Electric cars charged at night make the US electric grid unstable

Stanford, Cali – In theory, letting your electric car charge overnight to be ready in the morning seems like a good idea. But in fact, research suggests that doing so does more harm in the long run. It costs more to charge your electric car at night, Stanford scientists say, and that could strain the local electric grid.

Instead, the researchers suggest drivers switch to charging their cars at work or at public charging stations. Another added advantage of daytime charging at a public terminal is that it reduces greenhouse gas emissions.

With the effects of climate change becoming more visible than ever — frequent wildfires, widespread flooding, powerful hurricanes — car companies expect people to start investing in electric-powered cars in the future. For example, Californians are expected to buy more electric cars as the state plans to ban sales of gasoline cars and light trucks in 2035.

“We encourage policy makers to consider utility rates that encourage daily charging and incentivize investment in charging infrastructure to shift drivers from home to work for charging,” says co-lead author of the study, Ram Rajagopal, associate professor of civil and environmental engineering at the University of Stanford, as it stands.

To date, electric cars make up 1 million or 6% of car sales in California. The state’s goal is to increase that number to five million electric vehicles by 2030. However, the study authors say that changing from gas to electric will cause strain in the electric grid when there are 30% more than 40% of cars on the road.

Siobhan Powell, M.D., mechanical engineering and lead study author explains. And it’s not just California and the Western states. All states may need to rethink their electricity pricing structures as electric vehicle charging needs increase and their grid changes.”

If half of the vehicles in the western United States were electric, the team estimates that it would take more than 5.4 gigawatts of energy storage — the equivalent of five large nuclear power reactors — to charge the cars. However, if people charge their electric cars at work instead of at home, the demand for electricity is expected to drop to 4.2 gigawatts.

California currently uses time-of-use rates to encourage people to use electricity at night such as running the dishwasher and charging cars. However, the authors argue that as demand for electric vehicles increases, this strategy is outdated and will soon cause demand to rise as supply declines. More specifically, the teams say that if a third of homes charge their electric cars at 11 p.m., or whenever electricity prices fall, the local grid will become unstable.

“The findings from this paper have two profound implications: one is that price signals are not aligned with what would be best for the network – and price payers. The second is that it calls for thinking about investments in charging infrastructure in the places where people work,” says Inas. Azevedo, associate professor of energy science and engineering and co-lead author.

“We need to move quickly toward decarbonizing the transportation sector, which accounts for the bulk of California’s emissions,” Azevedo adds. “This work provides great insight into how to get there. Let’s make sure we follow policies and investment strategies that allow us to do so in a sustainable way.”

The study was published in nature energy.

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