Equipment Grounding

In a solar electrical system, everything needs to be grounded.  That means that there needs to be electrical continuity with every part of the system, including all of the rails on the roof, and every panel frame.

Code Rules About Grounding
The NEC requires any unsheathed ground wire to be #6 AWG or the size of the largest conductor.  It also insists that ground wire outside of conduit must be unsheathed, therefore all ground wire on the roof is #6 AWG.  Many installers will continue the #6 size ground wire all the way to the inverter.

After the ground wire has effectively connected every part of a system, it makes its way to the grounding electrode conductor terminal in the inverter.  Then, it goes out to a ground rod.

The color of ground wire is green.

Ground wire from the roof, connecting to the combiner box
on a bus bar, then continuing to the inverter 

Split Bolts and Acorn Clamps, used for grounding