Fueled not powered. I doubt it simply because of the logistics of carting around/piping such vasts amounts of hydrogen. I think we'd see a new kind of transport or other alternative fuels long before we use hydrogen. Notice where development is going at the moment and how alternative fuels (such as lpg) are already availible in inner city areas. People GENUINELY interested in trying some of this stuff out should try getting their car converted to run on gas. Its not overtly expensive although it'll hog a lot of space (back seats or the boot). Advantages are cheap fuel, quick to start, less polution, no congestion charing (in London), cheaper road tax etc. The only useful sustainable fuel source at the moment is solar power (yes it makes a difference even in overcast areas, if only for heating water). Wind power requires far too much land, creates a -*BAD WORD*- of a lot of noise and is not usually productive/reliable enough. Longterm effects unknown. Tidal powers is HORRIBLE to maintain and also have unknown longterm effects. Remember the creation of photovoltic panels requires posinous elements and that disposal/repair is expensive, if its even possible. Farmers are probably aware of the methane digester (dump all your crap and waste food in a digester and it'll provide odourless natural gas and fertiliser). At the end of the day, its the lowtech stuff that wins.