A typical system consists of a flywheel supported by rolling-element bearing connected to a motor–generator. The flywheel and sometimes motor–generator may be enclosed in a vacuum chamber to reduce friction and energy loss. . Flywheel energy storage (FES) works by spinning a rotor (flywheel) and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of conservation of energy; adding energy to the. . Flywheel energy storage stores electrical energy in the form of mechanical energy in a high-speed rotating rotor. The core technology is the rotor material, support bearing, and electromechanical control system. This chapter mainly introduces the main structure of the flywheel energy storage. . In Germany, a 600 kW storage system from STORNETIC is operated by a large municipal utility company. These are both based on carbon composite rotors. Two 3 MW-systems with steel rotors are operating in the Netherlands. These investments refer to a STORNETIC DuraStore unit (Fig. 1, 3) with a peak. . Fig. The magnetic coupling mechanism is the core component of the device; it is mainly composed of three parts: drivin shaft, driven shaft, and magnetic ring. Angular velocity diagram of energy storage flywhe energy to supply for the machine system. . Electrical energy storage systems (EESSs) enable the transformation of electrical energy into other forms of energy, allowing electricity to be stored and reused when needed.