It’s common to charge electric vehicles at night. That will be a problem.

As electric vehicles hit the road 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 “autonomy anxiety”. ”

But as EV owners plug in their cars, a problem looms: strains on the power grid if most drivers continue to charge their EVs at night.

According to a new study Stanford University researchers say if electric vehicle sales grow rapidly over the next decade – and most drivers continue to charge their electric cars at home – vehicle charging could put a strain on the power grid in the western United States, increasing net peak hour demand by 25%. This 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 electric vehicle charging is that it has nothing to do with filling up a car with gas. Charging an electric car takes time – while the fastest chargers can charge an EV battery to 80% in 20-30 minutes, most chargers are slower, taking 2-22 hours to reach a full charge. This means that approximately 80 percent of electric vehicle charging takes place at the owner’s home, at night, when the driver does not need the car and can leave enough time for charging.

But this charging pattern is at odds with the way electricity is increasingly being generated. The greatest demand for electricity occurs in the evening, between approximately 5 p.m. and 9 p.m. People come home from work, turn on the lights, watch TV, and do other energy-consuming activities. Solar panels, on the other hand, produce their energy in the middle of the day. The highest demand for electricity therefore occurs just when solar has started to switch off for the day.

In the Stanford study, the researchers modeled the charging behavior of residents of 11 western states, then analyzed the impact of that behavior on a power grid that is increasingly turning to renewables and other energy sources. clean energy sources.

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

One solution, the researchers say, is for more electric vehicle owners to switch to daytime charging, charging their cars at work or at public charging stations. If electric cars 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 strain on the electrical system and less storage. According to the study, in a scenario where 50% of cars are electric, switching from primarily domestic charging to mixed home-work charging could almost halve the amount of storage needed on the grid. Adding workplace and public chargers has the added benefit of also helping tenants or those who do not own a house have access to electric vehicles.

Siobhan Powell, postdoctoral researcher at ETH Zürich in Switzerland and lead author of the study, says now is the time to plan for the expansion of public and workplace billing. “We’re not saying, ‘Have no more home charging,’ or ‘limit home charging,'” she said. “We don’t want to discourage any load because it’s really important for adoption. But charging costs a lot of money, and we could make charging as convenient at work or in public as at home.

The authors also recommend modifying electricity price structures to better incentivize charging in the middle of the day. Currently, some utilities are offering very low electricity rates to consumers to charge their cars overnight. PG&E, for example, a California utility, offer to EV owners electricity for 25 cents a night between midnight and 7 am and 36 cents between 7 am and 2 pm. Ideally, according to Rajagopal and Powell, the cheapest fares should be in the middle of the day to incentivize charging when the sun is up.

Gil Tal, director of an electric vehicle research center at the University of California, Davis, who did not participate in the article, said current owners of electric vehicles need not worry. their charging habits. “We don’t need to hold back the adoption of electric cars,” he said. As more clean energy and storage are added to the grid, he says, many of these problems will be solved.

But he agrees that one of the benefits of electric vehicles is the flexibility of when they can charge. Switching to daily charging will help, whether charging at home during the day (for those who work from home) or providing chargers in the workplace.

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

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