Emission pay-back time of battery-powered versus fossil-fuel powered passenger vessel

The maritime sector, traditionally one of the hardest sectors to decarbonize, is currently rapidly changing driven by demands for emission reductions. Increasingly stringent regulatory frameworks, including the International Maritime Organization’s (IMO) net-zero ambitions and the European Union’s (EU) greenhouse gas (GHG) reduction targets are driving the maritime sector to adopt low-emission technologies and practices. Increased attention has been previously allocated by the scientific community to the exploration of alternative fuels and efficiency improvements. Nevertheless, the full life-cycle implications of completely electrifying passenger vessels remain insufficiently assessed.

This study estimates the emission pay-back time associated with replacing a conventional marine gas oil (MGO) powered passenger vessel with a concept vessel fully powered by battery and rigid auxiliary sails. The analysis assumes one year of continuous operation for both vessels along the traditional Norwegian coastal route. A life-cycle assessment (LCA) framework is applied. The system boundaries are covering the production of lithium iron phosphate (LFP) batteries with a net capacity of 60 MWh; sails manufacturing, installation, operation, and energy savings; charging infrastructure; energy requirements for vessel’s operation and end-of-life treatment. The resulting total carbon footprint for one year of operation is compared with the one corresponding to the reference vessel, the fossil-fuel powered one, where manufacture, operation, and disposal of diesel engines are considered.

The vessel’s operational energy demand is derived from real-world timetable data and reflects seasonal variations. The energy requirements range between 642 and 666 MWh per roundtrip. The assessment takes into consideration the battery losses as well as the depth-of-discharge constraints. Battery charging is modelled using realistic electricity mixes from Norwegian bidding zones NO2 to NO5 which are corresponding to the geographical route of the vessel. In contrast to the generic national-average electricity mixes usually applied in LCA studies, this dynamic approach for electricity modelling considers the spatial and temporal variations in electricity generation sources. This has a direct impact on the associated emission intensities of the electricity consumption of the vessel. The fossil-fuelled reference vessel requires approximately 50 000 MWh of gross energy annually, assuming an average engine efficiency of 37% and auxiliary heating partly supplied by oil-fired boilers. In contrast, the battery-electric vessel requires about 28 000 MWh per year, enabled by an optimized system design, high propulsion efficiency (around 90%), and improved heat recovery.

Our preliminary results highlight that the emissions pay-back period is highly sensitive to the carbon intensity of the electricity supply as well as to the spatial distribution of charging infrastructure localized in the harbours where the vessel stops. We find as critical for the operational feasibility the availability of high-power chargers in ports such as Ålesund and Trondheim.

Under the current Norwegian grid conditions and the power purchase agreements in place modelled here in the study, the pay-back time is sufficiently short. We therefor find that battery electrification can be one of the near-term decarbonization strategy for the maritime sector. Overall, our results show that full replacement of fossil-fuel coastal vessels with battery-electric solutions can deliver substantial GHG reductions, supporting both IMO and EU climate objectives.