That means the amount of the tax credit that exceeds your total tax liability would not be refunded to you. It would however be carried forward to the next year to offset future taxes.

For example: throughout the year, you generate a tax liability of $5,000 for which you had payroll withholding. Your solar tax credit is $7,000. You would receive a tax refund of $5,000. $2,000 of credits would roll forward to next year.

Here is a link that answers other questions.

Disclaimer, I am not a CPA. I just read CB a lot.