TED BlogDr Frank Ochmann, the head of BMW's clean energy development project spoke recently at the 2007 TED (Tech, Entertainment & Design) conference here in New York.He spoke about liquid hydrogen as the best source of fuel for next generation cars. BMW has gone the route of using low temperature liquid storage (cryogenic) for its cars.Given the current state of the technology these are probably the reasons:

Probably the best mass to volume ratio

Probably fastest in terms of refilling

Safer than high pressure gas storage

Weight of insulation is probably lower then the weight of metal hydrides

Existing distribution infrastructure can be partially re-used

Other storage systems not yet ready (alanate, solid matrix, nanofibre structures)

Dr Frank OchmannThere is widespread interest from several countries and a great deal of research has been focused on implementing a hydrogen economy. Storage devices are the major limitation.There are 3 ways to store hydrogen: a compressed gas, a cryogenic liquid or in a solid matrix. While the solid matrix version would be ideal it has not reached a state of development where it is commercially feasible, though some porus alumina more immediate promise than carbon nano-tubes they are both 'future' developments of the technology. Hydrogen makes a good energy carrier and in the near future as more energy potential is produced from biomass like ethanol, biocrude or synfuels it offers a practical means of delivering that energy in an easily usable form. Here are some excerpts from New York Times correspondent and technology blogger David Pogue from the TED conference:

BMW has the first fleet of hydrogen-powered cars (100, a quarter of which are in the U.S.). Other car companies, of course, are experimenting with hydrogen as fuel, but these 100 cars aren't hand-built prototypes or concept cars; they were factory built like any other BMW model, which is a significant milestone. 

 

Some car companies are experimenting with hydrogen gas; BMW's fleet uses liquid hydrogen, which must be kept at -423 degrees Fahrenheit. That's pretty cold; -459, after all, is absolute zero. The fuel is kept in a superthick insulated tank at the back of the car--a tank so bulky, it makes a visible bulge behind the rear seats.

AND, one way to get the message across:

Anyway, the advantage of hydrogen cars is that they don't pollute. The only thing coming out of their tailpipe is pure water vapor. In fact, each audience member was given a bottle of bottled water--whose label, instead of "Evian" or "Dasani," was "EXHAUST." (Dr. Ochmann took a swig from it to make the point.)

The entire text of the article is here:
NYTimes
NY Times Blog
David Pogue