Solar hydrogen production: a bottom-up analysis of different photovoltaic-electrolysis pathways

The conventional energy system is undergoing a transformation towards renewable energy technologies, as society strives for sustainable and green energy supply. This has created challenges, such as spatial and temporal imbalances of energy demand and feed-in arising from volatile renewable energy resources. A possible solution to this challenge is presented by hydrogen as a versatile chemical storage medium. Promising technologies for producing hydrogen from renewable energy include the production pathways photoelectrolysis (PEC) and photovoltaic-electrolysis (PV-EL). This paper examines three production pathways which differ in the connection and integration of the constituent photovoltaic (PV) and electrolysis (EL) subsystems by modelling the integrated system's behaviour under the various device designs and operational conditions. The model is based on the electrochemical processes and addresses losses and how the overall performance can be enhanced, in contrast to literature-based models. The efficiency of the subsystems, as well as the coupling efficiency, are predicted under various conditions, enabling the determination of optimum design and operational parameters. This analysis is enhanced by an application of the PV-EL pathways to the hourly weather conditions of Julich, Germany. The solar to hydrogen efficiency was found to drop as the level of integration increased. The study showed that varying weather conditions strongly affect the efficiency of integrated systems and should be further taken into account for future improvement and cost estimations of integrated device performance.