Photograph courtesy Makani Power
The landscape appears to pitch beneath the Makani Airborne Wind Turbine during a test flight near the start-up company's headquarters in Alameda, California.
Moving a wind turbine from a 328-foot (100-meter) tower to 1,640 feet (500 meters) above the ground would tend to double the available wind speeds, and increase the available power eightfold, says Cristina L. Archer, a University of Delaware engineering professor and one of Caldeira's former post-docs.
"Above 2,000 meters [6,562 feet] you get rapid gradients of winds, with the jet streams [at 30,000 feet (9,144) meters] being [the] Mecca of winds," Archer said.
Even though airborne wind pioneers are currently aiming at altitudes far below the jet stream, they face significant technological challenges as they try to bring wind power down to the ground. Long runs of wire can be expensive and prone to tangling. The devices could pose a risk to air traffic or the environment. They would also have to be protected from bad weather.
Joe Faust, editor of the website Upper Windpower, said in an email that research is under way on alternative transmission methods, including beaming power via lasers or microwaves, although such solutions are far off. More immediately viable, perhaps, has been the work on nonconductive tethers that transmit power by applying their motion to generators or fluid pumps, or by operating saws or moving carts.
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