A) Start off with the purchase price of the solar project. B) Subtract the tax incentives/credits and rebates. C) Estimate the new rate of your utility bill and calculate the savings per year. D) Divide the net solar system cost(the purchase price of panels minus the tax incentives/credits and rebates) by the annual savings  on the utility bill. E) Equals the amount of years it will take to pay off your solar system. EXAMPLE – NEW YORK (Estimated purchase price of panels 10kw) $35,000,  NYSERDA Rebate ($3,000 estimated), Federal Tax Credit (30% x (35,000-3,000) $9,600 – State tax credit $5000 = $17,400 total out of pocket cost divided by the estimated savings per year on your utility bill ($3,000 estimated) = 5.8 years to pay off your system.