It isn't renewable as in "it can be used again". The term renewable is to distinguish it from non-renewable energy which is energy from fossil fuel which the earth has a limited supply of.

Most renewable energy is sourced directly or indirectly from the sun which is, for all practical human purposes, an unlimited source of energy.

Direct solar is energy captured through solar panels. Indirect sources are like wind (caused by the sun heating the atmosphere), hydropower (sun evaporating water to cause rain that forms rivers that can be dammed) or biomass (plants that grow because of sunlight and used as fuel).

"renewable" energy not from the sun would be something like geothermal energy. It isn't strictly renewable but there is a lot of it, if we can tap it.