Image copyright Sky Windpower.

Flying Wind Turbines
Tech Level: 11

Wind power has often been touted as one of the most promising energy sources we can easily access. Clean and efficient and imminently renewable, wind power could provide a large percentage of the US’s current energy needs if a proper infrastructure is built up.

However, one of the biggest disadvantages with ground-based wind power stations is that winds do not always flow at a constant rate, and at times can die out altogether. Not a good thing for an industry trying to keep up with the demands of an energy-hungry society.

However, engineers at the San Diego startup company Sky Windpower have developed an ingenious solution: Put the power generating windmills 15,000 to 45,000 feet up in the air, where jet stream winds are strong and constant no matter the weather on the surface.

Sky Windpower plans on creating an array of these large "rotorcraft" tethered to the ground like enormous kites to catch and utilize such winds. Each rotorcraft would have four 130-foot long rotors, with one pair counter-rotating against the other to provide stability.

They would be tethered to the ground by three-inch thick cables, made up of a core of super-strong Vectran fibers and housing twin insulated aluminum filaments to carry the power loads. Each ground station would contain a large winch contained in a housing about the size of semi truck.

Each rotorcraft would start on the ground, and then would be fed power to their rotors so they could take off and maneuver like a helicopter. Once at the desired altitude, the motors would shut-off and the rotors would autogyro in the wind, keeping them aloft. The motors could be activated again if powered maneuvering is needed, but the rotor craft would mostly rely on its stabilizing rudders and tether to maintain its position. Once in place, the rotors would be tilted up at an angle to create more torque for spinning the turbines, on-board controls monitoring wind speed and direction and adjusting automatically.

Each individual rotorcraft is expected to generate up to 20 megawatts of power, and Sky Windpower envisions creating "farms" containing up to 600 of them on a single plot of land two hundred square miles (roughly 10 miles by 20 miles) in area. That would provide enough juice to power two Chicago-sized cities.

The task of coordinating so many rotorcraft in such a relatively tight airspace could be tricky. Automated GPS-guided computer controls will go a long way in helping such a problem, but the system would have to be constantly monitored live nonetheless. There’s also the problem of what happens if one of the rotorcraft’s tethers actually snaps. Though the autogyroing effect will mean that there is little chance fall like a brick, rotorcraft would simply not be that maneuverable. Its entirely possible that the rotorcraft could drift several dozen to several hundred miles along the jet stream and settle onto a heavily-inhabited area. Even in the best circumstances, having a 20-ton, 300-foot-wide rotorcraft settle onto your house would not be a good thing. Still, if the rotorcraft and their tethers are properly maintained and monitored, the chance of such a mishap would seem remote.

Air traffic would of course have to be rerouted away from the rotorcraft array, and its extremely high altitude will mean far fewer birds will become fouled in the spinning blades like they do with ground-based windmills.



"Windmills in the Sky," Popular Science, September 2005, pp. 38-39


Article added 11/10/07