A fundamental look at energy storage focusing primarily on flywheels and superconducting energy storage

Abstract This paper compares energy storage efficiency of Superconducting Energy Storage devices (SMES) with high speed flywheels employing magnetic bearings. Both solid cylinder and shell cylinder flywheels are examined from fundamental physics. Solid cylinder flywheels have a fixed energy density by weight and volume dependent only on the constitutive properties of the flywheel. For a target energy storage, the flywheel’s radius, length, and rotation speed are determined given the governing limitation on hoop stress and the requirement that operation will occur below the first bending mode. No design parameters are open for engineering judgment except the margin of safety. Thus the volume necessary to reach a target energy storage is well defined. The shell cylinder has only the thickness of the shell as an open design variable.