An investigation of non-uniformities in the longitudinal radiation flux profile of a single-axis tracking parabolic trough concentrator

The uniformity of the radiation flux profile along the focal line of a linear parabolic concentrator is typically
dependent on factors such as the mirror shape accuracy, gaps between mirrors and shading due to receiver
supports. For a photovoltaic trough concentrator, small regions of low radiation flux can have a large impact
on the entire system performance. Radiation flux profiles have been measured on the Combined Heat and
Power Solar Collectors developed at the Australian National University. 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.