基于棱镜二次聚光的高倍聚光模组聚光特性与三结电池光谱响应匹配与优化

目前Ⅲ-Ⅴ多结高倍聚光(HCPV)太阳电池实验室效率记录已高达46%,而相对应的模组效率与之相差仍较大,其中由于模组中聚光非理想性引起的损失就高达20%.本文通过建立光学模型和非均匀光照的三维电池电路网络模型,以Ⅲ-Ⅴ族三结电池为例,研究了菲涅耳透镜一次聚光、棱镜二次聚光的HCPV模组的聚光特性和光电特性.结果发现.由于光线非平行入射和-菲涅耳透镜的色散现象,使得沿光轴方向短、中、长波段聚光发散及聚光不均匀,从而造成了三结电池的上、中、下各子电池光谱响应失配损失,模组光电转换性能下降;进一步,通过采用棱镜二次聚光,能较好地改善聚光和温度均匀性;通过对光轴方向上短、中、长波段的聚光特性与三结电池光谱响应匹配优化,使得模组输出功率提高10%以上.模拟结果己得到实验验证.

Concentrating characteristics of Fresnel lens with prism secondary concentrator and optimization of high concentrating photovoltaic module with triple-junction cell

At present, Fresnel lens is commonly used as a concentrator in high concentrating photovoltaic (HCPV) module, and the triple-junction cell is currently one of the most common multi-junction cells used in it. The triple-junction cell is composed of three p-n junctions in series. Each sub-cell in it absorbs different-wavelength light. The solar cell efficiency of Ⅲ-V multi-junction high concentrating photovoltaic increases up to 46%, which the corresponding module efficiency is quite different from. The output power of the solar cell is related to not only the illumination energy, but also the spectral distribution and the uniformity of the illumination. The loss caused by the non-ideal concentration of the concentrator in the module is as high as 20%. After sunlight enters the lens, the direction of transmission of a monochromatic light is different, because a lens has different refractive index for different-frequency light. So the light disperses when leaving the lens, and thus the colors are arranged in a certain order to form a spectrum. Owing to the dispersion and the differences in refractive index among different spectral bands, the illumination distributions of the three spectral bands are different and non-uniform on the focal plane of lens. The divergence of light will obviously weaken the non-uniformity of the illumination on the solar cell surface. So the divergence angle of the light source has a greater influence on the cell performance because the non-uniformity of illumination has a negative influence on the performance of the cell.
In this paper, according to the establishment of optical model and three-dimensional cell circuit network model under non-uniform illumination, taking Ⅲ-V triple-junction cells for example, we study the concentrating characteristics and photovoltaic characteristics of HCPV module with Fresnel lens concentrator and prism secondary concentrator. The results show that due to the non-parallel incident light and dispersion of the Fresnel lens, the concentrating spots of short-wave light, medium-wave light and long-wave light are divergent and their illuminations are non-uniform, resulting in the spectral response mismatch loss of the three sub-cells in the triple-junction cell, and the photovoltaic performance of the HCPV module also declines. The results show that the secondary optics element is obviously effective in reducing the non-uniformity of the illumination and the temperature which the Fresnel lens creates. However, each waveband of light has a different spot size at the same position, similar to the Fresnel lens without the secondary optics element. So the varieties of cell performance at different positions are similar too. And, by optimizing the focusing characteristics of the three wave bands along the optical axis, the power output of the HCPV module can increase more than 10%. The simulation results are verified experimentally.