A sort of intuitive way to look at this is that electricity is a very high quality (low entropy?) energy source, whereas hydrogen is lower quality. Typically it's best to go from lower quality energy sources to high quality energy sources.
Photolysis will probably become practical on a large scale at consumer prices long before electrolysis does. And photolysis is the *real* "direct" way to make hydrogen. To date, there isn't a natural source of electricity that is in common use. And no, photolysis doesn't use plants, but it might use chlorophyl or something like it. Solar batteries anyone? At any rate, hydrogen for cars will likely be irrelevant unless we figure out how to store it in carbon nanotubes, because it seems likely to me that better fuel cells will become practical before hydrogen-requiring ones really are. There are fuel cells out there that will run on H2 and CO, which is the product of a reformer or of gasification of biomass. I believe there are cells that run on hydrocarbons as well. You could run your car on organic garbage and all that would come out would be CO2 and H2O. Regarding heavy water, aside from being hardly necessary for making plutonium, it happens to be useful in making reactors that can't melt down (CANDU I believe?) and reactors that run on cheaper and more common fuels like thorium, which produces U233 and ultimately no plutonium, which means the objections to reprocessing will likely go away and we can get 200x more energy out of the same amount of fuel. The current objections to nuclear power are really objections to current nuclear policy. -- Sean R. Lynch <http://sean.lynch.tv/>
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