Please take a look at the Illinois Model Zoning Ordinance here:

http://windfarmersnetwork.org/eve/forums?a=tpc&s=9131011&f=92410342&m=6180064372

Is there a setback standard for towers adjacent to transmission lines? I happen to own property adjacent to these lines and was wondering if there were any special considerions from a zoning aspect. Your thoughts would be appreciated.

Good question, John. At minimum, wind turbines would need to be set back enough so that the transmission towers don't interfere with turbine's exposure to the wind. So for that issue, the setback guidelines would be similar to other tall structures. You can read more about that in the National Wind Coordinating Committee's Siting and Permitting Handbook: http://www.nationalwind.org/pubs/permit/permitting2002.pdf

Generally it's good for a wind project to be close to transmission lines because it lowers the cost of connecting the turbines to the grid. However, I don't know if there's such thing as too close other than that they shouldn't interfere with the wind.

Does anybody else know the answer?

It is my understanding that some zoning codes, may require a setback from power lines in order to protect the lines from the very low probability of the tower failing and falling into the power lines. A setback might be say 1.1-1.25 times the height of the tower.

Time flies Construction is about to begin finally (within a few weeks). The answer it turned out is the distance of the top of the tower - so the fall down distance.