Abstract. CPV systems using 3-junction solar cells have proven good performance and reliability. As the performance of 3-junction cells is saturating [1], the logical next step is the introduction of 4-junction (4-J) solar cells into CPV modules. The current world record for cell efficiency under concentrated light of 46.0% was achieved using a wafer bonded Soitec 4-J cell (SmartCell TM ) [1][2][3][4]. This paper discusses a new module design, optimized for harvesting the full potential provided by this high cell efficiency. Prototype modules have been built in order to explore the design space. A module efficiency of 38.9% under concentrator standard test conditions has been achieved.

Recent investigations of silicone-on-glass (SoG) Fresnel lens concentrator optics have shown a dependence of the optical efficiency and module performance on lens temperature. It was shown that the temperature dependence is dominated by a reduction of the refractive index with increasing temperature and a deformation of the lens structure due to thermal expansion of the lens material. We succeeded in modeling these effects on a computer by simulating thermal deformations of the lens structure using the finite element method (FEM) and analyzing the resulting deformed structure using ray tracing simulations. In former work, we were able to demonstrate a very good match to high precision optical measurements of Fresnel lenses at varying temperatures. The detailed insight we gained through our measurements and computer simulations was used to develop and manufacture a lens with improved optical performance at the temperature interval which is relevant for operation within a concentrator photovoltaic module. For these optimized SoG lenses, detailed computer simulations predict a significant increase in optical efficiency when compared to non-optimized lenses. High precision measurements of the optical efficiency allowed us to verify our expectations and compare experimental results of a Fresnel lens optimized for operation under varying ambient temperatures to results obtained for non-optimized Fresnel lenses.

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