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NASA G2 flywheel. Flywheel energy storage (FES) 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 ...
The efficiency of a flywheel is determined by the maximum amount of energy it can store per unit weight. As the flywheel's rotational speed or angular velocity is increased, the stored energy increases; however, the stresses also increase. If the hoop stress surpass the tensile strength of the material, the flywheel will break apart.
Regenerative braking has a similar energy equation to the equation for the mechanical flywheel. Regenerative braking is a two-step process involving the motor/generator and the battery. The initial kinetic energy is transformed into electrical energy by the generator and is then converted into chemical energy by the battery.
A flywheel-storage power system uses a flywheel for energy storage, (see Flywheel energy storage) and can be a comparatively small storage facility with a peak power of up to 20 MW. It typically is used to stabilize to some degree power grids, to help them stay on the grid frequency, and to serve as a short-term compensation storage.
A metric of energy efficiency of storage is energy storage on energy invested (ESOI), which is the amount of energy that can be stored by a technology, divided by the amount of energy required to build that technology. The higher the ESOI, the better the storage technology is energetically.
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A KERS using a carbon fibre flywheel, originally developed for the Williams Formula One racing team, has been modified for retrofitting to existing London double-decker buses. 500 buses from the Go-Ahead Group will be fitted with this technology from 2014 to 2016, anticipated to improve fuel efficiency by approximately 20%. [34]
Most forms of uninterruptible power supply (UPS) can be either powered by battery or flywheel energy. These are ready for immediate use at the instant that the mains electricity fails, but the relatively small and finite amount of stored energy they contain makes them suitable for short periods of use, typically in the order of a few dozen minutes to a couple of hours depending on the actual load.