Compressed gas energy storage system capacity size design method and system

Abstract

The invention provides a compressed gas energy storage system capacity size design method and system, and the method comprises the steps: constructing a compressed gas energy storage machine system, and setting constraint conditions according to the power grid electricity price data of a distribution and storage region to obtain the determined energy storage capacity and energy storage power of the compressed gas energy storage system, and the operation return on investment of the compressed gas energy storage system; according to the energy storage capacity and the energy storage power, the maximum compressed gas energy storage system circulation efficiency serves as a second target function, key thermodynamic parameters of all components serve as decision variables, the compressor power, the heat exchange power and the high-low pressure gas storage bin volume are determined, and the complete compressed gas energy storage system capacity and the complete component size are obtained. According to the design method, the compressor power, the expansion machine power and the volume of the high-low pressure gas storage bin are determined, the operation condition of a power grid is less considered, and the problems that the investment cost is too high and the income is low can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the field of compressed gas energy storage systems, and in particular to a method and system for designing the capacity size of compressed gas energy storage systems. Background Art

[0002] Due to the rapid development of science and technology and economy in today's society, the global demand for fossil energy is increasing. However, due to the non-renewable nature of fossil energy, fossil energy is gradually exhausted. In order to meet the growing energy demand of mankind, renewable energy has gradually become the first choice for energy use in today's society. Among renewable energy, wind energy and solar energy account for the highest proportion. However, due to the intermittent and uncertain characteristics of renewable energy such as wind energy and solar energy, the safety and stability of renewable energy grid connection poses a huge challenge. In order to suppress the above shortcomings, energy storage system is an important measure to achieve stable access to the grid for renewable energy, and has gradually become a hot topic in academic research today. Common energy storage methods include battery energy storage, pumped storage and compressed gas energy storage, and compressed gas energy storage is divided into compressed air energy storage and compressed carbon dioxide energy storage. Compared with compressed air energy storage, compressed carbon dioxide energy storage system has the advantages of good thermodynamic properties, large energy storage capacity, compact structure and long service life, and has gradually attracted widespread attention from scholars and scientific research institutions. The key components of compressed gas energy storage system are mainly composed of low-pressure gas storage, compressor, high-pressure gas storage and expander. The working process of the compressed gas energy storage system for renewable energy distribution and storage is as follows: when the power supply is greater than the power demand, the gas in the low-pressure gas storage tank is compressed by the compressor to a high-pressure state and stored in the high-pressure gas storage tank, converting electrical energy into internal energy and completing the energy storage process; when the power demand is greater than the power supply, the high-pressure gas in the high-pressure gas storage tank is released to drive the output shaft of the expander to drive the generator to generate electricity, converting internal energy into electrical energy, meeting the power demand and completing the energy release process. The working process of the compressed gas energy storage system for power grid distribution and storage is as follows: when the power price is low, the compressor runs to compress the low-pressure gas in the low-pressure gas storage tank into the high-pressure gas storage tank to complete the energy storage process and convert electrical energy into internal energy; when the power price is high, the high-pressure gas in the high-pressure gas storage tank is released to drive the expander to drive the generator to generate electricity, converting internal energy into electrical energy and completing the energy release process, using the fluctuation of the power price to realize the profit.

[0003] The inventor believes that this technology has the following problems: 1. Most of the compressed gas energy storage systems currently put into pilot applications are designed from the perspective of the compressed gas energy storage system itself, without considering the impact of the actual operation of the power grid on the system scale design.

[0004] 2. Most of the compressed gas energy storage systems currently put into pilot applications first determine the energy storage capacity and power based on the energy storage system itself, and then directly connect the entire compressed gas energy storage system to the grid for profit. There is a lack of consideration of the operation of the power grid. The grid-connected compressed gas energy storage system is not of the optimal capacity size, which may cause problems such as high initial investment costs or low returns. Therefore, there is a lack of a design method for the optimal capacity size of compressed gas energy storage systems. Summary of the invention

[0005] The purpose of the present invention is to provide a method and system for designing the capacity size of a compressed gas energy storage system. The compressor power, expander power and the volumes of high and low pressure gas storage bins have been determined, and less consideration has been given to the operation of the power grid, resulting in the problem of excessively high investment costs and low returns. The design method provided by the present invention can effectively avoid this problem.

[0006] To achieve the above object, the present invention provides a method for designing the capacity size of a compressed gas energy storage system, comprising the following steps: S1. Construct a compressed gas energy storage system. According to the grid electricity price data in the distribution area, the return on investment of the CGES coupled with the grid is taken as the first objective function, the rated capacity and rated power of the CGES are taken as the first decision variable, and constraints are set to solve the first objective function with the maximum return on investment; wherein the first objective function includes the real-time energy storage power, rated power and rated capacity of the compressed gas energy storage system; S2. Based on the energy storage capacity and energy storage power, maximizing the cycle efficiency of the compressed gas energy storage system is taken as the second objective function, and the key thermodynamic parameters of each component are taken as the second decision variable. The compressor power, heat exchange power and the volume of the high and low pressure gas storage tanks are determined to obtain the complete compressed gas energy storage system capacity and component size.

[0007] Preferably, the components of the compressed gas energy storage system include a compressor, an expander, high and low pressure gas storage tanks, an electric motor, a generator, a coupling, an intercooler and a heater.

[0008] Preferably, the constraints are compressor and expander power constraints, charge and discharge state constraints, and compressed gas energy storage system SOC constraints.

[0009] Preferably, in step S1, the following steps are included: S11. Based on the on-grid electricity price in the distribution and storage area, the maximum return on investment of the CGES (Compressed Gas Energy Storage) coupled with the grid is the first objective function, with the rated capacity and rated power of the CGES as decision variables; S12, establishing a mathematical model that satisfies the discharge constraint and the gas storage capacity constraint, and inputting the model into the gurobi solver for solving; S13, if the iteration termination condition is met, output the CGES rated capacity and rated power, real-time stored energy power and SOC calculation results; if the iteration termination condition is not met, return to step S12.

[0010] Preferably, in step S2, the following steps are included: S21, input the rated capacity and expander power, set the CGES initial configuration, and establish the CGES model; S22, using thermodynamic parameters that have an important impact on the cycle efficiency of the compressed gas energy storage system as decision variables combined with the second objective function to establish a genetic algorithm; S23, after selecting, crossover and mutation of the genetic algorithm, the individual with the maximum fitness is obtained, i.e., the maximum cycle efficiency; S24, calculating the thermodynamic parameter values ​​of each component of the CGES system, and obtaining the compressor power, heat exchange power and circulating gas flow rate; S25, W exp =E CGES,rate When the energy storage capacity is calculated, the energy storage and release time are calculated; otherwise, the process returns to step S23; S26. When the energy storage and release processes should ensure that the gas circulation quality is the same, calculate the density of the high and low pressure gas storage warehouses, and calculate the volume of the high and low gas storage warehouses; otherwise, return to step S23.

[0011] Preferably, the thermodynamic parameters that have an important influence on the cycle efficiency of the compressed gas energy storage system include the compressor outlet temperature, the expander inlet temperature, and the compressor and expander inlet pressures.

[0012] A capacity dimensioning system for a compressed gas energy storage system, comprising: The power determination module is used to construct a compressed gas energy storage system. According to the power grid price data of the distribution area, the return on investment of the CGES coupled with the power grid is the first objective function, and the rated capacity and rated power of the CGES are the first decision variables. Constraints are set to solve the first objective function with the maximum return on investment. The size calculation module is used to determine the compressor power, heat exchange power and high and low pressure gas storage volumes based on the energy storage capacity and energy storage power, with maximizing the cycle efficiency of the compressed gas energy storage system as the second objective function and the key thermodynamic parameters of each component as the second decision variable, to obtain the complete compressed gas energy storage system capacity and component size.

[0013] An electronic device includes a memory and a processor, wherein a computer program is stored in the memory, and when the processor calls the computer program in the memory, the processor implements the steps of a method for designing the capacity size of a compressed gas energy storage system.

[0014] A storage medium stores computer executable instructions, which, when loaded and executed by a processor, implement the steps of a method for designing the capacity size of a compressed gas energy storage system.

[0015] Therefore, the present invention adopts the above-mentioned method and system for designing the capacity size of a compressed gas energy storage system, which can provide capacity size design guidance for equipping a power grid with a compressed gas energy storage system. The compressor power, expander power and the volume of high and low pressure gas storage bins have been determined, and less consideration has been given to the operation of the power grid, resulting in the problem of excessively high investment costs and low returns. The design method provided by the present invention can effectively avoid this problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the schematic diagram of the compressed gas energy storage system (grid-connected); Figure 2 is a flowchart of step S1; Figure 3 This is a flowchart of step S2.

[0017] Reference numerals 1. Electric motor; 2. Compressor; 3. Intercooler; 4. High-pressure gas storage tank; 5. First valve; 6. Heater; 7. Expander; 8. Generator; 9. Low-pressure gas storage tank; 10. Second valve; 11. Power grid; 12. First coupling; 13. Second coupling. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0019] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0020] The specific operating principle of the compressed gas energy storage system is as follows: during the period of low electricity prices, the second valve 10 is controlled to be opened and the first valve 5 is controlled to be closed. The electric energy from the power grid 11 is supplied to the motor 1. The motor 1 drives the first coupling 12 to drive the compressor 2 to compress the low-pressure gas from the low-pressure gas storage tank 9. When the high-temperature and high-pressure gas flows through the intercooler 3 and is cooled, the heat is recovered, and the gas finally enters the high-pressure gas storage tank 4 to complete the energy storage process.

[0021] During the peak period of electricity prices, the first valve 5 is controlled to open and the second valve 10 is controlled to close, so that the gas in the high-pressure gas storage tank is released and heated by the heater 6 to increase the working capacity. The high-temperature and high-pressure gas drives the expander to do work, and drives the second coupling 13 to drive the generator 8 to transmit electricity to the power grid 11. The gas after doing work enters the low-pressure gas storage tank 9, completing the energy release process.

[0022] Embodiment 1 The present invention provides a method and system for designing the capacity size of a compressed gas energy storage system, comprising the following steps: S1. Construct a compressed gas energy storage system. According to the grid electricity price data in the distribution and storage area, take the return on investment of the CGES coupled with the grid as the first objective function, take the rated capacity and rated power of the CGES as the first decision variable, and set constraints to solve the first objective function with the maximum return on investment; wherein, the first objective function includes the real-time energy storage power (expander power), rated power, and rated capacity (energy storage capacity) of the compressed gas energy storage system; the compressed gas energy storage system is composed of components such as a compressor, an expander, high and low pressure gas storage tanks, an electric motor, a generator, a coupling, an intercooler, and a heater.

[0023] The following steps are involved: S11. Based on the on-grid electricity price in the distribution and storage area, the maximum return on investment of the CGES coupled with the power grid is the first objective function. The first objective function includes the real-time energy storage power ( W exp,t , W com,t ), rated power , rated capacity , taking the CGES rated capacity and rated power as the first decision variable; Among them, the first objective function return on investment is shown in formula (1): (1); In the formula, For the return on investment, is the total annual revenue of the compressed gas energy storage system, is the total investment cost, and the total income and total investment cost are shown in formula (2) and formula (3) (2); In the formula, v ch,t and They represent the charging and discharging states respectively. and Represent the real-time power of expander and compressor respectively, Indicates the real-time electricity price.

[0024] (3); In the formula, and They are the rated power and rated capacity of the compressed gas energy storage system. and are the investment coefficients related to rated power and rated capacity, respectively. is the operation and maintenance cost. Among them, the investment coefficient and operation and maintenance cost can be expressed by formulas (4), (5), and (6).

[0025] (4); (5); (6); In the formula, and They are the one-time installation cost per unit rated power and per unit capacity, is the discount rate, For service life, is the operation and maintenance cost coefficient.

[0026] S12, establishing a mathematical model that satisfies the discharge constraint and the gas storage capacity constraint, and inputting the model into the gurobi solver for solving; The constraints are compressor and expander power constraints, charge and discharge state constraints, and compressed gas energy storage system SOC constraints.

[0027] The constraints of the mathematical model for discharge constraint and gas storage capacity constraint are: The power constraints of the compressor and expander are as follows: (7); (8); Charge and discharge state constraints: There are three states of compressed gas energy storage system: energy storage, energy release and standby. The constraint expression is as follows (9); (10); (11); The SOC constraint of the compressed gas energy storage system is expressed as follows (12); The electricity price data of the area that needs storage, the first objective function, and the constraints are input into the Gurobi solver to solve the first objective function with the maximum return on investment.

[0028] S13: The iteration termination condition MIPGap<0.01 is met, and the CGES rated capacity is output and rated power , real-time storage and release power ( W exp,t , W com,t ) and SOC calculation result; MIPGap≥0.01, return to step S12.

[0029] The SOC expression of the compressed gas energy storage system is as follows (13); In the formula, η com represents the compressor cycle efficiency, η exp Indicates the expander cycle efficiency; usually a constant value S2. Based on the energy storage capacity and energy storage power, maximizing the cycle efficiency of the compressed gas energy storage system is taken as the second objective function, and the key thermodynamic parameters of each component are taken as the second decision variable. The compressor power, heat exchange power and the volume of the high and low pressure gas storage tanks are determined to obtain the complete compressed gas energy storage system capacity and component size.

[0030] The following steps are involved: S21, input the rated capacity and expander power, set the CGES initial configuration, and establish the CGES model; S22. A genetic algorithm is established by taking the thermodynamic parameters that have an important influence on the cycle efficiency of the compressed gas energy storage system as the second decision variable and combining it with the second objective function; the thermodynamic parameters that have an important influence on the cycle efficiency of the compressed gas energy storage system include the compressor outlet temperature, the expander inlet temperature, and the compressor and expander inlet pressures.

[0031] The cycle efficiency of the compressed gas energy storage system is shown in formula (14): (14); In the formula, is the expander power, is the compressor power, is the compression heat recovered by the intercooler, is the amount of heat before entering the expander.

[0032] S23, after selecting, crossover and mutation of the genetic algorithm, the individual with the maximum fitness is obtained, i.e., the maximum cycle efficiency; S24, calculate the thermodynamic parameter values ​​of each component of the CGES system, and calculate the compressor power, heat exchange power and circulating gas flow (energy storage flow m ch and energy release flow rate m dis ); The compressor and expander power are shown below (15); (16); In the formula, and are the energy storage and energy release flows, and are the compressor inlet and outlet enthalpies, and They are the inlet and outlet enthalpy values ​​of the expander respectively. The enthalpy values ​​of the compressor and the expander can be queried by calling the refpropm physical property library and using the thermodynamic parameter values ​​of each component of the compressed gas energy storage system. For example, the compressor inlet enthalpy value is calculated as shown in the following formula.

[0033] (17); T com,in Indicates the compressor inlet temperature, P com,in Indicates the compressor inlet pressure.

[0034] The remaining thermodynamic parameters can be queried and calculated using the refpropm physical property library.

[0035] The heat transfer power is shown as follows: (18); The heat calculation of the intercooler and heater is shown in the above formula, where is the gas flow rate through the heat exchanger, and It is the enthalpy of the gas at the inlet and outlet of the heat exchanger.

[0036] S25, W exp =E CGES,rate When the energy storage capacity is calculated, the energy storage and release time are calculated; otherwise, the process returns to step S23; The rated power and energy storage capacity have been determined. Therefore, in the genetic algorithm for optimizing cycle efficiency, the rated power is generally the expander power, and the expander power is limited to a certain value by adjusting the energy release flow rate. In addition, the energy storage capacity is used to calculate the energy storage release time as shown in the following formula (19); (20); In the cyclic operation of the compressed gas energy storage system, the total mass of gas in the energy storage and release cycle processes should be ensured to be the same. The mathematical expression is shown below.

[0037] (twenty one); (twenty two); (twenty three); S26, M ch =M dis When the density of high and low pressure gas storage warehouses is calculated, the volume of high and low gas storage warehouses is calculated; otherwise, return to step S23.

[0038] During the genetic operation process, it is necessary to continuously adjust the expander flow and the compressor flow to meet the constraints, select, cross and mutate the population of the genetic algorithm, and finally obtain the individual with the maximum fitness, that is, the maximum cycle efficiency of the compressed gas energy storage system. At this time, the values ​​of the thermodynamic parameters of each component under the maximum cycle efficiency of the compressed gas energy storage system are obtained, and the compressor power, heat exchange power, energy storage flow and energy release flow can be calculated.

[0039] The total mass of the cycle process is calculated by formula (20), and the thermodynamic parameter values ​​of the compressed gas energy storage system obtained by genetic algorithm optimization are used to call the refpropm physical property library to obtain the gas density in the high and low pressure gas storage bins, and the volumes of the high and low pressure gas storage bins are calculated using the following formula.

[0040] (twenty four); (25); In the formula, and are the volumes of high and low pressure gas storage tanks, and They are the densities of high and low pressure gas storage tanks respectively.

[0041] A capacity dimensioning system for a compressed gas energy storage system, comprising: The power determination module is used to construct a compressed gas energy storage system. According to the power grid price data of the distribution area, the return on investment of the CGES coupled with the power grid is the first objective function, and the rated capacity and rated power of the CGES are the first decision variables. Constraints are set to solve the first objective function with the maximum return on investment. The size calculation module is used to determine the compressor power, heat exchange power and high and low pressure gas storage volumes based on the energy storage capacity and energy storage power, with maximizing the cycle efficiency of the compressed gas energy storage system as the second objective function and the key thermodynamic parameters of each component as the second decision variable, to obtain the complete compressed gas energy storage system capacity and component size.

[0042] The electronic device provided by the present invention includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps in the above-mentioned method embodiments are implemented. Alternatively, when the processor executes the computer program, the functions of the modules / units in the above-mentioned device embodiments are implemented.

[0043] The computer program may be divided into one or more modules / units, and the one or more modules / units are stored in the memory and executed by the processor to accomplish the present invention.

[0044] The device may be a computing device such as a desktop computer, a notebook, a PDA, a cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0045] The processor can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0046] The memory may be used to store the computer programs and / or modules, and the processor implements various functions of the terminal device by running or executing the computer programs and / or modules stored in the memory and calling the data stored in the memory.

[0047] If the module / unit integrated in the terminal device is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, the steps of the above-mentioned various method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0048] Therefore, the present invention adopts the above-mentioned compressed gas energy storage system capacity size design method and system. The compressor power, expander power and the volume of high and low pressure gas storage tanks have been determined, and the operation of the power grid is less considered, resulting in the problem of excessively high investment costs and low returns. The design method provided by the present invention can effectively avoid this problem.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for designing the capacity size of a compressed gas energy storage system, characterized in that: The following steps are involved: S1. Construct a compressed gas energy storage system. According to the grid electricity price data in the distribution area, the return on investment of the CGES coupled with the grid is taken as the first objective function, the rated capacity and rated power of the CGES are taken as the first decision variable, and constraints are set to solve the first objective function with the maximum return on investment; wherein the first objective function includes the real-time energy storage power, rated power and rated capacity of the compressed gas energy storage system; S2. Based on the energy storage capacity and energy storage power, maximizing the cycle efficiency of the compressed gas energy storage system is taken as the second objective function, and the key thermodynamic parameters of each component are taken as the second decision variable. The compressor power, heat exchange power and the volume of the high and low pressure gas storage tanks are determined to obtain the complete compressed gas energy storage system capacity and component size.

2. A method for designing the capacity size of a compressed gas energy storage system according to claim 1, characterized in that: The components of the compressed gas energy storage system include a compressor, an expander, high and low pressure gas storage tanks, an electric motor, a generator, a coupling, an intercooler and a heater.

3. A method for designing the capacity size of a compressed gas energy storage system according to claim 1, characterized in that: The constraints are compressor and expander power constraints, charge and discharge state constraints, and compressed gas energy storage system SOC constraints.

4. A method for designing the capacity size of a compressed gas energy storage system according to claim 1, characterized in that: In step S1, the following steps are included: S11, based on the on-grid electricity price in the distribution and storage area, the return on investment of the CGES coupled with the power grid is the first objective function, and the rated capacity and rated power of the CGES are the first decision variables; S12, establishing a mathematical model that satisfies the discharge constraint and the gas storage capacity constraint, and inputting the model into the gurobi solver for solving; S13, if the iteration termination condition is met, output the CGES rated capacity and rated power, real-time stored energy power and SOC calculation results; if the iteration termination condition is not met, return to step S12.

5. A method for designing the capacity size of a compressed gas energy storage system according to claim 1, characterized in that: In step S2, the following steps are included: S21, input the rated capacity and expander power, set the CGES initial configuration, and establish the CGES model; S22, establishing a genetic algorithm by taking a thermodynamic parameter having an important influence on the cycle efficiency of the compressed gas energy storage system as the second decision variable and combining it with the second objective function; S23, after selecting, crossover and mutation of the genetic algorithm, the individual with the maximum fitness is obtained, i.e., the maximum cycle efficiency; S24, calculating the thermodynamic parameter values ​​of each component of the CGES system, and obtaining the compressor power, heat exchange power and circulating gas flow rate; S25, W exp =E CGES,rate When the energy storage capacity is calculated, the energy storage and release time are calculated; otherwise, the process returns to step S23; S26. When the energy storage and release processes ensure that the gas circulation quality is the same, the density of the high and low pressure gas storage warehouses is calculated, and the volume of the high and low gas storage warehouses is calculated; otherwise, return to step S23.

6. A method for designing the capacity size of a compressed gas energy storage system according to claim 1, characterized in that: Thermodynamic parameters that have an important impact on the cycle efficiency of the compressed gas energy storage system include the compressor outlet temperature, the expander inlet temperature, and the compressor and expander inlet pressures.

7. A system for designing the capacity and size of a compressed gas energy storage system, characterized in that: include The power determination module is used to construct a compressed gas energy storage system. According to the power grid price data of the distribution area, the return on investment of the CGES coupled with the power grid is the first objective function, and the rated capacity and rated power of the CGES are the first decision variables. Constraints are set to solve the first objective function with the maximum return on investment. The size calculation module is used to determine the compressor power, heat exchange power and high and low pressure gas storage volumes based on the energy storage capacity and energy storage power, with maximizing the cycle efficiency of the compressed gas energy storage system as the second objective function and the key thermodynamic parameters of each component as the second decision variable, to obtain the complete compressed gas energy storage system capacity and component size.

8. An electronic device, characterized in that: It comprises a memory and a processor, wherein a computer program is stored in the memory, and when the processor calls the computer program in the memory, the steps of a method for designing the capacity size of a compressed gas energy storage system as claimed in any one of claims 1 to 6 are implemented.

9. A storage medium, characterized in that: The storage medium stores computer executable instructions, which, when loaded and executed by a processor, implement the steps of a method for designing capacity dimensions of a compressed gas energy storage system as described in any one of claims 1 to 6.

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