Electric cars are usually charged at night. This will be a problem.

As electric cars hit the roads across the country, hundreds of thousands of Americans are beginning to learn the ins and outs of car charging: how to install home chargers, where to find public charging stations, and how to avoid the dreaded “range anxiety.” »

But as EV owners plug in their cars, there’s a problem: pressure on the grid if most drivers continue to charge their EVs at night.

If sales of electric vehicles grow rapidly over the next decade — and most drivers continue to charge their EVs at home — vehicle charging could strain the power grid in the western United States, increasing net peak demand by 25 percent, according to a new study from Stanford University researchers. That could be a problem as the West struggles to keep the lights on amid heat waves and rising electricity demand.

The first thing to know about EV charging is that it’s nothing more than filling your car with gasoline. Charging an electric car takes time — while the fastest chargers can charge an electric car’s battery to 80 percent in 20 to 30 minutes, most chargers are slower, taking anywhere from two to 22 hours for a full charge. That means about 80 percent of EV charging happens at the owner’s home overnight — when the driver doesn’t need the car and can leave plenty of time to charge.

The mass adoption of electric cars will change everything we know about cars, from driving them to repairing them. But the change will be uneven. (Video: Lee Powell/The Washington Post, Photo: Brian Monroe/The Washington Post)

But such a charging scheme is at odds with how electricity is increasingly generated. The greatest demand for electricity occurs in the evening, approximately from 5 to 9 p.m. People come home from work, turn on the lights, watch TV, and engage in other energy-consuming activities. Meanwhile, solar panels generate power in the middle of the day. Therefore, the highest demand for electricity occurs exactly when the solar array begins to shut down for the day.

In the Stanford study, researchers modeled the charging behavior of residents in 11 western states and then analyzed how that behavior would affect a grid that is increasingly shifting to renewables and other clean energy sources.

“When 30 or 40 percent of cars are electric, that will start to have a significant impact on what we do with the grid,” said Ram Rajagopal, a professor of civil and environmental engineering at Stanford University and one of the study’s authors. Even if drivers wait for peak hours and set their cars to charge at 11pm or later, they will be using electricity at precisely the time when renewable energy is not available. This could lead to increased carbon emissions and the need for more batteries and storage in the grid.

One solution, the researchers say, is for more EV owners to switch to charging during the day, charging their cars at work or at public chargers. If EVs are charged in the late morning and early afternoon, when the grid has excess solar capacity that is not being used, there will be less load on the electrical system and less need for storage. According to the study, in a scenario where 50 percent of cars are electric, switching from mostly home charging to a combination of home and work charging could almost halve the amount of storage needed in the network. Adding workplace and public chargers has the added benefit of also helping renters or non-homeowners access EVs.

Siobhan Powell, a research fellow at ETH Zürich in Switzerland and lead author of the study, says now is the time to plan for the expansion of public and work fares. “We’re not saying, ‘Stop charging at home’ or ‘limit charging at home,'” she said. “We don’t want to discourage any charging because it’s really important for adoption. But charging costs a lot of money, and we could make it just as convenient to charge at work or in public than at home.”

The authors also recommend changing the structure of electricity prices to better incentivize charging in the middle of the day. Currently, some utilities are offering consumers ultra-low electricity rates to charge their cars overnight. For example, PG&E, a California utility, offers electric car owners 25 cents a night of electricity between midnight and 7 a.m. and 36 cents between 7 a.m. and 2 p.m. Ideally, Rajagopal and Powell say, the cheapest rates should be in the middle of the day to encourage charging when the sun is shining.

Gil Tal, director of the Electric Vehicle Research Center at UC Davis, who was not involved in the work, said current EV owners don’t need to worry about their charging models. “We don’t need to hit the brakes on EV adoption,” he said. As more clean energy and storage is added to the grid, many of these problems will be solved, he said.

But he agrees that one of the advantages of electric cars is the flexibility of when they can be charged. Whether it’s charging at home during the day (for those who work from home) or providing chargers at work, switching to daytime charging will be beneficial.

Policymakers should “put chargers where cars park during the day,” he said.

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