Flywheel energy storage (Energy density)


A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheel energy storage works by accelerating a rotor to a very high speed 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 system correspondingly results in an increase in the speed of the flywheel. A typical system consists of a rotor suspended by bearings inside a vacuum chamber to reduce friction, connected to a combination electric motor and electric generator. The maximum energy density of a flywheel single-material, isotropic rotor is mainly dependent on the rotor’s geometry and the properties of the material being used.

Related formulas


EThe kinetic energy of the rotor (J)
mThe rotor's mass (kg)
KThe rotor's geometric shape factor (dimensionless)
σThe tensile strength of the material (Pa)
ρ The material's density (kg/m3)