Oh, no, what can I do now? My career reporting on high gas prices and the race to build fuel-efficient cars is over!

What’s left to report on now that a colleague has emailed me a story about a Japanese company, Genepax, that has invented a “car that runs on nothing but water.” The next thing you know, they’ll invent one that runs on air. Oh, they did that, too? I guess a new era of conflict-free, ultra-green motoring is upon us.

Not.

What is it that leads not only bloggers but respectable TV networks to write so uncritically about stuff like this? Let me make it clear here: There’s no energy-free lunch. You can’t get cars to run on air without expending tons of energy to compress that air. And the range of a car on compressed air is 10 to 15 miles at best.

Genepax has shown a conventional fuel-cell car that runs on hydrogen, and it won’t head down the road on water unless it carries an expensive, heavy electrolyzer on board the car. It says that it will run for an hour on just a liter of water! Great, but what did it cost to extract hydrogen from that water, and how much does the electrolyzer cost?

"This sounds like one of those 'violates the second law of thermodynamics' deals we saw weekly at General Motors," says Byron McCormick, who headed fuel-cell development at the automaker. "There is no source of energy available to a moving car to replace the energy needed to break water."

Larry Moulthroup of Proton Energy Systems in Connecticut, which lent me my fuel-cell Toyota Highlander, offers some thoughts on how the water car might work. "The speculator in me imagines that perhaps within the trunk-mounted white box there is a reaction, perhaps aluminum oxidation, that is producing hydrogen at or near atmospheric pressure, which in turn is being purified and then is is being used in possibly a hydrogen-air fuel cell to generate the electricity for the drive motor," he said. "Maybe, but I just don’t know."

Automakers investigated a version of the Genepax solution when Daimler proposed that cars carry big tanks of methanol, then use an on-board reformer to extract hydrogen on the fly. It wasn’t economical, and confident reports that the automaker would have hundreds of thousands of those cars on the road by 2006 fell by the wayside. Maybe we’ll see commercial fuel-cell cars by 2015, but they’ll carry compressed hydrogen gas, not reformers or electrolyzers.

Note that although the post on cars that run on water is from this month, the gullible Reuters video is from 2008. Not much has been heard from Genepax since, though there was a brief vogue in homemade water bottle-based electrolyzers you could add to your car and instantly achieve a zillion mpg:

Here’s another naïve water-based power video, this time from Fox in 2006. Again, an automaker was supposedly negotiating with this backyard inventor, but nothing came of it:

And don’t get me started on air cars, which in the form of the perennially coming technology from French company MDI have gotten huge amounts of free publicity despite many years of failing to deliver on production plans. Here’s Popular Mechanics saying they are coming to our shores in 2009 or 2010, with maybe 1,000 miles of range. And for just $18,000! The last we heard, Indian automaker Tata was interested.

Electric battery cars have range problems, and they’re expensive — but they actually work. We can buy them now in the form of cars like the Nissan Leaf and Chevy Volt. They’re not vaporware. Trust me on the cars that run on air or water. You might as well harness a unicorn to your chariot and run with that.

For a little fun, watch this video for some step-by-step instruction on how you, too, can harness limitless power from an innocent bottle of water.

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