Photovoltaic water electrolysis reaching 31.3% solar-to-H2 conversion efficiency under outdoor operating conditions

Abstract Hydrogen generation from renewable energy sources allows balancing the intermittent nature of solar and wind power. The chemical energy stored in hydrogen can be efficiently converted back to electricity using fuel cells or hydrogen can be used in chemical processes or as secondary energy carrier in heat and gas markets. Several approaches have been investigated but most of them have a low conversion efficiency. Here we present a high-performance photovoltaic/electrolysis module that splits water molecules using the photovoltage of multi-junction solar cells. A Fresnel lens array concentrates direct sunlight onto photovoltaic cells with an open-circuit voltage above 4 V. These solar cells are electrically interconnected to the cathode and anode of two series-connected polymer electrolyte membrane electrolysis cells. A demonstrator with a lens area of 64 cm 2 was measured outdoors, converting up to 31.3% of sunlight energy into chemical energy according to the higher heating value of hydrogen.