The term 'SOURCE OF SOLAR ENERGY' can be answered with the three-letter word 'SUN'. The SUN is a star located at the center of our solar system and is the primary source of energy for life on Earth. It is composed mostly of hydrogen and helium and produces energy through nuclear fusion reactions. Solar energy is the energy that is produced by the SUN and is used to power many of our everyday activities, such as heating, cooling, and lighting.