An energy storage system in which a renewable power production facility, such as one having a wind energy collector, is used to power a compressor situated adjacent a wellbore. During periods of non-peak load on the electric power grid, the compressor is used to compress atmospheric gases and transfer these gases to a subterranean zone, where the gases are stored. During peak load periods, pressurized gases are allowed to flow from the subterranean zone, through the wellbore and to the surface. At the surface, the gases may be processed to remove residual hydrocarbons, and heated. Heat may be provided by combustion of the hydrogen output of an electrolyzer. The gases are then used to power a electric power production device which delivers alternating current to the power grid.