Airborne wind turbine
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An airborne wind turbine is a design concept for a wind turbine that is supported in the air without a tower.[1] When the generator is on the ground,[[2]] then the tethered aircraft (kite, kytoon) need not carry the generator mass or have a conductive tether. When the generator is aloft, then a conductive tether would be used to transmit energy to the ground, either mechanically or through electrical conductors. Some systems would have the advantage of tapping an almost constant wind and doing so without a set of slip rings or yaw mechanism, without the expense of tower construction. Kites and 'helicopters' come down when there is insufficient wind; kytoons and blimps resolve the matter. Also, bad weather such as lightning or thunderstorms, could temporarily suspend use of the machines, probably requiring them to be brought back down to the ground and covered. Some schemes require a long power cable and, if the turbine is high enough, an aircraft exclusion zone. When the generator is ground-based, the tether need not be conductive. As of 2008, no commercial airborne wind turbines are in regular operation. [3]
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[edit] Aerodynamic variety
Bryan Roberts, a professor of engineering at the University of Technology, in Sydney, Australia, has proposed a helicopter-like craft which flies to 15,000 feet (4,600 m) altitude and stays there, held aloft by wings that generate lift from the wind, and held in place by a cable to a ground anchor. According to its designers, while some of the energy in the wind would be 'lost' on lift, the constant and potent winds would allow it to generate constant electricity. Since the winds usually blow horizontally, the turbines would be at an angle from the horizontal, catching winds while still generating lift. Deployment could be done by feeding electricity to the turbines, which would turn them into electric motors, lifting the structure into the sky.
The Dutch ex-astronaut and physicist Wubbo Ockels, working with the Delft University of Technology, has designed, and demonstrated[1], an airborne wind turbine he calls a "Laddermill". It consists of an endless loop of kites. The kites lift one end of the endless loop, (the "ladder") up, and the released energy is used to drive an electric generator.
A team from Worcester Polytechnic Institute has developed a smaller scale kite power system with an estimated output of about 1 kW. It uses a kiteboarding kite to induce a rocking motion in a pivoting beam.
The Kitegen uses a prototype vertical-axis wind turbine. It is an innovative plan (still in the construction phase) that consists of one wind farm with a vertical spin axis, and employs kites to exploit high-altitude winds. The Kite Wind Generator (KWG) or Kitegen is claimed to eliminate all the static and dynamic problems that prevent the increase of the power (in terms of dimensions) obtainable from the traditional horizontal-axis wind turbine generators. Generating equipment would remain on the ground, only the airfoils are supported by the wind. Such a wind power plant would be capable of producing the energy equivalent to a nuclear power plant, while using an area of few square kilometres, without occupying it exclusively. (The majority of this area can still be used for agriculture, or navigation in the case of an offshore installation.)
KiteLab's Dave Santos of Ilwaco, Washington, has been advancing single-surface wingmills to generate useful electricity with the generator ground-based. [4]
The Rotokite is an innovative project wich has been developed on the basis of Gianni Vergnano's idea. It uses aerodynamic profiles, similar to the ones of kites that have been rotated on its own axel, for emulating the performance of a big propeller at high altitude. The use of the rotation principle simplifies radically the difficult problem of checking the flight of the kites and eliminates the technical difficulties due to the lengths of cables, enabling the production of eolian energy at very low costs.
The Heli Wind Power is a project of Gianni Vergnano that recovers the concept of the Flying Electric Generator introducing two features aimed to lighten the system so it can produce energy with winds with less intensity. In fact, this project regards from one side the lightening of rotors by using tie-rods and from the other side the mechanical transmission to the ground of the energy wich has been generated through special pulleys. Eliminating the electric generators from the structure at high altitude represents a double advantage: the reduction of the weight and to eliminate the necessity of the electric cables that could attract thunderbolts. As far as the power transmission in concerned the recent innovations regarding the field of fibers permit to think about a closed cable that operates between two systems of pulleys with interconnected multiple wheels.
[edit] Aerostat and kytoon variety
Balloons or kytoons can be added to the mix to keep systems up without wind, but balloons leak slowly and have to be resupplied with lifting gas, possibly patched as well. Very large, sun heated balloons may solve the helium or hydrogen leakage problems.
An Ontario based company called Magenn Power Inc. has developed a turbine called the Magenn Air Rotor System (MARS). The 100-foot (30 m)-wide MARS system uses a horizontal rotor in a helium suspended apparatus which is tethered to a transformer on the ground. Magenn states that their technology provides high torque, low starting speeds, and superior overall efficiency thanks to its ability to deploy higher in comparison to non-aerial solutions. Magenn claims to be putting the first of the MARS product line, a 10 kW model, on the market by 2010.[5] The first prototypes have been built by TCOM in April 2008.[6]
The Twind Technology concept uses a pair of captive balloons at an altitude of 800 meters. The tether cables transmit force to a rotating platform on the ground.
Each balloon has a sail connected to it. The two balloons move alternately, the balloon with the sail open moves downwind and draws the other balloon upwind, and then the motion reverses. The tether cable can be used to turn the shaft of a generator to produce electrical energy
[edit] Estimated costs
Sky Windpower estimate that their technology will be capable of producing electricity for $0.02 per KWh, while a system of raising a kite to a high altitude while turning a generator on the ground, and then changing its shape so that it can be drawn back down with less energy than it produced on the way up, has been estimated to be capable of producing electricity for $0.01 per KWh[7] - both numbers being significantly lower than the current price of non-subsidized electricity.
[edit] Patents for airborne wind energy (AWE)
- US Patent 7129596 Hovering wind turbine by Aleandro Soares Macedo; filed: Oct 31, 2004; issued: Oct 31, 2006
- US Patent 6781254 Windmill kite by Bryan William Roberts; filed: Oct 17, 2002; issued: Aug 24, 2004.
[edit] References
- ^ David Cohn. "Windmills in the Sky". Wired News: Windmills in the Sky. San Francisco: Wired News. http://www.wired.com/news/planet/0,2782,67121,00.html?tw=wn_tophead_2. Retrieved on July 28 2006.
- ^ http://www.energykitesystems.net/methods/index.html Airborne Wind Energy Generation Systems
- ^ What are some known kite electricity methods?
- ^ KiteLab
- ^ "Magenn Power Inc. corporate website". http://www.magenn.com. Retrieved on December 14 2008.
- ^ Mazzella, Diana (2008-04-03). "Airborne turbine tested at TCOM; Magenn: MARS makes wind power mobile". The Daily Advance. http://www.dailyadvance.com/news/content/news/stories/2008/04/03/0403turbineDM.html?cxtype=rss&cxsvc=7&cxcat=7. Retrieved on 2008-11-23.
- ^ Getting wind farms off the ground | Economist.com
[edit] External links
- Xercesblue: a summing up of the projects and the problems concerning the upper level generation
- Wired Magazine
- Kite Generator home page
- KiteGen project: control as key technology for a quantum leap in wind energy generators
- WPI Kite Power Team
- Sky Windpower
- Makani Power
- TWIND Technology
- Electricity-Generating Kite Systems EGKS
- Included in Time´s 2008 Best Inventions
- Magenn Power Inc. - air rotor products
[edit] See also
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