The sun is the main source of energy on Earth, because about 173 PW (or 173 million GW) of solar energy reaches our planet every year, which is more than 10,000 times the world's energy demand.
Geothermal energy uses the earth's heat to produce electricity. The temperature of the subsurface allows it to heat the upper layers of the Earth and underground water bodies.
Bioenergy is universal. Heat, electricity, and fuel can be produced from solid, liquid, and gaseous biomass. And plant and animal waste is used as a renewable raw material.