Experimental Characterization of Low-Speed Passive Discharge Losses of a Flywheel Energy Storage System

Flywheel energy storage has a wide range of applications in grids and transportation. The adoption high-performance components made this technology viable alternative for substituting or complementing other devices. systems are subject to passive discharge attributed primarily electrical machine losses, bearing rolling friction, aerodynamic drag the flywheel rotor. In present study, measurements presented complete experiments using system featuring vacuum enclosure. Best-fit equations were applied test data compared analytical models. Analysis best-fit indicates that they may serve as empirical models approximating under given conditions. Bearing which varied linearly with velocity but otherwise unaffected throughout experiments, larger than at low air pressures velocities. Aerodynamic became significant exceeded approximately 3400 rpm. was found be most source all velocities pressures. Based on these findings, it is recommended maintain low-pressure environment enclosure decouple from rotor whenever possible eliminate associated losses.