An air separation unit is integrated with a power generating plant to improve the efficiency of power generation. The methods and systems improve the efficiency of power generation by utilizing liquid nitrogen from the air separation unit as the working fluid in a turbine. The liquid nitrogen is pressurized while in the liquid state. After warming the pressurized nitrogen stream by cooling the air for the air separator unit, the compressed nitrogen is expanded in a turbine to perform work. After expansion, the nitrogen is vented to ambient air. The nitrogen in its pressurized state can be used for energy storage and/or for smoothing out power demand on a power grid.