What's the Volt's MPG? There's No Easy Answer

Get ready to do a lot of math if you're keen on buying a Chevy Volt and want to compare fuel costs between electric and gasoline cars. It'll be a sharp change from what auto shoppers have been doing for years: simply eyeballing the gas-mileage ratings displayed on new-car stickers in dealer showrooms.

As major automakers start to roll out plug-in electric hybrids (the Volt) or all-electric cars (Nissan's LEAF) later this year, consumers will see mileage numbers on the price stickers that will attempt to explain these cars' fuel economy. But what many shoppers could end up finding is confusion.

That's because the federal Environmental Protection Agency is still working on rules for determining fuel ratings and labels for these alternative-fuel vehicles. At the same time, the EPA also is working with the National Highway Traffic Safety Administration on labels for greenhouse-gas emissions for electric cars. The complication there: how to take into account emissions from power plants, not just the cars' tailpipes.

The EPA expects to propose the new rules this summer, after which it will take public comments and make revisions before adopting the final versions.

How Will Consumers Compare Cars?

But in the meantime, many automakers are preparing to launch cars that run either completely on an electric motor or on a combination of an electric motor and gasoline engine. Both GM and Nissan (NSANY) plan to start shipping the Volt and LEAF, respectively, later this year. Ford, Toyota and others intend to follow suit later.

The big question that all these carmakers are grappling with is how they should label the fuel economy of their models. Since these cars can run on electricity alone, should they be labeled in miles per kilowatt-hour or in kilowatt-hour per miles? If so, how can consumers compare the mileage ratings of electric cars with gasoline vehicles' familiar miles-per-gallon (MPG) ratings?

Further muddying the mileage picture: Consumers will need to know their electricity rates, which can fluctuate from day to night. To calculate per-mile operating costs, rather than monitoring gas-pump prices, they'll have to pay closer attention to their utility bills.

"Engineers say we need to give consumers lots of data, so instead of two numbers, you'll have maybe six or even 10 numbers," says Michael Love, national regulatory affairs and powertrain planning manager at Toyota (TM). "But that probably won't work -- people's eyes would glaze over. So the debate is: How do you give them valid information without overwhelming them?"

The Making of a Marketing Dilemma

The lack of adequate labeling rules has made it particularly difficult for GM to talk about the Volt's fuel economy, which is the first in a new category of cars. The Volt comes with a primary, battery-powered electric motor and a small backup gasoline engine. Charging the Volt's lithium-ion battery will require plugging a cord into a regular wall socket or especially designed equipment for speedier charging. GM announced pricing and financing options for the Volt earlier this week.

GM says the Volt's battery can last 40 miles, after which the gasoline engine kicks in to extend the driving range for another 300 miles. It hasn't divulged the size of Volt's gas tank, except to say it's less than 10 gallons.

GM came up with these driving-range numbers based on current EPA testing procedures. The rub is that the EPA has no rules for calculating the final fuel ratings of plug-in electric hybrids -- the numbers consumers would need to comparison-shop and figure out how much they might have to spend on fuel per trip or month.

GM once touted 230 MPG for its Volt by using a method under consideration by the EPA. That number raised eyebrows and then disappeared from the Volt marketing campaign when the EPA reportedly decided not to use that formula. Nissan also tossed out an eye-popping 367 MPG for its LEAF last year, using the same proposed method, but it has stopped promoting that figure as well.

Until Further Review

Right now, carmakers can use existing EPA rules to come up with fuel ratings for all-electric cars, ratings that can be expressed in kilowatt hours per 100 miles, Love says. But the EPA is looking at whether to adjust those numbers to better reflect mileage that consumers can achieve in every-day driving conditions. Since adopting MPG labeling in the 1970s, the EPA has had to twice modify how mileage is determined because consumers complained that they weren't close to getting the fuel economy listed on the labels, he says.

So for now, electric-car manufacturers are holding off while the EPA completes its review. Nissan currently trumpets only the LEAF's range of 100 miles per charge, which is the limit of its range because it's all-electric, with no gas-powered backup.

GM is working with the EPA to come up with an interim label for the Volt launch later this year, says Tony Posawatz, vehicle line director for the Volt. "It's probable that the label for the Chevy Volt will only last one year, until the standard is here," Posawatz says.

What Should the Label Say?

Given that MPG refers to how much distance you get per gallon of gasoline, an equivalent for electric range would be miles per kilowatt-hour. But some carmakers have looked at kilowatt hours per 100 miles, which better reflects electricity usage.

For example, BMW came up with a fuel economy of 33 kilowatt-hours per 100 miles for city driving for its Mini E (36 kilowatt hours per 100 miles on the highway) when it launched a field trial of its Mini E last year. But like other manufacturers, BMW also is waiting for the EPA to complete its work on mileage ratings for all types of electric vehicles before settling on a final version of its Mini E label.

For automakers, figuring out the labels is only part of the challenge of selling electric cars. They expect to face lots of questions from consumers about how to translate those numbers into fuel costs. For one thing, consumers will have to know, at least roughly, their electric rates, which few could recite off-hand currently. Plus, electricity tends to be more expensive during the day or early evening, when demand is high, and cheaper overnight.

Mileage -- or Carbon Footprint?

Aside from fuel economy, consumers also will have to learn about emission ratings, which reflect the federal government's desire to raise awareness of climate change and to curtail carbon emissions. And in that labeling, the EPA has to take into account emissions from the cars themselves and from electricity generation at power plants, Love says. And even that effort has added complexity because electricity from coal-fired power plants would have higher emissions than power from renewable sources such as solar or hydroelectric power.

And if the electric-car market really takes off, automakers expect a move away from MPG standards altogether. "In the future we'll see a trend toward carbon dioxide emission labeling," Posawatz says. "We've been trained on MPG for decades now, and it's not a measure of goodness."

In the meantime, consumers better be ready to bring their calculators and utility bills when they go out shopping for electric cars.