Energy analysis of large cruise ships case study of thermal and electric demands and supply during different scenarios

• Energy flow analysis of a 300 m cruise ship based on real operational data. • Up to 57% of thermal energy is dumped during sea mode; overall efficiency as low as 52%. • Surplus steam-based battery charging yields 9 MWh/week for zero-emission port stays. • Slow steaming reduces fuel use by 9% and thermal dumping by up to 17%. • ORC integration shows low efficiency (approx. 7%) and limited retrofit viability. Cruise ships, with their intricate energy infrastructure, exhibit a level of complexity comparable to that of urban energy systems. In context, large cruise vessels rank among the most energy-intensive mobile infrastructures. During sea operation, conventional cruise ships typically consume on the order of 140–150 t fuel per day, with the largest vessels reaching approximately 250 t per day. Even when alongside, they maintain substantial auxiliary loads, often requiring electrical power in the megawatt range. Against the backdrop of international shipping emissions of roughly 1,076 Mt CO 2 e in 2018 which counts to around 3% of global anthropogenic emissions, improving cruise-ship energy efficiency is therefore relevant both to meeting sector-wide decarbonisation objectives and to mitigating local air-emission burdens in port cities [1] . This study presents a detailed assessment of the energy demands of a 300-metre-long cruise ship with a capacity of approximately 4,300 passengers during a seven-day voyage. The analysis considers three distinct operational modes: sailing at sea, manoeuvring (e.g., harbour entry), and port stays. Fuel input is systematically traced and divided into thermal and electrical energy pathways, enabling a mode-specific evaluation of energy flows and system efficiency. The results reveal that up to 57% of thermal energy is rejected during sea operations, with overall system efficiency ranging from 52% (sea mode) to 67% (harbour mode). The feasibility of utilising surplus steam for battery charging is demonstrated, offering approximately 9 MWh of electrical storage over the course of one week to support zero-emission port operations. Furthermore, the integration of an Organic Rankine Cycle (ORC) was investigated. While technically feasible, its relatively low efficiency (approx.7%) and system complexity present challenges for retrofitting existing ships. In contrast, slow steaming was found to reduce fuel consumption by 9% and thermal dumping by 15–17%, representing a practical and readily deployable strategy for improving energy efficiency and reducing emissions. These findings provide new insights into the operational energy performance of cruise vessels and offer a robust foundation for data-informed optimisation strategies to support the maritime sector’s transition towards low-emission and energy-efficient operation.