Ray tracing for simulation of a light guide efficiency

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

This work is a feasibility study on using a light guide instead of a heat transfer loop for the energy transfer from the focal point of a concentrator to the heat absorber, The guide consists of two pipe bends, with internal reflecting surfaces. A polar mount setup then allows for single axis rotation where one bend is fixed and the other rotates. The seasonal solar change in declination will then give some variation in the entry angles for the rays at the inlet of the light guide. Two particular cases have been compared. In the first, the rays enter into the light guide with diverging angles, as the guide is positioned at the focal point of a parabolic dish. In the second case, a secondary reflector generates parallel rays at the entrance of a guide positioned below a central hole in the primary receiver. The study is made using a ray tracer which has been developed for concentrating solar reflector systems. Energy losses through a light guide can be associated with the number of internal reflections in the guide, and the number of back scattered rays through the tube inlet. The ray tracer is described briefly and sensitivity studies are made with variations in the tube lengths, surface reflectivity and the inlet ray angles.