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Fuzzy Math: Electric Cars and the New Emissions Standards

The Environmental Protection Agency has been shifting course under the new administration do do more protecting of the environment. As part of...



The Environmental Protection Agency has been shifting course under the new administration do do more protecting of the environment. As part of this new approach, the agency recently issued new fuel efficiency standards for cars and trucks and rightfully got a lot of positive press for it. Car companies will have to have a fleetwide average of 35.5 mpg by 2016.

But with the Nissan Leaf and the Chevy Volt coming out, the EPA faced some new questions about how to calculate the "fuel efficiency" of electric vehicles. Nick Chambers at Gas 2.0 explains the problem:

According to the new rules, the first 200,000 electric cars that any manufacturer sells will count as zero emissions and essentially unlimited mpg vehicles towards that manufacturer’s CAFE credits. But, after a given manufacturer sells their 200,000 EV allotment, any further electric cars sold will then be assigned a pollution number based on how much carbon dioxide is released as a result of generating the electricity to power them.

But, as several writers have now pointed out, how could you possibly assign a straight carbon dioxide pollution number per kilowatt of electricity generated? One of the strengths of our electric grid is how diverse our electrical energy sources are. Some areas of the country run mostly off of coal power, but some places — like where I live in central Washington state — are powered almost entirely off of hydro. So you can see right away that coming up with some average amount of pollution per kilowatt of electricity for the entire United States would penalize some areas more than others.


Here's one solution: You could rate an electric vehicle's efficiency based on the prevalent sources of electricity in the state where it's sold. So a plug-in Leaf sold in Washington state would have better efficiency rating than one sold in a state that relies on coal power. That would provide an incentive for manufacturers to sell their cars in cleaner states—and to pressure states to shift to renewable sources of electricity.

That wouldn't be entirely fair, though, because not all states are blessed with great solar, wind, or hydroelectric potential. It would also make it more difficult for manufacturers to plan ahead because they wouldn't know exactly what sources of power different states would be using in the future.

But I'm not convinced this is a real problem anyway. If a manufacturer is selling more than 200,000 electric vehicles, it has a hit, and won't need the fuel efficiency bonus to incentivize production. Cumulative Prius sales only reached 1 million in 2008. And economic pressures will push us towards renewable sources of electricity anyway. The national average for pollution per kilowat of electricity is going to fall as we get closer to grid parity and more wind power comes online.

Just for fun, though, I calculated the carbon dioxide per mile of an electric vehicle versus a standard passenger car. (I used these three sources for my numbers.) It's a rough estimate, to be sure, but I found that even if an electric car were powered entirely by coal electricity it would produce only 310 grams of carbon dioxide per mile. A normal car that gets 34 miles per gallon would produce 258 grams of carbon dioxide per mile. So even if we imagine that we use nothing but coal power, electric vehicles would still almost meet the new 2016 efficiency standards. I don't think we need to worry about EVs not getting their due in the EPA's new rules.

Image: Nissan LEAF, a Creative Commons Attribution (2.0) image from nostri-imago's photostream










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