An
airborne wind turbine is a design concept for a
wind turbineA wind turbine is a device that converts kinetic energy from the wind into mechanical energy. If the mechanical energy is used to produce electricity, the device may be called a wind generator or wind charger. If the mechanical energy is used to drive machinery, such as for grinding grain or...
that is supported in the air without a tower. Airborne wind turbines may operate in low or high altitudes; they are part of a wider class of airborne wind energy systems (AWE) addressed by high-altitude wind power. When the generator is on the ground, then the tethered aircraft 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 or used aloft or beamed to receivers using microwave or laser. Airborne turbine systems would have the advantage of tapping an almost constant wind, without requirements for
slip ringA slip ring is a method of making an electrical connection through a rotating assembly. Slip rings, also called rotary electrical interfaces, rotating electrical connectors, collectors, swivels, or electrical rotary joints, are commonly found in electric motors, electrical generators for AC...
s or
yaw mechanismThe yaw drive is an important component of the horizontal axis wind turbines' yaw system. To ensure the wind turbine is producing the maximal amount of electric energy at all times, the yaw drive is used to keep the rotor facing into the wind as the wind direction changes. This only applies for...
, and without the expense of tower construction. Kites and 'helicopters' come down when there is insufficient wind;
kytoonsA captive plane is an aircraft which does not fly free, but is held like a kite by a rope from the "pilot" or mooring...
and
blimpA blimp, or non-rigid airship, is a floating airship without an internal supporting framework or keel. A non-rigid airship differs from a semi-rigid airship and a rigid airship in that it does not have any rigid structure, neither a complete framework nor a partial keel, to help the airbag...
s resolve the matter. Also, bad weather such as
lightningLightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
or
thunderstormA thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
s, 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. As of 2011, no commercial airborne wind turbines are in regular operation.
Aerodynamic variety
An aerodynamic airborne wind power system relies on the wind for support.
Bryan Roberts, a professor of engineering at the University of Technology, in Sydney, Australia, has proposed a helicopter-like craft which flies to 15000 feet (4,572 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-
astronautAn astronaut or cosmonaut is a person trained by a human spaceflight program to command, pilot, or serve as a crew member of a spacecraft....
and
physicistA physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
Wubbo OckelsProf. Dr. Wubbo Johannes Ockels is a Dutch physicist and a former ESA astronaut. In 1985 he participated in a flight on a space shuttle , making him the first Dutch citizen in space. He was not the first Dutch-born astronaut, as he is preceded by the naturalized American Lodewijk van den Berg, who...
, working with the
Delft University of TechnologyDelft University of Technology , also known as TU Delft, is the largest and oldest Dutch public technical university, located in Delft, Netherlands...
in the
NetherlandsThe Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
, has designed and demonstrated an airborne wind turbine he calls a "
LaddermillA Laddermill is a hypothetical airborne wind turbine consisting of a long string or loop of power kites.The loop or string of kites would be launched in the air by the lifting force of the kites, until it is fully unrolled, and the top reaches a height determined by designers and operators; some...
". 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 Sept'09 paper from
Carbon Tracking Ltd., Ireland has shown the
capacity factorThe net capacity factor or load factor of a power plant is the ratio of the actual output of a power plant over a period of time and its potential output if it had operated at full nameplate capacity the entire time...
of a kite using ground-based generation to be 52.2%, which compares favorably with terrestrial wind-farm capacity factors of 30%.
A team from
Worcester Polytechnic InstituteWorcester Polytechnic Institute is a private university located in Worcester, Massachusetts, in the United States.Founded in 1865 in Worcester, WPI was one of the United States' first engineering and technology universities...
in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
has developed a smaller-scale with an estimated output of about 1 kW. It uses a kiteboarding kite to induce a rocking motion in a pivoting beam.
The
Kitegen KiteGen is a concept developed in Italy for a wind harnessing machine that takes power from high altitude winds. The vertical axis orientation of the rotation is intended to eliminate the static and dynamic problems that prevent the increase in size of conventional wind turbines...
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 KiteGen is a concept developed in Italy for a wind harnessing machine that takes power from high altitude winds. The vertical axis orientation of the rotation is intended to eliminate the static and dynamic problems that prevent the increase in size of conventional wind turbines...
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, and only the airfoils are supported by the wind. Such a wind power plant would be capable of producing the energy equivalent to a nuclear 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.)
Dave Santos, of KiteLab in Ilwaco, Washington, has been advancing single-surface wingmills to generate useful electricity with a ground-based generator.
The Rotokite is developed from Gianni Vergnano's idea. It uses aerodynamic profiles similar to kites that have been rotated on their own axis, emulating the performance of a propeller. The use of the rotation principle simplifies the problem of checking the flight of the kites and eliminates the difficulties due to the lengths of cables, enabling the production of wind energy at low cost. The Heli Wind Power is a project of Gianni Vergnano that uses a tethered kite.
In August 2011 the German company SkySails, producer of kites for ship propulsion, announced a kite-based wind power system for on- and offshore applications that is supposed to be "30% cheaper than current offshore solutions".
Aerostat variety
An aerostat-type wind power system relies at least in part on
buoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
to support the wind-collecting elements. Aerostats vary in their designs and resulting lift-over-drag aerodynamic characteristic; the kiting effect of higher lift-over-drag shapes for the aerostat can effectively keep an airborne turbine aloft; a variety of such kiting balloons were made famous in the
kytoonA kytoon is a kite with a significant amount of aerostatic lift from a lighter than air gas carried within.The primary advantage of a kytoon is that it remains up and at a reasonably stable position above the tether point, irrespective of the wind.The kytoon has been used in peace and war...
by Domina C. Jalbert.
BalloonsAn aerostat is a craft that remains aloft primarily through the use of buoyant lighter than air gases, which impart lift to a vehicle with nearly the same overall density as air. Aerostats include free balloons, airships, and moored balloons...
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 balloonsA solar balloon is a balloon that gains buoyancy when the air inside is heated by the sun's radiation, usually with the help of black or dark balloon material. The heated air inside the solar balloon expands and has lower density than the surrounding air. As such, a solar balloon is similar to a...
may solve the helium or hydrogen leakage problems.
An
OntarioOntario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
based company called Magenn is developing a turbine called the Magenn Air Rotor System (MARS). The 1000 feet (304.8 m)-wide MARS system uses a horizontal rotor in a
heliumHelium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
suspended apparatus which is tethered to a transformer on the ground. Magenn claims 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. The first prototypes were built by TCOM in April 2008.No production units have been delivered.
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 or perform other works (grinding, sawing, pumping).
Estimated costs
Sky Windpower estimates that its 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 - both numbers being significantly lower than the current price of non-subsidized electricity.
External links
See also
- Kite
A kite is a tethered aircraft. The necessary lift that makes the kite wing fly is generated when air flows over and under the kite's wing, producing low pressure above the wing and high pressure below it. This deflection also generates horizontal drag along the direction of the wind...
- Kite mooring
Kites are given mooring by many methods. Watercraft and aircraft traditionally have the term "mooring" applied to making the watercraft or aircraft fast to some external object...
- Kite types
Kites are tethered flying objects which fly by using aerodynamic lift, requiring wind, , for generation of airflow over the lifting surfaces.-Kite types:...
- Kite applications
The kite is used to do certain things; one kite or many kites are applied to achieve certain purposes, objectives, or tasks, that is: applications. Humans have applied the kite to bring perceived benefits during peace and war alike. New applications for the kite continue to be found...
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