Natural fuel sources are renewable energy sources that come from natural sources such as plants, animals, and the earth. Biomass is a type of natural fuel source that is derived from organic matter such as wood, agricultural waste, and other plant materials. Peatbog is another type of natural fuel source that is formed from partially decayed vegetation and is found in wetlands and bogs. Both biomass and peatbog are renewable energy sources that can be used to generate electricity and heat.