Life cycle navigation through future energy carriers and propulsion options for the energy transition in shipping

Abstract: The shipping industry's heavy reliance on fossil fuels has a detrimental effect on the global climate, human health, and the natural environment. The shipping sector now relies on the use of cheap and energy-dense heavy fuel oil and is perceived as ‘difficult-to-decarbonize’. Presently the shipping sector is adopting incremental emission reduction measures related to operational and technological energy efficiency solutions. However, to meet the global climate target, the transition from fossil-based marine fuels to renewable energy carriers is needed. Electro-fuels, which are produced from low-carbon electricity, or direct use of electricity with battery storage, are two pathways for energy transition included in this thesis. This thesis aims to assess the possible influence of the above two decarbonization paths based on energy demand, environmental performance, and economic performance across the whole life cycle of ships. The assessment is performed for hydrogen, ammonia, methanol, and battery-electric on three case study vessels using prospective life cycle assessment (pLCA) and life cycle costing (LCC). The pLCA is based on systems thinking used for the environmental assessment of emerging technologies that are in an early stage of development, and the LCC is used for the economic assessment of technologies over the life cycle based on the same systems thinking. To understand the environmental and economic tradeoffs for decision making an integrated assessment of pLCA and LCC is employed in the thesis. Considering the complexity and challenges of integration, a framework termed ‘integrated life cycle framework’ is developed for this thesis, allowing for consistent assessment to understand tradeoffs. This framework can be useful for other transport sectors. The study shows that there is a substantial potential for reducing the environmental impact of shipping through the studied pathways; however, this depends on the carbon intensity of the electricity used in fuel production. Technically, not all fuels are suitable for all vessels. Their suitability is primarily determined by the amount of fuel required for bunkering and the amount of space available onboard. Reduced climate impact comes at the expense of several other impact categories, such as human toxicity, water use, and resource use (minerals and metals). For the same type of fuel, fuel cells have greater impact reduction potential than engine options; however, engines are more cost competitive. Fuel price and utilization rate also influence cost competitiveness. The total life cycle cost of all the studied options is significantly higher than the conventional diesel option, and the critical parameter is the cost of the fuel. The cost of fuel is sensitive to the price of electricity. The carbon abatement cost estimated in this study shows that policies should be designed to imply at least a cost of 250–300 €/tCO2eq for emitting greenhouse gases to make the assessed fuel options cost competitive.