Capacity determination device and method for storage battery system, storage battery system based on same, and power supply system provided together with storage battery system

Provided is a capacity determination device which determines the capacity of a storage battery of a storage battery system that is used together with a wind power generation system, the capacity determination device comprising an input unit and a processing unit. The input unit inputs: data of an operation condition that needs to be satisfied for the protection of the storage battery and is a condition relating to the scope of at least one of a charging/discharging output and a remaining storage amount of the storage battery; data of an output fluctuation limitation condition that is required to be satisfied by a combined output to a power system for which the output of the wind power generation system and the output of the storage battery system are combined, and is a condition relating to fluctuation of the combined output with respect to time; and power generation output data that indicates the time-sequential output of the wind power generation system. The processing unit determines the storage battery capacity by using, as an indicator, a violation amount which is calculated from the power generation output data and the capacity of the storage battery in such a way that the operating condition is satisfied, and indicates the extent to which deviation occurs from the output fluctuation limitation condition.