An influx of plug-in electric vehicles (PEVs) charging without coordination could prove challenging to the nation’s electric grid, according to research by the Department of Energy’s National Renewable Energy Laboratory (NREL).

Matteo Muratori, a transportation and energy systems engineer at NREL and author of the new Nature Energy paper, “Impact of Uncoordinated Plug-in Electric Vehicle Charging on Residential Power Demand,” created a computer simulation to explore the effects of in-home charging on the grid.

Previous research into the amount of energy required by homes hasn’t taken into account plug-in electric vehicles, says Muratori. “Given that more people are choosing to drive these types of vehicles and charging them at home, this additional demand should not be overlooked.”

The simulation concluded that a PEV market share of up to 3 percent, which translates to about 7.5 million vehicles, does not significantly impact total residential power demand. More than 600,000 plug-in electric vehicles were on the road at the end of 2016, including about 150,000 sold during the year.

At-home charging could tax local distribution networks. Muratori also looked at the impact PEV charging might have on a residential distribution transformer. In this case, he says that a problem arises when drivers in a geographic area begin 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 and might require upgrades to the electricity distribution infrastructure,” according to Muratori’s paper.

The research also looked at whether the household used the less powerful Level 1 charging option or the more powerful — and 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 says the higher demand could shorten the expected life of a transformer.

NREL says that 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 facilitate PEV integration. Future research, Muratori says, should focus on understanding consumer behavior to determine charging requirements, and the choice between using Level 1 and Level 2 residential charging equipment.