NREL Charges Forward to Reduce Time at EV Stations
Shortening recharge times may diminish range anxiety, increase EV market viability
Oct. 25, 2017
Speeding up battery charging is crucial to improving the convenience of owning and driving an electric vehicle (EV). The Energy Department's National Renewable Energy Laboratory (NREL) is collaborating with Argonne National Laboratory (ANL), Idaho National Laboratory (INL), and industry stakeholders to identify the technical, infrastructure, and economic requirements for establishing a national extreme fast charging (XFC) network.
Drivers can pump enough gasoline in 10 minutes to carry them a few hundred miles. Most of today's fast charging stations take 20 minutes to provide 50-70 miles of electric driving range. A series of articles in the current edition of the Journal of Power Sources summarizes the NREL team's findings on how battery, vehicle, infrastructure, and economic factors impact XFC feasibility.
"You can charge an EV today at one of 44,000 stations across the country, but if you can't leave your car plugged in for a few hours, you may only get enough juice to travel across town a few times," says NREL Senior Engineer and XFC Project Lead Matthew Keyser. "We're working to match the time, cost, and distance that generations of drivers have come to expect—with the additional benefits of clean, energy-saving technology."
While XFC can help overcome real (and perceived) EV driving range limitations, the technology also introduces a series of new challenges. More rapid and powerful charging generates higher temperatures, which can lead to battery degradation and safety issues. Power electronics found in commercially available EVs are built for slower overnight charging and may not be able to withstand the stresses of higher voltage battery systems which are expected for higher power charging systems. XFC's extreme, intermittent demands for electricity could also pose challenges to grid stability.
The XFC research team is exploring solutions for these issues, examining factors related to vehicle technology, gaps in existing technology, new demands on system design, and additional thermal management requirements. Researchers are also looking beyond vehicle systems to consider equipment and station design and potential impact on the grid.
NREL's intercity travel analysis revealed that recharge times comparable to the time it takes to pump gas will require charge rates of at least 400 kW. Current DC Fast Charging rates are limited to 50-120 kW, and most public charging stations are limited to 7kW. XFC researchers have concluded that this will necessitate increases in battery charging density and new designs to minimize potential related increases in component size, weight, and cost. It appears that a more innovative battery thermal management system will be needed if XFC is to become a reality, and new strategies and materials will be needed to improve battery cell and pack cooling, as well as the thermal efficiency of cathodes and anodes.
"Yes, this substantial increase in charging rate will create new technical issues, but they are far from insurmountable—now that we've identified them," says NREL Engineer Andrew Meintz.
Development of a network of XFC stations will depend on cost, market demand, and management of intermittent power demands. The team's research revealed a need for more extensive analysis of potential station siting, travel patterns, grid resources, and business cases. At the same time, it is clear that any XFC network will call for new infrastructure technology and operational practices, along with cooperation and standardization across utilities, station operators, and manufacturers of charging systems and EVs.
These studies provide an initial framework for effectively establishing XFC technology. The initiative has attracted keen interest from industry members, who realize that faster charging will ultimately lead to wider market adoption of EV technologies.
NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.