Correction: An earlier version of this story incorrectly stated that the District has just over 6,000 registered electric vehicles. The correct number is 600. This version has been updated.


In this file photo, electric cars are parked at a charging station at the University of Maryland at College Park. (Sarah L.Voisin/The Washington Post)

Pepco wants to offer a lower rate to D.C. residents who own electric vehicles to see if it can help ease potential strains on the power grid by getting them to charge up during off-peak times.

The District has just over 600 registered electric vehicles, but Pepco officials say they are expecting that number to soar as the vehicles become less expensive and can travel farther between charges. Two electric vehicles charging simultaneously on the same street taxes the neighborhood transformer about the same as an entire household, utility officials say.

Pepco officials say that the utility can handle the increasing demand for electricity from the growth in electric cars but that it must be more spread out. Transformers in residential areas will last longer and cost less to upgrade or replace, they say, if more motorists wait to charge their batteries until after their neighbors returning home from work have cooled or heated their homes, cooked dinner and finished any laundry.

The utility is asking the D.C. Public Service Commission to approve a study of how much vehicle owners would be willing to forgo charging their cars immediately after getting home from work if they could pay less to do so. Under the proposal, the owners would pay a lower rate for plugging in between 8 p.m. and noon.

“We want to get ahead of any potential reliability concerns,” said Rob Stewart, Pepco’s smart-grid and technology manager. “We know people are coming home every day and plugging that vehicle in to charge. . . . We want to test whether we can incentivize people to not charge when there’s maximum demand on our distribution system.”

As the federal government, along with states and localities across the country, have granted tax breaks and other incentives to encourage consumers to buy environmentally friendly electric and hybrid vehicles, utilities have pondered how to provide additional power and prevent their systems from becoming overwhelmed.

Stewart said Pepco is particularly concerned about the potential for “clustering,” when multiple electric vehicles charging in proximity can strain a neighborhood transformer designed to serve five to 10 homes.

Last year, the Maryland Public Service Commission approved Pepco’s request to allow owners of electric vehicles to pay higher or lower rates for all of their household use based on whether they used the electricity during peak period or off-peak hours. Stewart said Pepco sought that special rate after a similar two-year pilot in Maryland found that electric-vehicle owners generally took advantage of off-peak rates.

Will Beckett, membership chairman for the Electric Auto Association, a California-based advocacy group, said he has paid lower electric rates for charging his car between midnight and 6 a.m. since 2005. Beckett, who lives in Aptos, near Santa Cruz, said his Chevrolet Bolt is one of six hybrid or electric vehicles on his two-block street. If they all charged their cars during peak periods, he said, there could be trouble.

“You’re not just plugging in, but you’re using a lot of power when you plug in — more than an air conditioner, more than an electric clothes dryer,” Beckett said.

Many people probably charge their cars immediately after getting home from work out of habit, he said. He said most would gladly set the car to charge at a later time if it meant saving even more money than they already save on gas.

Although costs vary greatly based on local electricity rates and gas prices, Beckett said, charging an electric car typically costs about a third of what an owner would pay to fill the gas tank.

Asked whether he had ever heard of a utility struggling to deliver power because of electric vehicles taxing the system, Becket said, “Not yet — but we’re only 2 percent of the vehicles on the road at this stage.”

Under Pepco’s proposed study, D.C. residents who own electric vehicles could sign up for different options.

Some could agree to pay 5 cents per kilowatt-hour to charge their cars off-peak between 8 p.m. and noon, and 13 cents per kilowatt-hour for charging between noon and 8 p.m. The rest of their household electricity use would be billed at their usual rate.

Others could sign up for a discounted “whole house” rate and pay lower or higher rates during those same peak and off-peak periods for all their energy use.

In some cases, Pepco also would share the costs of buying or installing charging stations or the vehicle charging equipment for residents or condominium and apartment building owners.

Stewart said that the study is expected to cost $1.7 million over two years and that applications for participation would be accepted a month after the public service commission approves it. The commission has not set a date for considering the proposal, he said.