The credit has NOTHING to do with your withholding.
Take a look at the Form 1040. (the 2023 form is going to be almost exactly the same)
https://www.irs.gov/pub/irs-pdf/f1040.pdf
the solar credit reduces your tax liability - that is line 22. That means that to take full advantage of the tax credit, Line 22 must be at least the amount of the credit ... any unused credit can be carried forward.
Your withholding and any estimated payments are applied beginning on Line 25 so have no impact on the tax credit. This is where folks get confused. They think that line 34 has to be at least as much as the credit to get the credit, Not True.
Line 22 is what you owe (your "tax liability"); Lines 25-34 is how you pay what you owe... usually the withholdings. So if the credit brings your tax liability down to zero (and you have no other taxes owed) then you will get all the withholding paid as a refund.
