The credit can't be larger than your tax liability. Your tax liability is what the government keeps at the end of the day. If you had $15,000 of withholding and got an $8000 refund, your liability was $7000. If you had $9000 of withholding and got an $8000 refund, your liability was $1000.
The credit can't be larger than your liability. Any leftover credit will be carried forward to next year.
