Rating a Stationary Energy Storage System Within a Fast Electric Vehicle Charging Station Considering User Waiting Times

The use of stationary energy storage at the fast electric vehicle (EV) charging stations can buffer the energy between the electricity grid and EVs, thereby reducing the maximum required grid connection power and potentially mitigating the need for grid infrastructure upgrade. In this paper, a method is presented that sizes the stationary energy storage based on an acceptable average waiting time of drivers arriving at a fast-charging station. The novelty of this paper is the focus on the relationship between the size of stationary energy store and the user waiting time. This relationship is often ignored; however, it is critical to obtain the optimum capacity of stationary energy store. An example charging station location is chosen where there are currently eight chargers capable of 120-kW charging and a 500-kW grid connection. It is demonstrated that the method can be used at this location to design a charging station with stationary energy storage to support future 400-kW charging without upgrading the current grid connection infrastructure. With future charging, using a stationary energy storage with a capacity of 1000 kWh reduces the maximum grid power from 1800 to 500 kW.