Charging EVs At Home Overnight May Not Be The Cheapest Option For Much Longer

A benefit of owning an electric car is being able to conveniently recharge it at home overnight when power demand is low and electricity rates are especially cheap. But with the state pushing for a huge expansion in EV sales to curb carbon emissions, this kind of nighttime charging may not be such a bargain for much longer and could further strain the electrical grid, according to a new Stanford University study.

In the study published today in Nature Energy, researchers estimate the impact of rising EV ownership in the western U.S. could boost power demand as much as 25% by 2035, the year when California has banned the sale of new gasoline-powered passenger vehicles. That means charging after 11 p.m. will get more expensive and push utility operators to boost power generation.

Instead, the study says more EV charging should be done during midday hours—ideally at work or public stations—when wind and solar power supplies are at their peak, sometimes producing more energy than the grid can handle. State officials should “consider utility rates that encourage day charging and incentivize investment in charging infrastructure to shift drivers from home to work for charging,” said Ram Rajagopal, one of the study’s authors and an associate professor of civil and environmental engineering at Stanford.

Transitioning U.S. drivers to battery power from gasoline and diesel models is seen as one of the best options for slowing climate-damaging carbon emissions, but getting there won’t be simple or painless. Costs for EVs, such as those made by Elon Musk’s TeslaTSLA
, remain far higher than for conventional autos and keep them out of reach for most mass-market consumers. On top of that, there’s not enough public charging infrastructure to keep tens of millions of additional EVs powered up. Also, finding all the lithium and other metals needed for their batteries may be a big challenge.

California, the biggest EV market in the U.S., has more than a million battery-powered vehicles in operation, accounting for about 6% of all passenger vehicles on the road. The state wants to raise that to 5 million by 2030, approaching the 30% market share level. At that point, the electrical grid will “experience significant stress” unless more capacity is added and charging behavior changes, Rajagopal said.

California and western U.S. states will likely feel the impact sooner, owing to the popularity of EVs in that region, but the rest of the country will also need to make similar adjustments to accommodate the shift to EVs, the researchers said. The study was funded by the California Energy Commission, National Science Foundation and the Bits & Watts Initiative, with financial support from Volkswagen.