Modeling and simulation of fleet vehicle batteries for integrated logistics and grid services

Vehicle to grid technologies (V2G) utilize the batteries in electric vehicles (EV) to provide ancillary services to the electric power grid. In order to maintain a 60-hertz frequency in the electric grid, there exists a wholesale market for frequency regulation (FR), a specific type of ancillary service. This paper examines V2G technology for providing FR, while focusing on the effect FR service has on battery life, state of charge, and potential revenue. Fleet vehicles are prime candidates for FR, as most are only active a portion of the day. During FR, a small amount of charge is drawn and released from the battery several times a minute, each cycle helping to stabilize the electric grid. Battery degradation, the loss of battery capacity over time, is crucial to the feasibility of V2G. Degradation is influenced by several factors including temperature, total electrical throughput, and the rate energy is taken from the battery. Using historical frequency regulation signals coupled with a throughput based equation for battery degradation, a model analyzes the effects of FR on battery life, battery state of charge, and revenues generated. An analytical simulation written in Java, and a conceptual simulation made in Simio are used for analysis. Results suggest that FR does not dramatically alter the state of charge of a battery and has a minimal impact on battery life. Furthermore, the revenues from FR far exceed costs of degradation. The findings support that V2G will enable a lower total cost of ownership for electric vehicles.