Techno-economic and environmental assessment of hybrid propulsion systems based on solid oxide fuel cells for short-sea shipping

Solid oxide fuel cells (SOFCs) are receiving increasing attention in the maritime sector as a decarbonisation option, owing to their high efficiency, fuel flexibility, and low pollutant emissions. This work investigates the retrofit of existing natural gas-fuelled vessels equipped with internal combustion engines (ICEs) through the integration of SOFC technology, using a short-sea RoPax ferry as a case study. A reference ICE-only configuration is compared with two SOFC-based hybrid layouts, including a fully integrated system exploiting anode off-gas recirculation. Detailed component models accounting for part-load operation are employed to perform a fully integrated assessment of energy performance, emissions, and economic feasibility. Sensitivity analyses on key parameters, including SOFC investment cost, fuel price, and vessel residual lifetime, are performed to identify the boundary conditions under which SOFC hybridisation becomes cost-effective. The results show that SOFC-based baseload supply significantly improves overall efficiency by mitigating inefficient ICE operation at partial loads. Compared to the ICE-only configuration, daily fuel consumption and CO 2 emissions are reduced by approximately 18%. Additional improvements from anode-off gas utilisation are observed but remain limited due to the relatively small SOFC-to-ICE size ratio imposed by the vessel operational profile. However, these benefits are expected to increase for vessel typologies characterised by higher baseload demand and longer sailing distances. From an environmental perspective, SOFC-powered harbour operation enables an almost complete abatement of NO x and CO emissions (above 90%), highlighting the strong potential of SOFC systems to improve air quality in port areas. Finally, the economic analysis indicates that the vessel residual lifetime plays a key role in determining the viability of SOFC retrofitting. Under current assumptions, cost parity is approached for residual lifetimes above approximately 15 years. In addition, the proposed solution becomes increasingly attractive when considering expected medium- to long-term reductions in SOFC investment costs and the inclusion of carbon pricing. Overall, the results highlight SOFC-ICE hybridisation as an effective pathway to improve the efficiency and environmental performance of short-sea shipping.