Is solar tax credit in the year it was installed or the year granted "Permission To Operate"?

[burksfam001]

Installed in 2018 and installers were done; then it is normal and customary to wait months into 2019 until local operations tells you it is okay to turn it on; after we got the official letter, we simply flipped the on switch.

[MinhT]

You can claim the solar tax credit in the year your solar equipment is installed and paid.