The powerful thrust of ocean-spawned winds can zip a kite surfer across the sea's surface at up to 55 miles per hour. Engineers are now trying to harvest the power in that wind to generate electricity. The Wing 7 airborne wind turbine pictured here is a prototype of a leading contender for the job. The autonomous, lightweight device is tethered to land or to a floating platform; when wind speeds pick up, four rotors fly it up above 820 feet in a circle perpendicular to the wind. As the air rushes across the carbon-fiber wing, the rotors generate electricity by spinning permanent magnets. “The rotors are both propellers and turbines,” notes mechanical engineer Corwin Hardham, CEO and co-founder of Makani Power, which created the Wing 7. An onboard computer makes constant adjustments.