You can play with your available space and the power available from the different turbines. The bigger and larger the turbines, the more cost effective, in general. One has to take installation costs into account.
Here is a table about the way to locate the different sizes, in general:
|Large (6 meters high)||Land or very strong roof|
|Medium (4.5 meters high)||Land or strong roof|
|Small (2.7 meters high)||Land or regular roof|
|Mini (1 meter high)||Personal size for a garden, a camping trip, a boat|
What size generator do you pick for the large and medium models? In general, you will get the best returns as follows:
|Wind Speed in meters per second||Generator capacity in kilowatts|