The method and the apparatus described are used for generating electrical energy in a combined system comprising a power plant and a low-temperature air separation unit. A feed air stream is compressed in a main air compressor, cooled, and introduced into a distillation column system having a high-pressure column and a low-pressure column. A first oxygen-enriched stream from the distillation column system is introduced into the power plant. In a first operating mode, cryogenic liquid from the distillation column system is introduced into a liquid tank and is stored there at least in part. In a second operating mode, stored cryogenic liquid is removed from the liquid tank and introduced into the distillation column system. A second process fluid from the distillation column system is heated and then actively depressurized in a hot expansion turbine. In addition, in the second operating mode, a nitrogen-enriched product stream from the high-pressure column is also heated to a high temperature and then depressurized in the hot expansion turbine.