The climatic response of thermally integrated photovoltaic–electrolysis water splitting using Si and CIGS combined with acidic and alkaline electrolysis

The Horizon 2020 project PECSYS aims to build a large area demonstrator for hydrogen production from solar energy via integrated photovoltaic (PV) and electrolysis systems of different types. In this study, Si- and CIGS-based photovoltaics are developed together with three different electrolyzer systems for use in the corresponding integrated devices. The systems are experimentally evaluated and a general model is developed to investigate the hydrogen yield under real climatic conditions for various thin film and silicon PV technologies and electrolyser combinations. PV characteristics using Si heterojunction (SHJ), thin film CuInxGa1-xSe2, crystalline Si with passivated emitter rear totally diffused and thin film Si are used together with temperature dependent catalyst load curves from both acidic and alkaline approaches. Electrolysis data were collected from (i) an Pt-IrO2–based acidic and (ii) a NiMoW-NiO–based and (iii) a Pt-Ni foam–based alkaline electrolysis systems. The calculations were performed for mid-European climate data from Julich, Germany, which will be the installation site. The best systems show an electricity–to–hydrogen conversion efficiency of 74 % and over 12 % STH efficiencies using both an acidic and alkaline approach and is validated with a smaller lab scale prototype. The results show that the lower power delivered by all the PV technologies under low irradiation is balanced by the lower demand for overpotentials for all the electrolysis approaches at these currents, with more or less retained solar-to-hydrogen (STH) efficiency over the full year if the catalyst area is the same as the PV area for the alkaline approach. The total yield of hydrogen instead follows the irradiance, where a yearly hydrogen production of over 35 kg can be achieved for a 10 m2 integrated PV-electrolysis system for several of the PV and electrolyser combinations that also allow a significant (100-fold) reduction in necessary electrolyser area for the acidic approach. Measuring the catalysts systems under intermittant- and ramping conditions with different temperatures, a 5% lowering of the yearly hydrogen yield is extracted for some of the catalysts systems while the Pt-Ni foam–based alkaline system showed uneffected or evern slighly increased yearly yield under the same conditions.