| In order to improve the competitiveness of the concentrator photovoltaic technology,it is necessary to improve the performance of concentrator photovoltaic products and reduce the power generation cost.The industrial efficiency of 40% has been achieved for Ga In P/Ga In As/Ge mutijunction solar cell,while the efficiency of concentrating photovoltaic modules is much lower.Through analysis,it is found that the concentrator is one of the main reasons for efficiency loss.The traditional flat-plate Fresnel concentrator is usually designed basing on the imaging principle,whose performance is not good.There are many problems such as serious dispersion causing the decrease of the optical efficiency and spectro-spatial nonuniformities causing the decrease of the short circuit current,fill factor and the cell efficiency.The concentrator with good performance is needed to improve the industrial efficiency of concentrating photovoltaic modules.Therefore,the work in this paper is carried out in support of the National 863 projects(2011AA050507).The new Fresnel concentrator is designed by the method of analysis,simulation and experimental study.The application of the new Fresnel concentrator is also studied in concentrator photovoltaic technology.The specific research results are as follows:1.The theoretical calculation model is established for performance evaluation.The optical loss of the Fresnel lens is quantified and the detailed theoretical analysis of the optical efficiency is carried out.The theoretical calculation model of uniformity is established based on the ray-tracing method.2.A novel Fresnel lens with improved uniformity is designed especially for GaIn P/GaIn As/Ge multijunction solar cell.The new Fresnel lens is designed by the multi-wavelength and multi-focus method,taking full account of the multijunction solar cell spectral response characteristic and the material’s refractive index dispersion curve.The optical performance of the new Fresnel lens is verified by ray-tracing simulation.Results indicate that the new Fresnel lens achieves uniformity more than 75%,optical efficiency than 80% with the broadband solar spectrum from 300 nm to 1800 nm and every subcell’s spectral response bands.3.The electrical characteristic of the concentrator photovoltaic monomodule is analyzed by the method of simulation and experimental research.On the basis of the equivalent circuit,a kind of simplified 3-D distributed grid circuit model is established,and the I-V characteristics of concentrated multi-junction solar cells are simulated by LTspice and Matlab under the condition of non-uniform radiation.The electrical performance of the monomodule is analyzed by 3-D distributed grid circuit model and ray tracing method.The simulation results show that conversion efficiency of the designed monomodule is 32.4%,which is 8% higher than that of traditional monomodule.On the basis of simulation research,the Fresnel concentrator’s optical performance and the monomodule’s electrical characteristic are tested outdoors.4.The new Fresnel concentrator photovoltaic module is fabricated.The acceptance angle of the module is more than 1° by increasing a coniform device with large diameter,reducing the requirement for tracking precision and improving the reliability of the module.The encapsulation materials and the structure of the m odule are determined based on thermal analysis and cost considerations.By optimizing the encapsulation process and controlling the installation error,the sample module is prepared.The electrical and temperature characteristic of the module has been test ed.The results show that the module efficiency is 27.9% and the maximum output power is 89.39 W,when direct irradiance is 850 W/m~2.Besides,the module can well satisfy the cooling requirements,the module temperature is at the range of 40 ~55 ℃ during most time of the day,and the highest temperature is 60.5 ℃. |
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