Nov 10 2009

Kite Power: From Toys to Terawatts

Posted by: Jonathan Marshall

In the short list of the world's best jobs, designing kites to produce renewable energy has to be right up there--the perfect combination of excitement, imagination and do-goodism.

So it was an enviable group of inventors, entrepreneurs and university researchers who gathered last week at Chico State University and Oroville from at least six countries for the world's first conference on high-altitude wind energy.

Their common focus was on finding ways to tap the vast energy potential of winds high in the atmosphere, including the mighty jet stream. And their common question, in the words of one speaker, was "how do we put together the industry?"

Kite power, as some call it, is one of those far-out but potentially game-changing sources of renewable energy. But in the judgment of Scientific American, "By the standards of revolutionary technologies, . . . high-altitude wind looks relatively straightforward and benign."

In a major study published in 2005, Cristina Archer (organizer of the Chico State conference) and her Stanford University thesis adviser, engineering professor Mark Jacobson, calculated that the amount of wind energy available just 80 meters above the earth's surface is 35 times the world's total power consumption.

"It's free energy, continuously guaranteed aslong as the Earth is what it is," Archer says.

At about six miles up, the jet stream produces even more energy--as much as 100 times the world's current consumption. But it will take more than a little engineering wizardry to tap.

Accordingly, a lot of playful wizards have put on their serious thinking caps.

Google-financed Makani Power, with an amazing engineering and creative team based in Alameda, is pursuing large kite designs that could produce megawatts of power. "This is the dawn of the new age of kites," said former CEO Saul Griffith.

The Italian company Kite Gen aims to deploy giant kites at an altitude of about 3,000 feet to exploit the faster wind speeds available at higher altitudes. As winds carry them aloft, the kites' unspooling tethers spin an alternator, generating power. Each kite may be able to produce about 3 megawatts of power.

But where would a developer put these kites to avoid bringing down an unwary 747? In otherwise off-limits airspace.

"To help visualizing the existing unexploited potential," the company notes, "just consider that the flight-prohibited area over a nuclear power plant can easily get to contain 1 GW of wind power, equal to the power of the plant itself."

An even more ambitious concept under development at Delft University in the Netherlands is an enormous loop of kits that turns like a ferris wheel in the sky. It could rise up to 30,000 feet and generate 100 MW of power.

In addition to all the obvious engineering challenges of operating generators so high in the sky, kite power has at least one other drawback: its energy source isn't completely reliable. Apparently even high-altitude winds die out about five percent of the time, something of a nuisance if you are running a hospital, operating a semiconductor fabrication line or watching the Superbowl.

"While there is enough power in these high altitude winds to power all of modern civilization, at any specific location there are still times when the winds do not blow," said Ken Caldeira at the Carnegie Institution's Department of Global Ecology at Stanford. "This means that you either need back-up power, massive amounts of energy storage, or a continental or even global scale electricity grid to assure power availability. So, while high-altitude wind may ultimately prove to be a major energy source, it requires substantial infrastructure."

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