15-06-2012, 12:59 PM
FLYWHEEL ENERGY STORAGE SYSTEM
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INTRODUCTION
Flywheel energy storage systems store kinetic energy (i.e. energy produced by motion) by constantly spinning a compact rotor in a low-friction environment. When short-term back-up power is required (i.e. when utility power fluctuates or is lost), the rotor's inertia allows it to continue spinning and the resulting kinetic energy is converted to electricity.
It works by accelerating a rotor to a very high speed and maintaining the energy in the system as rotational energy. When energy is extracted from the system, the flywheel's rotational speed is reduced as a consequence of the principle of conservation of energy adding energy to the system correspondingly results in an increase in the speed of the flywheel.
Most FES systems use electricity to accelerate and decelerate the flywheel, but devices that directly use mechanical energy are being developed.
Advanced FES systems have rotors made of high strength carbon filaments, suspended by magnetic bearings, and spinning at speeds from 20,000 to over 50,000 rpm in a vacuum enclosure. Such flywheels can come up to speed in a matter of minutes much quicker than some other forms of energy storage.
THEORY
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 wheels’ 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 U.S. quarter 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.
CONCEPT
The devise proposed is a light charged flywheel energy storage device shown below. The devise is composed of a long cylindrical flywheel made of high strength glass (failure stress ~ 3.5 GPa) attached to an electric motor. The flywheel is designed as an elongated solid cylinder rather than the traditional disc style flywheel to maximize inertia in a smaller space. (A flywheel the size of a standard compact disc and a flywheel the size of a role of U.S. nickels have equivalent moments of inertia)
The entire apparatus is mounted on frictionless magnetic bearings and is evacuated nearly 99%. The remaining atmosphere directly surrounding the glass flywheel is composed of a mixture of helium and air to reduce the effects of wind on the performance of the flywheel and to allow for the charging of the flywheel to take place. The flywheel is charged (spun) using electromagnetic radiation.
APPLICATIONS
Road Transportation
In the 1950s, flywheel-powered buses, known as gyrobuses. There is ongoing research to make flywheel systems that are smaller, lighter, cheaper and have a greater capacity. It is hoped that flywheel systems can replace conventional chemical batteries for mobile applications, such as for electric vehicles. Proposed flywheel systems would eliminate many of the disadvantages of existing battery power systems, such as low capacity, long charge times, heavy weight and short usable lifetimes.