ELECTRIC VEHICLESCharging Cars at Home at Night Is Not the Way to Go: Study

By Mark Golden

Published 29 September 2022

The move to electric vehicles will result in large costs for generating, transmitting, and storing more power. Shifting current EV charging from home to work and night to day could cut costs and help the grid, according to a new Stanford study.

The vast majority of electric vehicle owners charge their cars at home in the evening or overnight. We’re doing it wrong, according to a new studyBy Stanford University researchers.

In March, the research team published a paper on a model they created for charging demand that can be applied to an array of populations and other factors. In the new study, published Sept. 22 in Nature Energy, they applied their model to the whole of the Western United States and examined the stress the region’s electric grid will come under by 2035 from growing EV ownership. In a little over a decade, they found, rapid EV growth alone could increase peak electricity demand by up to 25%, assuming a continued dominance of residential, nighttime charging.

To limit the high costs of all that new capacity for generating and storing electricity, the researchers say, drivers should move to daytime charging at work or public charging stations, which would also reduce greenhouse gas emissions. This finding has policy and investment implications for the region and its utilities, especially since California moved in late August to ban sales of gasoline-powered cars and light trucks starting in 2035.

“We encourage policymakers to consider utility rates that encourage day charging and incentivize investment in charging infrastructure to shift drivers from home to work for charging,” said the study’s co-senior author, Ram Rajagopal, an associate professor of civil and environmental engineering at Stanford.

In February, cumulative sales of EVs in California reached one million, accounting for about 6 percent of cars and light trucks. The state has targeted five million EVs on the road by 2030. When the penetration hits 30 percent to 40 percent of cars on the road, the grid will experience significant stress without major investments and changes in charging habits, said Rajagopal. Building that infrastructure requires significant lead time and cannot be done overnight.

“We considered the entire Western U.S. region, because California depends heavily on electricity imports from the other Western states. EV charging plus all other electricity uses have consequences for the whole Western region given the interconnected nature of our electric grid,” said Siobhan Powell, lead author of the March study and the new one.