Product Pick of the Week - Makani Power's Airborne Wind Turbines (AWT)

The world’s strongest winds race high in the sky, but that doesn’t mean they’re out of reach as a potentially potent energy source. Flying, swooping, and floating turbines are being developed to turn high-altitude winds into electricity. The challenges are huge, but the potential is immense. Scientists estimate the energy in the jet streams is 100 times the amount of power used worldwide annually. Cristina Archer, an atmospheric scientist at the California State University in Chico, said there is “not a doubt anymore’’ that high-altitude winds will be tapped 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. 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.

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.

As the turbines eventually aim higher, advocates say there are plenty of remote and offshore no-fly areas where they won't interfere with aircraft and have minimal interaction with people.

Still, any nearby residents must be convinced there's no danger from falling turbines while accepting a view that includes flying objects attached to long tethers that carry the energy to the ground. High-altitude turbines also won't escape the various environmental concerns that face conventional turbines, such as their effect on bird flight.

And each turbine concept awaits extensive testing on its reliability, durability and effectiveness, said Felker, director of NREL's National Wind Technology Center.

Keeping the turbines operating autonomously over long periods in changing weather may be the biggest obstacle, Felker said.

"You have powerful reasons to stay aloft as much as possible," he said. "What do you do when a thunderstorm comes by? Do you recover (the device)? Do you land? ... How do you operate in the real world?"

Different companies have proposed answering that question in different ways.

A "kite" being developed by Makani Power of Alameda, Calif., looks like a glider with four high-speed rotors that launch it into flight, then switch modes to generate electricity that's carried down the tether.

An onboard computer steers the kite in a wide circle, mimicking the path of the tip of a giant wind turbine blade. That allows the device to interact with a larger wind area, increasing the amount of energy it can capture in the same way increasing the size of a sail increases the potential speed of a sailboat, said Damon Vander Lind, Makani's chief engineer.

Makani Power is one of those companies developing Airborne Wind Turbines (AWT) to extract energy from the powerful, consistent winds at high altitudes. Makani’s AWT is a rigid wing that flies at altitudes between 300 and 600 meters.

Turbines on the leading edge of the wing face into the wind as it flies and generates energy, which is transmitted to the ground along a tether.

Makani AWTs will produce energy at an unsubsidized real cost competitive with coal-fired power plants, the current benchmark of the lowest cost source of power.

Makani Power is therefore the recipient of Popular Mechanic’s 2011 Breakthrough Innovator Award in the Energy Category, an honor that culminated with a reception at the Hearst Tower in New York City.

The Breakthrough Awards recognize the innovators and products that dramatically advanced the fields of technology, medicine, space exploration, automotive design, environmental engineering, and more.

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