Wind harvester: The Makani Airborne Wind Turbine sits on a runway outside of Oakland, California. The craft generates electrical power during flight.
In a concrete control tower of a decommissioned naval air base just outside Oakland, California, a team of engineers is building what might best be called a hybrid of an unmanned aerial vehicle and a wind turbine.
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.
This craft, developed by Makani Power, is a long-shot bid to tackle one of the world’s toughest problems: getting clean, cheap energy. Currently, wind power costs from five to 10 cents per kilowatt-hour—but the price of electricity from burning coal can fall below four cents per kilowatt-hour. Makini Power, however, aims to bring down the price of wind energy to three cents per kilowatt-hour.
With wind energy, most of the cost of generating power is tied up in building and maintaining huge blades and turbines. Makani believes its vehicle will cost less to build than conventional turbines and will harvest wind energy more effectively, because its flying pattern lets it generate energy under more wind conditions. “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.”
The company has carried out a series of test flights, including a flight this fall during which the carbon-fiber prototype with a 26-foot wingspan generated five kilowatts of power. Within two years the company hopes to have an 88-foot wing that generates 600 kilowatts—around a third what a large conventional wind turbine can generate. A gargantuan wing to generate five megawatts is on the drawing board.
The company’s project has drawn some interest from funders. Google has put $15 million into the company, and in September 2010, Makani won a $3 million grant from the Department of Energy’s ARPA-E program, which funds high-risk ideas that could lead to what the agency calls “transformational and disruptive energy technologies.”
Hardham is an avid kite surfer, and in mid-2006 he was working for engineering firm Squid Labs when he hit upon the idea of using similar aerodynamics to generate energy. (In kite surfing, the rider stands on a board and is pulled by a large nylon parachute.) Today, the 20-person company occupies Spartan, military-issue facilities with a machine shop in the rear and an assembly area up front. Composites are baked in a shipping container outdoors; the old control tower’s aerie serves as a lunchroom and occasional bar. Hardham describes the company’s situation as both “humble” and “perfect.” He says, “There’s an obvious advantage to being more nimble than big corporations.”
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.