Like I said, I'm an EE, so an ME or aero engineer should jump in with an explanation. Seems to me that VAWTs run on the small differences in forward vs. backward air resistance of the blades to give torque to the rotor. They have no way of aiming the air flow; but this is an advantage when you don't want the complexity of steering, or the wind is variable in angle. HAWTs rely in the inclined plane principle and most of the incident air is used in pushing on the blade. I've seen VAWT designs that use ducting or blades that feather into the wind on the return side; they increase the forward/backward resistance to give greater output, but are much more complicated or bulky. But you can put the generator on a fixed point at the bottom, a big advantage. You can't generalize and say one is better than the other. I'd expect that big turbine buyers do their calculations carefully, and for their given constraints the HAWT is the obvious answer.
vandamme, thanks for the honest answer. You said VAWTs had been studied a lot so that tells us they're not a new idea. But it also makes some of us wonder why they haven't been deployed more. You said they are less efficient than horizontal ones, so I was wondering why/how, hence my question about some comparative data between VAWTs and horizontal designs. Just because 99% of what's being used is Version A, that doesn't mean it's the best technology, only that it's the current dominating technology. It does sound like VAWTs would be worthwhile in some locations and situations and it would be interesting to know which ones.
Wind farms must be big enough so that changes in wind coming from one turbine to another can be balanced out. Beyond that, many (most?) of these farms are tied into utilities which do load balancing, just like on any other complex distributed system.
@ Nancy Golden, You are right in saying that people often jump on bandwagon without asking the right counter questions. Your horse and slaughterhouses example is not off the topic at all and points in the right direction. Euphoria of going green is all right, but it should not stop the experts from pondering over the relevant points. If someone asks critical questions, he is not necessarily against the idea. He is actually trying to raise the question so that it can be addressed before it's too late.
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