Abstract
"Green" hydrogen production via polymer electrolyte membrane (PEM) electrolyzers must overcome significant energy penalties and high costs to become competitive in renewables-based energy systems. Adaptive operating strategies for PEM electrolyzers-by dynamically adjusting current density, pressure, and temperature-have demonstrated efficiency improvements in simple energy systems. However, their effectiveness in the context of complex power-to-X energy systems featuring variable downstream synthesis processes remains unclear. This work shows that integrated optimization of PEM electrolyzer operating parameters in conjunction with downstream methanation processes (MP) delivers substantial system-wide efficiency and cost benefits under dynamic hydrogen demand and pressure conditions. To demonstrate this, an equation-oriented process model of a PEM electrolysis system is embedded within a higher-level energy system model to compare sequential optimization (where the electrolyzer adapts to predetermined MP operating decisions) against integrated optimization (where electrolyzer and MP operating decisions are determined simultaneously). Sequential optimization delivers 7.3% operating cost savings compared to conventional fixed-parameter operation. In comparison, integrated optimization achieves 9.9% cost reductions and 7.8% decreases in electrolysis system electricity consumption. Operating pressure emerges as the most critical parameter, with electrolyzer electricity consumption exhibiting markedly higher sensitivity than MP electricity consumption. The analysis reveals fundamental trade-offs between component-level and system-level efficiency, demonstrating that prioritizing electrolyzer efficiency optimization yields superior system-wide performance. These findings establish that system-wide coordination through integrated optimization approaches substantially enhances the economic viability of "green" hydrogen supply in complex power-to-X energy systems.