor at position 30 at T0 and P2, leaves the compressor at position 31 at T0+ < T1+ and P1, absorbs heat from the HTS medium in hot-side CFX 2, enters turbine 3 at position 34 at T1+ and P1, leaves the turbine at position 35 at T1 > T0 and P2 and finally rejects heat to the CTS medium in cold side CFX 4, returning to its initial state at position 30 at T0 and P2 .

[00100] The HTS medium at temperature T1+ can be stored in a first hot-side thermal storage tank 6, the HTS medium at temperature T0+ can be stored in a second hot-side thermal storage tank 7, the HTS medium at temperature T0+ can be stored in a second hot-side thermal storage tank 7, the CTS at temperature T1 may be stored in a first cold-side thermal storage tank 8, and the CTS medium at temperature T0 may be stored in a second cold-side thermal storage tank 9 during both loading and unloading modes. . In one implementation, the inlet temperature of the HTS medium at position 32 can be switched between T1+ and T0+ by switching between tanks 6 and 7, respectively. Similarly, the inlet temperature of the CTS medium at position 36 can be switched between T1 and T0 by switching between tanks 8 and 9, respectively. Switching between tanks can be achieved by including a valve or valve system (e.g., valve systems 12 and 13 in Figure 7) to switch connections between the hot-side heat exchanger 2 and the hot-side tanks 6 and 7 , and/or between the cold-side heat exchanger 4 and the cold-side tanks 8 and 9 as required for loading and unloading modes. In some implementations, connections may be connected on the working fluid side, while connections from storage tanks 6, 7, 8 and 9 to heat exchangers 2 and 4 remain static. In some examples, flow paths and connections to heat exchangers may depend on the design (e.g., shell-and-tube) of each heat exchanger. In some implementations, one or more valves may be used to change the direction of the working fluid and heat storage medium through the counterflow heat exchanger upon loading and unloading. Such configurations may be used, for example, due to the high thermal storage capabilities of the heat exchanger component, to reduce or eliminate temperature transients, or a combination thereof. In some implementations, one or more valves can be used to change the direction of the working fluid only, while the direction of the HTS or CTS can be changed by changing the pumping direction, thus maintaining the counterflow configuration. In some implementations, different valve configurations may be used for the HTS and CTS. Additionally, any combination of valve configurations can be used. For example, the system may be configured to operate using different valve configurations in different situations (e.g., depending on system operating conditions).

[00101] In the discharge mode shown in Figures 3 and 5, the working fluid 20 can enter the compressor 1 at position 30 at a pressure P and a temperature T (e.g., at T0, P2). As the working fluid passes through the compressor, work W1 is consumed by the compressor to increase the pressure and temperature of the working fluid (e.g., to To+, Pi), as indicated by Pf and Tf at position 31. discharge mode, the temperature T0+ of the working fluid leaving the compressor and entering the hot side CFX 2 at position 3i is lower than the temperature of the HTS 2i medium entering the hot side CFX 2 at position 32 of a first hot side thermal storage tank 6 at a temperature Ti+ (i.e. T0+ < Ti+). As these two liquids pass into thermal contact with each other in the heat exchanger, the temperature of the working fluid increases as it moves from position 3i to position 34, absorbing heat Qi from the HTS medium, while the temperature of the medium of HTS in turn decreases as one moves from position 32 to position 33, releasing heat Qi to the working fluid. In one example, the working fluid leaves the hot-side CFX 2 at position 34 at temperature Ti+ and the HTS medium leaves the hot-side CFX 2 at position 33 to the second hot-side thermal storage tank 7 at temperature T0+ . The heat exchange process can occur at a constant or nearly constant pressure, so that the working fluid leaves CFX hot side 2 at position 34 at a higher temperature but at the same pressure Pi, as indicated by P and Tf at position 34. Similarly, the temperature of the HTS 2i medium decreases in the hot-side CFX 2, while its pressure may remain constant or nearly constant.

[00102] Upon exiting the hot-side CFX 2 at position 34 (e.g., at T1+, P1), the working fluid 20 undergoes expansion in turbine 3 before exiting the turbine at position 35. During expansion, the pressure and the working fluid turbine temperature decreases (e.g., to T1, P2), as indicated by Pj and Tj at position 35. The magnitude of work W2 generated by the turbine depends on the enthalpy of the working fluid entering the turbine and the degree of expansion. In discharge mode, heat is added to the working fluid between positions 31 and 34 (in hot-side CFX 2) and the working fluid is expanded back to the pressure at which it initially entered the compressor at position 30 (e.g. , P2). The compression ratio (e.g. P1/P2) in compressor 1 is equal to the expansion ratio in turbine 3 and the enthalpy of the gas entering the turbine is greater than the enthalpy of the gas leaving the compressor, the work W2 generated by turbine 3 is greater than the work W1 consumed by compressor 1 (i.e. W2 > W1).

[00103] Because heat has been added to the working fluid in hot-side CFX 2, the temperature T1 at which the working fluid exits the turbine at position 35 is higher than the temperature T0 at which the working fluid initially entered the compressor in position 30. To close the cycle (i.e., to return the pressure and temperature of the working fluid to their initial values T0, P2 in position 30), the heat Q2 is rejected by the working fluid into the CTS medium 22 on cold side CFX 4 between positions 35 and 30 (i.e. between turbine 3 and compressor 1). The CTS medium 22 enters the cold-side CFX 4 at position 36 from a second cold-side thermal storage tank 9 at temperature T0 and leaves the cold-side CFX 4 at position 37 to a first thermal storage tank cold side 8 at temperature T1, while the working fluid 20 enters the cold side CFX 4 at position 35 at temperature T1 and leaves the cold side CFX 4 at position 30 at temperature T0. Again, the heat exchange process can occur at a constant or nearly constant pressure, so that the working fluid leaves CFX cold side 2 at position 30 at a higher temperature but same pressure P2, as indicated by P and Tj at position 30. Similarly, the temperature of the medium of CTS 22 increases in cold-side CFX 2, while its pressure may remain constant or nearly constant.

[00104] During discharge, heat Q2 is added to the CTS medium and heat Q1 is removed from the HTS medium, where Q1 > Q2. A net amount of work W2 - W1 is generated, since the work W1 used by the compressor is less than the work W2 generated by the turbine. A device that generates work while moving heat from a hot body or thermal storage medium to a cold body or thermal storage medium is a heat engine; thus, the pumped thermal system in discharge mode operates as a heat engine.

[00105] Figure 6 is a simplified schematic perspective view of a working fluid system closed in the pumped thermal system in Figures 2-3. As indicated, the working fluid 20 (contained within the piping) circulates clockwise between the compressor 1, the hot-side heat exchanger 2, the turbine 3 and the cold-side heat exchanger 4. The compressor 1 and The turbine 3 may be grouped together on a common mechanical rod 10 such that they rotate together. In some implementations, compressor 1 and turbine 3 may have separate mechanical rods. A motor/generator 11 (e.g. including a synchronous motor - synchronous generator converter on a single common shaft) provides power to and from the turbomachinery. In this example, the compressor, turbine and motor/generator are all located on a common shaft. The tubes at positions 32 and 33 transfer hot-side thermal storage fluid to and from the hot-side heat exchanger 2, respectively. The tubes at positions 36 and 37 transfer the cold-side thermal storage fluid to and from the cold-side heat exchanger 4, respectively.

[00106] Although the system of Figure 6 is illustrated as comprising a compressor 1 and turbine 3, the system may include one or more compressors and one or more turbines, which may operate, for example, in a parallel configuration, or alternatively in a series configuration or a combination of parallel and series configurations. In some examples, a system of compressors or turbines may be assembled such that a certain compression ratio is achieved. In some cases, different compression ratios (e.g., over charge and discharge) may be used (e.g., by connecting or disconnecting, in a parallel and/or series configuration, one or more compressors or turbines of the compressor or turbine system ). In some examples, the working fluid is directed to a plurality of compressors and/or a plurality of turbines. In some examples, the compressor and/or turbine may have temperature-dependent compression ratios. The arrangement and/or operation of the turbomachinery and/or other system elements can be adjusted depending on temperature (e.g. to optimize performance).

[00107] Figure 7 is a simplified schematic perspective view of the pumped thermal system in Figures 2-3 with hot-side and cold-side storage tanks and a closed-loop working fluid system. In this example, the HTS medium is a molten salt and the CTS medium is a low temperature liquid. One, two or more first hot side tanks 6 (at temperature T1+) and one, two or more second hot side tanks 7 (at temperature T0+), both to maintain the HTS medium, are in fluid communication with a valve 13 configured to transfer HTS medium to and from hot side heat exchanger 2. One, two or more cold side first tanks 8 (at temperature T1) and one, two or more cold side second tanks 9 (at temperature T0), both for maintaining the CTS medium, are in fluid communication with a valve 12, configured to transfer the CTS medium to and from the cold side heat exchanger 4.

[00108] Thermal energy reservoirs or storage tanks may be thermally insulated tanks that may contain a suitable amount of the relevant thermal storage medium (e.g., heat storage fluid). Storage tanks can allow relatively compact storage of large amounts of thermal energy. In one example, the hot side tanks 6 and/or 7 may have a diameter of about 80 meters, while the cold side tanks 8 and/or 9 may have a diameter of about 60 meters. In another example, the size of each (i.e., hot side or cold side) thermal storage for a 1 GW plant operating for 12 hours might be about 20 medium-sized oil refinery tanks.

[00109] In some implementations, a third set of tanks containing storage media at temperatures intermediate between the other tanks may be included on the hot side and/or the cold side. In one example, a third storage or transfer tank (or set of tanks) at a temperature intermediate to the temperatures of a first tank (or set of tanks) and a second tank (or set of tanks) may be provided. A set of valves can be provided to switch the storage medium between different tanks and heat exchangers. For example, thermal media may be directed to different sets of tanks after leaving the heat exchangers, depending on the operating conditions and/or the cycle being used. In some implementations, one or more additional sets of storage tanks at different temperatures may be added on the hot side and/or the cold side.

[00110] Storage tanks (e.g., hot-side tanks comprising hot-side thermal storage medium and/or cold-side tanks comprising cold-side thermal storage medium) can operate at ambient pressure. In some implementations, storing thermal energy at ambient pressure can provide safety benefits. Alternatively, the storage tanks may operate at elevated pressures, such as, for example, at a pressure of at least about 2 atm (0.20265 MPa), at least about 5 atm (0.506625 MPa), at least about 10 atm (1.01325 MPa), at least about 20 atm (2.0265 MPa), or more. Alternatively, storage tanks may operate at reduced pressures, such as, for example, at a maximum pressure of about 0.9 atm (0.0911925 MPa), a maximum of about 0.7 atm (0.0709275 MPa). ), maximum about 0.5 atm (0.0506625 MPa), maximum about 0.3 atm (0.0303975 MPa), maximum about 0.1 atm (0.0101325 MPa), maximum about of 0.01 atm (0.00101325 MPa), maximum about 0.001 atm (0.000101325 MPa), or less. In some cases (e.g. when operating at higher/higher or lower pressures or to prevent contamination of the thermal storage medium), storage tanks may be sealed from the surrounding atmosphere. Alternatively, in some cases, storage tanks may not be sealed. In some implementations, tanks may include one or more pressure regulation or relief systems (e.g., a valve for safety or system optimization).

[00111] As used herein, the first hot side tank(s) 6 (at temperature T1+) may contain HTS medium at a higher temperature than the second hot side tank(s) 7 (at temperature T0+), and the first cold side tank(s) 8 (at temperature T1) may contain CTS medium at a higher temperature than the second cold side tank(s) 9 (at temperature T0). During charging, the HTS medium in the first hot-side (higher temperature) tank(s) 6 and/or CTS medium in the second cold-side tank(s) 9 can be refilled. During discharge, HTS medium in the first hot-side tank(s) 6 and/or CTS medium in the second cold-side tank(s) 9 may be consumed.

[00112] In the previous examples, in both modes of operation, two of the four storage tanks 6, 7, 8 and 9 are feeding thermal storage medium to heat exchangers 2 and 4 at inlets 32 and 36, respectively, and the other two tanks are receiving thermal storage medium from heat exchangers 2 and 4 from outlets 33 and 37, respectively. In this configuration, the feed tanks may contain a storage medium at a certain temperature due to previous operating conditions, while the temperatures of the receiving tanks may depend on current system operation (e.g., operating parameters, loads, and/or input energy). Receiving tank temperatures can be adjusted by Brayton cycle conditions. In some cases, receiving tank temperatures may differ from desired values due to deviations from predetermined cycle conditions (e.g., variation in absolute pressure in response to system demand) and/or due to the generation of entropy within the system. In some cases (e.g. due to entropy generation), at least one of the four tank temperatures may be higher than desired. In some implementations, a radiator may be used to reject or dissipate this waste heat to the environment. In some cases, heat rejection to the environment can be improved (e.g. using evaporative cooling, etc.). The waste heat generated during the operation of the thermal systems pumped here can also be used for other purposes. For example, waste heat from one part of the system can be used in other parts of the system. In another example, waste heat may be supplied to an external process or system, such as, for example, a manufacturing process requiring low-grade heat, commercial or residential heating, thermal desalination, commercial drying operations, etc.

[00113] Components of pumped thermal systems of the disclosure may exhibit suboptimal performance, leading to losses and/or inefficiencies. The largest losses in the system can occur due to inefficiencies in the turbomachinery (e.g. compressor and turbine) and heat exchangers. Losses due to heat exchangers can be small compared to losses due to turbomachinery. In some implementations, losses due to heat exchangers can be reduced to near zero with proper design and expense. Therefore, in some analytical examples, losses due to heat exchangers and other possible small losses due to pumps, the motor/generator and/or other factors may be neglected.

[00114] Losses due to turbomachinery can be quantified in terms of adiabatic efficiencies nc and nt (also known as isentropic efficiencies) for compressors and turbines, respectively. For large turbomachines, typical values can vary between nc = 0.85 - 0.9 for compressors and nt = 0.9 - 0.95 for turbines. The actual amount of work produced or consumed by a cycle can then be expressed as cycle can then be expressed as specific constants of the working fluid, where r is the compression ratio (that is, the ratio of the highest pressure to the lowest pressure), and Y = cp/cv is the specific heat ratio of the working fluid. Due to compressor and turbine inefficiencies, more work is required to achieve a given compression ratio during compression, and less work is generated during expansion for a given compression ratio. Losses can also be quantified in terms of the polytropic, or single-stage, efficiencies, ncp and ntp, for compressors and turbines, respectively. The polytropic efficiencies are related to the adiabatic efficiencies nc and nt by the equations

[00115] In examples where nc = nt = 1, pumped thermal cycles of the disclosure may follow identical paths in both charge and discharge cycles (e.g., as shown in Figures 4 and 5). In examples where nc < 1 and/or nt < 1, compression in the compressor can lead to a greater increase in temperature than in the ideal case for the same compression ratio, and expansion in the turbine can lead to a smaller decrease in temperature in the ideal case.

[00116] In some implementations, the polytropic efficiency of the compressor may be at least 0.3, at least 0.5, at least 0.6, at least 0.7, at least 0.75, at least 0.8, at least about 0.85, at least about 0.9, at least about 0.91, at least about 0.92, at least about 0.93, at least about 0.96, or more. In some implementations, the polytropic efficiency of the NTP compressor may be at least about 0.3, at least about 0.5, at least about 0.6, at least about 0.7, at least about 0, 75, at least about 0.8, at least about 0.85, at least 0.9, at least about 0.91, at least about 0.92, at least about 0.93, at least about 0.96, at least about 0.97 or more.

[00117] T0+, T1+ were previously defined as the temperatures reached at the outlet of a compressor with a given compression ratio r, adiabatic efficiency nc and inlet temperatures of T0, T1 respectively. In some examples, these four temperatures are related by the equation

[00118] Figure 8 shows an exemplary heat storage load cycle for a water (CTS)/molten salt (HTS) system with nc = 0.9 and nt = 0.95. The dashed lines correspond to nc = nt = 1 and the solid lines show the load cycle with nt = 0.95 and nc = 0.9. In this example, the CTS medium on the cold side is water, and the HTS medium on the hot side is molten salt. In some cases, the system may include 4 heat storage tanks. In the charging cycle, the working fluid at T0 and P2 can exchange heat with a CTS medium in the cold-side heat exchanger 4, whereby its temperature can increase to T1 (assuming a negligible pressure drop, its pressure may remain P2). In compressor 1 with nc = 0.9, the temperature and pressure of the working fluid can increase from T1, P2 to T1+, P1. The working fluid can then exchange heat with an HTS medium in the hot-side heat exchanger 2, such that its temperature can decrease (at constant pressure P1, assuming negligible pressure drop). If the working fluid enters turbine 3 with nt = 0.95 at temperature T0+ and expands back to its original pressure P2, its temperature at exit from the turbine may not be T0. Instead, the working fluid can enter the turbine at a temperature and exit the turbine at temperature T0 and pressure P2. In some examples, temperatures are related by the relationship . In some examples, is the temperature at which the working fluid enters the inlet of a turbine with adiabatic efficiency and compression ratio r to exit at temperature T0.

[00119] In some implementations, the temperature can be incorporated into charging cycles of the disclosure by first exchanging heat of the working fluid with the HTS medium from T1+ to T0+, followed by further cooling of the working fluid. for , as illustrated by section 38 of the cycle in Figure 8.

[00120] Figure 9 shows an exemplary heat storage discharge (extraction) cycle for the molten water/salt system in Figure 8 with nc = 0.9 and nt = 0.95. The dashed lines correspond to nc = nt = 1 and the solid lines show the load cycle with nt = 0.95 and nc = 0.9. In the discharge cycle, the working fluid at T1 and P2 can exchange heat with a CTS medium in the cold-side heat exchanger 4, whereby its temperature can decrease at T0 (assuming negligible pressure drop, the your pressure may remain P2). In compressor 1 with nc = 0.9, the temperature and pressure of the working fluid can increase from T0, P2 to T0+, P1. The working fluid can then exchange heat with an HTS medium in the hot-side heat exchanger 2, such that its temperature can increase (at constant pressure P1, assuming negligible pressure drop). The working fluid entering the turbine 3 in cannot exit the turbine at temperature TI as in the load cycle, but can instead exit at a temperature , where, in some examples, . In some examples, and the temperature at which the working fluid leaves the outlet of a turbine with adiabatic efficiency and compression ratio r after entering the turbine inlet at temperature T1+.

[00121] In some implementations, the temperature can be incorporated into the discharge cycles of the disclosure by first cooling the working fluid exiting the turbine in for TI, as illustrated by section 39 of the cycle in Figure 9, followed by heat exchange of the working fluid with the CTS medium from T1 to T0.

[00122] The charge and discharge cycles can be closed by additional heat rejection operations in sections 38 (between TO+ and ) and 39 (between and IT), respectively. In some cases, closing cycles by heat rejection in sections of the cycles where the working fluid can reject heat to the environment at low cost can eliminate the need for additional heat input into the system. Sections of the cycles in which the working fluid can reject heat to ambient temperature may be limited to sections in which the temperature of the working fluid is sufficiently high above ambient temperature for ambient refrigeration to be feasible. In some examples, heat may be rejected to the environment in sections 38 and/or 39. For example, heat may be rejected using one or more working fluids to aerate radiators, intermediate water cooling, or various other methods. In some cases, the heat rejected in sections 38 and/or 39 may be used for another useful purpose, such as, for example, cogeneration, thermal desalination and/or other examples described herein.

[00123] In some implementations, cycles can be closed by varying the compression rates between charge and discharge cycles, as shown, for example, in Figure 10. The ability to vary the compression rate at charge and discharge can be implemented, for example, by varying the rotational speed of the compressor and/or turbine, by variable stator pressure control, by bypassing a subset of the compression or expansion stages in loading or unloading by the use of valves, or by using pairs dedicated compressor/turbine units for loading and unloading mode. In one example, the compression ratio in the discharge cycle in Figure 9 can be changed such that heat rejection in section 39 is not used, and only heat rejection in section 38 in the charge cycle is used. Varying the compression ratio can allow heat (i.e. entropy) to be rejected at a lower temperature, thereby increasing the overall round-trip efficiency. In some examples of this configuration, the charge compression ratio, rc, can be adjusted such that , and on discharge, the compression ratio rD can be adjusted such that . In some cases, the upper temperatures Ti+ and Ti may be identical in charge and discharge and no heat removal may be required in this portion (also “leg” here) of the cycle. In these cases, the temperature T0+ at the load (e.g. ) and the temperature To+ at discharge (e.g. ) may be different and heat may be rejected (also “dissipated” or “discarded” here) to the environment between the temperatures It is . In an implementation where only the storage media exchanges heat with the environment, a heat rejection device (e.g., devices 55 and 56 shown in Figure 16) can be used to lower the temperature of the CTS from for between discharging and charging.

[00124] Figure 10 shows an example of a cycle with variable compression rates. The compression ratio can be greater at discharge (when work is produced by the system) than at load (when work is consumed by the system), which can increase the overall efficiency of the system. For example, during an 80 load cycle with , a lower compression ratio of < 3 can be used; during a discharge cycle 81 with , a compression ratio > 3 can be used. The upper temperatures reached in the two cycles 80 and 81 can be T1 and T1+, and no excess heat can be rejected.

[00125] The compression rate can vary between loading and unloading, in such a way that the heat dissipation to the environment necessary to close the cycle during both loading and unloading occurs between temperatures (the temperature of the working fluid before entering the turbine during the load cycle) and (the temperature of the working fluid when it leaves the compressor during discharge), and not above temperature T1 (the temperature of the working fluid before it enters the compressor under load and/or leaves the turbine under discharge). In some examples, no heat is rejected at a temperature above the lowest temperature of the HTS medium.

[00126] In the absence of system losses and/or inefficiencies, as, for example, in the case of pumped thermal systems comprising heat pump(s) and heat engine(s) operating at the zero/isentropic entropy creation limit, a given amount of heat QH can be transferred using a given amount of work W in heat pump (load) mode, and the same QH can be used in heating (discharge) mode to produce the same work W, leading to a unit round-trip efficiency (i.e. 100%). In the presence of system losses and/or inefficiencies, the round-trip efficiency of pumped thermal systems can be limited by how much the components deviate from ideal performance.

[00127] The round trip efficiency of a pumped thermal system can be defined as . In some examples, with an approximation of ideal heat exchange, the round-trip efficiency can be derived by considering the net work output during the cycle. and the net work input during the load cycle, using the equations for work and temperature given above.

[00128] Round-trip efficiencies can be calculated for different configurations of pumped thermal systems (e.g., for different classes of thermal storage media) based on the efficiencies of the turbomachinery components, nc and nt.

[00129] In one example, Figure 11 shows the round-trip efficiency contours for a water/salt system, such as, for example, the water/salt system in Figures 8 and 9 with T0 = 273 K ( 0 °C), at T1 = 373 K (100 °C) and a compression ratio of r = 5.65 chosen to achieve compatibility with the salt(s) on the hot side. Examples of round-trip efficiency contours at values of of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90% are shown as a function of the efficiencies of the nc and nt components on the x and y axes, respectively. The symbols ⊕ and ⊕ represent the approximate range of adiabatic efficiency values of current turbomachinery. The dashed arrows represent the direction of efficiency increase.

[00130] Figure 12 shows the round-trip efficiency contours for a cooler storage/salt system, such as, for example, a hexane/salt system with a gas-to-gas heat exchanger in Figures 13, 14, 17 and 18, with T0 = 194 K (-79 °C), at T1 = 494 K (221 °C) and a compression ratio of r = 3.28. Examples of round-trip efficiency contours at values of of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90% are shown as a function of the efficiencies of the nc and nt components on the x and y axis, respectively. The symbols ⊕ and ⊕ represent the approximate range of adiabatic efficiency values of current turbomachinery. As discussed in detail elsewhere, the use of hexane, heptane and/or other CTS media capable of low temperature operation can result in significant system efficiency improvements.

C. Pumped thermal storage cycles with recovery

[00131] Another aspect of the disclosure is directed to pumped thermal systems with recovery. In some situations, the terms regeneration and recovery may be used interchangeably, although they may have different meanings. As used herein, the terms "recovery" and "recovery" generally refer to the presence of one or more additional heat exchangers where the working fluid exchanges heat with itself during different cycles of a thermodynamic cycle through continuous heat exchange without storage. intermediate thermal. The round-trip efficiency of pumped thermal systems can be substantially improved if the allowable temperature ranges of storage materials can be extended. In some implementations, this can be done by choosing a material or medium on the cold side that can go to temperatures below 273 K (0 °C). For example, a CTS medium (e.g., hexane) with a lower temperature limit of about T0 = 179 K (-94 °C) can be used in a system with a molten salt HTS medium. However, T0+ (i.e., the lowest temperature of the working fluid in the hot-side heat exchanger) at some (e.g., modest) compression ratios may be below the freezing point of the molten salt, making the molten salt unviable. as the means of HTS. In some implementations, this can be resolved by including a working fluid in the working fluid (e.g. gas-to-gas) heat exchanger (also "scavenger" here) in the cycle.

[00132] Figure 13 is a schematic flowchart of working fluid and heat storage medium of a pumped thermal system in a load/heat pump mode with a gas-gas heat exchanger 5 for the working fluid. The use of the gas-to-gas heat exchanger can allow the use of a cooler heat storage medium on the cold side of the system. The working fluid can be air. The working fluid can be dry air. The working fluid can be nitrogen. The working fluid can be argon. The working fluid can be a mixture of mainly argon mixed with another gas such as helium. For example, the working fluid may comprise at least about 50% argon, at least about 60% argon, at least about 70% argon, at least about 80% argon, at least about 90 % argon or about 100% argon, with helium balance.

[00133] Figure 17 shows a heat storage charge cycle for the storage system in Figure 13 with a cold-side storage medium (e.g., liquid hexane) capable of going down to approximately 179 K (-94 °C ) and a molten salt as hot-side storage, and nc = 0.9 and nt = 0.95. The CTS medium can be hexane or heptane and the HTS medium can be molten salt. In some cases, the system may include four heat storage tanks.

[00134] In one implementation, during charging in Figures 13 and 17, the working fluid enters the compressor at T1 and P2, leaves the compressor at T1+ and P1, rejects heat Q1 to the middle of HTS 21 in hot-side CFX 2 , which leaves hot-side CFX 2 to T1 and P1, rejects heat Qrecup (also “Qregen” here, as shown, for example, in the accompanying drawings) to the cold-side (low pressure) working fluid in the heat exchanger or recuperator 5, leaves recuperator 5 at T0+ and P1, rejects heat to the environment (or other heat sink) at section 38 (e.g. a radiator), enters turbine 3 at and P1, leaves the turbine at TO and P2, absorbs heat Q2 from the middle of CTS 22 in the cold-side CFX 4, which leaves the cold-side CFX 4 at T0+ and P2, absorbs heat Qrecup from the hot side work (high pressure) in the heat exchanger or recuperator 5 and finally leaves the recuperator 5 at T1 and P2, returning to its initial state before entering the compressor.

[00135] Figure 14 is a schematic flowchart of the working fluid and heat storage medium of the pumped thermal system in Figure 13 in discharge/heat engine mode. Again, the use of the gas-to-gas heat exchanger may allow the use of cooler heat storage fluid (CTS) and/or cooler working fluid on the cold side of the system.

[00136] Figure 18 shows a heat storage discharge cycle for the storage system for the storage system in Figure 14 with a cold-side storage medium (e.g., liquid hexane) capable of going down to 179 K ( -94 °C) and a molten salt as hot-side storage, and nc = 0.9 and nt = 0.95. Again, the CTS medium may be hexane or heptane and the HTS medium may be molten salt, and the system may include 4 heat storage tanks.

[00137] During the discharge in Figures 14 and 18, the working fluid enters the compressor at T0 and P2, leaves the compressor at T0+ and P1, absorbs heat Qrecup from the cold side (low pressure) working fluid at heat exchanger or recuperator 5, leaves recuperator 5 at T1 and P1, absorbs heat Q1 from the middle of HTS 21 in hot-side CFX 2, leaves hot-side CFX 2 at T1+ and P1, enters turbine 3 at Ti+ and Pi, leaves the turbine in , and P2, rejects heat to the environment (or other heat sink) in section 39 (e.g. a radiator), rejects heat Qrecup to the hot (high pressure) working fluid in the heat exchanger or recuperator 5, enters cold-side CFX 4 at T0+ and P2, rejects Q2 heat to the middle of CTS 22 in cold-side CFX 4, and finally exits cold-side CFX 4 at T0 and P2, returning to its initial state before entering in the compressor.

[00138] In another implementation, shown in Figure 15, the charging cycle remains the same as in Figures 13 and 17, except that the working fluid leaves the recuperator 5 at and Pi (instead of at T0+ and P1, as in Figures 13 and 17), enters turbine 3 at and Pi, leaves the turbine at To and P2, absorbs heat Q2 from the medium of CTS 22 having a temperature (instead of at T0+ as in Figures i3 and i7) into cold-side CFX 4, and exits cold-side CFX 4 at and P2 (instead of at To+ and P2 as in Figure i3) before re-entering the recuperator 5. The heat between temperatures To+ and it is no longer rejected directly from the working fluid into the environment (as in section 38 in Figures i3 and i7).

[00139] During the discharge in Figure i6, the discharge cycle remains the same as in Figures i4 and 8B, except that the temperature of the HTS medium deposited in tank 7 is changed. The working fluid leaves the recuperator 5 in and Pi (instead of Ti and Pi, as in Figures i4 and 8B) and absorbs heat Qi from the HTS medium 2i into the hot-side CFX 2. The HTS medium leaves the hot-side CFX 2 having a temperature (instead of Ti as in Figures i4 and i8). The working fluid then leaves hot side CFX 2 at Ti+ and Pi, enters turbine 3 at Ti+ and Pi, and exits the turbine at and P2 before reentering the stove 5. The heat between temperatures and Ti is no longer rejected directly from the working fluid into the environment (as in section 39 in Figures i4 and i8). As in Figure i4, the CTS medium enters tank 8 at temperature T0+.

[00140] After discharge in Figure 16, in preparation for charging in Figure 15, heat exchange with the environment can be used to cool the HTS medium 21 from the temperature T1 used in the discharge cycle to the temperature used in the charging cycle. Likewise, heat exchange with the environment can be used to cool the CTS 22 medium from the temperature T0+ used in the discharge cycle to the temperature used in the charging cycle. Unlike the configuration in Figures 13 and 14, where the working fluid may need to reject a substantial amount of heat (in sections 38 and 39, respectively) at a rapid rate, in this configuration, the hot and cold side storage medium can be cooled at an arbitrarily slow rate (e.g., by radiating away or by other means of releasing heat into the environment).

[00141] As shown in Figure 16, in some implementations, heat can be rejected from the CTS medium to the environment by circulating the CTS medium in tank 8 in a heat rejection device 55 that can absorb heat from of the CTS medium and reject heat to the environment until the CTS medium cools from temperature To+ to temperature . In some examples, the heat rejection device 55 may be, for example, a radiator, a thermal bath containing a substance such as water or salt water, or a device immersed in a natural body of water such as a lake, river or ocean. In some examples, the heat rejection device 55 may also be an air cooling apparatus, or a series of tubes that are thermally connected to a solid reservoir (e.g., tubes embedded in the ground).

[00142] Similarly, in some implementations, heat may be rejected from the HTS medium to the environment by circulating the HTS in tank 7 in a heat rejection device 56 which may absorb heat from the HTS medium and reject the heat to the environment until the HTS medium cools from the temperature at temperature Ti. In some examples, the heat rejection device 56 may be, for example, a radiator, a thermal bath containing a substance such as water or salt water, or a device immersed in a natural body of water such as a lake, river or ocean. In some examples, the heat rejection device 56 may also be an air cooling apparatus or a series of tubes that are thermally connected to a solid reservoir (e.g., tubes embedded in the ground).

[00143] In some implementations, heat rejection to the environment through the use of thermal storage medium may be used in conjunction with variable compression ratio charge and/or discharge cycles described, for example, in Figure 10. In this system, only the CTS medium can exchange heat with the environment. Such a system can also be implemented with a recuperator to extend the temperature ranges of the HTS and CTS media in the cycles.

[00144] In some implementations, three separate cold-side storage tanks at respective temperatures To, , It is can be used (for example, an extra tank can be used in addition to tanks 8 and 9). During heat exchange in the cold-side CFX 4 in the discharge cycle, the heat of the working fluid leaving the recuperator 5 can be transferred to the CTS medium in the -tank. The CTS medium may be cooled in/by, for example, the heat rejection device 55 before entering the -tank. In some implementations, three separate hot-side storage tanks at respective temperatures TI, , It is can be used (for example, an extra tank can be used in addition to tanks 6 and 7). During heat exchange in the hot side CFX 2 in the discharge cycle, heat from the working fluid leaving the recuperator 5 can be transferred to the HTS medium in the -tank. The HTS medium may be cooled in/by, for example, the heat rejection device 56 before entering the T1-tank. Rejecting heat to the environment in this way can have several advantages. In a first example, it can eliminate the need for a potentially expensive working fluid for the ambient heat exchanger that is capable of absorbing heat from the working fluid at a rate proportional to the energy input/output of the system. HTS and CTS media can instead reject heat over extended periods of time, thereby reducing the cost of cooling infrastructure. In a second example, it may allow the decision about when heat is rejected to the environment to be delayed, so that the exchange of heat to the environment can be carried out when the temperature (e.g. room temperature) is more favorable.

[00145] In the charge and discharge cycles of Figures 13 and 17 and Figures 14 and 18, respectively, the same compression ratios and temperature values are used for both charge and discharge. In this configuration, the round trip efficiency can be about nstored = 74%, as given by To = 194 K (-79 °C), Ti = 494 K (221 °C). nt = 0.95, nc = 0.9 and r = 3.3.

[00146] Thus, in some examples involving working fluid for working fluid recovery, heat rejection on the hot side (high pressure) of the closed load cycle can occur in three operations (heat exchange with the HTS medium, followed by recovery, followed by heat rejection to the environment), and heat rejection on the cold (low pressure) side of the closed discharge cycle can occur in three operations (heat rejection to the environment, followed by recovery, followed by exchange of heat with the CTS medium). As a result of recovery, the higher temperature HTS tank(s) 6 may remain at T1+ while the lower temperature HTS tank(s) 7 may now be at temperature T1 > T0+, and the lower temperature CTS tank(s) 9 may remain at T0 while the higher temperature CTS tank(s) 8 may now be at temperature T0+ < T1.

[00147] In some cases, recovery can be implemented using heat exchanger 5 for direct heat transfer between the working fluid on the high pressure side and the working fluid on the low pressure side. In an alternative configuration, an additional pair (or plurality) of heat exchangers together with an additional heat transfer medium or fluid (e.g., a thermal heat transfer fluid that is liquid in an appropriate temperature range, such as, for example, Therminol®) can be used to achieve recovery. For example, an additional heat exchanger can be added in series with the cold side heat exchanger and an additional heat exchanger can be added in series with the hot side heat exchanger. The additional heat transfer medium can be circulated between the two additional heat exchangers in a closed cycle circuit. In other examples, one or more additional heat exchangers may be placed in other parts of the system to facilitate recovery. Furthermore, one or more additional heat transfer media or mixtures thereof may be used. The one or more additional heat transfer medium fluids may be in fluid or thermal communication with one or more other components, such as, for example, a cooling tower or a radiator.

[00148] In one example, hexane or heptane can be used as a CTS medium and the nitrate salt can be used as an HTS medium. On the low pressure side of the cycle, the operating temperatures of pumped thermal storage cycles can be limited by the melting point of hexane (178 K or -95 °C) at T0 and the melting point of nitrate (494 K or 221 °C) in T1. On the high pressure side of the cycle, operating temperatures can be limited by the boiling point of hexane (341 K or 68 °C) at T0+ and the decomposition of nitrate (873 K or 600 °C) at T1+. Under these conditions, the high pressure and low pressure temperature ranges can overlap so that recovery can be implemented. Actual temperatures T0, T1, T0+ and T1+ and pressure ratios implemented in hexane/nitrate systems may differ from the above limits.

[00149] In some examples, recovery may allow the compression ratio to be reduced. In some cases, reducing the compression ratio can result in reduced compressor and turbine losses. In some cases, the compression ratio may be at least about 1.2, at least about 1.5, at least about 2, at least about 2.5, at least about 3, at least about 3.5, at least about 4, at least about 4.5, at least about 5, at least about 6, at least about 8, at least about 10, at least about 15, at least about of 20, at least around 30 or more.

[00150] In some cases, T0 may be at least about 30 K, at least about 50 K, at least about 80 K, at least about 100 K, at least about 120 K, at least about 140 K, at least about 160 K, at least about 180 K, at least about 200 K, at least about 220 K, at least about 240 K, at least about 260 K, or at least about 280 K. In some cases, T0+ may be at least about 220 K, at least about 240 K, at least about 260 K, at least about 280 K, at least about 300 K, at least 320 K, at least at least 340K, at least 360K, at least about 380K, at least about 400K, or more. In some cases, the temperatures T0 and T0+ may be restricted by the ability to reject excess heat to the environment at room temperature. In some cases, the T0 and T0+ temperatures may be constrained by the CTS operating temperatures (e.g., a phase transition temperature). In some cases, the temperatures T0 and T0+ may be restricted by the compression ratio used. Any description of temperatures T0 and/or T0+ herein may be applied to any system or method of the disclosure.

[00151] In some cases, T1 may be at least about 350 K (176.667 °C), at least about 400 K (204.444 °C), at least about 440 K (226.667 °C), at least about 480 K (248.889 °C), at least about 520 K (271.111 °C), at least about 560 K (293.333 °C), at least about 600 K (315.556 °C), at least about 640 K (337.778 °C), at least about 680 K (360 °C), at least about 720 K (382.222 °C), at least about 760 K (404.444 °C), at least about 800 K (426.667 °C), at least about 840 K (448.889 °C), at least about 880 K (471.111 °C), at least about 920 K (493.333 °C), at least about 960 K (515.556 °C ), 1000 K (537.778 °C), at least about 1100 K (593.3333 °C), at least about 1200 K (648.8889 °C), at least about 1300 K (704.4444 °C ), at least about 1400 K (760 °C), or more. In some cases, T1+ may be at least about 480 K (248.889 °C), at least about 520 K (271.111 °C), at least about 560 K (293.333 °C), at least about 600 K ( 315.556 °C), at least about 640 K (337.778 °C), at least about 680 K (360 °C), at least about 720 K (382.222 °C), at least about 760 K (404.444 °C) C), at least about 800 K (426.667 °C), at least about 840 K (448.889 °C), at least about 880 K (471.111 °C), at least about 920 K (493.333 °C) , at least about 960 K (515.556 °C), at least about 1000 K (537.778 °C), at least about 1100 K (593.3333 °C), at least about 1200 K (648.8889 ° C), at least about 1300 K (704.4444 °C), at least about 1400 K (760 °C), at least about 1500 K (815.5556 °C), at least about 1600 K ( 871.1111 °C), at least about 1700 K (926.6667 °C), or more. In some cases, the T1 and T1+ temperatures may be restricted by the HTS operating temperatures. In some cases, the T1 and T1+ temperatures may be restricted by the thermal limits of the metals and materials being used in the system. For example, a conventional solar salt may have a recommended temperature range of approximately 560-840 K (293.333-448.889 °C). Various system improvements, for example, greater round trip efficiency, greater power, and greater storage capacity can be realized as available materials, metallurgy, and storage materials improve over time and allow different temperature ranges to be achieved. Any description of T1 and/or T1+ temperatures herein may be applied to any system or method of the disclosure.

[00152] In some cases, the round-trip storage efficiency (e.g., electricity storage efficiency) with and/or without recovery may be at least about 5%, at least about 10%, at least about of 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60% %, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, or at least about 95%.

[00153] In some implementations, at least a portion of the heat transfer in the system (e.g., heat transfer to and from the working fluid) during a charge and/or discharge cycle includes heat transfer with the environment (e.g. , heat transfer in sections 38 and 39). The remainder of the heat transfer in the system may occur through thermal communication with thermal storage medium (e.g., thermal storage medium 21 and 22), through heat transfer in recuperator 5, and/or through various heat transfer processes. heat within system boundaries (i.e., not with the surrounding environment). In some examples, the environment may refer to gaseous or liquid reservoirs surrounding the system (e.g., air, water), any system or medium capable of exchanging thermal energy with the system (e.g., another thermodynamic cycle or system, systems heating/cooling, etc.), or any combination thereof. In some examples, the heat transferred through thermal communication with the heat storage medium may be at least about 25%, at least about 50%, at least about 60%, at least about 70%, at least about about 80%, or at least about 90% of all heat transferred in the system. In some examples, the heat transferred via heat transfer in the recuperator may be at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%. , at least about 50%, or at least about 75% of all heat transferred in the system. In some examples, heat transferred through thermal communication with the heat storage medium and through heat transfer in the recuperator may be at least about 25%, at least about 50%, at least about 60%, at least about about 70%, at least 80%, at least about 90%, or even about 100% of all heat transferred in the system. In some examples, the heat transferred through heat transfer with the environment may be less than about 5%, less than about 10%, less than about 15%, less than about 20%, less than about 30%. %, less than about 40% less than about 50%, less than about 60%, less than about 70%, less than about 80%, less than about 90%, less than about 100% or even at 100% of all heat transferred in the system. In some implementations, all heat transfer in the system may be with the thermal storage medium (e.g., through CTS and HTS), and only the thermal storage medium may conduct heat transfer with the environment.

[00154] The pumped thermal cycles of the disclosure (e.g., the cycles in Figures 13 and 14) can be implemented through various configurations of pipes and valves to transport the working fluid between the turbomachinery and heat exchangers. In some implementations, a valve system may be used so that different cycles of the system may be switched while maintaining the same or nearly the same temperature profile in at least one, across a subset, or across all of the heat exchangers. counterflow in the system. For example, the valve can be configured so that the working fluid can pass through the heat exchangers in opposite flow directions in loading and unloading and flow directions of the HTS and CTS medium are reversed by reversing the direction of the pumps.

[00155] In some implementations, the system with a recuperator may have a different compression and/or expansion rate at loading and unloading. This may then involve heat rejection at only one or both heat rejection locations 38 and 39 as shown in Figure 5C along the lines described above.

[00156] Figure 19 is a schematic flowchart of hot-side recharging in a pumped heat cycle in solar mode with heating a solar salt by solar energy alone. The system may include a solar heater to heat the hot-side heat storage. The HTS medium 21 in the second hot thermal storage tank 7 of a discharge cycle, such as, for example, the HTS medium of the discharge cycle in Figure 14, can be recharged within the element 17 using the heating provided by radiation. solar. The HTS medium (e.g., molten salt) may be heated by solar heating from temperature T1 in the second hot thermal storage tank 7 to temperature T1+ in the first hot thermal storage tank 6.

[00157] In some implementations, such as, for example, for the systems in Figures 19 solar heat for heating the HTS medium (e.g., from T1 = 493 K (220 °C) to T1+ = 873 K (600 °C )) can be supplied by a concentrating solar installation. In some examples, a small-scale concentrating facility may be used to provide heat. In some cases, the concentrated solar installation may include one or more components to achieve high solar concentrating efficiency, including, for example, high-performance actuators (e.g. adaptive fluidic actuators manufactured from polymers), a multiplication control system , dense heliostat layout etc. In some examples, the heat supplied to heat the HTS medium (e.g., in element 17) may be a waste heat flow from the concentrating solar installation.

[00158] Figure 20 is a schematic flowchart of a pumped thermal system discharge cycle that can be coupled with external heat input (e.g., solar, combustion) with heat rejection to the environment. Such a discharge cycle can be used, for example, in situations where the hot-side recharge capacity (e.g. using solar heating, waste heat or combustion) is greater than the cold-side recharge capacity. Solar heat can be used to charge the HTS 21 medium in storage tanks from T1 to T1+, as described elsewhere here. The discharge cycle may operate similarly to the discharge cycle in Figure 3, but after exiting the turbine 3, the working fluid 20 may proceed to the cold-side CFX 4 heat exchanger 4 where it exchanges heat with a medium intermediate thermal storage (ITS) 61 having a temperature lower than T0 at or near ambient temperature. The ITS medium 61 enters the cold-side CFX 4 from a second intermediate thermal storage tank 59 at temperature T0 (e.g., room temperature) and leaves the cold-side CFX 4 to a first intermediate thermal storage tank 60 the temperature , while the working fluid 20 enters the cold side CFX 4 at temperature and exits the CFX cold side 4 at temperature T0. The working fluid enters compressor 1 at T0 and P2, leaves the compressor at T0+ and P1, absorbs heat Q1 from the medium of HTS 21 in hot-side CFX 2, leaves hot-side CFX 2 at T1+ and P1, enters turbine 3 in T1+ and P1, leaves the turbine in and P2, Q2 rejects heat Q2 from its medium of ITS 61 in cold-side CFX 4, and leaves cold-side CFX 4 at T0 and P2, returning to its initial state, before entering the compressor.

[00159] In some implementations, the ITS medium 61 may be a liquid throughout the range of To to . In other implementations, the medium of ITS 61 may not be liquid throughout the range from To to , but may be supplied to the counterflow heat exchanger 4 at a higher flow rate so as to achieve a smaller temperature rise across the counterflow heat exchanger (e.g., such that the temperature of the ITS medium at the exchanger outlet of counterflow heat 4 is less than ) while cooling the working fluid for TO. In this case, the temperature of the ITS medium in tank 6o may be lower than . The ITS medium in tank 60 may exchange heat with the environment (e.g., through a radiator or other implementations described herein) to cool back to the temperature To. In some cases, the ITS medium may then be returned to tank 59. In some cases, the heat deposited in the ITS medium may be used for various useful purposes, such as, for example, residential or commercial heating, thermal desalination, or other uses described elsewhere.

[00160] Figure 21 is a schematic flowchart of a discharge cycle of a thermal system pumped in solar mode or heated mode of combustion with heat rejection for an intermediate fluid circulated in a thermal bath at room temperature. The discharge cycle may operate similarly to the discharge cycle in Figure 2o, but after exiting the turbine 3, the working fluid 2o may proceed to the cold-side CFX 4 where it exchanges heat with a circulating medium or intermediate fluid 62. through a thermal bath 63 at temperature T0 at or near room temperature. The intermediate medium or fluid 62 (e.g., Therminol®, or a heat transfer oil) may be used to exchange heat between the working fluid 20 and a thermal bath 63 in the cold-side CFX 4. The use of the intermediate fluid 62 may provide an advantage over contacting a heat sink or cheap medium (e.g. water) directly with the working fluid. For example, direct contact of this thermal medium with the working fluid in the cold-side CFX 4 may cause problems, such as, for example, evaporation or over-pressurization (e.g., explosion) of the thermal medium. The intermediate fluid 62 may remain in the liquid phase throughout at least a portion of, or a significant portion of, the operation in the cold-side CFX 4. When the intermediate fluid 62 passes through the thermal bath 58, it may be sufficiently cooled to circulate back to the cold side CFX 4 to cool the working fluid from , for To. Thermal bath 63 may contain a large amount of inexpensive heat sink material or medium, such as, for example, water. In some cases, the heat deposited on the heat sink material may be used for various useful purposes, such as, for example, residential or commercial heating, thermal desalination, or other uses described elsewhere herein. In some cases, the heat sink material can be rebalanced with the ambient temperature (e.g., through a radiator or other implementations described herein).

[00161] In some implementations, the discharge cycles in Figures 20 and/or 21 may include a recuperator, as described in greater detail in examples throughout the disclosure. Such systems can be implemented using the temperatures T1+, T1, T0+ and T0, described in greater detail elsewhere.

D. Solar-assisted pumped thermal storage cycles with intercooling

[00162] In some cases, the pumped thermal system may provide heat sources and/or cold sources for other installations or systems, such as, for example, through co-location with a gas-to-liquids (GTL) installation or a gas-to-liquids (GTL) installation. of desalination. In one example, the GTL installations may make use of one or more cold reservoirs in the system (e.g., the CTS medium in tank 9 for use in oxygen separation in the GTL installation) and/or one or more hot reservoirs in the GTL installation. system (e.g. the HTS medium in tank 6 for use in a Fischer-Tropsch process in the GTL installation). In another example, one or more hot reservoirs or one or more cold reservoirs in the pumped thermal system may be used for the operation of thermal desalination methods. Other examples of possible uses of heat and cold include co-location or heat exchange with building/area heating/cooling systems.

[00163] Conversely, in some cases, the pumped thermal system may utilize waste heat sources and/or waste cold sources from other facilities or systems, such as, for example, through co-location with a natural gas import or export terminal. liquefied. For example, a source of residual cold may be used to cool the cold-side thermal storage medium 22. In some implementations, cold-side charging using residual cold may be combined with recharging the hot-side thermal storage medium 21 by external heat input (e.g. solar, combustion, waste heat, etc.). In some cases, the recharged storage medium can then be used in a discharge cycle, such as the discharge cycles in Figures 14 or 16. In some cases, the pumped thermal system can be used as a heat engine with a residual heat source serving as a hot-side heat input and a residual cold source serving as a cold-side heat sink. In another implementation, the hot-side storage medium can be recharged using a modified version of the cycle shown in Figure 15, where the temperature T0 is about room temperature. and corresponds to a temperature above ambient temperature. In some examples, a waste heat source may be used to provide the required heat at a temperature of at least to heat the working fluid and/or CTS medium to . In another implementation, an intermediate fluid (e.g., Therminol®) that can remain liquid between temperatures and TO can be used to transfer heat from the waste heat source to the working fluid.

E. Pumped thermal systems with dedicated compressor/turbine pairs

[00164] In a further aspect of the disclosure, pumped thermal systems comprising multiple working fluid systems, or working fluid flow paths, are provided. In some cases, the components of the thermal system pumped in charging and discharging modes may be the same. For example, the same compressor/turbine pair can be used in charge and discharge cycles. Alternatively, one or more system components may differ between charging and discharging modes. For example, separate compressor/turbine pairs can be used in charge and discharge cycles. In one implementation, the system has a set of heat exchangers, and a common set of HTS and CTS tanks that are loaded or unloaded by two pairs or sets of compressors and turbines. In another implementation, the system has a common set of HTS and CTS tanks, but separate sets of heat exchangers and separate sets of compressors and turbines.

[00165] Pumped thermal systems with recovery, utilization of external sources of heat, cold and/or residual heat/cold can benefit from having separate compressor/turbine pairs as a result of operating turbomachinery in large and/or different temperature ranges in loading and unloading modes. For example, temperature changes between charge and discharge cycles can lead to a period of thermal adjustment or other difficulties during the transition between cycles (e.g., issues or factors related to metallurgy, thermal expansion, Reynolds number, compression ratios dependent on temperature, or bearing friction and/or tip clearance, etc.). In another example, turbomachines (e.g., turbomachines used in systems with recovery) may operate at a relatively low pressure rate (e.g., with relatively few compression steps), but at relatively high temperatures during compression and expansion. The temperature ranges may change (e.g., change as in Figures 17 and 18) between charging and discharging modes. In some cases, operation over wide temperature ranges during compression and/or expansion can complicate the design of a combined compressor/turbine for both charging and unloading. Additionally, recovery, incorporation of waste heat/cold and/or other features of the pumped thermal system can reduce the compression ratio of the compressor/turbine in the charging cycle and/or the discharge cycle, thereby reducing the cost associated with duplication. of compressor/turbine assemblies.

[00166] Figures 22 and 23 show pumped thermal systems with separate compressor 1/turbine 3 pairs for charge mode C and discharge mode D. The separate compressor/turbine pairs may or may not be grouped together on a common mechanical rod . In this example, compressor/turbine pairs C and D may have separate shafts 10. The shafts 10 may rotate at the same speed or different speeds. Separate compressor/turbine pairs or working fluid systems may or may not share heat exchangers (e.g., heat exchangers 2 and 4).

[00167] In the example of Figure 22, the system has a common set of HTS tanks 6 and 7 and CTS tanks 8 and 9. The system has separate pairs of heat exchangers 2 and 4 and separate pairs of compressor 1/turbine 3 for charge mode C and discharge mode D. The HTS and CTS storage medium flow paths for the charge cycle are shown as solid black lines. The HTS and CTS storage media flow paths for the discharge cycle are shown as dashed gray lines.

[00168] In the example of Figure 23, the system, shown in a load configuration, has a set of heat exchangers 2 and 4, and a common set of HTS tanks 6 and 7 and CTS tanks 8 and 9. The HTS and CTS tanks can be loaded by a compressor/turbine assembly C, or unloaded by a compressor/turbine assembly D, each assembly comprising a compressor 1 and a turbine 3. The system can switch between sets C and D using valves 83. In the example of Figure 22, the system, again shown in a charging configuration, has a common set of HTS tanks 6 and 7 and CTS tanks 8 and 9. The HTS and CTS tanks can be charged by the charging assembly C that includes a first set of heat exchangers 2 and 4, the compressor 1 and the turbine 3. The HTS and CTS tanks can be discharged by switching to a separate discharge assembly C that includes a second set of exchangers 2 and 4, compressor 1 and turbine 3.

[00169] In one example, if the compressor and turbine loading and unloading sets in Figures 22 and 23 are not operated at the same time, the loading and unloading sets may share a common set of heat exchangers that are switched between the pairs of turbomachines using valves 83. In another example, if the sets or pairs of charging and unloading turbomachines in Figures 22 and 23 are operated at the same time (e.g., for one set to charge, after intermittent generation, and the other is discharged at the same time, after charging), then each set of turbomachinery can have a dedicated set of heat exchangers. In this case, the loading and unloading sets may or may not share a set of HTS and CTS tanks.

[00170] In some implementations, separate sets or pairs of compressors/turbines may be advantageously used in pumped thermal systems used with intermittent and/or variable electrical power inputs. For example, a first compressor/turbine assembly may be used in a load cycle that follows wind and/or solar energy (e.g., electrical energy input from wind and/or solar energy systems) while a second compressor assembly /turbine can be used in a discharge cycle that follows charge (e.g., output of electrical power to an electrical grid). In this configuration, pumped thermal systems placed between a power generation system and a load can assist in smoothing out variations/fluctuations in input and/or output power requirements.

F. Hybrid pumped thermal systems

[00171] According to another aspect of the disclosure, pumped thermal systems can be augmented by additional energy conversion processes and/or can be used directly as energy conversion systems without energy storage (i.e., as power generation systems). power). In some examples, pumped thermal systems can be modified to allow direct power generation using natural gas, diesel fuel, petroleum gas (e.g., propane/butane), dimethyl ether, fuel oil, wood chips, landfill gas , hexane, hydrocarbons, or any other combustible substance (e.g., fossil fuel or biomass) to add heat to the working fluid on a hot side of a working fluid cycle and a cold heat sink (e.g., water) to remove Heat from the working fluid on one side comes from the working fluid cycle.

[00172] Figures 24 and 25 show pumped thermal systems configured in generation mode. In some examples, the pumped thermal systems may be modified by adding two additional heat exchangers 40 and 41, four additional valves 19a, 19b, 19c and 19d, a heat sink (e.g., a water cooling system; water from a fresh water reservoir such as a river, a lake or a reservoir, salt water from a salt water reservoir such as a sea or an ocean, air cooling using radiators, fans/blowers, convection or an environmental heat sink such as soil /earth, cold air, etc.) 42, and a heat source (e.g., a combustion chamber with an oxidizer-fuel mixture) 43. The heat source 43 can exchange heat with a first of two additional heat exchangers 40 , and the heat sink 42 can exchange heat with a second of two additional heat exchangers 41. The heat source 43 can be used to exchange heat with the working fluid 20.

[00173] The heat source 43 may be a combustion heat source. In some examples, the combustion heat source may comprise a combustion chamber for combustion of a combustible substance (e.g., a fossil fuel, a synthetic fuel, municipal solid waste (MSW), or biomass). In some cases, the combustion chamber may be separated from the heat exchanger 40. In some cases, the heat exchanger 40 may comprise the combustion chamber. The heat source 43 may be a waste heat source, such as, for example, waste heat from an electrical plant, an industrial process (e.g., furnace exhaust).

[00174] In some examples, a solar heater, a combustion heat source, a waste heat source, or any combination thereof, may be used to heat the hot side heat storage fluid and/or the working fluid . In one example, the working fluid can be heated directly using any of these heat sources. In another example, the hot side heat storage fluid (or HTS medium) can be heated using any of these heat sources. In another example, the hot-side heat storage fluid (or HTS medium) can be heated in parallel with the working fluid using any of these heat sources.

[00175] The pumped thermal systems in Figures 24 and 25 can be operated as hybrid systems. For example, valves 19a, 19b, 19c and 19d can be used to switch between two modes. When the valves are in a first position, the system can operate as a pumped thermal storage system (e.g. closed system in charge/discharge mode). In this configuration, the working fluid 20 (e.g., argon or air) can exchange heat with an HTS medium (e.g., molten salt) in the hot-side heat exchanger 2 and with a CTS medium (e.g., hexane ) on the cold side heat exchanger 4. When the valves are in a second position, the system can operate as a power generation system (e.g., open system in generation mode). In this configuration, heat exchangers 2 and 4 can be bypassed, and the working fluid 20 can exchange heat with the combustion chamber 43 in the hot-side heat exchanger 40 and with the heat sink 42 in the hot-side heat exchanger 40. cold 41. The configuration and/or design of heat transfer processes (e.g. heat transfer in heat exchangers) described here in relation to pumped thermal systems can also be applied to hybrid pumped thermal systems and vice versa. For example, the heat sink 42, the heat source 43, the heat exchangers 40 and 41, and/or the amount of heat transferred on the cold side and/or the hot side may be configured to decrease or minimize entropy generation. associated with heat transfer processes and/or maximize system efficiency.

[00176] In some implementations, hybrid systems can operate in storage and generation modes simultaneously. For example, valves 19a, 19b, 19c and 19d may be configured to allow a given split between a working fluid flow rate to the heat exchangers 40 and 41 and a working fluid flow rate to the heat exchangers. heat 2 and 4. Alternatively, hybrid systems can operate exclusively in storage mode, or exclusively in generation mode (for example, as a natural gas peaking plant). In some cases, the split between modes may be selected based on system efficiency, available electrical power input (e.g., based on availability), desired electrical power output (e.g., based on load demand) etc. For example, thermal efficiency of an ideal system (i.e., assuming isentropic compression and expansion processes, ideal heat transfer processes) operating exclusively in generation mode could be the thermal efficiency of a working fluid subjected to a Brayton cycle ideal. In some examples, thermal efficiencies in hybrid systems of the disclosure (e.g., exclusive and/or split mode operation) may be at least about 10%, at least 20%, at least about 30%, at least about 40%. %, at least about 50%, at least about 60%, or more.

[00177] Heat source 43 can be used to exchange heat with an HTS medium (e.g., a molten salt). For example, the combustion heat source 43 may be used to heat the HTS medium 21. In some cases, instead of using the combustion heat source 43 to exchange heat in the heat exchanger 40 or to exchange heat between gases of combustion from the combustion heat source and the working fluid, the combustion heat source 43 can be used to heat the HTS medium 21 between the two HTS tanks 7 and 6.

[00178] Figure 26 is a schematic flowchart of hot side recharging in a pumped heat cycle through heating by heat source 43 (e.g., combustion heat source, waste heat source). In one example, the heat source 43 is a waste heat source, such as a waste heat source from a refinery or other processing facility. In one example, the heat source 43 is obtained from the combustion of natural gas to ensure delivery of electricity even if the pumped thermal system runs out of charged storage medium. For example, recharging the hot-side storage medium using heat source 43 may provide an advantage over recharging using electricity or other means (e.g., the price of electricity at present may be very high). The heat source 43 can be used to heat the HTS medium 21 from the temperature T1 in tank 7 to the temperature T1+ in tank 6. The HTS medium can then be used in the CFX 2 to exchange heat with the working fluid. in a discharge cycle, such as, for example, the discharge cycles in Figures 20 and 21.

[00179] In some examples, such as, for example, when the CTS medium is a combustible substance, such as a fossil fuel (e.g., hexane or heptanes), burning the CTS medium stored in the CTS tanks (e.g., tanks 8 and 9) can be used to provide thermal energy to heat the HTS medium as shown, for example, in Figure 26 or for operation of the cycles in the configurations shown, for example, in Figures 24 and 25.

[00180] The systems of the disclosure may be capable of operating either in an electricity storage cycle only (comprising heat transfer with an HTS medium and a CTS medium below ambient temperature) or in an ambient cycle heat engine , where, in a discharge mode, heat is input from the HTS medium to the working fluid and rejected to the environment rather than to the CTS medium. This capability may allow the use of heating the HTS with combustible substances (e.g., as shown in Figure 26) or the use of solar heating of the HTS (e.g., as shown in Figure 19). Heat rejection to ambient temperature can be implemented using, for example, the discharge cycles in Figures 20 and 21. In some cases, heat can be rejected to the environment with the aid of ITS medium 61 or intermediate medium 62 .

[00181] Aspects of disclosure can be combined synergistically. For example, systems capable of operating in both an electricity storage cycle only and a heat engine for ambient cycle may comprise a recuperator. Any description regarding such hybrid systems without a recuperator can be readily applied to hybrid systems with a recuperator in at least some configurations. In some cases, hybrid systems can be implemented using, for example, the parallel configuration with valves in Figure 24. For example, the counterflow heat exchangers 4 in Figures 20 and 21 can be implemented as separate counterflow heat exchangers 67 to exchange heat with the environment, and may be used in combination with cold-side counterflow heat exchangers 4 of the disclosure.

[00182] In some implementations, the systems herein may be configured to allow switching between different cycles of the disclosure using a shared set of valves and tubes. For example, the system can be configured to alternate between the electricity-only charge cycle (as shown, for example, in Figure 15), the electricity-only discharge cycle (as shown, for example, in Figure 16), and the heat engine for ambient cycle (as shown in Figure 21).

G. Pumped thermal systems with pressure regulation power control

[00183] In one aspect of the disclosure, the pressure of working fluids in pumped thermal systems can be controlled to achieve power control. In one example, the energy supplied to a closed system in charge mode and/or the energy extracted from the closed system in discharge and/or generation mode (e.g., work input/output using rod 10) is proportional to the rate mass or molar flow rate of the circulating working fluid. The mass flow rate is proportional to density, area and flow velocity. The flow speed can be kept fixed in order to achieve a fixed shaft speed (e.g. 3600 rpm or 3000 rpm according to the electrical grid requirements of 60 and 50 Hz, respectively). Thus, as the pressure of the working fluid changes, the mass flow rate and power can change. In one example, as mass flow increases in a discharge and/or generation mode, more load must be added to the system to maintain a constant rotating shaft speed, and vice versa. In another example, if the load is reduced during operation in a discharge and/or generation mode, the reduced load can cause the rod speed to increase, thereby increasing the mass flow rate. For some period of time, before the heat stored in the thermal capacity of the heat exchangers themselves is dissipated, this increase in mass flow rate can lead to an increase in energy supplied, in turn increasing rod speed. Rod speed and power may continue to increase uncontrollably, resulting in a runaway of the rotating shaft. In some examples, pressure regulation may allow control and thus stabilization of leakage, by adjusting the quantity (e.g. density) of circulating working fluid in accordance with system requirements. In an example where shaft speed (and turbomachinery, such as a turbine, connected to the shaft) begins to run away, a controller can reduce the mass of the circulating working fluid (e.g., mass flow rate) to decrease the energy supplied, in turn, decreasing rod speed. Pressure regulation can also allow an increase in mass flow rate in response to an increase in load. In each of these cases, the flow rates of the HTS and CTS media through the heat exchangers can be adapted to the heat capacity of the working fluid passing through the heat exchangers.

[00184] In some examples, the working fluid pressure in the closed system can be varied using an auxiliary working fluid tank in fluid communication with the closed system. In this configuration, the energy input/output can be decreased by transferring the working fluid from the closed-loop circuit to the tank, and the energy input/output can be increased by transferring the working fluid from the tank to the closed-loop circuit. closed cycle. In one example, when the working fluid pressure is decreased, less heat can be transferred between thermal storage tanks on the hot and cold sides of the system, as a result of which the mass flow rate decreases and less energy can be input to /issued by the system.

[00185] As the working fluid pressure is varied, the compression ratios of the turbomachinery components can remain substantially unchanged. In some cases, one or more operating parameters and/or configuration (e.g., variable stators, rod speed) of turbomachinery components may be adjusted in response to a change in working fluid pressure (e.g., to obtain performance desired from the system). Alternatively, one or more pressure ratios may change in response to a change in working fluid pressure.

[00186] In some cases, reduced cost and/or reduced parasitic power consumption can be achieved by using the power control configuration over other configurations (e.g., using a throttling valve to control the flow of power fluid). work). In some examples, varying the working fluid pressure while keeping the temperature and flow velocity constant (or nearly constant) can lead to the generation of negligible entropy. In some examples, an increase or decrease in system pressure can lead to changes in, for example, the efficiency of turbomachinery.

[00187] Figure 27 shows an example of a pumped thermal system with energy control. The temperature of the working fluid on the hot and cold sides of the system can remain constant or nearly constant for a given period of time regardless of the mass flow rate of the working fluid due to the large thermal capacities of heat exchangers 2 and 4 and/or or the hot and cold side thermal storage medium in tanks 6, 7, 8 and 9. In some examples, the flow rates of the HTS and CTS media through heat exchangers 2 and 4 are varied in conjunction with a change in working fluid pressure in order to maintain temperatures in the heat exchangers and working fluid optimized over longer periods of time. Thus, pressure can be used to vary the mass flow rate in the system. One or more auxiliary tanks 44 filled with working fluid 20 (e.g., air, argon, or argon-helium mixture) may be in fluid communication with a hot (e.g., high pressure) side of the pumped thermal system and/or a cold (e.g. low pressure) side of the pumped thermal system. In some examples, the auxiliary tank may be in fluid communication with the working fluid adjacent to an inlet of the compressor 1 and/or adjacent to an outlet of the compressor 1. In some examples, the auxiliary tank may be in fluid communication with the fluid working fluid adjacent to a turbine inlet 3 and/or adjacent to a turbine outlet 3. In further examples, the auxiliary tank may be in fluid communication with the working fluid in one or more location systems (e.g., one or more locations on the high pressure side of the system, the low pressure side of the system, or any combination thereof. For example, the auxiliary tank may be in fluid communication with the working fluid on a high pressure side and a low pressure side. closed cycle low pressure. In some cases, fluid communication on the high pressure side may be provided after the compressor and before the turbine. In some cases, fluid communication on the low pressure side may be provided after the turbine and before the compressor. In some cases, the auxiliary tank may contain working fluid at a pressure intermediate to the high and low system pressures. The working fluid in the auxiliary tank can be used to increase or decrease the amount of working fluid 20 circulating in the closed cycle of the pumped thermal system. The amount of working fluid circulating in the closed cycle can be decreased by draining the working fluid from the high pressure side of the closed cycle into the tank through a fluid path containing a valve or mass flow controller 46, thereby charging the tank 44. The amount of working fluid circulating in the closed cycle can be increased by draining the working fluid from the tank to the low pressure side of the closed cycle circuit through a fluid path containing a valve or flow controller. mass 45, thus unloading tank 44.

[00188] Power control on longer time scales can be implemented by changing the working fluid pressure and adjusting the flow rates of hot-side thermal storage fluids 21 and cold-side 22 through heat exchangers 2 and 4, respectively.

[00189] In some examples, the flow rates of thermal storage means 21 and/or 22 may be controlled (e.g., by a controller) to maintain given inlet and outlet temperatures of the heat exchanger. In some examples, a first controller(s) may be provided to control flow rates (e.g., mass flow rates) of thermal storage medium, and a second controller may be provided to control the mass flow rate. (e.g., by controlling mass, mass flow rate, pressure, etc.) of the working fluid.

H. Pumped thermal systems with pressure encapsulated motor/generator

[00190] In another aspect of the disclosure, pumped thermal systems with an encapsulated pressure motor/generator are provided. The pressure encapsulated engine/generator can be provided as an alternative to configurations where a rod (also “crankshaft”) penetrates through a working fluid containment wall (where it may be exposed to one or more relatively high pressure differentials). to connect to a motor/generator outside the working fluid containment wall. In some cases, the rod may be exposed to working fluid pressures and temperatures in the low pressure portion of the working fluid cycle, the high pressure portion of the working fluid cycle, or both. In some cases, crankshaft seal(s) capable of containing the pressures to which the crankshaft is exposed within the working fluid containment wall may be difficult to manufacture and/or difficult to maintain. In some cases, a rotary seal between high and low pressure environments may be difficult to achieve. Therefore, coupling the compressor and turbine to the engine/generator can be challenging. In some implementations, the motor/generator may therefore be placed entirely within the low-pressure portion of the working fluid cycle, such that the outer pressure vessel or working fluid containment wall may not need to be removed. penetrated.

[00191] Figure 28 shows an example of a pumped thermal system with an encapsulated pressure generator 11. The motor/generator is encapsulated within the pressure vessel or working fluid containment wall (shown as dashed lines) and only conductors electrical feed passage 49 penetrate through the pressure vessel. A thermal insulation wall 48 is added between the engine/generator 11 and the working fluid in the low pressure portion of the cycle. The technical requirements for obtaining an adequate seal through the thermal insulation wall may be less stringent due to the pressure being the same on both sides of the thermal insulation wall (for example, both sides of the thermal insulation wall may be located in the portion low cycle pressure). In one example, the low pressure value may be approximately 10 atm (1.01325 MPa). In some cases, the engine/generator can be adapted for operation at elevated surrounding pressures. An additional thermal insulation wall 50 may be used to create a seal between the compressor outlet 1 and the turbine inlet 3 in the high pressure portion of the cycle. In some examples, placing the engine/generator on the cold side of pumped thermal systems may be beneficial to engine/generator operation (e.g., cooling a superconducting generator).

I. Pumped thermal systems with variable stator pressure rate control

[00192] Another aspect of the disclosure relates to pressure control in working fluid cycles of thermal systems pumped using variable stators. In some examples, the use of variable stators in turbomachinery components can allow pressure rates in working fluid cycles to be varied. The variable compression ratio can be realized by means of movable stators in the turbomachine.

[00193] In some cases, pumped thermal systems (e.g., the systems in Figures 17 and 18) can operate at the same compression ratio in both the charging and discharging cycles. In this configuration, heat can be rejected (e.g. to the environment) in section 38 in the charging cycle and in section 39 in the discharge cycle, where the heat in section 38 can be transferred at a lower temperature than the heat in section 39. In alternative configurations, the compression ratio can be varied by switching between the charge cycle and the discharge cycle. In one example, variable stators can be added to the compressor and turbine, thus allowing the compression ratio to be adjusted. The ability to vary the compression ratio between charge and discharge modes may allow heat to be rejected only at the lowest temperature (e.g., heat may be rejected at section 38 in the charge cycle, but not at section 39 of the discharge cycle). In some examples, a greater portion (or all) of the heat rejected to the environment is transferred at a lower temperature, which can increase the round-trip efficiency of the system.

[00194] Figure 29 is an example of variable stators in a compressor/turbine pair. Compressor 1 and turbine 3 can have variable stators, so the compression ratio of each can be adjusted. Such adjustment can increase round-trip efficiency.

[00195] The compressor and/or turbine may (each) include one or more compression stages. For example, the compressor and/or turbine may have multiple rows of repeating features distributed along its circumference. Each compression stage can include one or more feature lines. Rows can be arranged in a certain order. In one example, the compressor 1 and the turbine 3 each comprise a sequence of a plurality of inlet guide vanes 51, a first plurality of rotors 52, a plurality of stators 53, a second plurality of rotors 52 and a plurality of of output guide vanes. 54. Each plurality of features may be arranged in a line along the circumference of the compressor/turbine. The configuration (e.g., direction or angle) of the stators 53 can be varied, as indicated in Figure 29.

[00196] The compressor/turbine pair can be combined. In some cases, a compressor outlet pressure may be approximately the same as a turbine inlet pressure, and a compressor inlet pressure may be approximately the same as the turbine outlet pressure; thus, the pressure rate through the turbine can be the same as the pressure rate through the compressor. In some cases, inlet/outlet pressures and/or pressure ratios may differ by a certain amount (e.g., to account for pressure drop in the system). The use of variable stators in the compressor and turbine can allow the compressor and turbine to remain compatible as the compression ratio is varied. For example, by using variable stators, compressor and turbine operation can remain within suitable operating conditions (e.g., within a certain range or at a certain point on their respective operating maps) as the compression ratio is varied. Operation within given ranges or at given points on turbomachinery operating maps can allow turbomachinery efficiencies (e.g., isentropic efficiencies) and the resulting round-trip storage efficiency to be maintained within a desired range. In some implementations, the use of variable stators may be combined with other methods to vary compression ratios (e.g. variable shaft rotational speed, bypass of turbomachinery stages, gears, power electronics, etc.)

J. Pumped thermal system units comprising pumped thermal system subunits

[00197] Another aspect of the disclosure relates to controlling the charge and discharge rate over the entire range from maximum charge/energy input to maximum discharge/energy output through the construction of pumped thermal system units comprised of pumped thermal system subunits. In some examples, pumped thermal systems may have a minimum energy input and/or output (e.g., minimum energy input and/or minimum energy) above 0% of the maximum energy input and/or output (e.g., input maximum power output and/or maximum power output), respectively. In these cases, a single unit by itself may be capable of moving continuously from minimum power input to maximum power input and from minimum power output to maximum power output, but may not be able to move continuously from input power. minimum energy to minimum energy output (i.e., from minimum energy input to zero energy input/output and from zero energy input/output to minimum energy output). An ability to continuously move from minimum energy input to minimum energy output can allow the system to continuously move from maximum energy input to maximum energy output. For example, if both output power and input power can be turned off to zero during operation, the system can continuously vary the power consumed or supplied over a range from the maximum input (e.g., by acting as a load on the grid) for maximum output (e.g. acting as a generator on the grid). Such functionality can increase (e.g. more than double) the continuously passable range of the pumped thermal system. Increasing the continuously passable range of the pumped thermal system can be advantageous, for example, when the continuously passable power range is used as a metric to determine the value of grid assets. Furthermore, such functionality may allow disclosure systems to track variable load, variable generation, intermittent generation, or any combination thereof.

[00198] In some implementations, composite pumped thermal system units comprising multiple pumped thermal system subunits can be used. In some cases, each subunit may have a minimum energy input and/or output above 0%. The continuous passage of energy from the maximum energy input to the maximum energy output may include the combination of a certain number of subunits. For example, an adequate (e.g., sufficiently large) number of subunits may be required to obtain continuous acceleration. In some examples, the number of subunits may be at least about 2, 5, 10, 20, 30, 40, 50, 100, 200, 500, 750, 1000 and the like. In some examples, the number of subunits is 2, 5, 10, 20, 30, 40, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750 , 800, 850, 900, 950, 1000 or more. Each subunit can have a certain energy capacity. For example, each subunit may have a power capacity that is less than about 0.1%, less than about 0.5%, less than about 1%, less than about 5%, less than about 10 %, less than about 25%, less than about 50%, or less than about 90% of the total energy capacity of the composite pumped thermal system. In some cases, different subunits may have different energy capacities. In some examples, a subunit has a power capacity of about 10 kW, 100 kW, 500 kW, 1 MW, 2 MW, 5 MW, 10 MW, 20 MW, 50 MW, 100 MW or more. The continuous passage of energy from maximum energy input to maximum energy output may include controlling the input and/or output of each subunit (e.g., energy input and/or energy output) separately. In some cases, the subunits may be operated in opposite directions (e.g., one or more subunits may operate in power input mode, while one or more subunits may operate in power output mode). In one example, if each subunit of the pumped thermal system can be continuously passed between a maximum power input and/or output downward to about 50% of the maximum power input and/or output, respectively, three or more system subunits thermal combined into a composite pumped thermal system unit that can be continuously passed from maximum power input to maximum power output. In some implementations, the composite pumped thermal system may not have a fully continuous range between maximum input power and maximum output power, but may have a greater number of operating points in this range compared to a non-composite system.

K. Energy storage system units comprising energy storage system subunits

[00199] Another aspect of the disclosure relates to controlling the charge and discharge rate over a complete range from the maximum charge/energy input to the maximum discharge/energy output through the construction of energy storage system units. compounds made up of energy storage system subunits. In some examples, energy storage systems may have a minimum energy input and/or output (e.g., minimum energy input and/or minimum energy output) above 0% of the maximum energy input and/or output (e.g. maximum power input and/or maximum power output), respectively. In these cases, a single unit by itself may be capable of moving continuously from minimum power input to maximum power input and from minimum power output to maximum power output, but may not be able to move continuously from input power. minimum energy to minimum energy output (i.e., from minimum energy input to zero energy input/output and from zero energy input/output to minimum energy output). An ability to continuously move from minimum energy input to minimum energy output can allow the system to continuously move from maximum energy input to maximum energy output. For example, if both output power and input power can be completely reset to zero during operation, the system can continuously vary the power consumed or supplied over a range from the maximum input (e.g., acting as a load on the grid) for maximum output (e.g. acting as an on-grid generator). Such functionality can increase (e.g., more than double) the continuously passable range of the energy storage system. Increasing the continuously passable range of the energy storage system can be advantageous, for example, when the continuously passable energy range is used as a metric to determine the value of grid assets. Furthermore, such functionality may allow disclosure systems to track variable load, variable generation, intermittent generation, or any combination thereof.

[00200] In some implementations, composite energy storage system units composed of multiple energy storage system subunits may be used. In some examples, any energy storage system with power input/output capabilities that can benefit from a composite configuration can be used. In some examples, systems with energy input and/or output capabilities that can benefit from a composite configuration may include multiple energy storage and/or generation systems, such as natural gas or combined cycle power plants. , fuel cell systems, battery systems, compressed air energy storage systems, pumped hydroelectric systems, etc. In some cases, each subunit may have a minimum energy input and/or output above 0%. The continuous passage of energy from the maximum energy input to the maximum energy output may include the combination of a certain number of subunits. For example, an adequate (e.g., sufficiently large) number of subunits may be required to obtain continuous acceleration. In some examples, the number of subunits may be at least about 2, 5, 10, 20, 30, 40, 50, 100, 200, 500, 750, 1000 and the like. In some examples, the number of subunits is 2, 5, 10, 20, 30, 40, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750 , 800, 850, 900, 950, 1000 or more. Each subunit can have a certain energy capacity. For example, each subunit may have a power capacity of less than about 0.1%, less than about 0.5%, less than about 1%, less than about 5%, less than about 10%, less than about 25%, less than about 50%, or less than about 90% of the total energy capacity of the composite energy storage system. In some cases, different subunits may have different energy capacities. In some examples, a subunit has a power capacity of about 10 kW, 100 kW, 500 kW, 1 MW, 2 MW, 5 MW, 10 MW, 20 MW, 50 MW, 100 MW or more. The continuous passage of energy from maximum energy input to maximum energy output may include controlling the input and/or output of each subunit (e.g., energy input and/or energy output) separately. In some cases, the subunits may be operated in opposite directions (e.g., one or more subunits may operate in power input mode, while one or more subunits may operate in power output mode). In an example, if each subunit of the energy storage system can be continuously cycled between a maximum energy input and/or output up to about 50% of the maximum energy input and/or output, respectively, three or more such subunits of Energy storage system can be combined into a composite energy storage system unit that can be continuously switched from maximum energy input to maximum energy output. In some implementations, the composite energy storage system may not have a fully continuous range between maximum power input and maximum power output, but may have an increased number of operating points in that range compared to a non-composite system. compound.

L. Control systems

[00201] The present disclosure provides computer control systems (or controllers) that are programmed to implement methods of the disclosure. Figure 30 shows a computer system 1901 (or controller) that is programmed or otherwise configured to regulate various process parameters of energy storage and/or recovery systems disclosed herein. Such process parameters may include temperatures, flow rates, pressures, and entropy changes.

[00202] The computer system 1901 includes a central processing unit (CPU, also "processor" and "computer processor" herein) 1905, which may be a single-core or multi-core processor, or a plurality of processors for processing parallel. The computer system 1901 also includes memory or memory location 1910 (e.g., random access memory, read-only memory, flash memory), electronic storage unit 1915 (e.g., hard disk), communications interface 1920 (e.g., e.g., network adapter) for communicating with one or more other systems and peripheral devices 1925, such as cache, other memory, data storage, and/or electronic video adapters. The memory 1910, the storage unit 1915, the interface 1920, and the peripheral devices 1925 are in communication with the CPU 1905 via a communication bus (solid lines), such as a motherboard. The storage unit 1915 may be a data storage unit (or data repository) for storing data. The computer system 1901 may be operatively coupled to a computer network (“network”) 1930 with the aid of the communication interface 1920. The network 1930 may be the Internet, an internet and/or extranet, or an intranet and/or extranet that is in communication with the Internet. The 1930 network, in some cases, is a telecommunications and/or data network. Network 1930 may include one or more computer servers, which may enable distributed computing, such as cloud computing. The network 1930, in some cases with the assistance of the computer system 1901, may implement a peer-to-peer network, which may allow devices coupled to the computer system 1901 to behave as a client or a server.

[00203] The computer system 1901 is coupled to an energy storage and/or recovery system 1935, which may be as described above or elsewhere in this document. The computer system 1901 may be coupled to various unit operations of the system 1935, such as flow regulators (e.g., valves), temperature sensors, pressure sensors, compressor(s), turbine(s), electrical switches, and photovoltaic modules. System 1901 may be directly coupled, or be part of system 1935, or be in communication with system 1935 via network 1930.

[00204] The CPU 1905 can execute a sequence of machine-readable instructions, which can be incorporated into a program or software. Instructions may be stored in a memory location, such as memory 1910. Examples of operations performed by CPU 1905 may include fetching, decoding, executing, and writing back.

[00205] With continued reference to Figure 30, the storage unit 1915 can store files such as drivers, libraries, and saved programs. The storage unit 1915 can store user-generated programs and recorded sessions, as well as output(s) associated with the programs. The storage unit 1915 may store user data, e.g., user preferences and user programs. The computer system 1901 in some cases may include one or more additional data storage units that are external to the computer system 1901, such as located on a remote server that is in communication with the computer system 1901 via an intranet or the Internet.

[00206] Computer system 1901 may communicate with one or more remote computer systems via network 1930. For example, computer system 1901 may communicate with a remote computer system of a user (e.g., operator). Examples of remote computer systems include personal computers, slate or tablet PCs, telephones, smart phones, or personal digital assistants. The user can access the computer system 1901 through the network 1930.

[00207] The methods described herein may be implemented by means of machine-executable code (e.g., computer processor) stored in an electronic storage location of computer system 1901, such as, for example, in memory 1910 or storage unit electronic 1915. Machine-executable or machine-readable code may be provided in the form of software. During use, code may be executed by processor 1905. In some cases, code may be retrieved from storage unit 1915 and stored in memory 1910 for immediate access by processor 1905. In some situations, electronic storage unit 1915 may be deleted, and machine-executable instructions are stored in memory 1910.

[00208] The code may be precompiled and configured for use with a machine that has a processor adapted to execute the code, or may be compiled at run time. The code may be provided in a programming language that can be selected to allow the code to be executed in a pre-compiled or as-compiled form.

[00209] Aspects of the systems and methods provided herein, such as computer system 1901, may be incorporated into programming. Various aspects of technology can be considered as “products” or “articles of manufacture” typically in the form of machine (or processor) executable code and/or associated data that are transported or incorporated into a type of machine-readable medium. Machine-executable code can be stored in an electronic storage unit, such as memory (e.g., read-only memory, random access memory, flash memory) or a hard drive. “Storage” media may include any or all of the tangible memory of computers, processors, or the like, or associated modules, such as various semiconductor memories, tape drives, disk drives, and the like, that can provide non-transitory storage at any time for software programming. All or part of the software may sometimes be communicated over the Internet or various other telecommunications networks. Such communications, for example, may allow the loading of software from one computer or processor to another, for example, from a management server or host computer to the computer platform of an application server. Thus, another type of medium that can contain software elements includes optical, electrical, and electromagnetic waves, such as those used in physical interfaces between local devices, across wired and optical terrestrial networks, and across various air links. The physical elements that carry such waves, such as wired or wireless connections, optical connections or the like, can also be considered as media supporting the software. As used herein, unless restricted to non-transitory “tangible” storage media, terms such as “computer or machine-readable medium” refer to any medium that participates in providing instructions to a processor for execution.

[00210] Thus, a machine-readable medium, such as computer executable code, can take many forms, including, but not limited to, a tangible storage medium, a carrier wave medium, or physical transmission medium. Non-volatile storage media include, for example, optical or magnetic disks, such as any of the storage devices in any computer(s) or the like, as may be used to implement databases, etc. shown in the drawings. Volatile storage media includes dynamic memory, such as the main memory of such a computer platform. Tangible transmission media include coaxial cables; copper wire and fiber optics, including the wires that make up a bus within a computer system. Carrier wave transmission media may take the form of electrical or electromagnetic signals, or acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example: a floppy disk, a floppy disk, a hard disk, a magnetic tape, any other magnetic medium, a CD-ROM, DVD or DVD-ROM, any other optical medium, paper tape, punched cards, any other physical storage medium with hole patterns, a RAM, a ROM, a PROM and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave carrying data or instructions, cables or links carrying such a carrier wave, or any other medium from which a computer can read programming code and/or data. Many of these forms of computer-readable media may be involved in transporting one or more sequences of one or more instructions to a processor for execution.

III Illustrative Variable Pressure Inventory Control Systems

[00211] Figure 31 and 32 illustrate examples of closed cycle systems, such as Brayton systems, and include a working fluid flowing through at least one compressor 3103, a hot-side heat exchanger 3107, a turbine 3105 and a cold-side heat exchanger 3109. A thermal storage medium may flow between the hot storage container (“HSC”) 3113 and the cold storage container (“CSC”) 3115 through the hot-side heat exchanger 3107 Other thermal storage medium may flow between the HSC 3117 and the CSC 3119 through the cold-side heat exchanger 3109. The fluid paths are as indicated in the individual Figures and the flow direction of a fluid in a given fluid path is indicated by one or more arrows. Each of the fluids, components and/or fluid paths identified above may be the same or similar to the previously described closed cycle elements (e.g., Brayton cycle), such as working fluid 20, compressor 1, side heat exchanger hot 2, turbine 3, cold side heat exchanger 4, HTS medium 21, HTS tank 7, HTS tank 6, CTS medium 22, CTS tank 8 and CTS tank 9. Figure 31 and 32 are illustrative only and other fluids, components and/or fluid paths may be present. Some components, such as a heat exchanger or hot-side or cold-side tanks, can be replaced with other components that serve a similar thermal purpose.

[00212] Figure 31 illustrates a variable pressure inventory control system 3100 implemented in a Brayton cycle heat engine. The heat engine may be reversible (i.e., operate as a heat pump) and may take the form of other heat engines and/or reversible heat engines described herein and may include additional components beyond those shown in the illustration. The heat engine may include a generator/engine 3101 that may generate electricity and distribute some or all of the generated electricity to a grid system, including a local, municipal, regional, or national electrical grid. When the heat engine is in power generation mode (i.e., discharge mode), the generator/engine 3101 can also be practically referred to as just a generator, since it can function primarily or entirely as a device for generating electricity. The generator/engine 3101, as illustrated, may include an alternator, a high-speed alternator, and/or power electronics (e.g., power frequency conversion electronics) to manage, convert, and/or modify electrical phase, voltage, current and frequency of generated and/or distributed energy. The generator/engine 3101 may be mechanically coupled to the compressor 3103 and the turbine 3105. The compressor 3103 and the turbine 3105 may be coupled to the generator/engine 3101 through one or more rods 3123. Alternatively, the compressor 3103 and the turbine 3105 can be coupled to the 3101 generator/motor through one or more gearboxes and/or rods.

[00213] The heat engine may include a hot side heat exchanger 3107 coupled downstream from the compressor 3103 and upstream of the turbine 3105. Additionally, the heat engine may include a cold side heat exchanger 3109 coupled upstream of the compressor 3103 and downstream of the turbine 3105. In the heat engine, a working fluid may circulate through a closed-loop fluid path that includes, in sequence, the compressor 3103, the hot-side heat exchanger 3107 , turbine 3105, and cold-side heat exchanger 3109. The closed-cycle fluid path may include a high-pressure leg 3106 and a low-pressure leg 3108. The high-pressure leg 3106 may be all or a portion of the closed cycle fluid path downstream of the compressor 3103 and upstream of the turbine 3105. Additionally, the low pressure leg 3108 may be all or part of the closed cycle fluid path upstream of the compressor 3103 and downstream of the turbine 3105 The working fluid pressure in the high pressure leg 3106 may be greater than the working fluid pressure in the low pressure leg 3108. Non-limiting examples of working fluids include air, argon, carbon dioxide or gas mixtures.

[00214] Within the hot-side heat exchanger 3107, the working fluid circulating through the closed-loop fluid path may contact a first thermal fluid. Preferably, the first thermal fluid may be a molten salt. The 3107 hot side heat exchanger may be a counterflow heat exchanger. The hot HSC 3113 can be coupled to the hot side heat exchanger 3107. Additionally, the CSC 3115 can be coupled to the hot side heat exchanger 3107. When the heat engine is in power generation mode, a pump 3102 can pump the first thermal fluid from the HSC 3113, through the hot side heat exchanger 3107, and to the CSC 3115. As shown, the pump 3102 is connected between the HSC 3113 and the hot side heat exchanger 3107; however, the pump 3102 may be connected anywhere in the first thermal fluid path, including between the hot-side heat exchanger 3107 and the CSC 3115. For example, when the heat engine operates as a heat pump in a energy storage mode (i.e., charge mode), a pump such as pump 3102 can be connected between the hot-side heat exchanger 3107 and the CSC 3115 and can first pump thermal fluid from the CSC 3115 , through the hot side heat exchanger 3107 and to the HSC 3113. Additionally, the pump 3102 may be a variable speed pump and/or be one or more pumps. Additionally, as used herein, hot storage and cold storage are used to reflect relative temperatures between storage containers that may share a common thermal storage medium and do not necessarily refer to locations within a hot side or cold side of an engine. heat or heat pump.

[00215] Within the cold-side heat exchanger 3109, the working fluid circulating through the closed-loop fluid path may come into contact with a second thermal fluid, which may be different from the first thermal fluid. Preferably, the second thermal fluid may be an alkane, such as hexane. The 3109 cold side heat exchanger may be a counterflow heat exchanger. The CSC 3119 can be coupled to the 3109 cold-side heat exchanger. Additionally, the HSC 3117 can be coupled to the 3109 cold-side heat exchanger. When the heat engine is in power generation mode, a 3104 pump can pump the second the CSC 3119, through the cold side heat exchanger 3109, and into the HSC 3117. As shown, the pump 3104 is connected between the CSC 3119 and the cold side heat exchanger 3109; however, pump 3104 can be connected anywhere in the second thermal fluid path, including between cold-side heat exchanger 3109 and HSC 3117. For example, when the heat engine operates as a heat pump in mode of energy storage, a pump, such as pump 3104, can be connected between the cold-side heat exchanger 3109 and the HSC 3117 and can pump the second thermal fluid from the HSC 3117, through the heat exchanger 3109 and for the CSC 3119. Additionally, the pump 3104 may be a variable speed pump and/or may be one or more pumps. A heat rejection device 3121, for example a cooling tower, can be connected to the HSC 3117 and the second thermal fluid can circulate through the heat rejection device 3121. The heat rejection device 3121 can be used to reject excess heat in the second thermal fluid to another medium, such as atmospheric air. Heat may alternatively or additionally be rejected by other means or at other locations within the system, as described herein with reference to other embodiments of heat engines or reversible heat engines.

[00216] The heat engine may further include at least one high pressure tank 3132 and an intermediate pressure tank 3134. The high pressure leg 3106 may be connected to the high pressure tank 3132 by a hot side valve 3133. In addition Furthermore, the high pressure leg 3106 can be connected to the intermediate pressure tank 3134 by a hot side valve 3135. As shown, the hot side valves 3133 and 3135 are downstream of the hot side heat exchanger 3107 and upstream from turbine 3105; however, hot-side valves 3133 and 3135 may be connected to high-pressure leg 3106 at other locations, including downstream of compressor 3103 and upstream of hot-side heat exchanger 3107.

[00217] The low pressure leg 3108 may be connected to the high pressure tank 3132 by a cold side valve 3136. Additionally, the low pressure leg 3108 may be connected to the intermediate pressure tank 3134 by a cold side valve 3137. As shown, cold-side valves 3136 and 3137 are downstream of cold-side heat exchanger 3109 and upstream of compressor 3103; however, cold side valves 3133 and 3135 may be connected to the low pressure leg 3108 at other locations, including upstream of the cold side heat exchanger 3109 and downstream of the turbine 3105.

[00218] Each of valves 3133, 3135, 3136 and 3137 may be any suitable valve capable of allowing and blocking the flow of working fluid, including a gate valve, globe valve, plug valve, ball valve, valve butterfly, check valve, pinch valve, and diaphragm valve. In some embodiments, valves 3133, 3135, 3136 and 3137 may each be the same type of valve. However, in other embodiments, at least two of the valves 3133, 3135, 3136 and 3137 may be different types of valves.

[00219] The sensors may be located at various locations throughout the heat engine or external to the heat engine. The sensors may be configured to determine and/or report one or more operating conditions inside or outside the system. In the example embodiment illustrated in Figure 31, pressure sensors may be located at or near various inputs and outputs for components within the system. For example, the pressure sensor 3142 may determine and report the pressure of the working fluid in the high pressure leg 3106, the pressure sensor 3144 may determine and report the pressure of the working fluid in the low pressure leg 3108, the pressure sensor 3144 may determine and report the pressure of the working fluid in the low pressure leg 3108, the pressure 3146 may determine and report pressure of the working fluid in the high pressure tank 3132 and the pressure sensor 3148 may determine and report the pressure of the working fluid in the intermediate pressure tank 3134. As illustrative examples, the operating conditions may include readings sensor readings (e.g. working pressure in high pressure leg 3106) and/or a combination of sensor readings and/or a derived value based on the sensor readings (e.g. difference between working fluid pressure in tank high pressure leg 3132 and the pressure of the working fluid in the high pressure leg 3106). In practical application, the illustrated sensors may reflect multiple sensors in a fluid path (e.g., the pressure sensor 3142 may be two or more pressure sensors in the high pressure leg 3106).

[00220] Alternatively or additionally, other types of sensors that determine and/or report one or more system operating conditions may be located throughout the illustrated system. The 3152a sensor can determine and report turbine torque, turbine rotation, generator torque and/or generator RPM. If rod 3123 is a common rod and not a split rod between turbine 3105 and compressor 3103, then sensor 3152a may also determine and report compressor torque and/or compressor RPM. Alternatively, sensor 3152b may determine and report compressor torque and/or compressor RPM. The 3154 sensor may be connected to the 3101 generator/engine and various discrete components included therein, such as alternators and/or power electronics. The sensor 3154 may also connect to an electrical power link between the generator/motor 3101 and the electrical grid to which the generator/motor 3101 is supplying electrical power. The sensor 3154 can determine and report current, voltage, phase, frequency and/or the amount of electrical energy generated and/or distributed by the generator/motor 3101 and/or its associated discrete components. Sensor 3156 can determine and report the phase of the grid and sensors 3154 and 3156 can together or in combination determine and report a phase difference between the generated electrical power and the grid.

[00221] Each of valves 3133, 3135, 3136 and 3137 can be connected to one or more control devices. For example, hot side valve 3133 and cold side valve 3136 can be connected to control devices 3162 and 3166, respectively. Control devices 3162 and 3166 may be configured to operate valves 3133 and 3136 to control the flow of working fluid through high pressure tank 3132. Thus, control device 3162 may be capable of operating the hot side valve. 3133 to (i) allow flow of working fluid from high pressure leg 3106 to high pressure tank 3132 and (ii) block flow of working fluid from high pressure leg 3106 to high pressure tank 3132 high pressure leg 3132. Likewise, the control device 3166 may be capable of operating the cold side valve 3136 to (i) allow flow of working fluid from the high pressure tank 3132 to the low pressure leg 3108 and (ii) blocking the flow of working fluid from the high pressure tank 3132 to the low pressure leg 3108.

[00222] Furthermore, the hot side valve 3135 and the cold side valve 3137 can be connected to the control devices 3164 and 3168, respectively. Control devices 3164 and 3168 may be configured to operate valves 3135 and 3137 to control the flow of working fluid through the intermediate pressure tank 3134. Thus, control device 3164 may be capable of operating the hot side valve 3135 to (i) allow the flow of working fluid from the high pressure leg 3106 to the intermediate pressure tank 3134 and (ii) block the flow of working fluid from the high pressure leg 3106 to the intermediate pressure tank 3134 intermediate pressure leg 3134. Similarly, the control device 3168 may be capable of operating the cold side valve 3137 to (i) allow flow of working fluid from the intermediate pressure tank 3134 to the low pressure leg 3108 and ( ii) block the flow of working fluid from the intermediate pressure tank 3134 to the low pressure leg 3108.

[00223] Each of the control devices 3162, 3164, 3166 and 3168 may be in communication with one or more controllers 3172, 3174, 3176 and 3178. Each, some or all of the controllers 3172, 3174, 3176 and 3178 may be separate controllers with independent or coordinated control over control devices 3162, 3164, 3166 and 3168. Alternatively, each, some or all of the controllers 3172, 3174, 3176 and 3178 may be considered a single controller with control over one or more of control devices 3162, 3164, 3166 and 3168. Each of controllers 3172, 3174, 3176 and 3178 may be capable of directing one or more control devices 3162, 3164, 3166 and 3168 to operate valves 3133, 3135, 3136 and 3137 for changing a flow amount of the working fluid. For example, the controller 3172 may be capable of issuing an instruction to control the device 3162 to open or close the hot side valve 3133 by a specified amount (e.g., open, partially open, closed, partially closed). Controllers 3172, 3174, 3176 and 3178 may have any practical form known in the art, including those commonly used in industrial control systems, such as PLC controllers.

[00224] Each of the controllers 3172, 3174, 3176 and 3178 may also be in communication with one or more of the sensors. For clarity of illustration, connections are not shown in Figure 31 between each of the controllers 3172, 3174, 3176 and 3178 and each of the illustrated sensors with which they may be communicating, but it should be understood that each of the controllers 3172 , 3174, 3176 and 3178 may be capable of receiving sensor data from a relevant sensor. Controllers 3172, 3174, 3176, and 3178 may be in communication with and receive data from the sensors in any practical manner, including wired electrical data communication, wireless data communication, optical transmission and/or intermediate sources, or through other forms known in the art.

[00225] Each of controllers 3172, 3174, 3176 and/or 3178 may be capable of comparing data or calculated data reported from one or more sensors with data reported from one or more other sensors, historical sensor data, internal adjustments or the like. comparators. For example, a controller 3172, 3174, 3176 and/or 3178 may compare data reported from at least two of the sensors 3142, 3144, 3146 and 3148. Additionally, the controllers 3172, 3174, 3176 and/or 3178 may determine a phase difference between generated electrical power and grid power by comparing data reported from sensors 3154 and 3156.

[00226] A heat engine may further include one or more recuperative heat exchangers (or “scavengers”) that can transfer heat between the working fluid at various stages within the closed-loop flow path. Figure 32 illustrates a 3200 variable pressure inventory control system implemented in a Brayton cycle heat engine. The 3200 variable pressure inventory control system is similar to the 3100 variable pressure inventory control system, except that the 3200 variable pressure inventory control system includes a 3211 recuperative heat exchanger. reference number that in the 3100 system are of the same configuration and function in a similar manner unless otherwise specified.

[00227] Preferably, the recuperative heat exchanger 3211 is a counterflow heat exchanger. As illustrated in the heat engine example in Figure 32, the recuperative heat exchanger 3211 comes into thermal contact with the working fluid downstream of the compressor 3103 and upstream of the hot side heat exchanger 3107 with the downstream working fluid. of the turbine 3105 and upstream of the cold-side heat exchanger 3109, preferably counterflow. In system 3200, the working fluid may circulate through a closed-loop fluid path that includes, in sequence, the compressor 3103, the recuperative heat exchanger 3211, the hot-side heat exchanger 3107, the turbine 3105, the recuperative heat exchanger 3211 again (in thermal counterflow contact with the previous flow), the cold side heat exchanger 3109, and back to compressor 3103. Other variations are possible and this flow path is for illustrative purposes only. The closed cycle fluid path may include a high pressure leg 3206 and a low pressure leg 3208. The high pressure leg 3206 may be all or a portion of the closed cycle fluid path downstream of the compressor 3103 upstream of the turbine 3105. The low pressure leg 3208 may be all or a portion of the closed cycle fluid path upstream of the compressor 3103 and downstream of the turbine 3105. The working fluid pressure in the high pressure leg 3206 may be greater than working fluid pressure in the low pressure leg 3208.

[00228] There may be no recuperative heat exchangers in a heat engine, or there may be more than one recuperative heat exchanger in a heat engine and the one or more recuperative heat exchangers may be located at alternative locations than the location shown in the circulation diagram illustrated in Figure 32.

A. Example of Working Fluid Removal from the Closed Cycle Fluid Path

[00229] In a Brayton cycle system, it may be desirable to remove an amount of working fluid from the closed cycle fluid path to reduce the energy of the system. In some embodiments, removing an amount of working fluid from the closed-loop fluid path may reduce the mass flow rate of the working fluid in the closed-loop fluid path and thereby reduce the speed of a rotating rod. compressor and/or turbine rotating shaft. Reducing the speed of the rotating rod(s) can, in turn, reduce the amount of electricity generated by the system.

[00230] Using the illustration in Figure 31, a working fluid may be circulated in a closed-loop fluid path that includes, in sequence, the compressor 3103, the hot-side heat exchanger 3107, the turbine 3105, and the heat exchanger 3107. cold side heat pump 3109. The closed cycle fluid path includes high pressure leg 3106 and low pressure leg 3108.

1. Example of removal with a single pressure tank

[00231] In some implementations, variable pressure inventory control with a single pressure tank, such as high pressure tank 3132, may be implemented to reduce energy in system 3100. In one implementation, in system 3100, where the compression ratio of the compressor 3103 and the turbine 3105 is 5, the high pressure leg 3106 has a nominal (e.g. initial) pressure of 50 bar (5 MPa), the low pressure leg 3108 has a nominal pressure of 10 bar (1 MPa) and the high pressure tank has a nominal pressure of 11 bar (1.1 MPa), opening the hot side valve 3133 with the other valves 3135, 3136 and 3137 closed, may result in a system state 3100 in which the working fluid pressure in the high pressure leg 3106 can decrease to 25 bar (2.5 MPa) and working fluid pressure in the high pressure tank 3132 can increase to 25 bar (2.5 MPa). Correspondingly, the working fluid pressure in the low pressure leg 3108 can decrease to 5 bar (0.5 MPa). The amount of time for pressures to change in system 3100 may be based, at least in part, on a ratio of the volume of the high pressure tank 3132 to the volume of the closed cycle fluid path.

[00232] Variable pressure inventory control with a single tank has some limitations. For example, a large volume tank may be required to significantly reduce the pressure in the closed cycle fluid path if a large quantity of working fluid is circulated. The large volume tank will have to be rated to operate through the entire pressure range of the 3106 high pressure leg, and this can be very expensive to build and maintain. Additionally, to use pressure-based (i.e., non-pumped) inventory control from the tank to manage the circulation of the working fluid mass, the pressure operating point in the 3132 high pressure tank must be between the pressures on high pressure leg 3106 and low pressure leg 3108.

2. Example of removal with two pressure tanks

[00233] Variable pressure inventory control with two pressure tanks, such as high pressure tank 3132 and intermediate pressure tank 3134, can be implemented to further and/or more effectively reduce system energy output 3100. Beneficially, dual-tank variable pressure inventory control can improve the range of power outputs at which the 3100 system can operate. In discharge mode, variable pressure inventory control with two tanks can be implemented for, among other things, charge following and frequency regulation of the electricity generated by the 3100 system. And in charge mode, variable pressure inventory control with Two tanks can be implemented for, among other things, variable charging of the 3100 system.

[00234] In an exemplary embodiment, a first quantity of working fluid may be removed from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg 3106 and the high-pressure tank 3132, such that that the working fluid pressure in the high pressure leg 3106 decreases and the working fluid pressure in the high pressure tank 3132 increases. Additionally, the first fluid connection can be closed. Furthermore, a second amount of working fluid from the closed-loop fluid path may be removed by opening a second fluid connection between the high pressure leg 3106 and the intermediate pressure tank 3134, such that the fluid pressure working fluid pressure in the high pressure leg 3106 decreases and working fluid pressure in the intermediate pressure tank 3134 increases. In some embodiments, the first fluid connection may take the form of hot side valve 3133 and the second fluid connection may take the form of hot side valve 3135. However, in other embodiments, the first fluid connection and/or The second fluid connection can take different forms. For example, the first fluid connection and/or the second fluid connection may be two or more valves arranged in series or parallel. As another example, the first fluid connection and/or the second fluid connection may be one or more other components, including flanges, fittings, couplings and/or gaskets.

[00235] In one implementation, in system 3100, where the compression ratio of compressor 3103 and turbine 3105 is 5, the high pressure leg 3106 has a nominal pressure of 50 bar, the low pressure leg 3108 has a nominal pressure 10 bar (1 MPa), the high pressure tank has a nominal pressure of 10 bar (1 MPa), and the intermediate pressure tank has a nominal pressure of 5 bar (0.5 MPa), opening the hot side valve 3133 with the other valves 3135, 3136 and 3137 closed, may result in a first state of the system 3100 in which the working fluid pressure in the high pressure leg 3106 may decrease to 25 bar (2.5 MPa) and the pressure of the working fluid in the high pressure tank can 3132 can increase to 25 bar (2.5 MPa). In the first state, the working fluid pressure in the low pressure leg 3108 can decrease to 5 bar (0.5 MPa) and the working fluid pressure in the intermediate pressure tank 3134 can still be 5 bar (0.5 MPa). Then, closing the hot side valve 3133 and opening the hot side valve 3135 with the other valves 3136 and 3137 closed may result in a second state of the system 3100 in which the working fluid pressure in the high pressure leg 3106 may decrease. to 10 bar (1 MPa) and working fluid pressure in the intermediate pressure tank 3134 can increase to 10 bar (1 MPa). In the second state, the working fluid pressure in the low pressure leg 3108 may decrease to 2 bar (0.2 MPa) and the working fluid pressure in the high pressure tank 3132 may still be at 25 bar (2.5 MPa).

[00236] Control devices 3162 and 3164 can operate the hot side valve 3133 and the hot side valve 3135, respectively. In some implementations, the hot side valve 3133 may be closed by the control device 3162 when the working fluid pressure in the high pressure tank 3132 reaches a first threshold pressure value. The first threshold pressure value can be set in several ways. In some embodiments, the first threshold pressure value may be defined as an equilibrium pressure between the working fluid pressure in the high pressure leg 3106 and the working fluid pressure in the high pressure tank 3132. Furthermore, in In some embodiments, the first pressure threshold value may be defined as a pressure less than an equilibrium pressure between the working fluid pressure in the high pressure leg 3106 and the working fluid pressure in the high pressure tank 3132. In addition Furthermore, in some embodiments, controller 3172 may determine an operating condition of system 3100 and the first threshold pressure value may be set based on the determined operating condition. The first threshold pressure value can be set based on any of the operating conditions described above, including turbine torque, turbine RPM, generator torque, and generator RPM; and current, voltage, phase, frequency and/or amount of electrical energy generated and/or distributed by the generator and/or its discrete components. Additionally, in some implementations, the hot side valve 3135 may be opened by the control device 3164 in response to the control device 3162 closing the hot side valve 3133.

[00237] Furthermore, in some implementations, the hot side valve 3135 may be closed by the control device 3164 when the pressure of the working fluid in the intermediate pressure tank 3134 reaches a second threshold pressure value. The second threshold pressure value can be set in a similar manner to setting the first threshold pressure. In some embodiments, the second threshold pressure value may be defined as an equilibrium pressure between the working fluid pressure in the high pressure leg 3106 and the working fluid pressure in the intermediate pressure tank 3134. Furthermore, in In some embodiments, the second pressure threshold value may be defined as a pressure less than an equilibrium pressure between the working fluid pressure in the high pressure leg 3106 and the working fluid pressure in the intermediate pressure tank 3134. In addition Furthermore, in some embodiments, controller 3174 may determine an operating condition of system 3100 and the second threshold pressure value may be set based on the determined operating condition. The second threshold pressure value may be set based on any of the operating conditions in which the first threshold pressure value is set.

[00238] In another example embodiment, the hot side valve 3133 may be closed by the control device 3162 when the working fluid pressure reaches the first threshold pressure value. Pressure sensors 3142, 3144, 3146 and/or 3148 may determine and report to controller 3172 working fluid pressures in system 3100. Controller 3172 may, based on at least one of the operating conditions reported by the sensors, drive the device control valve 3162 to close the hot side valve 3133. In some embodiments, the hot side valve 3133 may be closed when the working fluid pressure in the high pressure leg 3106 reaches the first threshold pressure value. Furthermore, in some embodiments, the hot side valve 3133 may be closed when the working fluid pressure in the low pressure leg 3108 reaches the first threshold pressure value. Furthermore, in some embodiments, the hot side valve 3133 may be closed when the pressure of the working fluid in the high pressure tank 3132 reaches the first threshold pressure value. Additionally, the hot side valve 3133 may be closed by the control device 3162 when a pressure derived from the working fluid reaches the first threshold pressure value. The derived pressure can be any combination of working fluid pressure in the high pressure leg 3106, working fluid pressure in the low pressure leg 3108, working fluid pressure in the high pressure tank 3132, and working fluid pressure in the intermediate pressure tank 3134.

[00239] In another example embodiment, the hot side valve 3135 may be closed by the control device 3164 when the working fluid pressure reaches the second threshold pressure value. Pressure sensors 3142, 3144, 3146 and/or 3148 may determine and report to controller 3174 working fluid pressures in system 3100. Controller 3174 may, based on at least one of the operating conditions reported by the sensors, direct the device control valve 3164 to close the hot side valve 3135. In some embodiments, the hot side valve 3135 may be closed when the working fluid pressure in the high pressure leg 3106 reaches the second threshold pressure value. Furthermore, in some embodiments, the hot side valve 3135 may be closed when the working fluid pressure in the low pressure leg 3108 reaches the second threshold pressure value. Additionally, the hot side valve 3135 may be closed by the control device 3164 when a pressure derived from the working fluid reaches the second threshold pressure value. The derived pressure can be any combination of working fluid pressure in the high pressure leg 3106, working fluid pressure in the low pressure leg 3108, working fluid pressure in the high pressure tank 3132, and the working fluid pressure in intermediate pressure tank 3134.

[00240] Although the example of removing working fluid from the closed-loop fluid path was described above with reference to system 3100, working fluid may also be removed from the closed-loop fluid path. of system 3200. Working fluid may be removed from the closed-loop fluid path of system 3200 in a manner similar to removing working fluid from the closed-loop fluid path of system 3100.

B. Example of Adding Working Fluid to the Closed Cycle Fluid Path

[00241] In a Brayton cycle system, it may be desirable to add an amount of working fluid to the closed cycle fluid path to increase the energy of the heat engine. For example, it may be desirable to add an amount of working fluid back into the closed cycle fluid path that was previously removed from the closed cycle fluid path.

[00242] In some embodiments, adding an amount of working fluid to the closed-loop fluid path can increase the mass flow rate of the working fluid in the closed-loop fluid path and thereby increase the velocity and/or increase the torque applied to a compressor rotating rod and/or a turbine rotating rod. Increasing the speed of the rotating rod(s) and/or increasing the applied torque can, in turn, increase the amount of electricity generated by the system. In variable pressure inventory control embodiments described herein, removing an amount of working fluid from the closed-loop fluid path and adding the amount of working fluid back to the closed-loop fluid path may be reversible processes.

[00243] Using the illustration in Figure 31, a working fluid may circulate a closed-loop fluid path that includes, in sequence, the compressor 3103, the hot-side heat exchanger 3107, the turbine 3105, and the heat exchanger cold side 3109. The closed cycle fluid path includes high pressure leg 3106 and low pressure leg 3108.

[00244] In an exemplary embodiment, a first quantity of working fluid may be added to the closed-loop fluid path by opening a first fluid connection between the low pressure leg 3108 and the intermediate pressure tank 3134, where the tank intermediate pressure leg 3134 contains working fluid at a first storage pressure greater than the pressure of the working fluid in the low pressure leg 3108, such that the pressure of the working fluid in the low pressure leg 3108 increases and the pressure of working fluid in intermediate pressure tank 3134 decreases. Additionally, the first fluid connection can be closed. Furthermore, a second amount of working fluid can be added to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg 3108 and the high-pressure tank 3132, where the high-pressure tank 3132 contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg 3108, such that the working fluid pressure in the low pressure leg 3108 increases and the pressure of the working fluid in the high pressure tank 3132 decreases. In some embodiments, the first fluid connection may take the form of the cold side valve 3137 and the second fluid connection may take the form of the cold side valve 3136. However, in other embodiments, the first fluid connection and/or the second fluid connections can have different shapes. For example, the first fluid connection and/or the second fluid connections may be two or more valves arranged in series or in parallel. As another example, the first fluid connection and/or the second fluid connection may be one or more other components, including flanges, fittings, couplings and/or gaskets.

[00245] For example, in system 3100, where the compression ratio of compressor 3103 and turbine 3105 is 5, high pressure leg 3106 has a nominal pressure of 10 bar (1 MPa), low pressure leg 3108 has a nominal pressure of 2 bar (0.2 MPa), the 3132 high pressure tank has a nominal pressure of 25 bar (2.5 MPa), and the intermediate pressure tank has a nominal pressure of 10 bar (1 MPa) , opening the cold side valve 3137 with the other valves 3133, 3135 and 3136 closed may result in a first state of the system 3100 in which the working fluid pressure in the low pressure leg 3108 may increase to 5 bar (0.5 MPa) and the pressure of the working fluid in the intermediate pressure tank 3134 can decrease to 5 bar (0.5 MPa). In the first state, the working fluid pressure in the high pressure leg 3106 can increase to 25 bar (2.5 MPa) and the pressure in the high pressure tank 3132 can be 25 bar (2.5 MPa). Then, closing the cold side valve 3137 and opening the cold side valve 3136 with the other valves 3133 and 3135 closed may result in a second state of the system 3100 in which the working fluid pressure in the low pressure leg 3108 may increase. to 10 bar (1 MPa) and working fluid pressure in high pressure tank 3132 can decrease to 10 bar (1 MPa). In the second state, the working fluid pressure in the high pressure leg 3106 can increase to 50 bar (5 MPa) and the working fluid pressure in the intermediate pressure tank 3134 can be 5 bar.

[00246] Control devices 3166 and 3168 can operate the cold side valve 3136 and the cold side valve 3137, respectively. In some implementations, the cold side valve 3137 may be closed by the control device 3168 when the working fluid pressure in the intermediate pressure tank 3134 reaches a first threshold pressure value. The first threshold pressure value can be set in several ways. In some embodiments, the first threshold pressure value may be defined as an equilibrium pressure between the working fluid pressure in the low pressure leg 3108 and the working fluid pressure in the intermediate pressure tank 3134. Furthermore, in In some embodiments, the first threshold pressure value may be defined as a pressure less than an equilibrium pressure between the working fluid pressure in the low pressure leg 3108 and the working fluid pressure in the intermediate pressure tank 3134. In addition Furthermore, in some embodiments, controller 3178 may determine an operating condition of system 3100 and the first threshold pressure value may be set based on the determined operating condition. The first threshold pressure value can be set based on any of the operating conditions described above, including turbine torque, turbine RPM, generator torque, and generator RPM; and current, voltage, phase, frequency and/or amount of electrical energy generated and/or distributed by the generator and/or its discrete components. Additionally, in some implementations, the cold side valve 3136 may be opened by the control device 3166 in response to the control device 3168 closing the cold side valve 3137.

[00247] Furthermore, in some implementations, the cold side valve 3136 may be closed by the control device 3166 when the pressure of the working fluid in the high pressure tank 3132 reaches a second threshold pressure value. The second threshold pressure value can be set in a similar manner to setting the first threshold pressure value. In some embodiments, the second threshold pressure value may be defined as an equilibrium pressure between the working fluid pressure in the low pressure leg 3108 and the working fluid pressure in the high pressure tank 3132. Furthermore, in In some embodiments, the second pressure threshold value may be set to a pressure less than an equilibrium pressure between the working fluid pressure in the low pressure leg 3108 and the working fluid pressure in the high pressure tank 3132. Additionally, in some embodiments, controller 3176 may determine an operating condition of system 3100 and the second threshold pressure value may be set based on the determined operating condition. The second threshold pressure value may be set based on any of the operating conditions in which the first threshold pressure value is set.

[00248] In another example embodiment, the cold side valve 3137 may be closed by the control device 3168 when the working fluid pressure reaches the first threshold pressure value. Pressure sensors 3142, 3144, 3146 and/or 3148 may determine and report to controller 3178 working fluid pressures in system 3100. Controller 3178 may, based on at least one of the operating conditions reported by the sensors, direct the device control valve 3168 to close the cold side valve 3137. In some embodiments, the cold side valve 3137 may be closed when the pressure of the working fluid in the high pressure leg 3106 reaches the first threshold pressure value. Furthermore, in some embodiments, the cold side valve 3137 may be closed when the working fluid pressure in the low pressure leg 3108 reaches the first threshold pressure value. Furthermore, in some embodiments, the cold side valve 3137 may be closed when the working fluid pressure in the intermediate pressure tank 3134 reaches the first threshold pressure value. Additionally, the cold side valve 3137 may be closed by the control device 3168 when a pressure derived from the working fluid reaches the first threshold pressure value. The derived pressure can be any combination of the working fluid pressure in the high pressure leg 3106, the working fluid pressure in the low pressure leg 3108, the working fluid pressure in the high pressure tank 3132, and the pressure of the working fluid in the high pressure leg 3132. work on intermediate pressure tank 3134.

[00249] In another example embodiment, the cold side valve 3136 may be closed by the control device 3166 when the working fluid pressure reaches the second threshold pressure value. Pressure sensors 3142, 3144, 3146 and/or 3148 may determine and report to controller 3176 working fluid pressures in system 3100. Controller 3176 may, based on at least one of the operating conditions reported by the sensors, drive the device control valve 3166 to close the cold side valve 3136. In some embodiments, the cold side valve 3136 may be closed when the pressure of the working fluid in the high pressure leg 3106 reaches the second threshold pressure value. Furthermore, in some embodiments, the cold side valve 3136 may be closed when the working fluid pressure in the low pressure leg 3108 reaches the second threshold pressure value. Furthermore, in some embodiments, the cold side valve 3136 may be closed when the pressure of the working fluid in the intermediate pressure tank 3134 reaches the second threshold pressure value. Additionally, the cold side valve 3136 may be closed by the control device 3166 when a pressure derived from the working fluid reaches the second threshold pressure value. The derived pressure can be any combination of the working fluid pressure in the high pressure leg 3106, the working fluid pressure in the low pressure leg 3108, the working fluid pressure in the high pressure tank 3132, and the pressure of the working fluid in the high pressure leg 3132. work on intermediate pressure tank 3134.

[00250] Although the example of adding working fluid to the closed-loop fluid path was described above with reference to system 3100, working fluid can be added to the closed-loop fluid path of system 3200 as well. Working fluid may be added to the closed-loop fluid path of system 3200 in a similar manner to which working fluid is added to the closed-loop fluid path of system 3100.

[00251] Although the first and second threshold pressure values are described above in both the example of removing working fluid to the closed cycle fluid and example of adding working fluid to the closed cycle fluid path, the first and second threshold pressure values may be different. In some embodiments, at least one threshold pressure value related to the removal of working fluid to the closed cycle path may be different from at least one threshold pressure value related to the addition of working fluid to the fluid path. closed cycle.

C. Quiescent Mode

[00252] Referring again to Figure 31, the illustrated heat engine is illustrated in power generation mode. As discussed in relation to Figures 1-5 and Figures 13-18, Brayton cycle systems can operate in charge or discharge modes, where the discharge mode is generally consistent with the conversion of stored thermal energy into a substantial amount of electrical energy for distribution to a grid or other significant energy user and load mode is generally consistent with storing substantial amounts of thermal energy in the system for later use. However, the Brayton cycle system can also operate in quiescent mode, where the system is neither producing a significant amount of electrical energy nor storing a significant amount of thermal energy.

[00253] Pumps and/or turbomachinery not operating in a quiescent mode will cause the temperature profile in a Brayton cycle heat exchanger to be significantly different from the desired temperature profile when the heat exchanger is operating in quiescent mode. loading or unloading. This difference can lead to long ramp-up times for a Brayton cycle system to come online and begin delivering or accepting power. It can also lead to additional thermal stresses with the change in temperature. Advantageously, the variable pressure inventory control described herein can be implemented to operate the compressor and turbine at a very low speed to "leak" heat into or out of the heat exchangers to maintain a desired temperature profile in the heat exchangers. heat that allows a rapid transition to optimized operation in charge or discharge modes. For example, a power system may be operated in a quiescent mode such that the cycle is operated at a level sufficient to circulate working and/or thermal fluids, but is effectively generating zero or negligible net electrical energy. In quiescent mode, the variable pressure control inventory control described herein can be implemented to maintain the desired mass flow rate in the closed-loop fluid path so that when the system transitions to, for example, discharge mode, heat exchangers are already operating at or close to operating temperatures. In this way, the transition from quiescent to discharge modes can take very little time, for example, less than 15 seconds.

D. Variable Pressure Inventory Control with Three or More Pressure Tanks

[00254] Although the examples described above involve variable pressure inventory control with two tanks, in other examples, variable pressure inventory control can be implemented in Brayton cycle systems that include three or more pressure tanks. Variable pressure inventory control with three or more pressure tanks may be similar in form to variable pressure inventory control with the high pressure tank and the intermediate pressure tank described above.

[00255] In some implementations, working fluid may be removed from the closed cycle fluid path by opening a respective fluid connection between each tank of the three or more pressure tanks and a high pressure leg of the cycle fluid path. closed, such that the working fluid pressure in the high pressure leg decreases and the working fluid pressure in each tank of the three or more pressure tanks increases. In some implementations, opening the respective fluid connections between each tank of the three or more pressure tanks and the high-pressure leg of the closed-loop fluid path may involve opening each of the fluid connections sequentially and after pressure. have increased in another pressure tank.

[00256] Additionally, in some implementations, working fluid may be added to the closed-loop fluid path by opening a respective fluid connection between each tank of the three or more pressure tanks and a low-pressure leg of the flow path. closed cycle fluid, where each tank contains working fluid at a respective storage pressure greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the pressure of the working fluid in each tank of the three or more tanks pressure decreases.

III. Illustrative Methods

[00257] Figure 33 is a flowchart illustrating a variable pressure inventory control method 3300, in accordance with an example embodiment. Illustrative methods, such as method 3300, may be performed in whole or in part by a component or components of a closed-loop system, such as system 3100 and system 3200.

[00258] As shown by block 3302, method 3300 may involve, in a closed-loop system, circulating a working fluid through a closed-loop fluid path including, in sequence, a compressor, a hot-side heat exchanger, and a hot-side heat exchanger. , a turbine and a cold-side heat exchanger. The closed-loop fluid path may include a high-pressure leg and a low-pressure leg.

[00259] As shown by block 3304, method 3300 may involve removing a first amount of working fluid from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank. , such that the working fluid pressure in the high pressure leg decreases and the working fluid pressure in the high pressure tank increases.

[00260] As shown by block 3306, method 3330 may involve closing the first fluid connection when the working fluid pressure in the high pressure tank reaches a first threshold pressure value.

[00261] As shown by block 3308, method 3300 may involve removing a second amount of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and a pressure tank. intermediate pressure, such that the working fluid pressure in the high pressure leg decreases and the working fluid pressure in the intermediate pressure tank increases.

[00262] In some embodiments, the closed cycle system may include a closed Brayton cycle system. Furthermore, in some embodiments, the first threshold pressure value may be defined as an equilibrium pressure between the working fluid pressure in the high pressure leg and the working fluid pressure in the high pressure tank. Furthermore, in some embodiments, the first threshold pressure value may be set to a pressure less than an equilibrium pressure between the working fluid pressure in the high pressure leg and the working fluid pressure in the high pressure leg. pressure.

[00263] Furthermore, in some embodiments, method 3300 may further involve operating the closed-cycle system in a power generation mode, where a generator coupled to the turbine produces electrical energy; determine an operational condition of the power generation system; and setting the first pressure threshold value based on determining the operating condition of the power generation system.

[00264] Furthermore, in some embodiments, method 3300 may further involve closing the second fluid connection when the working fluid pressure in the intermediate pressure tank reaches a second threshold pressure value. In some embodiments, the second threshold pressure value may be defined as an equilibrium pressure between the working fluid pressure in the high pressure leg and the working fluid pressure in the intermediate pressure tank. Furthermore, in some embodiments, the second threshold pressure value may be defined as a pressure less than an equilibrium pressure between the working fluid pressure in the high pressure leg and the working fluid pressure in the intermediate pressure tank. . Furthermore, in some embodiments, method 3300 may further involve operating the closed-cycle system in a power generation mode, in which a generator coupled to the turbine produces electrical energy; determine an operational condition of the power generation system; and defining the second threshold pressure value based on determining the operating condition of the power generation system.

[00265] Figure 34 is a flowchart illustrating a variable pressure inventory control method 3400, in accordance with an example embodiment. Method 3400 may be performed in whole or in part by a component or components of a closed-loop system, such as system 3100 and system 3200.

[00266] As shown by block 3402, method 3400 may involve, in a closed-loop system, circulating a working fluid through a closed-loop fluid path including, in sequence, a compressor, a hot-side heat exchanger, and a hot-side heat exchanger. , a turbine and a cold-side heat exchanger. The closed-loop fluid path may include a high-pressure leg and a low-pressure leg.

[00267] As shown by block 3404, method 3400 may involve removing a first amount of working fluid from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank. , such that the working fluid pressure in the high pressure leg decreases and the working fluid pressure in the high pressure tank increases.

[00268] As shown by block 3406, method 3400 may involve closing the first fluid connection when the working fluid pressure reaches a first threshold pressure value.

[00269] As shown by block 3408, method 3400 may involve removing a second amount of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and a pressure tank. intermediate pressure, such that the working fluid pressure in the high pressure leg decreases and the working fluid pressure in the intermediate pressure tank increases.

[00270] In some embodiments, closing the first fluid connection may involve closing the first fluid connection when the working fluid pressure in the high pressure leg reaches the first threshold pressure value. Furthermore, in some embodiments, closing the first fluid connection may involve closing the first fluid connection when the working fluid pressure in the low pressure leg reaches the first threshold pressure value.

[00271] Figure 35 is a flow chart illustrating a variable pressure inventory control method 3500, in accordance with an example embodiment. Method 3500 may be performed in whole or in part by a component or components of a closed-loop system, such as system 3100 and system 3200.

[00272] As shown by block 3502, method 3500 may involve, in a closed-loop system, circulating a working fluid through a closed-loop fluid path including, in sequence, a compressor, a hot-side heat exchanger, and a hot-side heat exchanger. , a turbine and a cold-side heat exchanger. The closed-loop fluid path may include a high-pressure leg and a low-pressure leg.

[00273] As shown by block 3504, method 3500 may involve adding a first amount of working fluid to the closed-loop fluid path by opening a first fluid connection between the low pressure leg and an intermediate pressure tank, in that the intermediate pressure tank contains working fluid at a first storage pressure greater than the pressure of the working fluid in the low pressure leg, such that the pressure of the working fluid in the low pressure leg increases and the pressure of working fluid in the intermediate pressure tank decreases.

[00274] As shown by block 3506, method 3500 may involve closing the first fluid connection when the working fluid pressure in the intermediate pressure tank reaches a first threshold pressure value.

[00275] As shown by block 3508, method 3500 may involve adding a second amount of working fluid to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg and a high-pressure tank, in that the high pressure tank a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the pressure of the working fluid in the high-pressure tank decreases.

[00276] In some embodiments, the first threshold pressure value may be defined as an equilibrium pressure between the working fluid pressure in the low pressure leg and the working fluid pressure in the intermediate pressure tank. Furthermore, in some embodiments, the first threshold pressure value may be defined as a pressure greater than an equilibrium pressure between the working fluid pressure in the low pressure leg and the working fluid pressure in the intermediate pressure tank. .

[00277] Furthermore, in some embodiments, method 3500 may further involve operating the closed-cycle system in a power generation mode, in which a generator coupled to the turbine produces electrical energy; determine an operational condition of the power generation system; and setting the first threshold pressure value based on determining the operating condition of the power generation system.

[00278] Furthermore, in some embodiments, method 3500 may further involve closing the second fluid connection when the pressure of the working fluid in the high pressure tank reaches a second threshold pressure value. In some embodiments, the second threshold pressure value may be defined as an equilibrium pressure between the working fluid pressure in the low pressure leg and the working fluid pressure in the high pressure tank. Furthermore, in some embodiments, the second threshold pressure value may be defined as a pressure greater than an equilibrium pressure between the working fluid pressure in the low pressure leg and the working fluid pressure in the high pressure tank. . Furthermore, method 3500 may further involve operating the closed cycle system in a power generation mode, in which a generator coupled to the turbine produces electrical energy; determine an operational condition of the power generation system; and setting the second threshold pressure value based on determining the operating condition of the power generation system.

[00279] Figure 36 is a flowchart illustrating a variable pressure inventory control method 3600, in accordance with an example embodiment. Method 3600 may be performed in whole or in part by a component or components of a closed-loop system, such as system 3100 and system 3200.

[00280] As shown by block 3602, method 3600 may involve, in a closed-loop system, circulating a working fluid through a closed-loop fluid path including, in sequence, a compressor, a hot-side heat exchanger, and a hot-side heat exchanger. , a turbine and a cold-side heat exchanger. The closed-loop fluid path may include a high-pressure leg and a low-pressure leg.

[00281] As shown by block 3604, method 3600 may involve adding a first amount of working fluid to the closed-loop fluid path by opening a first fluid connection between the low pressure leg and an intermediate pressure tank, in that the intermediate pressure tank contains working fluid at a first storage pressure greater than the pressure of the working fluid in the low pressure leg, such that the pressure of the working fluid in the low pressure leg increases and the pressure of working fluid in the intermediate pressure tank decreases.

[00282] As shown by block 3606, method 3600 may involve closing the first fluid connection when the working fluid pressure reaches a first threshold pressure value.

[00283] As shown by block 3608, method 3600 may involve adding a second amount of working fluid to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg and a high-pressure tank, in that the high pressure tank a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the pressure of the working fluid in the high-pressure tank decreases.

[00284] In some embodiments, closing the first fluid connection may involve closing the first fluid connection when the working fluid pressure in the high pressure leg reaches the first threshold pressure value. Furthermore, in some embodiments, closing the first fluid connection may involve closing the first fluid connection when the working fluid pressure in the low pressure leg reaches the first threshold pressure value.

IV. Illustrative non-transitory machine-readable medium

[00285] Some or all of the functions described above and illustrated in Figures 33-36 may be performed by a computing device in response to the execution of instructions stored on a non-transitory computer-readable medium. The non-transitory computer-readable medium may be, for example, a random access memory (RAM), a read-only memory (ROM), a flash memory, a cache memory, one or more magnetically encoded disks, one or more disks optically encoded, or any other form of non-transitory data storage. The non-transitory computer-readable medium may also be distributed among multiple data storage elements, which may be located remotely from each other. The computing device that executes the stored instructions may be the computer system 1901 as described and illustrated in Figure 30.

[00286] The non-transitory computer-readable medium may store instructions executable by a processor (e.g., CPU 1905) to perform various functions. The functions may include, in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot-side heat exchanger, a turbine, and a hot-side heat exchanger. cold, wherein the closed-cycle fluid path comprises a high-pressure leg and low-pressure leg; remove a first quantity of working fluid from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank such that the working fluid pressure in the high pressure decreases and the pressure of the working fluid in the high pressure tank increases; closing the first fluid connection when the working fluid pressure in the high pressure tank reaches a first threshold pressure value; and removing a second amount of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and an intermediate-pressure tank such that the pressure of the working fluid in the leg high pressure tank decreases and the pressure of the working fluid in the intermediate pressure tank increases.

[00287] Furthermore, the functions may include in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg; remove a first quantity of working fluid from the closed-loop fluid path by opening a first fluid connection between the high-pressure leg and a high-pressure tank such that the working fluid pressure in the high pressure decreases and the pressure of the working fluid in the high pressure tank increases; closing the first fluid connection when the working fluid pressure reaches a first threshold pressure value; and removing a second amount of working fluid from the closed-loop fluid path by opening a second fluid connection between the high-pressure leg and an intermediate-pressure tank such that the pressure of the working fluid in the leg high pressure tank decreases and the pressure of the working fluid in the intermediate pressure tank increases.

[00288] Furthermore, the functions may include in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold-side heat exchanger, wherein the closed-loop fluid path comprises a high-pressure leg and a low-pressure leg; adding a first amount of working fluid to the closed-loop fluid path by opening a first fluid connection between the low pressure leg and an intermediate pressure tank, wherein the intermediate pressure tank contains working fluid at a pressure of storing greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the intermediate pressure tank decreases; closing the first fluid connection when the working fluid pressure in the intermediate pressure tank reaches a first threshold pressure value; and adding a second amount of working fluid to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg and a high-pressure tank, wherein the high-pressure tank contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the high pressure tank decreases.

[00289] Furthermore, the functions may include in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot side heat exchanger, a turbine and a cold-side heat exchanger, wherein the closed-loop fluid path comprises a high-pressure leg and a low-pressure leg; adding a first amount of working fluid to the closed-loop fluid path by opening a first fluid connection between the low pressure leg and an intermediate pressure tank, wherein the intermediate pressure tank contains working fluid at a pressure of storing greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the intermediate pressure tank decreases; closing the first fluid connection when the working fluid pressure reaches a first threshold pressure value; and adding a second amount of working fluid to the closed-loop fluid path by opening a second fluid connection between the low-pressure leg and a high-pressure tank, wherein the high-pressure tank contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the high pressure tank decreases.

V. Conclusion

[00290] Although various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, the true scope and spirit being indicated by the following claims.

Claims (21)

1. A method characterized by the fact that it comprises: in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot-side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg, wherein the closed cycle system comprises: (i) a first fluid connection between the leg high-pressure heat exchanger and a high-pressure tank and connected to the high-pressure leg between a hot-side heat exchanger outlet and a turbine inlet, (ii) a second fluid connection between the high-pressure leg and a intermediate pressure and connected to the high pressure leg between the hot side heat exchanger outlet and the turbine inlet, (iii) a third fluid connection between the low pressure leg and the intermediate pressure tank and connected to the low pressure between a cold-side heat exchanger outlet and a compressor inlet, and (iv) a fourth fluid connection between the low pressure leg and the high pressure tank and connected to the low pressure leg between the outlet of the cold side heat exchanger and the compressor inlet, and wherein the closed cycle system is configured to cycle between a charging mode and a discharging mode; operate the closed cycle system in discharge mode, in which a generator coupled to the turbine produces electrical energy; determine an operating condition of the closed-loop system; defining a first threshold pressure value based on determining the operating condition of the closed-loop system; remove a first quantity of working fluid from the closed-loop fluid path by opening the first fluid connection such that the working fluid pressure in the high pressure leg decreases and the working fluid pressure in the tank decreases. high pressure increases; close the first fluid connection when the working fluid pressure in the high pressure tank reaches the first threshold pressure value; and removing a second amount of working fluid from the closed-loop fluid path by opening the second fluid connection such that the pressure of the working fluid in the high-pressure leg decreases and the pressure of the working fluid in the tank intermediate pressure increases. 2. Method according to claim 1, characterized by the fact that the closed cycle system comprises a closed Brayton cycle system. 3. Method according to claim 1, characterized by the fact that the first threshold pressure value is defined as an equilibrium pressure between the pressure of the working fluid in the high pressure leg and the pressure of the working fluid in the high pressure tank. 4. Method according to claim 1, characterized by the fact that the first threshold pressure value is defined as a pressure less than an equilibrium pressure between the pressure of the working fluid in the high pressure leg and the pressure of the working fluid in the high pressure tank. 5. The method of claim 1, further comprising closing the second fluid connection when the pressure of the working fluid in the intermediate pressure tank reaches a second threshold pressure value. 6. Method according to claim 5, characterized in that the second threshold pressure value is defined as an equilibrium pressure between the working fluid pressure in the high pressure leg and the working fluid pressure in the intermediate pressure tank. 7. Method according to claim 5, characterized in that the second threshold pressure value is defined as a pressure less than an equilibrium pressure between the pressure of the working fluid in the high pressure leg and the pressure of the working fluid in the intermediate pressure tank. 8. Method, according to claim 5, characterized by the fact that it further comprises: determining a second operational condition of the closed cycle system; and setting the second threshold pressure value based on determining the second operating condition of the closed-loop system. 9. Method characterized by the fact that it comprises: in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot-side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg, wherein the closed cycle system comprises: (i) a first fluid connection between the leg high-pressure heat exchanger and a high-pressure tank and connected to the high-pressure leg between a hot-side heat exchanger outlet and a turbine inlet, (ii) a second fluid connection between the high-pressure leg and a intermediate pressure and connected to the high pressure leg between the hot side heat exchanger outlet and the turbine inlet, (iii) a third fluid connection between the low pressure leg and the high pressure tank and connected to the low pressure between a cold-side heat exchanger outlet and a compressor inlet, and (iv) a fourth fluid connection between the low pressure leg and the intermediate pressure tank and connected to the low pressure leg between the outlet of the cold side heat exchanger and the compressor inlet, and wherein the closed cycle system is configured to cycle between a charging mode and a discharging mode; operate the closed cycle system in discharge mode, in which a generator coupled to the turbine produces electrical energy; determine an operating condition of the closed-loop system; defining a first threshold pressure value based on determining the operating condition of the closed-loop system; remove a first quantity of working fluid from the closed-loop fluid path by opening the first fluid connection such that the working fluid pressure in the high pressure leg decreases and the working fluid pressure in the tank decreases. high pressure increases; close the first fluid connection when the working fluid pressure reaches the first threshold pressure value; and removing a second amount of working fluid from the closed-loop fluid path by opening the second fluid connection such that the pressure of the working fluid in the high-pressure leg decreases and the pressure of the working fluid in the tank intermediate pressure increases. 10. The method of claim 9, wherein closing the first fluid connection comprises closing the first fluid connection when the working fluid pressure in the high pressure leg reaches the first threshold pressure value . 11. The method of claim 9, wherein closing the first fluid connection comprises closing the first fluid connection when the working fluid pressure in the low pressure leg reaches the first threshold pressure value . 12. Method characterized by the fact that it comprises: in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot-side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg, wherein the closed cycle system comprises: (i) a first fluid connection between the leg high-pressure heat exchanger and a high-pressure tank and connected to the high-pressure leg between a hot-side heat exchanger outlet and a turbine inlet, (ii) a second fluid connection between the high-pressure leg and a intermediate pressure and connected to the high pressure leg between the hot side heat exchanger outlet and the turbine inlet, (iii) a third fluid connection between the low pressure leg and the intermediate pressure tank and connected to the low pressure between a cold-side heat exchanger outlet and a compressor inlet, and (iv) a fourth fluid connection between the low pressure leg and the high pressure tank and connected to the low pressure leg between the outlet of the cold side heat exchanger and the compressor inlet, and wherein the closed cycle system is configured to cycle between a charging mode and a discharging mode; operate the closed cycle system in discharge mode, in which a generator coupled to the turbine produces electrical energy; determine an operating condition of the closed-loop system; defining a first threshold pressure value based on determining the operating condition of the closed-loop system; adding a first quantity of working fluid to the closed-loop fluid path by opening the third fluid connection, wherein the intermediate pressure tank contains working fluid at a first storage pressure greater than the pressure of the working fluid in the low pressure leg, such that the pressure of the working fluid in the low pressure leg increases and the pressure of the working fluid in the intermediate pressure tank decreases; close the third fluid connection when the working fluid pressure in the intermediate pressure tank reaches the first threshold pressure value; and adding a second amount of working fluid to the closed-loop fluid path by opening the fourth fluid connection, wherein the high-pressure tank contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the high pressure tank decreases. 13. The method of claim 12, wherein the first threshold pressure value is defined as an equilibrium pressure between the working fluid pressure in the low pressure leg and the working fluid pressure in the intermediate pressure tank. 14. Method according to claim 12, characterized by the fact that the first threshold pressure value is defined as a pressure greater than an equilibrium pressure between the pressure of the working fluid in the low pressure leg and the pressure of the working fluid in the intermediate pressure tank. 15. The method of claim 12, further comprising closing the fourth fluid connection when the pressure of the working fluid in the high pressure tank reaches a second threshold pressure value. 16. The method of claim 15, wherein the second threshold pressure value is defined as an equilibrium pressure between the working fluid pressure in the low pressure leg and the working fluid pressure in the high pressure tank. 17. The method of claim 15, wherein the second threshold pressure value is defined as a pressure greater than an equilibrium pressure between the pressure of the working fluid in the low pressure leg and the pressure of the working fluid in the high pressure tank. 18. Method, according to claim 15, characterized by the fact that it further comprises: determining a second operational condition of the closed cycle system; and setting the second threshold pressure value based on determining the second operating condition of the closed-loop system. 19. A method characterized by the fact that it comprises: in a closed cycle system, circulating a working fluid through a closed cycle fluid path including, in sequence, a compressor, a hot-side heat exchanger, a turbine and a cold side heat exchanger, wherein the closed cycle fluid path comprises a high pressure leg and a low pressure leg, wherein the closed cycle system comprises: (i) a first fluid connection between the high pressure and a high pressure tank and connected to the high pressure leg between a hot side heat exchanger outlet and a turbine inlet, (ii) a second fluid connection between the high pressure leg and a pressure tank intermediate and connected to the high pressure leg between the hot side heat exchanger outlet and the turbine inlet, (iii) a third fluid connection between the low pressure leg and the intermediate pressure tank and connected to the low pressure leg pressure between a cold-side heat exchanger outlet and a compressor inlet, and (iv) a fourth fluid connection between the low pressure leg and the high pressure tank and connected to the low pressure leg between the exchanger outlet of cold-side heat and the compressor inlet, and wherein the closed-loop system is configured to cycle between a charging mode and a discharging mode; operate the closed cycle system in discharge mode, in which a generator coupled to the turbine produces electrical energy; determine an operating condition of the closed-loop system; defining a first threshold pressure value based on determining the operating condition of the closed-loop system; adding a first quantity of working fluid to the closed-loop fluid path by opening the third fluid connection, wherein the intermediate pressure tank contains working fluid at a first storage pressure greater than the pressure of the working fluid in the low pressure leg, such that the pressure of the working fluid in the low pressure leg increases and the pressure of the working fluid in the intermediate pressure tank decreases; close the third fluid connection when the working fluid pressure reaches the first threshold pressure value; and adding a second amount of working fluid to the closed-loop fluid path by opening the fourth fluid connection, wherein the high-pressure tank contains working fluid at a second storage pressure greater than the first storage pressure and greater than the working fluid pressure in the low pressure leg, such that the working fluid pressure in the low pressure leg increases and the working fluid pressure in the high pressure tank decreases. 20. The method of claim 19, wherein closing the third fluid connection comprises closing the third fluid connection when the working fluid pressure in the high pressure leg reaches the first threshold pressure value . 21. The method of claim 19, wherein closing the third fluid connection comprises closing the third fluid connection when the working fluid pressure in the low pressure leg reaches the first threshold pressure value .