An influx of plug-in electric vehicles (PEVs) charging without coordination could prove challenging to the nation’s electric grid, according to research conducted by the US Department of Energy’s National Renewable Energy Laboratory (NREL).
Dr. Matteo Muratori, a transportation and energy systems engineer at NREL, developed highly resolved models of residential power demand and PEV use to assess the impact of uncoordinated in-home PEV charging on residential power demand. He found that although the increase in aggregate demand might be minimal even for high levels of PEV adoption, uncoordinated PEV charging could significantly change the shape of the aggregate residential demand, with impacts for electricity infrastructure, even at low adoption levels.
He also found that clustering effects in vehicle adoption at the local level might lead to high PEV concentrations even if overall adoption remains low, significantly increasing peak demand and requiring upgrades to the electricity distribution infrastructure. This effect is exacerbated when higher in-home power charging is adopted. His paper is published in Nature Energy.
Previous research into the amount of energy required by homes hasn’t taken into account plug-in electric vehicles. Given that more people are choosing to drive these types of vehicles and charging them at home, this additional demand should not be overlooked.—Matteo Muratori
The simulation concluded that a PEV market share of up to 3%—about 7.5 million vehicles—does not significantly impact the aggregate residential power demand. More than 600,000 plug-in electric vehicles were already on the road at the end of 2016, a figure that includes about 150,000 sold during the year.
Muratori also looked at the impact PEV charging might have on a residential distribution transformer. In this case, a problem arises when motorists gathered in a geographic area began buying these vehicles and plugging them in to recharge upon returning home—a practice known as uncoordinated charging. Even without large numbers of PEVs on the road, this clustering effect will significantly increase the peak demand seen by distribution transformers, thereby potentially requiring the upgrades, he found.
The research also looked at whether the household used the less-powerful Level 1 charging option or the more-powerful—and therefore faster—Level 2 charging option. Muratori found that as more PEVs are added to a neighborhood, and a higher charging power is adopted, the distribution infrastructure might no longer reliably support the local electricity demand. He also noted the higher demand could shorten the expected life of a transformer.
The electric load profiles used in this paper, including household demand and PEV charging with a 10-minute resolution, are available for download in the NREL Data Catalog.
Earlier studies on how PEVs might affect the grid assumed utilities would have some control over when charging occurs, referred to as coordinated charging, which will greatly facilitate PEV integration. Muratori noted that might be true in the future, but not necessarily.
His research didn’t focus on using PEVs to return a battery charge to the grid to increase the reliability of the electric system. Future research, Muratori said, should focus on understanding consumer behavior to determine charging requirements, and the choice between using Level 1 and Level 2 residential charging equipment.
Matteo’s work raises important issues for a world with increasing electrification of the vehicle fleet, and leaves us with clear avenues for additional research. We need to continue looking at the synergies between electric vehicles and buildings, especially to make sure the grid remains safe and resilient.—John Farrell, NREL’s laboratory program manager for vehicle technologies
Matteo Muratori (2018) “Impact of uncoordinated plug-in electric vehicle charging on residential power demand” Nature Energy doi: 10.1038/s41560-017-0074-z