Study On Solar CPV/T Hybrid System With Solar Cells Coated Spectrum Splitting Film

Solar energy is a kind of renewable and clean energy, the utilization of solar energy is important for energy conservation and environmental protection. Photovoltaic (PV) power generation and solar thermal utilization are the main solar energy utilization methods. Solar radiation flux is very low, using solar concentrator, for example trough, tower, dish, and linear Fresnel reflector concentrator (LFR), can utilize solar energy with high efficiency and low cost. Among of them, LFR has characteristics of simple structure, easy maintenance, and good wind resistance. LFR concentrator consisting of flat mirrors can reflect and generate uniform flux on focal plane, which can reduce the influence of non-uniform of energy flux to PV conversion efficiency. In concentrating photovoltaic (CPV) systems, radiation flux on cell surface is high, and the energy which would not be converted into electricity will make the temperature of solar cells increasing, and therefore affect the PV conversion efficiency. Thus, cooling system is required. This thermal energy can be utilized to improve the efficiency of solar energy utilization, but the temperature of the fluid is normally restricted to a low temperature to ensure efficient operation of solar cells. Based on the spectrum splitting technique, a beam splitter is used to separate the concentrated solar radiation into two parts:one for the PV power generation and the other for thermal utility. Thus, the temperature of thermal utilization system will not be restricted by the temperature of solar cells. But the system equipped with beam splitter is complex and the beam splitter is at risk of thermal stress fracture. In this thesis, it is proposed that the spectrum splitting film is coated on solar cells’surface, a CPV/T system construction is optimized and theoretical analysis is carried out on it.Firstly, a CPV/T system using a linear Fresnel reflector as a concentrator and with solar cells coated spectrum splitting film. According to principles of geometric optics, the equations were established for the positional relationship between the various parts of the structure. The parameters of system construction were optimized according to the objective functions of area utilization ratio and geometric concentration ratio. The widths, installation locations, the mounting angles of each reflective mirror were obtained.Secondly, optical simulation for the proposed system was performed based on the Monte Carlo ray tracing method. The results show that the solar radiation flux distribution on the focal plane is uniform, which is suitable for PV power generation. The optimum mounting location of thermal receiver was obtained through optical simulation for the proposed CPV/T system. A secondary mirror was proposed and can collect the leaked approximate 27% of solar radiation.Thirdly, spectrum splitting film was designed on the basis of the interference theory of light with Si as the substrate and TiO2 and SiO2 as the high and low refractive index materials. It has a high transmittance in 380-1200nm band and high reflectivity in other band. The transmitted solar radiation is for PV power generation, and the reflected solar radiation is for photo-thermal conversion.Finally, the system efficiency was theoretically analyzed. On the basis of the spectral transmittance curve of the designed film, the transmitted AM1.5D solar radiation for PV power generation through the film was calculated. According to the performance parameters of solar cells, the generated power and efficiency were deduced. According to the spectral reflectance curve of the designed film and absorption property of thermal receiver surface, the thermal efficiency of the CPV/T system was obtained. The results show that at the conditions of solar cells temperature of 25 ℃ and thermal energy temperature of 300 ℃, the power generation efficiency of PV utilization part of the CPV/T system is 32.39%, the exergy efficiency of thermal utilization part is 23.79%, and the total exergy efficiency of the CPV/T system is 24.66%, which is higher than that of CPV system.