What goes into powering my electric vehicle?

2012 Ford Focus Electric charging port

For many buyers, a major selling point of electric vehicles (EVs) is the absence of a tailpipe. AutoEcoRating confirms that in nearly all instances, EVs score a lot higher than their conventional internal combustion counterparts. However, even as green as they are, driving so-called “zero emission vehicles” such as the Nissan Leaf or Ford Focus Electric still creates emissions. The electricity that charges the batteries is generated at power plants, and depending the region, greater or lesser amounts of CO2 and other pollutants are emitted when energy resources are burned to produce the electricity.

U.S. average net electricity generation by fuel source

The utilities that feed the U.S. grid create electricity from a variety of sources. The adjoining pie chart shows a breakdown of average U.S. power generation as of 2010, the most recent data to which we’ve calibrated the AutoEcoRating algorithm.

Most power comes from fossil fuels, mainly coal and natural gas. The smokestack emissions that directly harm health, result in acid rain or cause other forms of local and regional pollution are still significant, even though they have been slowly but surely reduced over the years. Global warming pollutants such as CO2 and other greenhouse gases from power plants, however, are yet to be meaningfully controlled. That’s a point of contrast with cars because fuel economy regulations already put a legal constraint on the average rate at which new vehicles can emit CO2.

For power generation, nuclear energy is also a major source and although its direct emissions are negligible compared to those from fossil fuel, it involves radiation risks. Hydroelectric dams, wind turbines, solar panels and geothermal generators all harvest forms of renewable energy for which the direct emissions are zero or very small.

State-by-state variations in greenhouse gas emissions from electric power generation

The mix of power plants that feed an EV’s battery varies greatly with the geographic location of your charging station. In the Pacific Northwest and some New England states, a large portion of electricity comes from hydroelectric dams. Charging up in those regions makes for very clean EV driving. Conversely, the Rocky Mountain region and much of the Midwest rely on coal for a majority of their power, and so the environmental benefits of driving an EV in those states are not so great.

A sense of how the global warming profile of electric power varies around the country is shown in the adjoining map. By default, AutoEcoRating evaluates EVs and their plug-in hybrid (PHEV) cousins like the Chevy Volt using national average emission rates. Emissions data reported by utility companies to federal agencies suggest that across states and regions, the GHG emissions from power generation range roughly from 50% below to 50% above the national average.

So what does this mean for the environmental performance of your EV? If you happen to live near coal country, the electricity that powers your EV will create a lot more pollution than electricity generated in the Pacific Northwest. To date, however, most electric car sales have been targeted to the left and right coasts, and so chances are that the typical EV owner is charging up with electrons from cleaner-than-average power sources. That’s clearly good news for the planet.


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