Energy storage system

Abstract

The utility model provides an energy storage system which comprises an energy storage tank group which comprises a plurality of energy storage tanks which are communicated in series, and part of the energy storage tanks are filled with spacer fluid; the air energy storage module can store and release energy by utilizing compression and expansion of air, and is connected with the energy storage tank group, so that compressed air pushes the spacer fluid to flow to the downstream in the first flowing direction when entering the energy storage tank group, and carbon dioxide in the energy storage tank located at the downstream of the spacer fluid is extruded; and the carbon dioxide energy storage module can store and release energy by utilizing phase change of carbon dioxide, and the carbon dioxide energy storage module is connected with the energy storage tank group, so that when the carbon dioxide enters the energy storage tank group, the carbon dioxide pushes the spacer fluid to flow towards the upstream in the downstream direction of the first flowing direction so as to extrude the compressed air in the energy storage tank located at the upstream of the spacer fluid. In this way, isolation of two working media, namely compressed air and carbon dioxide, is achieved in the energy storage stage and the energy release stage, and therefore the energy storage efficiency and the stability of the energy storage system are improved.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to an energy storage system. Background Art

[0002] Compressed gas energy storage technology mainly includes compressed air energy storage and compressed carbon dioxide energy storage. The former realizes power energy storage by compressing the air in the atmosphere into high-pressure gas storage. The advantage is that the atmosphere does not need to be stored, but the disadvantage is that the high-pressure gas storage cost is high. The latter realizes power energy storage by compressing and liquefying carbon dioxide gas for storage. The advantage is that the storage cost of liquefied carbon dioxide is low, but the disadvantage is that the storage volume of low-pressure carbon dioxide gas is too large. Combining compressed air energy storage and compressed carbon dioxide energy storage can form a new compressed air energy storage technology solution. Compressed air energy storage is responsible for compressed air energy storage in the low-pressure stage, and compressed carbon dioxide energy storage is responsible for compressed air energy storage in the high-pressure stage. How to properly handle the isolation of the two working fluids, air and carbon dioxide, is the key process. Utility Model Content

[0003] In view of this, the present application provides an energy storage system, which couples an air energy storage module and a carbon dioxide energy storage module and is capable of maintaining isolation between the two working fluids of air and carbon dioxide during the energy storage and release process.

[0004] In order to achieve the above objectives, this application provides the following technical solutions:

[0005] An energy storage system, comprising:

[0006] An energy storage tank group, comprising a plurality of energy storage tanks connected in series, and some of the energy storage tanks are filled with isolation fluid;

[0007] An air energy storage module, which can store and release energy by compression and expansion of air, and is connected to the energy storage tank group, so that when the compressed air enters the energy storage tank group, it pushes the isolation liquid to flow downstream in the upstream of the first flow direction, so as to squeeze the carbon dioxide in the energy storage tank located downstream of the isolation liquid;

[0008] A carbon dioxide energy storage module is capable of storing and releasing energy by utilizing the phase change of the carbon dioxide. The carbon dioxide energy storage module is connected to the energy storage tank group so that when the carbon dioxide enters the energy storage tank group, it pushes the isolation liquid to flow upstream from the downstream in the first flow direction to squeeze the compressed air in the energy storage tank located upstream of the isolation liquid.

[0009] Optionally, in the above-mentioned energy storage system, the multiple energy storage tanks connected in series include a first energy storage tank, a second energy storage tank, and a plurality of intermediate energy storage tanks located between the first energy storage tank and the second energy storage tank, the first energy storage tank is connected to the air energy storage module, the second energy storage tank is connected to the carbon dioxide energy storage module, and each of the intermediate energy storage tanks is connected to the air energy storage module and the carbon dioxide energy storage module.

[0010] Optionally, in the above energy storage system, the energy storage tank group includes a first energy storage tank, a second energy storage tank, and a plurality of intermediate energy storage tanks located between the first energy storage tank and the second energy storage tank, the first energy storage tank is connected to the air energy storage module, and the second energy storage tank is connected to the carbon dioxide energy storage module.

[0011] Optionally, in the above energy storage system, in a first state where the compressed air has not entered the energy storage tank group, the isolation liquid is located in the first energy storage tank; in a second state where the carbon dioxide has not entered the energy storage tank group, the isolation liquid is located in the second energy storage tank.

[0012] Optionally, in the above energy storage system, an anti-stick coating is provided inside the energy storage tank to prevent the isolation liquid from adhering to the inner wall of the energy storage tank.

[0013] Optionally, in the above energy storage system, the isolation liquid is a lubricating oil that is insoluble in the compressed air and the carbon dioxide.

[0014] Optionally, in the above energy storage system, the material of the anti-stick coating is polyethylene or polytetrafluoroethylene.

[0015] Optionally, in the above energy storage system, the cross-sectional shape of the energy storage tank is circular.

[0016] The present application provides an energy storage system, in which some energy storage tanks are filled with isolation liquid, and each of the remaining energy storage tanks is filled with compressed air or carbon dioxide. From the above structure, it can be seen that the isolation liquid is an isolation medium that isolates compressed air and carbon dioxide. Air can be transferred between energy storage tanks by pushing the isolation liquid in the energy storage tank, so that the isolation liquid occupies the spatial position of the energy storage tank where the carbon dioxide gas was originally located, thereby transferring the carbon dioxide gas in the energy storage tank. Similarly, carbon dioxide can be transferred between energy storage tanks by pushing the isolation liquid in the energy storage tank, so that the isolation liquid occupies the space of the energy storage tank where the compressed air was originally located, thereby transferring the compressed air. In this way, the isolation of the two working fluids, compressed air and carbon dioxide, is achieved in both the energy storage and energy release stages, thereby improving the energy storage efficiency and the stability of the energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0018] Figure 1 A schematic diagram of the composition of the energy storage system provided in an embodiment of the present application;

[0019] Figure 2 A schematic diagram of the initial state of the energy storage system provided in an embodiment of the present application;

[0020] Figure 3 A schematic diagram of the energy storage process of the energy storage system provided in an embodiment of the present application;

[0021] Figure 4 A schematic diagram of the energy storage end state of the energy storage system provided in an embodiment of the present application;

[0022] Figure 5 Schematic diagram of the energy release process of the energy storage system provided in an embodiment of the present application.

[0023] exist Figure 1-Figure 5 middle:

[0024] 1. First energy storage tank; 2. Second energy storage tank; 3. Intermediate energy storage tank; 4. Isolation liquid; 5. Air energy storage module; 51. Compressed air; 6. Carbon dioxide energy storage module; 61. Carbon dioxide; 62. Liquid carbon dioxide storage tank. DETAILED DESCRIPTION

[0025] The present application provides an energy storage system, which couples an air energy storage module and a carbon dioxide energy storage module and is capable of maintaining isolation between two working fluids, air and carbon dioxide, during energy storage and release.

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0027] like Figure 1-Figure 5As shown, an embodiment of the present application provides an energy storage system, which couples an air energy storage module 5 and a carbon dioxide energy storage module 6, and both of the above energy storage modules are connected to an energy storage tank group, which includes a plurality of energy storage tanks connected in series, and some of the energy storage tanks are filled with isolation liquid 4. It should be noted that the number of some energy storage tanks is preferably 1 energy storage tank, or some of the energy storage tanks are adjacent to each other and connected in series in the flow direction, and each of the remaining energy storage tanks is filled with compressed air 51 or carbon dioxide 61. In the energy storage stage, the air energy storage module 5 compresses the air from the atmosphere and transports it to the energy storage tank. The compressed air 51 pushes the isolation liquid 4 to flow downstream in the upstream of the first flow direction, that is, the compressed air 51 squeezes the isolation liquid 4 in the energy storage tank, and the isolation liquid 4 is transferred from one energy storage tank to another energy storage tank downstream. At the same time, the carbon dioxide 61 in the other energy storage tank downstream is isolated and transferred by the isolation liquid 4, thereby avoiding the mixing of the compressed air 51 and the carbon dioxide 61. In the energy release stage, the carbon dioxide energy storage module 6 expands the carbon dioxide 61 and generates electricity, and then pushes the isolation liquid 4 to flow upstream in the downstream of the first flow direction (that is, the actual flow direction of the carbon dioxide 61 is the opposite direction of the first flow direction). In other words, the carbon dioxide 61 squeezes the isolation liquid 4 in the energy storage tank, and the isolation liquid 4 is transferred from one energy storage tank to another energy storage tank upstream. At the same time, the compressed air 51 in the other energy storage tank upstream is isolated and transferred by the isolation liquid 4, thereby avoiding the mixing of the compressed air 51 and the carbon dioxide 61.

[0028] It should also be noted that the first flow direction refers to the flow direction of the compressed air 51 during the energy storage stage.

[0029] It should also be noted that the carbon dioxide energy storage module 6 also includes a liquid carbon dioxide storage tank 62 , which is used to contain compressed and liquefied carbon dioxide 61 .

[0030] As can be seen from the above structure, the isolation liquid 4 is an isolation medium for isolating the compressed air 51 and the carbon dioxide 61. The compressed air 51 can push the isolation liquid 4 in the energy storage tank to transfer between the energy storage tanks, so that the isolation liquid 4 occupies the space position of the energy storage tank where the carbon dioxide 61 was originally located, thereby transferring the carbon dioxide 61 in the energy storage tank, so that the two media of compressed air 51 and carbon dioxide 61 are kept in an isolated state. Similarly, the carbon dioxide 61 can push the isolation liquid 4 in the energy storage tank to transfer between the energy storage tanks, so that the isolation liquid 4 occupies the space of the energy storage tank where the compressed air 51 was originally located, thereby transferring the compressed air 51, so that the two media of compressed air 51 and carbon dioxide 61 are kept in an isolated state. In this way, the isolation of the two working fluids of compressed air 51 and carbon dioxide 61 is achieved in both the energy storage and energy release stages, thereby improving the energy storage efficiency and the stability of energy storage.

[0031] Furthermore, a plurality of energy storage tanks connected in series include a first energy storage tank 1, a second energy storage tank 2, and a plurality of intermediate energy storage tanks 3 located between the first energy storage tank 1 and the second energy storage tank 2. The first energy storage tank 1 is connected to the air energy storage module 5, the second energy storage tank 2 is connected to the carbon dioxide energy storage module 6, and each intermediate energy storage tank 3 is connected to the air energy storage module 5 and the carbon dioxide energy storage module 6. The connection mode of the above energy storage tank group and the air energy storage module 5 and the carbon dioxide energy storage module 6 enables the compressed air 51 in the energy storage stage to be compressed by the carbon dioxide energy storage module 6 and stored in the liquid carbon dioxide storage tank 62 by squeezing the isolation liquid 4, so that the carbon dioxide 61 gas in each energy storage tank is directly compressed by the carbon dioxide energy storage module 6 and stored in the liquid carbon dioxide storage tank 62; in the energy release stage, the carbon dioxide 61 can be compressed by the isolation liquid 4, so that the compressed air 51 in each energy storage tank is directly expanded by the air energy storage module 5 to generate electricity, and then discharged to the atmosphere.

[0032] For the purpose of explanation, energy storage tank No. 1 in the following text refers to the first energy storage tank 1, energy storage tank No. N+1 refers to the second energy storage tank 2, and the energy storage tanks between energy storage tank No. 1 and energy storage tank No. N+1 refer to multiple intermediate energy storage tanks 3, and the above 1-N+1 are arranged in the order of natural numbers, where N is greater than or equal to 1.

[0033] More specifically, for the energy storage stage, such as Figure 2-Figure 4 As shown, one energy storage tank is filled with isolation liquid 4, the rest are filled with carbon dioxide 61 at a specified pressure, and the liquid carbon dioxide storage tank 62 is in an empty state. Assuming that the energy storage tank filled with isolation liquid 4 is No. 1, the air energy storage module 5 fills compressed air 51 into energy storage tank No. 1, the isolation liquid 4 is filled into energy storage tank No. 2, and the carbon dioxide 61 in energy storage tank No. 2 is compressed and liquefied by the carbon dioxide energy storage module 6 and then filled into the liquid carbon dioxide storage tank 62; then, the gas compression process of energy storage tank No. 2 and energy storage tank No. 3 is completed; and so on, finally, the gas compression process of energy storage tank No. N and energy storage tank No. N+1 is completed; at the end of the gas compression, one energy storage tank is filled with isolation liquid 4, the rest are filled with compressed air 51 at a specified pressure, and the liquid carbon dioxide storage tank 62 is in a full state.

[0034] For the energy release stage, Figure 4 and Figure 5 As shown, this process is opposite to the energy storage process, that is, the energy storage tank filled with isolation liquid 4 is No. N+1, liquid carbon dioxide storage tank 62 releases liquid carbon dioxide 61, and carbon dioxide 61 is charged into energy storage tank N+1 after gasification and power generation by carbon dioxide energy storage module 6, isolation liquid 4 is charged into energy storage tank No. N, and air 51 in energy storage tank No. N is discharged into the atmosphere after power generation by air energy storage module 5; then, the deflation process of energy storage tank No. N-1 and energy storage tank No. N-2 is completed; and so on, finally, the deflation process of energy storage tank No. 2 and energy storage tank No. 1 is completed; when the deflation is completed, it is restored to Figure 2 The starting state.

[0035] It can be seen that the connection between the above-mentioned multiple intermediate energy storage tanks 3 and the air energy storage module 5 and the carbon dioxide energy storage module 6 enables the carbon dioxide 61 and the compressed air 51 to be compressed or expanded in time, that is, the energy is stored or released in time, and the response of the entire energy storage system is very rapid.

[0036] In addition to the above-mentioned connection forms of the air energy storage module 5, the carbon dioxide energy storage module 6 and the energy storage tank group, the connection forms of the air energy storage module 5, the carbon dioxide energy storage module 6 and the energy storage tank group can also be that the energy storage tank group includes a first energy storage tank 1, a second energy storage tank 2, and a plurality of intermediate energy storage tanks 3 located between the first energy storage tank 1 and the second energy storage tank 2, the first energy storage tank 1 is connected to the air energy storage module 5, and the second energy storage tank 2 is connected to the carbon dioxide energy storage module 6.

[0037] More specifically, for the energy storage stage, one energy storage tank is filled with isolation liquid 4, the rest are filled with carbon dioxide 61 at a specified pressure, and the liquid carbon dioxide storage tank 62 is in an empty state. Assuming that the energy storage tank filled with isolation liquid 4 is No. 1, the air energy storage module 5 fills compressed air 51 into energy storage tank No. 1, the isolation liquid 4 is charged into energy storage tank No. 2, the carbon dioxide 61 in energy storage tank No. 2 is charged into energy storage tank No. 3, and the carbon dioxide 61 gas in energy storage tank No. 3 is charged into energy storage tank No. 4, and so on. Finally, the carbon dioxide 61 in energy storage tank No. N enters energy storage tank No. N+1, and the carbon dioxide 61 in energy storage tank No. N+1 is compressed by the carbon dioxide energy storage module 6 and stored in the liquid carbon dioxide storage tank 62; at the end of the compression, one energy storage tank is filled with isolation liquid 4, the rest are filled with compressed air 51 at a specified pressure, and the liquid carbon dioxide storage tank 62 is in a full state.

[0038] As for the energy release process, this process is opposite to the energy storage process, that is, the energy storage tank filled with isolation liquid 4 is No. N+1, the liquid carbon dioxide storage tank 62 releases liquid carbon dioxide 61, and the carbon dioxide energy storage module 6 gasifies and generates electricity before charging carbon dioxide 61 into energy storage tank No. N+1, the isolation liquid 4 is charged into energy storage tank No. N, the compressed air 51 in energy storage tank No. N is charged into energy storage tank No. N-1, the compressed air 51 in energy storage tank No. N-1 is charged into energy storage tank No. N-2, and so on. Finally, the compressed air 51 in energy storage tank No. 2 enters energy storage tank No. 1, and the compressed air 51 in energy storage tank No. 1 is discharged into the atmosphere after being generated electricity by the air energy storage module 5 system.

[0039] This connection form allows the air energy storage module 5 to always use the compressed air 51 in energy storage tank No. 1 for expansion and power generation, and the carbon dioxide energy storage module 6 to always use the carbon dioxide 61 gas in energy storage tank No. 2 and compress it and store it in the liquid carbon dioxide storage tank 62. Multiple intermediate energy storage tanks 3 are connected in series, and one of the air 51 and carbon dioxide 61 squeezes the other by squeezing the isolation liquid 4.

[0040] It can be seen that the above connection structure is simple, has fewer pipelines, and is convenient for installation and maintenance of the energy storage system.

[0041] In the first state where the compressed air 51 does not enter the energy storage tank group, the isolation liquid 4 is located in the first energy storage tank 1; in the second state where the carbon dioxide 61 does not enter the energy storage tank group, the isolation liquid 4 is located in the second energy storage tank 2. That is, the position of the isolation liquid 4 is limited. Figure 2 As shown, when energy storage has not started, the isolation liquid 4 is located in the first energy storage tank 1, and the first energy storage tank 1 is connected to the air energy storage module 5. When energy release has not started, the isolation liquid 4 is located in the second tank, and the second tank is connected to the carbon dioxide energy storage module 6. It can be seen that in the initial state of energy storage and energy release, the isolation liquid 4 is always located at the end of the energy storage tank group rather than the middle position. This arrangement allows air 51 or carbon dioxide 61 to flow in isolation from the beginning or end of the energy storage tank group, making full use of the space of the energy storage tank group and improving the energy storage efficiency.

[0042] In addition, in the first state where the compressed air 51 has not entered the energy storage tank group, the isolation liquid 4 may not be located in the first energy storage tank 1, but in one of the multiple intermediate energy storage tanks 3; in the second state where the carbon dioxide 61 has not entered the energy storage tank group, the isolation liquid 4 may not be located in the second energy storage tank 2, but in one of the multiple energy storage tanks.

[0043] In some optional embodiments, an anti-stick coating is provided inside the energy storage tank to prevent the isolation liquid 4 from adhering to the inner wall of the energy storage tank. The provision of the anti-stick coating allows the isolation liquid 4 to enter other energy storage tanks when the compressed air 51 or carbon dioxide 61 squeezes the isolation liquid 4, so as to prevent the isolation liquid 4 from adhering to the inner wall of the energy storage tank and occupying the internal space of the energy storage tank, thereby adversely affecting the storage of energy.

[0044] Wherein, the material of the anti-stick coating is polyethylene or polytetrafluoroethylene.

[0045] In addition, the anti-stick coating can also be a fluoride coating, a silane coating, or a ceramic coating; or, the energy storage tank can also be made of a rigid material with an anti-stick function.

[0046] In some optional embodiments, the isolation liquid 4 is a lubricating oil that is incompatible with the compressed air 51 and the carbon dioxide 61 . In this way, the air 51 or the carbon dioxide 61 is prevented from being miscible with the isolation liquid 4 , thereby avoiding energy waste.

[0047] In addition, the isolation liquid 4 can also dissolve the compressed air 51 or the carbon dioxide 61, but the solubility is very small.

[0048] The lubricating oil may be mineral oil, synthetic lubricating oil or other common engineering materials which are incompatible with or have very low solubility in the compressed air 51 and the carbon dioxide 61 .

[0049] In some optional embodiments, the cross-sectional shape of the energy storage tank is circular, that is, the energy storage tank is spherical, and there is no dead angle inside the sphere, so that when the compressed air 51 or the carbon dioxide 61 squeezes the isolation liquid 4, the isolation liquid 4 can be smoothly transferred, so that the isolation liquid 4 always completely isolates the two working media of the compressed air 51 and the carbon dioxide 61, and improves energy storage.

[0050] In addition, the cross-sectional shape of the energy storage tank may not be a perfect circle, but an oblate circle.

[0051] The basic principles of the present application are described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, effects, etc. mentioned in the present application are only examples and not limitations, and it cannot be considered that these advantages, strengths, effects, etc. are required by each embodiment of the present application. In addition, the specific details disclosed above are only for the purpose of illustration and ease of understanding, not for limitation, and the above details do not limit the present application to being implemented by adopting the above specific details.

[0052] The block diagrams of the devices, apparatuses, equipment, and systems involved in this application are only illustrative examples and the schematic diagrams require or imply that they must be connected, arranged, and configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these devices, apparatuses, equipment, and systems can be connected, arranged, and configured in any manner. Words such as "including", "comprising", "having", and the like are open words, referring to "including but not limited to", and can be used interchangeably with them. The words "or" and "and" used here refer to the words "and / or", and can be used interchangeably with them, unless the context clearly indicates otherwise. The words "such as" used here refer to the phrase "such as but not limited to", and can be used interchangeably with them.

[0053] It should also be noted that in the apparatus, device and method of the present application, each component or each step can be decomposed and / or recombined. Such decomposition and / or recombination should be regarded as equivalent solutions of the present application.

[0054] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present application. Therefore, the present application is not intended to be limited to the aspects shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

[0055] It should be understood that the qualifiers "first", "second", "third", "fourth", "fifth" and "sixth" used in the description of the embodiments of the present application are only used to more clearly explain the technical solutions and cannot be used to limit the scope of protection of the present application.

[0056] The above description has been given for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although multiple example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions and sub-combinations thereof.

Claims

1. An energy storage system, characterized in that: include: An energy storage tank group, comprising a plurality of energy storage tanks connected in series, and some of the energy storage tanks are filled with isolation fluid; An air energy storage module, which can store and release energy by compression and expansion of air, and is connected to the energy storage tank group, so that when the compressed air enters the energy storage tank group, it pushes the isolation liquid to flow downstream in the upstream of the first flow direction, so as to squeeze the carbon dioxide in the energy storage tank located downstream of the isolation liquid; A carbon dioxide energy storage module is capable of storing and releasing energy by utilizing the phase change of the carbon dioxide. The carbon dioxide energy storage module is connected to the energy storage tank group so that when the carbon dioxide enters the energy storage tank group, it pushes the isolation liquid to flow upstream from the downstream in the first flow direction to squeeze the compressed air in the energy storage tank located upstream of the isolation liquid.

2. The energy storage system according to claim 1, characterized in that: The multiple energy storage tanks connected in series include a first energy storage tank, a second energy storage tank, and a plurality of intermediate energy storage tanks located between the first energy storage tank and the second energy storage tank, the first energy storage tank is connected to the air energy storage module, the second energy storage tank is connected to the carbon dioxide energy storage module, and each of the intermediate energy storage tanks is connected to the air energy storage module and the carbon dioxide energy storage module.

3. The energy storage system according to claim 1, characterized in that: The energy storage tank group includes a first energy storage tank, a second energy storage tank, and a plurality of intermediate energy storage tanks located between the first energy storage tank and the second energy storage tank. The first energy storage tank is connected to the air energy storage module, and the second energy storage tank is connected to the carbon dioxide energy storage module.

4. The energy storage system according to claim 2 or 3, characterized in that: In a first state where the compressed air does not enter the energy storage tank group, the isolation liquid is located in the first energy storage tank; in a second state where the carbon dioxide does not enter the energy storage tank group, the isolation liquid is located in the second energy storage tank.

5. The energy storage system according to claim 1, characterized in that: An anti-stick coating is provided inside the energy storage tank to prevent the isolation fluid from adhering to the inner wall of the energy storage tank.

6. The energy storage system according to claim 1, characterized in that: The isolation fluid is lubricating oil that is incompatible with the compressed air and the carbon dioxide.

7. The energy storage system according to claim 5, characterized in that: The material of the anti-stick coating is polyethylene or polytetrafluoroethylene.

8. The energy storage system according to claim 1, characterized in that: The cross-sectional shape of the energy storage tank is circular.

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