ELECTRICITY STORAGE SYSTEM

An electricity storage system includes a plurality of strings, a solar power generation device, and an array system that executes control of matching voltage, phase, and frequency of a slave string with those of a master string. The array system acquires information on a remaining discharge power capacity and a remaining charge power capacity of each of the plurality of strings, determines a string having the remaining discharge power capacity equal to or less than a first threshold and a string having the remaining charge power capacity equal to or less than a second threshold as a low-capacity string, and selects the master string based on a total value of the remaining discharge power capacity and the remaining charge power capacity of each master candidate string excluding the determined low-capacity string.