Air cars in our future? Probably, but not soon.

What's the next big step in automotive transport?

For years, true believers have talked about cars that run on water—but you haven't seen one running down the street yet. How about one running on air?

(Photos: Three of MDI's prototype air car models: In red the six-seat family car, middle in blue is the pickup, and bottomo is the the hot little three-seater Mini-CAT. Photo credit: MDI.)

Air cars already exist in working prototypes, and in foreign countries, several models are ready for roll-out as early as next year.

The air, of course, is compressed air.

And the manufacturers are touting efficiency numbers that border on astounding. Fill the air tank for a couple of bucks and do your 25-mile daily round-trip commute all week without needing a refill. You say your pickup gets 20 miles to the gallon and you're paying $3.50 a gallon? The same week costs you $22.

The average fuel car in the U.S. gets 24 or so miles per gallon. Hybrids achieve as much as 45 to 60. Electric cars, when you calculate the amount of fuel that's burned to produce the power to recharge them, are reputed to come in at 150 to 200 miles per gallon.

Now come compressed air cars.

The fuel is used to compress air, which is carried in tanks. Several different engine designs have been developed, some traditional-looking piston engines, others looking like rotary engines.

The French firm Moteur Developpment International has licensed its technology to firms in India and Spain, and says folks in those countries will be able to buy cars by next summer (2008). (See MDI's website, www.theaircar.com)

The Indian automaker Tata is estimating its car will have a 125-mile range on air alone, and that filling the air tanks will cost about $2. Just for comparison, let's quadruple that figure to account for Hawai'i's electricity costs. That's $8 for 125 miles, or 16 miles to the dollar, or six cents a mile. The financial equivalent of nearly 60 miles a gallon.

But some references suggest the Tata car will get twice that efficiency. And if Hawai'i electric firms established variable rate schedules, charging lower rates during late-night low-use periods, the cost to run the car gets cheaper still.

Now we're talking the energy efficiencies equivalent to electric cars, without the batteries to deal with.

Like hybrids, some air cars will carry their own little generators on board, which run on fuel and recharge the air tanks in a few hours. With this handy feature, they're talking about cars that can go 1,000 miles between fill-ups.

A South Africa firm, Zero Pollution Motors, for several years has touted a proposed air car called e.Volution, which appears to be using the MDI template.

A Korean firm, Energine Corp., has developed a prototype hybrid compressed air car, the pneumatic-hybrid electric vehicle (PHEV). Its power sources are both electric motors and compressed air, and it uses its batteries to run a compressor and to power the motors. (www.energine.com, a site challenging for English speakers because much of it is in Korean.)

Engineair Pty. Ltd.. in Melbourne, Australia, has a rotary air engine that it has used in a variety of small vehicles. (www.engineair.com.au) But the company is not a car manufacturer, but apparently is looking for applications for its engine.

The problems with getting a compressed air car into your garage are several.

First, the announced production deadlines for these kinds of things are notoriously slippery, and until they're rolling in significant numbers, we won't be knowing what the potential problems and victories really are. For instance, while some folks are announcing the Tata air car will be out next year, Tata's own website says it has simply acquired a license to employe MDI technologies and it “envisages Tata’s supporting further development and refinement of the technology, and its application and licensing for India.”

Another issue is that everybody says it will be difficult to get the cars approved for use in the U.S. They tend to be quite a bit smaller than your average SUV, are very light, and need to be crash-tested, one assumes.

But price apparently won't be a major problem compared to other vehicles. Most references to date cite compressed air cars from $5,000 to a little more than $10,000.

One huge benefit over electric and hybrid cars is that you don't need to haul around a heavy weight in batteries that have a limited lifespan and constitute toxic waste when it's time to replace them.

For Hawai'i, a car like this would seem to be a perfect fit, although some doubtless will criticize them as glorified golf carts. But these cars are no smaller than some of the ultra-compacts currently available.

© 2007 Jan W. TenBruggencate