Engineers working at the Vehicle Testing and Integration Facility (VTIF) enjoy a stunning view of the Denver skyline. However, some days the view includes Denver’s ‘brown cloud’ — air pollution caused in part by vehicle emissions. While disheartening, the brown cloud helps the engineers focus on future technologies that will drastically reduce — and ultimately eliminate — those emissions.
Researchers at the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) are advancing a more sustainable transportation future by incorporating advanced electric vehicle technology, expanded use of renewable energy resources for vehicle charging, and grid integration.
“Our goal is to target the key innovations necessary to accelerate the rate of adoption for electric drive vehicles,” said Bob Rehn, group manager for testing and analysis at NREL’s Center for Transportation Technologies and Systems (CTTS). “In addition, our efforts are focused on scenarios that will incorporate expanded use of renewable energy resources to charge those vehicles.”
The Right Tool for the Job
The VTIF, which has been in operation for just over a year, was built with a specific focus on testing electric vehicles, charging options, and grid integration, all of which are critical for expanded transportation infrastructure around plug-in electric vehicles (PEVs).
“There are a lot of entities investigating components of electric vehicles, grid integration, or infrastructure,” said NREL Vehicle Systems Engineer Mike Simpson. “There are very few places looking at how they all come together as a much larger, connected system. This facility was designed from the ground up to specifically address that intersection point.”
Capabilities at the VTIF include vehicle energy management within smart grids, vehicle charge integration with renewable energy resources, bi-directional vehicle charge testing and demonstration, and vehicle thermal management. Four test bays at the facility allow for multiple tests to be conducted at once in controlled environments and can accommodate a wide variety of vehicles, including one test bay built specifically to conduct testing on heavy-duty vehicles. An upcoming addition to the facility is an 18-kilowatt solar array, which will be tied directly to vehicle charging and will allow researchers to do expanded work around the use of solar energy to charge electric vehicles within microgrids.
Better Charges and Better Grids
Further advances in how electric vehicles charge — and how they interact with power grids while charging — is critical to the future deployment of PEV technology. Much of the work being done at the VTIF is centered on this effort and is being done in collaboration with efforts at NREL’s new Energy Systems Integration Facility (ESIF).
“We’re bringing together systems that have never had a reason to talk to one another before,” Simpson said. “There are enormous opportunities to bring value to this intersection of vehicle and grid, which will increase adoption of these technologies.”
Key VTIF research is focused around smart charging. Smart charging involves direct communication between a vehicle and a charging station, bringing information that allows grid operators, charging stations, and potentially the vehicles themselves to decide when and how to charge the vehicle. The average electric vehicle sits, undriven, for 20 to 22 hours out of a day, but only takes 2 to 4 hours to charge using current technology. This makes an electric vehicle a very flexible load on the power grid.
This flexibility creates opportunities for NREL researchers focused on smart charging applications that will leverage the most economical and environmentally sustainable charging options — all while still allowing for on-demand use of the vehicle by the driver.
A four-hour fill up doesn’t quite compete with gasoline engines for on-the-road demand, so engineers are exploring scenarios for fast charging. A fast charge can potentially recharge an electric vehicle in 15 to 25 minutes if the battery is close to empty. This technology employs the conversion of alternating current (AC) grid power to direct current (DC) power, which can be delivered directly to the battery pack. This method allows for faster charges using smaller charging equipment.
Additionally, VTIF researchers are exploring opportunities for bi-directional charging. Bi-directional, or vehicle-to-grid (V2G), charging employs smart charging capabilities but also allows for the vehicle to discharge back to the grid, which turns the vehicle battery into a grid storage device. This capability is of particular interest when combined with microgrids. A microgrid is a potentially self-sufficient segment of the grid that is connected to the power grid at large but has the ability to provide and manage its own energy. In a future scenario where there may be variable production from intermittent renewable sources, readily available storage could buffer that variability. With bi-directional charging, electric vehicles have the potential to play that role, and the vehicle becomes an asset in a smart grid or microgrid. Particular areas of interest for this technology emerge around emergency backup power or the use of vehicle fleets for this purpose.
“We need to be exploring all of the different value streams to enable wider electric vehicle adoption and improved interaction with the grid,” Simpson said. “We can implement all of these different tactics in harmony with one another here at the VTIF. It’s a very exciting opportunity.”
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