A company called Green Energy Technologies, has developed a efficient wind tunnel product. According to Jetson Green, "The WindCube is the urban-friendly rooftop application and the WindMAX is the tower application for high power users. The turbine is designed on Bernoulli's Principle. The cube captures wind and pulls it into the center of the cube where the turbine is, and in the process, the velocity of the wind increases and propels the blades to generate electricity. The increase in velocity is helpful because it allows building owners to generate wind power where wind may not be as powerful. The technology is ideal for urban buildings, big-box retailers, malls, etc., because it powers the building and allows you to net meter."Apparently, the payback period is in 3-7 years. The wind tunnels are made out of recycled steel and have fiberglass blades. Real-world installations include a WindCube on a building in Ohio, and two WindMAX towers in Texas.
Via: Jetson Green