Based in the San Francisco Bay Area, Makani Power has been working on a radically different wind turbine design to capture strong, high-altitude winds since 2006. This photo shows its 30-kilowatt prototype wing. When in flight, it is tethered to a cable and can generate power by flying in a circular path. See related story, Lightweight wing harvests offshore wind.
This image shows how a cable is tethered to the wing, making essentially a kite. The cable can be used to power the wing when it needs to get started or to transmit electricity to the grid. The system has been tested in different flight modes and the company hopes to have a commercial-scale, 600-kilowatt machine completed by 2016.
One of the innovations in the turbine design are rotors that can act either as a propeller to fly the device or as power generators. When it initially takes off, the device flies a bit like a helicopter. Then it positions itself to fly into the wind and generates electricity from the energy in the crosswind.
The turbine has a sophisticated control system where it can perch itself and take off when there is sufficient wind to generate electricity. If there's too much wind, too little wind, or it needs maintenance, the wing can fly itself onto the perch. The perch can be a floating platform, like a buoy, for offshore wind use.