For those wondering how Prius Prime gets to $4502 US Federal tax credit. - 2500+417+(3.8 x 417)=4501.6
Note--that is a credit against tax owed (or already paid for the year). It is not a refundable credit. You do not get more than your total federal income tax for the year. If you can't use the full amount, it's lost. I think it is applied against the total tax shown on your 2019 form 1040 line 16.