Flying Wind Turbines Reach for High-Altitude Power

Turbines Ready for Takeoff

Like the wing of a propeller plane without a cockpit, a Makani Airborne Wind Turbine stirs the air in a California field where it is being tested to capture high-altitude wind power.

Anyone who has climbed a mountain, a tower, or even a tall tree knows that winds get stronger at greater heights. There's less drag resistance from objects on the ground. That's why wind energy prospectors typically weld their expensive turbines to high towers, because the most important factor in power production is how fast the wind blows past the blades.

But what if turbines could reel in the power whirling above the reach of those tall towers?

Airborne wind energy pioneers, from North America to Italy and Australia, aim to find out. The technology is still in its infancy, although Makani's system—pictured above—has received notable backing from Google's philanthropic arm and the U.S. government. The concept also gained support in a new study published September 9 in the journal Nature Climate Change, which focused on the steady, fast high-altitude currents, and concluded that there's enough power in Earth's winds to be a primary source of near-zero-emission electric power as the global economy continues to grow through the 21st century.

Resembling a drone aircraft on a string, the Makani Airborne Wind Turbine takes flight at its test site, the decommissioned U.S. Navy air station at  Alameda on San Francisco Bay.

By eliminating 90 percent of the material associated with a conventional wind turbine-largely by getting rid of the tower—the designers say they hope to reduce cost while accessing stronger winds.

The winged device is tethered to the ground and flies in large vertical circles at altitudes between 800 and 1,950 feet (250 and 600 meters). Its four wind turbines rotate as the craft moves. According to Makani Power, the speed of the craft increases along with wind speed.

Makani Power's website says the company is developing a 600-kilowatt (kW) prototype. That's considered the size of a medium commercial wind turbine; for comparison, a 600 kW land-based turbine installed in 2009 at University of Maine at Presque Isle generated 680,000 kilowatt-hours of electricity in its first year, enough to power about 60 average U.S. homes. But an airborne wind turbine might deliver more or less power, depending on the boost of stronger, more consistent winds or the cost of trickier operation.

Makani was founded in 2006 and received $10 million in initial start-up capital from Google's foundation, plus support from the U.S. Department of Energy.

One of Makani's three co-founders, Corwin Hardham, has told reporters he was inspired by his hobby of kite-surfing. It's not a coincidence that Alameda has a beach that is popular with Bay Area kite-surfers. It also isn't far from Google headquarters; the company's founders, Sergey Brin and Larry Page, are known to be avid kite-surfers.

Courtesy: NGC