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National Drive Electric Week in Florida. Image courtesy of CleanTechnica


Yes, More EVs = Fewer Emissions

If this past Super Bowl was any indication, the time is now for electric vehicles. The growth of EVs has been phenomenal over the past few years, with just over 2 million EVs on US roads by mid-2021. Yet we need to put about 70 million EVs on the road (as well as decrease the number of vehicle miles traveled) by the end of this decade if the United States is to reach its climate goals.

The Myth

Some people believe that charging all of those electric vehicles would put a huge strain on our electric grid and actually increase carbon emissions. The batteries for those EVs need to be charged somehow, and, these people argue, if the grid still has electricity from fossil fuels on it, that growth in EVs will create more pollution. The truth is quite the opposite.

The Reality

The reality is that in the United States today, EVs already deliver about 60–68 percent fewer emissions than gas- and diesel-powered vehicles. And when those EVs are charged smartly they can further reduce emissions by an additional 18 percent and even become a grid resource.

Smart charging means using technology to align your charging with an optimized time, such as when electricity is the cheapest or cleanest or when there’s excess renewable electricity on the grid that might otherwise be curtailed. One such technology is Automated Emissions Reduction (AER), which automatically shifts the timing of your EV charging to sync with times of cleaner energy and avoid times with dirtier energy.

A recent RMI and WattTime report found that with AER technology, emissions reductions are possible across all regions of the United States, even those with the dirtiest grids. And as grids receive an increasing amount of electricity from renewable energy, the savings from emissions-optimized charging will increase.

In fact, when 70 million EVs are on the road (one in four cars), emissions-optimized smart charging is the equivalent of taking an additional 5.73 million internal combustion engine (ICE) vehicles off the road. Even today, charging 1 million EVs at the right times is equivalent to taking between 20,000 and 80,000 ICE vehicles off the road.

RMI and WattTime found that we can maximize those savings even more by optimizing charging depending on the local grid mix, while also taking into consideration marginal emissions (the emissions associated with an increase or decrease in electricity use). For example, you can often reduce emissions by charging EVs in the Midwest, which relies more heavily on wind power, in the evening, and charging EVs in California, which has more solar power, during the day.

And using faster charging can reduce emissions even more. This is because if you can leave your car at a fast charger for longer, where it might only have to charge for 20 to 30 percent of the time it is there, there is more flexible time to take advantage of periods when grid emissions are lower. For example, if you leave your car plugged in overnight for eight hours, but it only needs to charge for two of those hours, there is a lot of flexibility as to when the charging actually occurs.

Everyone Wins

Smart charging our vehicles has benefits beyond lowering greenhouse gas emissions. It can save EV owners and utilities money. Sometimes, when there is excess renewable energy on the grid (on a very sunny and cold day, or an extremely windy day) this energy gets curtailed — the energy output gets reduced due to production exceeding demand or due to transmission constraints. If utilities can encourage EV drivers to shift their charging to these times, when energy is cheaper and cleaner, it helps balance the grid and everyone wins.

Download RMI and WattTime’s latest report, More EVs, Fewer Emissions.

By Laurie Stone

© 2021 Rocky Mountain Institute. Published with permission. Originally posted on RMI Outlet.

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Since 1982, RMI (previously Rocky Mountain Institute) has advanced market-based solutions that transform global energy use to create a clean, prosperous and secure future. An independent, nonprofit think-and-do tank, RMI engages with businesses, communities and institutions to accelerate and scale replicable solutions that drive the cost-effective shift from fossil fuels to efficiency and renewables. Please visit for more information.


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