Nec 2014 690.47(d) exception number 2 additional array grounding electrodes shall not be required if located within 6 feet of the premises wiring electrode. What is premises wiring electrode? EGC thats bonded to premises electrode?
The electrode is the pipe, rod, UFER, or other thing that is in the earth. With a UFER you might be able to claim that the whole concrete foundation counts.
I have one AHJ that reads this to say that if your solar arrays within 6 feet horizontally of the existing electrode(s), then you can invoke the exception. Most other AHJs I deal with are thankfully not enforcing 690.47 (D) at all. One of them is making us run an ireversibly spliced GEC to the existing electrode, but they don't care where it is so the exception isn't coming into play.