"""""""""As a real estate appraiser and broker I would consider these things to be an "external obsolescence"""""""""".
Because you are a real estate appraiser, I'm certain that to consider it "external obsolescence", then you would know how important it is to go out an "prove it" beyond just saying "becasue I'm a real estate appraiser and broker and I say so". You must know that the TVA, in my region, will prove that powerlines and substations do not matter whatsoever. So be ready to prove it beyond a shadow of a doubt, because I can guarantee you the windmill companies have their own studies proving the contrary.
""""Something similar to a large trash dump land fill project, or a HUGE power transmission line (except on poles TWICE as tall as a water tower) moving into an area. """""
I don't see how an eco friendly windmill would be like a trash dump or a huge power transmission line, but I'm no expert on any of the above.
""""What effect does something like that normally have on property values? """"
The Tennesse Valley Authority will tell you none, and give you their supporting documentation. You'll need to do the same, to achieve any chance of success of resitance.
