Method for operating a heat exchange system with - at least one heat exchange chamber with heat exchange chamber boundaries which surround at least one heat exchange chamber interior of the heat exchange chamber, wherein - the heat exchange chamber boundaries comprise at least one first opening for guiding in an inflow of at least one heat transfer fluid into the heat exchange chamber interior and at least one second opening for guiding out an outflow of the heat transfer fluid out of the heat exchange chamber interior; - at least one heat storage material is arranged in the heat exchange chamber interior such that a heat exchange flow of the heat transfer fluid through the heat exchange chamber interior causes a heat exchange between the heat storage material and the heat transfer fluid; characterised in that - during a charging process with a heat transfer from the heat transfer fluid to the heat storage material a heat transfer fluid having a temperature higher than 700°C is used, - during a discharging process with a heat transfer from the heat storage material to the heat transfer fluid a discharge temperature of the discharged transfer fluid is controlled to be maintained constant until the discharge temperature falls below a design temperature of a steam generator which is suppliable with the discharged transfer fluid, wherein the temperature is maintained constant by mixing of a heat transfer fluid coming from the heat exchange chamber interior with a heat transfer fluid having a temperature lower than 300°C coming from a bypass piping system for piping the heat transfer fluid without being guided through the exchange chamber interior. - at least one heat exchange chamber with heat exchange chamber boundaries which surround at least one heat exchange chamber interior of the heat exchange chamber, wherein - the heat exchange chamber boundaries comprise at least one first opening for guiding in an inflow of at least one heat transfer fluid into the heat exchange chamber interior and at least one second opening for guiding out an outflow of the heat transfer fluid out of the heat exchange chamber interior; - at least one heat storage material is arranged in the heat exchange chamber interior such that a heat exchange flow of the heat transfer fluid through the heat exchange chamber interior causes a heat exchange between the heat storage material and the heat transfer fluid; - during a charging process with a heat transfer from the heat transfer fluid to the heat storage material a heat transfer fluid having a temperature higher than 700°C is used, - during a discharging process with a heat transfer from the heat storage material to the heat transfer fluid a discharge temperature of the discharged transfer fluid is controlled to be maintained constant until the discharge temperature falls below a design temperature of a steam generator which is suppliable with the discharged transfer fluid, wherein the temperature is maintained constant by mixing of a heat transfer fluid coming from the heat exchange chamber interior with a heat transfer fluid having a temperature lower than 300°C coming from a bypass piping system for piping the heat transfer fluid without being guided through the exchange chamber interior.