Sizing of energy storage systems for connection power reduction and power smoothing of electric vehicle charging plazas

Abstract

The increasing number and charging power of electric vehicles might cause severe troubles for electrical grids motivating a need for investments in grid upgrades. The issues caused by high and intermittent energy demand of electric vehicle charging plazas can be solved with energy storage systems. This article covers sizing of stationary energy storage systems for electric vehicle charging plazas. Energy storage systems are sized to constrain the highest amount of power that the charging plaza takes from the grid below a particular power limit and restrict the rate of change in the grid power draw below a particular ramp rate limit. This is the first study concerning sizing of energy storage systems to smooth variations in the power that the charging plazas take from the grid. The power limit was altered from 10% to 100% and the ramp rate limit from 1 to 25 %/min in relation to the rated charging power of the charging plaza. This study was based on two years of measurement data compiled from eight direct current fast charging stations located in southern California, USA. The results show that the power and energy capacity requirements for an energy storage system used solely for reducing grid connection power below 50% increase only a little if the same energy storage system is used simultaneously also for reducing the rate of change in the grid power draw to comply with a ramp rate limit of 5 %/min or higher. However, use of the energy storage system for both purposes simultaneously increased the share of total electric vehicle charging energy that ran through the energy storage system increasing the degradation of the energy storage system.