Energy storage plant

Abstract

To provide an energy storage plant capable of effectively storing an energy by using a storage tank of which a volume is small.SOLUTION: An energy storage plant is an energy storage plant that performs a charging and a discharging by a compression and an expansion of an operation fluid as a liquid in a gas, a normal temperature, and a high voltage in a normal temperature and an atmospheric pressure, comprising a low-pressure side contained 1; a compression machine 3; a dynamo-electric motor 9; an expansion machine 6; a power generator 10; a high-pressure side container 5; a first thermal exchanger 2; a second thermal exchanger 4; a first heat storage tank 7; and a second heat storage tank 8. The operation fluid stored in the pressure side container, is heated by the second thermal exchanger, and the expansion machine is operated by the operation fluid after a circulation of the second thermal exchanger, and the power generator is driven. By a cold heat stored in the first heat storage tank, the operation fluid is cooled by the first heat storage tank after the circulation of the expansion machine, and it becomes a state of the liquid or a solid, and the operation fluid after the circulation of the expansion machine, is stored into the low pressure side container.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an energy storage device. [Background technology]

[0002] When generating electricity from variable renewable energy sources such as solar power and wind power, the power output fluctuates greatly depending on the solar radiation and wind conditions. For example, solar power cannot generate electricity at night, and even during the day, the power output is small if it is rainy or cloudy. The same is true for wind power, where the power output fluctuates depending on the wind direction and speed.

[0003] On the other hand, in order to keep the power frequency within a certain range and stabilize the power system, it is necessary to always balance the supply and demand of electricity within the area to which electricity is supplied.

[0004] A typical technology for smoothing or leveling the power output of such variable renewable energy sources is a storage battery that stores electricity when surplus power is generated and supplements it during power shortages. However, other known technologies include compressed air energy storage (CAES), which uses surplus power generated to compress air, stores energy as air pressure and heat, and reconverts it into electricity using a turbine generator or the like when needed.

[0005] CAES requires a large-scale storage facility for storing compressed air when storing energy. However, it is difficult to simultaneously maintain the strength against internal pressure and increase the size of a high-pressure gas tank. Another option is to use underground caverns, but it is difficult to find underground caverns that meet these conditions. For this reason, CAES has not become widespread.

[0006] A similar technology to CAES is liquefied CO2 energy storage (see, for example, Patent Document 1). This technology uses carbon dioxide as the working fluid. Carbon dioxide liquefies at about 65 atmospheres even at room temperature, so it is possible to reduce the volume of high-pressure gas tanks compared to CAES.

[0007] However, in the case of liquefied CO2 energy storage, the working fluid, CO2, must also be stored on the low-pressure side. In other words, in the case of CAES, the low-pressure air after discharge is released into the atmosphere, and atmospheric air is taken in from the outside during charging, so there is no need to consider a container for the low-pressure side, but in the case of liquefied CO2 energy storage, a container for low-pressure CO2 is required. With liquefied CO2 energy storage, there is an issue that the volume of the low-pressure container must be large. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special table number 2022-520218 Summary of the Invention [Problem to be solved by the invention]

[0009] In Patent Document 1, a container for storing a gaseous working fluid other than the atmosphere that is in pressure equilibrium with the atmosphere, that is, an expandable balloon, is used as the low-pressure container for liquefied CO2 energy storage. In this document, to store 100 MWh of energy, the high-pressure tank requires a volume of about 1,000 m3, while the balloon requires a volume of about 400,000 m3.

[0010] However, in a country like Japan, with little flat land and frequent wind and flood damage, storing carbon dioxide in a huge dome is not realistic.

[0011] An object of the present invention is to efficiently store energy using a small-volume storage tank in an energy storage plant that performs charging and discharging by compressing and expanding a working fluid. [Means for solving the problem]

[0012] According to the present invention, there is provided an energy storage plant which performs charging and discharging by compressing and expanding a working fluid which is a gas at room temperature and atmospheric pressure and a liquid at room temperature and high pressure, comprising: a low-pressure vessel configured to store the working fluid in a liquid state or a solid state; a compressor which compresses the working fluid; a motor which drives the compressor; an expander which operates by the expansion of the working fluid; a generator which is driven by the expander; a high-pressure vessel configured to store the working fluid at a pressure higher than that of the low-pressure vessel; a first heat exchanger disposed between the low-pressure side vessel and the compressor and between the low-pressure side vessel and the expander, for heating or cooling the working fluid; a second heat exchanger disposed between the high-pressure side vessel and the compressor and between the high-pressure side vessel and the expander, for heating or cooling the working fluid; a first heat storage tank connected to the first heat exchanger and for storing cold heat of the working fluid via a first heat exchange fluid that exchanges heat with the working fluid in the first heat exchanger; and a second heat storage tank connected to the second heat exchanger and for exchanging heat with the working fluid in the second heat exchanger. and a second heat storage tank that stores heat of the working fluid via a second heat exchange fluid that is supplied to the low-pressure side container and a second heat storage tank that stores heat of the working fluid via a second heat exchange fluid that is supplied to the high ... In the discharge process, the working fluid stored in the high-pressure side container is heated by the second heat exchanger using the heat stored in the second heat storage tank, the working fluid after flowing through the second heat exchanger is used to operate the expander to drive the generator, the working fluid after flowing through the expander is cooled by the first heat exchanger using the cold heat stored in the first heat storage tank to make it liquid or solid, and the working fluid after flowing through the first heat exchanger is stored in the low-pressure side container.

[0013] According to this configuration, in the discharging process, the first heat exchanger cools the working fluid from a gaseous state to a liquid state or a solid state, and stores the working fluid in the liquid state or solid state in the container, thereby making it possible to reduce the volume of the container on the low pressure side. In addition, in the charging process, after the working fluid is compressed, the second heat exchanger cools and liquefies the working fluid, thereby making it possible to reduce the volume of the container on the high pressure side.

[0014] Furthermore, during the charging process, the first heat storage tank stores the cold heat obtained from the working fluid in the first heat exchanger, and the second heat storage tank stores the heat obtained from the working fluid in the second heat exchanger, and during the discharging process, the second heat exchanger uses the heat stored in the second heat storage tank during the charging process, and the first heat exchanger uses the cold heat stored in the first heat storage tank during the charging process, thereby enabling efficient charging and discharging.

[0015] In addition, by storing the cold and heat of the working fluid via the first heat exchange fluid and the second heat exchange fluid, it is possible to separate the medium for heat exchange from the medium for heat storage. For example, the material for the medium for heat exchange can be selected based on the melting point and boiling point, while the material for the medium for heat storage can be selected based on the heat capacity and cost.

[0016] Preferably, the low pressure side vessel is more highly insulated than the high pressure side vessel.

[0017] This allows the container to remain in a liquid or solid state for an extended period of time when fully discharged.

[0018] Preferably, the first heat exchanger and the second heat exchanger are of countercurrent flow.

[0019] By adopting a countercurrent type heat exchanger, the difference between the temperature of the working fluid at the inlet of the heat exchanger and the temperature of the heat exchange fluid at the outlet of the heat exchanger, and the difference between the temperature of the working fluid at the outlet of the heat exchanger and the temperature of the heat exchange fluid at the inlet of the heat exchanger are made as close as possible, so that the charging process or discharging process can be carried out without using an auxiliary temperature adjustment device as much as possible in cooling or heating before or after compression or expansion.

[0020] Preferably, the cooling system further comprises an auxiliary cooler connected to the first heat exchanger or the first heat storage tank.

[0021] This makes it possible to reliably liquefy or solidify the working fluid during the discharge process even when there is insufficient cold energy in the heat storage tank.

[0022] Preferably, a first auxiliary heat exchanger is provided inside or around the low-pressure side container, and a first auxiliary heat storage tank is provided connected to the first auxiliary heat exchanger, and the first auxiliary heat storage tank stores cold heat from the low-pressure side container via a first auxiliary heat exchange fluid that exchanges heat with the low-pressure side container in the first auxiliary heat exchanger.

[0023] This allows the working fluid in the container to be vaporized early during the charging process, facilitating the circulation of the working fluid inside the plant. The first auxiliary heat storage tank may be in communication with the first heat storage tank.

[0024] Preferably, a second auxiliary heat exchanger is provided inside or around the high-pressure side container, and a second auxiliary heat storage tank is provided connected to the second auxiliary heat exchanger, and the second auxiliary heat storage tank stores heat from the high-pressure side container via a second auxiliary heat exchange fluid that exchanges heat with the high-pressure side container in the second auxiliary heat exchanger.

[0025] This allows the working fluid in the high-pressure vessel to be vaporized early during the discharge process, facilitating the circulation of the working fluid within the plant. The second auxiliary heat storage tank may be in communication with the second heat storage tank.

[0026] Preferably, the compressor and the expander are the same.

[0027] This makes it more cost-effective and space-saving compared to a configuration in which a compressor and an expander are separately provided.

[0028] Preferably, the working fluid is carbon dioxide.

[0029] This allows for a smaller volume of high pressure gas tanks compared to compressed air storage with readily available working fluids.

[0030] Preferably, the pressure inside the high pressure vessel is 55 to 80 atmospheres when fully charged.

[0031] This allows the use of minimal material in the high pressure vessel, which is cost effective. Effect of the Invention

[0032] According to the present invention, since the low-pressure vessel is also configured to store the working fluid in a liquid or solid state, it is possible to realize an energy storage plant that efficiently stores energy using a small-volume storage tank. [Brief description of the drawings]

[0033] [Figure 1] 1 is a schematic configuration diagram of an energy storage plant according to an embodiment of the present invention. [Diagram 2] 2 is a Ts diagram for the charging and discharging processes of the energy storage plant of FIG. 1. FIG. [Diagram 3] 2 is a PV diagram of the charging and discharging processes of the energy storage plant of FIG. 1. [Figure 4] 1 is a graph showing the relationship between the pressure of carbon dioxide at 20° C. and the product of pressure and volume. [Diagram 5] 1 is a graph showing the relationship between the pressure of carbon dioxide at 30° C. and the product of pressure and volume. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Next, an embodiment of the present invention will be described with reference to the attached drawings. Various features shown in the following embodiments can be combined with each other. In addition, each feature can be an independent invention. Note that the drawing in Figure 1 is merely an explanatory diagram for explaining the present invention, and therefore the device configuration is shown schematically or conceptually.

[0035] 1. Energy storage plant configuration 1, an energy storage plant according to an embodiment of the present invention includes a low-pressure side vessel 1, a first heat exchanger 2, a compressor 3, a second heat exchanger 4, a high-pressure side vessel 5, and an expander 6. The energy storage plant also includes a first heat storage tank 7, a second heat storage tank 8, an electric motor 9, and a generator 10. The energy storage plant further includes an auxiliary cooler 11, a first auxiliary heat exchanger 12, a first auxiliary heat storage tank 13, a second auxiliary heat exchanger 14, and a second auxiliary heat storage tank 15.

[0036] The energy storage plant of this embodiment performs charging and discharging by compressing and expanding a working fluid. In the charging process, the working fluid is compressed, and in the discharging process, the working fluid is expanded to generate power. In this embodiment, the working fluid is carbon dioxide.

[0037] As shown in FIG. 1, a low-pressure vessel 1, a first heat exchanger 2, a compressor 3 or an expander 6, a second heat exchanger 4 and a high-pressure vessel 5, through which a working fluid flows, are connected by pressure-resistant pipes.

[0038] The electric motor 9 and the generator 10 may be configured as a single device that functions both as an electric motor and a generator.

[0039] It is preferable that the compressor 3 and the expander 6 are of the turbo type. However, if the fluctuation of the charging power is large, it is preferable to adopt a screw type for part of the compressor. It is also preferable that the compressor 3 and the expander 6 are of the multi-stage type. In addition, the compressor 3 and the expander 6 may be the same device that serves both as a compressor and an expander.

[0040] The first heat exchanger 2 and the second heat exchanger 4 are preferably of a plate type or a shell-and-tube type, and desirably perform heat exchange in a countercurrent manner.

[0041] The first heat exchange fluid used in the first heat exchanger 2 and the first auxiliary heat exchange fluid used in the first auxiliary heat exchanger 12 are preferably fluids that remain liquid in the range of a minimum temperature of about minus 50° C. to a maximum temperature of about 30° C. For example, a mixture of glycerin and ethanol may be used as this fluid.

[0042] The second heat exchange fluid used in the second heat exchanger 4 is preferably a fluid that maintains a liquid state in the range of approximately a minimum temperature of 0° C. to a maximum temperature of 210° C. For example, this fluid may be synthetic oil or pressurized water, which is water with its boiling point increased by applying pressure.

[0043] The maximum temperature of the second auxiliary heat exchange fluid used in the second auxiliary heat exchanger 14 may be lower than that of the second heat exchange fluid. For this reason, it is considered to use water, for example, as the second auxiliary heat exchange fluid.

[0044] The heat storage material used in the first heat storage tank 7, the second heat storage tank 8, the first auxiliary heat storage tank 13, and the second auxiliary heat storage tank 15 may be an inexpensive solid material such as sand, soil, ash, gravel, etc. It is desirable to insulate the heat storage material by covering it with, for example, glass wool.

[0045] The low-pressure vessel 1 stores the working fluid in a low-temperature liquid state (or solid state). The pressure inside the low-pressure vessel 1 remains roughly constant at about 7 atmospheres during both the charging and discharging processes.

[0046] During the charging process, as charging progresses, the proportion of liquid in the low-pressure container 1 decreases and the proportion of gas increases, and at full charge, all of it is gas. During the discharging process, as discharging progresses, the proportion of liquid in the low-pressure container 1 increases, and at full discharge, all of it is liquid.

[0047] During the charging and discharging processes, if the internal pressure of the low-pressure container 1 deviates from 7 atm, the internal pressure is adjusted by adjusting the heat exchange speed. In particular, during the discharging process, if the cooling of the working fluid by the first heat exchanger 2 and the first auxiliary heat exchanger 12 is insufficient, the auxiliary cooler 11 is used to cool the working fluid. By keeping the pressure inside the low-pressure container 1 at about 7 atm, the temperature range in which the fluid is liquid (about 7°C, between approximately -56°C and -49°C) can be secured. This is because if the pressure inside the low-pressure container 1 falls below about 5 atm, the fluid will change state between gas and solid without passing through a liquid state, making it difficult to circulate, and if the pressure is too high, the pressure difference with the high-pressure side will become small, resulting in a decrease in the amount of stored electricity.

[0048] The temperature inside the low-pressure vessel (1) varies within a range of a minimum of about minus 50°C to a maximum of about 30°C.

[0049] The shape of the low-pressure vessel (1) is assumed to be cylindrical. For stirring, the low-pressure vessel (1) is preferably placed horizontally on the ground (with the axis passing through the center of the cylinder parallel to the ground) and is capable of rotating around the central axis of the cylinder. The low-pressure side vessel (1) is insulated by using a vacuum insulation material for the outer vessel or by covering the vessel with glass wool, etc. The low-pressure side vessel (1) is configured to be at least more highly insulated than the high-pressure side vessel (5).

[0050] It is preferable that the first auxiliary heat exchanger (12) adopts a jacket tank type in which a jacket portion is provided between the inner tank of the low-pressure side vessel (1) and the insulating layer, or adopts a throw-in type in which a heat transfer tube is installed inside the low-pressure side vessel (1).

[0051] The high-pressure side container (5) stores the working fluid in a high-temperature, high-pressure liquid state. The pressure inside the high-pressure side container (5) varies from the pressure in the low-pressure side container (1) to a maximum of about 70 atmospheres. During the charging process, the pressure inside the high-pressure side container (5) increases as charging progresses. When the pressure inside the high-pressure side container (5) exceeds a certain value, a gas-liquid mixture is formed, and when fully charged, all of the liquid is present. During the discharging process, the pressure inside the high-pressure side container (5) decreases as discharging progresses, the proportion of liquid decreases, and when fully discharged, the pressure becomes gas with the same pressure as the pressure in the low-pressure side container (1).

[0052] The temperature inside the high-pressure side container 5 is kept constant at approximately 29° C. During the charging and discharging processes, if the temperature inside the high-pressure side container 5 deviates from approximately 29° C., the temperature is adjusted by adjusting the heat exchange rate. By keeping the temperature inside the high-pressure side container 5 at approximately 29° C., the electrolyte liquefies when the pressure inside the high-pressure side container 5 reaches approximately 70 atmospheres during the charging process, and vaporizes immediately when the pressure is reduced during the discharging process.

[0053] The shape of the high pressure side vessel 5 is assumed to be cylindrical. The material of the high pressure side vessel 5 is assumed to be an aluminum alloy, a steel material, a carbon fiber, or the like. When a large high pressure side vessel 5 is used, if it is made of an aluminum alloy or a steel material, it may be difficult to transport due to weight restrictions, so that it is preferable to use carbon fiber, which has a high specific strength (strength / specific gravity).

[0054] The second auxiliary heat exchanger 14 preferably adopts a jacket tank type and has a shape that covers the periphery of the high-pressure side vessel 5. This is because the inside of the high-pressure side vessel 5 becomes high pressure, and therefore no changes are required to the structure of the high-pressure side vessel 5 for heat exchange. However, since the jacket tank type does not provide high efficiency in heat exchange, it is desirable to make the high-pressure side vessel 5 as elongated as possible and increase the area available for heat exchange.

[0055] 2. Charging and discharging operations of energy storage plants Figure 2 shows a Ts diagram for one embodiment where the pressure on the low pressure side is about 7 atmospheres and the maximum pressure on the high pressure side is about 70 atmospheres. As shown here, during the charging process, the working fluid first changes from a liquid to a gas (A→B), is then heated in the gaseous state (B→C), compressed (C→D), cooled in the gaseous state (D→E), and is further cooled and changes from the gas to a liquid (E→F). The approximate temperatures and pressures for each state are as shown in Figure 2. During the discharging process, the same process occurs in the opposite direction.

[0056] Figure 3 shows the PV diagram in the above embodiment. The approximate temperatures and approximate volumes in each state are as shown in Figure 3.

[0057] In the above embodiment, when the low-pressure side vessel 1 has a volume of about 55 m3, the high-pressure side vessel 5 has a volume of about 100 m3, and about 62 tons of carbon dioxide is used as the working fluid, the amount of stored electricity is about 3 MWh. In this case, when fully charged, the amount of cold heat stored in the first heat storage tank 7 and the first auxiliary heat storage tank 13 is about 25 GJ, and the amount of heat stored in the second heat storage tank 8 and the second auxiliary heat storage tank 15 is about 22 GJ. When fully charged, the minimum temperature of the first heat storage tank 7 and the first auxiliary heat storage tank 13 is about minus 49°C, and the maximum temperature of the second heat storage tank 8 and the second auxiliary heat storage tank 15 is about 210°C.

[0058] As described above, according to the present invention, a liquefied CO2 energy storage plant can be realized cost-effectively. The cost of the high-pressure side vessel 5 is important in terms of the cost of a liquefied CO2 energy storage plant, and the cost depends on the internal pressure and volume of the high-pressure side vessel 5 when fully charged. If the high-pressure side vessel is cylindrical, the mass of the material required for the high-pressure side vessel is roughly proportional to the internal pressure and to the volume. For this reason, it is necessary to consider a cycle in which the product of the internal pressure and the volume when fully charged is as small as possible. Figures 4 and 5 are graphs showing the relationship between the pressure of carbon dioxide at 20°C and 30°C, respectively, and the product of the pressure and the volume. Thus, the cost-effective storage pressure when storing liquefied CO2 at room temperature is considered to be about 55 atm to 80 atm at most. This is a level close to or lower than the critical pressure.

[0059] 3. Variations The present invention can also be implemented in the following aspects.

[0060] In the above embodiment, the energy storage plant includes the auxiliary cooler 11, the first auxiliary heat exchanger 12, the first auxiliary heat storage tank 13, the second auxiliary heat exchanger 14, and the second auxiliary heat storage tank 15. However, as long as it is possible to keep the pressure of the low-pressure side vessel 1 and the temperature of the high-pressure side vessel 5 constant, these configurations are not essential.

[0061] In the above embodiment, the pressure in the low-pressure container 1 is kept at about 7 atmospheres. However, as long as the working fluid in the low-pressure container 1 can be stored as a liquid or solid during complete discharge, the pressure in the low-pressure container 1 to be kept constant is not limited to this. For example, the pressure in the low-pressure container 1 can be between 1 atmosphere and the maximum pressure in the high-pressure container 5. In addition, instead of keeping the pressure in the low-pressure container 1 constant, the pressure may be controlled to be maintained between 1 atmosphere and the maximum pressure in the high-pressure container 5. Furthermore, the state of the working fluid in the low-pressure container 1 may be controlled by changing the pressure while maintaining the temperature at a constant value or within a constant range, rather than by changing the temperature while maintaining the pressure at a constant value or within a constant range.

[0062] In the above embodiment, the temperature inside the high pressure side vessel 5 is kept at about 29°C. However, the temperature inside the high pressure side vessel 5 to be kept constant may be between 15°C and 30°C, which is generally considered to be room temperature. Also, instead of keeping it constant, the temperature may be controlled to be kept between 15°C and 30°C. By maintaining the high pressure side temperature within the room temperature range, it becomes possible to facilitate practical operation. Furthermore, the state of the working fluid inside the high pressure side vessel 5 may be controlled by changing the temperature while maintaining the pressure at a constant value or within a constant range, rather than controlling the temperature by changing the pressure.

[0063] In the above embodiment, the working fluid is carbon dioxide. However, the working fluid is not limited to carbon dioxide as long as the working fluid is a fluid that is a gas at room temperature and atmospheric pressure and a liquid at room temperature and high pressure. For example, the working fluid may be nitrous oxide. [Explanation of symbols]

[0064] 1 Low pressure vessel 2 First heat exchanger 3. Compressor 4 Second heat exchanger 5 High pressure vessel 6. Expander 7 First heat storage tank 8 Second heat storage tank 9 Electric motor 10. Generator 11 Auxiliary cooler 12 First auxiliary heat exchanger 13 First auxiliary heat storage tank 14 Second auxiliary heat exchanger 15 Second auxiliary heat storage tank

Claims

1. An energy storage plant that charges and discharges by compressing and expanding a working fluid that is a gas at room temperature and atmospheric pressure and a liquid at room temperature and high pressure, A low-pressure vessel configured to store the working fluid in a liquid or solid state; A compressor that compresses the working fluid; an electric motor that drives the compressor; an expander that operates by expanding the working fluid; A generator driven by the expander; a high pressure vessel configured to store the working fluid at a higher pressure than the low pressure vessel; a first heat exchanger disposed between the low-pressure vessel and the compressor and between the low-pressure vessel and the expander, the first heat exchanger heating or cooling the working fluid; a second heat exchanger disposed between the high-pressure side vessel and the compressor and between the high-pressure side vessel and the expander, the second heat exchanger heating or cooling the working fluid; a first heat storage tank connected to the first heat exchanger and configured to store cold heat of the working fluid via a first heat exchange fluid that exchanges heat with the working fluid in the first heat exchanger; a second heat storage tank connected to the second heat exchanger and configured to store heat of the working fluid through a second heat exchange fluid that exchanges heat with the working fluid in the second heat exchanger; Equipped with In the charging process, The working fluid stored in the low-pressure side container is heated by the first heat exchanger to be turned into a gaseous state, and the cold energy of the working fluid is stored in the first heat storage tank; The working fluid after flowing through the first heat exchanger is compressed by the compressor, The working fluid after flowing through the compressor is cooled by the second heat exchanger, and heat of the working fluid is stored in the second heat storage tank; The working fluid after passing through the second heat exchanger is stored in the high-pressure side container, In the discharge process, The working fluid stored in the high-pressure side container is heated by the second heat exchanger using the heat stored in the second heat storage tank; The expander is operated by the working fluid after flowing through the second heat exchanger to drive the generator. The working fluid after flowing through the expander is cooled by the first heat exchanger using the cold stored in the first heat storage tank to make the working fluid in a liquid state or a solid state; The working fluid after passing through the first heat exchanger is stored in the low-pressure side container. Energy storage plants.

2. 2. The energy storage plant of claim 1, The energy storage plant, wherein the low pressure side vessel is more highly insulated than the high pressure side vessel.

3. 3. The energy storage plant according to claim 1 or 2, The energy storage plant, wherein the first heat exchanger and the second heat exchanger are of a countercurrent type.

4. 3. The energy storage plant according to claim 1 or 2, An energy storage plant comprising a subcooler connected to the first heat exchanger or the first heat storage tank.

5. 3. The energy storage plant according to claim 1 or 2, A first auxiliary heat exchanger is provided inside or around the low-pressure side container, and a first auxiliary heat storage tank is provided connected to the first auxiliary heat exchanger, The first auxiliary heat storage tank stores cold heat of the low-pressure side container via a first auxiliary heat exchange fluid that exchanges heat with the low-pressure side container in the first auxiliary heat exchanger.

6. 3. The energy storage plant according to claim 1 or 2, A second auxiliary heat exchanger is provided inside or around the high-pressure side vessel, and a second auxiliary heat storage tank is provided connected to the second auxiliary heat exchanger, The second auxiliary heat storage tank stores heat of the high-pressure side vessel via a second auxiliary heat exchange fluid that exchanges heat with the high-pressure side vessel in the second auxiliary heat exchanger.

7. 3. The energy storage plant according to claim 1 or 2, The energy storage plant, wherein the compressor and the expander are the same machine.

8. 3. The energy storage plant according to claim 1 or 2, 1. An energy storage plant, wherein the working fluid is carbon dioxide.

9. 9. The energy storage plant of claim 8, 1. The energy storage plant, wherein the pressure inside the high pressure side vessel is 55 to 80 atmospheres when fully charged.

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