Energy Transition towards Sustainable Shipping: Environmental and Economic Life Cycle Considerations

Doktorsavhandling, 2025

Shipping accounts for over 80% of global trade by volume. Its heavy dependence on fossil fuels significantly impacts the climate, human health, and the environment. In response to increasing pressure to reduce shipping greenhouse gas (GHG) emissions, the International Maritime Organization has set an ambitious target of achieving net-zero emissions "by or around" 2050. However, the shipping sector remains a hard-to-abate industry due to its international nature and dependence on heavy fuel oil, a cheap and energy dense option but highly polluting byproduct of crude oil refining. These challenges are compounded by system-level knowledge gaps, which hinder the development of informed decision-making and strategies to identify sustainable and economically viable alternatives.

The thesis adopts a systems-thinking approach to explore the energy transition of the shipping sector, focusing on environmental and economic trade-offs of alternative fuels and technologies for ships. It employs three tools: life cycle assessment (LCA), life cycle costing (LCC), and energy system modeling (ESM). Prospective life cycle thinking is used to assess emerging technologies through a novel Integrated Life Cycle Framework, enabling consistent economic and environmental evaluation of decarbonization scenarios by integrating LCA and LCC. The emerging technologies assessed are grouped into five key mitigation strategies: adoption of electro-fuels (e.g. e-methanol), blue fuels (e.g. blue ammonia), biofuels (e.g. biomethanol), battery-electric propulsion (e.g. lithium battery), and onboard carbon capture technology (e.g. post carbon capture). The assessment is performed for different types of ships.

The ESM tool used in this thesis is the Global Energy Transition (GET) model. The GET model is adapted to analyze possible shipping climate policy measures, with enhanced details (adding different ship types) in the shipping sector module and energy carrier supply chain. Additionally, LCA is integrated with GET to provide a comprehensive understanding of well-to-wake climate impacts while also evaluating other environmental effects linked to energy transitions.

The LCA results indicate that electro-fuels synthesized using wind power and used in fuel cells offer the greatest potential for GHG reduction among the assessed fuel and propulsion options. The LCC results show that all alternative fuel options have higher total life cycle costs compared to conventional diesel, with fuel costs being the key component. Among the options, bio-methanol and onboard carbon capture have the lowest carbon abatement costs. For ferries operating on short, regular routes, battery-electric propulsion stands out as the most promising option, offering both significant emission reductions and cost competitiveness. The same result can be observed from the GET model for ferries and cargo vessels operating in short distances. For long-distance shipping, the GET model results suggest that ammonia is the most cost-effective fuel under ambitious CO2 reduction policy scenarios. However, the LCA result shows the importance of reducing the emission of nitrogen-based compounds from ammonia-based engines which could lead to environmental impacts like eutrophication and acidification and limit GHG reductions. This thesis underscores the critical role of alternative fuels and technologies in reducing GHG emissions from the shipping sector. It also highlights the importance of addressing environmental trade-offs and economic challenges to support the development of sustainable and cost-effective strategies for decarbonizing this hard-to-abate sector.