GaAs/silicon PVMirror tandem photovoltaic mini‐module with 29.6% efficiency with respect to the outdoor global irradiance

Balance‐of‐system costs now dominate the installed cost of photovoltaic systems, causing the annually averaged module efficiency to become a primary system cost driver. The resulting continued push towards higher module efficiencies, coupled with the dominance of single‐axis tracking in the utility‐scale PV market, may create an opportunity for a low‐concentration tandem module technology. Here, we demonstrate such a tandem, using the “PVMirror” concept, on the mini‐module scale. The tandem couples a (concentrating) silicon PVMirror having an aperture area of 156.25 cm2 with a gallium arsenide receiver to achieve 29.6% efficiency with respect to the outdoor global irradiance. Unlike most concentrating technologies, the silicon PVMirror collects some of the diffuse light, but the tandem would nevertheless achieve 31% efficiency in the absence of diffuse light, as in a laboratory measurement. The same tandem technology can be implemented with a wide‐bandgap thin‐film PVMirror and silicon receiver—a potentially cost‐competitive combination—when efficient wide‐bandgap cells have been developed. We present a low‐concentration “PVMirror” tandem concept based on single‐axis tracking. Though a concentrating technology, it collects diffuse light, as the primary optic is a PV module. We demonstrated this tandem concept by using a silicon mini‐module as a PVMirror and a gallium arsenide mini‐module as a receiver and hit 29.6% efficiency with respect to the outdoor global irradiance, which is the highest‐efficiency silicon‐based tandem reported with an area larger than 5 cm2 (the aperture of our tandem is 156 cm2).