Photovoltaic-photothermal-thermoelectric coupling system capable of efficiently utilizing sunlight

Abstract

The invention discloses a photovoltaic-photothermal-thermoelectric coupling system capable of efficiently utilizing sunlight. The system comprises a photovoltaic power generation module, a photo-thermal module and a thermoelectric power generation module, the photovoltaic power generation module is located on the upper layer of the whole system and is composed of a light condensation layer and a photoelectric conversion layer, and the photoelectric conversion layer converts photons in solar energy into electric energy through a photovoltaic cell; the photo-thermal module captures low-energy photons in sunlight through a heat absorption material, converts photon energy which cannot be utilized by a photovoltaic cell into heat energy through infrared radiation, and provides heat energy for the thermoelectric power generation module through heat conduction; and the thermoelectric power generation module is closely connected with the photo-thermal module, absorbs heat generated by the photovoltaic power generation module and the photo-thermal module and converts the heat into electric energy, and the thermoelectric material of the thermoelectric power generation module is a magnesium-based thermoelectric material. The problems of low energy conversion efficiency and high cost in the existing photovoltaic technology can be effectively solved, the utilization rate of solar energy is improved, and the method has remarkable application value in the field of renewable energy utilization.

Description

Technical Field

[0001] The present invention relates to the field of renewable energy technology, and in particular to a photovoltaic-photothermal-thermoelectric coupling system for efficiently utilizing sunlight. Background Art

[0002] At present, photovoltaic power generation (PV) is a major way to utilize solar energy. PV power generation converts solar energy into electrical energy with the help of the photoelectric effect of semiconductor materials, but a large amount of heat is still lost during the solar energy conversion process, which not only reduces the conversion efficiency but also may damage the battery materials. Therefore, heat recovery has become a technical problem that needs to be solved urgently.

[0003] Thermoelectric power generation is based on the Seebeck effect, which uses temperature gradients to directly convert thermal energy into electrical energy. Commonly used thermoelectric materials such as Bi2Te3 and PbTe can stably output electricity under a certain temperature gradient. They have a simple structure without moving parts, high reliability and stability, and are suitable for harsh environments such as space, polar regions, and deep sea. In recent years, a "photovoltaic-thermoelectric hybrid system" that combines thermoelectric technology with photovoltaic technology has been proposed. This system can use the electricity generated by photovoltaic cells and can also use thermoelectric modules to recover the heat of photovoltaic cells. For example, it is based on the combination of multi-junction photovoltaic cells and Bi2Te3 thermoelectric generators. The solar energy is concentrated on the photovoltaic cells through a concentrating system, and the thermoelectric generator recovers the heat from the back of the cell to generate additional electricity. Existing technologies include split-beam solar thermoelectric power generation systems, stacked concentrating photovoltaic thermoelectric systems, etc.

[0004] Although the photovoltaic-thermoelectric hybrid system has shown high efficiency in experiments, the existing technology still has some limitations; the existing photovoltaic-thermoelectric device system is complex in design, and it usually adopts a spectroscopic or stacked design. The spectroscopic system transmits light of different wavelengths to the photovoltaic cell and the thermoelectric module respectively through a spectroscopic device, which can theoretically improve the efficiency of the system, but this design requires a high-precision spectroscopic device, resulting in a significant increase in cost. The stacked design directly installs the thermoelectric module on the back of the photovoltaic cell. The thermoelectric module uses the heat generated by the photovoltaic cell to generate electricity, and the temperature difference is not enough; in addition, the energy management of the existing photovoltaic-thermoelectric device is imperfect: the optimal operating temperatures of the photovoltaic cell and the thermoelectric module are inconsistent. The working efficiency of the photovoltaic cell is higher at low temperatures, while the thermoelectric module requires a higher temperature difference to generate electricity effectively. Therefore, the temperature matching of the photovoltaic cell and the thermoelectric module in the existing technology is difficult to achieve, resulting in limited improvement in the overall efficiency of the system.

[0005] In summary, although the existing photovoltaic-thermoelectric composite system has certain technical advantages, it still has significant limitations in terms of efficiency improvement, system design complexity and cost control. These shortcomings limit its promotion and widespread application in practical applications. Summary of the invention

[0006] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a photovoltaic-photothermal-thermoelectric coupling system that efficiently utilizes sunlight; the system is suitable for working in a space environment, and through the coordinated work of photovoltaic, photothermal and thermoelectric modules, it can achieve efficient utilization of the full spectrum of solar energy and efficient recovery of heat energy, solving the problems of low solar energy utilization efficiency, inefficient use of heat, poor system stability and poor performance in harsh environments in the prior art; the present invention converts the heat energy generated by the photothermal effect into electrical energy, breaking through the limitation of single power generation of traditional photovoltaic modules and achieving efficient cascade utilization of energy. The technical solution of the present invention is specifically described as follows.

[0007] The present invention provides a photovoltaic-photothermal-thermoelectric coupling system for efficiently utilizing sunlight, which comprises a photovoltaic power generation module, a photothermal module and a thermoelectric power generation module; wherein:

[0008] Photovoltaic power generation module: It is located at the upper layer of the entire system and consists of a light-collecting layer and a photoelectric conversion layer. The light-collecting layer is used to concentrate solar energy on the photovoltaic cell components of the photoelectric conversion layer, and the photovoltaic cells are used to convert photons in solar energy into electrical energy;

[0009] Photothermal module: It captures low-energy photons and infrared radiation in sunlight through heat-absorbing materials, converts the photon energy that cannot be used by photovoltaic cells into thermal energy, and provides thermal energy for thermoelectric power generation modules through heat conduction;

[0010] Thermoelectric power generation module: It is connected to the photothermal module. It absorbs the heat generated by the photovoltaic power generation module and the photothermal module, converts the heat into electrical energy based on the Seebeck effect of thermoelectric materials, and dissipates the excess heat to the external environment through radiation.

[0011] In the present invention, in the photovoltaic power generation module, the focusing layer is used to solve the problem of insufficient light intensity per unit area. The focusing layer adopts a focusing Fresnel lens design of a wide-angle short-focus microlens, which can concentrate solar energy on the photovoltaic cell assembly, thereby significantly improving the efficiency of light energy utilization; using optical focusing principles and macro focusing technology, through precise surface design and the application of high dielectric constant material polymethyl methacrylate (PMMA), the sunlight is collected to the maximum extent and focused on a smaller area, thereby enhancing the light intensity received by the photovoltaic cell and improving the focusing efficiency by about 200 times. The focusing device provides sufficient photons for the photovoltaic device, and the multi-junction semiconductor photovoltaic device prepared by the advanced low-pressure metal organic chemical vapor deposition technology (LP-MOCVD) enables the photovoltaic system of the present invention to absorb light waves in various spectral bands. The open circuit voltage of the photovoltaic sheet under the focusing function is as follows:

[0012]

[0013] Where Voc(1sun) is the open circuit voltage under 1 sun; n is the diode factor. In solar photovoltaic cells, n is 2 to 3; T is the absolute temperature; k is the Ehrman constant (1.38×10 -23 J / k; q is the electron charge (1.6×10 -19 Coulomb); C is the concentration ratio, which is measured in units of 1 sun. It has been calculated that when the solar concentration multiple is 100 times, the open circuit voltage gain can reach 18%. The photovoltaic cell is a triple-junction gallium arsenide solar cell, and the photoelectric conversion layer uses photovoltaic cells to convert photons in solar energy into electrical energy. The current mainstream triple-junction gallium arsenide solar cell type is LM (GaInP / GaAs / Ge). This structure is grown on a germanium substrate, has high conversion efficiency and excellent radiation resistance, and is also the photovoltaic layer structure scheme adopted by the present invention.

[0014] In the present invention, in the photothermal module, the heat absorbing material forms a heat absorbing layer with a porous structure. The heat absorbing material is foamed graphene. The porous structure helps to improve the light absorption efficiency and ensure uniform distribution of light, thereby avoiding local damage to the photothermal module due to excessive concentration of light energy.

[0015] In the present invention, the photovoltaic power generation module is connected to the photovoltaic power generation module via a heat conduction layer, and the material of the heat conduction layer is aluminum nitride.

[0016] In the present invention, in the thermoelectric power generation module, the key indicators of the thermoelectric device include: device internal resistance ≤ 100 mΩ, output power ≥ 0.6 W, and energy conversion efficiency ≥ 12%.

[0017] In the present invention, in the thermoelectric power generation module, the thermoelectric device is composed of a plurality of thermoelectric monocouples connected in series or in parallel through conductive materials, and each thermoelectric monocouple is composed of an N-type thermoelectric single arm and a P-type thermoelectric single arm connected in series through conductive copper electrodes; the thermoelectric material adopts magnesium-based thermoelectric material, wherein the p-type thermoelectric figure of merit ZT≥1.5, and the n-type thermoelectric figure of merit ZT≥2.0.

[0018] In the present invention, the thermoelectric single arm is composed of an electrode contact layer, a transition layer and a thermoelectric material layer. The electrode contact layer is copper doped with a small amount of nickel, and the transition layer is nickel and titanium metal from top to bottom. The thermoelectric materials in the N-type thermoelectric single arm and the P-type thermoelectric single arm are N-type magnesium-based material Mg3(Sb,Bi)2 and P-type magnesium-based material MgAgSb, respectively.

[0019] In the present invention, the thermal expansion coefficient of the copper electrode matches that of the thermoelectric material to reduce the stress caused by the thermal expansion difference; the copper electrode has excellent electrical and thermal conductivity, which helps to efficiently conduct current and heat; the interface has high bonding strength, which can effectively ensure the long-term stability of the system; the contact resistance and contact thermal resistance at the interface are small, which reduces the loss of current and heat flow. Through the design of the transition layer and the electrode contact layer, the interface matching between the electrode and the thermoelectric material is optimized, and the diffusion phenomenon between the electrode material and the thermoelectric material is avoided.

[0020] In the present invention, magnesium-based thermoelectric materials are used, which effectively break through the performance limitations of traditional Bi2Te3 thermoelectric materials in low and medium temperature zones. The core advantages are: first, the thermoelectric performance of magnesium-based thermoelectric materials significantly improves the system's utilization efficiency of photovoltaic heat and photothermal effects; second, the wide operating temperature range ensures the stable operation of the system in various complex environments; finally, the excellent environmental adaptability enables it to maintain efficient and stable energy output under extreme conditions such as high radiation and high light intensity. These innovative features make the present invention significantly superior to traditional silicon-based photovoltaic cells in terms of energy conversion efficiency, and are particularly suitable for high-end application scenarios such as aerospace, providing a more efficient and reliable solution for satellite power supply systems.

[0021] In the present invention, the hot end of the thermoelectric monocouple and the two sides of the conductive copper electrode are respectively connected to the aluminum nitride ceramic sheets to absorb the heat generated by the photovoltaic power generation module and the photothermal module; the cold end of the thermoelectric monocouple adopts a high-emissivity metal material layer as a heat dissipation system to achieve heat dissipation, and the high-emissivity metal is nickel.

[0022] In the present invention, the electric energy generated by the thermoelectric module is output together with the electric energy of the photovoltaic cell to the energy storage or load of the system, thereby realizing the cascade conversion of solar energy.

[0023] In the present invention, the materials used in the photovoltaic power generation module, the photothermal module and the thermoelectric power generation module are all high temperature resistant, radiation resistant and corrosion resistant materials to ensure the stable operation of the system in extreme environments.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] By introducing the photothermal module, the present invention effectively utilizes the full spectrum of solar energy, especially the low-energy photons and infrared radiation. By converting the heat energy generated by the photothermal effect into electrical energy, the limitation of the single power generation of traditional photovoltaic modules is broken through, and the cascaded and efficient utilization of energy is achieved, which avoids energy waste and greatly improves the energy conversion efficiency of the overall system.

[0026] The present invention can still maintain stable operation in a high temperature environment, through a thermal management mechanism, that is, using a high heat conduction method to dissipate the heat generated by the photovoltaic module to the aluminum nitride high light transmittance and high heat conduction layer and further conduct it to the thermoelectric module through a high thermal conductivity copper electrode, and the heat generated by the photothermal module is directly transferred to the thermoelectric module through the copper electrode layer to ensure that the temperature of the photovoltaic cell and the thermoelectric module is maintained within the optimal working range, while avoiding the problem of efficiency reduction of traditional systems at high temperatures. The hot and cold ends of the thermoelectric module directly generate a suitable temperature difference. The present invention uses a high-emissivity metal material (nickel) as a cold end heat dissipation system to ensure efficient heat dissipation. This system design effectively guarantees stable operation in a space environment. The radiation-resistant and anti-corrosion materials used enable the system to maintain reliable power generation performance for a long time in space, ocean or other extreme environments, ensuring the long life of the system and efficient energy conversion.

[0027] According to the open circuit voltage formula of the three-junction gallium arsenide photovoltaic film concentration mode, at a working temperature of 400K, 100 times the concentration condition can increase the open circuit voltage by 18%, and 200 times the concentration can achieve a voltage gain of 21%. The energy conversion efficiency of the multi-junction photovoltaic cells on the market is about 31% to 32%; and the thermoelectric module is at the hot end temperature of 370K at the thermoelectric module equilibrium temperature of the engineering simulation, and the cold end temperature in the extraterrestrial environment is about 3K, so the temperature difference reaches about 370K, and the thermoelectric energy conversion efficiency is about 10%-12%. Through theoretical analysis and prediction, the present invention can finally achieve a conversion efficiency of about 35%-45% after the coordinated use of the photothermal effect and the thermoelectric module. Compared with single crystal silicon components (20-25%) and polycrystalline silicon components (18-22%), it has a significant efficiency advantage; at the same time, through the reuse of heat energy, the efficiency performance is also better than the CPV system (more than 30%) that relies only on high-efficiency multi-junction cells.

[0028] In the market competition, this project has unique advantages: although traditional photovoltaic modules have cost advantages, their energy utilization efficiency is insufficient; although the CPV system has high photoelectric efficiency, it fails to achieve waste heat utilization; although the PV-TE system can provide heat, its application scenarios are limited. In contrast, this project not only significantly improves the overall power generation efficiency through innovative energy cascade utilization solutions, but also achieves efficient energy conversion and significantly reduces long-term operating costs. This breakthrough solution provides an innovative option for the photovoltaic power generation field that combines technological leadership and economic benefits.

[0029] In addition, the present invention innovatively uses a new type of magnesium-based thermoelectric material, which effectively breaks through the performance limitations of traditional thermoelectric materials in the low and medium temperature range. This important technological breakthrough brings three core advantages: first, the excellent thermoelectric performance significantly improves the system's utilization efficiency of photovoltaic waste heat and photothermal effects; second, the wide operating temperature range ensures the stable operation of the system in various complex environments; finally, the excellent environmental adaptability enables it to maintain efficient and stable energy output under extreme conditions such as high radiation and high light intensity. These innovative features make the present invention significantly superior to traditional silicon-based photovoltaic cells in terms of energy conversion efficiency, and is particularly suitable for high-end application scenarios such as aerospace, providing a more efficient and reliable solution for satellite power supply systems.

[0030] Finally, the present invention achieves a hundredfold reduction in the amount of solar panels used through an innovative short-focus lens focusing system, significantly reducing product costs and satellite payloads. In terms of system design, through sophisticated structural optimization and the application of high-performance materials, the operating stability and service life of the equipment in various environments have been greatly improved. From the perspective of the full life cycle cost, the system has significant advantages: first, the significant reduction in material usage directly reduces the initial investment; second, the excellent stability and durability significantly reduce maintenance costs and replacement frequency; finally, although the improvement of thermoelectric modules and photovoltaic technology has brought about a certain increase in costs, the material saving effect brought by the focusing system far exceeds this part of the investment, achieving effective control of the overall manufacturing cost. This innovative design provides a solution that combines performance and cost advantages for the aerospace field. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The figure is a schematic diagram of the overall structure of a photovoltaic-photothermal-thermoelectric coupling system for efficiently utilizing sunlight.

[0032] Figure 2 Schematic diagram of TE thermocouple material composition distribution and structure.

[0033] Figure 3 The energy conversion efficiency diagram of the thermoelectric material used in the present invention under different temperature differences is obtained through numerical simulation and experimental verification.

[0034] Numbers in the figure:

[0035] 1- Focusing lens, 2- Photothermal film, 3- TE thermocouple (comprising a copper electrode contact layer doped with a small amount of nickel and a transition layer composed of nickel and titanium), 4- triple-junction gallium arsenide PV film layer, 5- AlN (aluminum nitride) high light transmittance and high thermal conductivity layer, 6- copper electrode layer, 7- nickel high radiation material layer. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0037] In view of the problems of low energy utilization efficiency and poor application performance in harsh environments of existing photovoltaic-thermoelectric composite systems, the present invention proposes a coupling system of integrated photovoltaic, photothermal and thermoelectric modules that efficiently utilizes sunlight, which is an energy conversion device combining photovoltaic and thermoelectric. By combining photovoltaic, photothermal and thermoelectric technologies, the overall energy conversion efficiency and stability of the system are significantly improved, especially in harsh environments with high temperature and high radiation.

[0038] The photovoltaic-photothermal-thermoelectric coupling system for efficiently utilizing sunlight provided by the present invention includes a photovoltaic power generation component, a concentrating system for concentrating solar energy on a photovoltaic cell component, and a thermoelectric module. The photovoltaic cell component adopts a multi-junction photovoltaic cell, etc., and the thermoelectric module is made of thermoelectric materials such as P-type MgAgSb and N-type Mg3(Sb,Bi)2. The concentrating system concentrates solar energy on the photovoltaic cell component, and while the photovoltaic cell component generates electrical energy, part of the heat generated by it is also collected; the photons transmitted by the photovoltaic layer are absorbed by the photothermal layer to generate thermal energy, and combined with the photovoltaic heat generation, thermal energy is provided to the thermoelectric layer; the thermoelectric module converts thermal energy into electrical energy, thereby improving the energy conversion efficiency of the entire module system. The present invention also provides an energy conversion method combining photovoltaics and thermoelectrics, firstly using a concentrating system to concentrate solar energy on a photovoltaic cell component, so that the photovoltaic cell component generates electrical energy through the photoelectric effect, and then using a thermoelectric module to recover the heat generated by the photovoltaic cell and the photothermal layer component, and converting the heat into electrical energy through the Seebeck effect, thereby realizing efficient and comprehensive utilization of solar energy. The device and method of the present invention can effectively solve the problem of heat waste in existing photovoltaic technology, improve the utilization rate of solar energy, and have significant application value in the field of renewable energy utilization.

[0039] The following is the detailed composition and working principle of the system of the present invention.

[0040] System composition and structure Figure 1 As shown, it includes a photovoltaic power generation module, a photothermal module and a thermoelectric power generation module;

[0041] Photovoltaic power generation module (PV module): It consists of a light-collecting layer and a photoelectric conversion layer, and uses photovoltaic cells to convert photons in solar energy into electrical energy. Using high-efficiency triple-junction gallium arsenide solar cells, these cells have higher photoelectric conversion efficiency and are particularly suitable for working under conditions of high radiation or high light intensity. In the design of the focusing system, a precise optical solution is used to focus a 50mm×50mm lens to a 3.8mm×3.8mm photovoltaic sheet. When the photovoltaic sheet converts energy at an efficiency of 30%, the remaining approximately 70% of the energy is efficiently transmitted to the thermoelectric module through the photothermal film, realizing the cascade utilization of energy.

[0042] Photothermal module: The photothermal film layer of the present invention is made of inorganic lightweight material - foamed graphene, which has excellent photothermal performance and is suitable for use as a photothermal absorption layer in an extraterrestrial environment, achieving efficient solar energy absorption and heat generation, providing thermal energy for thermoelectric devices and converting it into electrical energy. More thermal energy can also be provided to the thermoelectric module through heat conduction, further improving the energy utilization rate of the system. The porous structure helps to improve the absorption efficiency of light and ensure uniform distribution of light, thereby avoiding local damage to the photothermal module due to excessive concentration of light energy. The heat in the photothermal module can be used directly for power generation or stored for subsequent use.

[0043] Thermoelectric power generation module (TE module): The thermoelectric module is located below the photothermal film and the copper electrode layer. It absorbs the heat generated by the photovoltaic cell and the photothermal module and converts the heat generated by the photovoltaic cell into electrical energy through the Seebeck effect of the thermoelectric material. The thermoelectric power generation module uses new high-efficiency materials (magnesium-based thermoelectric materials) and electrode contact layers and transition layers composed of copper, nickel, titanium, etc. These materials can maintain high thermoelectric conversion efficiency under high temperature conditions. In the thermoelectric power generation module, the key indicators of the thermoelectric device include: device internal resistance ≤ 100mΩ, output power ≥ 0.6W, energy conversion efficiency ≥ 12%.

[0044] First, the photovoltaic power generation module is located at the upper layer of the entire system. It is the part that directly receives sunlight and converts it into electrical energy. Sunlight irradiates the surface of the photovoltaic cell. The semiconductor material in the photovoltaic cell absorbs high-energy photons and converts them into electrical energy through the photoelectric effect. The converted direct current is output to the energy storage or load of the system through the circuit. In the process of photovoltaic cells converting light energy, due to the limited energy conversion efficiency of photovoltaic cells, part of the light energy that is not converted will accumulate on the surface of the photovoltaic cell in the form of heat energy, causing the surface temperature of the cell to rise. The photothermal module captures low-energy photons and infrared radiation in sunlight through the heat-absorbing material foam graphene. These photons cannot be effectively used by photovoltaic cells due to insufficient energy, but through the photothermal module, they can be converted into thermal energy. Finally, the heat generated by the photovoltaic cell will be conducted to the copper electrode layer through the AlN (aluminum nitride) high-transmittance and high-thermal conductivity layer and further conducted to the thermoelectric module just below the electrode layer, and the heat generated by the photothermal module will be directly conducted to the thermoelectric module just below the electrode layer through the electrode layer. Thermoelectric modules are made of high-efficiency magnesium-based thermoelectric materials, which can convert thermal energy into electrical energy through the Seebeck effect after receiving a temperature difference. The electrons in the thermoelectric module move due to the temperature difference, thereby generating voltage and generating electricity. The electrical energy generated by the thermoelectric module is output to the system's energy storage or load together with the electrical energy of the photovoltaic cell, achieving dual energy conversion. In addition, the excess heat generated by the photovoltaic cell can also be recovered through the photothermal module, which can absorb this excess heat and store or conduct it to other modules.

[0045] The Seebeck effect is the first thermoelectric effect, which refers to the thermoelectric phenomenon that two different conductors or semiconductors produce a voltage difference due to temperature difference. The direction of the thermoelectric potential is that the electrons flow from negative to positive at the hot end. In a circuit composed of different materials A and B, when the temperatures of the two contact points are different, thermocurrent and thermoelectric potential will be generated, and its direction depends on the direction of the temperature gradient. The cause of the Seebeck effect is that carriers move and accumulate from the hot end to the cold end under the temperature gradient, forming a potential difference and reverse charge flow. When dynamic equilibrium is reached, a stable thermoelectric potential is generated. Semiconductors have a large thermoelectric potential and can be used as thermoelectric generators. The potential difference generated between the A and B nodes can be calculated by a formula, and its value depends on the relative Seebeck coefficient of the two materials. The positive or negative coefficient is determined by the carrier type of the material and has nothing to do with the size and direction of the temperature difference. The Peltier effect is the reverse process of the Seebeck effect. It is generated by two materials with large differences in carrier concentration and energy level in a closed loop under the action of an external electric field, and heat exchange occurs with the outside world at the node. Based on this effect, semiconductor refrigeration and temperature control technology can be developed. When a constant current is passed through different materials A and B in series, heat absorption and heat release will occur, and it is related to the direction of the current. The heat variable per unit time is proportional to the current, and the proportionality coefficient is the relative Peltier coefficient. The heat change depends on the energy barrier of the node interface. The Thomson effect is the third thermoelectric effect. When the current passes through a uniform conductor with a temperature gradient, heat will be absorbed or released in addition to Joule heat. It is different from the Peltier effect. It is a single conductor that forms a potential energy difference under a temperature difference. When the carriers are transported, a barrier transition occurs to produce heat absorption or heat release. The heat change caused by the Thomson effect per unit time of the entire conductor can be calculated by a formula. According to the theory of non-reversible thermodynamics, the Seebeck coefficient, Peltier coefficient and Thomson coefficient have a Kelvin relationship.

[0046] The efficiency of thermoelectric power generation and thermoelectric cooling is determined by the dimensionless figure of merit ZT. Therefore, improving the ZT value of thermoelectric materials is the key to improving the conversion efficiency of thermoelectric devices. The dimensionless figure of merit ZT is defined as follows:

[0047]

[0048] Where T is the absolute temperature, S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and S 2 σ is also called power factor (PF). Generally speaking, high thermoelectric performance requires excellent electrical properties and low thermal conductivity, but these parameters are highly coupled with carrier concentration. Usually, the carrier concentration range corresponding to the best thermoelectric performance is 10 19 -10 20 cm -3 between.

[0049] Thermoelectric devices are generally composed of multiple thermoelectric single couples connected in series or in parallel, and can be designed into a variety of different configurations. Thermoelectric single couples are the most basic structure of thermoelectric devices. Each thermoelectric single couple is composed of an N-type thermoelectric single arm and a P-type thermoelectric single arm connected in series through a guide plate (electrode) with higher electrical conductivity. Then, multiple thermoelectric single couples are repeatedly arranged according to a certain rule, and an electrically insulating ceramic substrate with good thermal conductivity is installed on both sides to form a thermoelectric device.

[0050] The thermoelectric material in the thermoelectric device adopts magnesium-based thermoelectric material, wherein the p-type thermoelectric figure of merit ZT≥1.5 and the n-type thermoelectric figure of merit ZT≥2.0.

[0051] The present invention is designed as Figure 2 The N-type TE thermocouple consists of a Cu (a small amount of Ni doping) layer, a Ni layer, a Ti layer, and a Mg3(Sb,Bi)2 layer from top to bottom. As for the P-type thermocouple, only the Mg3(Sb,Bi)2 layer is replaced with the MgAgSb layer, and the other components and structures remain unchanged.

[0052] The output performance of thermoelectric power generation devices is usually expressed in terms of the maximum conversion efficiency η max and the maximum output power P max Assume that during the service of the thermoelectric device, the temperature of the high temperature end and the low temperature end are T h and T c , the theoretical maximum conversion efficiency of the device is η max Defined as:

[0053]

[0054] in, is the average temperature, and ZT is the dimensionless thermoelectric figure of merit. This indicates that the maximum conversion efficiency of the device is η max It is only related to the temperature difference between the hot and cold ends of the device and the ZT of the thermoelectric arm. When the temperature difference between the hot and cold ends of the device is fixed, the greater the thermoelectric figure of merit ZT of the material, the higher the conversion efficiency of the thermoelectric device. According to the completed calculation simulation and experiments, the energy conversion efficiency of the material used at different temperatures (converted from the ZT value) is as follows Figure 3 As shown, under extreme temperature difference conditions outside the earth, the energy conversion efficiency can reach about 10%-15%.

[0055] In general, the present invention realizes the efficient utilization of solar energy through the coordinated work of photovoltaic, photothermal and thermoelectric modules. Photovoltaic modules are responsible for converting high-energy photons, thermoelectric modules generate electricity through heat recovery and temperature difference, and photothermal modules absorb low-energy photons and manage heat, so that the entire system can fully convert both solar light and heat energy into electrical energy, significantly improving the overall energy conversion efficiency of the system. According to the experiments we have demonstrated (such as Figure 3), from the experimental results, we can know that when the temperature difference is about 400K, the corresponding thermoelectric energy conversion efficiency can reach 10-12%. It is expected that in the actual application scenario in space, the cold end is 3K, and the hot end will reach an equilibrium temperature of 370K under the combined action of photovoltaic, photothermal and thermal management modules. That is, we can increase the energy conversion efficiency by about 10% on the basis of the 31% energy conversion efficiency of photovoltaic devices, so that the final comprehensive energy conversion efficiency can reach 35-45%.

[0056] In summary, the present invention realizes the efficient utilization of the full spectrum of solar energy through the deep coordination of photovoltaic, photothermal and thermoelectric modules. The system can not only convert high-energy photons, but also effectively utilize low-energy photons and thermal energy, significantly improving the comprehensive utilization efficiency of energy, and greatly surpassing the performance of traditional photovoltaic systems. Dual technical breakthroughs have been achieved in system design: First, while the thermoelectric module effectively provides additional power output by utilizing the heat generated by the photovoltaic cell, it adjusts the operating temperature of the photovoltaic cell, and works together with the high-radiation material layer to avoid the efficiency attenuation problem caused by high temperature; second, the innovative use of high-performance magnesium-based materials significantly improves the thermoelectric conversion efficiency of the system under extreme temperature and air pressure environments. In terms of environmental adaptability, through the comprehensive application of high-temperature resistant, radiation-resistant and anti-corrosion materials, combined with the precise thermal management of the photothermal module, the stable operation of the system in harsh environments such as high temperature, high radiation and high humidity is ensured. This innovative breakthrough has greatly expanded the application scenarios of solar energy utilization and provided a reliable technical solution for energy supply in special environments.

[0057] In contrast, the present invention not only significantly improves the overall power generation efficiency through an innovative energy cascade utilization scheme, but also realizes efficient energy conversion and significantly reduces long-term operating costs. This breakthrough solution provides an innovative option for the photovoltaic power generation field that combines technological leadership and economic benefits.

Claims

1. A photovoltaic-photothermal-thermoelectric coupling system for efficient utilization of sunlight, characterized in that: It includes photovoltaic power generation modules, photothermal modules and thermoelectric power generation modules; wherein: Photovoltaic power generation module: It is located at the upper layer of the entire system and consists of a light-collecting layer and a photoelectric conversion layer. The light-collecting layer is used to concentrate solar energy on the photovoltaic cell components of the photoelectric conversion layer, and the photovoltaic cells are used to convert photons in solar energy into electrical energy; Photothermal module: It captures low-energy photons and infrared radiation in sunlight through heat-absorbing materials, converts the photon energy that cannot be used by photovoltaic cells into thermal energy, and provides thermal energy for thermoelectric power generation modules through heat conduction; Thermoelectric power generation module: It is connected to the photothermal module. It absorbs the heat generated by the photovoltaic power generation module and the photothermal module, converts the heat into electrical energy based on the Seebeck effect of thermoelectric materials, and dissipates the excess heat to the external environment through radiation.

2. The coupling system according to claim 1, characterized in that: In the photovoltaic power generation module, the focusing layer adopts a focusing Fresnel lens design with a wide-angle short-focus microlens. The material is polymethyl methacrylate, and the photovoltaic cell is a triple-junction gallium arsenide solar cell.

3. The coupling system according to claim 1, characterized in that: In the photothermal module, the heat absorbing material forms a heat absorbing layer with a porous structure, and the heat absorbing material is foamed graphene.

4. The coupling system according to claim 1, characterized in that: The photovoltaic power generation module is connected to the photovoltaic power generation module through a heat conduction layer, and the material of the heat conduction layer is aluminum nitride.

5. The coupling system according to claim 1, characterized in that: In the thermoelectric power generation module, the key indicators of the thermoelectric device include: device internal resistance ≤ 100 m , output power ≥ 0.6 W, energy conversion efficiency ≥ 12%.

6. The coupling system according to claim 1, characterized in that: In the thermoelectric power generation module, the thermoelectric device is composed of multiple thermoelectric couples connected in series or in parallel through conductive materials. Each thermoelectric couple is composed of an N-type thermoelectric single arm and a P-type thermoelectric single arm connected in series through conductive copper electrodes. The thermoelectric material adopts magnesium-based thermoelectric material, among which the p-type thermoelectric figure of merit ZT≥1.5 and the n-type thermoelectric figure of merit ZT≥2.

0.

7. The coupling system according to claim 6, characterized in that: The thermoelectric single arm is composed of an electrode contact layer, a transition layer and a thermoelectric material layer. The electrode contact layer is copper doped with a small amount of nickel, and the transition layer is nickel and titanium metal from top to bottom. The thermoelectric materials in the N-type thermoelectric single arm and the P-type thermoelectric single arm are N-type magnesium-based material Mg3(Sb,Bi)2 and P-type magnesium-based material MgAgSb respectively.

8. The coupling system according to claim 6, characterized in that: The hot end of the thermocouple and the conductive copper electrode are connected to aluminum nitride ceramic sheets on both sides to absorb the heat generated by the photovoltaic power generation module and the photothermal module; the cold end of the thermocouple uses a high-emissivity metal material layer as a heat dissipation system to achieve heat dissipation, and the high-emissivity metal is nickel.

9. The coupling system according to claim 1, characterized in that: The electric energy generated by the thermoelectric power generation module is output together with the electric energy of the photovoltaic cell to the energy storage or load of the system, realizing the cascade conversion of solar photon energy.

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