How Green Is a Tesla, Really?

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Sept. 9 2013 5:15 AM

How Green Is a Tesla, Really?

As green as a golf cart? A Prius? An SUV?

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The stacks from the Gavin coal burning power plant tower over the landscape on February 4, 2012 in Cheshire, Ohio.
The Gavin coal plant tower in Cheshire, Ohio. Coal still provides much of the nation's electricity—including that which powers zero-emission cars.

Photo by Benjamin Lowy/Getty Images

Second, electric vehicles are more environmentally destructive to manufacture, starting with the energy required to produce their lithium-ion batteries. Those battery packs today are big, bulky, and extremely expensive to manufacture—especially Tesla’s, which is larger and more powerful than that of its competitors. And many electric-vehicle batteries contain rare-earth minerals that are hard to come by and costly to extract. The Tesla’s AC induction motors don’t use rare-earth magnets, but even the company’s engineers would admit that the Model S takes more energy to produce than, say, a Toyota Camry. The question is how long it takes to close that initial gap once you start driving your zero-emissions Tesla. The more you drive it, the greener it becomes.

That leads to the third main argument against the Model S: that it hogs more power than advertised. Weiss reckons that the Model S’s energy-efficiency is dragged down heavily by “vampire load,” or the power that drains from the battery while the car is not in use. Those idle losses played a starring role in John Broder’s famous New York Times piece about running out of juice on a Tesla test drive. Otherwise satisfied owners complain that their cars lose battery range just sitting in the garage.

Vampire load plays a significant role in Weiss’ calculations. In August, though, Tesla delivered on its promise to address the issue in a firmware upgrade. CleanTechnica put the reduction in idle losses at 50 to 70 percent, but Tesla will not confirm the amount. A bigger blow to Weiss’ “dirty as an SUV” argument: as Green Car Reports’ David Noland pointed out in a thorough response, Weiss took into account the carbon footprint of the Tesla’s fuel source, but ignored the carbon footprint of gasoline production. Weiss also assumed, probably erroneously, that people drive the Model S far fewer miles each year than they do the average gas-powered car. Still, Noland agreed that Tesla’s power-consumption estimates may be on the optimistic side. Rejecting the Toyota Highlander comparison, he puts the Model S’s emissions closer to those of the Lilliputian Scion iQ. Not bad for a 4,600-pound luxury sedan.

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It’s true, meanwhile, that several studies have cast doubt on the overall environmental benefits of electric cars, including a 2010 report from the National Academy of Sciences. That report is indeed sobering—but less so when you consider that the nation’s electrical grid is already cleaner today than it was at the time of the report. And as a bevy of IEEE officials were quick to point out, Zehner’s “Unclean at Any Speed” (which relied on the NAS report) glosses over a larger body of peer-reviewed research that finds electric cars are cleaner than internal-combustion cars even in coal-heavy states. Still, Zehner is right to say that these studies, including one by the Union of Concerned Scientists in 2012, tend to give short shrift to the full life-cycle impacts of electric cars.

But there’s a reason scientists aren’t scrambling to write papers evaluating the precise present-day tradeoffs between electric cars and their internal-combustion counterparts. The present is short, and the future is long. Environmental trade-offs are changing all the time, mostly in electric cars’ favor. Natural gas has already reduced coal’s share of the national energy mix in recent years. And the new power added to the U.S. grid each year is skewed much more heavily toward renewables than the current mix. If that trend holds, the Model S and other electric cars will only get cleaner. Besides, a lot of electric-car owners are already investing in solar power to charge their vehicles. Meanwhile, Tesla, Nissan, and other automakers are working feverishly to increase the efficiency and reduce the cost of batteries. The technology isn’t advancing exponentially, as it has with computer processors, but it is advancing.

To use the nation’s reliance on dirty coal as an argument against electric cars is to get things backward. Rather, the prospect of making cars far greener than they are today should count as yet another argument against the nation’s continued reliance on dirty coal.

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