Performance evaluation of a nonimaging secondary reflector on a commercial parabolic trough concentrator

Abstract

Parabolic trough concentrators are a proven technology in the field of solar power. Solar radiation is reflected by a linear parabolic mirror and concentrated onto the surface of an absorber tube with the purpose of increasing the thermal energy of a fluid that flows within for commercial, industrial or residential applications. The minimum diameter of an absorber tube relies exclusively from the light cone originating from the parabola, which is why, reducing its diameter increases the total average radiation. The use of secondary reflectors are a viable way to increase the total radiation concentration at the absorber tube without sacrificing collection efficiency. The performance of multiple tailored seagull-type secondary reflectors were evaluated under several conditions. A Matlab script to design the various secondary reflectors was created to generate different secondary reflector designs. The various secondary reflectors were evaluated by the simulation program SolTrace. Compared to a simple absorber tube, the absorber tube with a secondary reflector experienced average radiation intensity over 600% of the original oversized absorber while only suffering an absorbed power loss of below 5%. Under the scenario that included a glass tube surrounding the absorber and the secondary reflector size being limited as well by the glass tube, the absorber experienced concentration increases from approximately 460% up to 600% and losses of approximately 10%. The results show that the seagull-type secondary reflector can be implemented to improve performance of parabolic trough concentrators.