Sensitivity analysis of electrolyzer minimum load for capacity optimization in off-grid offshore wind–solar green hydrogen systems

Electrolyzer performance is a key determinant of the viability of renewable-powered green hydrogen systems. Proton exchange membrane (PEM) electrolyzers, despite their higher capital costs, are expected to provide greater flexibility through low-load operation. This study presents a sensitivity analysis of the minimum operating load of PEM electrolyzers in an off-grid offshore wind and solar energy system with battery storage, using weather data from Choshi, Japan. Scenario analyses for 2030 and 2050 reveal that lowering the minimum load significantly reduces hydrogen production costs by enabling continuous operation under variable renewable output and decreasing the required battery capacity. A threshold-like trend reversal was observed around a 4% minimum load, where the contribution of wind power to cost reduction differed between 2030 and 2050. At this threshold, the dominant cost-reduction mechanism shifts from decreasing battery capacity to enhancing renewable energy utilization. This threshold coincides with the switching behavior of key system parameters, particularly the electrolyzer capacity and curtailment ratio, indicating a structural change in the cost–performance relationship between 2030 and 2050. These findings suggest that the optimal operating load depends on the relative decline rates in the costs of wind, solar, battery, and electrolyzer technologies. Overall, lowering the electrolyzer minimum load enhances operational flexibility, allowing a wider range of electrolyzer capacities to operate efficiently under intermittent renewable energy supply. The results underscore the critical role of low-load-operable electrolyzers in optimizing the design and economics of off-grid renewable hydrogen systems.