If I understand your example, then yes, you will get the credit.
The credit can be refunded up to your tax liability. Your tax liability is what the government gets to keep (not counting self-employment tax and certain penalties). If you normally have $5500 of withholding and get a $500 refund, then your tax liability (what the government kept) was $5000. Likewise, if you had $4000 of withholding and paid an additional $1000 when you filed, your liability was $5000. This is shown on line 22 of form 1040.
If you have a $5000 liability before the solar credit, and the credit was $5000, then it would cancel out your income tax liability and you would get a full refund of all your withheld taxes. If the solar credit was $6000, then it would cancel out your $5000 liability, you would get a full refund of your withholding, and you would carry forward the last $1000 to next year.
