Remember the Hindenburg? That is your future with hydrogen. How would you like to have all those mini-Hindenburgs careening down the freeway?
On a serious note, it takes much more energy to obtain the hydrogen than you gain from it. Perhaps if we had the matter-antimatter engines on Star Trek, we could use that energy to extract the hydrogen. Wait a minute, if we had those engines, why would we need hydrogen?
UPDATE: I need to respond to comments below. You can take all the wind power, solar power, etc. on earth and you can't produce enough to make hydrogen work. Why? Because the collectors are too large and take too much space. The vast amount of space needed to amass solar power is prohibitive. Where would you grow the crops, put the roads or put houses? With rapidly explanding population, space is more at a premium. The NIMBY crowd (Not In My Back Yard) will stop large scale use of solar and wind. (Ironically the environmentalists are ususally the loudest in the NIMBY chorus.)
Wind power is even more problematic. I am familiar to the sub-polar areas of northern Canada, for instance, and it does not have the wind resources that further south has.
The amount of energy needed to convert hydrogen to a usuable fuel is prohibitive. That is pure and simple physics! Energy is energy--matter is matter in ordinary applicatons. It takes so much energy to make a compound, i.e. water, and it takes at least an equal amount of energy to break that compound into its component parts--no short-cuts or magic exists.
The solution under present technology, of course, is E=MC2. The atom has unbelievable energy, as we all know, and we must get on with it and junk all this solar, wind, biomass etc. That shall not solve our needs. (I suppose we could keep a few demonstration projects to salve the feelings of the tree-huggers.)
If we can contain fusion reactions that is something else. The problem is the prohibitive amount of energy needed to commence the reaction. Also how do you control something as hot as the sun? There are no free lunches.
