Flywheel energy storage Totally Explained

Everything about Flywheel Energy Storage totally explained

Flywheel Energy Storage (FES) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. The energy is converted back by slowing down 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-composite filaments that spin at speeds from 20,000 to over 50,000 rpm in a vacuum enclosure and use magnetic bearings. Such flywheels can come up to speed in a matter of minutes -- much quicker than some other forms of energy storage., high energy densities (~ 130 W·h/kg, or ~ 500 kJ/kg), and large maximum power outputs. The energy efficiency (ratio of energy out per energy in) of flywheels can be as high as 90%. Typical capacities range from 3 kWh to 133 kWh.

Applications

Transportation

In the 1950s flywheel-powered buses, known as gyrobuses, were used in Yverdon, Switzerland, and there's 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. Flywheels may have been used in the experimental Chrysler Patriot, though that has been disputed .
Recently, there has been a new incentive to develop continuously variable transmissions (CVTs) for use in the new kinetic energy recovery systems (KERS) proposed for Formula One motor racing. (In 2009, F1 is introducing new rules that will lower the environmental impact of the sport. Part of this is to recover deceleration energy that can be stored for acceleration.).

Uninterruptible power supply

Flywheel power storage systems in current production (2001) have storage capacities comparable to batteries and faster discharge rates. They are mainly used to provide load leveling for large battery systems, such as an uninterruptible power supply and for maintaining power quality in renewable energy systems.
Flywheel maintenance in general runs about one-half the cost of traditional battery UPS systems. The only maintenance is a basic annual preventive maintenance routine and replacing the bearings every three years, which takes about four hours.. Using a continuously variable transmission (CVT), energy is recovered from the drive train during braking and stored in a flywheel. This stored energy is then used during acceleration by altering the ratio of the CVT. . In motor sports applications this energy is used to improve acceleration rather than reduce Carbon Dioxide emissions - although the same technology can be applied to road cars to improve fuel efficiency. Automobile Club de l'Ouest, the organizer behind the annual 24 Hours of Le Mans event and the Le Mans Series, is currently "studying specific rules for LMP1 which will be equipped with a kinetic energy recovery system."

Advantages and disadvantages

Flywheels are not affected by temperature changes as are chemical rechargeable batteries, nor do they suffer from memory effect. They are also less potentially damaging to the environment, being made of largely inert or benign materials. Another advantage of flywheels is that by a simple measurement of the rotation speed it's 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 once broken, and so instead of large chunks of high-velocity shrapnel one simply gets a containment vessel filled with red-hot sand. Still, many customers of modern flywheel power storage systems prefer to have them embedded in the ground to halt any material that might escape the containment vessel.
   When used in vehicles, flywheels also act as gyroscopes, since their angular momentum is typically of a similar order of magnitude as the forces acting on the moving vehicle. This property may be detrimental to the vehicle's handling characteristics while turning. On the other hand, this property could be utilised to improve stability in curves. Conversely, the effect can be almost completely removed by mounting the flywheel within an appropriately applied set of gimbals, where the angular momentum is conserved without affecting the vehicle (see Properties of a gyroscope).
   An alternative solution to the problem is to have two joined flywheels spinning synchronously in opposite directions. They would have a total angular momentum of zero and no gyroscopic effect. However, problems arise when the difference between the momentum of each flywheel is anything other than zero. Both wheels must be maintained at the same speed to maintain this advantage. Strictly speaking, two flyweels would exert a huge torqueing moment around the central point, trying to bend the axle. However, if the axle were sufficiently strong, no gyroscopic forces would have a net effect on the sealed container, so no torque would be measured externally.

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