The concentrating system includes concentrator, secondary concentrator, reflector, etc. in the application of concentrating photovoltaic, the main considerations are the multiple of concentrating, the radiation intensity distribution and spectrum of the spot after concentrating.
According to the optical principle, concentrators can be divided into refraction concentrator, reflection concentrator, composite concentrator, thermal photovoltaic concentrator, etc. There are two kinds of refractive concentrators used in concentrating photovoltaic: Fresnel lens and ordinary lens. Fresnel lens is a planar condenser. Fresnel lens has the advantages of light weight, low cost and simple structure. The specific design belongs to the category of non imaging optics, which has no focal plane defined by optical elements, and can produce light intensity gain much better than that of traditional imaging optics. Fresnel lens can be divided into two types: bow and complete plane. The arcuate Fresnel lens has better optical properties
The transmission efficiency is also affected by the lens material, processing technology and solar irradiation time, and there are different degrees of dispersion.
There are several types of reflective concentrators, such as parabolic mirror, flat plate, parabolic trough and combined parabolic surface (CPC). The reflective materials are mainly silver plated glass and aluminum plated surface, and some use high reflectivity film of polymer materials to make reflective surface. The advantage of reflective focusing is that there is no dispersion phenomenon, the spot radiation distribution is uniform, and the reflection efficiency can be close to 100%. Concentrator photovoltaics advantage is that it can achieve a larger concentration ratio in a relatively small size. Some studies have proposed that the secondary reflective lens can be coated optically to realize the splitting of sunlight in different bands, Therefore, the composite photovoltaic power generation system composed of solar cells sensitive to different bands can be selected to improve the photoelectric conversion efficiency of the whole system. The disadvantage is that the structure is relatively complex and the tracking accuracy is high.
In practical applications, due to the influence of the accuracy of the solar tracking system and the wind direction, the actual solar incident direction often deviates slightly from the axial direction of the concentrator, and the light intensity distribution of the solar cell surface spot will decline rapidly.