A method and device for generating electrical energy in a combined system of power plant, cold storage system and air compression system. The air compression system has a primary air compressor for generating a primary compressed air flow at a first pressure level. The power plant has a combustion unit which operates at a second pressure level and generates a combustion gas from which electrical energy is generated. The cold storage system has means for generating cold from compressed air, means for storing cold thus produced and means for generating a compressed air flow at the second pressure level using the stored cold. In a first operating mode (charging mode), a first compressed air flow is introduced from the air compression system into the cold storage system to charge the cold reservoir. In a second operating mode (discharging mode), the first compressed air flow generated in the primary air compressor, is introduced into the cold storage system to discharge the cold reservoir and to generate a third compressed air flow at the second pressure level, which is introduced into the combustion unit. The air compression system has a first booster for boosting compressed air compressed in the primary air compressor to the second pressure level. In a third operating mode (normal mode), the entire primary compressed air flow generated in the primary air compressor is boosted in the first booster to the second compressed air level and introduced into the combustion unit.