A firestorm of controversy has erupted in response to recent claims about plug-in hybrids and electric vehicles, calling attention to the fact that a new universal standard for fuel efficiency will soon be needed.
The controversy began last week after General Motors claimed during a press conference that its Chevrolet Volt prototypes are achieving city fuel economy numbers of 230 mpg. GM's announcement, which attracted an avalanche of press commentary, was followed days later by a Nissan "tweet" stating that its forthcoming battery-operated Leaf electric vehicle will get an astonishing 367 mpg.
The announcements were greeted by awe, skepticism and calls for a universal standard for measurement of fuel efficiency. Many in the engineering community said automotive consumers would be better served by a standard that employs kilowatt-hours, joules or a form of so-called "miles per gallon equivalent."
"We're now moving from a single-fuel era to a multiple-fuel era," noted Eric Cahill, senior director for the Progressive Automotive X Prize, a foundation dedicated to aiding the development of affordable, energy-efficient vehicles. "Consequently, miles-per-gallon just doesn't stand up anymore, especially when you're talking about burning multiple fuels."
Indeed, GM's announcement has come under some public scrutiny precisely because the Chevy Volt runs on both battery and gasoline power. The vehicle, which employs electric motors to drive its wheels, is exclusively powered by a battery charge for approximately 40 miles, after which it burns gasoline in an internal combustion engine to re-charge itself. Many bloggers and automotive experts have argued that it's meaningless to employ a miles-per-gallon number, especially without GM's explanation of how its engineers arrived at that figure.
"Nobody knows how they made the calculation," said John Shore, senior advisor to the Automotive X Prize Foundation. "They just said they are basing it on what they think the (forthcoming) EPA standard is going to be. That makes it very difficult to evaluate or criticize."
GM says it has been deluged by media requests for more information, but adds that its use of an EPA draft methodology (not yet officially released by the EPA) prevents it from offering details on the calculations. It did say; however, that the 230-mpg figure did not take electrical energy usage into account.
"It's a pure miles-per-gallon-of-gas figure," noted GM spokesman Rob Peterson.
Peterson added that Internet-based stories about GM's use of a 51.1-mile driving cycle to make the calculations are fabrications. (Assuming a 40-mile battery range, the 51.1-mile cycle would have meant that GM ran the car on gasoline for only 11.1 miles.) "It's an absolute myth," Peterson said.
Nissan, which published its 367-mpg number within days of GM's announcement, said it also employed an EPA methodology. The company's calculation was simpler; however, because the Leaf operates only on battery power. Nissan told Design News that the Leaf currently consumes 0.223 kW-hr/mile. Using an EPA-based figure of 82.049 kW-hr/gal, Nissan engineers calculated the car's miles-per-gallon equivalency to be 367 miles, said Scott Vazin, director of product communications for Nissan and Infiniti.
"When the vehicle comes out, we believe it will be in the range of 360 mpg," Vazin said.
Still, experts said that the methods now being used by automakers lack universality and transparency. To be usable by consumers, any method will need both of those qualities, they said.
"You're doing consumers a disservice," Cahill added. "Automakers may get some ‘green-wash' with consumers by publishing those numbers. But as the consumers get confused and skeptical, they will discount those numbers. Then they won't be able to differentiate one model from the next."
The Progressive Auto X Prize Foundation has suggested that the auto industry adopt a miles-per-gallon equivalency standard (MPGe) that would provide a single answer, no matter whether the vehicle was powered by gasoline, electricity, or some other alternative means. The organization, which is supported by Consumer Reports magazine in its MPGe effort, contends that consumers would be better served by a miles per gallon equivalency figure, than by the use of kilowatt-hours, joules, or some other unit that's not understood by the public.
GM told Design News that it supports the idea of a standard method, but for now it is sticking with the EPA's draft methodology. "At this stage, we're building awareness for the Volt, and it's important for us to communicate a metric that people understand," Peterson said. "We're not going to say that the Volt is burning so-many joules to the mile. Nobody would understand that."