The alternative energy fad has a new poster boy. European technology company MDI has designed a car that can run entirely on compressed air, at least at speeds below 35 mph. Word is they’re going to be cheap, too, with an expected sticker price under $18,000 for a six-seater. Better still, with normal fuel only needed above 35 mpg to heat the air being used, the promise is over 100 mpg. Likely, it’s too good to be true.

At the light concern level, experts are questioning whether it’s possible to break the 100 mpg mark with a real-sized car instead of a test model, since 75 is about the proven limit so far. More significantly, and pointing to the true problem with this and so many other alternative energy proposals, is that actually creating the compressed air for the fuel is no easy feat. We’re talking a need for 4500 pounds per square inch of air pressure, which according to a Georgia Tech engineer is “above what you normally find even in an industrial setting.” So, is this actually more efficient?

The air car isn’t the first to raise concerns like this. Fuel created from corn ethanol has long been blasted as actually not more carbon efficient (and hence not more environmentally friendly) to use than gasoline. Solar panels are still not as cost-effective as they should be, and even Mr. Obama missed the most recent vote to uphold government sponsorship for solar panel and wind power source installation. Different people will give you different sources, of course, but it’s pretty clear to me that there’s no clear consensus that the alternative energy plans being presented now have got plenty of holes.

So why do we still see them? I think, really, that what we’re really seeing is design and marketing geared not necessarily at actually saving energy, but simply at saving consumers money at the pump. It doesn’t matter to consumers, fiscally, if it’s actually more energy- and pollution-efficient to use gasoline straight-up instead of gas-plus-air or gas-plus-ethanol. Consumers save money by buying less gasoline, and so a car promising better mpg regardless of external costs is easier on the wallet. If you actually buy into the efficiency argument being made and get a warm fuzzy feeling about buying an “environmentally friendly” car, so much the better. But the manufacturers’ goal still seems to be selling cars, not helping the planet, and we should probably be looking for more efficient ways to make alternative fuels, not new ways to use them at the current standard.