How much technological progress is needed to make solar hydrogen cost-competitive?

Cost-effective production of green hydrogen is a major challenge for global adoption of a hydrogen economy. Technologies such as photoelectrochemical (PEC) or photocatalytic (PC) water splitting and photovoltaic + electrolysis (PV+E) allow for sustainable hydrogen production from sunlight and water, but are not yet competitive with fossil fuel-derived hydrogen. Herein, open-source software for techno-economic analysis (pyH2A) along with a Monte Carlo-based methodology for modelling of technological progress are developed. Together, these tools allow for the study of required technological improvement to reach a competitive target cost. They are applied to PEC, PC and PV+E to identify required progress for each and derive actionable research targets. For PEC, it is found that cell lifetime improvements (> 2 years) and operation under high solar concentration (> 50-fold) are crucial, necessitating systems with high space-time yields. In case of PC, solar-to-hydrogen efficiency has to reach at least 6% and lowering catalyst concentration (< 0.2 g/L) by improving absorption properties is identified as a promising path to low-cost hydrogen. PV+E requires ca. 2 or 3-fold capital cost reductions for photovoltaic and electrolyzer components. We hope that these insights can inform materials research efforts to improve these technologies in the most impactful ways.