Renewable Energy - Biogas

This uses animal and plant waste (poo and compost!) to create energy by allowing it to rot in a sealed container.  As it rots, the bacteria gives off lots of gas, which is mainly methane.  Methane burns well and is used in power stations and for small household uses like cooking and heating.  It is cheap, easy to produce and uses up waste from farming but carbon dioxide can be released into the atmosphere at the same time and methane is explosive.