Tesla Gets New "Green" Kudos. And Here's How Prius Beat the Volt and Leaf
The Tesla Roadster has a new title to honk about: cleanest emissions car in the world. Another winner and a green-car surprise: Prius, which trumped the Chevy Volt or Nissan Leaf.
This is according to John DeCicco, a professor at the University of Michigan who just announced these results from his new AutoEcoRating system.
DeCicco's plans to rate the whole fleet, but as an interim step, he compared four cars. The Tesla's great score was expected. But he found that the Toyota Prius, a conventional hybrid, has a greener score than the much-touted (and more electric) GM's Chevy Volt and Nissan's Leaf.
Finding the smokestacks in "zero" emissions
Why didn't the Volt and Leaf do better? Electric cars have to be rated on their entire lifecycles, not just on what happens when they're on the road. DeCicco wants to give consumers "a full green comparison,'' he said in an interview, "not the spin you get from 'zero emission' marketing hype." His system measures emissions from the tailpipe, of course, but also from manufacturing and from the fuel system.
"Zero emission" is definitely a misnomer, because the electricity comes from the grid, and that means smokestacks. And the emissions are different if you're charging up your Leaf in the coal-dependent Midwest or in much-cleaner California. But, to keep things simpler, DeCicco uses Department of Energy and EPA data to develop a national energy grid average that is 50 percent coal and 20 percent nuclear, with the rest various "others" (including hydro, wind and solar).
In DeCicco's measurement, total lifecycle environmental impact is expressed as tons of carbon dioxide equivalent per year. When he crunches those numbers, Tesla gets a low rating of 5.6 tons annually, versus 6.1 for the Toyota Prius (the new plug-in hybrid version is probably cleaner), 6.5 for the Leaf and 7.8 for the Volt. That's in comparison to the average compact car (with 27 mpg fuel economy), which puts out a lot more CO2 -- 10.9 tons a year.
What's Coming Out of the Tailpipe?
In terms of overall eRatings (with higher numbers being better), the Tesla gets a green score of 224, compared to 204 for the Prius, 193 for the Leaf (which is twice as clean as the average car) and 160 for the Volt (40 percent cleaner than the average car). That poor average compact is stuck at 114.
A look at the chart (right) has the gritty details. The Prius, despite being a hybrid with a tailpipe, has very little tailpipe emissions. That's because it's a Partial-Zero Emissions Vehicle (PZEV), with the added benefit of no evaporative emissions from the fuel system. On California's rating scale, that's the cleanest rating before zero emission for battery cars.
Numbers for the Chevrolet Volt, which has a gas engine acting as a generator, go up because of what's coming out the tailpipe, because it was rated an Ultra-Low Emissions Vehicle (ULEV). It may not actually be dirtier than the Prius, but the latter has a longer battery pack warranty (a key to the higher reaches of emissions ratings).
DeCicco points out that he's a one-man operation (with a student intern), and so hasn't rated the whole fleet yet. But he has made some interesting comparisons. DeCicco has a long history with this kind of rating. He created Yahoo's environmental vehicle ratings, and also developed a ratings book for the American Council for an Energy-Efficient Economy (ACEEE). His earlier rating systems mostly look at conventional cars and hybrids, but the new system is designed to confront the special challenges posed by the newer battery cars without tailpipes.
Mini versus Mini: The E Scores
Comparing the Mini Cooper with the Mini E electric variant, he finds the EV winning hands down. The standard Mini hardtop comes in at 122, but the Mini E is in Leaf territory with 197. That's based on the gas Mini with a six-speed automatic being rated at 28 mpg overall, and the electric one a 98 mpg equivalent. The energy savings are huge in a Mini E, says intern Antonia Chan.
And DeCicco has also rated some top subcompacts, finding them very close in the green scores. The Toyota Yaris (132) beats out the Hyundai Accent (129), Honda Fit (129), Kia Forte (eco version, 127), and standard Forte (122). These ratings are for specific trim packages too detailed to go into here.
Is the Yaris the car for green-minded subcompact buyers? Maybe. But you still have to go kick the tires.
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Photo: Jim Motavalli