Something that's always puzzled me is how very large three or two (or even one!) bladed HAWTs manage to make full use of the wind that passes through their swept area. I've tried to illustrate above as best I can, what I'm getting at. How does wind that is passing through a huge gap in between two blades, over a hundred feet from them, manage to exert any effect on them whatsoever? If a theoretical turbine was built with one blade, a mile long, how would it be driven by the wind that was on the opposite side to the blade, if the rotational speed was 0.3 RPM? (I'm guessing at how low the RPM would be, but you get the idea.) The wind speed is relatively constant, between a maximum and a minimum speed. That will never change. The tip speed ratio is also relatively constant, and there's nothing we can do to make the turbine turn significantly faster. So we are left with the conclusion (at least, I am) that the bigger a HAWT becomes, the slower its blades turn, and since the wind speed is relatively constant, this means that more and more wind will pass through the spaces between the blades.
If anybody can explain why this isn't so to me, I'd be very grateful!
