The use of energy enables humans to improve their welfare by helping them to feed themselves, keep warm and so on. Primary energy has not undergone any conversion between production and consumption. In other words, primary energy encompasses the forms of energy that are directly consumed as they are found in nature, without any processing. The various sources of primary energy that we can use are fossil and mineral resources (coal, oil, gas, uranium) and renewable energies (hydro, solar, wind, biomass, geothermal).
Secondary energy forms are used by consumers in a refined, processed form. The liquid petroleum products derived from crude oil, such as gasoline, diesel, and kerosene; fuel from biomass; biodiesel; solar collector energy; and thermal geothermal are among the secondary energy forms.
Tertiary energy forms involve one or more transformations of energy. Electric energy, in any way it is produced, is a tertiary form of energy. Nuclear energy, wind power, and most of the other renewable energy sources when they are used to produce electricity contribute to the supply of tertiary energy.