This Combination Wind And Solar System Perches On the Edge Of A Building's Roof
By Ben Schiller
Wind turbines often don't work well on top of buildings. With all the other structures in the way in urban areas, the wind speeds aren't fast enough, and the blades fail to turn. You sometimes get the feeling the developer put the thing there not to generate power, but to make some kind of environmental statement.

photo credit: <a href="https://www.flickr.com/photos/fusionpanda/2539637337/">fusionpanda</a> via <a href="http://photopin.com">photopin</a> <a href="http://creativecommons.org/licenses/by-nc/2.0/">cc</a>