Energy storage is needed when the demand is lower than the supply, and part of the supply (or better say production) is stored for times when the demand will be higher.
This is very much the case with solar energy, production is feasible only over daylight while demand is spread over day and night, in residencies it might peak at evenings. (also it is the case with wind turbines)
Since electricity is a flow of electrons and it can't be stored as such, the way to store electricity is first to convert it to other types of energy. (Batteries - chemical energy, pump water into elevated reservoirs - potential energy, pump air into high pressure caves, melt salt - thermal energy). Later, when the demand increases - the stored energy is converted back to electricity.