QueenBee wrote:In my mind it's clear that this work was needed to install solar and even if you end up installing solar next year IMO I would include the cost of it in your federal tax credit. AFAIC the worst case is you get audited and they do a thorough review of all your documentation and decide that it is not included and you have to repay that part of the credit back. Not very likely and IMO it's in the spirit of the intention of the credit.
If you are referring to the Federal tax credit, I believe it is more than just the spirit of the code. If I remember correctly, the instructions stated that you should treat all expenditures as if they occurred within the tax year that the system was put into service, even if they were made over multiple years. I could be wrong, so please check the instructions yourself.