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Why electric cars should be charged at public charging stations in the daytime

Researchers examined the stress the power grid will experience from the rise of electric cars.

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Charging of electric vehicles in the daytime would restrain extra costs for electricity systems, according to a new Stanford University study.
(Amy Adams/Stanford University via SWNS)

By Alice Clifford via SWNS

Electric car drivers should move to daytime charging at public charging stations by 2035 to save electricity and help reduce greenhouse gas emissions, according to new research from Stanford.

The study focused on the western United States and examined the stress the region's electric grid will come under in the next 13 years from the rise of electric cars.

They found that once 50 percent of cars in the region are electric, more than 5.4 gigawatts of energy storage would be needed if people kept charging them at home in the evening. This is the same as five nuclear power reactors.

If people charged their cars at work during the day instead, the storage needed would only be 4.2 gigawatts.

At a local level, if a third of homes in a neighborhood had an electric car, and most of the owners continued charging it overnight, the local grid could become unstable.

There is concern that when the percentage of electric vehicles in the area hits around 30 to 40 percent, the grid will struggle to keep up, meaning huge investment needs to be made now to support this rise in the future.


Today, California has excess electricity during late mornings and early afternoons, thanks mainly to its solar capacity.

If most electric vehicles were to charge during these times, then cheap power would be used instead of wasted.

Ram Rajagopal, an associate professor of civil and environmental engineering at Stanford, and co-senior author of the study, published in Nature Energy, said: "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."

This rise of electric vehicles is inevitable in this area, as in August, California moved to ban sales of gasoline-powered cars and light trucks by 2035.

In February, cumulative sales of electric vehicles in California reached a million, accounting for about six percent of cars and light trucks on the roads. This is hoped to rise to five million by 2030.

Dr. Siobhan Powell, lead author of the study, and postdoctoral researcher at ETH Zurich University, said: "We considered the entire western US region because California depends heavily on electricity imports from the other western states.

"Electric vehicle charging, plus all other electricity uses, have consequences for the whole western region given the interconnected nature of our electric grid.

“We were able to show that with less home charging and more daytime charging, western U.S would need less generating capacity and storage, and it would not waste as much solar and wind power."

However, this isn't just an issue in western states. Dr. Powell said: "All states may need to rethink electricity pricing structures as their electric vehicle charging needs increase and their grid changes."

There will be many challenges in the way of this plan. Commercial and industrial customers could be charged a lot if they allow their employees to all charge their cars at work, inevitably putting companies off installing chargers.

Dr. Ines Azevedo, co-senior author of the study, and associate professor of energy science and engineering at the Stanford Doerr School of Sustainability, said: “The findings from this paper have two profound implications: the first is that the price signals are not aligned with what would be best for the grid – and for ratepayers.

"The second is that it calls for considering investments in a charging infrastructure for where people work."

Dr. Azevedo added: “We need to move quickly toward decarbonizing the transportation sector, which accounts for the bulk of emissions in California. This work provides insight on how to get there.

"Let’s ensure that we pursue policies and investment strategies that allow us to do so in a way that is sustainable.”

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