Are electric cars greener? Depends on where you live

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Long thought a thing of the future, electric cars are becoming mainstream. Sales in the United States of plug-in, electric vehicles nearly doubled last year. Credible forecasts see the number rising within a decade to half a million vehicles per year, which would easily exceed sales of the Toyota Camry today.

Although the technology for electric cars is improving quickly, the industry still depends heavily on public policy - such as the $7,500 subsidy that the federal government gives everyone who buys one. The rationale for such aggressive policy support is, in part, rooted in the idea that these cars cause less pollution. Indeed, conspicuously "green" consumers dominate sales of electric vehicles, just as they did initially for hybrid vehicles such as the Toyota Prius.

But whether electric cars are actually greener depends on where the comes from. Our research, along with other studies, finds that electric cars are not necessarily the environmentally friendly choice when it comes to the of - the pollutant of greatest concern for .

It is true that electric cars have no tailpipe emissions (they don't even have tailpipes!), which means they can help clear local air. But the electricity used to charge these vehicles comes mainly from power plants that burn coal or natural gas, with coal being the biggest emitter. Other sources of electricity - wind, solar, hydro and nuclear - generate zero emissions.

Figuring out whether the electricity is more environmentally friendly than just burning gasoline directly in cars depends on statistical sleuthing to estimate changes in emissions within the overall electricity grid in response to the additional electricity needed to charge an electric car. We've done this using data on every hour of every day for recent years across the nation, and the results are striking.

Where and when electric cars are charging affects how their emissions compare with the alternatives of a conventional or hybrid car. In some places and at some times, electric cars generate more emissions. We find, for example, that charging an electric car at night in the upper Midwest will generate more carbon dioxide per mile driven than the average conventional car that burns gasoline. In contrast, electric cars in the western United States and Texas always generate lower emissions than even a hybrid, and this arises because rather than coal tends to be used for generating the additional electricity in these regions.

Our findings are based on how electricity is actually generated and current technologies that determine the efficiency of vehicles. But how might things change in the future to affect whether electric cars will reduce emissions and therefore help address climate change? We know the fuel economy of non-electric cars will increase in the coming years. The U.S. Environmental Protection Agency has nearly doubled the average fuel efficiency goal for cars by 2025. Meanwhile, the manufacturers of electric cars are seeking to significantly increase the distance that one can drive on a charge.

But the critical driver of electric-car emissions is how the electricity is generated. And this is where the future of electric cars as a means for addressing climate change is related to the future of power plant regulations. The EPA is in the process of developing its "Clean-Power Plan" to reduce emissions from . This, along with other rules, will make the electricity sector cleaner and help ensure that electric vehicles are the green choice down the road.

More than 100 years ago were the dominant and most promising technology for powering personal automobiles. But oil won that battle and reigned over the 20th century. Now electricity is poised to make a comeback, and might yet power the transportation sector this century. The push is due in large part to concerns about climate change, so it is important to have policies that ensure are part of the solution rather than the problem.

Explore further

Could hydrogen vehicles take over as the 'green' car of choice?

More information: Joshua Graff Zivin is a professor in the Economics Department and School of International Relations at the University of California, San Diego. Matthew Kotchen is a professor of economics at Yale University. Erin Mansur is a professor at the Tuck School of Management at Dartmouth. All three authors are research associates at the National Bureau of Economic Research. They wrote this for the Los Angeles Times.

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Nov 25, 2014
electric cars aren't going to take over because they are greener. they are going to take over because utilties are eventually going to realize they can compete with big oil.

once the batteries are about right, and the electronics and brains of the cars are getting cheaper. ---the per mile cost of of electric driving in terms of TIME to charge and Cost per mile in dollars, will be competitive with filling a tank of gas, and cheaper.

time is the key obstacle. fast charging batteries are around the corner...

Nov 25, 2014
"electric cars aren't going to take over because they are greener. they are going to take over because utilties are eventually going to realize they can compete with big oil."

We've known it since we did the electric vehicle study in Cupertino with POD vehicles in the mid 1980's. While on EPRI electric vehicle committees who voted money for years to fund what we knew were losers, so we could get where we are today.

EPRI fitted an electric bus with induction panels underneath so it could park over the charge coil buried in the parking place and get charged while it did its idle time. We will probably charge our cars like that, too (opportunity alert!), instead of hooking them up every day.

Nov 26, 2014
My LEAF is charged by 100% wind power so it certainly is green. Electric cars are the future of low carbon emission transport. Owners have the power to choose green energy companies (well in the UK we do). Many electric car owners also have solar panels on their houses.

Nov 26, 2014
[But whether electric cars are actually greener depends on where the electricity comes from.

Most power companies offer a deal where they have to buy the amount of kWhours you use per year from green sources. So while the actual amps that fuel your car may come from a nuclear powerplant overall you have at least the option of filling up with green energy (whereas with fossil fuels you never have that option)

Nov 26, 2014
If solar energy got even 1% of the tax dollars as oil exploration (recently revealed to be 2 trillion tax dollars per/year) Then we could have solar panels on every roof of every house and warehouse. Electricity would be so cheap and green people wouldn't care if it wasn't used.

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