Steering shipping towards energy sustainability: alternative fuels in decarbonization policies

The maritime industry faces a critical challenge in meeting the carbon reduction targets set by the International Maritime Organization. Achieving these targets requires a mix of solution that encompasses the use of renewable energies, alternative fuels, as well as the implementation of cutting-edge technologies. This paper investigates the potential impact of alternative fuels, their influence on meeting carbon intensity metrics, and the role of various policies, including incentives and taxation, in accelerating the transition to low- and zero-emission solutions. A dynamic energy simulation tool is exploited to analyse the environmental and energy performance of different cruise ship, considered as case study, taking into account varying on-board loads, different fuel types, and potential future energy scenarios. The analysis includes methanol, liquefied natural gas, and heavy fuel oil, with both fossil-based and bio-based variants of methanol and LNG being considered, comparing their impacts in different regulatory and technological settings. A key part of the study focuses on the design of polygeneration systems and fuel strategies, considering both short- and long-term energy requirements. For each ship in the study, the simulation tool assesses thermal loads, waste heat recovery potential, and the energy flows within the ship system. To meet the imposed targets, the exploitation of green fuels should be foreseen, covering at least 63 % of the fuel demand by 2040. This will require the adoption of policy measures such as taxation and incentives on the adoption of alternative fuels, in order to guide stakeholders in developing effective strategies for achieving emission reduction. Possible solutions include the implementation of port-based technologies, such as cold ironing. By integrating alternative fuels with shore-side connections, ships can reduce emissions while docked, decreasing their reliance on alternative fuels. This approach could lead to a reduction in the demand for green fuels, with green fuels accounting for only 58 % of the current fuel demand by 2040.