k, I know I am a late-comer to this discussion, but...
-hydrogen is seperated from water by electrolysis-- you use energy to seperate the atoms out, and when they combine back together they release that energy. No extra energy is created, even in a perfect world you'd have the same amount of energy put in as taken out, thus no energy left over to power the vehicle.
-regenerative braking or wind tubines only recoup some of the energy already expended. You have to make the car move in the first place to make these work, and unless you are going downhill or have a strong wind (not headwind) naturally, that initial energy must come from somewhere. Even if we say they are 100% efficient (which they aren't), there is still no energy left on the table to get the car into motion to begin with.
All of this is just side-dressing to the real question-- where to get the "extra" energy from, to get the car moving. I assume the idea is to not burn things (ie fossil fuels, bio diesel, natural gas, etc), and that leaves very few options:
-Solar panels are a good source of "free" energy, but aren't quite there when it comes to supplying enough energy reliably. Close, but no cigar.
-electric grid, ie an electric car.
-you.
My personal choice? A combination of electrc grid and you. Have you ever heard of the "Twike"?
http://www.twike.us/TWIKE_an _overview_usa.pdf I have been following them for a long time, and they are one of the very few "alternative" vehicles that seem to have a good balance between practicality and "green-ness." And since they've been around a few years they apparently aren't a fly-by-night organization. They're even approved for sale in the US, so I assume they have dot approval, which is really saying something.
I was also thinking that if a person set up a solar panel system at home to charge it off of, it could almost be totally self-sufficient.
alas, the price is hovering around $28k and I just can't justify it...
<edit> sorry for the hijacking of the thread, but all this talk of regenerative braking and free energy and whatnot reminded me of this car... I mean, what better source of free energy than your muscles?