Evaluation of transition towards zero emission commuter ferries : Comparative Analysis of Fuel-based and Battery-based Marine Propulsion System from financial and environmental perspectives

Abstract: The purpose of this study is to compare the life-cycle cost and environmental impact of the existing fuel-based propulsion system, on public commuter ferries in Stockholm, with a battery based propulsion system. The study is divided into multiple layers. First, the operating characteristics of the route Line 80 within Stockholm’s waterborne public transportation (WPT) are collected, such as fuel consumption, propulsion power output, speed, voyage time and propulsion system configuration. Second, based on the energy demand of the route, important parameters related to the existing fuel-based propulsion system and the battery-based propulsion system are accounted for and modeled. Third, Life Cycle Assessment (LCA) and the cost assessment methods are applied to examine the effectiveness of the electrification of commuter ferries on a financial and environmental scale. With the help of the software GaBi 2020, GREET 2020, and other literature studies, the environmental impacts at the construction, use and end-of-life (EOL) phase are evaluated. There are in total 8 scenarios considered, 4 for the fuel-based and 4 for the battery-based propulsion system. The environmental performance of these 8 scenarios are discussed in terms of Globalwarmingpotential(GWP), Acidificationpotential(AP), Eutrophicationpotential(EP) and Photo-chemical ozone creation potential (POCP). Themostpollutingphaseistheusephase for all scenarios. Propulsion system powered by diesel (scenario 1) is considered as a reference for comparative analysis of 7 other scenarios. The best performing system is the one powered by batteries with the assumption of an electricity mix based on hydro, wind and nuclear power, which is scenario 7 and 8 with a net reduction of GWP by more than 98%, AP by 90%, EP by 96%, and the POCP by 96%. If we consider the current Swedish electricity mix (scenario 5 and 6), the decrease in GWP, AP, EP and POCP are 90%, 80%, 82% and 91% respectively. Alternative fuels also present promising results for GWP in comparison to diesel (with the origin of the feed-stock creating mostly negative impacts) but the contribution to other impact categories is significantly higher. With inputs from the industry and the environmental evaluation, the cost assessment compares the costs related to fuel-based and battery-based propulsion systems with different energy sources. For the battery-based system, 3 scenarios are modeled for two different types of Li-ion batteries. The vessels in the developed scenarios are charged more frequently than the existing electric vessel and the number of charging stations is varied. The costs that are included in the assessment are the initial capital cost, the cost for fuel/electricity, maintenance cost, end-of-life cost and emissions cost. When concerning all the cost categories, the battery-based system is more cost-efficient than a fuel-based system, if run on the Swedish electricity mix, due to the lower cost for electricity and emissions. The reduction of cost is more than 68% when comparing traditional diesel with battery-based systems, but the source of the electricity is very important.