Financing something is the same as buying it.  So if hes on the hook for the debt, its the same as buying outright...Im sure lots of people have to finance something in that price range.

As Lisa said, this "lease" is just payment plan for purchasing it.

However, your title said "2020".  If it was installed in 2020, then the Solar Credit only applies on the 2020 tax return (for the full amount).

They were installed in 2018 but never put down to write off. Taxpayer is now doing 2020 and 2021 taxes so always behind 

Thats too bad, looks like you need to amend 2018 (refunds are gone for 2018) and see if anything is left to carryover to 2019, then amend 2019 (still time for a 2019 refund to be issued).  Thats a big chunk of credit to lose.

"They were installed in 2018 but never put down to write off."

That's not how to determine when something gets reported. Neither is "every year I pay for it."

The significant tangible item is what qualifies or not. The regulations use "placed in service" and or "completed" for the determination. If you install something in 2018, but it is not inspected and approved for use until 2020, you would have something that was "placed in service" in 2020.

"Taxpayer is now doing 2020 and 2021 taxes so always behind"

You don't get to save things and use them in the tax year most advantageous for you. You use them in the tax year to which they apply.