Multi-objective optimisation of hydrogen and methanol-based hybrid power systems for service operation vessels: A techno-economic and environmental analysis

Decarbonising offshore-wind service operation vessels (SOVs) requires fuel-pathway choices that balance cost, emissions, and onboard integration. This study develops a bi-level techno-economic and environmental optimisation framework for a 5 000 GT offshore wind farm SOV, coupling NSGA-II architecture sizing with second-by-second rule-based energy management. The three alternative pathways compared are dual-fuel methanol engines (DFME), liquid-hydrogen proton-exchange membrane fuel cells (PEMFC), and methanol-reforming fuel cells (MRFC). The framework minimises capital expenditure, lifecycle operating expenditure, and well-to-wake carbon intensity over a representative 14-day mission profile, with TOPSIS used to select one balanced decision case from each Pareto front. A unified β ∗ / Γ ∗ metric is introduced to quantify the weight reallocation or deck-volume expansion associated with each pathway. Relative to the diesel baseline, the TOPSIS designs reduce well-to-wake carbon intensity by 68.7% for DFME, 83.3% for MRFC, and 93.6% for PEMFC, while increasing lifecycle cost from 29.14 MUSD to 96.89–110.72 MUSD. No pathway is universally dominant across cost, emissions, and integration-related indicators. DFME provides the lowest lifecycle cost and highest technology readiness. MRFC offers the most favourable weight-and-volume fit among the deep-decarbonisation options. PEMFC achieves the largest carbon reduction only when the green-hydrogen production emission factor remains below approximately 2.1 kgCO 2 e/kgH 2 .