Some 300 meters up in the air, enough wind blows to provide 400 terrawatts of power, according to a recent analysis—or more than 20 times more power than the world as a whole presently uses. But getting up that high is challenging; a traditional wind turbine would be too tall. So Makani Power and others are designing alternatives.

Here the California-based company's prototype Wing 7 shows how it could fly guided solely by computer and use its specially-designed rotors both for thrust and to extract power from the wind.