Developments to flywheel energy storage

A flywheel energy storage device comprising:

• a housing, wherein the housing is sealed to separate an interior of the housing from an external environment;
• a rotor mounted on an axle within the housing, the rotor configured to rotate relative to the housing;
• a fluid contained within the housing to compress the rotor;
• means for maintaining the pressure of the fluid substantially at equilibrium with or greater than the pressure of the external environment;
• and
• wherein the housing is a pressure vessel only capable of withstanding a pressure less than the pressure of the fluid.

A rotor for use in a flywheel energy storage device, the rotor comprising:

• a rotor;
• an axle coupled to the rotor;
• a shell layer encasing the rotor and coupled to the axle via a bearing, the shell layer having a first shape, wherein the bearing allows the shell layer to rotate around the rotor about an axis of rotation that is concentric with the axle, and wherein at least one of the following conditions apply:
• the cross section of the shell layer, when drawn in a plane in which the axis of rotation lies, defines a closed, substantially convex shape having top and bottom surfaces that intersect the axis of rotation, and wherein each of the top and bottom surfaces comprise a continuous curve;
• and
• the shell layer defines a closed three dimensional, substantially convex shape having top and bottom surfaces that intersect the axis of rotation, and wherein each of the top and bottom surfaces comprise a portion having continuous curvature.