Even with favorable policy frameworks, green hydrogen has not been cost-competitive in Europe. Optimizing hydrogen production can reduce the Levelized Costs of Hydrogen (LCOH). In this research, an electrolysis system model is developed to optimize hydrogen production in two industrial settings. The model incorporates technical aspects such as part-load behavior, stack degradation, and energy inputs (i.e., electricity price and volume projections). Mid-scale hydrogen production for heavy-duty transport refuelling in Germany has the lowest LCOH at 8 <euro>/kg (with a 16 MWel electrolysis system), whereas large-scale hydrogen production for the refinery industry in Portugal achieves 4 <euro>/kg (with a 128 MWel system). The study reveals that the optimal system configuration depends on energy prices, technology costs, efficiency, load flexibility, and storage options. This study could be helpful in operationalizing hydrogen production systems (e.g., stack operation and replacement strategies) depending on energy supply and hydrogen demand over the lifetime.