Free-form Fresnel RXI Köhler design with spectrum-splitting for photovoltaics

Abstract

Here we present a novel optical design of the high concentration photovoltaics (HPCV) nonimaging concentrator (>500x) with built-in spectrum splitting concept. The primary optical element (POE) is a flat Fresnel lens and the secondary optical element (SOE) is a free-form RXI-type concentrator with a band-pass filter embedded in it, both POE and SOE performing Kohler integration to produce light homogenization on the target. It uses the combination of a commercial concentration GaInP/GaInAs/Ge 3J cell and a concentration Back-Point-Contact (BPC) silicon cell for efficient spectral utilization, and external confinement techniques for recovering the 3J cell's reflection. Design targets equivalent cell efficiency ~46% using commercial 39% 3J and 26% Si cells, and CPV module efficiency greater than 38%, achieved at a concentration level larger than 500X and wide acceptance angle (±1°). A first proof-of concept receiver prototype has been manufactured using a simpler optical architecture (with a lower concentration, ~100x and lower simulated added efficiency), and experimental measurements have shown up to 39.8% 4J receiver efficiency using a 3J with peak efficiency of 36.9%.