Low-tech Magazine: Small windmills put to the test
A year-long Dutch study of 12 popular small windmills determined that 47 of any one type of windmill would be required to power the average Dutch household (which uses 1/3 the energy of an American household), and that rotor diameter was the primary determining factor in how much energy the windmill could generate. Rotor diameters among the models tested (3 broke so the results only list 9 of the windmills tested) varied from 1 meter to 5 meters with energy generation increasing with rotor diameter. Meanwhile, a nearby windmill with an 18 meter diameter rotor cost 17% more than the total cost of all 12 windmills in the test but generated almost 20 times as much energy. The conclusion drawn from this study that it was more cost-effective to invest in a few large windmills than many small ones.