A Carnot battery system coupling a transcritical Rankine cycle with a carbon dioxide heat pump

Abstract

The present invention relates to a Carnot battery system that couples a transcritical Rankine cycle with a carbon dioxide heat pump, belonging to the field of energy storage technology. The system comprises a transcritical carbon dioxide cycle, a molten salt cycle, and a transcritical water vapor Rankine cycle, and implements three operating modes: a rated mode, a charging mode, and a power generation mode. In the rated mode, the transcritical carbon dioxide cycle, the molten salt cycle, and the transcritical water vapor Rankine cycle operate simultaneously, achieving both charging and power generation. In the charging mode, the transcritical water vapor Rankine cycle does not operate, and the system absorbs excess electricity and converts it into thermal energy for storage. In the power generation mode, the transcritical carbon dioxide cycle does not operate, and the thermal energy stored in the system is converted back into electrical energy. The system of the present invention has a maximum round-trip efficiency of 66.27%, addressing the problems of conventional Carnot battery systems, such as low round-trip efficiency, small thermal storage capacity due to low thermal storage temperature, and high energy loss due to temperature mismatch between the thermodynamic cycle and the thermal storage medium.

Description

Technical Field

[0001] The present invention belongs to the field of energy storage technology, and specifically relates to a novel high-temperature Carnot battery energy storage system that couples a transcritical carbon dioxide cycle with a transcritical water vapor Rankine cycle and adopts dual heat storage working fluids. Background Art

[0002] Carnot batteries, also known as heat pump energy storage, use surplus electricity to drive the charging process, storing the electricity as heat. When electricity is needed, the stored heat energy drives a thermodynamic cycle to generate electricity, achieving power conversion. Conventional Carnot battery systems that use the Rankine cycle for power generation generally have low evaporation temperatures, resulting in low power generation efficiency. The water vapor Rankine cycle, however, is limited by the evaporation temperature of water and operates at relatively low temperatures, typically around 310-337°C. This significantly limits the round-trip efficiency of the Carnot battery system. Organic Rankine cycles, on the other hand, are limited by conventional refrigerants, hydrocarbons, and siloxanes, with a maximum operating temperature of only around 300°C, resulting in low efficiency. The transcritical water vapor Rankine cycle is widely used in coal-fired and nuclear power plants for its high efficiency, energy conservation, and environmental friendliness. The high-temperature, high-pressure steam entering the turbine expands and produces work, resulting in higher power generation efficiency.

[0003] The temperature matching of the thermodynamic cycle and the heat storage medium is a key issue in improving the performance of the Carnot battery system. The efficiency of the resistance heater used in the charging process is low, and the maximum efficiency of the resistance heater is about 0.95, which means that the heat generated by consuming a large amount of electricity cannot be fully utilized, the heat loss is large, and the matching is poor. An alternative option is to use a heat pump cycle for the charging process. The performance coefficient of the heat pump is generally greater than 1. Among them, the transcritical carbon dioxide heat pump cycle has greater application potential. The natural working fluid carbon dioxide has the advantages of low cost, environmental protection, non-flammability and high heat transfer performance. By utilizing the heat transfer characteristics of the working fluid in the supercritical and subcritical states, the transcritical carbon dioxide cycle enables the charging and power generation cycles to have good temperature matching with the heat storage medium.

[0004] On the other hand, neither sensible nor latent heat storage alone can provide a good thermal match with subcritical cycles. Pressurized water thermal storage is only suitable for medium- and low-temperature thermal energy storage. As the storage temperature increases, the tank wall thickness increases, reducing cost-effectiveness. Molten salt is a common thermal storage medium in high-temperature thermal storage. It has excellent thermal stability and heat transfer capabilities, but its high melting point, approximately 221°C, limits its thermal storage capacity. Summary of the Invention

[0005] In order to solve the problems of low round-trip efficiency of conventional Carnot battery systems and temperature mismatch between the thermodynamic cycle and the heat storage medium, the present invention provides a Carnot battery system coupled with a transcritical Rankine cycle and a carbon dioxide heat pump.

[0006] A Carnot battery system coupled with a transcritical Rankine cycle and a carbon dioxide heat pump comprises a transcritical carbon dioxide cycle loop, a molten salt cycle loop, and a transcritical water vapor Rankine cycle loop;

[0007] The transcritical carbon dioxide circulation loop is composed of an evaporator 1, a first preheater 2, a second preheater 3, a compressor 4, a first heat exchanger 5, a second heat exchanger 6 and a carbon dioxide turbine 7;

[0008] The outlet of the carbon dioxide side of the evaporator 1 is connected in series to the low-temperature end side of the first preheater 2, the low-temperature end side of the second preheater 3, and the inlet of the compressor 4. The outlet of the compressor 4 is connected in series to the carbon dioxide side of the first heat exchanger 5 and the high-temperature end side of the second preheater 3. The outlet of the high-temperature end of the second preheater 3 is divided into two paths, one of which is connected in series to the high-temperature section side of the first preheater 2, and the other is connected in series to the carbon dioxide side of the second heat exchanger 6. The outlet of the carbon dioxide side of the second heat exchanger 6 and the outlet of the high-temperature section of the first preheater 2 are connected in parallel to the inlet of the carbon dioxide turbine 7. The outlet of the carbon dioxide turbine 7 is connected to the inlet of the carbon dioxide side of the evaporator 1.

[0009] The molten salt circulation loop is composed of a low-temperature molten salt tank 8, a first molten salt pump 9, a molten salt side of a first heat exchanger 5, a high-temperature molten salt tank 10, a second molten salt pump 11, a molten salt side of a water preheater 16, a molten salt side of a steam generator 17, a molten salt side of a superheater 18, a molten salt side of a first reheater 20, and a molten salt side of a second reheater 21.

[0010] The outlet of the low-temperature molten salt tank 8 is connected in series with the first molten salt pump 9, the molten salt side of the first heat exchanger 5, the high-temperature molten salt tank 10 and the second molten salt pump 11 in sequence; the outlet of the second molten salt pump 11 is divided into two paths, one path is connected in series with the molten salt side of the second reheater 21, the molten salt side of the steam generator 17 and the molten salt side of the first reheater 20, and the other path is connected in series with the molten salt side of the superheater 18, the outlet of the molten salt side of the superheater 18 is connected in parallel with the inlet of the molten salt side of the steam generator 17; the outlet of the molten salt side of the steam generator 17 is connected in parallel with the inlet of the molten salt side of the water preheater 16; the outlet of the molten salt side of the water preheater 16 and the outlet of the molten salt side of the first reheater 20 are connected in parallel with the inlet of the low-temperature molten salt tank 8;

[0011] The transcritical steam Rankine cycle loop is composed of a low-temperature water tank 12, a first water pump 13, a water vapor side of the second heat exchanger 6, a high-temperature water tank 14, a second water pump 15, a water vapor side of a water preheater 16, a water vapor side of a steam generator 17, a water vapor side of a superheater 18, a high-pressure turbine 19, a water vapor side of a first reheater 20, a water vapor side of a second reheater 21, a low-pressure turbine 22, a condenser 23, and a third water pump 24, which are connected in series in sequence.

[0012] The Carnot battery system implements three operating modes, namely, a rating mode, a charging mode, and a power generation mode.

[0013] Further technical requirements are as follows:

[0014] The rated mode is that the transcritical carbon dioxide circulation loop, the molten salt circulation loop and the transcritical water vapor Rankine cycle loop operate simultaneously to achieve charging and power generation.

[0015] In the charging mode, the transcritical water vapor Rankine cycle does not work, and the system absorbs excess electricity and converts it into thermal energy for storage.

[0016] In the power generation mode, the transcritical carbon dioxide circulation loop does not work, and the thermal energy stored in the system is converted into electrical energy again to meet power demand and peak regulation.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are embodied in the following aspects:

[0018] 1. This invention combines a conventional transcritical carbon dioxide heat pump cycle system with a transcritical water vapor Rankine cycle, and for the first time proposes a novel dual-heat storage medium high-temperature Carnot battery system for energy storage. This system addresses the problems of low round-trip efficiency in conventional Carnot battery systems, low heat storage capacity due to low heat storage temperature, and high energy loss due to temperature mismatch between the thermodynamic cycle and the heat storage medium. When the system's main steam temperature and pressure are 540°C and 24.1MPa, respectively, the transcritical water vapor Rankine cycle's power generation efficiency is 41.46%. When the system's carbon dioxide evaporation temperature is 10°C, the transcritical carbon dioxide heat pump's coefficient of performance is 1.6, and the high-temperature Carnot battery system's round-trip efficiency can reach a maximum of 66.27%, a significant improvement over the conventional Carnot battery system's round-trip efficiency of around 60%.

[0019] 2. This invention features a unique dual-tank molten salt and dual-tank water energy storage solution. Molten salt thermal storage is one of the most mature sensible heat storage technologies currently available. It offers advantages such as low vapor pressure, high thermal stability, and high compatibility with steel. However, its high melting point, approximately 221°C, limits its application in medium- and low-temperature thermal storage. To address this challenge, this invention uses pressurized water instead of molten salt to store medium- and low-temperature thermal energy. A transcritical CO2 heat pump cycle converts electrical energy into thermal energy and stores it in the thermal storage medium. The outlet temperature of compressor 4 reaches 570°C. To further enhance the temperature matching between the cycle and the thermal storage medium and reduce throttling losses in the heat pump, the high- and low-temperature ends of the heat pump are separated, releasing heat to the molten salt and water working fluids, respectively. In this invention, the molten salt absorbs heat from the high-temperature end of the heat pump through the first heat exchanger 5 and is heated to 560°C. The high-temperature molten salt working fluid is stored in the high-temperature molten salt tank 10 and subsequently used to drive a transcritical water vapor Rankine cycle for power generation. After the high-temperature end releases heat to the molten salt working fluid, the low-temperature end continues to exchange heat with water through the second heat exchanger 6, further utilizing the thermal energy of the CO2. The water absorbs the heat from the low-temperature end and is heated to a temperature of 150-280°C. This system's unique dual thermal storage medium of molten salt and water achieves cascaded heat storage, fully utilizing the heat of the CO2 working fluid while avoiding the drawback of traditional transcritical CO2 heat pumps, which suffers from excessively high condensing temperatures and results in a reduced COP.

[0020] 3. Water has the following advantages as a working medium for heat storage, heat transfer, and transcritical Rankine cycle: (1) Molten salt stores high-quality heat, while water stores medium- and low-quality heat. The stepped heat storage configuration strengthens the temperature matching between the thermodynamic cycle and the heat storage medium. Compared with the conventional transcritical carbon dioxide heat pump system using molten salt for heat storage, in which carbon dioxide passes through the throttle valve and generates huge irreversible losses, the carbon dioxide in the present invention is cooled by molten salt to a temperature of 340-370°C, and then further cooled by water to a temperature of 45-160°C, which greatly reduces the throttling loss. (2) The use of water as a working medium for storing medium and low-temperature heat reduces the use of molten salt, reduces the cost of heat storage, and improves economic benefits. (3) After storing heat, water is directly fed into the transcritical Rankine cycle as a power cycle medium, avoiding the additional investment cost of using a molten salt / water heat exchanger and reducing the irreversible loss caused by secondary heat exchange. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the system structure of the present invention;

[0022] Figure 2 This is the workflow diagram for the charging working mode;

[0023] Figure 3 This is the working flow diagram of the power generation working mode;

[0024] Figure 4 is the temperature entropy diagram corresponding to each state point of the system;

[0025] Figure 5 is the tq diagram corresponding to each heat exchanger in the system.

[0026] superior Figure 1-4 Sequence number: evaporator 1, first preheater 2, second preheater 3, compressor 4, first heat exchanger 5, second heat exchanger 6, carbon dioxide turbine 7, low-temperature molten salt tank 8, first molten salt pump 9, high-temperature molten salt tank 10, second molten salt pump 11, low-temperature water tank 12, first water pump 13, high-temperature water tank 14, second water pump 15, water preheater 16, steam generator 17, superheater 18, high-pressure turbine 19, first reheater 20, second reheater 21, low-pressure turbine 22, condenser 23 and third water pump 24. DETAILED DESCRIPTION

[0027] The present invention will be further described below through embodiments with reference to the accompanying drawings.

[0028] Example

[0029] See also Figure 1 A Carnot battery system coupled with a transcritical Rankine cycle and a carbon dioxide heat pump includes a transcritical carbon dioxide cycle loop, a molten salt cycle loop and a transcritical water vapor Rankine cycle loop.

[0030] The transcritical carbon dioxide circulation loop is composed of an evaporator 1 , a first preheater 2 , a second preheater 3 , a compressor 4 , a first heat exchanger 5 , a second heat exchanger 6 and a carbon dioxide turbine 7 .

[0031] The outlet of the carbon dioxide side of the evaporator 1 is connected in series with the low-temperature end side of the first preheater 2, the low-temperature end side of the second preheater 3 and the inlet of the compressor 4. The outlet of the compressor 4 is connected in series with the carbon dioxide side of the first heat exchanger 5 and the high-temperature end side of the second preheater 3. The outlet of the high-temperature end of the second preheater 3 is divided into two paths, one path is connected in series with the high-temperature section side of the first preheater 2, and the other path is connected in series with the carbon dioxide side of the second heat exchanger 6. The outlet of the carbon dioxide side of the second heat exchanger 6 and the outlet of the high-temperature section of the first preheater 2 are connected in parallel to the inlet of the carbon dioxide turbine 7. The outlet of the carbon dioxide turbine 7 is connected to the inlet of the carbon dioxide side of the evaporator 1.

[0032] The molten salt circulation loop is composed of a low-temperature molten salt tank 8, a first molten salt pump 9, the molten salt side of the first heat exchanger 5, a high-temperature molten salt tank 10, a second molten salt pump 11, the molten salt side of the water preheater 16, the molten salt side of the steam generator 17, the molten salt side of the superheater 18, the molten salt side of the first reheater 20 and the molten salt side of the second reheater 21.

[0033] The outlet of the low-temperature molten salt tank 8 is connected in series with the first molten salt pump 9, the molten salt side of the first heat exchanger 5, the high-temperature molten salt tank 10 and the second molten salt pump 11; the outlet of the second molten salt pump 11 is divided into two paths, one path is connected in series with the molten salt side of the second reheater 21, the molten salt side of the steam generator 17 and the molten salt side of the first reheater 20, and the other path is connected in series with the molten salt side of the superheater 18, and the outlet of the molten salt side of the superheater 18 is connected in parallel with the inlet of the molten salt side of the steam generator 17; the outlet of the molten salt side of the steam generator 17 is connected in parallel with the inlet of the molten salt side of the water preheater 16; the outlet of the molten salt side of the water preheater 16 and the outlet of the molten salt side of the first reheater 20 are connected in parallel to the inlet of the low-temperature molten salt tank 8.

[0034] The transcritical water vapor Rankine cycle loop is composed of a low-temperature water tank 12, a first water pump 13, the water vapor side of the second heat exchanger 6, a high-temperature water tank 14, a second water pump 15, the water vapor side of the water preheater 16, the water vapor side of the steam generator 17, the water vapor side of the superheater 18, a high-pressure turbine 19, the water vapor side of the first reheater 20, the water vapor side of the second reheater 21, the low-pressure turbine 22, the condenser 23 and the third water pump 24, which are connected in series in sequence.

[0035] The present invention has three working modes, namely, rated mode, charging mode and power generation mode.

[0036] The rated mode is that the transcritical carbon dioxide cycle loop, molten salt cycle loop and transcritical water vapor Rankine cycle loop operate simultaneously to achieve charging and power generation.

[0037] In the charging mode, the transcritical water vapor Rankine cycle does not work, and the system absorbs excess electricity and converts it into thermal energy for storage.

[0038] In the power generation mode, the transcritical carbon dioxide circulation loop does not work, and the thermal energy stored in the system is converted into electrical energy again to meet power demand and peak regulation.

[0039] The specific working principles of the three working modes are described as follows:

[0040] (1) Rated mode

[0041] See also Figure 1The transcritical CO2 circulation loop and the transcritical steam Rankine cycle operate simultaneously, with the first molten salt pump 9, the second molten salt pump 11, the first water pump 13, the second water pump 15, and the third water pump 24 in operation. The CO2 at the outlet of evaporator 1 is preheated twice before being compressed and heated in compressor 4. The CO2 at the outlet of compressor 4 releases heat to the molten salt and water, then passes through the liquid CO2 turbine 7 to perform work before returning to evaporator 1. After absorbing heat from the CO2, the molten salt and water enter the high-temperature molten salt tank 10 and high-temperature water tank 14, respectively. The high-temperature molten salt at the top of the high-temperature molten salt tank 10 enters the second reheater 21, superheater 18, steam generator 17, water preheater 16, and first reheater 20, respectively, where it releases heat to the working water in the transcritical steam Rankine cycle. The hot water at the top of the high-temperature water tank 14 flows directly into the transcritical steam Rankine cycle as the working medium. After absorbing heat from the molten salt, it enters the high-pressure and low-pressure turbines to perform work. In this mode, the system is used to achieve power dispatchability and peak shaving and valley filling.

[0042] Based on the heat provided by the transcritical CO2 heat pump and the heat absorbed by the transcritical Rankine cycle, there are three operating conditions in rated mode. Case I: The heat provided by the transcritical CO2 cycle exactly equals the heat absorbed by the transcritical water vapor Rankine cycle. The flow rate entering the high-temperature molten salt tank 10 and the high-temperature water tank 14 exactly equals the flow rate out, and the liquid levels in all four tanks remain unchanged. Case II: When the heat provided by the transcritical CO2 cycle exceeds the heat absorbed by the transcritical water vapor Rankine cycle, the flow rate entering the high-temperature molten salt tank 10 and the high-temperature water tank 14 exceeds the flow rate out, causing the liquid level in the high-temperature molten salt tank 10 and the high-temperature water tank 14 to rise, while the liquid level in the low-temperature molten salt tank 8 and the low-temperature water tank 12 to fall. Case III: When the heat provided by the transcritical CO2 cycle is less than the heat absorbed by the transcritical water vapor Rankine cycle, the flow rate entering the high-temperature molten salt tank 10 and the high-temperature water tank 14 is less than the flow rate out, causing the liquid level in the high-temperature molten salt tank 10 and the high-temperature water tank 14 to fall, while the liquid level in the low-temperature molten salt tank 8 and the low-temperature water tank 12 to rise.

[0043] (2) Charging mode

[0044] See also Figure 2, the transcritical water vapor Rankine cycle on the right is not working, and only the transcritical carbon dioxide cycle on the left is working. The first molten salt pump 9 and the first water pump 13 are running. The carbon dioxide working fluid at the outlet of the evaporator 1 passes through the first preheater 2 and the second preheater 3 in sequence, and is compressed into a high-temperature and high-pressure state in the compressor 4. The carbon dioxide working fluid at the outlet of the compressor 4 passes through the first heat exchanger 5 and the second heat exchanger 6 respectively to release heat to the molten salt and water and store the heat in the high-temperature molten salt tank 10 and the high-temperature water tank 14. The carbon dioxide working fluid after heat release passes through the liquid carbon dioxide turbine 7 to further recover the expansion work and then returns to the evaporator 1. In this mode, the system is used to consume excess electricity and convert it into thermal energy for storage.

[0045] (3) Power generation mode

[0046] See also Figure 3 The transcritical CO2 cycle is inoperative, while the second molten salt pump 11, second water pump 15, and third water pump 24 are operational. The high-temperature molten salt working fluid at the top of the high-temperature molten salt tank 10 enters the second reheater 21, superheater 18, steam generator 17, water preheater 16, and first reheater 20, releasing heat to the working water in the transcritical steam Rankine cycle. Hot water at the top of the high-temperature water tank 14 flows directly into the transcritical steam Rankine cycle as the working medium, absorbing the heat of the molten salt working fluid to a supercritical state. It then enters the high-pressure turbine 19 to produce work. The exhaust steam at the outlet of the high-pressure turbine 19 is reheated to high-temperature steam through the first and second reheaters 20, 21, and then enters the low-pressure turbine 22 to expand and produce work. In this mode, the stored thermal energy is converted back into electrical energy to meet power demand and for peak load regulation.

[0047] As can be seen from Table 1, the temperature range of the low-temperature molten salt tank of the Carnot battery system of the present invention is 320°C to 350°C, and the carbon dioxide evaporation temperature is 10°C. Figure 1 The letters in the figure represent the state points of the Carnot battery system of the present invention. The temperature entropy diagram corresponding to each state point can be found in Figure 4When the low-temperature molten salt tank temperature reaches 345°C, the round-trip efficiency of the Carnot battery system reaches a maximum of 66.27%. The thermodynamic parameters at each state point are shown in Table 1. Figure 5 shows the tq diagram of each heat exchanger at maximum round-trip efficiency. Referring to Figure 5(a), state points a" and b" represent the molten salt inlet states of the second reheater 21 and superheater 18, respectively. The high-temperature molten salt works in sequence to heat the second reheater 21, superheater 18, steam generator 17, water preheater 16, and first reheater 20, with their minimum heat exchange temperature differences of 20.0, 20.0, 64.4, 71.8, and 30.2°C, respectively. The corresponding heat exchange capacities are 17.54, 22.80, 45.98, 0.86, and 1.90 MW, respectively. Referring to Figure 5(b), the first preheater 2 accounts for the majority of the heat exchange and has the largest heat exchange temperature difference. State point q represents the state of the carbon dioxide working fluid at compressor outlet 4. The high-temperature carbon dioxide working fluid passes through the first heat exchanger 5 and the second heat exchanger 6, heating the molten salt and water to state points z and d, respectively. Under optimal operating conditions, the minimum heat exchange temperature differences of the first preheater 2, the second preheater 3, the first heat exchanger 5, and the second heat exchanger 6 are 14.0, 10.0, 10.0, and 12.7°C, respectively, and the heat exchange capacities are 115.83, 16.92, 88.23, and 24.90 MW, respectively.

[0048] Table 1. Thermodynamic parameters at each state point at maximum round-trip efficiency

[0049]

[0050]

[0051] It will be easily understood by those skilled in the art that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A Carnot battery system coupling a transcritical Rankine cycle with a carbon dioxide heat pump, characterized by: Including transcritical carbon dioxide circulation loop, molten salt circulation loop and transcritical water vapor Rankine cycle loop; The transcritical carbon dioxide circulation loop is composed of an evaporator (1), a first preheater (2), a second preheater (3), a compressor (4), a first heat exchanger (5), a second heat exchanger (6) and a carbon dioxide turbine (7); The outlet of the carbon dioxide side of the evaporator (1) is connected in series with the low-temperature end side of the first preheater (2), the low-temperature end side of the second preheater (3) and the inlet of the compressor (4); the outlet of the compressor (4) is connected in series with the carbon dioxide side of the first heat exchanger (5) and the high-temperature end side of the second preheater (3); the outlet of the high-temperature end of the second preheater (3) is divided into two paths, one path is connected in series with the high-temperature section side of the first preheater (2), and the other path is connected in series with the carbon dioxide side of the second heat exchanger (6); the outlet of the carbon dioxide side of the second heat exchanger (6) and the outlet of the high-temperature section of the first preheater (2) are connected in parallel with the inlet of the carbon dioxide turbine (7); and the outlet of the carbon dioxide turbine (7) is connected with the inlet of the carbon dioxide side of the evaporator (1); The molten salt circulation loop is composed of a low-temperature molten salt tank (8), a first molten salt pump (9), a molten salt side of a first heat exchanger (5), a high-temperature molten salt tank (10), a second molten salt pump (11), a molten salt side of a water preheater (16), a molten salt side of a steam generator (17), a molten salt side of a superheater (18), a molten salt side of a first reheater (20), and a molten salt side of a second reheater (21); The outlet of the low-temperature molten salt tank (8) is sequentially connected in series with the first molten salt pump (9), the molten salt side of the first heat exchanger (5), the high-temperature molten salt tank (10) and the second molten salt pump (11); the outlet of the second molten salt pump (11) is divided into two paths, one path is sequentially connected in series with the molten salt side of the second reheater (21), the molten salt side of the steam generator (17) and the molten salt side of the first reheater (20), and the other path is sequentially connected in series with the molten salt side of the superheater (18), the outlet of the molten salt side of the superheater (18) is connected in parallel with the inlet of the molten salt side of the steam generator (17); the outlet of the molten salt side of the steam generator (17) is connected in parallel with the inlet of the molten salt side of the water preheater (16); the outlet of the molten salt side of the water preheater (16) and the outlet of the molten salt side of the first reheater (20) are connected in parallel with the inlet of the low-temperature molten salt tank (8); The transcritical water vapor Rankine cycle loop is composed of a low-temperature water tank (12), a first water pump (13), a water vapor side of a second heat exchanger (6), a high-temperature water tank (14), a second water pump (15), a water vapor side of a water preheater (16), a water vapor side of a steam generator (17), a water vapor side of a superheater (18), a high-pressure turbine (19), a water vapor side of a first reheater (20), a water vapor side of a second reheater (21), a low-pressure turbine (22), a condenser (23) and a third water pump (24) connected in series in sequence; The Carnot battery system implements three operating modes, namely, a rating mode, a charging mode, and a power generation mode.

2. The Carnot battery system of claim 1, wherein: The rated mode is that the transcritical carbon dioxide circulation loop, the molten salt circulation loop and the transcritical water vapor Rankine cycle loop operate simultaneously to achieve charging and power generation.

3. The Carnot battery system of claim 1, wherein: In the charging mode, the transcritical water vapor Rankine cycle does not work, and the system absorbs excess electricity and converts it into thermal energy for storage.

4. The Carnot battery system of claim 1, wherein: In the power generation mode, the transcritical carbon dioxide circulation loop does not work, and the thermal energy stored in the system is converted into electrical energy again to meet power demand and peak regulation.

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