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. ROTOR was a huge and elaborate air defence Radar system built by the British Government in the early 1950s to counter possible attack by Soviet Bombers A flywheel is a mechanical device with significant Moment of inertia used as a storage device for Rotational energy. The rotational energy or angular kinetic energy is the Kinetic energy due to the rotation of an object and is part of its total kinetic 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. ^[1]

Advanced FES systems have rotors made of high strength carbon-composite filaments that spin at speeds from 20,000 to over 50,000 rpm ^[2] in a vacuum enclosure and use magnetic bearings. A magnetic bearing is a bearing which supports a load using Magnetic levitation. Such flywheels can come up to speed in a matter of minutes -- much quicker than some other forms of energy storage. ^[2]

Contents 1 Main components 1.1 Rotor 1.2 Bearings 2 Physical characteristics 3 Applications 3.1 Transportation 3.2 Uninterruptible power supply 3.3 Laboratories 3.4 Amusement Ride 3.5 Pulse power 3.6 Motor sports 4 Advantages and disadvantages 5 See also 6 References

Main components

A typical system consists of a rotor suspended by bearings inside a vacuum chamber to reduce friction, connected to a combination electric motor/electric generator. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner.

Rotor

First generation flywheel energy storage systems use a large steel flywheel rotating on mechanical bearings. Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 Newer systems use carbon-fiber composite rotors that have a higher tensile strength than steel and are an order of magnitude lighter. Tensile strength \sigma_{UTS} or S_U is the Stress at which a material breaks or permanently deforms

Bearings

Magnetic bearings are necessary; in conventional mechanical bearings, friction is directly proportional to speed, and at such speeds, too much energy would be lost to friction. A magnetic bearing is a bearing which supports a load using Magnetic levitation. Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e

The expense of refrigeration led to the early dismissal of low temperature superconductors for use in magnetic bearings. High-temperature superconductor (HTSC) bearings however may be economical and could possibly extend the time energy could be stored economically. High-temperature superconductors (abbreviated high Tc or HTS) are a family of superconducting Ceramic materials largely Hybrid bearing systems are most likely to see use first. HTSC bearings have historically had problems providing the lifting forces necessary for the larger designs, but can easily provide a stabilizing force. Therefore, in hybrid bearings, permanent magnets support the load and HTSC are used to stabilize it. The reason superconductors can work well stabilizing the load is because they are good diamagnets. Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied Magnetic field, thus causing a repulsive effect In hybrid-bearing systems, a conventional magnet levitates the rotor, but the high temperature superconductor keeps it stable. If the rotor tries to drift off center, a restoring force due to flux pinning restores it. Flux pinning is the phenomenon that magnetic flux lines do not move (become trapped or "pinned" in spite of the Lorentz force acting on them inside a This is known as the magnetic stiffness of the bearing. Rotational axis vibration can occur due to low stiffness and damping, which are inherent problems of superconducting magnets, preventing the use of completely superconducting magnetic bearings for flywheel applications.

Since flux pinning is the important factor for providing the stabilizing and lifting force, the HTSC can be made much more easily for FES than for other uses. HTSC powders can be formed into arbitrary shapes so long as flux pinning is strong. An ongoing challenge that has to be overcome before superconductors can provide the full lifting force for an FES system is finding a way to suppress the decrease of levitation force and the gradual fall of rotor during operation caused by the flux creep of SC material. Flux pinning is the phenomenon that magnetic flux lines do not move (become trapped or "pinned" in spite of the Lorentz force acting on them inside a

Parasitic losses such as friction, hysteresis, and eddy currents of both magnetic and conventional bearings in addition to refrigerant costs can limit the economical energy storage time for flywheels. In short Parasitic Loss is a loss that a parasite consumes from its host which may or may not be beneficial to the host Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e A system with hysteresis can be summarised as a system that may be in any number of states independent of the inputs to the system An eddy current (also known as Foucault current) is an electrical phenomenon discovered by French physicist Léon Foucault in However, further improvements in superconductors may help eliminate eddy current losses in existing magnetic bearing designs as well as raise overall operating temperatures. Even without such improvements, however, modern flywheels can have a zero-load rundown time measurable in years. (The 'zero-load rundown time' measures how long it takes for the device to come to a standstill when it is not connected to any other devices. If an electric circuit has a well-defined output terminal the circuit connected to this terminal (or its Input impedance) is the load. )

Physical characteristics

For the basic physics of a flywheel, see Flywheel Physics. A flywheel is a mechanical device with significant Moment of inertia used as a storage device for Rotational energy.

Compared with other ways of storing electricity, FES systems have long lifetimes (lasting decades with little or no maintenance^[2]; full-cycle lifetimes quoted for flywheels range from in excess of 10⁵, up to 10⁷)^[3], high energy densities (~ 130 W·h/kg, or ~ 500 kJ/kg), and large maximum power outputs. Energy density is the amount of Energy stored in a given system or region of space per unit Volume, or per unit Mass, depending on the context although 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. ^[2] Rapid charging of a system occurs in less than 15 minutes. ^[4]

Applications

Transportation

In the 1950s flywheel-powered buses, known as gyrobuses, were used in Yverdon, Switzerland, and there is ongoing research to make flywheel systems that are smaller, lighter, cheaper, and have a greater capacity. The 1950s Decade refers to the years of 1950 to 1959 inclusive See also Electric bus A Gyrobus is an Electric bus that uses Flywheel energy storage, not Overhead wires like a Trolleybus. Yverdon-les-Bains (called Eburodunum and Ebredunum during the Roman era is a municipality in the district of Yverdon Switzerland (English pronunciation; Schweiz Swiss German: Schwyz or Schwiiz Suisse Svizzera Svizra officially the Swiss Confederation 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 ^[5]. The Chrysler Patriot was a Turbine -powered hybrid Sports-prototype Racing car built by Chrysler in 1993 as a Concept car

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. A continuously variable transmission ( CVT) is a transmission which can change steplessly through an infinite number of effective gear ratios between maximum A regenerative brake is a mechanism that reduces Vehicle speed by converting some of its Kinetic energy into another useful form of energy (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. )^[1]

Flywheel systems have also been used experimentally in small electric locomotives for shunting or switching, e. "Electric Trains" redirects here For the 1995 Squeeze single see Electric Trains (song. A switcher or shunter ( Great Britain: shunter; Australia: shunter or yard pilot; USA: switcher (or g. the Sentinel-Oerlikon Gyro Locomotive. Sentinel Waggon Works Ltd was a British company based in Shrewsbury, Shropshire that made steam powered lorries ("road locomotives" Larger electric locomotives, e. g. British Rail Class 70, have sometimes been fitted with flywheel boosters to carry them over gaps in the third rail. The British Rail class 70 was a class of three 3rd rail Co-Co Electric locomotives The initial two were built by the Southern Railway at A third rail is a method of providing Electricity to power a railway through a continuous rigid conductor alongside the railway track or between the rails Advanced flywheels, such as the 133 kWh pack of the University of Texas at Austin, can take a train from a standing start up to cruising speed. ^[2]

The Parry People Mover is a railcar which may be powered by a flywheel. Parry People Movers (PPM is a British company manufacturing lightweight railbuses that use Flywheel energy storage (FES to store energy for traction A railcar (not to be confused with a railway car) is a self-propelled railway Vehicle designed to Transport passengers It was trialed on Sundays for 12 months on the Stourbridge Town Branch Line in the West Midlands, England during 2006 and 2007, and will be introduced as a full service by the train operator London Midland in December 2008 once two units have been ordered^[6]. The Stourbridge Town Branch Line is a short (08 mile railway Branch line, in Stourbridge, West Midlands, England. The West Midlands is a Metropolitan county in western central England with a population of 2591300 England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland London Midland is a Train operating company in the United Kingdom.

Uninterruptible power supply

Flywheel power storage systems in current production (2001) have storage capacities comparable to batteries and faster discharge rates. Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. 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. An uninterruptible power supply ( UPS) also known as a continuous power supply ( CPS) or a battery backup is a device which maintains a continuous In its broadest sense power quality is a set of boundaries that allows Electrical systems to function in their intended manner without significant loss of performance or life Renewable energy is Energy generated from Natural resources mdashsuch as Sunlight, Wind, Rain, tides and geothermal

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. ^[4]

Laboratories

A long-standing niche market for flywheel power systems are facilities where circuit-breakers and similar devices are tested: even a small household circuit-breaker may be rated to interrupt a current of 10,000 or more amperes, and larger units may be have interrupting ratings of 100,000 or 1,000,000 amperes. Obviously the enormous transient loads produced by deliberately forcing such devices to demonstrate their ability to interrupt simulated short circuits would have unacceptable effects on the local grid if these tests were done directly off building power. So typically such a laboratory will have several large motor-generator sets, which can be spun-up to speed over some minutes; then the motor is disconnected before a circuit-breaker is tested. Other similar applications are in tokamak and laser experiments, where very high currents are also used for very brief intervals. A tokamak is a machine producing a toroidal Magnetic field for confining a plasma. A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission.

Amusement Ride

The Incredible Hulk roller coaster at Universal's Islands of Adventure features a rapidly accelerating uphill launch as opposed to the typical gravity drop. The Incredible Hulk Coaster is a Steel roller coaster located in Universal's Islands of Adventure in Orlando, Florida, USA. Universal's Islands of Adventure is a Theme park located in Orlando, Florida. This is achieved through powerful traction motors that throw the car up the track. See also Electric vehicle, Electric motor A traction motor is a type of Electric motor used to power the driving wheels of a vehicle such as To achieve the brief very high current required to accelerate a full coaster train to full speed uphill, the park utilizes several motor generator sets with large flywheels. Without these stored energy units, the park would have to invest in a new substation and risk browning-out the local energy grid every time the ride launches. A power outage (also known as power cut, power failure, power loss, or blackout) is the loss of the Electricity supply to an

Pulse power

Since FES can store and release energy quickly, they have found a niche providing pulsed power (see compulsator).

Motor sports

The FIA has included the use of KERS (see kinetic energy recovery system) as part of its Formula 1 2009 Sporting Regulations^[7]. A regenerative brake is a mechanism that reduces Vehicle speed by converting some of its Kinetic energy into another useful form of energy Using a continuously variable transmission (CVT), energy is recovered from the drive train during braking and stored in a flywheel. A continuously variable transmission ( CVT) is a transmission which can change steplessly through an infinite number of effective gear ratios between maximum This stored energy is then used during acceleration by altering the ratio of the CVT. ^[8]. 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^[9].

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. The Automobile Club de l'Ouest (Automobile Club of the West - referring to the western region of France sometimes abbreviated to ACO, is the largest Automotive group The 24 Hours of Le Mans ( 24 Heures du Mans) is a sports car endurance race held annually since near the town of Le Mans, Sarthe, The Le Mans Series (LMS is a European Sports car racing endurance series based around the 24 Hours of Le Mans race and run by the Automobile Club de l'Ouest A Le Mans Prototype (commonly abbreviated as LMP) is a type of custom-built Race car intended for Sports car racing and Endurance racing, most "^[10]

Advantages and disadvantages

Flywheels are not affected by temperature changes as are chemical rechargeable batteries, nor do they suffer from memory effect. See also Rechargeable electricity storage system A rechargeable battery, also known as a storage battery, is a group of two or more secondary Memory effect, also known as lazy battery effect or battery memory, is an effect observed in nickel cadmium Rechargeable batteries that causes them to They are also less potentially damaging to the environment, being made of largely inert or benign materials. In English to be inert is to be in a state of doing little or nothing 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 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. A gyroscope is a device for measuring or maintaining orientation, based on the principles of Angular momentum. In Physics, the angular momentum of a particle about an origin is a vector quantity equal to the mass of the particle multiplied by the Cross product of the position 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). A gimbal is a pivoted support that allows the rotation of an object about a single axis A gyroscope is a device for measuring or maintaining orientation, based on the principles of Angular momentum.

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. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about 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.

See also

• List of energy topics
• Compulsator
• Grid energy storage
• Lofstrom loop
• Plug-in hybrid
• Rechargable battery
• Regenerative braking
• Supercapacitor

References

• Sheahen, T. This is a list of energy topics which identifies articles and categories that relate to energy in general Grid energy storage is used to manage the flow of electrical energy A launch loop or Lofstrom loop is a design for a belt based Maglev Orbital launch system that would be around 2000 km long and maintained at A plug-in hybrid electric vehicle ( PHEV) is a Hybrid vehicle with batteries that can be recharged by connecting a plug to an Electric power See also Rechargeable electricity storage system A rechargeable battery, also known as a storage battery, is a group of two or more secondary A regenerative brake is a mechanism that reduces Vehicle speed by converting some of its Kinetic energy into another useful form of energy Electric double-layer capacitors, also known as supercapacitors, electrochemical double layer capacitors ( EDLCs) or ultracapacitors , P. (1994). Introduction to High-Temperature Superconductivity. Plenum Press, New York. pp. 76-78, 425-431.
• El-Wakil, M. , M. (1984). Powerplant Technology. McGraw-Hill, pp. 685-689.
• Koshizuka, N. , Ishikawa, F. ,Nasu, H. , Murakami, M. , Matsunaga, K. , Saito, S. , Saito, O. , Nakamura, Y. , Yamamoto, H. , Takahata, R. , Itoh, Y. , Ikezawa, H. , Tomita, M. (2003). Progress of superconducting bearing technologies for flywheel energy storage systems. Physica C 386, pp. 444–450.
• Wolsky, A. , M. (2002). The status and prospects for flywheels and SMES that incorporate HTS. Physica C372–376, pp. 1495–1499.
• Sung, T. , H. , Han, S. , C. , Han, Y. , H. , Lee, J. , S. , Jeong, N. , H. , Hwang, S. , D. , Choi, S. , K. (2002). Designs and analyses of flywheel energy storage systems using high-Tc superconductor bearings. Cryogenics V. 42, pp. 357–362.
• http://www.parcon.uci.edu/OLD_WEBSITE/paper/eeenergy.htm
• http://infoserve.sandia.gov/cgi-bin/techlib/access-control.pl/1997/970443.pdf
• http://www.wtec.org/loyola/scpa/04_02.htm
• NASA Power and Propulsion Office: Highlights and Accomplishments
• Development at LLNL using passive maglev to levitate the rotor
• More on flywheels

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