Low total lifetime cost is essential for the adoption of zero-emission ship energy systems, which must meet operational power demands while complying with onboard safety regulations. However, many studies rely on a simplified, averaged or insufficiently representative load profile and treat system design, operation, and integration feasibility separately, which can distort lifetime cost assessments and result in practically infeasible retrofit concepts. This study investigates how a hydrogen-based ship energy system can be optimally sized, operated, and arranged onboard to minimize total lifetime cost while satisfying operational constraints and stability requirements for a general cargo vessel retrofit. A representative power profile is synthesized from one year of operational data using a probability-based downsampling method and then used in a mixed-integer nonlinear lifetime cost optimization with discrete placement and ballast decisions, solved using the SCIP solver. The optimal retrofit comprises 1.4 MW of fuel cells, 180 kWh of batteries, and a 146 m³ liquefied hydrogen (LH₂) tank, requires 171 t of ballast to satisfy trim and vertical stability constraints, and is primarily driven by fuel costs, which account for 74% of the total lifetime cost. Overall, the results indicate that the viability of hydrogen-based ship retrofits primarily depends on LH₂ storage integration constraints and hydrogen price assumptions, and that the proposed framework provides a practical basis for lifetime cost assessment of feasible retrofit designs.

This study presents a framework for designing and optimizing ship energy systems including weather-driven speed variability and navigation safety constraints. Navigation risks including resonance, surf-riding, and successive high-wave impacts, are calculated using five years of hourly weather data. Random speed variations (up to ±5%) are applied to a baseline speed profile to capture operational uncertainty, and safety-based speed reductions (up to 40%) are applied when required. Course changes are excluded. Treating navigation risks as constraints, operating profiles are generated for different weather conditions. For a conceptually retrofitted cargo ship, hydrogen fuel cell and battery capacities, and their power distribution, are optimized for each operating profile to minimize lifetime energy system cost and assess the effects of weather-induced power variation. Results show that speed and weather variability can significantly change power demand, requiring fuel cell capacities between 700 and 1500 kW. The most common configuration is a 1200 kW fuel cell system with 180 kWh of battery capacity, covering 39% of laden profiles, while full power coverage requires 1500 kW. Lifetime cost outcomes exhibit a 5th–95th percentile spread of −10.3% to +11.1% relative to mean cost. The results demonstrate the significant influence of weather variability on system sizing and cost.

Fuel cell-battery electric drivetrains are attractive alternatives to reduce the shipping emissions. This research focuses on emission-free cargo vessels and provides insight on the design, lifetime operation and costs of hydrogen-hybrid systems, which require further research for increased utilization. A representative round trip is created by analysing one-year operational data, based on load ramps and power frequency. A low-pass filter controller is employed for power distribution. For the lifetime cost analysis, 14 scenarios with varying capital and operational expenses were considered. The Net Present Value of the retrofitted fuel cell-battery propulsion system can be up to $ 2.2 million lower or up to $ 18.8 million higher than the original diesel mechanical configuration, highly dependent on the costs of green hydrogen and carbon taxes. The main propulsion system weights and volumes of the two versions are comparable, but the hydrogen tank (68 tons, 193 m³) poses significant design and safety challenges.

This paper presents a comprehensive literature review of the state-of-the art modeling and optimization methods for the power and propulsion systems of ships. Modeling is a tool to investigate the performance of actual systems by running simulations in the virtual world. There are two main approaches in modeling: physics-based and data-driven, which are both covered in detail in this survey paper. The output from the simulations might not be optimal in terms of certain performance criteria such as energy consumption, fuel cost etc. Hence, it is vital to optimize the systems considering the efficient interaction between the components, to yield the optimal performance for the integrated vessel's powertrain. In this paper, the optimization case studies, for the ship energy systems, will be divided in terms of a) optimal design (topology and sizing), b) optimal control and energy management strategies, c) combined optimal design and control. Tables that summarize the literature review outcomes will also be presented at the end of each section. The main outcome is that limited literature is available for optimizations of ship powertrains using data-driven models, especially surrogate models. Surrogate-assisted optimizations for integrated ship energy systems can yield optimal solutions at fast computational speeds, with sufficient accuracy, even for complex, nested, multi-level, multi-objective optimizations.