Evaluation of a PV Powered EV Charging Station and its Buffer Battery

This research analyses the operation of a solar PV powered electric vehicle charging station with energy storage that has been developed and demonstrated at the University of California – Davis, West Village, the largest planned zero-energy consumption community in the U.S. The intelligent energy management approach introduces solar PV electrical energy forecasting and EV charging demand projection to optimize the state of charge (SOC) of the buffer battery. The charging station has been operated continuously and routinely used by several EV users for a year. The actual operation shows that a workplace charging station equipped with a buffer battery and with intelligent energy management can lower and reduce the station’s peak power demand and reduce the energy exchange with the utility grid by a factor of 2. The battery recharging power demand was shifted away from the on-peak time periods to the off-peak time periods, which will benefit the charging station owner from less energy use during peak periods when time-of-use rates are higher. The standard cell voltage deviation of the 220 cells was calculated to analyse the battery cell consistency during the resting, charging, and discharging periods. The analysis shows that the 220 50Ah cells show excellent voltage consistency with voltage deviation of less than 0.005 V within the battery SOC of 20-80%. The voltage deviation doubles when the battery SOC reaches 90%. The comparison of cell voltage deviation at the beginning and after one year operation indicates that the battery shows perfect cell voltage consistency and there is no obvious consistency deterioration during the battery resting, charging and discharging periods.