Flywheel Energy Storage
The kinetic energy stored in a solid disk or cylinder shaped flywheel is proportional to its speed and diameter according to equation (1)
Ek = ½ Iw2 (1)
where Ek is the kinetic energy, I is the moment of inertia around its center of mass, and w is the angular velocity, and equation (2)

I = ½ r2m (2)

where r is the radius of the flywheel and m is the mass.1

Upon examination of the above equations it is obvious that two situations are possible: Build a colossal flywheel that spins slow enough to not throw itself apart or build a small Herculean flywheel that can be spun extremely fast. It is easy and rather amusing to envision large wheels attached to buildings being spun by wind and water with birds changing their pirch as the slow megalithic wooden wheelsâ„¢ spokes fall in and out of parallel or even larger wheels rolling down inclined tracks attached to movable motors only to be drug back up the incline by sturdy bulls. What is harder to envision are flywheels no bigger than a coin or compact disc contained in near 100% vacuum chambers being spun at thousands or revolutions per minute on magnetic bearings. While several problems are associated with either option, the latter shall be examined.

The easiest method of increasing the kinetic energy in the flywheel is to increase the angular velocity. Due to the increase of radial and hoop stresses (depending on design) associated with increasing angular velocity lighter stronger monofilament materials are desired. Currently several flywheel materials are used, none of which have a tensile strength greater than 2 GPa2. However a special type of glass, that is 50 times stronger posses an even larger tensile strength and lends itself as a flywheel material.


read more information from
http://gmicNews/Amoroso-Flywheel%20Energy%20Storage.doc
http://osti.gov/bridge/servlets/purl/918509-Cud1it/