Vanadium redox flow batteries application to electric buses propulsion: Performance analysis of hybrid energy storage system

This paper presents a comparison between different battery energy storage systems (ESS) suitable for an urban electric bus. The investigation starts from a daily energy consumption analysis of a bus route in term of batteries state of charge (SOC). Specifically, three different ESS configurations are modelled basing on experimental data: LiFePO4 battery pack, LiFePO4 battery coupled with PEM fuel cell stack and a hybrid battery system composed by LiFePO4 and vanadium redox flow batteries (VRFBs). Moreover, authors provide an evaluation about the battery life through the application of the rainflow-counting algorithm on the yearly SOC trends of each system. As result, the proposed analysis highlights the favorable effect on the ESS due to the introduction of VRFB in the system. The improvements are found both on the net daily operating hours (one hour longer than the conventional case) and on the life expectancy of the LiFePO4 battery (over 9 years, with a gain factor of 5). The obtained results can be considered as a starting point for a wider study focused both on the ESS sizing and on the routes planning of a city buses fleet.