Solar deduction states "The tax credit is 30% of the costs for assembly, preparation, and installation as well as piping/wiring." Can I deduct payments made this year?

If the improvement was installed in tax year 2022, that is the year you would need to use to apply for the credit.

Although you did not pay until 2023, you no doubt signed an agreement and were obligated to pay in 2022 when the install was done.