This article, from the Economist, discusses a design by Sky WindPower, a San Diego based company, which takes the form of a kite with four helicopter-style rotors.
The rotors keep the kite afloat, 10km up in the atmosphere, where wind speeds are extremely high, and also drive dynamos, that generate electricity, which is transmitted to the ground.
When the winds are low, the dynamos can be reversed, to keep the rotors spinning and hence maintain the kite's height.