Anairborne wind turbine is a design concept for awind turbine with a rotor supported in the air without a tower,[1] thus benefiting from the higher velocity and persistence of wind at high altitudes, while avoiding the expense of tower construction,[2] or the need forslip rings oryaw mechanism. An electrical generator may be on the ground or airborne. Challenges include safely suspending and maintaining turbines hundreds of meters off the ground in high winds and storms, transferring the harvested and/or generated power back to earth, and interference with aviation.[3]
Airborne wind turbines may operate in low or high altitudes; they are part of a wider class of Airborne Wind Energy Systems (AWES) addressed byhigh-altitude wind power andcrosswind kite power. When the generator is on the ground,[4] 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.Kites and helicopters come down when there is insufficient wind;kytoons andblimps may resolve the matter with other disadvantages. Also, bad weather such aslightning orthunderstorms, 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, aprohibited airspace zone. As of 2022, few commercial airborne wind turbines are in regular operation.[5]
Anaerodynamic airborne wind power system relies on the wind for support.
In one class, the generator is aloft; an aerodynamic structure resembling akite, tethered to the ground, extracts wind energy by supporting a wind turbine. In another class of devices, such ascrosswind kite power, generators are on the ground; one or more airfoils or kites exert force on a tether, which is converted to electrical energy. An airborne turbine requires conductors in the tether or some other apparatus to transmit power to the ground. Systems that rely on a winch can instead place the weight of the generator at ground level, and the tethers need not conduct electricity.
Aerodynamic wind energy systems have been a subject of research interest since at least 1980.[6] Multiple proposals have been put forth but no commercial products are available.[7][8]Other projects for airborne wind energy systems include:
An aerostat-type wind power system relies at least in part onbuoyancy to support the wind-collecting elements. Aerostats vary in their designs and resultinglift-to-drag ratio; 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 thekytoon byDomina Jalbert.
Balloons can be incorporated 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.
AnOntario based company called Magenn[17] was developing a turbine called the Magenn Air Rotor System (MARS).[18] A future 1,000-foot (300 m)-wide MARS system would use a horizontal rotor in ahelium 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.[19] The first prototypes were built by TCOM[who?] in April 2008. No production units have been delivered.[20]
Boston-basedAltaeros Energies uses a helium-filled balloon shroud to lift a wind turbine into the air, transferring the resultant power down to a base station through the same cables used to control the shroud. A 35-foot prototype using a standardSkystream 2.5kW 3.7m wind turbine was flown and tested in 2012. In fall 2013, Altaeros was at work on its first commercial-scale demonstration in Alaska.[21][22]
Another concept, released in 2023, proposed a helium-filled balloon with attached sails, which create pressure and drive the rotation of the system around its horizontal axis. The kinetic energy is transferred to a generator on the ground through ropes in circular motion.[23]
How do you safely suspend airborne turbines hundreds or thousands of feet off the ground? How do you keep them aloft for long periods of time in high winds without having to perform frequent, costly maintenance? And what about interference with aviation?
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