Decarbonising maritime shipping through multi-fuel solid oxide fuel cell pathways : synergies and trade-offs between environmental and social sustainability metrics

Background: The global shipping sector is a relevant source of environmental impacts responsible for 3% of anthropogenic CO2 emissions, and for 20% and 12% of NOx and SO2 emissions respectively [1,2]. With the global shipping industry consistently growing, the emission level from international shipping will continue to increase in the coming years. In view of this prospect, the International Maritime Organisation (IMO) has set environmental targets to reduce CO2 emissions by 70% and greenhouse gas (GHG) emissions by 50% by 2050, compared to the 2008 levels [1]. The FuelSOME projects aims to contribute to these goals through an alternative propulsion system for long-distance maritime shipping. FuelSOME develops a scalable and multi-fuel capable energy generation system based on Solid Oxide Fuel Cell (SOFC) technology, which can be operated on e-fuels from ammonia, methanol or hydrogen. We assessed the environmental and social impacts of this system compared to the conventional heavy fuel oil (HFO) system. Product system: The considered scope for the sustainability analysis of the FuelSOME system is Well-to-Wake, quantifying the full life cycle impacts for a given fuel pathway. The life cycle stages of the FuelSOME system can be divided into feedstock production, fuel production, fuel processing, production of the propulsion system, use phase and the end-of-life phase (Figure 1). As the system focuses on e-fuels for ammonia, hydrogen and methanol, the feedstock production includes the provision of electricity from photovoltaic (PV) energy generation systems, wind energy generation systems and electricity from grid mixes. The functional unit of the considered system is defined as 1 tkm transportation of a maritime vessel with a power output of 10 MW. Background data used for this assessment are ecoinvent [3] and PSILCA [4] for the environmental and social context respectively, while the foreground data is project-specific information. Environmental impacts: • From the different scenarios for ammonia, hydrogen and methanol analysed, only e-fuels from wind and PV power compete with the fossil-based reference case, which depicts GHG emissions of 11.9 g of CO2-eq per tkm (Figure 1). • Among the different e-fuels, e-hydrogen shows lower environmental impacts compared to e-ammonia and considerably lower impacts compared to e-methanol. ➢ E-ammonia: Synthesis from hydrogen to ammonia increases GHG emissions ➢ E-methanol: pressurised CO2 consumption during synthesis • Majority of e-fuel scenarios are dominated by the fuel production, due to the electricity needed in the different processes such as electrolysis and infrastructure production. Social impacts: • Social risks arise primarily during ship operation, which was assumed equal across all scenarios. The remaining social risks in the e-fuel scenarios arise mainly in the respective electricity sectors (Figure 2). • The analysis of the social indicator ‘fair salary’ shows that the e-fuel scenarios are associated with slightly lower social risk compared to the fossil reference. This was found to be true for most indicators analysed. Conclusion: To reach decarbonisation goal of -50% GHG emissions, ships need to be powered using hydrogen or ammonia made from 100% low carbon renewable energy.