Prisms with Total Internal Reflection as Solar Reflectors.

摘要

For the sake of good optical efficiency,the reflectivity rho of mirror surfaces in solar collectors should be as high as possible. Until now,most solar reflectors have used aluminum with values of rho in the 80to 90percent range. Even the best material,silver,allows reflectivities only up to 95percent. With total internal reflection (TIR),on the other hand,the effective reflectivity is limited only by absorption in the transparent medium,and absorption losses can as easily be kept below five percent. In certain solar collectors,conventional mirrors can be replaced by an array of small rectangular glass prisms,an optical trick well known from binoculars. The only problem is that TIR occurs for a restricted range of incidence angles,limited by the low value of the refractive index n approximately equal to 1.5of commonly available glass or acrylic. However,an additional degree of freedom is gained in the design of solar collectors because only concentration,not imaging,is relevant. The suitability of TIR prismatic reflectors for solar energy collection is investigated systematically. (ERA citation 02:009540)