these are resources found in nature that are self-regenerating:
sunlight geothermal heat tides wind biomass
These sources are normally used to produce clean (or green ) energy. This production does not lead to climate change and does not involve emission of pollutants.
A related term is sustainable energy: this concept refers to generating energy with an awareness of the future, i.e. in a way that would enable future generations to meet their energy needs too. The concept is related not only to renewables, but also to energy efficiency