You can do a simple conversion on natural gas or propane generators to have them run off of biogas. I remember reading about a pig farmer that would send all the pig droppings to the basement of the pig barn where he had it setup to collect the biogas from it. The biogas ran a generator that powered the whole pig farm and there was enough extra to sell to the grid. It doesn't take much biomaterial or pressure to run a cooking or light burner, but for a generator you would need a lot of biomaterial or just the right kind. Thanks @eggmeister :D