Two questions

Daisy, speaking as a homeowner who has done this kind of installation, this seems to be a somewhat loose and variable criteria, depending of what area you live in.  The installation must be in compliance with local building and electrical codes, which can be found by doing a search of your state and local laws. A licensed contractor is generally familiar with these codes, but a do-it-yourselfer, needs to research this and perhaps get a permit, or an inspector to certify the installation. As an example, in this area, a wind turbine must have a set-back distance from structures and roadways, and a height restriction, depending on the power rating of the turbine, and have a noise characteristic which is not offensive to neighbors, and no lighting or lighting in compliance with FAA rules. There are many variables in local and state codes, so what is good for one, may not be good for all.