An ESS composed of a plurality of battery racks, the ESS comprising: a forced discharge device configured to forcibly discharge the ESS power; a main output line configured to form a current path between the plurality of battery racks and an electronic device; a forced discharge line configured to form a current path between the plurality of battery racks and the forced discharge device; and an ESS control unit configured to set which line among the main output line or the forced discharge line each of the plurality of battery racks is connected to, wherein each of the plurality of battery racks comprises: a fire detection unit configured to detect a fire of the battery rack; and a switching unit configured to connect a battery rack to the main output line or the forced discharge line under the control of the ESS control unit; and wherein the ESS control unit comprises: a forced discharge battery rack setting module configured to set a battery rack to be forcibly discharged among the plurality of battery racks when receiving a fire detection signal from the fire detection unit; and a discharge order setting module configured to set a discharge order of a battery rack to be forcibly discharged; to check the ID of a battery rack where a fire occurs and to detect the ID of a battery rack adjacent to the battery rack where the fire occurs; to set at least one battery rack adjacent the battery rack where the fire occurs as a discharge battery rack; or to set all battery racks constituting the ESS as a discharge battery rack. a forced discharge device configured to forcibly discharge the ESS power; a main output line configured to form a current path between the plurality of battery racks and an electronic device; a forced discharge line configured to form a current path between the plurality of battery racks and the forced discharge device; and an ESS control unit configured to set which line among the main output line or the forced discharge line each of the plurality of battery racks is connected to, wherein each of the plurality of battery racks comprises: a fire detection unit configured to detect a fire of the battery rack; and a switching unit configured to connect a battery rack to the main output line or the forced discharge line under the control of the ESS control unit; and wherein the ESS control unit comprises: a forced discharge battery rack setting module configured to set a battery rack to be forcibly discharged among the plurality of battery racks when receiving a fire detection signal from the fire detection unit; and a discharge order setting module configured to set a discharge order of a battery rack to be forcibly discharged; to check the ID of a battery rack where a fire occurs and to detect the ID of a battery rack adjacent to the battery rack where the fire occurs; to set at least one battery rack adjacent the battery rack where the fire occurs as a discharge battery rack; or to set all battery racks constituting the ESS as a discharge battery rack. a fire detection unit configured to detect a fire of the battery rack; and a switching unit configured to connect a battery rack to the main output line or the forced discharge line under the control of the ESS control unit; and wherein the ESS control unit comprises: a forced discharge battery rack setting module configured to set a battery rack to be forcibly discharged among the plurality of battery racks when receiving a fire detection signal from the fire detection unit; and a discharge order setting module configured to set a discharge order of a battery rack to be forcibly discharged; to check the ID of a battery rack where a fire occurs and to detect the ID of a battery rack adjacent to the battery rack where the fire occurs; to set at least one battery rack adjacent the battery rack where the fire occurs as a discharge battery rack; or to set all battery racks constituting the ESS as a discharge battery rack. a forced discharge battery rack setting module configured to set a battery rack to be forcibly discharged among the plurality of battery racks when receiving a fire detection signal from the fire detection unit; and a discharge order setting module configured to set a discharge order of a battery rack to be forcibly discharged; to check the ID of a battery rack where a fire occurs and to detect the ID of a battery rack adjacent to the battery rack where the fire occurs; to set at least one battery rack adjacent the battery rack where the fire occurs as a discharge battery rack; or to set all battery racks constituting the ESS as a discharge battery rack.