so i just recently came across the idea of a device called a wood gasifier. the basic idea is to heat up wood to the point that it releases a gas that is combustible enough to run most engines instead of gasoline. the link im posting here is a small very simplified version of one. the guy making it sorta stutters a bit but its still an interesting idea. and if you could scale it up enough i imagine it would be a viable source of energy for a very long time, depending on how much wood you have sitting around.
http://www.youtube.com/watch?v=Mgu9BdHeUYg
(of course instead of a propane stove like this person is using, you would use a wood or charcoal fire for a heat source)
---there are also many other designs that are a bit more complicated and might be a bit more evicient but this still seems to work.
