Flywheel batteries for electric vehicles

American flywheel Systems of Seattle has patented a system that uses twin lightweight, counter-rotating rim wheels (200,000 rpm) that revolve on frictionless, magnetic bearings. The device is enclosed in an evacuated housing. AFS has completed a computer comparison of a GM Inpact electric vehicle fitted with 32 lead acid batteries against the same vehicle with 20 AFS flywheel storage devices.