Development of Superconducting Magnetic Bearing for 300 kW Flywheel Energy Storage System

The world's largest-class flywheel energy storage system (FESS), with a 300 kW power, was established at Mt. Komekura in Yamanashi prefecture in 2015. The FESS, connected to a 1-MW megasolar plant, effectively stabilized the electrical output fluctuation of the photovoltaic (PV) power plant caused by the change in sunshine. The FESS uses a superconducting magnetic bearing (SMB) to levitate a heavy weight flywheel rotor without mechanical contact. The SMB consists of high-temperature superconducting coils (HTS coils) made of rare-Earth-Ba 2 Cu 3 O y , superconducting tapes, and high-temperature superconducting plates (HTS plates) made of YBa 2 Cu 3 Oy. The HTS plates in the rotor axis received the levitation forces in the magnetic field generated by the HTS coils in the stator. At first, the SMB was tested alone to check its cooling properties and to measure the levitation force. In the factory test, the SMB was confirmed to levitate the 4000-kg load, and its performance and basic reliability were verified. In the verification test, at Mt. Komekura, the FESS rotor reached a maximum of 2950 r/min, and the FESS was charged and discharged at 300 kW in the PV plant.