WO2013119327A1

WO2013119327A1 - Thermodynamic energy storage

Info

Publication number: WO2013119327A1
Application number: PCT/US2012/071582
Authority: WO
Inventors: Leonid Goldstein
Original assignee: Leonid Goldstein
Priority date: 2012-02-09
Filing date: 2012-12-24
Publication date: 2013-08-15

Abstract

An energy storage system, based on certain thermodynamic properties of gas and liquid, storing energy in the form of heat, pressure and/or material phase changes. One aspect of it is an energy storage device, comprising a vessel with flexible walls, a mechanism for pumping superheated liquid into the vessel, a thermal insulation of the vessel and an electrical generator, driven by energy obtained from the superheated liquid from the vessel.

Description

THERMODYNAMIC ENERGY STORAGE

DESCRIPTION

BACKGROUND OF THE INVENTION

Wider usage of renewable energy sources, such as wind and solar energy, for electrical power generation, requires storing energy for use in times when the primary energy source is not available or not sufficient. Large number of energy storage technologies exist. Nevertheless, most of them are not economically viable. This invention contributes to solving the problem of economical energy storage.

SUMMARY OF THE INVENTION

This invention is generally directed to energy storage and combination of energy storage with wind energy conversion devices. Especially, it is directed to energy storage technology, based on gas and liquid thermodynamics: storing energy in the form of heat, pressure and material phase changes.

One aspect of the invention is an energy storage device, comprising a vessel with flexible walls, a mechanism for pumping superheated liquid into the vessel, a thermal insulation of the vessel and an electrical generator, driven by energy obtained from the superheated liquid from the vessel. The vessel can be placed underground, so that the ground walls resist pressure from the superheated liquid. Alternatively, the vessel can be placed underwater at certain depth, so that the pressure of outside water compensates pressure of the superheated liquid inside of the vessel. Usual water is a suitable liquid here.

Another aspect of the invention is an energy storage device, comprising a cavity for compressed air, an air compressor, an electrical generator, driven by the compressed air; a device for adding water to air immediately after or before compression; a thermally insulated vessel for superheated water inside the cavity and a device for mixing the superheated water with the compressed air, leaving the cavity.

Another aspect of the invention is a method of heating air, exiting a compressed air storage system, comprising steps of spraying water into this air, letting the water freeze, removing resulting ice or mix of ice and cold water. The air, heated in such way, can be used to rotate a turbine, which would ultimately rotate a rotor of an electrical generator.

Another aspect of the invention is an energy storage device comprising a cavity for compressed air, an air compressor, a first expander for the compressed air, a second expander for the compressed air, an electrical generator, driven by the first and the second expanders; a device for adding water into the air after the first expander but before the second expander, until the water freezes and a device for removing the resulting ice or mix of the ice and the water from the air before it enters second expander.

The thermal energy of superheated water can be converted into mechanical energy for electrical generator by pumping out superheated water, letting some of it to become steam and using steam to rotate a steam turbine (the arrangement known as "flash stream" in geothermal power plants); or by getting superheated water to transfer its heat to a liquid with lower boiling point (LBPL) than water, and using vapor of that liquid to rotate a turbine - arrangement known as "binary cycle" in geothermal power plants. Examples of LBPL are pentane, butane and ammonia.

Another aspect of the invention is a wind energy conversion device comprising a rotating axle, driven by wind energy; an electrical generator with a rotor, rotationally connected to the axle; an energy storage device, in which energy accumulation means are driven by the axle and energy recovery means drive the electrical generator; and the energy is stored in the form of compressed gas and/or heat. In this aspect, when instant wind power exceeds nominal capacity of the electrical generator, the excess energy is accumulated in the energy storage device. When the wind power is below nominal capacity of the electrical generator by certain margin, the mechanical energy is drawn from the storage and used to produce additional electrical energy. If the wind speed is below cut in speed, all electrical energy is supplied from the stored energy of the storage. Thus, energy waste in converting mechanical energy into electrical energy and then electrical energy into mechanical energy is avoided. Also, the electrical generator is re-used for both energy generation from the wind and from the mechanical energy of the energy storage. Two or more energy storage devices of different types can be provided, for example: one for short term storage (for leveling instant peaks and troughs of the wind power and improving power quality), and one for medium or long term storage (overcoming wind intermittence over days or months). Such wind energy conversion device (WECD) will be capable of producing nameplate amount of electrical energy for almost all the time, like conventional energy plants, with interruptions for predictable maintenance. Short term storage can be in the form of compressed air, while long term storage can be in the form of heat.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. The illustrations omit details not necessary for understanding of the invention, or obvious to one skilled in the art, and show parts out of proportion for clarity. In such drawings:

Fig. 1 Schematic diagram of a wind turbine coupled to a thermodynamic energy storage Fig. 2 A side sectional view of an underwater gas energy storage Fig. 3 A perspective view of an underwater bladder

Fig. 4 A side sectional view of an underwater air-water storage

Fig. 5 A side sectional view of an underwater compressed air-heat storage

Fig. 6 A side sectional view of underwater air bladder and a separate superheated water

Fig. 7 A side sectional view of one form an underground superheated water vessel

Fig. 8 A side sectional view of another form of an underground superheated water vessel

Fig. 9 A schematic view of a multi vessel storage system

Fig. 10 A schematic view of another multi vessel storage system

DETAILED DESCRIPTION OF THE INVENTION

For clarity, we will introduce the following definitions:

Charging phase of an energy storage device - the phase when the device accumulates energy, supplied from an outside source.

Discharging phase of an energy storage device - the phase when the device returns the accumulated, or stored, energy to an outside destination.

Superheated liquid means liquid at a temperature above its boiling point at atmospheric pressure. Superheated liquid remains liquid under certain pressure higher than atmospheric pressure.

In the description below, same numbers denote same elements, possibly modified for use in different embodiments.

Fig. 1 shows one embodiment of the invention. It comprises a wind rotor 101, which transfers its motion to the rotor of an electrical generator 103 through a gearbox 102. The rotor of electrical generator 103 is on an axle 104. Rotation of axle 104 can be transferred to an air compressor 105 via a coupling 106. In the charging phase, compressor 105 compresses air and pumps it to a compressed air reservoir 108 through a pipe (or a hose) 107. In the discharging phase the air from reservoir 108 is sent through a pipe (or a hose) 109 to a turboexpander 110, that rotates axle 104 of the rotor of electrical generator 103 through a coupling 111. A control system 112 is provided. Compressor 105 and turboexpander 110 can be implemented as one and the same device, such as a centrifugal turbine. There may be an additional heat reservoir inside or outside air reservoir 108. An underwater bladder can be used as compressed air reservoir 108. Other thermodynamic storage systems can be used in place of air reservoir 108. For example, one such system can collect and store separately heat, produced by air compression, and cold, produced by expansion of compressed air. Turboexpander 110 can be driven by water steam or some refrigerant in its gaseous state, coming from such

thermodynamic storage. Some embodiments of possible thermodynamic storages are described below. Some other are known in the art, including from patent applications publications 2010/0257862 and 2010/0251711 by Howes et al.

Control system 112 ensures operation of this embodiment as follows. When mechanical power on the axle 104 of generator 103 is within pre-defined margin of the nominal capacity of generator 103 (for example, between a lower margin 90% and an upper margin 105% of it), both couplings 106 and 111 are disengaged, and all mechanical power is converted into electrical energy. When available power increases above the upper margin, coupling 106 is engaged, and some of the power is used to drive compressor 105, that compresses outside air and puts the compressed air into reservoir 108. The generated heat can be collected separately or dissipated into atmosphere. Compressor 105 continues to work until reservoir 108 is full or power on axle 104 drops below 100% of nominal capacity of generator 103. When the mechanical power, available on axle 104 drops below the lower margin, the compressed air from reservoir 108 is allowed to exit through turboexpander 110, rotating the turbine. Coupling 111 is engaged, and additional power from the turbine is supplied to generator 103. Turboexpander 110 is stopped and coupling 111 is disengaged when supply or pressure of air in reservoir 108 drops below some pre-defined value.

Fig. 2 shows another embodiment of the invention. This embodiment is a compressed energy storage system, deployed in a water body, such as an ocean, a sea or a lake. A bladder (that can be also called a bag) 201 for compressed air is installed on the bottom of the ocean at a depth between 100 and 1,000 meters. The bladder has flexible and foldable, waterproof walls 202 and a soft floor 203. Floor 203 is necessary to prevent water and debris from the bottom from filling up the bladder. Floor 203 is sitting inside a steel ring 204, and is connected to it without any gap. Ring 204 is partially driven into the bottom of the ocean. Ring 204 prevents build up of water pressure under floor 203 of bladder 201 and additionally holds bladder 201 down as an anchor. Ring 204 can have small suction anchors 205, used to drive ring 204 into the bottom in time of system deployment. Constructed this way, bladder 201 with compressed air is held down mostly by the pressure of water column above it. The details of bladder 201 prior to deployment are shown in Fig. 3. Its flexible walls 202 are foldable, and preferably folded and kept inside of steel ring 204 for transportation prior to deployment. It has a hole 301 on top to allow connecting of a hose or a pipe. Going back to Fig. 2, a hose (or a pipe) 206 with a bidirectional valve 217 at the end connects to bladder 201 and is used for transfer of compressed air to and from the bladder. When bladder 201 is being deployed from a ship, it is connected to a folded hose 206 and is brought down to the bottom. There, small suction anchors are driven into the bottom, partially driving into the bottom ring 204. Then, small amount of air is pumped into bladder 201, letting its top to rise above the bottom. After that, additional air, pumped into bladder 201, will increase its volume, up to a maximal volume, achieved when all folds are completely unfolded. The air pressure stays constant and approximately equal to the outside water pressure.

An energy converting sub-system 207 is floating on the surface, anchored at the bottom with a chain 214 and a suction anchor 215. Energy converting sub-system 207 comprises electrical motor-generator 212. To store energy, a motor-generator 212 is used as a motor, driving a compressor 213 that compresses outside air and sends compressed air to bladder 201 through a valve 217. The heat, generated in the process, is removed and stored separately or dissipated in the atmosphere or water. To obtain stored energy, the system opens a valve 218 and lets compressed air to pass through two staged air turbine. In a first turboexpander 208 some of the energy of the compressed air is converted into mechanical energy of turbine rotation. In the process, air cools to temperatures significantly below 0 degrees Celsius. A water injector 210 draws external water and injects it into the cold air. The water cools down and turns into ice, while heating the air to almost 0 degrees Celsius, and thus increasing its energy and pressure. The ice and remaining water are removed through a drain 211. In a second turboexpander 209 more energy of this air is converted into mechanical energy of turbine rotation. The turbine rotates rotor of motor-generator 212 which produces electrical energy, acting as an electrical generator. A control system 216 switches the system between phases, which include at least a phase of charging (storing energy) and discharging (recovering stored energy). Instead of motor-generator 212, external source of mechanical energy (such as a wind) can be used to drive a compressor 213, and the mechanical energy can be outputted to increase electrical power produced by some other energy conversion device. The system can be used on land, if bladder 201 is replaced with some other air reservoir. Multiple bladders 201 can be used with a single generator.

In this embodiment, pressure of water compensates most of buoyancy of air in the bladder and most of the pressure of air inside the bladder. There will be some difference in the internal and external pressure, because the pressure inside of the bladder is the same at any height in the bladder, while water pressure slightly higher at the bottom than at the top (every 10 meters of height add 1 atmosphere to this difference).

Various materials can be used for walls 202 and floor 203, such as polyester, strong

polyethylene, aramids, para-aramids etc. A reciprocal engine can be used instead of the turbine. There can be other usages for a bladder of such form and construction, such as storing natural gas or methane.

In another embodiment, sharing many details with a previous one, a bladder 401 is provided on the bottom, and a vessel 402 is provided inside of bladder 401. Vessel 402 stores superheated water, which is the storage of the heat in this embodiment. Vessel 402 has walls that are waterproof and water resistant inside, and have thermal insulation, such as glass wool or fiber wool layer. It has holes 405 with possible pressure valves in its top part. A pipe 406 connects top hole of vessel 402 with hose 206. A bidirectional valve 407 separates pipe 406 and hose 206. Superheated water 404 is in vessel 402. Vessel 402 is attached to the top and side walls of 202 of bladder 401 by ropes 409. Pressure inside vessel 402 is equal (or almost equal, if pressure valves are employed) to pressure in bladder 401 outside of vessel 402, which, in turn, is equal to water pressure on the bottom. This pressure keeps superheated water inside vessel 402 liquid. For example, on the depth 150 meters the pressure is 16 atmospheres, letting water to remain liquid at the temperature of 200 degrees.

An energy converting sub-system 410 is floating on the surface, anchored at the bottom with a chain 214 and a suction anchor 215. Energy converting sub-system 410 comprises electrical motor-generator 212. To store energy, motor-generator 212 is used as a motor, driving a compressor 411 that compresses outside air. An outside water is added to the air in time of compression, or immediately prior to compression or immediately after the compression through an injector 412. This water cools the system and the compressed air and moves in the pipes together with the compressed air. The amount of added water is sufficient to make the temperature of water-air mix slightly below water boiling point in vessel 402. When compressor 411 is in use, water with the compressed air arrives into vessel 402 through pipe 406, but only air leaves through holes 405. So, the water, containing most of the heat of compression, is stored in the vessel 402, while compressed air is stored inside of the bladder and cools farther, losing its heat to the water outside the bladder. Nevertheless, compressed air, surrounding vessel 402, serves as an additional insulation for superheated water.

Thus, both mechanical energy of compressed air and heat are accumulated inside of bladder 401 and can be stored for significant time, limited mostly by quality of thermal insulation of superheated water. For longer storage times, holes 405 should be equipped with valves, not allowing water vapors to easily escape vessel 402 and mix with cold air in the bladder.

When it is desired to obtain electrical energy from the system, valve 217 is closed, valves 407 and 218 are opened, and water-air mix is allowed to flow toward a turboexpander 413, pushed by compressed air pressure. It is useful to maintain exact proportion between air and water in the mix, so a mixing device 408 is employed. As water-air-steam mix passes through turboexpander 413 and transfers its mechanical energy to a turbine, its temperature drop, and the water in the mix gives its heat to the air. At the exit from turboexpander 413 the air's temperature is slightly below ambient. Turboexpander 413 rotates rotor of motor-generator 212, which produces electricity. A control system 414 controls operations in this embodiment.

Some advantages of this system should be noted:

a) efficiency of the system can be theoretically close to 100%, since all the heat, produced in the compression phase, is recovered and re-used in the electricity producing phase b) the compressed air in the storage has the same pressure at all time at any level of filling of the storage c) the stored water has the same temperature at any level of filling of the storage d) no heat exchanger for heat transfer between two separate gases or liquids is required; heat is always kept in the water, which is mixed with air when heat transfer is desired

Instead of using motor-generator 212, external source of mechanical energy (such as a wind) can be used to drive compressor 411, and mechanical energy can be outputted to increase electrical power produced by other energy conversion device. Further, the same physical device can be used in both roles of compressor 411 and turboexpander 413, with gas flow reversed. Multiple bladders 401 can be used with a single generator. This embodiment can be practiced on land as well as on water. On the land an underground cavern is used instead of bladder 401, and water vessel 402 is placed inside of it.

Fig. 5 shows another embodiment of the invention. This embodiment is similar to the embodiment in Fig. 4, because in both the heat is stored inside bladder 401. In the current embodiment, though, the heat is stored inside of a pile of gravel or rocks 501, covered with a thermo insulating dome 502. Dome 502 can be flexible and made of heat resistant fabric with glass wool or fiber wool insertions. In this embodiment, gravel 501 serves both as heat storage and heat exchanger.

In the charging phase, very hot air from compressor 411 is pumped through pipe 406 and then through the gravel pile 501, giving the gravel much of its heat. Dome 502 does not reach walls 202 of the bladder, so the pumped air exits at the lower part of gravel pile 501. The compressed air stays in the bladder mostly outside of the gravel pile 501, where it cools down. Insulating dome 502 allows gravel pile to maintain its heat for long time. In the discharging phase, compressed air from the bladder exits through pipe 406. Most of that air enters gravel pipe 501 near its bottom and passes through it on its way out, heating up to almost gravel temperature. Hot air enters turboexpander 413, which rotates rotor of electrical generator 212. In this embodiment, grave pile 501 can serve as an additional weight, letting bladder to become substantially wider than it would be in similar embodiments without gravel pile. A variant of this embodiment does not use ring 204, having weight of the gravel to compensate most of buoyancy of bladder 401. The refinements, used in the previous embodiments, are possible in this embodiment as well. This embodiment can be practiced on land as well as on water. On the land an underground cavern is used instead of bladder 401, and one or multiple gravel/rock piles 501 are created, each with its own dome 502. If multiple gravel piles are used, each of them has a separate pipe 406, all joining external hose or pipe 206.

Another embodiment is shown in Fig. 6. It has many elements from the embodiments, shown in the Fig. 2 and Fig. 4. The most prominent difference is in the presence of an underwater bag (or a second bladder) 601, filled with superheated liquid. One variant of this embodiment uses outside water as such liquid. The walls of bag 601 are flexible and foldable, so its volume increases, as more water is pumped into it, and decreases as water is pumped out of it. Because it is filled with water, the inside and outside pressure on its walls is always equal, even if the height of bag 601 is significant. For the same reason, bag 601 has nearly neutral buoyancy. It is anchored with a chain 605 to a small anchor 606 on the bottom. The walls of bag 601 are thermally insulating. For example, the wall can contain an external skin 602, an internal skin 603 and an intermediate layer 604. Intermediate layer 604 can be glass wool or fiber wool and be filled with water. External skin 602 ensures strength and provides protection against underwater impacts. Multiple layers of insulation can be used. Increasing size of bag 601 decreases need in insulation. A hose (or a pipe) 608 is inserted into bag 601 at the top, with a bidirectional valve 607 near the point of connection.

This embodiment contains two energy storages: a short term storage in the form of bladder 201 with compressed air, and a long term storage in the form of superheated water bag 601. In the charging phase, electrical moor-generator 212 runs a compressor-turboexpander 609, that compresses outside air. Water is injected into the air being compressed, and takes away some of the heat of the compressed air. This allows to cool the compressed air below temperatures, dangerous to the equipment, and store some heat separately from the compressed air. The superheated water is removed through a drain 610, then flows through a pipe 611 and is pumped by a pump 614 into bag 601. Meanwhile, compressed air enters bladder 201. If bladder 201 is full, compressed air is released into atmosphere. Unlike embodiments in Fig. 2, 4, 5, described above, bladder 201 is partially thermo insulating. " Partially" means that the heat losses are small for the short times, for which this storage is designed. Such partial insulation can be achieved by making walls 202 multi layer, with glass wool or fiber wool and air inside. Or this can be achieved by using a second, smaller bladder inside of bladder 201.

This embodiment has two kinds of discharging phases: short term and long term. In the short term discharging phase, the hot compressed air from bladder 201 flows back to compressor- turboexpander 609, and, expanding, rotates a turbine, which rotates the rotor of motor- generator 212, which produces electrical energy. Since a large part of the heat, originally generated in the compression phase, remains in the compressed air, its temperature does not drop too much below ambient in the process of expansion, allowing efficient energy recovery. In the long term discharging phase, pump 614 pumps superheated water from bag 601. The water is released from the pressure in the pipe 612, and partially boils. The resulting steam rotates a steam turbine 613, which rotates rotor of motor-generator 212, which produces electrical energy. The system is controlled by an electronic control system 615. Control system 615 always uses compressed air from bladder 201 first and switches to use of superheated water only when usa ble supply of air is exhausted.

A cubic meter of superheated water can store much more useful energy than a cubic meter of compressed air, at the same pressure. Thus, long term storage in this embodiment can store much more energy, than short term storage. This embodiment can be practiced at depths between 50 and 1,000 meters. The amount of energy, stored by each type of storage in this embodiment, grows with increase in depth. The amount of energy in superheated water in bag 601 is determined by the water temperature, and the maximal temperature is determined by pressure. For example, depth of 150 meters allows to store water at 200 degrees Celsius, depth of 400 meters allows water at 250 degrees, depth of 900 meters allows water at 300 degrees. One cu bic meter of superheated water at the depth of 150 meters can produce same amount of electrical energy, as 100 cubic meters of water, pumped to the height of 1,000 meters in pumped hydro. Even more energy can be produced in more efficient (and complex) embodiments, similar to binary cycle geothermal plants.

This embodiment can be used as a standalone grid connected energy storage. The short term storage can be used to level short term (minutes to hours) peaks and troughs in the power availability. The short term sub-system can switch from idle to generating electricity within seconds. This is compared with the gas turbines, that require minutes to start. The long term energy storage can be used to level fluctuations in power availability diurnally and even seasonally.

This embodiment can be also used as a part of a wind energy conversion device (WECD). In this case, mechanical energy from WECD can be used to drive compressor 609 in the charging phase, and mechanical energy can be outputted to the rotor of the generator of the WECD in the discharging phase, making motor-generator 212 unnecessary. When working as a part of WECD, the short term subsystem can be used to absorb short term fluctuations in the wind power, caused by rapid changes in wind velocity and direction. The long term subsystem can be used to produce energy on the days without wind.

In a variation of this embodiment, there is another reservoir for warm water near the surface (not shown on the picture). Non evaporated hot water from pipe 612 and condensed steam after expander 613 get into this reservoir. The water in this reservoir has temperature near 100 degrees Celsius. Injector 412 draws hot water from this reservoir, rather from outside. This system is more efficient as it avoids need to heat water from external source to 100 degrees, at the expense of slightly higher complexity.

Functions of compressor and turboexpander of compressor-turboexpander 609 can be separated into two separate devices - a compressor and a turboexpander. A reciprocal engine can be used instead of the turbine.

A variant of this embodiment is an embodiment, which uses other than water liquid in the bag 601. Typically, this will be a liquefied gas (i.e. a substance that is in gaseous state at normal temperature and pressure). In one such embodiment pentane is used as the liquid in bag 601. In this embodiment, the vapors of pentane cannot be released into atmosphere, so pentane moves in closed cycle. There should be another storage bag for cold liquid pentane near the surface, and a heat exchanger to allow pentane to receive heat from the compressed air. In this embodiment, hot liquid pentane from bag 601 boils in pipe 612, rotates turbine while expanding and cooling in turboexpander 613. Cold pentane is pumped through heat exchanger, heats up and goes back to bag 601. Since liquid pentane is much lighter than water, a large anchor or weight should be used instead of light anchor 606 to keep bag 601 in place. Additionally, bag 601 should be reinforced and equipped with strops to resist pull of the chain, tying it to the anchor, and variations in the external pressure, which are not compensated by internal hydrostatic pressure. Butane or ammonia can be used instead of pentane. Another variant uses a separate bag with superheated water and a container with a mix of liquid oxygen and liquid nitrogen. Liquid oxygen and nitrogen are obtained by expanding compressed air, after heat from it was removed by water, injected into it and drained to bag 601, and it was additionally cooled by the outside water. The energy is recovered by letting liquid oxygen and nitrogen boil in contact with the superheated water from bag 601, and passing resulting gas through a turboexpander, which rotates rotor of the electrical generator.

Another aspect of the invention is an inexpensive underground storage for superheated liquid, such as water, or compressed air, shown in Fig. 7. It comprises a human made underground cavern 701 in the form of rounded rectangle or oval in vertical section, and round in the horizontal section. A light weight inflatable bag 702 is placed inside of cavern and inflated with air or liquid vapors. After inflation, bag 702 takes the form, closely resembling the form of the cavern, and its walls are in contact with the walls of cavern 701 in most area. Thus, any internal pressure is resisted by the walls of cavern 701, when compressed air or water under pressure are pumped into bag 702. This construction can be used for storage of superheated water, which can be stored under pressures 15 - 300 atmospheres and temperatures of 200 - 370 degrees Celsius. The walls of bag 702 can be thermally insulated with suitable materials, such as glass wool or fiber wool. The construction may have a concrete roof 703. A pipe 704 for pumping in and out water or air with a valve 705 are provided. Fig. 7 further shows water 706 and water vapors 707 above it. It should be noted, that the pressure of vapors 707 does not change much, as long as there is at least some water present and the temperature of the water does not change much. This nearly constant pressure protects bag 702 from collapsing.

This construction can be created in a number of ways. In one of them, a developer digs a cylindrical basin in the ground. Then the developer inserts bag 702 and builds roof 703 above it. The developer inserts pipe 704 and partially inflates bag 702, so it begins to support roof 703 and the walls of cavern 701. Then the excavated earth is put on top of roof 703 and compacted. As more earth is put on top of the roof, more air is pumped into bag 702, increasing internal pressure. Few weeks after all earth is put on top, the system is ready for full pressure operation.

Cavern 701 can also be constructed using a controlled blast, or by removing some material from a natural cavern, or using an existing mine. Bag 702 in a shrunk form can be brought into cavern 702 through a small opening, and then inflated inside. This aspect of the invention allows building inexpensive energy storage in most places, not limited to places with natural underground caverns, required for CAES, or high-low reservoirs, required for pumped hydro.

Fig. 8 shows another variation of this aspect of invention, in which there is no roof, but there is earth, piled directly on top of bag 702. It can be earth, excavated in time of digging cavern 701.

Fig. 9 shows a thermodynamic energy storage according to another embodiment of the invention. It is similar to the embodiment, depicted on Fig. 6, so only differences will be described here. This embodiment contains an underground container 901 for superheated water, an above ground or near ground container 902 for hot water and a container 903 for compressed air. Containers 901 and 903 can be of the construction, shown in Fig. 7 or Fig. 8. In the charging phase, motor-generator is used to power compressor-turboexpander 609, which compresses air. Simultaneously with or immediately before or immediately after compression, warm water from container 902 is injected into the air through a valve 910 and a pipe 904, and removes some of its heat. After heating up, this water is removed through a drain 610 and a pipe 611 and pumped into container 901 trough a valve 908. Water in container 901 is stored at the temperature between 200 and 370 degrees Celsius, while water in container 902 is stored at the temperature of 100 degrees Celsius or below. Slightly cooled, but still hot air is stored in its container 903. In the short term discharging phase, still hot compressed air from container 903 is sent through compressor-turboexpander 609, where it rotates the turbine, which rotates the rotor of motor-generator 212, which produces electrical energy. In the long term discharging phase, superheated water from container 901 is pumped through a valve 909 and a pipe 612, where it partially boils. Steam is sent through steam turbine 613, which rotates the rotor of electrical motor-generator 212, which generates electricity. Condensed steam and non boiled water are sent through a pipe 905 and a valve 911 back to container 902. Direction of water movement is shown with arrows in water pipes. Compressor-turboexpander 609 can be separated into a compressor and a turboexpander, and motor-generator 212 can be separated into a motor, a generator connected to the turboexpander and a generator, connected to steam turbine 613. Operations and other enhancements and variations, described for the

embodiment from Fig. 6 can be used here as well. Additionally, this embodiment can be more efficient, because underground hot water storage allows higher pressure and higher temperature of the superheated water.

Fig. 10 shows a thermodynamic energy storage according to another embodiment of the invention. It is similar to the embodiment, depicted on Fig. 9. The working gas in this embodiment is the air or nitrogen, obtained from the air. Thus, this embodiment contains a container for liquid air or liquid nitrogen. In the charging phase, motor-generator is used to power compressor 1013, which compresses air. Simultaneously with or Immediately before or immediately after compression, hot water from container 902 is injected into the air through a valve 910 and a pipe 904, and removes some of its heat. After heating up, this water is removed through a drain 610 and a pipe 611 and pumped into container 901 through valve 908. Then, second round of cooling is performed by injecting again water from container 902 through a pipe 1008 into the air, letting it to exchange heat with the air and draining it through a drain 1010 and a pipe 1009 back to container 902. Water in container 901 is stored at the

temperature between 200 and 370 degrees Celsius, while water in container 902 is stored at the temperature between 80 and 150 degrees Celsius. The compressed air is stored in storage 903 for short time. When a short term need for additional electrical energy is communicated to a control system 1014, a valve 1007 opens and compressed air is sent to an air liquefier 1003. Movement of the air in the pipes is shown in the hollow arrows, while movement of water is shown in solid arrows. An air liquefier 1003 contains a turboexpander 1004. Details of an air liquefier of this type (Siemens cycle) construction and operation are well known and are not described here. Liquid air from liquefier 1003 flows to a liquid air storage 1001. In the same time, the turbine of a turboexpander 1004 rotates the rotor of motor-generator 212, which generates electrical energy. This method of containing compressed air in container 903 for short time (minutes or even seconds) is especially effective when this energy storage system is used in combination with WECD. Wind strength significantly fluctuates each few seconds or minutes. Using this short term discharging cycle, the system can compress air in the time of window gusts (peaks), using excessive power, keep it compressed for short time, then expand and liquefy it in times of calm (troughs), while producing power. When a long term need for additional electrical energy is communicated to control system 1014, it first performs a short term discharging phase, as described above, with all usable compressed air in storage 903. Then, a long term discharging phase starts. Liquid air from container 1001 is pumped through a valve 1006, heated up from ambient air in a heat exchanger 1005. Water from container 902 can be used in this exchanger, too (not shown on the picture). In the same time, valve 909 is opened and superheated water from container 901 is mixed with air that exited heat exchange 1005, heating it up to temperature 100 degrees Celsius. Hot air violently expands, enters a turboexpander 1011 and rotates its turbine, which rotates the rotor of motor-generator 212, which generates electrical energy. The long term subsystem can be used to produce energy on the calm days, when used with WECD.

The system in Fig. 10 has high thermodynamic efficiency at the cost of some additional complexity. It can be simplified in multiple ways. One of the ways is to drop compressed air container 903 and the idea of short discharging cycle, and always send cooled air directly to liquefier 1003. Another way is to drop second cooling cycle (pipes 1008, 1009 and drain 1010). Another way is to drop both water containers 901 and 902 and allow liquid air to boil from heat exchange with ambient air and/or water. Turboexpander 1011 and compressor 609 can be combined. Multiple simplifications, described above, can be used simultaneously. On the other hand, instead of motor-generator 212 three devices - a motor, rotating compressor 1013, a generator, rotates by turboexpander 1011 and a generator, rotated by turboexpander 1004 - can be used. This embodiment can be used as a standalone grid connected energy storage. The short term storage can be used to level short term (minutes to hours) peaks and troughs in the power availability. The short term sub-system can switch from idle to generating electricity within seconds. The long term energy storage can be used to level fluctuations in power availability diurnally and even seasonally. This embodiment can be also used as a part of WECD. In this case, mechanical energy from WECD can be used to drive compressor 1013 in the charging phase, and mechanical energy can be outputted to the rotor of the generator of the WECD in the discharging phases, making motor-generator 212 unnecessary.

Thus, a thermodynamic energy storage is described in conjunction with multiple specific embodiments. While above description contains many specificities, these should not be construed as limitations on the scope, but rather as exemplification of several embodiments thereof. Many other variations are possible.

Claims

What is claimed is:

[Claim 1] An energy storage device, comprising:

a vessel with flexible walls;

means for pumping superheated liquid into the vessel;

a thermal insulation of the vessel;

an electrical generator, driven by energy obtained from the superheated liquid from the vessel.

[Claim 2] The device of claim 1, where superheated liquid is water.

[Claim 3] The device of claim 2, wherein the vessel is placed underground.

[Claim 4] The device of claim 2, wherein the vessel is placed underwater.

[Claim 5] An energy storage device, comprising:

a cavity for compressed air;

an air compressor;

an electrical generator, driven by the compressed air;

means for adding water to air immediately after or before compression;

a thermally insulated vessel for superheated water inside the cavity;

means for mixing the superheated water with the compressed air, leaving the cavity.

[Claim 6] The device of claim 5, further comprising:

a turbine, working from a steam-air mix;

an electrical generator, coupled to the turbine.

[Claim 7] A method of heating air, exiting a compressed air storage, comprising steps of: spraying water into the air, exiting the compressed air storage;

letting the water freeze;

removing resulting ice.

[Claim 8] The device of claim 7, further comprising:

a turbine, working from the compressed air;

an electrical generator, coupled to the turbine.