Hybrid power and propulsion systems for ships: Current status and future challenges

Increasing environmental concerns are driving the shipping industry to take strict measures to deal with greenhouse gas emissions. International Maritime Organization drives the industry to find more efficient and environmentally friendly power systems. To mitigate harmful emissions, researches on marine alternative fuels, operational improvements like slow steaming or predictive maintenance, and additional emission abatement technologies are not sufficient. The use of electricity as the main energy vector is one of the ways to improve the shipping propulsion system's efficiency. In this study, power generation technologies, energy storage components, energy management systems, and hybrid propulsion topologies are reviewed. Diesel engines, fuel cells, solar and wind power as renewable energy sources are discussed as power generation units. On the energy storage side, batteries, supercapacitors, and flywheels are presented and described. Three common hybrid propulsion configurations, serial, parallel, and serial-parallel architectures are detailed with their pros and cons by highlighting commonly used energy management systems and optimization methods. Lastly, criteria for hybrid system selection are defined according to eight different ship types and assessed by providing a generic methodological approach. It is shown that electrical components and architectural design should be elaborated according to operational and architectural characteristics for ships. In short term, it is concluded that internal combustion engines are still the major hybridization element with different energy storage systems. New regulations on the mitigation of harmful emissions will accelerate the transition to hybrid power which is an important option for the ultimate zero-carbon shipping goal.