Dr Rashidi has designed a system to mount four wind turbines onto a silo-like structure that could be placed on city roofs. The original helical design (pictured at left) attempts to solve the perennial problem facing wind turbines placed on buildings in urban environments: Wind speeds that are too variable and turbulent to make these turbines truly effective.

His design, been refined into a silo shape, accelerates the wind hitting the turbine enabling them to generate power more consistently than other building-mounted designs.

That said, these really aren't designed to be competitive with the large commercial models that most people think of when 'wind turbine' is mention. Dr Rashidi's design can be expected to produce 8 kilowatts per hour according to a recent article in Reuters, a fraction of a fraction of that of large turbines.

Currently the Cleveland Indian's are planning on installing one of the Rashidi wind turbines at their stadium.

You can see the arm upon which the small wind turbines are attached on the side of this tower.

From: http://www.treehugger.com/files/2009/06/new-york-city-building-water-towers-could-be-turned-into-wind-turbines.php