>>536537632
All electricity storage systems are just converting electricity into some other form of energy to be stored. Batteries turn electrical energy into chemical potential energy, which is later turned back into electrical energy. (It's called "potential" energy because it's being stored to be released later on)

Another way to create a storage system is by moving something heavy up to a higher position (creating gravitational potential energy) and reversing it later on by running a generator off dropping the weight. Pic related.