Abstract: A system includes a drive shaft, a motor-generator coupled to the drive shaft, a compressor coupled to the drive shaft and configured to output compressed air to a cavern, and a turbine coupled to the drive shaft and configured to receive air from the cavern. The system includes a first thermal energy storage (TES) device, a combustor configured to combust a flammable substance and generate an exhaust stream to the turbine, and controller. The controller is configured to control flow of the air to heat the air as it passes through the first TES, cause the flammable substance to flow to the combustor, operate the combustor to combust the air with the flammable substance to generate an exhaust stream into the turbine, and control the motor-generator to generate electrical energy from energy imparted thereto from the turbine via the drive shaft.