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How Much Do Electric Cars Pollute? Depends on When and Where You Plug In

May 19, 2016

The transportation sector ranks as one of the U.S. leading sources of greenhouse gas (GHG) emissions, closely following electricity production. In 2014, vehicles alone produced 26% of the total U.S. GHG emissions, equivalent to producing more than 1.7 million metric tons of CO2.

With the goal of reducing GHG emissions associated with the transportation sector, policymakers have begun supporting measures to increase electric vehicle (EV) adoption while simultaneously raising the question: are EVs really zero-emission? A recently-published NREL report, funded by the U.S. Department of Energy's (DOE) Vehicle Technologies Office as part of the Workplace Charging Challenge Initiative, addresses this very question.

Researchers found that the potential for emissions reduction depends on when and where drivers charge their vehicles. The report presents emissions findings for a variety of light-duty plug-in electric vehicle models under four charging scenarios and five electricity grid profiles. Researchers found that emissions are highly dependent on the percentage of fossil fuels in the electricity mix at the charging location, and there are notable differences in emissions between vehicles charged on high-carbon versus low-carbon grids. Despite this, the study indicates that EVs charged on high-carbon grids produce fewer carbon emissions than those produced by conventional vehicles.

Additionally, emissions are affected by the time at which charging occurs. Researchers found that restricting charging to off-peak hours results in higher total emissions for all vehicle types, compared to other charging scenarios that are more flexible. Alternatively, allowing drivers to charge their EVs anytime and providing access to workplace charging yields the lowest level of emissions for the majority of electricity grid profiles.

The study suggests that reducing fossil fuel use in the electricity sector and encouraging workplace charging (which allows for more miles to be driven on electricity) are two important factors in achieving the greatest emissions reduction.

To learn more, read the full post on the DOE Office of Energy Efficiency & Renewable Energy Clean Cities blog .

—Nicolene Durham