Device and method for generating electrical energy

The method involves producing storage fluid containing less than 40 mol-% of oxygen from input air (1) in an air treatment system (2), and storing storage fluid as deep cooled fluid (3) in a fluid tank (4) in an operating mode. The deep cooled fluid is removed from the tank. Mechanical energy is produced from a produced gaseous high pressure storage fluid (10) and a high pressure air (11). A part of the produced mechanical energy is converted into electrical energy (105) in another operating mode. A part of compressed air produced in a gas turbine-air compressor (101) is used as the input air. The produced gaseous high pressure storage fluid is a gaseous high pressure-nitrogen. An independent claim is also included for a device for generating electrical energy in a combined system of a gas turbine-power plant and an air treatment system.