[altitudinous]

A similar concept is the Snowy Hydro project in Australia - essentially it is a battery for clean energy generators such as wind and solar when they cannot generate. There are two lakes - one at the top of a mountain and one at the bottom. When the wind is blowing or the sun is shining the wind generators and the solar panels power pumps that pump water from the bottom lake up to the top lake. When the sun is down or the wind is not blowing and electricity cannot be generated from panels or wind, water is run using gravity from the top lake to the bottom lake through a turbine, generating electricity that way and ensuring constant supply.