The critical technology in a flywheel energy storage system is the flywheel itself. The company has built a very high-energy flywheel that is lighter weight and smaller for a given energy than any other flywheel on the market. 

The flywheel has demonstrated very low stresses at extremely high speeds and can intrinsically “growth-match” to minimize the centrifugal stresses at high speeds. The design uses high-strength graphite composite materials which are wound much like a spool of thread but can withstand very high stress levels without failing.

This breakthrough in technology is due to the way Optimal attaches this high strength composite flywheel rotor-rim to a shaft. The single most critical limitation in the development of a high energy density flywheel has been in devising a method for attaching the composite rotor to the shaft without destroying the composite as it spins at very high speeds.

Although graphite composite materials are much higher strength than even the most sophisticated high alloy steels, the composite matrix that binds the fibers together is very weak.  As other flywheels have attempted to spin to very high speeds, the composite matrix has tended to pull apart at the attachment to the shaft.  This has always destroyed other flywheels before they could reach high speeds.

The energy stored in a flywheel is proportional to the speed at which it spins, raised to the second power. Accordingly, the stresses in the flywheel also increase proportionately with the speed of the flywheel raised to the second power. This has limited the speeds flywheels can attain.  Optimal has built a self-expanding flywheel hub that does not allow the fiber matrix to pull apart when the flywheel spins at very high speeds.

The hub design creates a “growth-matched” expansion of the hub with the composite rotor that keeps the composite matrix from pulling apart.  This is due to the action of the breakthrough technology in the design of the self-expanding Optimal Flywheel Hub.

In fact, high speed tests of the Optimal Flywheel confirm that the growth-matching is constant even as the flywheel continues to spin faster, virtually assuring that the composite matrix remains intact at even super high speeds (more than 3X the speed of sound at the rotor-tip). This has allowed the company to produce flywheel prototypes that have stored more energy for a given weight and size than any other flywheel in the world, or more than 900 W-hr of energy in a 24 lb flywheel.