When working with tax advantaged renewable energy projects, figuring out what exactly can go into the tax credit basis can be quite a challenge! Looking into some specific issues, I came across this great resource that Deloitte put together.
A good general rule when determining whether something can be included in tax credit basis is to ask oneself:
"Is this a physical part of the energy generation system?"
With this in mind, it becomes clear that a fence around your solar array is not basis eligible, but that racking systems are. Improved roads to the property are not, but ladders or walkways REQUIRED for maintenance would be. Permits themselves are not, but the site plan and engineering drawings required may be, if these are required for the construction team to install the system and the system could not be built without them otherwise.