Airborne Wind Energy Conversion Systems

Flying Windmills

Sky Windpower's uses an aerodynamic, airborne generator design, consisting of a tethered rotor craft.¹⁰   The apparatus would initially get into position under its own power by being pushed skywards by motor-powered propellors which would revert to generators once in position.¹¹   The windmill would float instead of fall, since lift generated by wind would overcome the craft's weight, while also generating power.¹²

Laddermills

The Laddermill is an aerodynamic, ground-based geneartor design concept pioneered by Delft University of Technology in the Netherlands under the leadership of Wubbo Ockels, professor of sustainable engineering and a former astronaut.¹³   The Laddermill operates by utilizing a number of kite wings connected to a cable, forming a giant loop of ascending and decending kites.  Wind causes upward lift on the wings, as with an airplane wing, and by changing the wing's angle of attack these forces can be either amplified or diminished.¹⁴ Wings on one side of the loop are angled to produce maximum lift, while those on the other side are angled to produce only enough lift to support themselves in the air.  The resulting force difference between the two ends of the cable drives the wheel to which the cable is attached.  Connecting this wheel to a generator produces electricity.¹⁵   After extensive modelling, the system was successfully tested on Aug. 29, 2007.¹⁶

Blimps

Magenn's Air Rotor System (MARS) design is an aerostatic, airborne generator consisting of a helium blimp with with Savonius-style scoops which cause the apparatus to rotate around a horizontal axis.  This generates electrical energy via motors at the attachment-points to its tether.¹⁷   This electrical energy is transferred down the 1000-foot tether for immediate use, to a set of batteries for later use, or to the power grid. Helium keeps the device in the air, while its rotation generates the "Magnus effect," providing additional lift and keeping the MARS stabilized within a controlled and restricted location.  This enables it to adhere to Federal Aviation Administration guidelines.¹⁸

Balloons

Twind Technology's uses an aerostatic, ground-based generator design involving a tethered, connected pair of balloons with sails attached. The balloons move alternately: one balloon with an open sail uses wind energy to move downwind, drawing the other balloon upwind.  The motion then reverses, with one balloon using a sail and the wind to pull the other. As the balloons move, the tether cable turns the shaft of the ground generator to produce electrical energy or perform other necessary works like pumping or grinding. 

Magenn Air Rotor System

Source: http://gas2.org/2009/08/18/magenn-wi...ine-in-the-sky. Author: Gas 2.0. Permission: Creative Commons Share Alike.

Inconsistency

- Electrical Storms

- Even jet streams fail.  Ken Caldeira of the Carnegie Institution’s Department of Global Ecology points out that though " there is enough power in these high altitude winds to power all of modern civilization, at any specific location there are still times when the winds do not blow. Even over the best areas, the wind can be expected to fail about five percent of the time. This means that you either need back-up power, massive amounts of energy storage, or a continental or even global scale electricity grid to assure power availability. So, while high-altitude wind may ultimately prove to be a major energy source, it requires substantial infrastructure.”¹⁹

Safety

falling kites/airplanes?(Blimp designs overcome most of these)

Interfering with major bird migratory patterns

This is already a problem with wind farms, although some wind farms are now being outfitted with radar technology designed to anticipate bird flying patterns and shut down wind turbines accordingly.  A new farm, operated by the Spanish firm Iberdrola Renewables, uses radar technology developed by Florida based DeTect, Inc that is able to detect approaching birds up to four miles away, assess their altitude, numbers and visibility, and analyze weather conditions to determine if they are in danger of flying into turbine blades.  If they are, the turbines will  automatically shut down and restart when the birds are a safely away.²⁰   Similar radar detection technology is also being tested for airborne wind energy designs, though it should be noted that certain blimp designs pose a much smaller threat to birds than rotating-blade designs.