Oct 30, 2012

Flywheel energy storage, application in F1 (KERS)


Application in F1

Advantages and Disadvantages
Flywheels are not as adversely affected by temperature changes, can operate at a much wider temperature range, and are not subject to many of the common failures of chemical rechargeable batteries.[30] Unlike lithium ion polymer batteries which operate for a finite period of roughly 36 months, a flywheel can potentially have an indefinite working lifespan. Flywheels built as part of James Watt steam engines have been continuously working for more than two hundred years.[31] Working examples of ancient flywheels used mainly in milling and pottery can be found in many locations in Africa, Asia, and Europe.[32][33] They are also less potentially damaging to the environment, being largely made of inert or benign materials. Another advantage of flywheels is that by a simple measurement of the rotation speed it is possible to know the exact amount of energy stored. However, use of flywheel accumulators is currently hampered by the danger of explosive shattering of the massive wheel due to overload.
One of the primary limits to flywheel design is the tensile strength of the material used for the rotor. Generally speaking, the stronger the disc, the faster it may be spun, and the more energy the system can store. When the tensile strength of a flywheel is exceeded the flywheel will shatter, releasing all of its stored energy at once; this is commonly referred to as "flywheel explosion" since wheel fragments can reach kinetic energy comparable to that of a bullet. Consequently, traditional flywheel systems require strong containment vessels as a safety precaution, which increases the total mass of the device. Fortunately, composite materials tend to disintegrate quickly to red-hot powder once broken, instead of large chunks of high-velocity shrapnel. Still, many customers of modern flywheel energy-storage systems prefer to have them embedded in the ground to halt any material that might escape the containment vessel.
An additional limitation for some flywheel types is energy storage time. Flywheel energy storage systems using mechanical bearings can lose 20% to 50% of their energy in 2 hours.[34] Much of the friction responsible for this energy loss results from the flywheel changing orientation due to the rotation of the earth (a concept similar to a Foucault pendulum). This change in orientation is resisted by the gyroscopic forces exerted by the flywheel's angular momentum, thus exerting a force against the mechanical bearings. This force increases friction. This can be avoided by aligning the flywheel's axis of rotation parallel to that of the earth's axis of rotation.

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