Thermal energy storage is leveraged to store thermal energy extracted from a bottom cycle heat engine. The thermal energy stored in the thermal energy storage is used to supplement power generation by the bottom cycle heat engine. In one embodiment, a thermal storage unit storing a thermal storage working medium is configured to discharge thermal energy into the working fluid of the bottom cycle heat engine to supplement power generation. In one embodiment, the thermal storage unit includes a cold tank containing the thermal storage working medium in a cold state and a hot tank containing the working medium in a heated state. At least one heat exchanger in flow communication with the bottom cycle heat engine and the thermal storage unit facilitates a direct heat transfer of thermal energy between the thermal storage working medium and the working fluid used in the bottom cycle heat engine.