A Study on a 5kW Marine ESS System Based on Reused EV Batteries Replacing Diesel Generators

This study presents a design and onboard demonstration of a 5kW marine energy storage system (ESS) using repurposed electric vehicle (EV) batteries to replace conventional diesel generators on small vessels. The proposed system consists of three 2.4kWh EV battery modules connected in series, providing a total storage capacity of 7.2kWh, and a pure sine-wave inverter delivering a rated AC output of 5kW at 220V and 60Hz. The ESS can be charged from shore power and is designed to be expandable to include photovoltaic charging sources. A battery management system (BMS) continuously monitors key parameters such as state of charge (SOC), state of health (SOH), and state of energy (SOE), ensuring safe operation by protecting against overcharge, overdischarge, overcurrent, and cell imbalance. Field tests conducted on a coastal working vessel under realistic operating conditions showed that the system can supply combined lighting and HVAC loads for approximately 2.6h while maintaining the battery temperature below 47°C and output voltage variation within ±2%. Compared with the previously implemented 3kW or 7kW system, the 5kW ESS provides a balanced trade-off between endurance time, installation space, and cost, making it suitable as a standard rating for small and medium-sized ships. The results confirm that the proposed system can effectively replace diesel generators during berthing and low-speed operations and can contribute to greenhouse gas reduction and noise abatement in port areas.