Abstract: The current invention provides several options, depending on specific plant needs, to improve the efficiency and power output of a plant at low loads, reduce the lower limit of power output capability of a gas turbine while at the same time increasing the upper limit of the power output of the gas turbine, thus increasing the capacity and regulation capability Of a new or existing gas turbine system. One aspect of the present invention relates to an energy storage and retrieval system for obtaining useful work from an existing source of a Gas Turbine (GT) power plant while preferably providing an efficient heated air inlet charger.