An optimization approach for managing electric vehicle and reused battery charging in a vehicle to grid system under an electricity rate with demand charge

Abstract

Recently, migration from internal combustion cars to electric vehicles (EVs) has received increasing attention from both public and private stakeholders as one viable solution towards energy sustainability and security. US DOE projects over 120 million Light-duty ground vehicles owned by commercial & industrial electric ratepayers (e.g., forklifts in manufacturers and warehouses, shuttles on university campuses) to be electrified. On the other hand, the short life cycle of EV batteries, where current practices require lithium-ion (Li-ion) battery packs to be replaced when capacity drops to 70%–80%, poses a serious concern over the sustainability of a large-scale EV fleet system. These batteries, however, can provide abundant source of stationary energy. This paper considers a commercial & industrial electricity ratepayer’s electric fleet system consisting of reused batteries renewable energy sources, and a supporting vehicle to grid infrastructure, and optimizes the total electricity bill that includes “demand charge”, a substantial amount of charge unique to commercial & industrial electric ratepayers compared to residential users. We propose a novel optimal EV, battery and solar activity scheduling (OEVBSAS) model to coordinate various energy sources and usage. The OEVBSAS model is tested with a case study that involves an electricity subsystem, consisting of electric campus shuttle fleet, solar panels and reused EV battery systems, at a Turkish university that is subject to “demand charge”. Computational results indicate that the integrated system, coupled with the optimal activity scheduling solution, is able to decrease the total electricity cost by more than 5% and improve the peak to average ratio by 4%.