How Green is Your EV?


The American Council for an Energy-Efficient Economy just released its annual guide to the greenest vehicles. For the first time, an electric vehicle (the Mitsubishi i-MiEV) ranked highest. This factoid stirred up for me an issue that is not discussed often enough, and is understood even less. When driving an EV, where you charge the batteries will determine whether or not the vehicle is greener than driving a gasoline car.

An EV powered by the average U.S. grid works out to about 207 grams of CO2 per mile, while the average new light duty vehicle sold in 2012 in the US emits 263 grams, according to the EPA. So on average, driving electric is greener than driving a 33 mpg car.

However, in states with generation mix that includes a lot of renewables (hydro, wind or solar) or nuclear power, the carbon footprint of driving electric is clearly cleaner than your average automobile. In states where coal is still king, the carbon footprint of an EV can actually be worse.

To illustrate the carbon footprint by state, below is a comparison of the emissions of an i-MiEV when driven in five states that are greener than the average and five states where you’d be better off driving a car with a fuel-efficient internal combustion engine.

As an alternative, customers in many states can choose to purchase electricity from renewable sources, which is the greenest way to drive. Or, you can install solar panels on your roof, and net out more clean energy produced than consumed.

This state by state breakdown is really the tip of the iceberg when it comes to understanding true EV emissions. Significant differences in carbon density occur between utilities within a state (such as hydro-rich western Oregon versus the coal-dependent eastern part of the state).

Also, the time of day that you charge can have a great influence on the generation mix too, as some regional grids with substantial amounts of solar can be relatively green at mid-day. Since most EV charging is expected to occur overnight, states with higher percentages of wind power at night would enable greener EV driving.

As I’ve explained before, our knowledge about how green the grid is at any moment in time is woefully inadequate today. In general, though, you can be confident that going electric is better, from a carbon emissions standpoint, than driving your old gas-guzzler.

Article by John Gartner, appearing courtesy the Matter Network.

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1 Comment

  1. The grid is an interconnected and complex system. Showing EV GHGs by state is impractical and misleading. Likely, the figure is based on the state’s generation mix, but each of the nation’s grids cross state boundaries. This can be better for EVs and worse, depending upon the state and the time of day. The fact is, you don’t know exactly where that electron came from. For EVs to help climate, we have to decarbonize the entire grid, not just states where EVs are popular. See the EPA’s eGrid for the best available tool on this topic —