Second stage reflective and refractive optics for concentrator photovoltaics

In this paper we report on research activities at the Fraunhofer Institute for Solar Energy Systems (ISE) in the area of secondary optics for concentrator modules. The underlying module technology is based on 40×40 mm² Fresnel lenses, passive copper based heat spreaders and triple-junction III–V solar cells. Currently reflective as well as refractive secondaries are investigated. First results show an increased acceptance angle of up to +/−0.9°, which permits a better use of circumsolar radiation and reduces the accuracy requirements on assembly, alignment, and tracking technology. A very promising first result of our research on secondary optics is a module with an outdoor efficiency of 28.5 %, which is the highest module efficiency achieved at the Fraunhofer ISE so far.