Modeling photovoltaic-electrochemical water splitting devices for the production of hydrogen under real working conditions

Abstract

Photoelectrochemical splitting of water is potentially a sustainable and affordable solution to produce hydrogen from sun light. Given the infancy stage of technology development, it is important to compare the different experimental concepts and identify the most promising routes. The performance of photoelectrochemical devices is typically measured and reported under ideal irradiation conditions, i.e. 1 sun. However, real-life operating conditions are very different, and are varying in time according to daily and seasonal cycles. In this work, we present an equivalent circuit model for computing the steady state performance of photoelectrochemical cells. The model allows for a computationally efficient, yet precise prediction of the system performance and a comparison of different devices working in real operating conditions. To this end, five different photoelectrochemical devices are modeled using experimental results from literature. The calculated performance shows good agreement with experimental data of the different devices. Furthermore, the model is extended to include the effect of illumination and tilt angle on the hydrogen production efficiency. The resulting model is used to compare the devices for different locations with high and low average illumination and different tilt angles. The results show that including real illumination data has a considerable impact on the efficiency of the PV-EC device. The yearly average solar-to-hydrogen efficiency is significantly lower than the ideal one. Moreover, it is dependent on the tilt angle, whose optimal value for European-like latitude is around 40°. Notably, we also show that the most performing device through the whole year might not necessarily be the one with highest sun-to-hydrogen efficiency for one-sun illumination.