Theoretical and experimental performance of a two-stage (50X) hybrid spectrum splitting solar collector tested to 600 °C

A hybrid concentrating photovoltaic/concentrating solar power spectrum splitting collector has been designed, developed, and experimentally tested. The two-stage optical system pairs a parabolic trough with a compound parabolic concentrating secondary, generating 50X geometric concentration on the thermal absorber. Double-junction indium gallium phosphide/gallium arsenide solar cells integrated into the secondary reflector generate electricity from photons with energy greater than ∼1.4 eV and reflect the remaining lower energy infrared photons to the thermal absorber for optimal spectral utilization. Simulations predict an optical efficiency of 64%, thermal efficiency of 52% at 600 °C, and efficiency of the back-reflecting concentrating photovoltaic subsystem of 6%. The collector has been developed into a working prototype and tested on-sun up to 600 °C using suspended solid particulate (alumina based) heat transfer fluid. The prototype demonstrates an optical efficiency of 63% and a net solar-to-electric efficiency of the concentrating photovoltaic subsystem of 4%. Thermal efficiency is much lower in the prototype collector and the potential causes have been examined. Overall, this work demonstrates a two-stage collector design, the ability of back-reflecting solar cells to operate as spectrum splitting devices, and the feasibility of an internally circulated solid particulate heat transfer fluid which enables high temperature operation beyond what is currently achievable with existing heat transfer fluids.