Flywheel energy storage (FES) works by accelerating a rotor () to a very high speed and maintaining the energy in the system as. When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of ; adding energy to the system correspondingly results in an increase in the speed of th.
First-generation flywheel energy-storage systems use a large steel flywheel rotating on mechanical bearings. Newer systems use carbon-fiber composite rotors that have a higher tensile strength than steel and can store much more energy for the same mass. To reduce friction, magnetic bearings are sometimes used instead of mechanical bearings.
These unique properties give flywheel systems many advantages over other competing energy storage systems, particularly regarding performance, adaptability and longevity.
How efficient is a flywheel system?
Due to their simple design and frictionless characteristics, flywheel systems can reach very high efficiencies of 70-95%, where only a small fraction of the energy is lost during storage.
Unlike some much-hyped green energy storage solutions such as sand batteries and underground hydrogen storage, flywheel energy storage technology has been used for hundreds of years and is proven within its niches. So far, it seems like we should have covered the world with flywheels by yesteryear.
Traditional flywheel systems require strong containment vessels as a safety precaution, which increases the total mass of the device. The energy release from failure can be dampened with a gelatinous or encapsulated liquid inner housing lining, which will boil and absorb the energy of destruction.
What is a 30 MW flywheel grid system?
A 30 MW flywheel grid system started operating in China in 2024. Flywheels may be used to store energy generated by wind turbines during off-peak periods or during high wind speeds. In 2010, Beacon Power began testing of their Smart Energy 25 (Gen 4) flywheel energy storage system at a wind farm in Tehachapi, California.