Californians charged electric cars the wrong way, says a study

A new study by Stanford researchers suggests that electric car drivers who plug in while napping at night should eventually modify their charging behavior to protect California’s power grid.

For years, electric vehicle owners have been told to charge in the middle of the night when energy demand is lowest. Nighttime pricing was encouraged through lower rates and bulletins from state officials.

But in a study published Thursday in the scientific journal Nature Energy, a team of researchers concluded that most drivers should instead switch to daytime charging at work or at public charging stations. They said this would reduce strain on the grid and limit the amount of money the state has to invest in expanding the electricity system.

“Our best-case scenario was one dominated by a lot of workplace charges,” said Siobhan Powell, lead author and former Ph.D. mechanical engineering student. “It matters a lot when you add question in the future grid.”

The team of researchers at Stanford’s Precourt Institute for Energy found that daytime charging is preferable to overnight residential charging for one important reason: solar panels.

California already generates an abundance of electricity from solar parks during the daylight hours. But it wastes much of that energy because there is nowhere to store it, so utilities have to rely on electricity imported from other states and gas plants when the sun goes down.

Researchers behind the study used computer models to project how rising electric car sales could affect electricity demand in the western United States through 2035 and beyond.

Without major investments in the grid and changes in charging habits, the study concludes, charging for electric cars will greatly stress the grid when 30% to 40% of the cars on the road are electric vehicles. Only about 6% of cars and light trucks in California are electric today.

Powell said if drivers could change their 12-hour charging habits and connect between 8am and 2pm, it would significantly reduce that burden on the network and limit costs.

Without that change in behavior, the study predicts that more than 5.4 gigawatt hours of energy storage would be needed to power vehicle charging in the western United States at night. It is equivalent to the energy supplied by five large nuclear reactors.

Concerns about electric cars overloading the electricity grid are nothing new, although they have been a frequent source of misinformation in recent times.

Electric cars weren’t a driving factor behind the energy shortage that led California to repeatedly urge consumers to save to avoid continued blackouts amid a record 10-day heatwave earlier this month.

Some Republican and far-right critics had tried to link the crisis to Gov. Gavin Newsom’s policy requiring the state to ban the sale of most new gas cars by 2035.

Data from the Energy Commission clearly disproves these claims. Electric vehicle charging represents only 0.4% of the total energy load during the peak hours of a typical summer day, from 4pm to 9pm, when the grid is most at risk of failure.

The Stanford study does not suggest that vehicle charging is causing energy shortages today, but it does raise alarms about the long-term potential for problems such as increased sales of electric vehicles.

But the authors said California and other Western states can prepare for the transition by investing in building more charging stations in workplaces and other public places. If not, they said the state could be forced to rely on natural gas-powered power generators.

California’s budget this year includes $ 3 billion to build more public charging stations, and the state recently received $ 56 million from the federal government for that purpose. A provision of Nov. 8 ballot, Prop. 30, also proposes to raise taxes on wealthy people and pump money into electric vehicle charging stations and other projects to reduce greenhouse gas emissions.

Powell said the authors also recommend that utilities modify their off-peak rate structures to encourage late morning and early afternoon charging. PG&E currently offers lower rates for charging electric vehicles from 00:00 to 15:00 and data from the Energy Commission suggests that the vast majority of drivers charge at night.

The study says the existing structures for utility tariffs are a vestige of a time before the state had significant solar and wind power supplies, when demand threatened to outstrip supply during the day.

Ram Rajagopal, associate professor of civil and environmental engineering and co-author of the study, said some drivers will always need to get paid at home, especially those who don’t work outside the home.

But, he said, daytime charging outside the home will be cheaper and more efficient for the masses, especially those living in apartments without easy access to overnight charging stations.

“Due attention must be paid to daytime charging,” Rajagopal said. “You don’t keep gas stations at home.”

Dustin Gardiner (he / he) is a staff writer for the San Francisco Chronicle. Email: dustin.gardiner@sfchronicle.com Twitter: @dustingardiner

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