As electric vehicle (EV) owners learn how to install home chargers, find public charging stations and avoid range anxiety, the demand for power could burden the electric grid in western states at peak times by up to 25 percent if most charging is done at night, according to one Stanford University study. Unlike filling a car with gasoline, charging an electric car takes time. The fastest chargers on the market today can reach 80 percent in 20 to 30 minutes, but many are slower, taking between two and 22 hours to completion. Thus, around 80 percent of EV charging occurs overnight at home when the driver doesn’t need the car.

That charging pattern challenges the way electricity is generated and distributed. The largest need overall is in the evening from approximately 5 to 9 p.m. Photovoltaic panels produce energy during the middle of the day, so the highest electricity demand comes when solar is dormant.

“Once 30 or 40 percent of cars are EVs, it’s going to start significantly impacting what we do with the grid,” says Ram Rajagopal, a professor of civil and environmental engineering at Stanford University and one of the study’s authors. One solution is for more EV owners to shift to daytime charging at work or public charging stations.