Are Some EVs Greener Than Others?

Dec 27, 2014 11:00 AM EST | Matt Mercuro

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Not all electric vehicle owners are being as environmentally friendly as they think they are, according to a new Proceedings of the National Academy of Sciences study.

The study is important for those looking to buy a new car as they consider a number of different electric vehicle like the Tesla Model S, Chevrolet Spark EV, Ford Focus Electric, Kia Soul EV, and BMW i8.

Click here to read the full study, titled "Life Cycle Air Quality Impacts of Conventional and Alternative Light-Duty Transportation in the United States."

The study found that it depends on how the electricity to charge the EV's batteries is being produced.

"Our assessment of the life cycle air quality impacts on human health of 10 alternatives to conventional gasoline vehicles finds that electric vehicles (EVs) powered by electricity from natural gas or wind, water, or solar power are best for improving air quality, whereas vehicles powered by corn ethanol and EVs powered by coal are the worst," said the authors, researchers from the University of Minnesota.

Electric vehicles getting their charge from plants that generate electricity by using natural gas, water, solar power, or wind can reduce harmful impact by 50 percent or more compared to gasoline powered vehicles. Surprisingly, EVs charged by coal-fired plants or vehicles powered by corn ethanol can increase the impact by 80 percent.

Unfortunately, coal is used to generate a good amount of the nation's electricity, nearly 39 percent, according to the U.S. Department of Energy. Coal power is actually on the decline however.

A Department of Energy study pointed out that from 2002-'12 all but six U.S. states showed reductions in their coal use to generate electricity. States with declining coal usage are actually replacing it with power sources that are more environmentally friendly, according to the study.

The study points out that natural gas generates nearly 27 percent of the electricity in the U.S. Natural gas is followed by nuclear (19 percent), hydropower (7 percent), other renewable sources (6 percent), petroleum (1 percent) and other gases (less than 1 percent).

The researchers pointed out that the results of the study "should not be taken as a final statement that environmental improvements are best achieved by replacing existing light-duty vehicles with less-polluting light-duty vehicles, nor that EVs are the best technology for every transportation need. Instead, these results can be seen as an indication of how light-duty transportation fuels could shift to reduce or increase pollution, and as an encouragement into the research of less polluting, more sustainable transportation options for the future."

This could include EVs charged from a grid powered with sustainable energy sources.

Researchers determined that diesel, CNG (compressed natural gas) and gas-electric hybrid power have less total environmental impact than normal gasoline power plants. This means vehicles like Honda Civic CNG and Chevrolet Volt are probably good options. 

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