Today, the primary energy sources in the world are non-renewables such as oil, natural gas and coal. Especially, share of the natural gas has been increasing day by day due to causing less environmental pollution. As it is seen in the graph above, the most used energy source in the World is oil. As second coal and then natural gas with its rapidly growing production and consumption. Each time a particular energy soruce has gained importance at different period. Oil has taken the place of coal and then natural gas has become important. In coming years, alternative energy sources will have been important.
Clean energy sources are nuclear, wind, solar, bioenergy, wind, geothermal, wave, and tidal energy is hydroelectric. Besides, the development of combustion technology with flue gas retention techniques and technologies has been important for clean energy sector.