Chase is on to capture high-altitude wind for power

“This can be done, it can work,’’ she said.

The question is, when? Some companies project their technology will hit the market by the middle of the decade, but Fort Felker at the National Renewable Energy Laboratory says the industry is 10 years away from making a meaningful contribution to the nation’s electricity demands.

No company, for instance, has met the basic requirement of demonstrating its turbine can safely fly unsupervised for prolonged periods of time.

High-altitude wind power is similar to ground wind in the 1970s — facing questions but soon to prove its viability, said PJ Shepard of Oroville, Calif.-based Sky WindPower, which is developing a “flying electric generator.’’

“It’s kind of like the adjustment folks had to make when the Wright brothers started flying airplanes,’’ she said.

The lure of high-altitude wind is simple: Wind speed generally increases with its height above the ground as surface friction diminishes. Each time wind speed doubles, the amount of energy it theoretically holds multiplies by eight times.

The world’s most powerful winds circulate in the jet streams, which are found 4 to 10 miles off the ground and carry winds that regularly break 100 miles per hour.

The dream is to eventually tap the jet streams, but high-altitude wind companies are focusing for now below a 2,000-foot ceiling, above which complex federal air-space restrictions kick in. Adam Rein, cofounder of the Boston company Altaeros Energies, said his company calculates winds at the 2,000 foot level are up to 2 ½ times stronger than winds that can be reached by a typical 350-foot land turbine.

High-altitude wind advocates say their smaller, lightweight turbines will be far cheaper to build and deploy than windmills with huge blades and towers that must be drilled into land or the sea floor.

Those savings would mean inexpensive energy. With wide-scale use, advocates see a range of prices, from something comparable to land wind’s current 9 or 10 cents per kilowatt hour down to an astonishingly low 2 cents per kilowatt hour.