iceland on hydrogen fuel, page-5

You get hydrogen from water (one way or another) and when you burn it you mostly get water back. The volume of hydrogen is a function of the pressure you pump it in the tank.

Biodiesel is basically old cooking oil which is stored at atmospheric pressure. How much can you get of that to run a fleet of vehicles anyway. Maybe as an additive to normal diesel but basically it's for science hobbyists to avoid fuel tax and good luck to them. At least you can run normal trucks and diesel cars on it without conversion.

It should be possible to generate hydrogen-rich fuel gas using waste water and solar electricity. have a look at:

Click on TrueFuel