Carbon Footprint of Hydrogen Production with PEM Water Electrolysis: Effects of Electricity Generation Mix, Load-Shifting Strategies

Proton exchange membrane (PEM) water electrolysis is considered a promising route for low-carbon hydrogen production, yet the carbon footprint of the hydrogen produced may vary considerably with the structure of the electricity supply, the temporal operating strategy of the electrolyzer, and the system lifetime. This study examines these three factors within a single, transparent scenario framework. A 10 MW PEM system with a specific electricity consumption of 50 kWh/kg H2 and a 50% capacity factor is modeled. The electricity system is represented by coal, natural gas, onshore wind, and solar photovoltaic (PV) generation, combined into three mixes: fossil-dominated (F), balanced (B), and renewable-dominated (R). For each mix, a representative day with hourly source shares is defined, from which hourly carbon intensity is derived. Three operating strategies are compared: flat operation (LS0), moderate load shifting (LS1), and high load shifting (LS2), with progressively higher loads during the six lowest-carbon-intensity hours and lower loads during the intermediate- and high-carbon-intensity hours, while daily hydrogen output is held constant. System lifetimes of 10, 15, and 20 years are used to allocate the embodied emissions of electrolyzer manufacturing and stack replacement. The assessment is attributional and uses average life-cycle emission factors with perfect foresight; the main scenario analysis is based on constructed hourly electricity-mix profiles, while hydrogen storage is excluded from the system boundary. The resulting scenarios yield carbon footprints between approximately 7.4 and 29.9 kg CO2e/kg H2. Under LS2, the carbon footprint was reduced by 1.31, 3.13, and 2.74 kg CO2e/kg H2 for the F, B, and R mixes, respectively. Across the scenario ranges examined, the carbon footprint varied with the electricity mix and operating strategy, whereas changes associated with the evaluated system lifetimes were smaller.