Airborne wind turbine

An airborne wind turbine is a design concept for a wind turbine that is supported in the air without a tower. A tether would be used to transmit energy to the ground. These 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. The main disadvantage is that kites and 'helicopters' come down when there is insufficient wind. Also, bad weather conditions, such as lightning and/or thunderstorms, could temporarily suspend use of the machines, probably requiring them to be brought back down to the ground and covered. These schemes require a long power cable and, if the turbine is high enough, an aircraft exclusion zone. As of 2008, no commercial airborne wind turbines are in regular operation.

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 15000 ft 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, 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 Italian project called "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.)

Aerostat variety


Balloons can be added to the mix to keep the contraption 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 ft-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 in 2008. The first prototypes have been built by TCOM in April 2008.

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 - both numbers being significantly lower than the current price of non-subsidized electricity.