Well-known intermittency and low capacity factors of solar and wind resources prevent these technologies from fulfilling the demands of the energy transition on their own – at least in the near future. They require backup in the form of dispatchable resources, e.g., fossil-fired power plants and energy storage systems. Such systems must be nimble enough to address short-term fluctuations and maintain grid stability in addition to taking over the base load generation when renewable resources are not available. Aeroderivative gas turbines, small industrial gas turbines, gas-fired recip engines, and energy storage systems such as CAES, LAES, pumped hydro (PHS), and electric batteries are readily available technologies that can accomplish these tasks. Large-scale, long-duration systems such as CAES and PHS are discussed elsewhere in the book. Herein, the focus is on BESS and its integration with gas turbines and solar PV.