Holistic design guidelines for solar hydrogen production by photo-electrochemical routes

Device and system design choices for solar energy conversion and storage approaches require holistic design guidelines which simultaneously respect and optimize technical, economic, sustainability, and operating time constraints. We developed a simulation platform which allows for the calculation of solar-to-hydrogen efficiency, hydrogen price, device manufacture and operation energy demand, and the component degradation and replacement time of photo-electrochemical water splitting devices. Utilizing this platform, we assessed 16 different design types representing all possible combinations of a system: i) operating with or without irradiation concentration, ii) utilizing high-performing and highcost or low-performing but low-cost photoabsorbers, iii) utilizing high-performing and high-cost or lowperforming but low-cost electrocatalysts, and iv) operating with or without current concentration between the photoabsorber and the electrocatalyst. Our results show that device types exist with a global optimum (a Pareto point), simultaneously maximizing efficiency, while minimizing cost and the energy demand of manufacture and operation. In our examples, these happen to be the device types utilizing high irradiation concentration, as well as expensive photoabsorbers and electrocatalysts. These device types and designs were the most robust to degradation, exhibiting the smallest price sensitivity for increasing degradation rates. Other device types did not show a global optimum, but rather a set of partially optimized designs, i.e. a Pareto front, requiring a compromise and prioritization of either performance, cost, or manufacture and operation energy demand. In our examples, these happen to be the device types using low-cost photoabsorbers. The targeted utilization of irradiation and current concentration predicted that even device types utilizing expensive components can provide competitive solutions to photo-electrochemical water splitting. The quantification of the influence of component degradation on performance allows the suggestion of best practice for device operational time and component replacement. The framework and findings presented here provide holistic design guidelines for photo-electrochemical devices, and support the decision-making process for an integral and practical approach to competitive solar hydrogen production in the future.