Direct measurement and simulation techniques for analysis of radiation flux on a linear PV concentrator

For a linear reflective photovoltaic concentrator, small regions of low radiation flux can significantly reduce the output current of an entire array. Therefore, understanding the causes of light non-uniformities along the focal line is crucial in the design of a trough concentrator. Typically, the flux profile is dependent on factors such as the mirror shape accuracy, gaps between mirrors and shading due to receiver supports. Radiation flux profiles have been measured on the combined heat and power solar (CHAPS) collectors developed at the Australian National University (ANU). The results for the first prototype showed significant variation in the radiation flux intensity along the length. The effect of imperfections in the mirror shape has been studied using ray tracing techniques and the software package Opticad. The simulations allowed the individual effects of mirror shape imperfections, gaps between mirrors and shading to be examined. It was found that small variations from the ideal mirror shape could cause large variation in the longitudinal radiation flux profile. Finally, techniques to minimise the drop in performance of a PV concentrator due to flux non-uniformities are discussed, including use of bypass diodes and choice of solar cells.