Gap design and optical losses of compound parabolic concentrators

Compound parabolic concentrators (CPCs) have been widely used in solar thermal and photovoltaic electricity generating systems due to their simple structure without any tracking system. The reflectors of a typical ideal CPC contacts the absorber at the ends of absorber, but a gap must be left between the absorber and reflectors for practical applications due to practical requirements. In this article, three common design options of CPCs were presented and the optical losses through gaps were theoretically analyzed. A comparison of gap losses for three design options of a CPC was also made. The results showed that, for CPCs with flat absorbers, the preferable design option of gaps for minimizing optical loss was to truncate the reflectors adjacent to the absorber; for CPCs with a tubular absorber, the best way was to modify the virtual absorber of ideal CPCs to accommodate the actual tubular absorber so that a gap could be produced, the next was to truncate the reflectors near the absorber.