A comparison of electric vehicle Level 1 and Level 2 charging efficiency

As electric vehicle penetration grows, it is important to ensure that this new technology is deployed such that long-term efficiency and environmental benefits are maximized. In this study we examined the charging efficiency of Level 1 (120 Volt) and Level 2 (240 Volt) Electric Vehicle Supply Equipment (EVSE). Charging efficiency was defined as the percentage of power drawn from the electric grid that is actually taken up by the vehicle battery. We installed logging devices in 2 Nissan Leafs and 2 Chevrolet Volts in Vermont to track charging efficiency at each Level 1 and Level 2 charging event. Data was collected between June and November 2013 to provide a range of climatic conditions. Usable data was obtained from 115 charges and mean charging efficiency was found to be 85.7%. On average, Level 2 charging was 5.6% more efficient than Level 1 (89.4% vs. 83.8%). In those charges in which the battery took up less than 4 kWh, this difference in efficiency was even greater: 87.2% for Level 2 vs. 74.2% for Level 1. Efficiency gains of Level 2 charging also increased under low ( 70°F) temperatures. These results suggest that the impact of the observed efficiency gains may be biggest at public charging stations, where charging times tend to be short and climatic conditions more variable, rather than residential charging. Future research should consider the relative efficiency of DC Fast charging and wireless charging, as well as how charging efficiency varies among vehicle models and at lower temperatures (<;32°F).