Towers

We've gone over two very important things that we often think about here at Otherpower. The power in the wind is related to the *square* of the blade diameter (double diameter and you get 4 times the power) and the *cube* of the wind speed (double the wind speed and you get 8 times the power). You have a great deal of control over blade diameter -- you can choose what size machine you buy. What about the wind speed? It's often suggested that the most economical choice is to put up lots of machines on short towers, or mount your wind turbine(s) to the roof. Manufacturers say this stuff because it sells machines -- people do not like the idea that a tower costs money, and they love to hear that once they buy the wind turbine very little further cost/effort is required. However, the wind is your fuel and wind turbines need good clean non-turbulent fuel -- and unfortunately you don't find that on the ground or on your roof!
It is usually suggested by most reputable installers and manufacturers that the most cost-effective arrangement will be to get your wind turbine 30 feet above anything withing 300 feet. If you have turbulant 10 mph winds at 30 feet up and smooth 13 mph winds at 70 feet up then it makes sense to go a bit higher, get out of the turbulance and get into a slightly higher windspeed where you might have *twice* the energy available! This is not the sort of talk that sells wind turbines, but it is reality. In most good installations the cost of the tower is much greater than the cost of the machine itself and there is a good reason for that.