I've long been fascinated by the X-Prize approach of providing substantial (but not astronomical) incentives for key breakthroughs: private sub-orbital flight, lunar landers, and most relevantly for this blog, the Progressive Automotive X-Prize for a 100 mile-per-gallon car, which began in 2006. The latter competition has been won by a trio of extremely efficient cars with very different architectures, power sources, and appearances. Splitting a $10 million prize probably won't even come close to reimbursing these teams for the cost of developing their cars, but the associated visibility should lead to some valuable opportunities. In a larger sense, the competition has served another useful purpose, In addition to furthering the technology for continuing to improve the efficiency of mainstream automobiles, it provides a gold standard reference against which to gauge the lavish claims of fuel economy we've already begun to hear from the makers of various plug-in electric vehicles.

One of the main aspects that impressed me about the Automotive X-Prize was the determination of its founders to avoid the superficial approach of merely counting how many gallons of liquid fuel each competing car burned, in favor of a comprehensive energy consumption metric, MPGe, or miles per gallon equivalent, which is based on the gasoline-equivalent energy used, regardless of source or form. MPGe gave the X-Prize judges a fair and unbiased means of comparing cars running on gasoline, ethanol, hydrogen, electricity, or any other energy carrier, onboard or offboard.

Now, as long as our primary concern is reducing our dependence on imported oil, a simple view of gallons of gasoline consumed isn't all bad. Displacing gasoline with electricity or hydrogen produced from domestic energy sources provides important benefits for energy security and our balance of trade, even if it doesn't save much actual energy in the process. One of the main arguments for vehicle electrification is that we can generate electricity in many different ways, but we can only produce gasoline or effective liquid-fuel substitutes for it in a few ways. However, in the long run, total energy consumption matters, particularly because of its strong linkage with emissions. Running a Nissan Leaf or GM Volt on electricity generated from coal--as would be the case in large swaths of the country--certainly saves oil, but it doesn't do very much for the atmosphere or climate. That's where MPGe comes in, and that's why I was pleased that the EPA and Department of Transportation have proposed something similar in their new fuel economy stickers for cars.

So when you see an ad for a new plug-in car that claims that to get effectively 100, 200, or even 300 miles per gallon, you should take a careful look at it, both in terms of MPGe and the physical characteristics of the car in question. This is what a real 100 mpg 4-passenger car looks like: the 830 lb., one-cylinder engined Very Light Car of the Edison2 team--from Virginia, I might add. Or consider the 187 MPGe Wave II two-seater plug-in battery electric car from Li-ion Motors. Cars like this show what it takes to deliver that kind of efficiency on a comprehensive basis. If you're buying a plug-in production model in the next year or two, and it looks more like a normal passenger car than these do, with room for four or more passengers and equipped with all the usual accessories we've grown accustomed to, then you should recognize that while it might burn little or no fuel from petroleum, that's not the whole story.