Biomass Energy
All of the earth's living matter, its biomass, exists in a thin surface layer on the planet called the biosphere. This matter represents a tiny fraction of the total mass of the earth. It is an important store of energy and most significantly, it is one that is continually being replenished. The sun supplies the energy which is stored in plants then it is recycled naturally through a series of conversions involving chemical and physical process in the plant, the soil, the surrounding atmosphere and other living matter. This cyclical process can provide a fuel if we are able to capture some of the biomass at the stage where it is acting as a store of chemical energy. There are great environmental implications here, if our consumption does not exceed the natural level of recycling, in burning biofuels we generate no more heat and create no more carbon dioxide than would have been produced through natural processes. Therefore, we have an energy source whose use should have no deleterious environmental effect.
Historically we have used biomass energy ever since people started burning wood to cook food and keep warm. Today wood is still our largest biomass energy resource. However, many other forms of biomass can now be used. Common materials include plants, residues from agriculture or forestry and the organic component of municipal and industrial waste. You can also get electricity from . . . cows? Yes, cows. The technology works by composting the methane that's produced from organic material as it decomposes. Classic organic material is agricultural waste, as well as the waste found in landfills and generated at wastewater treatment plants.
You can see a PSE Biomass Project in action in Whatcom County, Washington, at the VanderHaak Dairy Digester as well as other PSE demo projects.