Numerical And Experimental Study Of Concentrating And Splitting Photovoltaic-Thermoelectric Hybrid System

Solar energy is an important renewable clean energy source,but solar energy development has long been a bottleneck problem of low conversion efficiency and high cost.Concentrated photovoltaic（CPV）power generation technology can better solve the above problems,and is an important development and research direction in the field of solar energy utilization.Since CPV power generation technology usually only uses ultraviolet light and visible light to generate electricity,infrared light,which accounts for about 42%of the total solar radiation energy,cannot be effectively utilized.In high-concentration light,the concentrated infrared light will bring a huge heat load to the solar cell,which in turn reduces power generation efficiency and reduces system reliability.Aiming at the above problems,this paper proposes a concentrating and splitting photovoltaic/cascaded thermoelectric generators hybrid system,which separates the infrared light from sunlight by spectral beam splitting technology,the collected infrared light can be used to generate electricity based on thermoelectric semiconductor power generation（TE）technology.Thereby,the full spectrum conversion of solar energy is realized,and the heat load of the solar cell is greatly reduced,hence,the overall efficiency and reliability of the system are improved.In this paper,the energy transfer law of concentrating and splitting photovoltaic/cascaded thermoelectric generators hybrid system was analyzed,and the overall power generation model of the hybrid system was established.By writing a model solving program based on the EES engineering equation solver,the cut-off wavelength,concentration ratio,and height ratio of cascade device were optimized,and the theoretical results were verified by experiments.The main research contents and results are as follows:Firstly,we conducted the structural design to the hybrid system.The hybrid structure adopts Fresnel lens to concentrate solar energy,and the beam splitter mirror structure is composed of ultra-white glass and multi-layer dielectric film.The photovoltaic unit uses GaInP/GaAs two-junction solar cell,and the thermoelectric unit adopts the gradient design with CoSb₃ generator cascaded Bi₂Te₃ generator.Then,the energy transfer model of the hybrid system was established based on the structure design.According to Seebeck effect,Partier effect and Thomson effect,as well as the power generation principles of concentrating solar cell,a numerical power generation model of hybrid system was established.Besides,by programming engineering equation of the hybrid system based on EES,the parameters which can affect the performance of the hybrid system were optimized,such as cutoff wavelength,ratio of optical concentration,height ratio of two TE generators and direct normal irradiation.The results shows that the hybrid system achieves the optimal power generation performance when the cutoff wavelength λ_k=900nm,height ratio of two TE generatorsτ=0.6,and the ratio of optical concentration C_F=1000.When direct normal irradiation DNI=1000W/m²,the hot-junction temperature can reach to 600K and middle temperature T_m can reach to 420K,the cold side temperature has a limited change and keeps at 300K,the temperature of solar cell T_cell can reach to 325K.The TE subsystem efficiency,the PV subsystem efficiency η_pv and hybrid system η_PV-TE are 8%,44%and 35%respectively.Finally,the outdoor test platform of the hybrid system was designed and established.The performance of the hybrid system was researched experimentally under the condition of better direct radiation irradiation and was compared with the optimized results.