The United States and the International Maritime Organization (IMO) have set ambitious goals for greenhouse gas (GHG) emission reductions, creating a significant impetus for the adoption of battery electric ships (BESs). In 2021, US domestic marine vessels emitted 21.9 million metric tonnes of carbon dioxide equivalent (CO2e), representing 3% of total US transportation emissions. While BESs offer a promising pathway to decarbonization, concerns remain regarding their feasibility and scalability due to challenges in battery technology, charging infrastructure, and weight constraints. This study addresses these concerns by analyzing the life-cycle costs and GHG emissions associated with electrifying a substantial portion of the US domestic shipping fleet. The plummeting cost of batteries, coupled with advancements in battery energy density, now presents a compelling opportunity for widespread adoption of BESs. The research aims to provide a comprehensive assessment of the economic and environmental implications of a large-scale transition to battery electric shipping, considering various scenarios for grid decarbonization and battery costs.

Existing literature has focused on estimating emissions from ship activities, with some studies conducting global assessments and others focusing on region-specific analyses. These previous studies, however, largely neglected the economic comparison of BESs to internal combustion engine (ICE) ships. Recent deployments of battery electric ferries in various countries highlight the potential of BESs for specific applications, particularly ferries with predictable routes. Other studies have explored the decarbonization potential of BESs, comparing them with alternative fuels and analyzing the influence of grid emissions on overall BES emissions. However, none have comprehensively addressed the broader regional or national implications of replacing ICEs with BESs on a significant scale, particularly concerning the economic feasibility under various operational assumptions.

The study employed a novel modeling tool, the Maritime Battery Electrification Simulator (MariBES), to assess the cost, equipment needs, and environmental benefits of converting US domestic shipping to battery electric. Data on vessel specifications and operations were drawn from three US vessel databases, and high-resolution Automatic Identification System (AIS) data were used to analyze ship activities. The MariBES tool integrates battery system sizing, charging scheduling, electricity and cost requirements, and lifetime GHG emissions. The analysis considered 6,323 US domestic ships under 1,000 gross tonnage, referred to as the 'Domestic Fleet', with a subset of 2,722 ships with sufficient AIS data for detailed analysis. Four capacity tiers (BESP100, BESP99, BESP95, and BESP90) were defined to represent the percentage of historical ICE trips a BES could serve, allowing for the examination of trade-offs between emissions reduction and battery size. The study incorporated techno-economic analysis (TEA) and life-cycle assessment (LCA) methodologies. TEA involved estimating levelized cost of transportation (LCOT) for both ICE and BES ships, considering fuel, battery capital costs, charging infrastructure, emissions, and the battery's end-of-life salvage value. The LCA quantified full life-cycle environmental impacts, including GHG emissions and criteria air pollutants. Three emission scenarios (business as usual, 95% decarbonization by 2050, and 95% decarbonization by 2035) and three economic scenarios (optimistic, intermediate, and challenging) were considered to reflect uncertainties in future power grid emissions and battery costs.

The key findings indicate that electrifying the 6,323 domestic vessels under 1,000 gross tonnage could reduce US domestic maritime GHG emissions by up to 73% below 2022 levels by 2035. The analysis revealed that up to 85% of battery electric ships (BESp99, serving 99% of historical trips) could become cost-effective compared to ICE ships in 2035 under a scenario with 95% electricity decarbonization by 2035 and intermediate cost assumptions. The cost-effectiveness of BESs is highly sensitive to the cost of carbon emissions; incorporating external costs associated with GHG emissions makes BES investments more attractive. The study estimated total annual electricity demand for the analyzed subset of ships at 3.8 TWh and 7.7 TWh for the entire Domestic Fleet. This demand is projected to concentrate at only 20 of the 150 major ports nationwide. The analysis showed that battery manufacturing emissions could be significantly mitigated (up to 72%) through second-life applications for batteries. A comparison of levelized cost of transportation (LCOT) indicated that BESp99 ships in passenger and inland-push tugboat categories have lower average LCOT compared to ICEs in 2035 under the intermediate cost scenario. The study also indicated that a significant proportion of vessels (67% on average, 89% of passenger ships) would require charging infrastructure of 5 MW or less.

The findings demonstrate the significant potential for GHG emission reductions through the electrification of the US domestic shipping fleet. The study's capacity tier approach highlights the feasibility of BESs by showing that reducing battery size by excluding a small percentage of longer trips can substantially improve cost-effectiveness. The concentration of charging demand at a relatively small number of ports suggests that targeted infrastructure investments can support large-scale electrification. The results underscore the importance of incorporating the social cost of carbon into economic assessments to accurately reflect the full environmental impact. The sensitivity of LCOT results to fuel and charging costs highlights the need for more accurate cost projections in future analysis. Achieving the study’s projected GHG emission reductions relies on timely implementation of policies that incentivize BES adoption and the decarbonization of the power grid.

This study provides a comprehensive assessment of the feasibility and scalability of battery electric ships for the US domestic shipping sector. The findings highlight the significant potential for GHG emission reductions and cost-effectiveness, particularly under scenarios with substantial power sector decarbonization and realistic battery cost reductions. Future research should focus on optimizing charging strategies, developing renewable-based microgrids at ports, exploring multiple smaller BESs as an alternative to single large ICE replacements, and considering the annual variation in ship activity.

The study's LCOT model is sensitive to fuel and charging cost projections, which inherently involve uncertainties. The analysis relies on one year of AIS data, which may not fully capture annual variations in ship activity. The study focuses on retrofitting existing ICE ships to BES rather than comparing the total cost of ownership between new ICE and new BES vessels. Finally, the analysis assumes that second-life battery applications will materialize, which introduces uncertainty into the overall cost analysis.