Optimising Bop for Green Hydrogen Production in PEM Electrolysis

Abstract The study investigates the optimisation of Balance of Plant (BOP) subsystems in Proton Exchange Membrane (PEM) electrolyser systems for green hydrogen production. The research highlights that BOP is not a secondary support unit, but a core contributor to overall efficiency, reliability, safety, and cost performance. Literature-based evidence indicates that 40–60 % of the total installed PEM electrolyser CAPEX is linked to BOP components rather than the stack itself. BOP inefficiencies can reduce net system efficiency by up to 10 percentage points, suggesting that high stack performance may still lead to weak plant-level results. Key BOP subsystems assessed include water purification, thermal management, power electronics, gas handling and purification, compression and storage, and control/safety systems. PEM electrolysis requires ultrapure water with conductivity below 0.1 µS/cm and stable operating temperatures typically between 50 and 80 °C. A quantitative case study of a 10 MW PEM plant is used to illustrate subsystem-level impacts on cost and energy consumption. In this case study, BOP energy consumption is approximately 6–10 kWh/kg H₂, with major losses from power electronics (3–4 kWh/kg) and compression/storage (2–4 kWh/kg). Total electricity use is assumed at 55 kWh/kg H₂, including BOP losses. With 6,000 operating hours/year, the plant produces about 1.09 million kg H₂/year (≈1,091 t/year). Under a base electricity price of 50 EUR/MWh, annual electricity cost reaches ~3.0 million EUR/year. Total CAPEX is assumed at 900 EUR/kW, resulting in 9.0 million EUR investment for the 10 MW plant. Using a 20-year lifetime and 8 % discount rate, the calculated LCOH is approximately 3.8 EUR/kg H₂. The results confirm that BOP optimisation is essential for reducing parasitic losses, improving net efficiency, and lowering the levelized cost of hydrogen.