You’ve got it right, it would be a larger refund as long as you have enough total tax liability. If the panels were, say, $30K, you would get a tax credit of $10K (30%). If you paid more than $10k total across the year, you would get that amount back when you file at the end of the year. If you paid less than $10K in taxes that year, say $7000, the remainder would roll over to the next year, when you could claim a credit of $3K against the next year’s taxes.