Non-conventional energy sources covers the concepts related to different alternative sources of energy derived from renewable energy sources. Non-renewable energy sources also called fossil fuels, in contrast to renewable energy sources, deplete over a period of time as these resources are limited. Coal, oil, natural gas and petroleum reserves can be extracted from the earth, the formation of which take place several millions of years from the buried plants and animals that lived since such a long time. Nuclear energy, produced from uranium, also comes under this category of energy sources. Nuclear fission reaction results in splitting of uranium atoms which liberates enormous amount of energy through the process called radioactive decay. Heat and electricity can be produced from the nuclear fission. Though uranium is available abundantly in the earth’s crust throughout, the fundamental drawback with this energy source is difficult and expensive mining of uranium and processing of it into the fuel to be used in nuclear power plants.· Nonrenewable energy sources that cannot be easily replenished

Renewable and nonrenewable energy sources can be used as primary energy sources to produce useful energy such as heat, or they can used to produce secondary energy sources such as electricity and hydrogen.