The Union of Concerned Scientists released a report today called "State of Charge" that finds that on average plug-in cars are less polluting than gasoline-powered vehicles in the U.S. But the greenhouse gases emitted from electric vehicles depends on the sources of electricity.
The study centers on a heated discussion in auto circles. Automakers have sometimes referred to electric vehicles as "zero emissions," which is misleading because most plug-in drivers charge their cars from electricity generated by burning coal or natural gas.
The Union of Concerned Scientists, a nonprofit, sought to clarify matters by doing a lifecycle analysis of greenhouse gas emissions that includes energy inputs from start to finish, not only during drive time.
It finds that charging an all-electric car, such as the Nissan Leaf, in regions dominated by coal results in global warming emissions equivalent to a car with a mileage rating between 31 miles per gallon to 40 mpg.
The coal-dominated regions are in the Midwest, representing 18 percent of the U.S. population. In this case, a hybrid Prius, for example, which gets about 48 mpg, would be less polluting than an all-electric car.
Electric vehicles charged in areas with cleaner sources of electricity yields the equivalent of over 50 miles per gallon, better than the most fuel-efficient gasoline or diesel cars today. Those areas include most of the western states and most of the states on the eastern seaboard, which rely more on hydropower, natural gas, or nuclear. These regions as "best" for plug-ins cover about 45 percent of the U.S. population.
"This report's analysis shows that consumers should feel confident that driving an electric vehicle yields lower global warming emissions than the average new compact gasoline-powered vehicle," according to the report.
The authors note there are other benefits to driving plug-in electric vehicles, including lower costs per mile and reducing oil consumption.
Plug-in electric vehicles come with a higher price tag, but the Union of Concerned Scientists study estimates that over the life of the car a driver could save over 6,000 gallons of gasoline and $13,000 by driving an all-electric vehicle, compared to an average compact gasoline car. That assumes $3.50 per gallon gasoline, the U.S. average for electricity prices which is 11 cents per kilowatt-hour, and 15,000 miles a year for 15 years.
Drivers can also lower their electric charging costs by taking advantage of off-peak rates or EV-specific rates.
The study comes at a time when more battery-electric and plug-in hybrid vehicles are coming out. The Nissan Leaf and Chevy Volt have been out for more than a year, while Ford and Mitsubishi are releasing all-electric cars and Toyota prepares to release a plug-in Prius hybrid.
The Union of Concerned Scientist analysis echoes previous studies in finding that on average, plug-in electric cars are less polluting than gasoline cars and cut oil consumption. It also underscores how fuel efficiency through hybrids or other efficient engine technologies can achieve significant gasoline reductions.
The study notes that projected increases in solar and wind on the grid means that the global warming emissions from an electric vehicle in those areas will decrease over time.