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See Inside January 2012

Patent Watch

Airborne power station



Courtesy of U.S. Patent and Trademark Office

Airborne power station: As a longtime resident of Seattle, Boeing engineer Brian J. Tillotson had often gazed up at the clouds and wondered how anyone living in such a sun-deprived place could ever hope to take advan­tage of solar power, the main offering of Boeing subsidiary Spectrolab. More than three years ago he came up with the answer: Why not build a power station above the clouds?

The idea, described in Patent No. 8,006,933 B2, has applications even in the brightest of locales. Between 20 to 30 percent of the sun’s power is lost in the earth’s lower atmosphere before you begin to account for unwanted haze or clouds. That is a technical challenge for Spectrolab, which makes efficient solar cells by using reflectors to amplify high concentrations of sunlight 400- to 800-fold. Spectrolab’s cells are used most often to power satellites orbiting far above the atmos­phere, which renders the problem moot. In 2008, however, Tillotson began looking for a way to adapt them for use by U.S. troops stationed in remote parts of Afghanistan, where security concerns requiring expensive convoys had driven the cost of delivering fuel to power diesel gen­erators to as high as $700 a gallon.

A floating power station, he realized, could solve that problem—and bring solar power to downtown Seattle, too. “You would only have to go up a few thousand feet to get quite a bit of benefit,” he notes. Tillotson envisions solar cells attached to an airship or dirigible, which would drop thousands of feet of lightweight trans­mis­sion cable down to a mooring. The U.S. Army is already experimenting with battlefield-surveil­lance dirigibles that get their power from the ground via cables. Boeing’s device would be similar, except power would move down.

Boeing has not yet built a prototype, Tillotson says, because engineers are “hoping to see some technological improvements that would make the floating power station a little more afford­able.” At the moment, dirigibles demand inten­sive upkeep. Helium must be replenished as often as once a week and repairs made regularly to their outer shell, which is battered by wind and weather. “It turns out, operationally, airships aren’t as simple as I like to imagine—at least the ones being used by the army,” he says. Over time, Tillotson observes, better sealant and material for the shell or hull will improve the economics by avoiding leaks when the dirigible gets knocked around.

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