The fixed monthly payments before month 18 of your loan are based on the assumption that you pay off your loan by the full amount of your eligible investment tax credit by month 18. There is no obligation to prepay your loan by month 18, and the discounted monthly payments during those first 18 months are intended to be an added benefit to you.
Your loan will automatically re-amortize at month 18. By that time, if you have failed to pay off the principal balance of your loan by the full amount of the ITC, State tax credits (eg. New York state tax credit), late fees, and capitalized interest your fixed monthly payments may increase. By that time, if you have paid off more than that, your fixed monthly payments may decrease.
With an Atmos loan, you can prepay your loan at any time without penalty. Through the life of your loan, your loan will be re-amortized (to reduce your fixed monthly payment) with all prepayments in excess of $500. So, if you aren’t able to make this payment by month 18, that’s OK. You’ll be able to make payments whenever you want through the life of your loan.