I kept getting hung up on how much I had actually paid in taxes, but in reality that doesn't have anything to do with it. The only number that matters is your total tax liability. I believe it is line 24 of your tax return. If that number is higher than $7,500, you'll get the full amount no matter how much in taxes you paid towards that liability.
I think what non-refundable means is that if your tax liability is below $7,500 - let's say it is $4,500, then you would only get $4,500 back.
I am not an accountant so please double check all of this with someone smarter than me. But that's how I made the decision and I ended up getting the full $7,500.