Magnetic systems for energy storage flywheels

Abstract

A flywheel system suitable for storing energy when demand for energy from a power plant is low, and from which energy can be retrieved when energy demand increases. The flywheel includes (a) a circular composite or metallic glass ring with a radial width limited to less than about 30 percent of the ring's outer radius, and (b) at least one spoke extending along a diameter of the ring, and attached to the ring at either end. The spoke has sufficient radial extendability due to either bending and elastic radial elongation, or only elastic elongation so that, when the flywheel rotates at operating speed, the spoke extends radially to match the radial growth of the ring, without subjecting the flywheel to significant tension at points of attachment of the spoke to the ring. In one embodiment, both flywheel ring and spoke are made of oriented high strength fibers embedded in a thermoplastic resin. Also provided are a magnetic bearing and motor/generator system that are of an axial-gap design so that magnets are held in a substantially fixed position relative to each other, as the flywheel expands radially under centrifugal forces. Further, both motor/generator and flywheel bearings utilize a system of permanent magnets alternating with a high magnetic permeability composition in order to produce highly uniform magnetic fields in the bearing to reduce magnetic drag and improve efficiency, and to produce high torque in the motor generator. The flywheel bearing assembly includes a bulk high temperature superconductive magnet that provides lateral stability to the flywheel.