Gww, if you want it debunked, I'll take a stab at it. What diameter do they use to measure the efficiency? They should use the large one. Now, nature has something to say about the process. The air that reaches the blades has to speed up so the same mass per unit time flows out of the back of the mill as flows into the scoop. Simple physics. But it takes a force (pressure) to make the air speed up. From natures viewpoint the thing looks like an obstacle, which it is. Consequently, the pressure rises in front of the scoop. That, in turn, deflects some of the air around the structure, reducing its effectiveness. At the end of the day the thing probably operates pretty much like a mill having the larger diameter, as all windmills have air deflected around them. That is, they are all obstacles and nature's goal is to keep the mass of air moving overall at a constant rate. You can get the flavor of this by considering air flowing around a tree. In that case all the air in front of the tree must be deflected. This requires a build up of a dome of pressure in front of the tree to provide the deflecting force. In the process the air flowing past the tree is sped up! In turn, the pressure there becomes less. This, in turn, results in a drop of pressure behind the tree, which results in the tree bending backwards. Same thing happens to you.
