ET24SWE0025 - Performance Evaluation of DC EVSE

As California continues to take a global leadership role in building and transportation decarbonization by aggressively pursuing energy efficiency and electrification measures to meet its climate goals, including its 2022 Scoping Plan to Achieve Carbon Neutrality (updated and released in November 2022 as required by California AB 32), the addition of electrically-powered equivalents to replace historically fossil-fueled appliances will have a serious impact on California’s total energy needs and its relative load shapes/profiles. A major California decarbonization activity currently underway is electrification of the light-duty vehicle fleet. Currently, plug-in electric vehicles (PEV) adoption remains low due to its relatively recent (2010) market introduction. However, adoption rates have increased significantly in recent years with estimates for PEV sales as high as six percent of all new vehicles purchased in 2022. As of 2022, the size of the light-duty fleet in California was 28.2 million vehicles. If just five percent of the gas-powered fleet were to electrify, the total annual energy required to meet California’s needs would be ~5563 GW-Hr annually. For this project, the research team will focus on two distinct electric vehicle service equipment (EVSE) categories; EVSE with an Alternating Current (AC) output, and EVSE with a Direct Current (DC) output. The PEV battery ultimately requires a DC source for charging and when connected to an AC charger the PEV’s on-board charge converter hardware is active. Using available published performance data, the research team estimates on-board charge converter hardware to be 80-92 percent efficient (www.ev-database.org). To date, power charging equipment under 30 kW is offered as AC Level 2, and it has relied on the vehicle’s charge converter to complete the total charging pathway to the battery. Recently industry has begun to develop and offer DC chargers in this power range. While most DC charger offerings in the <30 kW range are very new to the market and not yet Energy Star certified, there are a few DC systems that report a total system efficiency of 94-95 percent in the Energy Star Database. Assuming DC chargers are ~95 percent efficient and AC chargers including on-board losses are ~86 percent efficient, then if all of the PEVs currently in California opt to use DC charging, California could save up to 377 GW-Hr annually. This project will quantify the differences in EVSE charging efficiency between DC and AC chargers via a robust laboratory evaluation utilizing actual PEV components and commercialized EVSE. The project will also include analysis to quantify the state-wide impacts of DC charging including annual energy saved, demand reduction, and reductions of greenhouse gas emissions.

California's 2045 electrification goals require the deployment of electric vehicle supply equipment that minimizes energy losses while supporting a growing population of electric vehicles. Although DC charging is generally expected to be more efficient than AC charging, limited independently measured data exist to quantify differences in charging pathway efficiency across commercially available systems. 

This project evaluated the performance of commercially available AC and DC EVSE under controlled laboratory conditions to quantify charging efficiency, characterize energy losses, and assess potential energy savings associated with broader deployment of efficient charging technologies. Four AC Level 2 chargers and four DC Level 1 chargers were evaluated using a standardized testbed. Testing included discrete battery state-of-charge conditions and controlled power throughput scenarios. A second phase of testing evaluated continuous charging sessions from approximately 10% to 80% SOC using a subset of the evaluated chargers to characterize efficiency over a representative charging event. 

Across the evaluated operating conditions, AC EVSE achieved charging efficiencies between approximately 91% and 93%, while DC EVSE achieved efficiencies between 95% and 97%. ENERGY STAR certification did not consistently correspond to higher measured efficiency, with certified and non-certified AC products exhibiting similar performance. Phase 2 testing showed charging efficiency remained relatively stable throughout extended charging sessions and was in close agreement relative to discrete operating point testing. Economic analysis estimated annual electricity cost savings from DC charging ranged from approximately $10 to $27 per vehicle based on applied TOU structure. Extrapolating the measured efficiency differences to California's existing light-duty zero-emission vehicle fleet indicates potential statewide electricity savings of approximately 173 GWh annually and avoidance of roughly 50.3 million kilograms of carbon dioxide equivalent emissions. These findings demonstrate that DC EVSE provides a measurable charging efficiency advantage over AC EVSE under the various evaluated operating conditions.