The most important thing to consider is the order in which credits apply to taxes owed each year. Non-refundable always hits your tax liability first, then refundable credits. The FITC, a non-refundable tax credit, only hits your tax liability after a few other credits get deducted. For example, foreign tax credit, dependent care expenses, education credits (non-refundable ones), retirement savings credit, energy efficient doors, windows, and insulation, electric vehicle credit, child tax credit (most child tax credits), adoption credit Your tax liability is based on your income - which includes all types of income. Additional taxes that are levied such as self-employment taxes, minimal tax, penalties on early distribution, etc. come into effect after the solar tax credit is applied. So, someone who's self-employed making $100,000 each year will still have the $15,000 in self-employment taxes to pay even if they go solar.
There are other tax credits that hit first before the solar tax credit, and if they wipe out the liability before the tax credit can be applied, then you may not see any difference in your taxes owed despite having gone solar. Basically, you may never get to use your tax credit until a child turns 18. It just depends on how large of a tax liability you have.