A Car That Runs on Rocket Fuel, but Is it Green?

NASA just finished testing an experimental BMW sedan that can run on liquid hydrogen, better known as the rocket fuel used in space shuttles.

Talk about job perks:

During the test period, NASA personnel had full access to the fleet of BMW Hydrogen 7s, which run on a form of liquid hydrogen similar to what NASA uses in its shuttles. During their time with NASA, the vehicles - which feature a dual combustion engine capable of running on liquid hydrogen or gasoline and shifting seamlessly between the two - were conveniently refueled using the space center's liquid hydrogen fueling supply located on the space center's premises.

When running on hydrogen, the Hydrogen 7 -- previously covered on
Wired's auto blog and in this article -- doesn't produce any CO2
emissions. But does this really make them sustainable? We posted an article on hydrogen fuels by energy policy wonk Robert Zubrin a little while ago. Wrote
Zubrin,

The trouble is that making hydrogen requires more energy than the hydrogen so produced can provide. Hydrogen, therefore, is not a source of energy. It simply is a carrier of energy. And it is, as we shall see, an extremely poor one.

But one thing Zubrin didn't address was the possibility of using solar cells to produce hydrogen from water. Wired covered that a few years ago. If that can be done efficiently, maybe hydrogen-powered cars really would make sense. It sure beats gasoline.
The BMW Hydrogen 7 Test Period [Technology News Daily]