Patent ID: 8901893

Claim:
An electricity storage device being connected between an electrical power generator using natural energy for generating electricity and an electrical power system to which the electricity of the electrical power generator is supplied, and supplying electricity to the electrical power system, comprising: a storage battery, a controller, and an electrical power inverter performing charging and discharging of the storage battery based on an inverter electrical power instruction issued by the controller, wherein the controller comprises: a first setting portion setting a target supply electrical power based on the electrical power generation output of the electrical power generator and a charging state of the storage battery and, when a fluctuation rate deviates from a predetermined permissible electrical power fluctuation rate range, restricting the fluctuation rate of the target supply electrical power within the predetermined permissible electrical power fluctuation rate range; and a second setting portion setting an inverter target electrical power based on the target supply electrical power, wherein the predetermined permissible electrical power fluctuation rate range is changed according to a charging ratio of the storage battery, wherein the first setting portion is configured to set the target supply electrical power by using a charging-ratio-maintaining instruction to bring the charging ratio of the storage battery close to a target charging ratio; and the target charging ratio is configured to set by obtaining the target charging ratio corresponding to current time from a table, in which time and the target charging ratio are associated with each other.