System efficiency analysis of direct coupled PV–PEM electrolyzer systems

Green hydrogen is an important technology in the energy transition, with potential to decarbonize industrial processes, increase renewable energy use, and reduce reliance on fossil fuels, yet it currently accounts for less than 1% of global hydrogen demand. One promising approach to expand production is the direct coupling of photovoltaic–electrolyzer systems. In this study, overall and sub-system efficiencies were analyzed for different system setups, coupling points and operating conditions such as temperature and irradiance. The highest overall system efficiencies were found to be more than 18%. The effect of varying irradiances on the coupled efficiency was not more than 5.7%. Different system designs, optimized for different irradiances led to effects such as an increase in current density at the electrolyzer and, thus, an increase in the overvoltage, which resulted in an overall efficiency loss of more than 3%. A key finding was that aligning the PV maximum power point with the electrolyzer polarization curve enables consistently high system efficiencies across the investigated irradiances. The findings were validated with two real life systems, reproducing the coupling efficiencies of the model, with 12%–14% including loss factors and approximately 18% for a direct coupled system, respectively.