Battery Hybrid Energy Storage Systems for Full-Electric Marine Applications

The high cost of Lithium-ion battery systems is one of the biggest challenges hindering the wide adoption of electric vessels. For some marine applications, battery systems based on the current monotype topologies are significantly oversized due to variable operational profiles and long lifespan requirements. This paper deals with the battery hybrid energy storage system (HESS) for an electric harbor tug to optimize the size of the battery system. The impact of battery hybridization was investigated on three key performance indicators inclusive of cost, system efficiency, and battery weight. The design life of the battery system is considered to be 10 years, and NMC and LTO cell technologies are used as high-energy (HE) and high-power (HP) battery cells. The HESS design is based on a parallel full-active architecture with a rule-based energy management strategy. The results of this research indicate that battery hybridization can reduce the system cost by around 28% and 14% in comparison with a monotype battery with LTO and NMC cells, respectively. Although no noticeable difference in system efficiency is observed between the monotype system and HESS, battery hybridization reduces the total weight of the battery cells by more than 30% compared to monotype topology. This study implies that the hybridization of battery systems could be a promising solution to reduce the cost and weight of large battery packs in electric vessels.