As we know that the sun provides both heat and light energy for all living beings. It is the main source of energy as it supplies energy for all organisms directly or indirectly. It is the storehouse of energy. It also supports the existence of other sources of energy like fossils, solar energy, hydroelectricity, bio-fuel, and so on. So, we can say that all the energy sources are the outcome of solar energy. So, the sun is the main source of energy.