A review of flywheel energy storage systems: state of the art and ...
To achieve a higher energy capacity, FESSs either include a rotor with a significant moment of inertia or operate at a fast spinning speed. Most of the flywheel rotors are made of either composite or metallic materials. For example, the FESS depicted in Fig. 3 includes a composite flywheel rotor [12], whose operational speed is over 15,000 RPM.