Willow Rock Energy Storage Center

Willow Rock is a 500 MW / 4,000 MWh Advanced Compressed Air Energy Storage (A-CAES) facility in late-stage development in Kern County, California, able to deliver 8+ hours of energy on a full charge. During charging, off-peak or surplus grid electricity drives a compressor; the heat is pulled out of the compressed air and kept in above-ground thermal storage, and the air is held in a purpose-built underground hard rock cavern where a water head keeps the pressure constant. To discharge, the water head pushes the air back to the surface, where it is recombined with the stored heat and expanded through a turbine to generate electricity. The project targets renewables integration and transmission optimization, with a design life of 50+ years. Hydrostor says the process is non-combustible and needs less land and water than pumped hydro.