A compressed carbon dioxide energy storage system integrating solar concentrating and splitting photovoltaics and thermal energy

Abstract

The present invention relates to a compressed carbon dioxide energy storage system integrating solar concentrating and spectrophotovoltaic-thermal, comprising a solar concentrating and spectrophotovoltaic-thermal unit and a compressed carbon dioxide energy storage unit. The solar concentrating and spectrophotovoltaic-thermal unit comprises a concentrating device, a spectrophotovoltaic-thermal device and a multi-junction solar cell group, which separates sunlight into spectra of different wavelengths through concentration and spectrophotometry technology, and the multi-junction solar cell group can efficiently absorb and convert spectral energy of different wavelengths. The compressed carbon dioxide energy storage unit comprises a compression device, an expansion device, a gas storage device and a heat storage device, which can efficiently store and release energy to achieve a stable power supply. The system is also equipped with a heat recovery device for recovering heat energy that is not fully utilized, thereby further improving the overall efficiency. The present invention effectively solves the problems of low efficiency and intermittent nature of photovoltaic power generation, significantly improves the utilization rate of solar energy and the energy storage capacity of the system, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the field of solar photovoltaic power generation and energy storage technology, and relates to an integrated system utilizing spectral separation and compressed carbon dioxide energy storage technology. Specifically, it is a compressed carbon dioxide energy storage system integrating solar concentrating and spectral splitting photovoltaics and thermal energy, which improves photovoltaic power generation efficiency and energy storage capacity by optimizing energy utilization paths. Background Art

[0002] As an important form of clean and renewable energy, the large-scale application of photovoltaic power generation is one of the important ways to address climate change and achieve carbon neutrality. However, the current photovoltaic power generation technology still faces many challenges in practical application, which to some extent limits its large-scale application:

[0003] First, current photovoltaic power generation efficiency is far below the Landsberg limit. According to the second law of thermodynamics, the theoretical maximum efficiency of a single-junction solar cell, known as the Landsberg limit, is approximately 29.43%. However, the actual efficiency of commercial photovoltaic cells currently falls far short of this theoretical limit. For example, the maximum efficiency of single-crystalline silicon cells under laboratory conditions is approximately 26.7%, still a significant gap from the theoretical limit. This efficiency bottleneck severely restricts the economic viability and large-scale application of photovoltaic power generation.

[0004] Secondly, the intermittency of solar energy poses a significant challenge to large-scale energy storage. Because solar energy availability is affected by factors such as the diurnal cycle, seasonal variations, and weather conditions, its power output is unstable and intermittent. This conflicting characteristic collides with the grid's demand for stable and reliable power supply, necessitating the use of large-scale energy storage systems to balance supply and demand. However, existing energy storage technologies still struggle to meet the demands of large-scale photovoltaic power generation in terms of cost, capacity, and efficiency. This has led to widespread curtailment of solar power worldwide. During peak photovoltaic power generation periods, the grid is unable to fully absorb the excess power, forcing large amounts of photovoltaic power to be abandoned, resulting in a significant waste of energy resources.

[0005] Furthermore, existing energy storage systems primarily consist of two phases: charging and discharging. During the charging phase, solar photovoltaic cells provide power to the energy storage system. Solar photovoltaic cells operate by directly converting light energy into electricity through the photovoltaic effect. However, there are two main types of energy losses during this energy conversion process: first, photons with energies below the cell's band gap energy cannot be absorbed and utilized by the cell and are instead converted into heat; second, the excess energy in photons with energies above the cell's band gap energy is also dissipated as waste heat (thermalization). This lost spectral energy is converted into heat, causing the cell temperature to rise, which in turn reduces photovoltaic efficiency and battery life. Existing studies have shown that for every 1°C increase in photovoltaic cell temperature, its efficiency decreases by approximately 0.5%.

[0006] The technical bottleneck of energy storage systems has also seriously restricted the widespread application of photovoltaic power generation. Conventional battery energy storage technology is limited by factors such as capacity, charging and discharging speed, lifespan and cost, making it difficult to meet large-scale energy storage needs. Although pumped storage has high efficiency and large-capacity energy storage capabilities, it is limited by geographical conditions and is not suitable for all regions. Although flywheel energy storage technology has high power density and fast response capabilities, it has shortcomings in energy density and long-term energy storage stability. In addition, existing photovoltaic power generation systems often ignore the use of low-grade thermal energy. In the photovoltaic power generation process, a large amount of solar energy is converted into heat, but this part of the heat energy is usually directly discharged into the environment, resulting in energy waste.

[0007] In summary, current photovoltaic power generation technology still faces certain technical bottlenecks in terms of efficiency and energy storage, which restrict its large-scale application and promotion. Improving photovoltaic power generation efficiency, solving the problem of solar intermittency, achieving large-scale and efficient energy storage, fully utilizing various forms of solar energy, and reducing system costs are the technical challenges that urgently need to be addressed in the current photovoltaic power generation technology. Summary of the Invention

[0008] (1) Purpose of the invention

[0009] In response to the defects and shortcomings of existing photovoltaic power generation systems, such as low efficiency, difficulty in energy storage, and insufficient energy utilization, and to address at least one of these and other technical issues in the existing technology, the present invention proposes an integrated solar concentrating, spectrophotovoltaic-thermal compressed carbon dioxide energy storage system based on advanced spectrometry technology and photovoltaic cell technology and the unique characteristics of carbon dioxide. This system maximizes the use of uninterrupted solar power, solves the problem of spectral energy loss in photovoltaic cell energy conversion, and achieves stable solar energy output through efficient energy storage and discharge processes. By separating the solar spectrum below the band gap energy of the photovoltaic cell and converting it into thermal energy, the present invention optimizes the energy utilization path by combining it with a compressed carbon dioxide energy storage system, significantly improving the overall efficiency and economy of the system and ensuring the feasibility and reliability of photovoltaic power generation in large-scale applications.

[0010] (2) Technical solution

[0011] In order to achieve the purpose of the invention and solve the technical problems, the present invention adopts the following technical solutions:

[0012] A compressed carbon dioxide energy storage system integrating solar concentrating and splitting photovoltaics and thermal energy is used to improve solar energy utilization efficiency and achieve large-scale energy storage. It includes at least one solar concentrating and splitting photovoltaics and thermal energy unit and one compressed carbon dioxide energy storage unit. Specifically:

[0013] The solar concentrating and splitting photovoltaic-thermal unit comprises at least a concentrating device, a splitting device, and a multi-junction solar cell array, wherein: the concentrating device is used to collect and focus sunlight; the splitting device is arranged downstream of the optical path of the concentrating device, and is used to separate the focused sunlight into spectra of different wavelengths; the multi-junction solar cell array is arranged downstream of the optical path of the splitting device, and comprises a plurality of narrow-bandgap photovoltaic cells connected in series, and is used to absorb and convert spectral energy of different wavelengths and convert light energy into electrical energy;

[0014] The compressed carbon dioxide energy storage unit includes at least a compression device, an expansion device, a gas storage device, and a heat storage device, wherein: the compression device is used to compress carbon dioxide based on solar photovoltaic power, and includes at least a first compressor unit and a second compressor unit, both of which have power input ends electrically connected to the output end of the multi-junction solar cell array; the expansion device includes at least a first expander unit and a second expander unit, which are used to generate electricity by expanding carbon dioxide; the gas storage device includes at least a high-pressure gas storage tank and a low-pressure gas storage tank, which are used to store carbon dioxide in high-pressure and low-pressure states, respectively; the heat storage device includes at least a first compression heat storage heat exchanger, a second compression heat storage heat exchanger, a first solar heat storage heat exchanger, and a second solar heat storage heat exchanger, wherein: the first and second compression heat storage heat exchangers are respectively used to store heat energy generated by the first and second compressor units during the compression process; the first and second solar heat storage heat exchangers are both arranged downstream of the optical path of the spectrometer and are both used to collect and store heat energy converted from the spectral portion whose spectral energy is lower than the minimum band gap energy of the multi-junction solar cell array, and transfer the heat energy to the first and second expansion units respectively during the energy release process;

[0015] And among them:

[0016] The air inlet of the first compressor unit is connected to the outlet of the low-pressure gas storage tank through a pipeline, and the air outlet thereof is connected to the inlet of the high-pressure gas storage tank through a pipeline that passes through the hot side of the first compression heat storage heat exchanger, the second compressor unit, and the hot side of the second compression heat storage heat exchanger in sequence;

[0017] The outlet of the high-pressure gas storage tank is connected to the inlet of the low-pressure gas storage tank through a pipeline that passes through the cold side of the second compression heat storage heat exchanger, the cold side of the first solar heat storage heat exchanger, the first expansion unit, the cold side of the first compression heat storage heat exchanger, the cold side of the second solar heat storage heat exchanger, and the second expansion unit.

[0018] (3) Technical effects

[0019] Compared with the existing technology, the integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system of the present invention has the following beneficial and significant technical effects:

[0020] (1) The present invention achieves efficient solar energy conversion and large-scale energy storage by combining solar concentrating and spectrophotovoltaic technology with compressed carbon dioxide energy storage technology. By adopting a multi-junction solar cell group, it can effectively absorb and convert spectral energy of different wavelengths, greatly improving the photoelectric conversion efficiency. The multi-junction photovoltaic cell replaces the single-junction cell. The structural design of the multi-junction cell group enables it to utilize a wider solar spectrum, and its energy conversion efficiency is significantly improved compared with the traditional single-junction photovoltaic cell. In addition, the use of a spectrometer to separate the focused sunlight into spectra of different wavelengths not only optimizes the absorption of the photovoltaic cell, but also uses a concentrating separation method to separate the solar spectrum below the minimum band gap energy in the multi-junction cell. The separated solar spectrum is converted into heat energy and stored in the solar thermal energy storage device to increase the inlet air temperature of the expansion unit during the discharge process, further improving the overall energy utilization rate.

[0021] (2) The present invention has a highly efficient heat recovery capability. Since the working fluid exiting the expander still has a relatively high temperature due to the increased inlet temperature of the expander unit, the system is equipped with first and second heat recovery devices, which can recover the heat energy that is not fully utilized during the expansion process and re-transfer the recovered heat energy to the thermal energy storage system. By using the heat recovery device, the system can minimize heat energy loss during the circulation process, further improving the thermal efficiency and overall energy efficiency of the system.

[0022] (3) This invention effectively solves the intermittent problem of solar power generation. By integrating a compressed carbon dioxide energy storage unit, the system can store energy when there is sufficient solar energy and discharge it when there is insufficient sunlight or at night, thus achieving a stable power supply. Compressed carbon dioxide energy storage technology has high energy density and efficiency, and can significantly improve energy storage capacity without increasing system complexity, ensuring the reliable operation of the system under various operating conditions.

[0023] (4) The invented integrated solar concentrating and spectral photovoltaic-thermal compressed carbon dioxide energy storage system, through the synergistic effect of multi-junction solar cell arrays, compressed carbon dioxide energy storage units, thermal energy management systems and heat recovery devices, improves the photovoltaic efficiency and power generation of the CCES system during the discharge phase, thereby improving the overall utilization efficiency of solar energy, and has significant technological progress and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1Shown is a schematic diagram of the integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system of the present invention;

[0026] Figure 2 The figure shows the relationship between the round trip efficiency and the concentration ratio of the system under different cell materials when the system adopts single-junction cells;

[0027] Figure 3 Shown are the round-trip efficiency, the ratio of turbine output power to photovoltaic power generation, and the ratio of heat energy absorbed by CO2 from STES1 and STES2. R ST Schematic diagram of the relationship between;

[0028] Figure 4 The figure shows the relationship between the round-trip efficiency of the system and the outlet pressure of the first compressor unit 1 and the outlet pressure of the first expansion unit T1;

[0029] Figure 5 Shown is a schematic diagram of the relationship between the system round-trip efficiency (a) and the total solar spectrum utilization efficiency (b) and the concentration ratio in a multi-junction cell system.

[0030] Description of reference numerals:

[0031] Concentrating solar splitter photovoltaic-thermal unit OS, narrow bandgap photovoltaic cell Cell, first compressor unit C1, second compressor unit C2, first expansion unit T1, second expansion unit T2, high-pressure gas storage tank HPT, low-pressure gas storage tank LPT, first compression heat storage heat exchanger TES1, second compression heat storage heat exchanger TES2, first solar heat storage heat exchanger STES1, second solar heat storage heat exchanger STES2. DETAILED DESCRIPTION

[0032] For a better understanding of the present invention, the present invention will be further described below with reference to the embodiments. In the accompanying drawings, the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The described embodiments are only some embodiments of the present invention, rather than all embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0033] In response to the defects and shortcomings of existing photovoltaic power generation systems, such as low efficiency, difficulty in energy storage, and insufficient energy utilization, and to address at least one of these and other technical issues in the existing technology, the present invention proposes an integrated solar concentrating, spectrophotovoltaic-thermal compressed carbon dioxide energy storage system based on advanced spectrometry technology and photovoltaic cell technology and the unique characteristics of carbon dioxide. This system maximizes the use of uninterrupted solar power, solves the problem of spectral energy loss in photovoltaic cell energy conversion, and achieves stable solar energy output through efficient energy storage and discharge processes. By separating the solar spectrum below the band gap energy of the photovoltaic cell and converting it into thermal energy, the present invention optimizes the energy utilization path by combining it with a compressed carbon dioxide energy storage system, significantly improving the overall efficiency and economy of the system and ensuring the feasibility and reliability of photovoltaic power generation in large-scale applications.

[0034] Example 1

[0035] As a specific example, Figure 1 As shown, the integrated solar concentrating spectrophotovoltaic-thermal compressed carbon dioxide energy storage system of the present invention is used to improve the efficiency of solar energy utilization and realize large-scale energy storage, including a solar concentrating spectrophotovoltaic-thermal unit and a compressed carbon dioxide energy storage unit.

[0036] The solar concentrating and splitting photovoltaic-thermal unit (OS) of the present invention comprises at least a concentrator, a splitter, and a multi-junction solar cell array. The concentrator collects and focuses sunlight; the splitter, located downstream of the concentrator's optical path, separates the focused sunlight into spectra of different wavelengths; and the multi-junction solar cell array, located downstream of the splitter's optical path, comprises multiple series-connected narrow-bandgap photovoltaic cells, which absorb and convert spectral energy of different wavelengths and convert light energy into electrical energy.

[0037] The compressed carbon dioxide energy storage unit of the present invention comprises a compression device, an expansion device, a gas storage device, and a heat storage device. The compression device, used to compress carbon dioxide using solar photovoltaic power, comprises at least a first compressor unit C1 and a second compressor unit C2, both of which have power inputs electrically connected to the output of a multi-junction solar cell array. The expansion device comprises at least a first expander unit T1 and a second expander unit T2, used to generate electricity by expanding carbon dioxide. The gas storage device comprises a high-pressure gas tank HPT and a low-pressure gas tank LPT, which are used to store carbon dioxide at high and low pressures, respectively.

[0038] The heat storage device of the present invention includes a first compression heat storage heat exchanger TES1, a second compression heat storage heat exchanger TES2, a first solar heat storage heat exchanger STES1, and a second solar heat storage heat exchanger STES2. The first compression heat storage heat exchanger TES1 and the second compression heat storage heat exchanger TES2 are respectively used to store the heat energy generated by the first compressor unit C1 and the second compressor unit C2 during the compression process. The first and second solar heat storage heat exchangers STES2 are both arranged downstream of the optical path of the spectrometer and are both used to collect and store heat energy converted from the spectral portion with spectral energy lower than the minimum band gap energy of the multi-junction solar cell group. During the energy release process, the heat energy is transferred to the first expander unit T1 and the second expander unit T2, respectively.

[0039] In addition, the air inlet of the first compressor unit C1 is connected to the outlet of the low-pressure gas storage tank LPT through a pipeline, and its exhaust port is connected to the inlet of the high-pressure gas storage tank HPT through a pipeline, in sequence, through the hot side of the first compression heat storage heat exchanger TES1, the second compressor unit C2, and the hot side of the second compression heat storage heat exchanger TES2; the outlet of the high-pressure gas storage tank HPT is connected to the inlet of the low-pressure gas storage tank LPT through a pipeline, in sequence, through the cold side of the second compression heat storage heat exchanger TES2, the cold side of the first solar heat storage heat exchanger STES1, the first expansion unit T1, the cold side of the first compression heat storage heat exchanger TES1, the cold side of the second solar heat storage heat exchanger STES2, and the second expansion unit T2.

[0040] The basic working principle of the integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system of the present invention is as follows:

[0041] First, the solar concentrating and spectrophotovoltaic-thermal unit collects and focuses sunlight through a concentrating device. The focused sunlight enters the spectrometer, which separates the focused sunlight into spectra of different wavelengths. Subsequently, these spectra of different wavelengths are respectively guided to the multi-junction solar cell array. The multi-junction solar cell array includes multiple narrow-bandgap photovoltaic cells with different bandgap energies. These photovoltaic cells are arranged in series to absorb and convert spectral energy of different wavelengths, and efficiently convert light energy into electrical energy. Part of the generated electricity is directly output for use, and the other part is used to drive the compressed carbon dioxide energy storage unit.

[0042] The compressed CO2 energy storage unit comprises a compression device, an expansion device, a gas storage device, and a heat storage device. During the charging phase, electrical energy drives the compression device to compress the CO2. The low-pressure CO2 in the low-pressure gas storage tank (LPT) is compressed into a high-temperature, high-pressure gas by the first compressor unit (C1). The gas then enters the first compression and heat storage heat exchanger (TES1). In TES1, the CO2's thermal energy is transferred to a heat storage medium, which can be hot solar salts, Duratherm HF oil, or a combination of these, depending on the CO2 inlet temperature. The cooled CO2 then enters the second compressor unit (C2), where it is converted back into a high-temperature gas and its pressure is further increased. The CO2 from the second compressor unit (C2) enters the second compression and heat storage heat exchanger (TES2), where its heat is transferred to a heat transfer medium. The cooled CO2 from the second compression and heat storage heat exchanger (TES2) is then stored in the high-pressure gas storage tank (HPT), completing the charging process.

[0043] During the energy release phase, the CO2 in the high-pressure storage tank HPT first enters the second compression heat storage heat exchanger TES2 to absorb heat from the heat transfer medium. The heated CO2 then enters the first expander T1 to expand and generate power. The CO2 from the first expander T1 enters the first compression heat storage heat exchanger TES1 for reheating before entering the second expander T2 for further expansion and power generation. The CO2 leaving the second expander T2, at a pressure close to atmospheric pressure, enters the low-pressure storage tank LPT, completing the cycle.

[0044] The system also features a heat recovery unit, comprising a first heat recovery unit HR1 and a second heat recovery unit HR2, to recover unused heat energy from the expansion process. The first heat recovery unit HR1 is installed in the pipeline connecting the first expander unit T1 and the first compression heat storage heat exchanger TES1, while the second heat recovery unit HR2 is installed in the pipeline connecting the second expander unit T2 and the low-pressure gas storage tank LPT. This heat recovery unit further reduces heat loss and improves overall thermal efficiency.

[0045] In some preferred embodiments, the multi-junction solar cell group includes N narrow bandgap photovoltaic cells connected in series ( Figure 1 Cell 1 to Cell N), where N is an integer and N ≥ 2, and the N photovoltaic cells are arranged in order from high bandgap energy to low bandgap energy to achieve absorption and conversion of spectral energy at different wavelengths. In addition, each photovoltaic cell in the multi-junction solar cell array is made of semiconductor materials with different bandgap energies, including but not limited to Ge (germanium), Si (silicon), GaAs (gallium arsenide) and GaInP (gallium indium phosphide), to achieve efficient absorption and conversion of spectra at different wavelengths.

[0046] In some preferred embodiments, the focusing device can be configured to include multiple optical lenses or reflectors, such as Fresnel lenses or parabolic reflectors, which are used to focus incident sunlight onto the spectroscopic device to increase the intensity of the incident light and improve the photoelectric conversion efficiency. Simultaneously, the spectroscopic device can be configured to include multiple spectroscopic prisms, spectroscopic filters, or multi-layer dielectric film structures, which are used to separate the focused sunlight into spectra within a predetermined wavelength range and guide the spectra of different wavelengths to the corresponding photovoltaic cells and the first and second solar thermal storage heat exchangers, respectively, so that the multi-junction solar cell array and the first and second solar thermal storage heat exchangers can respectively utilize the spectral energy of different wavelengths.

[0047] In some preferred embodiments, the first compressor unit C1 and the second compressor unit C2 can be configured to each adopt a multi-stage compression structure, with the compression ratio of each stage being independently adjustable, wherein the compression ratio range of the first compressor unit C1 is 2:1 to 5:1, and the compression ratio range of the second compressor unit C2 is 3:1 to 8:1. By adjusting the compression ratio of each stage, the system can adapt to different solar input power and energy storage requirements, thereby improving the flexibility and efficiency of the system. Similarly, the first and second expansion units T1 and T2 can be configured to adopt a multi-stage expansion structure, with the expansion ratio of each stage being independently adjustable, wherein the expansion ratio range of the first expansion unit T1 is 3:1 to 6:1, and the expansion ratio range of the second expansion unit T2 is 2:1 to 4:1. By adjusting the expansion ratio of each stage, efficient energy conversion of carbon dioxide under different pressure and temperature conditions can be achieved, thereby improving the overall power generation efficiency of the system.

[0048] In some preferred embodiments, the design pressure range of the high-pressure gas storage tank HPT is 15MPa to 25MPa, and the design pressure range of the low-pressure gas storage tank LPT is 0.1MPa to 2MPa. Both gas storage tanks are manufactured from high-strength materials and equipped with thermal insulation structures, pressure monitoring, and safety pressure relief devices to ensure the safe operation of the system under both high and low pressure conditions. The first compression heat storage heat exchanger TES1 and the second compression heat storage heat exchanger TES2 use phase change thermal storage materials with phase change temperature ranges of 80°C to 120°C and 150°C to 200°C, respectively. The phase change thermal storage materials are selected from inorganic salts or metal alloys with high latent heat of fusion. They can efficiently absorb heat during compression and stably release heat energy during expansion, significantly improving the thermal energy utilization efficiency of the system. In addition, the first solar heat storage heat exchanger STES1 and the second solar heat storage heat exchanger STES2 use nanofluid as the heat transfer medium and nanomaterials such as carbon nanotubes or graphene are dispersed therein. The nanofluid has excellent thermal conductivity and photothermal conversion efficiency, and can effectively absorb and store the spectral part below the minimum band gap energy of the multi-junction solar cell group, thereby improving the overall solar energy utilization rate of the system.

[0049] In summary, the present invention achieves efficient solar energy utilization and energy storage by integrating solar concentrating and spectrophotovoltaic technology with compressed carbon dioxide energy storage technology, solves the problems of low efficiency and intermittent photovoltaic power generation, and significantly improves the overall performance and reliability of the system.

[0050] Example 2

[0051] Based on the above-mentioned Example 1, this Example 2 further analyzes the impact of different photovoltaic materials and multi-junction cell designs on system performance to optimize solar energy utilization efficiency and reduce heat loss.

[0052] This embodiment first adopts the commonly used photovoltaic material, Ge (bandgap energy E g=0.66eV)、Si( E g=1.12eV), GaAs ( E g = 1.42eV) and GaInP ( E g=1.81eV) to analyze the impact of different materials on system performance. The experimental results show that the system round-trip efficiency (RTE) increases with the battery band gap energy ( E g) decreases significantly with the increase of concentration ratio, but remains almost unchanged with the increase of concentration ratio, such as Figure 2 As shown. Figure 2 Within the concentration ratio range shown, the average values ​​for Ge are 92.4%, Si 92%, GaAs 89.5%, and GaInP 87.7%. Although the relative advantages of this system are more obvious for photovoltaic cells with larger band gap energies, for the sake of comparison with existing technologies, the most commonly used silicon photovoltaic panels are used for subsequent analysis. Figure 3 As shown in the figure, the round trip efficiency and the ratio of the output power of the expansion unit to the photovoltaic power generation power increase with R ST increases and R They reached their peak values ​​(92.3% and 88%) at ST = 0.6 but remained almost unchanged after decreasing.

[0053] In this Example 2, the effects of the outlet pressure (PT1,o) of the first compressor unit C1 and the outlet pressure (PC1,o) of the first expander unit T1 on the system performance were also studied. The results showed that as the outlet pressure ( P T1,o) and the outlet pressure of the first expansion unit T1 ( P C1,o), the round-trip efficiency peak appears in this system, and these two parameters directly affect the heat absorbed by CO2 in the first compression heat storage heat exchanger TES1, such as Figure 4 As shown. For a given P C1,o, RTE along with PAs T1,o increases, it then decreases. There is an optimal value where RTE reaches its maximum value. P T1,o, and optimal P T1,oWith P C1,o increases with the increase of P P When C1,o≤1.1MPa, RTE along with P When C1,o increases, it decreases. P When T1,o is between 1.3MPa and 1.7MPa, RTE First, with P As C1,o increases, it decreases, increases to a peak, and then decreases again. RTE Peak Best P C1,o with P T1,o increases with the increase.

[0054] In order to further improve the efficiency of solar energy utilization and reduce heat loss, this system adopts the design concept of multi-junction cells. For example, this system simulates and demonstrates the effects of 2-junction, 3-junction, 4-junction, 5-junction and 6-junction cells. In a multi-junction cell system, the relationship between the system round-trip efficiency, the total utilization efficiency of the solar spectrum and the concentration ratio is as follows: Figure 5 As shown. The round trip efficiency (RTE) increases with the increase of concentration ratio, while the increase margin decays with the increase of cell junction number. RTE rises with the increase of cell junction number, but the marginal benefit of the increase decays. The relative increase of RTE is much lower when the number of cell junctions is greater than 4 than when the number of cell junctions is less than or equal to 4. In this demonstration system, the average RTE of the 2-junction battery system is 92.1%, the average RTE of the 3-junction battery system is 92.3%, the average RTE of the 4-junction battery system is 92.4%, the average RTE of the 5-junction battery system is 92.5%, and the average RTE of the 6-junction battery system is 92.5%. Photovoltaic efficiency can be improved by increasing the number of cell junctions, but the separated solar spectrum energy used to increase the turbine inlet temperature will decrease (the minimum band gap energy decreases with the increase of cell junction number). Increasing the number of cell junctions will not lead to a significant increase in the RTE of this system. Total solar energy utilization efficiency ( η Overal) increases with the increase of concentration ratio and the number of cell junctions. In a large range, the average η overal The average for a 3-cell battery system is 59.7%. η overal The average of 4-junction battery system is 61.9%. η overal The average of 5-junction battery system is 63.4%. η overal The average of 6-junction battery system is 65.5%. ηoveral When the number of battery junctions exceeds 5, increasing the number of junctions is not very meaningful because η overal The absolute increase is less than 0.2%. Compared with the photovoltaic efficiency ηPV, η overal In the 2-junction cell system, the relative average increase is 13.2%, and in the 3-junction cell system, the relative average increase is 2.9%. The relative increase decreases with the increase of the number of cell junctions and also decreases with the increase of the concentration ratio. However, when the number of cell junctions is greater than 4, η overal becomes less than the photovoltaic efficiency ( η PV ),and η overal and η PV The difference between them increases with the number of cell junctions. This indicates that the system is more advantageous when the number of cell junctions is small (≤3), which is also in line with current engineering practice, because the manufacturing difficulty and cost of multi-cell batteries soars rapidly with the increase of cell junctions.

[0055] The above embodiments fully and effectively achieve the objectives of the present invention. Those skilled in the art will appreciate that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the above specific embodiments. Although the present invention has been described with reference to the embodiments currently considered to be the most practical and preferred, it should be understood that the present invention is not limited to the disclosed embodiments, and any modifications that do not deviate from the functional and structural principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A compressed carbon dioxide energy storage system integrating solar concentrating and splitting photovoltaics and thermal energy, comprising a solar concentrating and splitting photovoltaics and thermal energy unit and a compressed carbon dioxide energy storage unit, characterized in that: The solar concentrating and splitting photovoltaic-thermal unit comprises at least a concentrating device, a splitting device, and a multi-junction solar cell array, wherein: the concentrating device is used to collect and focus sunlight, the splitting device is arranged downstream of the optical path of the concentrating device, and the multi-junction solar cell array is arranged downstream of the optical path of the splitting device and comprises a plurality of narrow-bandgap photovoltaic cells connected in series; The compressed carbon dioxide energy storage unit includes at least a compression device, an expansion device, a gas storage device, and a heat storage device, wherein: The compression device comprises at least a first compressor unit and a second compressor unit, the power input ends of both units are electrically connected to the output end of the multi-junction solar cell group; The expansion device comprises at least a first expansion unit and a second expansion unit, both power output ends of which are connected to the power generation device; The gas storage device comprises at least a high-pressure gas storage tank and a low-pressure gas storage tank, which are used to store carbon dioxide in high-pressure and low-pressure states respectively; The heat storage device includes at least a first compression heat storage heat exchanger, a second compression heat storage heat exchanger, a first solar heat storage heat exchanger, and a second solar heat storage heat exchanger, wherein: the first compression heat storage heat exchanger and the second compression heat storage heat exchanger are respectively used to store heat energy generated by the first compressor unit and the second compressor unit during the compression process; the first solar heat storage heat exchanger and the second solar heat storage heat exchanger are both arranged downstream of the optical path of the spectrometer and are both used to collect and store heat energy converted from the spectral portion whose spectral energy is lower than the minimum band gap energy of the multi-junction solar cell group; And among them: The air inlet of the first compressor unit is connected to the outlet of the low-pressure gas storage tank through a pipeline, and the air outlet thereof is connected to the inlet of the high-pressure gas storage tank through a pipeline that passes through the hot side of the first compression heat storage heat exchanger, the second compressor unit, and the hot side of the second compression heat storage heat exchanger in sequence; The outlet of the high-pressure gas storage tank is connected to the inlet of the low-pressure gas storage tank through a pipeline that passes through the cold side of the second compression heat storage heat exchanger, the cold side of the first solar heat storage heat exchanger, the first expansion unit, the cold side of the first compression heat storage heat exchanger, the cold side of the second solar heat storage heat exchanger, and the second expansion unit.

2. The integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system according to claim 1 is characterized in that: The system also includes a heat recovery device for recovering waste heat, including at least a first heat recovery device and a second heat recovery device, wherein the first heat recovery device is arranged in series on the connecting pipeline between the first expansion unit and the first compression heat storage heat exchanger, and the second heat recovery device is arranged in series on the connecting pipeline between the second expansion unit and the low-pressure gas storage tank.

3. The integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system according to claim 1 is characterized in that: The multi-junction solar cell group includes N narrow-bandgap photovoltaic cells connected in series, where N is an integer and N≥2, and the N photovoltaic cells are arranged in sequence from high bandgap energy to low bandgap energy to achieve absorption and conversion of spectral energy of different wavelengths.

4. The integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system according to claim 1 is characterized in that: The light concentrating device includes a plurality of optical lenses or reflectors, and the optical lenses or reflectors are used to focus the incident sunlight onto the light splitting device.

5. The integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system according to claim 1 is characterized in that: The spectroscopic device includes multiple spectroscopic prisms, spectroscopic filters or multi-layer dielectric film structures, which are used to separate the focused sunlight into spectra within a predetermined wavelength range and guide the spectra of different wavelengths to the corresponding photovoltaic cells and the first and second solar heat storage exchangers respectively.

6. The integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system according to claim 1 is characterized in that: Both the first and second compressor groups adopt a multi-stage compression structure, and the compression ratio of each stage can be adjusted independently. The compression ratio range of the first compressor group is 2:1 to 5:1, and the compression ratio range of the second compressor group is 3:1 to 8:

1. By adjusting the compression ratio of each stage, different solar energy input power and energy storage requirements can be adapted.

7. The integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system according to claim 1 is characterized in that: The first and second expansion units adopt a multi-stage expansion structure, and the expansion ratio of each stage can be adjusted independently. The expansion ratio range of the first expansion unit is 3:1 to 6:1, and the expansion ratio range of the second expansion unit is 2:1 to 4:

1. By adjusting the expansion ratio of each stage, efficient energy conversion of carbon dioxide under different pressure and temperature conditions can be achieved.

8. The integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system according to claim 1 is characterized in that: The design pressure range of the high-pressure gas storage tank is 15MPa to 25MPa, and the design pressure range of the low-pressure gas storage tank is 0.1MPa to 2Mpa. Both gas storage tanks are made of high-strength materials and are equipped with insulation structures and pressure monitoring and safety pressure relief devices.

9. The integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system according to claim 1, characterized in that: The first and second compression heat storage heat exchangers use phase change heat storage materials, and their phase change temperature ranges are 80°C to 120°C and 150°C to 200°C respectively. The phase change heat storage materials are inorganic salts or metal alloys with high melting latent heat.

10. The integrated solar concentrating and splitting photovoltaic-thermal compressed carbon dioxide energy storage system according to claim 1, characterized in that: The first and second solar heat storage heat exchangers use nanofluid as heat transfer medium and carbon nanotubes or graphene nanomaterials are dispersed therein. The nanofluid is used to absorb and store the spectrum part below the minimum band gap energy of the multi-junction solar cell group.

Images