It is common to charge electric vehicles at night. It will be a problem.

As electric vehicles hit the country’s roads, hundreds of thousands of Americans are starting 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 when electric vehicle owners plug their cars in, there’s a looming problem: pressures on the power grid if most drivers keep charging their electric cars at night.

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, according to a new study by Stanford University researchers. in the western United States, increasing net demand at peak times to 25 percent. This could be a problem as the West struggles to keep the lights on amidst heat waves and rising electricity demand.

The first thing to know about electric vehicle charging is that it’s nothing like filling a car with gasoline. Charging an electric car takes time: While the fastest chargers can charge an EV battery by 80 percent in 20-30 minutes, most chargers are slower and take between two and 22 hours to get to. a full charge. This means that around 80 percent of electric vehicle charging takes place at the owner’s home, overnight, when the driver doesn’t need the car and can leave plenty of time for charging.

But that charging model is at odds with the way electricity is generated more and more. The greatest demand for electricity occurs in the evenings, between approximately 17:00 and 21:00. People come home from work, turn on the lights, watch TV, and do other energy-absorbing activities. The solar panels, meanwhile, produce their energy during the central hours of the day. The highest demand for electricity, therefore, occurs just as the solar has started shutting down for the day.

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

“Once 30 to 40 percent of cars are electric vehicles, it will start to significantly impact what we do with the grid,” said Ram Rajagopal, professor of civil and environmental engineering at Stanford University and one of the authors. of study. Even if drivers wait until after rush hour and set the car to recharge at 11pm or later, they will use the electricity exactly when renewable energy is not readily available. This could lead to increased carbon emissions and the need for more batteries and storage in the power grid.

One solution, the researchers say, is if more electric vehicle owners switch to daytime charging, charging their cars at work or at public chargers. If electric cars are recharged in the late morning and early afternoon, when the grid has excess solar capacity that is not being used, there will be less pressure on the electricity system and less need for storage. According to the study, in a scenario where 50 percent of cars are electric, a switch from most homes to a mix of home and work charging could nearly halve the amount of storage space needed on the network. The addition of public and workplace chargers has the added benefit of helping renters or non-homeowners access EVs as well.

Siobhan Powell, a postdoctoral researcher at ETH Zurich in Switzerland and lead author of the study, says the time has come to plan for the expansion of public and workplace charging. “We’re not saying, ‘No longer have home charging’ or ‘limit home charging’,” she said. “We do not want to discourage” whatever charge because it is really important for adoption. But there is a lot of money for charging and we could make charging at work or in public as convenient as it is at home. “

The authors also recommend changing electricity pricing structures to better incentivize mid-day charging. At the moment, some utilities offer very low electric rates for consumers to charge their cars overnight. PG&E, for example, a California utility company, offers electric vehicle owners electricity for 25 cents overnight between midnight and 7am and 36 cents between 7am and 2pm Ideally, according to Rajagopal and Powell, the cheapest rates should be mid-day to Incentive charging when it’s sunny.

Gil Tal, the director of an electric vehicle research center at the University of California at Davis who was not involved in the paper, said current electric vehicle owners don’t have to worry about their charging schemes. “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 argues, 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. It will be helpful to switch to daytime charging, either by charging at home during the day (for those who work from home) or by providing chargers in the workplace.

Politicians must “put the chargers where the cars are during the day,” he said.

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