The shipping industry has a notable share in global greenhouse gas emissions and other pollutants such as sulphur and nitrogen oxides. Fuel cells and batteries are identified as relatively new technologies for shipping with high potential and hydrogen is also considered as one of the most promising sustainable fuels, especially for smaller vessels. This research contributes to three identified knowledge gaps: (1) the potential of hydrogen propulsion for high-speed craft, (2) the hybridisation of fuel cells and batteries for marine applications and (3) the characteristics of the response of a hybrid fuel cell/battery propulsion system under transient loads. The objective of this research is to analyse these aspects based on a series of time domain simulations of various operational conditions.
A mathematical model of a fuel cell/battery propulsion system is developed in Matlab/Simulink. The developed model is used to analyse the energy consumption for various operational conditions of a test vessel. Based on this analysis, two configurations of fuel cell power and battery energy are selected. If the vessel sails at top speed, the fuel cell power stacks operate at maximum power and the battery operates as power booster. A strong correlation was found between the endurance at top speed and the battery size which is selected. A larger battery has a positive effect on endurance, but it also increases the displacement of the vessel significantly and, hence, required power.
Fuel cells are least responsive and these should be protected against high fluctuations in a short time. A fuel cell can only follow low-frequency transient loads. The battery is required to support in high-frequency load changes. Contrary to the fuel cell, both the battery and PMSM were found to have very favourable characteristics in transient conditions.
Finally, it is concluded that it is feasible to implement fuel cell/battery propulsion on high-speed craft. It is proposed that the fuel cell and hydrogen deliver the majority of the energy and use the battery as power booster and for transient support. Novel energy management strategies can deliver high system efficiencies in both full and part load and this is one of the main advantages of hybridisation.
The implementation of a fuel cell/battery system does, however, come at significant costs in terms of endurance and top speed due to the low volumetric energy density of hydrogen. It should be acknowledged that the functionality of the vessel is reduced. In addition to this, the storage of hydrogen requires some deck space, so the cargo capacity in terms of crew and material is also reduced. Therefore, it is recommended to redefine the user profile of the vessel.