Except as provided in subparagraph (B), an expenditure with respect to an item shall be treated as made when the original installation of the item is completed."
The question is, is installation "complete" if the property is installed, but hasn't been inspected? Suppose the inspector finds no errors, then maybe the installation was complete in December. But suppose the inspector finds an error and the installer has to come back; in that case, installation wasn't complete.
In other parts of the tax code, property must be "placed in service" which means installed, inspected, and turned on or placed in use. But that specific wording is not included in the energy property credits.
I don't know if there have been any audits or tax court cases on this specific issue. I think you could reasonably look at it either way, depending on how you want to file. But I would consider there to be a slight risk that, if audited, the auditor might look at the inspection date instead of the installation date.