DETERIORATION STATE ESTIMATION DEVICE FOR POWER STORAGE SYSTEM, DETERIORATION STATE ESTIMATION METHOD, AND POWER STORAGE SYSTEM OPERATION OPTIMIZATION METHOD

A degradation state estimation apparatus estimates a degradation state of a battery energy storage system including a secondary battery and a DC-AC converter. The apparatus includes an estimation arithmetic processing unit (27) that estimates an open circuit voltage (V)and an internal resistance (R) with respect to a charging rate of the secondary battery based on a charge-discharge voltage (V)and a charge-discharge current (I) of the secondary battery, and input-output power of the DC-AC converter, estimates efficiency (η) of the DC-AC converter and power consumption (E) of an auxiliary device of the DC-AC converter, and estimates charge-discharge energy efficiency (RTE) with respect to the charging rate of the secondary battery and a rated input-output ratio on an AC side of the DC-AC converter based on the estimated open circuit voltage, the internal resistance, the efficiency of the DC-AC converter, and the power consumption of the auxiliary device of the DC-AC converter.