How Should Consumers Compare EVs to Gasoline Vehicles?

Ask a Scientist - May 2012

M. Kadish of Venice, California asks, "Given that electric cars use energy produced by many different kinds of power plants, how can consumers reliably compare their energy usage and emissions to gasoline vehicles?" and is answered by Senior Analyst Don Anair, Master of Engineering.

Thanks for the question, Mitchel. Its premise is absolutely right: Electric vehicles (EVs) show tremendous promise to revolutionize the auto industry in coming years, but they are only as clean and sustainable as the power grid they plug into. That’s why I just co-authored a UCS report, State of Charge: Electric Vehicles’ Global Warming Emissions and Fuel Cost Savings Across the United States, offering consumers the information you are asking for. You can find many more details in the report itself, but I’ll try to offer a basic answer to your question here.

First of all, to accurately compare electric and gasoline vehicles, one has to take into account the emissions from producing the fuel as well as from consuming it. For gasoline vehicles, this means including emissions not only from propelling the car—i.e., burning the fuel in the engine—but also the emissions associated with extracting petroleum, refining it, and delivering it to the vehicle. For EVs, while no tailpipe emissions occur from consuming electricity to propel the vehicle, we still have to take into account the (often substantial) emissions that result from generating the electricity.

Because most drivers are familiar with the concept of miles per gallon (mpg)—the number of miles a car can travel on a gallon of gasoline—we decided to calculate an equivalent figure for EVs to make it easy for car buyers to compare the global warming emissions of electricity and gasoline powered vehicles. To do so, we analyzed the global warming emissions that would result at the power plant from charging a vehicle with a specific amount of electricity and then converted this estimate into a gasoline mile-per-gallon equivalent.

What did we find? Well, not surprisingly, the way you generate electricity makes an enormous difference in an EV’s global warming emissions. For example, if you were to charge a typical, midsize EV using electricity generated entirely by coal-fired power plants, its global warming emissions would be equivalent to the emissions from operating a gasoline vehicle with 30 mpg fuel economy. But if you charged that same vehicle with electricity derived exclusively from wind power, it would result in global warming emissions equivalent to that of a gasoline vehicle getting 3,900 mpg—more than a 100-fold difference.

Of course, because the electric grid in the United States is comprised of a mix of electricity generating sources which vary across the country, we needed to look more closely to make our analysis really useful for today’s consumers. To do so, we analyzed the global warming emissions you can expect when you plug in an EV in any one of 26 regions around the United States.

The good news is this: we found that no matter where you live in the United States, electric vehicles charged on the power grid have lower global warming emissions than the average compact gasoline-based vehicle sold today.

In many regions, such as for you, as a California resident, EVs are far and away the best choice from a global warming standpoint, with emissions far less than even the best gasoline hybrids now on the market. In fact, some 45 percent of Americans live in regions where this is the case (including California, most of New York, and the Pacific Northwest). Some 37 percent of Americans live in regions, such as Florida and most of Texas, where an electric vehicle has the equivalent global warming emissions of a 41 to 50 mpg gasoline vehicle, comparable, in other words, to the best gasoline hybrids available today. In some areas, however, such as the Rocky Mountain grid region covering Colorado and parts of neighboring states, coal makes up a large percentage of the power-plant mix, so in this region,  EVs, while still a good choice, deliver global warming emissions equivalent to a 31 to 40 mpg gasoline vehicle—in other words, similar to the most efficient non-hybrid gasoline-powered vehicles now on the market. We found that some 18 percent of Americans currently live in such regions.

The bottom line: no matter where you live, EVs offer a good choice when it comes to reducing global warming emissions, but just how good varies considerably depending on where the vehicle is charged. Still, it is worth bearing in mind that, while the environmental benefits of driving an EV vary by region, electric grids across the country are getting cleaner. Some 29 states and the District of Columbia are now implementing renewable electricity standards mandating that more electricity than ever before is generated from clean, renewable sources while an increasing number of older and dirtier coal plants are being retired. These changes will only increase the environmental benefits of EVs in the years to come.


Don Anair is an engineer in the California office of the Union of Concerned Scientists' (UCS) Clean Vehicles Program working on state and national transportation, air quality, and global warming policy. Before Mr. Anair came to UCS, he worked as a system design engineer for Applied Signal Technology where he received a patent for a new satellite communications product. Mr. Anair holds a bachelor's and master's degrees in electrical engineering from Cornell University.


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