An energy storage system is provided. The energy storage system includes a battery, a power conversion system, and an energy management system configured to control the power conversion system to supply power to the power consumption system using at least one of a power received from an outside or a power charged in the battery. The energy management system estimates power consumption amounts of the power consumption system for each unit time period in a predetermined time period, a reference power amount based on the battery power charged in the battery and the power consumption amounts, and based on the power consumption amounts and the reference power amount, controls the power conversion system to supply power to the power consumption system using the external power and the battery power during the predetermined time period.