Energy resources are of two types
(i) Non-renewable (exhaustible) energy resources are available in limited amount and develop over a longer period. These include coal, mineral oil, natural gas and nuclear power. Coal, petroleum and natural gas are the commenest source of energy being organic in their origin they are also known as fossil fuel.
(ii) Renewable (inexhaustible) energy resources are mostly biomass based and available in unlimited amount in nature since these can be renewable over relating short period of time. These include fire wood obtained from forest, petroplants, plant biomass, animal dung, solar energy, wind energy, water energy, geothermal and dendrothermal energy.
Biodegradable Any things that can be renewable harmless by natural process and therefore, does not cause harm if adequately dispersed or treated.
Degradable Any complex waste that can be broken down into simpler form.