I moved to the city a couple of years ago, and have noticed how clean the roofs always are. No leafs get up there. Further, from every roof there runs a pipe all the way along the edges of the roof, and to the ground in order to make the rain that ends on the roof go to the ground without pouring down on the windows. My idea is simply to put a little mill inside the pipes that go from the roof to the ground, the mill should run a simple generator in order to produce power. - Since the...