A couple startup companies are trying to create a new market for wind energy from "kites", which are really tethered UAVs flying circular patterns. Energy is generated by the props, which drive motors to act as turbines. The two are Makani Power, which is funded by Google, and Joby Energy, which also runs Joby Robotics, which we've been discussing in another thread for the closed-source Paparazzi IMU they just released.
The multiple-shot picture below shows Makani's UAV flying a typical pattern. A animation that shows it in action is here.
The Makani IMU-driven autopilot is described in detail here. Here a video showing it from the Ground Station perspective:
The Joby technology (shown at top) is similar, and appears to be a spin-off of Paparazzi's Booz IMU project. If you're familiar with the Booz quad-to-forward-flight aircraft, you'll recognize the videos on this page.
This month Popular Mechanics has a good article on both of them. It's not online yet, but here are the pages (click for full size):