The invention provides a method for controlling an interconnection system. An interconnection system combines a generator device, the output of which fluctuates, and a power storage compensation device to supply electric power to an electric power system. When, in the case of a power generation plan value of 0 kW or less, the sum of a power generated by the generator device and a load power within the enclosure of the interconnection system comes to take a receiving power direction in which a power is supplied from the electric power system, a non-transmission mode is set in which the operation of a sodium-sulfur battery constituting the power storage compensation device and compensating the fluctuation of the output of the generator device is stopped or the power generation plan value ina power generation plan of the interconnection system is set to the sum of the power generated by the generator device and the load power within the enclosure of the interconnection system.