Optical Analysis of Secondary Optics for Solar Concentrators with a View to Optimising Cell Metallisation

Although concentrated photovoltaic (CPV) systems can achieve high energy conversion efficiencies due to their use of concentrating optics and high-efficient multi-junction solar cells, power losses arising from the front surface reflection and metallization shading typically contribute a significant fraction to the total power loss for these devices. There is an opportunity to reduce these losses by optimizing the geometry of the metal contacts, however this requires an understanding of the optical flux and angular distribution of the light delivered to the surface of the cell. This study aimed to determine the influence of secondary optical elements (SOEs) in CPV systems on the optical flux and angular distribution of the light. The optical flux and angular distribution for refractive SOEs with straight and tapered sides were compared using ray-tracing simulations. It is shown that both SOEs can homogenize the flux distribution at the receiver. However, the ray angle range incident on the solar cell receiver remains the same for the homogenizer with straight edges and largely increased for the homogenizer with tapered sides. This has important implications for solar cell metal contact geometry design.