You've already received some good responses (particularly from /u/pjc50), but one particular point may not be real clear. Generally speaking, the power a wind

You've already received some good responses (particularly from /u/pjc50), but one particular point may not be real clear. Generally speaking, the power a wind turbine can generated is proportional to the entire swept area. So, other things being equal, it is better to go for longer blades to increase the area, rather than trying to "capture all the wind" in a smaller cross-sectional area. So the most efficient use of your wind turbine's mass (which is proportional to cost) is to make it as big as feasible.