What people think is the best time to charge EVs is wrong

What people think is the best time to charge EVs is wrong

A large increase in electric vehicles (EVs), needed to decarbonize the transportation system, could put a strain on the electrical grid in the western United States, according to a new study. But changing the habits of EV owners regarding how they charge their cars will help prevent this problem.

The findings suggest that decarbonisation needs to be considered more holistically: Rather than considering renewable energy infrastructure and electric car charging infrastructure separately, policymakers should consider the interplay between the two.

To come to that conclusion, researchers modeled the electricity needed to charge electric vehicles in 11 western United States states by 2035, based on plans for future electricity generating capacity. They calculated the electricity demand if 50% or 100% of the passenger car fleet is currently electric, and took into account the impact on the grid of different charging habits.

Current EV owners – the early adopters – tend to be relatively wealthy and own their own homes. Many have installed home chargers and charge their vehicles overnight, when electricity is cheaper and it is easy to recharge because their vehicles are not in use.

But if such habits continue as electric vehicle ownership becomes more widespread, they will put enormous strain on the power grid, the researchers report in Nature Energy. Now that 50% of the passenger car fleet is electrified, a predominance of home charging could increase peak electricity demand by 25%. If all passenger cars were electric, demand would increase to 50%.

The fundamental problem is that charging overnight is out of sync with the availability of renewable electricity, especially solar. So there are two options for meeting a surge in electricity demand for overnight charging: more fossil fuel-based electricity generation or more expensive battery storage to hold solar energy from daytime when it’s generated to nighttime when it’s needed. is.

The solution is to instead encourage people to charge their EVs during the day, by providing convenient and easily accessible charging stations at workplaces or other places where people park their cars during the day, the researchers said.

Peak net electricity demand could be up to 3.4 times greater if everyone charges their EV at night compared to a scenario where charging is encouraged during the day, the researchers calculated. Day charging would also save grid operators hundreds of millions or even billions of dollars in battery storage costs.

“Focusing on daytime charging to minimize the impact on the power grid is the first important conclusion of this study,” the researchers write. “Daytime charging scenarios benefit from their alignment with solar generation, while nighttime charging scenarios miss that opportunity.”

The researchers also found that charging controls — basically timers that regulate the flow of electricity to chargers based on electricity rates, ostensibly to reduce demand on the grid — can backfire as adoption of EVs increases.

For example, it is common for home chargers to go into effect at 9 p.m. That makes sense, considering EVs are relatively rare. But if everyone has an EV and starts charging their car at the same time, that’s a big problem.

Likewise, workplace chargers often have controls designed to smooth out spikes in charging demand or grid emissions throughout the day. But as renewable generation increases, much solar capacity remains untapped. “Uncontrolled charging in the workplace is well matched to solar power generation,” the researchers write — so go ahead and empty people’s cars when they plug them in when they arrive at work.

The results suggest policymakers should rethink electricity tariff structures as renewable energy generation and electric vehicle adoption increase, the researchers say. They also need to start planning and building convenient daytime charging options now, too, to put EV drivers’ charging habits on a path that is more sustainable in the long run.

“The development of new charging stations represents a powerful multi-year form of charging control to improve the impact of electric vehicle charging, support equitable widespread adoption, reduce emissions, support renewable integration and ease the transition to a low-carbon future. ” researchers write.

Source: Powell S. et al.Access and use of charging infrastructure to reduce the impact of the use of deep electric vehicles on the power grid.” Nature Energy 2022.

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