GB2605256A - Energy storage systems and methods - Google Patents

Abstract

A reversible thermodynamic energy storage system utilising water is disclosed. The system comprises first 20 and second 40 units for exchanging thermal energy of water medium and storing water medium, the second unit storing at a temperature and pressure higher than the first unit. Each unit is configured to condense and evaporate the water medium. The system further comprising a reversible rotary positive displacement engine unit 30 that acts in a first direction as a vacuum pump or compressor, for the water medium, driven for by a motor 50 and in a second direction (“backwards”) as an expander for the water medium to generate power. The motor generator 50 may be a conical screw rotor, delivering a high compression ratio. The storage tanks may comprise phase change materials to retain the thermal energy of the working fluid. Use of a screw rotor in a reversible process is also disclosed.

Description

Energy Storage Systems and Methods

Technical Field

Aspects of the present invention generally relate to energy storage, and in particular, to systems and methods that enable effective and efficient electrical energy storage by utilising the thermodynamics of water.

Background

Energy storage is a global problem that has been acknowledged for several years. As Nobel prize laureate physicist Robert B. Laughlin explained in his featured paper Pumped Thermal Grid Storage with Heat Exchange' (https://www.researchgate. net/publication/318870559_Pumped_thermal_grid_storag e_with_heat_exchange), the concept of pumped thermal energy is not only a niche solution to the energy storage problem but a global one and as such it will prevail. In order to realise this, he claims, all that is needed is "fine engineering and assiduous attention to detail".

Countless scientific journals, reports, concepts and analyses support the view that both small (0.5 -50kVV) to large scale (above 50kW), and short term (minutes) to long term (hours) energy storage can be achieved when thermal storage is taken into account. Robert B. Laughlin, in his paper, as well in his interview that took place due to the signing event of the NADINE (National Demonstrator for Isentropic Energy Storage) project, explained that a 'fully closed Brayton cycle' applies the metrics of safety, low cost, and high round-trip storage efficiency. However, Brayton cycles require extremely high operating temperatures for the heat exchanger, which presents numerous difficulties in terms of material limits, and very large equipment sizes are often required.

CHESTER (UGENT) (Compressed Heat Energy Storage: CARNOT Battery) is an existing system for inexpensive and site-independent storage of electric energy at the gigawatt-hour scale. It utilises a chemical refrigerant R-1233zd(E) and a piston io compressor (e.g. by VIKING) to perform Organic Rankine Cycles. Basic characteristics greatly limit the compression rate and the temperature range to only 160°C while the focus is for storage of energy from renewable energy sources. Another existing system called PUMPHEAT (KTH) uses conventional refrigerant compressors that cannot drive temperatures higher than 120° C, thus it finds applications limited to fossil fuel power is plants. Efficiency improvement here is achieved through lowering the steam condensation temperature (cool side) and storage increasing flexibility but without reducing the fossil fuel input per unit of electrical power produced. The focus in this regard is only on possible exploitation of excess heat for existing district heating networks.

U511156385B2 describes a system referred to as a 'Brayton Battery' that uses a closed Brayton cycle and a variety of thermal fluids (none of which are water) to transfer and store thermal energy as a means of energy storage. The system includes four storage tanks and a rather complicated fluid cycle which increases cost and complexity.

It is to these limitations, amongst others, that aspects of the present invention offer solutions.

Summary of the Invention

In a first independent aspect, there is provided a system comprising a first unit for exchanging thermal energy of water medium and storing water medium at a first temperature and first pressure and storing the thermal energy at the first temperature in a first latent thermal storage chamber, the system further comprising a second unit for exchanging thermal energy of water medium and storing water medium at a second temperature higher than the first temperature and at a second pressure higher than the first pressure, and storing the thermal energy at second temperature in a second latent thermal storage chamber, wherein each unit is configured to condense, accumulate and evaporate the water medium, the system further comprising a reversible, rotary positive displacement, high Compression Ratio, CR, (i.e. CR>1.5 but preferably CR>20) power unit (engine) that acts towards a first direction as a vacuum io pump or compressor, for the first pressure water medium, driven by mechanical power (for example, by an electric motor) when pumping vacuum and compressing the water medium, and reverse-acts towards a second direction ("backwards") as an expander, for the second pressure water medium, producing mechanical power (i.e. driving an electric power generator) when the water medium is expanding under pressure is difference. The high CR engine may be e.g. a reversible screw rotor compressor/expander for charging and discharging the units.

It will be appreciated that, in use, "water medium" will transition between liquid -vapour -saturated steam -super heated steam -condensate phases. Saturated steam refers to the gaseous state of water where there is zero liquid state while the temperature is equal to the boiling point for a given pressure (e.g. 100°C for lbar pressure), whereas super-heated steam refers to the state of water where the gaseous medium is at temperature higher than the boiling point for given pressure (e.g. 110°C for 1bar pressure).

It will be appreciated that "reversible" refers to a process that can be reversed via infinitesimal changes in one of its properties without substantial entropy production (e.g., dissipation of energy). A "reversible process" may thus be represented by a process that is at thermodynamic equilibrium. In some embodiments, in a reversible process, the direction of flow of energy is reversible. Alternatively, or in addition to, the general direction of operation of a reversible process (i.e. the direction of fluid flow) can be reversed, such as, e.g., from clockwise to counter-clockwise, and vice versa.

It will be appreciated that "rotary positive displacement" refers to a type of engine that transforms between pressure difference (between inflow and exit flow) of a working medium fluid that continually flows through it, and rotational mechanical power may be transmitted to an adjoint shaft (axis). In an example, in case of liquid pumps, 'positive displacement' refers to the moving fluid being captured in a cavity and then discharged by the engine. The displacement of fluid takes place by the cavities formed between the rotating and the static parts of the engine. Some of these pumps have expanding cavity at the low pressure (pump suction) side and a decreasing cavity at the high pressure (pump discharge) side. The liquid is sucked at the low-pressure inlet side io when the cavity expands and discharges it to the high pressure side when the cavity decreases. In the present example, gaseous medium water is flowing through the engine. When mechanical power is offered to rotate the positive displacement engine rotor, the gaseous water medium is forced to enter the engine from the low pressure side and exit on the high pressure side. When no mechanical power is transmitted to is the engine, but adequate pressure difference is applied between inflow and exit flow sides, then available high pressure gaseous water medium fills the high pressure side of the engine, and, due to the pressure difference the engine rotates in a reverse rotation, allowing the gaseous water medium to expand through its cavities and exit on the low pressure side, while offering back mechanical power to the shaft which can be exploited.

The present invention provides a versatile method and a system of energy storage that is clearly differentiated from the 'Brayton Battery' or similar known technologies, providing a simplified solution with fewer components and moving parts and design flexibility regarding temperature level of the first temperature unit and the second temperature unit thanks to the combined use of water medium and a rotary positive displacement engine unit. The system is referred to as the "CONDESTORE". Condensing the gaseous phase water medium exiting the engine is an important step of the proposed process that advantageously allows shrinking of the gaseous (vapour) water medium's volume by approximately 1000-fold when the low temperature storing takes place close to 0°C (or 100-fold if close to 100°C) at the low-pressure side and of high-pressure steam by approximately 104old at the high-pressure side. This greatly reduces the volume of the overall storage system compared to alternative steam storage technologies (i.e. steam accumulators).

Under the general area of "Pumped Heat Electrical Storage" (PHES), there are known categories of energy storage that utilise air as the heat transfer medium, such as, Adiabatic Compressed Air Storage (ACAES) and Liquified Air Energy Storage (LAES).

However, by contrast to the present invention, there are no current reversible energy storage PH ES systems that use water as the heat transfer medium. By way of contrast, the known Brayton Battery systems use Argon or Helium as medium; none of the prior are but has presented a solution that uses water in a versatile manner.

io Aspects of the invention have a number of differences over known methods of power storage, including its exploitation of water in its various states, as a thermal transfer and thermodynamic transformation medium, and use of a rotary positive displacement, high compression ratio, reversible, vacuum pump-compressor/expander engine. Compression ratio refers to the maximum achievable ratio of the two pressures before is and after being compressed with the compressing engine.

Advantageously, systems according to the invention enable a wide range of temperatures that can be selected for the first temperature unit and the second temperature unit, practically offering means to select among an extensive set of paired units. For example, one pair can work with the first unit at 10°C and the second unit at 220°C, or another pair with the first unit at 60°C and the second unit at 160°C. This may be achieved by selectively altering, by means of electronically controlled high precision mechanical valves, the flow and/or pressure of the water medium and also by regulating the speed of the rotary positive displacement engine (i.e., by regulating the rotational speed of the electric motor that drives the rotor), changing the compression ratio and the final pressures in the first and second unit, in accordance to specified settings, designed according to a user's selection for the first temperature unit and the temperature for the second temperature unit. The respective temperatures and pressures may be easily identified from defined, known water-tables of boiling water temperature at different pressure levels (see e.g. ir u-steam-piti 45 htnil) In order to increase the overall thermo-mechanical efficiency of the heat-pumping as storage (round-trip efficiency of storage), it is critical to take advantage and store and control the thermal energy exchanged with the water medium when condensing the water medium from vapour phase exiting the engine, to liquid phase in the first unit and from steam phase into liquid condensate phase in the second unit. Once stored, this thermal energy can be reused to re-evaporate the liquid phase before it is released again to the engine. For this purpose, the system comprises at least two units or "THermal-STOREs" ("THSTORES"), that each work in a two-way direction, both as a condenser and as an evaporator of the water medium; in combination with a Phase Change Material (PCM) that functions as a thermal storage medium of low cost and high latent heat capacity. The PCM is isolated from the water medium and the rest of io the system and only thermal energy is exchanged with water medium through means of heat exchanging surfaces. The reversible rotary engine that behaves as vacuum pump-compressor/expander coupled to the motor/generator, works with gaseous water medium and manages charging and discharging the THSTORES units accordingly.

Advantageously, the present solution simplifies the thermo-mechanical conversion process and reduces the number of components required, presenting a highly versatile solution that has a wide variety of applications, from fossil fuel power plant integration, seeking to maximize their output power efficiency and flexibility, to decentralised small storage systems, by storing electrical energy while exploiting the waste heat streams available; in each case maximising the overall electrical production efficiency of the application.

In preferred embodiments, the rotary positive displacement engine unit is configured to lower the pressure (e.g. to create partial vacuum of i.e., 0.001 bara on its suction side) in the first unit and raise the pressure in the second unit (e.g. to achieve water vapour medium compression up to high pressure steam of i.e. 20bara). This was found by the present inventors to be an optimum approach combined with steam/water as the medium to pump heat and store thermal energy at high density into the second unit.

In a dependent aspect, at least one of the at least two units further comprises a "heat exchanger" or a "heat exchange and heat transfer" element. Such an element can be a conventional heat exchanger or a more complex heat exchange and heat transfer element as a HeatPipe. By definition, a 'HeatPipe' comprises a two-phase medium (liquid/gaseous) hermetically enclosed in a hollow pipe made of highly thermal conductive material, with partial vacuum pressure conditions inside (as in Figure 3). The ideal positioning of a HeatPipe is vertical with the hot side below. The HeatPipe pipe material is of high thermal conductivity (metallic or other i.e. aluminium, copper etc.) acting as passive heat exchanger. Under external heat to the lower side of the HeatPipe rapid evaporation of the two-phase medium inside it takes place. Due to the vacuum an upward high-speed (example at speed of sound 340m/s) transition of the two-phase medium also takes place inside the HeatPipe and acts as the rapid heat io transfer medium that transfers heat towards the other (cooler) side of the HeatPipe pipe. Under gravitational force the two phase medium which condenses inside the HeatPipe cooler (upper) side returns to the hotter (lower) side of the HeatPipe. This type of Heatpipe is regarded also as a Thermosyphon HeatPipe. In a further dependent aspect, the HeatPipe comprises porous material, which covers as a thin layer the inside is surface of each HeatPipe pipe. Advantageously the porous material (such as wick) enables capillary forces to assist speeding the liquid mass transfer of the two-phase medium inside the pipe. In an example, the heat transfer elements are hermetically closed pipes of extreme vacuum that, depending on the chosen temperature level of the unit, enclose a carefully selected quantity and type of a two-phase medium, for example, Ethanol. It will be appreciated that alternative two-phase mediums may be used. The HeatPipe element advantageously facilitates the high-speed heat transfer that can be achieved between the three chambers (the lower, where water medium condenses, the PCM chamber and the upper where water medium evaporates) and the thermodynamic changes (evaporation and condensation of two-phase medium, as Ethanol, inside the HeatPipes, melting (fusion) and solidifying of the PCM, and condensation and evaporation of water medium in the lower and upper chambers) taking place inside each THSTORE unit, during charging and discharging of each of them.

In a dependent aspect, at least one of said units comprise a high latent heat material or a high latent heat composite material, of high latent thermal energy capacity; for example the material may be a phase change material (PCM) or a Composite PCM (cPCM). The selected material can store thermal energy in the form of latent heat. When a unit is charged, latent heat of fusion (melting and solidifying) is stored under

B

constant temperature. A phase change material (PCM) is a substance which releases/absorbs sufficient energy at phase transition under constant temperature to provide useful heat/cooling. Generally, the transition is from one of the first two fundamental states of matter -solid and liquid -to the other. The energy released/absorbed by phase transition from solid to liquid, or vice versa, the heat of fusion is generally much higher than the sensible heat. Sodium sulphate (Na2SO4-10H20), for example requires 252 J/g to melt when at melting/solidifying temperature of 32.4°C under lbara pressure. By melting and solidifying at the phase change temperature (PCT), a PCM is capable of storing and releasing large amounts io of energy compared to sensible heat storage. Heat is absorbed or released when the material changes from solid to liquid and vice versa; PCMs are accordingly referred to as latent heat storage (LHS) materials.

For the invention to advantageously achieve high speed phase changes of the water is medium: liquid -vapour-super heated steam -condensate, the THSTORE units may comprise, for example, a matrix of heat conductive material (such as, but not limited to, metallic fins or laminates or additive substances as graphene particles) and a large set of heat exchangers (in this example HeatPipes) inside the container chamber of the PCM to assist with thermal transfer within the PCM mass and thermal exchange with the pipe surface. A large number of HeatPipes ensures the high-speed heat transfer and thermal exchange between water/steam and the PCM to facilitate the required objectives of the applications.

The system contains at least two heat exchanging units, one operating at a lower temperature (i.e. 60°C) and lower pressure (for this example 0.2bara according to properties of saturated steam) and the other of a higher temperature (i.e. 160°C) and higher pressure (for this example -6.3bara). Each heat exchanging unit is a reversible thermodynamic system that can advantageously manage continuous phase changes of water states (i.e. forced evaporation and forced condensation) at high speed. For example, each unit may comprise an insulated chamber comprising PCM that encloses a matrix of thermal conductive material, attached or in proximity to the heat exchanger. The speed of thermal transfer is dependent on the temperature difference between the water medium in the respected chamber and the PCM and be effectively in the range of 10 -100 kW per m and per Kelvin (kW/m K) which is much higher in comparison with i.e. roughly 400 W/m K for Copper.

In a dependent aspect, at least one of said heat exchanging units comprises a first (lower) unit portion for condensing gaseous water medium ("condensing chamber") and a second (upper) unit portion for evaporating liquid water medium ("evaporating chamber"), wherein a first portion of the heat exchanger is located inside the first unit portion and wherein a second portion of the heat exchanger is located inside the second unit portion.

In a further dependent aspect, at least one of said heat exchanging units comprises a third unit portion comprising high latent heat (e.g. PCM) material for storing thermal energy ("PCM chamber"), wherein the thermal energy is transferred from the first unit portion (condensing chamber) when thermally charging the PCM material, or towards is the second unit portion (evaporating chamber) when thermally discharging the PCM material, wherein a third portion of the heat exchanger is located inside the third unit portion.

In a dependent aspect, at least one of said units comprises a fourth unit portion for accumulating the water medium ("condensate accumulator chamber") that is transferred through piping from the first unit portion (condensing chamber) when thermally charging the PCM, or is transferred from the fourth unit through another pipe by means of liquid pump towards the second unit portion (evaporating chamber) when thermally discharging the PCM.

In a further dependent aspect, the at least one of said units comprise condensate removal means, a steam trap, in communication with the first unit portion. In a further dependent aspect, the at least one of the at least two units comprises an atomiser in communication with the second unit portion.

For example, the condensing chamber (may be located beneath the PCM chamber, penetrated by the lower part of the heat exchanger (i.e. HeatPipes), with a gaseous water medium input pipe, controlled by a regulating valve, and a controlled water medium condensate removal system (i.e. a steam trap (210 in Figure 2A) that can be of various types, in example a venturi steam trap) with an exit pipe; and an evaporating chamber above the PCM chamber, penetrated by the heat exchanger (i.e. heatpipes) upper part, with a valve-controlled pipe for liquid water medium input, with a condensate spray (atomiser) system (212 as in Figure 2A) and a regulating-valve for gaseous water medium exit pipe. For both (water medium condenser and evaporator) chambers one may control the gaseous and liquid flows with control valves, for example. In this example the HeatPipe middle section penetrates the PCM chamber (23/43) in a way that the HeatPipes can thermally charge the PCM during thermal charging (while gaseous water medium being condensed in the condensing chamber (22/42) and removed through the steam trap (210/410) towards the condensate accumulator chamber) or thermally discharge the PCM during thermal discharging (while liquid water medium from the condensate accumulator chamber (21/41)) is pumped towards and through the atomiser inside the evaporating chamber (24/44), being evaporated and removed through the exit regulating-valve and pipe as gaseous is water medium).

In a dependent aspect, the system further comprises a valve and liquid pump 211 for controlling water medium flow from the fourth unit portion (condensate accumulator chamber (21/41)). It will be appreciated that adding additional thermal storage units to the system can increase the overall storage capacity of the system. In a dependent aspect, the system comprises at least one triode valve. Advantageously, triode valves are used so that thermal storage units comprising different PCMs can be added in parallel, allowing a more versatile range of storage applications. The thermal storage units can be charged/discharged accordingly, not only internally within the closed CONDESTORE system by dynamic controls (i.e. of speed or throughput) of the water medium engine, but they can also take advantage of external thermal flows and be thermally charged by them by means of additional external heat exchangers. This facilitates the advantage of utilising waste heat streams and solar heat that can charge any of thermal storage units, even without electrical input.

At the dynamic control level, in an example system, two valves may be used to control the water medium flow (gaseous or liquid state) input and output of each unit. Additional regulating valves for pressure, vacuum and flow can be used at other points according to the system size, to provide more fine-tuned control over the system.

It will be appreciated that adding additional rotary engine units to the system can increase the power performance (charging or discharging) of the system. In a dependent aspect, the system comprises at least one positive displacement engine.

Advantageously, positive displacement engines combined with a motor and generator each, are used so that pipes managing the flow of larger water medium quantities can be added in parallel, allowing a more versatile range of applications. The engines can manage larger flows and power loads when charged/discharged accordingly. This facilitates the advantage of managing a large variety of applications. In a dependent io aspect adding more engines in parallel increases the capacity of water medium that flows between the thermal storage units. This consequently increases the electrical power that can be absorbed by the motor units and generated by the generator units. In a dependent aspect adding more engines in series increases the compression ratio and the expands the limits of final pressures achieved (lower vacuum on the low is pressure side and higher pressure on the high pressure side).

In a dependent aspect, the system comprises a controller for controlling the positive displacement engine rotor speed, for example a variable speed driver, VSD, for the electric motor that drives the rotor. Whilst the speed of the motor coupled to the rotor (or, in the case of multiple engines and motors, their speed) can be controlled with a single VSD, alternative controls for the rotors' speed are within the scope of the invention. In another example the controller can be used to automate the opening and closing of control valves that are used to regulate the flow of the medium to and from the heat exchanging units and the engine unit(s).

Aspects of the present invention have many applications.

In a dependent aspect, there is provided a heat pump comprising a system according to aspects described above. In this manner, the heat pump can take advantage of low-grade enthalpy waste heat streams (for example: a waste heat fluid flow of exhaust flue at temperature 70°C can be exploited with means of a flue gas heat exchanger to charge a 60°C PCM unit) and with the help of an electrical motor produce low-cost useful steam of high pressure, e.g. 20 bar. Estimations based on rotary positive displacement engine compressors of high compression ratio (CR>15) show that the electrical Coefficient of Performance COP (the ratio of useful thermal energy output of the heat pump divided by the electrical energy input required for the motor: COP= kW thermal out/ kW electrical in) can be as high as 7 (COP=7) but becomes even higher than COP=15 as the final useful steam output pressure setpoint is reduced (i.e. if one only requires useful heat at 110°C temperature and the steam pressure is set to approximately 1.45 bara).

In a dependent aspect, there is provided an electrical storage system comprising a system according to aspects described above. Based on calculations, the round-trip io efficiency (round trip: from electrical power to storage back to electrical power) of the system as an electrical storage system, is expected to surpass 70%. Given that the size of the system can be quite small, (for example, a 10kW electrical power system that holds 5 hours of charge and discharge in full power input and output can be containerised within a standard EU 20 feet shipping container (-2.5mX2.5mX6m)) the is use of the system for electrical energy storage is extremely advantageous, especially regarding the levelised cost (LCOES) (Levelised Cost of Energy Storage), weight per unit of energy and per unit of power. Accordingly, systems according to aspects of the invention have applications in electrical vehicle charging stations, one of the biggest modern challenges to be solved globally. As versatile thermo-dynamic-electrical converters, systems according to aspects of the invention represent a dynamic multi-energy type storage solution that proves low enthalpy heat useful, without requiring special maintenance, tools, materials or posing risks, dangers and requirements for unsustainable methods and approaches to the users or close habitats, making it an advantageous system for energy storage over known systems.

In a first independent aspect, there is provided a reversible process for storing thermal energy of water medium, the process comprising the steps of: providing a first unit for exchanging thermal energy of water medium and storing the water medium at a first temperature and first pressure, and for storing the thermal energy at the first temperature in a phase changing material, PCM; providing a second unit for exchanging thermal energy of water medium and storing the water medium at a second temperature higher than the first temperature and at a second pressure higher than the first pressure, and for storing the thermal energy at the second temperature in the PCM, wherein each unit is configured to condense and evaporate the water medium, and wherein each unit is configured to melt and solidify their respective PCM; providing a positive displacement rotary engine unit for operating in a first direction as a vacuum pump or compressor for the first pressure water medium, the engine unit being driven by i.e. an electric motor when pumping vacuum or compressing the water medium creating a pressure difference, and for the same engine operating in a second direction as an expander for the second pressure water medium, driving an electric power generator, when the water medium is expanding through the engine under the pressure difference.

In a dependent aspect, a process according to aspects defined above further comprises the step of providing a single reversible rotary positive displacement engine for vapour and steam vacuum pumping/compression and expansion of the water medium. Advantageously, the reversible rotor engine withstands erosion from wet is steam droplets, variable throughput and high temperatures, without need for lubrication. In a further dependent aspect, the rotary positive displacement engine can be selected among a variety of designs that include all known types of rotary positive displacement designs, namely; internal gear, external gear, gerotor, vane, lobe, twin lobe, screw, twin screw, triple screw, spindle, scroll, eccentric screw, conical screw (as exemplified in Figure 4). Depending on the specific application and the consequent specifications regarding, for example, the temperature levels, the required compression ratio, the need for low vacuum or high pressure and finally the costs that can be kept to a minimum, the choice of the optimum rotor can be decided by case. Currently one of the most adequate engines is the conical screw rotor engine. The conical screw rotor engine can create a partial vacuum (i.e., down to 2 mbar) on its suction side which allows i.e. using a low temperature THSTORE unit with a critical point of 60°C or even less than 0°C. Therefore, this can take advantage of ideal thermodynamic properties of steam but at lower than the conventional temperature range (which is 100°C +) and with a high compression ratio of i.e. CR=20, which is the driver of mechanical power on the expander or the opportunity of a high COP heat-pump that produces low electrical input and high output pressure steam while taking advantage of low temperature (60°C) waste heat. It will be appreciated that the sizes of the conical screw rotor can vary, facilitating a reversible heat pump solution.

In a further independent aspect of the invention, there is provided a use of a screw rotor engine in a process of storing thermal energy of water medium. By definition rotary-screw engines use two very closely meshing helical screws, known as rotors, to i.e. compress or allow the controlled expansion of a gaseous medium. A rotary screw engine comprises of a meshing pair of helical lobed rotors contained in a casing which together form a working chamber, the volume of which depends only on the angle of rotation only on the angle of rotation. Other than the pair of screw rotors and the cylinder the structure consists of bearings, synchronous gears, seal assembly to optimise overall compression ratio and minimise internal pressure losses (leakage). In io particular embodiments, the process comprises steps of steam compression-expansion for energy heat-pumping and energy heat pump storage applications. Advantageously, a screw rotor compressor expander can be a reversible rotor engine, acting both as compressor and expander, offering the simplicity of managing and exploiting the power of steam as an ideal thermodynamic medium, according to the is needed operation.

A conical screw rotor engine is a type of rotary-screw rotor using a different topology from the typical dual-screw engine type, in effect it is a conical spiral extension of a gerotor. (A gerotor can function as a pistonless rotary engine, generally consisting of an inner and outer rotor, designed using a trochoidal inner rotor and an outer rotor formed by a circle with intersecting circular arcs). Because of this the conical screw rotor engine does not have the inherent "blow-hole" leakage path which, for example, in typical screw compressors is responsible for significant leakage through the assembly and makes low-speed operation impractical. This characteristic of conical screw rotors allows much higher compression ratios to be achieved in a single stage and feasible manufacturing even for 90% smaller size units compared to typical twin-screw compressors. Using a conical screw rotor we can achieve an extremely high compression ratio (CR = 20 per unit), and can withstand variable throughput and high temperatures which are important for feasible exploitation of the invention.

In a preferred application, the screw rotor engine is conical screw rotor engine. Using a conical screw rotor, for example of the type developed by Vert Rotor Technologies, but configured for water medium vacuum pumping, compression/expansion for energy heat-pumping and energy heat pump storage applications of the present invention, has particular advantages

Brief Description of the Drawings

Aspects of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which: io Figure 1 is a schematic of a "CONDESTORE" system and reversible process, showing the phase changes of water medium that flows through two THSTORE units mediated by a positive displacement rotor (vacuum pump -compressor/expander) engine.

Figures 2A, 2B represent a schematic of an example low temperature THSTORE is storage unit, highlighting the different components and chambers that facilitate and manage the water medium phases, the phase changes and flow direction in which they travel through the system, as well as the thermal exchanges, the thermal flows and thermal storage. The unit 20 is mirror identical to the high temperature THSTORE unit 40.

Figure 3 is a schematic showing the positioning and details of an isolated single HeatPipe unit within a relevant vertical part of three chambers of a THSTORE unit 20/40, paired with an illustration of the internal workings of a HeatPipe.

Figure 4 illustrates examples of positive displacement rotors (vacuum pumps-compressors-expanders) that may be used in systems according to the invention.

Figures 5 illustrates an example of a conventional screw rotor engine cut-off.

Figure 6 illustrates an example of a conical screw rotor engine cut-off by Vert Rotors.

Figure 7 is a schematic of an example process, highlighting the core components and phase changes of water medium throughout the system during charging and discharging.

Figure 8A is a schematic of an example process, highlighting the core components and phase changes of water medium throughout the system during charging.

Figure 8B is a schematic of an example process, highlighting the core components and phase changes of water medium throughout the system during discharging.

Figure 9 is a schematic of an example programmable computational process control system, that implements various methods of collecting data from various sources io (internal and external) to automatically regulate control of various components and maximise efficiency of the system in accordance to set parameters.

Detailed Description

is Figure 1 is a schematic of a ("CONDESTORE") system 10 for energy storage, comprising two thermal energy storage units ("THSTORE") or modules. The units 20, 40 operate in two reverse ways, meaning that they each act to condense and evaporate water medium, under the pressure conditions created by the reversible, positive displacement rotor engine (vacuum pump-compressor/expander) 30 located between them coupled to a motor and power generator (i.e. a motor, not shown). The rotor, by compressing or allowing expansion of the gaseous water medium, thermally charges and discharges the THSTORE units 20, 40.

With reference to Figure 2A, each THSTORE unit 20, 40 comprises a matrix of heat conductive material (not shown) and a plurality of multiple heat exchanging units in the form of vertical HeatPipes 300 acting as means of heat exchanging and heat transferring. The thermally conductive material (i.e. metal fins or graphene particles) may be dispersed within the mass of the phase change material (PCM). The HeatPipes 300 achieve rapid thermodynamic phase changes of the water medium in the Evaporator 24 or the Condenser 22 by facilitating high-speed efficient thermal exchange of the water medium outside the respected HeatPipe portions. The HeatPipes 300 achieve high speed thermal transfer of the two-phase medium (i.e. Ethanol) inside the HeatPipes. The HeatPipes 300 achieve high speed phase changes of the PCM outside the HeatPipe portions that are in the PCM chamber 23.

Each THSTORE unit 20/40 is configured and acts as means to convey the latent thermal energy released by the vapour water medium as it condenses, to the PCM, by use of the HeatPipes and to store this thermal energy in the form of latent heat of fusion in the PCM when thermally charging the THSTORE unit. In a reverse aspect, each THSTORE unit 20/40 is configured and acts as means to convey the latent thermal energy stored in the PCM 23/43 by use of the HeatPipes 300, during solidification of the PCM, and to allow the sprayed liquid absorb this heat as it evaporates, when thermally discharging the THSTORE unit.

Pure PCM materials, in example Sodium sulphate (Na2504.10H20), have by nature low thermal conductivity. Obvious this is a challenge and any PCM needs enhancing support in order to improve thermal conductivity of a PCM based system and achieve high-speed and high efficiency heat transfer between PCM chamber and the other two is chambers by case. The proposed approach of dispersing heat conductive material in the PCM mass and deploying a set of multiple vertical HeatPipes 300 plays significant role to accelerate each heat transfer step. The heat conductive material is preferably organised in a mesh matrix, for example formed by aluminium laminates, or copper wiring or fins. Alternatively, the heat conductive material is an additive material, in the form of dispersed particles in the PCM mass, forming together a Composite PCM (see Jiang et al. : "A novel composite phase change material for medium temperature thermal energy storage manufactured with a scalable continuous hot-melt extrusion method"). For example, graphite powder (highly conductive) granulates can be dispersed in Pentaerythritol PCM to form a high conductivity cPCM. Consequently, both thermodynamic processes of the water medium (namely condensing and evaporation) on the external surface of each of the HeatPipe unit wall which are exposed inside the evaporator chamber 24/44 (upper side) and inside the condenser chamber 22/42 (lower side) respectively are simplified and accelerated. Advantageously, a CONDESTORE unit 10 may utilise a large number of different interconnected THSTORE units 20/40 of a large variety of temperatures, based on the available cPCM materials in the market.

It will be appreciated that the choice of PCM in each unit 20, 40 defines the critical Phase Change Temperature PCT (critical point) which also indicates the pressure levels under which water phase changes will take place, which is in accordance to water properties as presented in water-steam tables (see e.g. Depending on pricing and availability, as well as criteria of sustainability, corrosiveness, and resource efficiency, many different pairs of low and high temperature PCMs can be chosen for the proposed THSTORE units. The overall number of THSTORE units, containing a different PCM for varied applications is not limited by the present invention. With means of parallel pipes and control valves a io multitude of THSTORE combinations can be feasibly available.

In particular applications, more than two types of THSTORE units can be used with PCMs of different critical temperature concurrently to utilise available heat sources, to charge the system and take advantage of the installed positive displacement rotor /5 vacuum pump-compressor/expander engine units. Different sets of THSTORE units may be used for different applications; example applications include but are not limited to: solar heat, biomass, renewables and waste heat, for example recovered from industrial processes.

Referring back to Figure 1, the overall reversible, bidirectional process in the CON DESTORE system 10 is illustrated between the lower temperature unit 20 and the higher temperature unit 40. The reversible rotary positive displacement engine 30 is located between the units 20, 40 coupled to a motor and a power generator (not shown). VVhile in use, each unit has a charging function mode and in a discharging function mode. When not in use, the THSTORE unit has a storage function that remains idle with minimum losses that can be minimal by use of insulation. Insulation of the THSTORE units as well as piping and subcomponents of the system is important and can be achieved with a large variety of low thermal conductivity materials (i.e. aerogel insulation).

When in electrical energy-charging mode, the motor 50 coupled to the compressor 30 absorbs electrical energy and drives development of under-pressure conditions through the vacuum regulating valve V2 in the (left upper) evaporating chamber 24 located at the top of the THSTORE unit 20. Due to the under pressure (partial vacuum) and with support by the liquid pump 211, liquid water medium from the low temperature THSTORE unit condensate accumulator chamber (lowest left) 21 is pumped (by pump 211) and sprayed through nozzles (212) in the (upper left) evaporator chamber 24. Due to low pressure conditions inside the evaporator chamber 24 and heat transferred through the HeatPipes 300 from the ACM chamber 23 (due to temperature difference ACT> evaporation temperature of the water medium), evaporation takes place in the evaporator chamber 24 and allows vaporised water medium to flow through vacuum regulator valve V2 and enter from the low pressure side in the rotary engine 30 where due to positive displacement compression it becomes high pressure compressed io steam or superheated steam depending on the rotor speed. This high pressure or superheated steam exits the engine 30 on the high pressure side and is conveyed through piping to the (low right) condensing chamber 42 of the high temperature THSTORE unit 40, where it releases enough heat (which is conveyed by HeatPipes 300 in the PCM chamber 43 due to temperature difference PCT< condensing temperature of the water medium) and becomes high pressure condensate, removed by means of steam trap (410) and stored in the condensate accumulation chamber (lowest right) 41 of the high temperature THSTORE unit 40.

In a similar aspect, when in electrical energy-discharging mode, reversing of the process takes place. The high-pressure condensate in the (lowest right) condensate accumulator chamber 41 is pumped (by pump 411) and sprayed through nozzles (412) in the (upper right) evaporator chamber 44. Due to lower pressure conditions inside the evaporator chamber 44 and heat transferred through the HeatPipes 300 from the ACM chamber 43 (due to temperature difference ACT> evaporation temperature of the water medium), evaporation takes place in the evaporator chamber 44 and becomes high pressure steam. When enough pressure is built, the pressure regulatory control valve V4 allows the steam to enter the rotor/expander 30 on the high pressure side, where due to positive displacement expansion the engine rotor turns and the mechanical power by means of the generator coupled to the rotor produces electrical power. Exiting the expander 30, low pressure and high volume vapour water medium enters through piping and Valve V1 the (lower left) condensing chamber 22 of the (left) low temperature THSTORE unit 20. In the condensing chamber 22 and due to highspeed thermal heat transfer, through the heatpipes 300 to the ACM chamber 23, low pressure condensate is formed and removed by means of steam trap 210 and stored in the condensate accumulation chamber (lowest left) 21 of the low temperature THSTORE unit 20 At least two modular THSTORE units 20, 40 are required for the system 10 to store energy (one high and one low temperature), with each working as a two-way thermodynamic system that manages high-speed, continuous phase-changes of water medium through controlled evaporation and condensation. More THSTORE units of same temperatures as the first two or of different temperature levels can be interconnected, in example, to exploit sources of thermal energy available i.e. through io heat exchangers at different temperatures. In case of abundant thermal sources at low cost (i.e. access to sea-water) where there is no need for ACM material to fill the ACM chamber, a lower cost alternative option can be applied. For example, a low temperature THSTORE unit can be used without ACM material in the ACM chamber but instead of ACM continuously pumped sea water could retain the temperature level is at chosen setpoint and allow the CONDESTORE to function efficiently.

Figures 2A and 2B illustrate an example low temperature unit 20/40. The unit comprises a ACM chamber 23/43 with ACM that encloses a high latent heat capacity cPCM material in contact to the external surface 35 of the HeatPipes 300 and the conductivity enhancing surfaces (i.e. fins). Each THSTORE unit 20/40 charges (absorbs and stores heat by melting) and discharges (releases heat, cools and solidifies) the enclosed thermal storage ACM, facilitated by multiple HeatPipes 300. Inside the ACM chamber 23/43 the HeatPipes 300 penetrate the bottom of the ACM chamber 23/43 and then penetrate the top of the condenser chamber 22/42 where they can function as the vapour water medium condensing heat exchanger, by absorbing heat from the gaseous water medium entering through the regulating valve V1N3. Preferably the unit 20 has a controlled condensate removal means in the form of a steam trap 210/410. Inside the ACM chamber 23/43 the HeatPipes 300 penetrate its top and then penetrate the bottom of the evaporating chamber 24/44, where they can function as water medium evaporators by transferring stored heat from the ACM to the pumped sprayed water medium condensate. Preferably, the unit 20/40 utilises a controlled condensate release sprayer/atomiser 212/412. Both the condensing and evaporating chambers 22/42, 24/44 control the water medium flow with regulating valves (V1N3, V2N4), as shown in Figures 2A, 2B.

The HeatPipes 300 are important for the functionality of each unit 20, 40. The HeatPipes 300 may be hermetically closed pipes of extreme vacuum that enclose a carefully selected type and quantity of two-phase medium (e.g. water, Ethanol, Methanol or other) that is dependent on the selected temperature range of the THSTORE units 20, 40. The HeatPipes 300 achieve rapid heat transfer to support the efficient and high speed thermodynamic phase changes of water in each unit 20, 40 in charging and discharging modes while transferring this heat to and from the PCM chambers 23/43 respectively.

Figure 3 shows a schematic of a single HeatPipe unit 300 within a portion of a THSTORE unit 20/40 and an illustration of the inner workings of a single HeatPipe unit 300. It will be appreciated that HeatPipe can work in a similar manner in either unit 20 or 40 under a given temperature range. The water medium evaporation chamber 24/44 is is shown it the top of the unit 20/40 representing an upper level of the unit 20/40. Here, liquid water medium is sprayed by means of sprayer nozzles 212/412, and due to thermal energy transferred by the HeatPipes 300, (due to temperature difference PDT< evaporation temperature of the water medium) rapid evaporation of water medium takes place outside the HeatPipe walls 35. A pressure or vacuum regulating valve V2/V4 controls the vapour exit towards the engine 30.

The PCM material is located in the PCM chamber 23/43 representing a middle level portion of the unit 20/40. Depending on the function mode, when charging (melting) the PCM in the PCM chamber 23/43, heat from the condensing chamber 22/42 (lower level) is conveyed by the HeatPipe 300 unit into the PCM chamber 23/43 to charge (melt) the PCM under constant temperature. Further, when discharging (cooling and solidifying) the PCM in the PCM chamber 23/43, heat from the PCM chamber 23/43 is conveyed to the evaporation chamber 24/44 (top portion of the THSTORE unit 20/40).

Fins and a matrix of heat conductive material (for example: aluminium laminates or graphene particles etc) not depicted here, are spread within the PCM mass in the PCM chamber 23/43 outside the HeatPipes 300 to increase thermal conductivity and heat transfer speed between PCM mass and the HeatPipes 300. In a similar aspect heat conductive material (fins and laminate) can increase the heat exchanging surface and speed in the evaporating chamber 24/44 and in the condensing chamber 21/41 The gaseous water medium condenser chamber 22/42 is located at a lower level of the unit 20/40. Vapour or steam entering this area is cooled inside the condenser chamber 22/42 by means of the HeatPipe 300 unit and condenses outside the HeatPipe surface. A condensate remover or steam trap 210/410 controls the exit of the liquid condensate. A regulating valve V1N3 controls the gaseous water medium in-flow, depicted on the figure, note it is within the scope of the invention for further io valves may be added to increase control over the system.

Inside the HeatPipe 300, a two-phase medium (liquid/gas) is enclosed, such as, for example Ethanol. The two-phase medium goes through the opposite phase changes against the water vapours externally surrounding the HeatPipe walls 35. At the lower is levels of the unit 300 the two-phase medium evaporates and elevates 351 to the upper levels at high speed (in the range of the speed of sound 340m/s). At the upper level, the two-phase medium releases heat through the HeatPipe walls 35, either inside the surrounding ACM of the ACM chamber 23/43, or even at a higher level inside the evaporator chamber 24/44 offering heat to the sprayed water condensate. There, the inner two-phase medium of the HeatPipe 300 continuously condenses 352 and returns to the lower portions or the bottom of the HeatPipe 300.

The HeatPipes 300 may be thermo-siphons which are cost-effective; the liquid phase mass transfer 352 taking place on the inner side of the HeatPipe wall 35 surfaces under gravitational force. It is within the scope of this invention for more expensive solutions to speed up the liquid return to the lower side, by use of an inner HeatPipe wall layer of porous material (wick) that enables capillary forces to assist speeding the liquid On this example also downward) liquid two-phase medium mass transfer. The use of HeatPipe units 300 is an extremely fast heat-transfer method that requires no moving parts or mechanical energy to take place, facilitating rapid phase changes of water for the process and improving the overall efficiency of the CONDESTORE 10 processs.

Figure 4 shows nine rotary positive displacement engine types considered for this application. Selection of a rotary positive displacement engine to play the role of reversible vacuum pump-compressor-expander 30 for the system 10, requires a variety of parameters to be considered, analysed, prioritised and identified by case of application requirements. Industry driven simplified methodologies foresee that determining throughput is important, while the final selection should be based on compression ratio requirement also.

For the system 10 described above, a screw rotor compressor/expander 30, shown in Figure 4 (as Screw compressor) and Figure 5, was found to gather many advantages, as these rotors may be easily upgraded to be used as reversible rotor engines, acting io both as a compressor and expander offering the simplicity of managing and exploiting the power of gaseous water medium (steam) as an ideal thermodynamic medium, according to the needed operation. They also achieve high compression ratio in the range of CR=20 while they can cope with variable throughput and high temperatures, without need for lubrication. Furthermore, they can withstand erosion from possible is formation of wet (liquid) droplets that are often found within the gaseous water medium.

Future improvements of screw rotor manufacturing can further improve these properties.

Specifically, the engine 30 may comprise conical screw rotor engines 301 for example in Figure 6 of the type developed by Vert Rotor Technologies, and apply them as reversible rotor engines for water vapour vacuum pumping, compression and expansion. By using such a positive displacement rotor component, the CON DESTORE 10 system's flexibility is enhanced with the ability to use water/steam as the thermodynamic medium, only at even lower temperature on the low temperature unit 20. This is due to the ability of conical screw rotors to create low partial vacuum on their suction side (down to 2mbar or lower), which makes it possible for the low temperature THSTORE unit 20 to be chosen and designed with a critical point of PCM temperature lower than 100°C, down to 60°C or 20°C or even below zero °C. This process is important as it exploits the use of water medium for heat pumping and thermal storage at lower temperatures while taking advantage of the same high compression ratio. This means steam can be expanded from, for example, 10 bar down to 0.5 bar, taking advantage of Compression Ratio CR=20 which is the driver of mechanical power on the expander shaft. Due to the flexible design of conical rotors that can be manufactured starting from an extremely small size (e.g. a few centimetres) to much larger (e.g. over a meter in diameter) they provide a feasible solution of reversible heat-pumping and electrical and /or thermal energy storage.

Figure 7 shows an example charging mode and an example discharging mode process with a (conical) screw rotor engine 30/301 as a compressor/expander and the coupling of the engine 30 to a motor / generator 50. During the charging mode, the motor 50 coupled to a (conical) screw rotor compressor 30/301 consumes electrical energy, driving under-pressure conditions through regulating valve V2 in the low pressure evaporating chamber 24. Due to the heat from the PCM chamber 23 though the HeatPipes 300, rapid evaporation of water medium takes place outside the HeatPipe walls 35, and the formed vapour is released out of the low temperature unit 20 in a controlled manner through the top regulating valve V2. This vapourised water medium then enters the (conical) screw rotor compressor 30/301 from the low pressure side, and in there, under mechanical positive displacement compression, it becomes is compressed (superheated) steam. This high-pressure steam is guided through piping and regulating valve V3 to the high temperature (low right) condenser chamber 42 where it releases heat which is conveyed and stored in the PCM chamber 43 of the high temperature THSTORE unit 40 by means of HeatPipes 300, so it becomes high pressure liquid water medium condensate which exits the through the steam trap (410) of the condensate chamber 42 and is guided through piping to the (right lowest) condensate accumulator chamber 41 of the high temperature unit 40. In Figure 7 the reverse process is also depicted.

Figure 8A shows an example charging mode process 10 with a (conical) screw rotor engine 30/301 as a compressor/expander ready to be coupled to a motor / generator 50. In a similar aspect to Figure 7, when in electrical energy charging mode. During the charging mode, the motor 50 coupled to a (conical) screw rotor compressor 30/301 consumes electrical energy, driving under-pressure conditions through regulating valve V2 in the low pressure evaporating chamber 24. Due to the heat from the PCM chamber 23 though the HeatPipes 300, rapid evaporation of water medium takes place outside the HeatPipe walls 35, and the formed vapour is released out of the low temperature unit 20 in a controlled manner through the top regulating valve V2. This vapourised water medium then enters the (conical) screw rotor compressor 30/301 from the low pressure side, and in there, under mechanical positive displacement compression, it becomes compressed (superheated) steam. This high-pressure steam is guided through piping and regulating valve V3 to the high temperature (low right) condenser chamber 42 where it releases heat which is conveyed and stored in the PCM chamber 43 of the high temperature THSTORE unit 40 by means of HeatPipes 300, so it becomes high pressure liquid water medium condensate which exits the through the steam trap (410) of the condensate chamber 42 and is guided through piping to the (right lowest) condensate accumulator chamber 41 of the high temperature unit 40.

io Figure 8B shows an example discharging mode process 10 with a (conical) screw rotor engine 30/301 as a compressor/expander ready to be coupled to a motor / generator 50. In a similar although reverse aspect to Figure 8A, when in electrical energy discharging mode, reversing of the process 10 takes place. The high-pressure condensate in the (lowest right) condensate accumulator chamber 41 is pumped by is means of liquid pump 411 and sprayed by means of atomiser 412 in the (upper right) evaporator chamber 44. Due to heat released from the PCM chamber 43, by means of HeatPipe units 300, evaporation of the sprayed water medium takes place in the evaporator chamber 44 and becomes high pressure steam. When enough pressure is built, the regulating valve V4 allows the steam to enter the rotor/expander engine 30/301 from the high pressure side and due to positive displacement expansion the rotor turns and the mechanical power by means of the generator 50 coupled to the rotor 30/301 is converted to electrical power. Exiting the expander 30/301 from the low pressure side, low pressure vapour water medium enters through piping and regulating valve V1 the (lower left) condensing chamber 22 of the (left) low temperature THSTORE unit 20. In the condensing chamber 22 and due to high-speed thermal heat transfer, through the heatpipes 300, to the PCM chamber 23, low pressure water medium condensate is formed and removed by means of steam trap (210) and then guided through piping and stored in the condensate accumulation chamber 21 of the low temperature THSTORE unit 20.

Figure 9 shows an example programmable computational process control system, that implements various methods of collecting data from various sources (internal and external) to automatically regulate control of various components and maximise efficiency of the system in accordance to set parameters.

In Figure 9 a programmable computational process control system 901 is configured to regulate various process parameters of subcomponents of our system. Such process parameters can include water medium temperatures, flow rates, pressures, PCM temperatures and pressures, at various monitored points in the components, piping and chambers. In a similar way these parameters may also include engine rotor speed, as well as electrical motor and generators electrical current, energy and power production and consumption parameters. The process control system 901 comprises a central processing unit (CPU, also "processor" and "computer processor" herein) 905, which can be a single core or multi core processor, or a plurality of processors for parallel processing. The computer system 901 further comprises a memory or memory location 910 (e.g., random-access memory, read-only memory, flash memory), electronic storage unit 915 (e.g., hard disk), communication interface 920 (e.g., network adapter) for communicating with one or more other systems, and peripheral is devices 925, such as cache, other memory, data storage and/or electronic display adapters. The memory 910, storage unit 915, interface 920 and peripheral devices 925 are in communication with the CPU 905 through a communication bus (solid lines), such as a motherboard. The storage unit 915 can be a data storage unit (or data repository) for storing data. The computer system 901 can be operatively coupled to a computer network ("network") 930 with the aid of the communication interface 920. The network 930 can be the Internet, an internet and/or extranet, or an intranet and/or extranet that is in communication with the Internet. The network 930 in some cases is a telecommunication and/or data network. The network 930 can include one or more computer servers, which can enable distributed computing, such as cloud computing.

The network 930, in some cases with the aid of the computer system 901, can implement a peer-to-peer network, which may enable devices coupled to the computer system 901 to behave as a client or a server. The computer system 901 is coupled to an energy storage and/or retrieval system 935, which can be as described above or elsewhere herein. The computer system 901 can be coupled to various unit operations of the system 935, such as flow regulators (e.g., valves), temperature sensors, pressure sensors, engine units, THSTORE units, compressor(s), turbine(s), vacuum pumps, electrical switches, and solar panel, or heat exchanging modules. The system 901 can be directly coupled to, or be a part of, the system 935, or be in communication with the system 935 through the network 930. The CPU 905 can execute a sequence of machine-readable instructions, which can be embodied in a program or software. The instructions may be stored in a memory location, such as the memory 910. Examples of operations performed by the CPU 905 can include fetch, decode, execute, and writeback. With continue reference to FIG. 9, the storage unit 915 can store files, such as drivers, libraries and saved programs. The storage unit 915 can store programs generated by users and recorded sessions, as well as output(s) associated with the programs. The storage unit 915 can store user data, e.g., user preferences and user programs. The computer system 901 in some cases can include one or more additional data storage units that are external to the computer system 901, such as io located on a remote server that is in communication with the computer system 901 through an intranet or the Internet. The computer system 901 can communicate with one or more remote computer systems through the network 930. For instance, the computer system 901 can communicate with a remote computer system of a user (e.g., operator). Examples of remote computer systems include personal computers (e.g., is portable PC), slate or tablet PC's (e.g., Apple0 iPad, Samsung® Galaxy Tab), telephones, Smart phones (e.g., Apple® iPhone, Android-enabled device, Blackberry8), or personal digital assistants. The user can access the computer system 901 via the network 930. Methods as described herein can be implemented by way of machine (e.g., computer processor) executable code stored on an electronic storage location of the computer system 901, such as, for example, on the memory 910 or electronic storage unit 915. The machine executable or machine readable code can be provided in the form of software. During use, the code can be executed by the processor 905. In some cases, the code can be retrieved from the storage unit 915 and stored on the memory 910 for ready access by the processor 905. In some situations, the electronic storage unit 915 can be precluded, and machine-executable instructions are stored on memory 910. The code can be pre-compiled and configured for use with a machine have a processer adapted to execute the code, or can be compiled during runtime. The code can be supplied in a programming language that can be selected to enable the code to execute in a pre-compiled or as-compiled fashion. Aspects of the systems and methods provided herein, such as the computer system 901, can be embodied in programming. Various aspects of the technology may be thought of as "products" or "articles of manufacture" typically in the form of machine (or processor) executable code and/or associated data that is carried on or embodied in a type of machine readable medium. Machine-executable code can be stored on an electronic storage unit, such memory (e.g., read-only memory, random-access memory, flash memory) or a hard disk. "Storage" type media can include any or all of the tangible memory of the computers, processors or the like, or associated modules thereof, such as various semiconductor memories, tape drives, disk drives and the like, which may provide non-transitory storage at any time for the software programming. All or portions of the software may at times be communicated through the Internet or various other telecommunication networks. Such communications, for example, may enable loading of the software from one computer or processor into another, for example, from a management server or host computer into the computer platform of io an application server. Thus, another type of media that may bear the software elements includes optical, electrical and electromagnetic waves, such as used across physical interfaces between local devices, through wired and optical landline networks and over various air-links. The physical elements that carry such waves, such as wired or wireless links, optical links or the like, also may be considered as media bearing the is 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. Hence, a machine readable medium, such as computer-executable code, may 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, such as may be used to implement the databases, etc. shown in the drawings. Volatile storage media include dynamic memory, such as main memory of such a computer platform. Tangible transmission media include coaxial cables; copper wire and fibre optics, including the wires that comprise a bus within a computer system. Carrier-wave transmission media may take the form of electric 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 therefore include for example: a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD or DVD-ROM, any other optical medium, punch cards paper tape, any other physical storage medium with patterns of holes, a RAM, a ROM, a PROM and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave transporting data or instructions, cables or links transporting such a carrier wave, or any other medium from which a computer may read programming code and/or data. Many of these forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to a processor for execution.

It is to be understood that the terminology used herein 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 herein, the singular forms of "a", "an" and "the" include plural references unless the context clearly dictates otherwise. In addition, unless defined otherwise, all technical and scientific terms used herein have the same io meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. While preferable embodiments of the present 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.

Claims (25)

1. CLAIMS1. A system comprising a first unit for exchanging thermal energy of water medium and storing the water medium at a first temperature and first pressure, the system further comprising a second unit for exchanging thermal energy of water medium and storing the water medium at a second temperature higher than the first temperature and at a second pressure higher than the first pressure, wherein each unit is configured to condense and evaporate the water medium, the system further comprising a rotary engine io unit for operating in a first direction as a vacuum pump or compressor for the water medium, the rotary engine unit being driven by a motor when pumping vacuum or compressing the water medium, and for operating in a second direction as an expander for the water medium, the rotary engine unit generating power by means of a generator when the water medium is is expanding.
2. 2. A system according to claim 1, wherein the rotary engine unit has a compression ratio greater than 1.5 when compressing the water medium.
3. 3. A system according to claim 2, wherein the rotary engine unit has a compression ratio greater than 20 when compressing the water medium.
4. 4. A system according to any one of the preceding claims, wherein the rotary engine unit is a screw rotor.
5. 5. A system according to any one of the preceding claims, wherein each unit comprises a phase change material or composite phase change material.
6. 6. A system according to any one of the preceding claims, wherein each unit comprises thermally conductive material.
7. 7. A system according to any preceding claim, wherein each unit comprises a plurality of closed evacuated pipes.
8. 8. A system according to claim 7, wherein each evacuated pipe comprises a two-phase medium.
9. 9. A system according to any one of the preceding claims, wherein at least one of said units comprises a first unit portion for condensing gaseous water medium and a second unit portion for evaporating liquid water medium, the at least one unit further comprising a heat exchanger, wherein a first portion of the heat exchanger is located inside the first unit portion and wherein a second portion of the heat exchanger is located inside the second unit portion.
10. 10. A system according to claim 9, wherein the at least one of said units comprises a third unit portion comprising high latent heat material for storing thermal energy under constant temperature, wherein the thermal energy is transferred from the first unit portion when thermally charging the material, and wherein the thermal energy is transferred towards the second unit portion when thermally discharging the material, wherein a third portion of the heat exchanger is located inside the third unit portion.
11. 11 A system according to claim 10, wherein the at least one of said units comprises a fourth unit portion for accumulating the liquid water medium that is transferred from the first unit portion when thermally charging the material, or towards the second unit portion when thermally discharging the material.
12. 12. A system according to claim 11, further comprising a valve and liquid pump for is controlling water medium flow from the fourth unit portion.
13. 13.A system according to any of claims 9 to 12, wherein the at least one of said units comprise condensate removal means in communication with the first unit portion.
14. 14. A system according to any of claims 9 to 13, wherein the at least one of the at least two units comprises an atomiser connected with the second unit portion.
15. 15. A system according to any one of the preceding claims, further comprising a controller for controlling the rotary engine unit.
16. 16. A system according to any one of the preceding claims, wherein the rotary engine unit comprises a rotary positive displacement engine and an electric motor for driving the engine.
17. 17. A system according to any one of claims 1 to 15, wherein the rotary engine unit comprises a rotary positive displacement engine and an electric generator driven by the engine.
18. 18. A system according to claim 16 when dependent on claim 15, wherein the controller comprises a variable speed driver for controlling the speed of the electric motor.
19. 19. A heat pump comprising a system according to any one of the preceding claims.
20. 20. An electrical storage system comprising a system according to any one of the preceding claims.
21. 21. A reversible process for storing thermal energy of water medium, the process comprising the steps of: providing a first unit for exchanging thermal energy of water medium and storing the water medium at a first temperature and first pressure, and for storing the thermal energy under constant temperature equal to first temperature; providing a second unit for exchanging thermal energy of water medium and storing the water medium at a second temperature higher than the first io temperature and at a second pressure higher than the first pressure, and for storing the thermal energy under constant temperature equal to second temperature, wherein each unit is configured to condense and evaporate the water medium, providing a reversible, positive displacement rotary engine unit for operating in is a first direction as a vacuum pump or compressor for the gaseous water medium, the rotary engine unit being driven by a motor when pumping vacuum or compressing the water medium, and for operating in a second direction as an expander for the water medium, the rotary engine unit generating power by means of a generator when the gaseous water medium is expanding.
22. 22.A reversible process according to claim 21, wherein the rotary engine unit comprises a reversible positive displacement rotor.
23. 23. A reversible process according to claim 22, wherein the rotor is one of the group of: internal gear, external gear, gerotor, vane, lobe, twin lobe, screw, twin screw, triple screw, spindle, scroll, eccentric screw, conical screw.
24. 24. Use of a screw rotor in a reversible process of compressing and expanding water medium for storing and producing electrical energy by storing thermal energy at higher temperature and higher pressure and by storing thermal energy at lower temperature and lower pressure.
25. 25. Use of a screw rotor according to claim 24, wherein the screw rotor is conical.