Wind Turbine-Alternator devices have an unusual "Economy of Size". The cost of facing any given area of weather, is a necklace-shaped function of (log) physical size, because one T to replace 4 of 1/2 the diameter weighs 8 times as much as any one of the 4, whilst the One A to stand in for the 4 of 1/4 the thro'put, is about half the cost. The cheapest size is, of course, when the T costs about the same as the A. This happens at around 1m diameter. Just under this and the gearbox disappears !
A very good design of "TAD" of at around this size can readily return 5% p.a. of its cost, which is about 50 x that from current (80m high) "technology". There are two other causes of this huge disparity. bertdotwindonatgmaildotcom