Granularity-Aware Capacity Planning of Alkaline and PEM Electrolyzers Under Heterogeneous Operating Stress

Off-grid renewable power-to-hydrogen (ReP2H) systems require coordinated capacity planning and operation of alkaline (ALK) and proton exchange membrane (PEM) electrolyzers. This study develops a mixed-integer linear programming model that jointly optimizes candidate-unit capacity, production–standby–idle states, and a technology-specific operating-stress proxy. The objectives combine net annualized cost, wind curtailment, and operating stress. For the 60 MW baseline operating day, the model selects 55 MW of ALK and 1 MW of PEM capacity, with 99.36% wind-power utilization and an electrolyzer-side levelized cost of hydrogen of 2.6864 CNY kg−1. This value excludes wind generation, compression, storage, water treatment, and other balance-of-plant costs. Stress-aware scheduling mainly changes unit dispatch, whereas standby reduces ALK switching. The unit-level module-size, capital-cost, and objective-weight comparisons associate the small baseline PEM share with discrete capacity increments and the tested economic preferences. With the baseline capacity fixed, the continuous full-year three-state simulation produces 3.0750 × 106 kg of hydrogen with 99.429% wind-power utilization at an electrolyzer-side cost of 3.3104 CNY kg−1 and reduces ALK startups by 29.25% relative to the two-state model. These results delimit the operating and scenario conditions under which the reported hybrid configuration applies.