Makani Power hopes that its flying windmill will reduce the cost of wind power from from five-to-10 cents per kilowatt-hour down to three cents per kilowatt-hour, below even the cost of coal:
The 120-pound craft has rotors on its wings to lift it into the sky helicopter-style; a thin tether attaches it to a platform. Once in the air, the craft begins to glide like a kite, its 26-foot wingspan tracing circles 250 feet overhead. Now the propellers become generators, spinning freely and generating electricity that flows down the taut tether — and, someday, into the local grid.
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“The magic is in flying crosswind,” says CEO Corwin Hardham, referring to how the vehicle moves perpendicular to the wind like a kite. “We use aerodynamics to move the rotors many times faster than the actual wind speed.”
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Makani’s technology is designed to take advantage of the relatively consistent winds that blow well above the ground. Conventional wind turbines top out at roughly 300 feet, with blade tips reaching 500 feet, beyond which it becomes prohibitively expensive to build stable structures. Researching the potential for wind power, Hardham came across a 1980 paper by Miles Loyd proposing a tethered wing that could elevate the business end of a windmill to any height.