Just got forward to the hydrogen-from-sunlight entry, and had to make this comment before continuing. There's two things (other than Big Oil money) that'll kill using hydrogen for fuel, except under extremely specialised circumstances like rocketry:

1) Hydrogen leaks like the bugger. The standard way to find a leak in a cryo situation (eg cooling down superconducting magnets) is to test for a helium leak, as it's almost as good at finding the least little leak as hydrogen, and it's easier to detect helium in vanishingly small amounts as there's not much of it in breathable air.

2) When hydrogen burns in air, the flame is invisible to the naked eye. The standard way in NASA of checking whether (and where) there's a hydrogen leak that's aflame is to carry a brush broom in front of yourself, bristles first, and see whether that catches fire.*

Put those two together, and *foom*. And *that*, medames et messieurs, is why the idea of using hydrogen as fuel gets, erm, shot down every time it's put forward, which is about once a decade.

* Perhaps that's where Sir Pterry got the idea from for CMOT Dibbler's patented dragon detector.