WASHINGTON — Not all owners of electric vehicles are being as environmentally friendly as they think they are, according to a new study published by the Proceedings of the National Academy of Sciences.
The study is a critical one for car shoppers as they consider a growing list of electric vehicles, including the BMW i3, BMW i8, Chevrolet Spark EV, Fiat 500e, Ford Focus Electric, Kia Soul EV, Nissan Leaf and Tesla Model S.
The study, "Life Cycle Air Quality Impacts of Conventional and Alternative Light-Duty Transportation in the United States," found that it all depends on how the electricity to charge the EV's batteries is being produced.
The authors, researchers from the University of Minnesota, explain: "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."
When it comes to dumping health-threatening pollutants into the air, according to the study, EVs getting their charge from plants that generate electricity using natural gas, wind, water or solar power, can reduce the harmful impact by 50 percent or more compared to gasoline-powered vehicles. But, surprisingly, EVs charged by coal-fired plants, or vehicles powered by corn ethanol, actually increase the impact by 80 percent or more.
And unfortunately, from an environmental perspective, according to the U.S. Department of Energy, coal is used to generate "a significant chunk" of the nation's electricity, about 39 percent.
But it turns out that coal power is on the decline. A Department of Energy assessment notes that from 2002-'12 all but six U.S. states showed reductions in their use of coal to generate electricity. And the states with declining coal usage are generally replacing it with power sources that the study identifies as considerably more environmentally friendly, most often natural gas.
According to the U.S. Energy Information Administration, natural gas currently generates about 27 percent of the electricity in the U.S., followed by nuclear (19 percent), hydropower (7 percent), other renewable sources (6 percent), petroleum (1 percent) and other gases (less than 1 percent).
The results of the study, the researchers point out, "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."
And that could include EVs charged from a grid powered with increasingly clean and sustainable energy sources.
In the meantime, what did the study have to say about other alternative-fuel options?
The researchers found that diesel, CNG (compressed natural gas) and gas-electric hybrid power all have less total environmental impact than conventional gasoline power plants. In that case, vehicles including the Chevrolet Volt and Honda Civic CNG may be good alternatives.
Edmunds says: Before investing in an EV, environmentally conscious consumers may want to find out how their electricity is generated — or consider other low-impact options.