Improving illumination and temperature distribution uniformity in high concentrating solar cells

High concentrating Photovoltaic (HCPV) has the potential to replace the expensive PV material with cheaper optical elements. The use of high solar concentration ratios with the triple junction III-V solar cells offers potential of high solar cell efficiency and power output. However, non-uniformity of the incident flux is detrimental to the CPV technology as this tends to cause hot spots and current mismatch leading to reduced electrical efficiency of the system and degrade the life of the solar cell. In this work, a point focus Fresnel lens was developed and the influence of using a small square reflector placed above the PV surface as a Secondary Optical Element (SOE) in alleviating the non-uniform illumination and temperature distribution was investigated. Also, the SOE height and material reflectivity influence on the optical performance was examined. This was done by implementing optical and thermal simulations using advanced ray tracing method and Multi-physics finite element software respectively. Incident rays distribution uniformity was evaluated using the standard deviation from the mean value. A low standard deviation indicates that most received rays by the solar cell are close to the mean value i.e. more uniform. Results show that a combination of introducing a short SOE (60mm) made from 95% reflective material above the PV and increasing the distance between the PV and the Fresnel lens (l) to 500mm significantly improve the surface illumination uniformity. The achieved uniformity standard deviation is less than 3 with minimum loss in received power i.e. 48.25W in case of introducing SOE and l=500mm compared to 49.07W where receiver placed at focus point.