This biodigester produces enough cooking gas for a family in Costa Rica from manure from grass-fed cows. That means they don’t have to buy gas they can barely afford and have to travel long distances to get. Seems like this could be used all over the world.
Here’s how it works, with full instructions on how to build one. Thomas Carmona spent two years there helping build them and blogs about that and related matters at GreenEnergyVideos.