Impact of ESS Capacity and Energy Management Strategy on Fuel Consumption in Hybrid Electric Propulsion Systems

With hybrid electric propulsion attracting increasing attention in the maritime sector, quantitative evaluation of fuel consumption benefits associated with energy storage system (ESS) integration remains limited. Through real operational data of 5000 GT class, this study builds a framework to explain the interactions between propulsion configuration, generator load sharing and ESS capacity. This study investigated three generator control strategies and four scenarios for ESS capacity (200–500 kWh) by applying unified FOC procedures. This study reveals that generator control logic can affect more than ESS capacity. Compared with mechanical propulsion (140.72 tons), rule-based control achieved an 11.45% reduction. Equal load sharing scored a 6.27% reduction gap of 5.18%. ESS capacity exhibited a nonlinear effect. FOC exhibited a meaningful threshold at 300 kWh (121.63 tons); beyond this point, additional capacity yielded improvements of less than 0.1 tons. Ironically, a 200 kWh setup resulted in FOC of 126.13 tons—higher than the electric propulsion without battery under rule-based control (124.60 tons). Therefore, ESS capacity and generator control logic should be considered at the same time. These outcomes can provide practical design criteria under realistic operating conditions.