Operational Efficiency and Emissions Assessment of Ship Hybrid Power Systems with Battery; Effect of Control Strategies

This paper thoroughly evaluates battery hybridization in terms of operational energy efficiency and emissions with the effect of control design, mainly load-sharing control strategies. First, a methodology is developed to estimate fuel consumption with input from load profile and control parameters. It is further used to evaluate fuel saving potential in hybrid power systems compared to conventional power systems with three different high-level hybrid control strategies (HCS). For comprehensive benchmarking, case studies are performed on four different ship types: cruise ship, RoPax ferry, bulk carrier, and container ship. The results show that fuel saving highly depends on the implemented control strategies as the first strategy saves 6.9-8.8% fuel, the second saves 3.8-8.5%, whereas the third strategy saves -0.9-1.8%; highlighting the need for proper control strategy selection. Further, based on the ship types, the cruise ship shows highest fuel saving potential through hybridization, whereas the container ship shows the least saving potential. Moreover, implementation of the proposed battery sizing in the power systems shows a potential to reduce the number of installed generator sets in all the ship types. Further, a brief techno-economic analysis of the proposed lithium-ion battery and diesel generator (DG) shows that both the weight and space required for battery system are less than the DG counterpart, making it appropriate for the new builds and the retrofits. In this case, the battery can supply nearly equal power as the generator, but only for almost an hour, yet making substantial fuel savings.