Numerical modelling and experimental validation of a low concentrating photovoltaic system

Concentrator solar cells need to be designed optimally depending on the concentrating photovoltaic (CPV) system, application and operating conditions to ensure the best system performance. The important factors while designing include concentration ratio, cell material properties, expected operating temperature, cell shape, bus bar configuration, number of fingers their size and spacing. The irradiation incident on the solar cell while being concentrated experiences several losses caused by the different physical phenomena's occurring in the system. A particular issue for CPV technology is the non-uniformity of the incident flux on the solar cell which tends to cause hot spots, current mismatch and reduce the overall efficiency of the system. Understanding of this effect and designing the cell while considering these issues, would help in improving the overall performance of the system. This study focuses on modelling a low concentrating photovoltaic system used for building integration, optimising the cell metallisation and analysing the effects of temperature on the overall output of the system. The optical analysis of the concentrator is carried out using ray tracing and finite element methods to determine electrical and thermal performance under operating conditions. Furthermore, an analysis is made to understand the effects of non-uniformity on the output of the device. About 0.5% absolute drop in solar cell efficiency was observed due to non-uniformity at 5o incident angle. A relative drop of 1.85% was observed in the fill factor due to non-uniformity of the flux distribution. A maximum cell temperature of 349.5 K was observed across the cell in both uniform and non-uniform conditions under an incident solar radiation of 1000 W/m2 which further reduced the performance of the solar cell. The solar cell design was also analysed by varying the number of fingers and the optimum grid design reported. A small prototype concentrator based on the design proposed was made using polyurethane and tested experimentally with the optimized solar cell design. On comparing the results obtained using the experimental data a good agreement in the system output could be seen. The difference in the overall system output was seen to be of the order of 11% which could be due to several losses occurring in the prototype which were not accounted in the model. © 2013 Published by Elsevier B.V. All rights reserved