Pumped-storage hydro is the most efficient large-scale energy storage mechanism. 70-80% round-trip efficiency. https://en.wikipedia.org/wiki/Pumped-storage_hyd

Pumped-storage hydro is the most efficient large-scale energy storage mechanism. 70-80% round-trip efficiency. https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity#Economic_efficiency https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...