Do I take the Energy Improvement Credit in the year they were completed or when they are billed/paid? And what if the costs were financed?

[smousseau]

The work was done the last week of December 2021 and not billed until 2022.

[Critter-3]

Billing is immaterial along with when the bill is actually paid.   What counts is when the system became operational and passed inspection.  

[smousseau]

Thank you!