[ZenGum]

TW, what's your reason for not taking hydrogen seriously as a fuel?

Here's what I have in mind:

Use photovoltaic cells to generate electricity from sunlight. Use that electricity to split water into hydrogen (and oxygen). Put the hydrogen into your car, run it through a fuel cell, drive, produce water as exhaust.

I see some problems - every time you change energy from one form to another there is loss. Present photovoltaics are inefficient. I don't know about the efficiency of electrolysis, or fuel cells. But with time, these things should improve, and economies of scale etc should lower the price.
Carrying hydrogen around is also a bit tricky, but doable. Many cars run on gas (as in LPG or CNG, not gasoline).