It's almost starting to look possible: clean, affordable hydrogen fuel cell-powered cars, available at an affordable price within our lifetimes.

I admit that I've been skeptical about the prospects for some time now. Companies developing this technology always seemed to promise it would become a reality "in 10 years." They were saying it in 1995, in 2000, in 2004 -- but in 2005, that changed.

In March 2005, hydrogen power pioneer Ballard Power (NASDAQ:BLDP) promised to prove to the world that it's possible to construct an affordable fuel cell vehicle within five years. Then, yesterday, June 16, 2005, the world's soon-to-be-largest car company, Toyota Motors (NYSE:TM), put a number to the second part of the fuel cell car equation: $50,000. According to Toyota board member Kazuo Okamoto, Toyota aims to reduce the price tag on a fuel cell-powered car from today's (largely theoretical) $1 million to a more accessible $50,000 by the year 2015.

At this point, quibblers are welcome to point out that Toyota followed the grand historical tradition of looking 10 years down the road in making its prediction. I noticed that, too. And I admit that I'd be even more sanguine about the prospects of hydrogen-powered locomotion becoming real if Toyota had picked any year other than 2015 as its target date. 2016. 2014. 2014 and three quarters -- anything but today's date plus 10 years. The whole "just a decade away" thing has just gotten really old.

Still, what's most noteworthy about Mr. Okamoto's prediction is that, just like Ballard with its five-year plan, Toyota's not promising pie in the sky -- it's talking hard numbers. In 10 years, the company expects to slash the price of a fuel-cell vehicle by 95%, figure out how to produce enough hydrogen to power commercial fleets, and work with partners and governments to set up a network of at least 1,000 fueling stations for those fleets.

It's also encouraging that Mr. Okamoto identified the primary obstacle to commercializing fuel cell vehicles: not developing the technology per se, but building a network of hydrogen fueling stations. From the tone of his comments, Mr. Okamoto seems to take it as a given that (a) the technology will work, and (b) the cars will sell at an affordable price by 2015.

The only question remaining, it seems, is whether any of the world's fuel cell researchers will remain solvent long enough to see their Hydrogen Dream become a reality.

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Fool contributor Rich Smith does not own shares in either company mentioned in this article.