Effect of Secondary Reflectors on Flux Distribution of a Fresnel Concentrator

Flat reflectors which have lower price compared with parabolic ones are used in Fresnel concentrator. Each Fresnel collector is comprised of a few flat reflectors which are placed parallel to each other near the ground. If effective width of flat reflectors is more than absorber tube diameter, reflected rays will be partly lost, hence low optical efficiency. By installing a secondary reflector above the absorber tube, lost rays are mostly redirected towards the absorber tube. This leads to a more uniform flux and a higher optical efficiency. In this research, effects of three geometries for the secondary reflector are investigated and the results are presented. One of these designs produces very uniform flux on the absorber tube whereas the second design leads to higher optical efficiency. A computer program has been employed to evaluate these effects.