Puel - fuel of the future?

I have a couple of Kunekune pigs...they produce an extraordinary amount of poo between them. Currently I remove it all from their paddock and store it under some trees. I have been making liquid fertiliser out of it for the garden and it seems to be working out OK (well nothing has died!)
I have to wonder if there isn't enough animal dung in the world to make all the fuel we need?
Anyone got ideas for any other uses for loads of pig dung?
p.s. they are strictly vegetarian pigs so its high class dung.