Solar Panel Payback Calculator: Why the Simple Answer Moves

October 17, 2026 · Homes and property

Solar panel payback is the number of years it takes for the savings on your electric bill to repay what the system cost: net cost divided by net savings a year. On an illustrative 8 kW system costing $23,000 and saving $1,314.40 a year, that is 17.5 years. That simple answer assumes electricity prices never change and the panels never age. Let prices rise 3% a year and output fall 0.5% a year and the same system pays back in 14.7 years. Cut the credit for exported power in half and it stretches to 19.3 years. The inputs that move the answer are yours to check, and this page shows how each one does it.

The solar panel payback formula

Net cost          = installed cost - rebates - tax credits you can use
First-year value  = kWh used at home × your rate per kWh
                    + kWh exported × export credit per kWh
Net savings       = first-year value - upkeep a year
Simple payback    = net cost / net savings

Return on investment follows from the same numbers: net savings divided by net cost is the first-year return, and lifetime savings minus the cost, divided by the cost, is the return over the life of the panels.

A note on the federal tax credit

The IRS states that the federal Residential Clean Energy Credit “is not available for any property placed in service after December 31, 2025” (IRS, Residential Clean Energy Credit). Older payback calculations that subtract a federal credit from the cost describe systems installed before that date. The worked example below uses no federal credit. Whether any state or local incentive applies to you is a question for your state energy office and a tax professional.

Worked example: an illustrative 8 kW system

Every figure here is an example to replace with your own quote and your own bill, not a market price or a production estimate for any location:

• 8 kW at $2.75 a watt installed, plus $1,000 of extra work (permits, electrical panel): $23,000, and with no rebate or credit that is also the net cost, $23,000
• Production of 1,300 kWh per kW a year: 10,400 kWh
• 70% of it used at home (7,280 kWh), the rest exported (3,120 kWh)
• You pay $0.16 per kWh; exports are credited at $0.08
• Upkeep of $100 a year

The value of the first year is $1,164.80 for electricity you no longer buy plus $249.60 of export credit, $1,414.40 in all. Less upkeep, net savings are $1,314.40. So:

Simple payback = $23,000 / $1,314.40 = 17.5 years

For your own production figure, ask the installer for an estimate based on your roof’s direction, tilt, shading and location, and compare quotes on kWh per year as well as on price.

Why the simple answer moves

Two things change every year, and they pull in opposite directions. If electricity prices rise, each kWh the panels make is worth more. As the panels age, they make fewer kWh. With prices rising 3% a year and output falling 0.5%, savings grow 2.49% a year, and the year-by-year picture looks like this:

The cost is recovered during year 15, at 14.7 years rather than 17.5: the assumed price rise more than offsets the aging. With flat prices and aging panels, payback slips the other way, into year 19. The price rise is an assumption, not a forecast: set it to zero to see what happens if it does not come.

Here is the same system under different assumptions:

The export credit and your self-use share move it too

In this example, each exported kWh is worth half a kWh used at home. That makes the share you use yourself a lever on payback, not a detail. Each cent cut from the export credit costs $31.20 a year on 3,120 kWh of exports. Halving the credit from $0.08 to $0.04 adds years to the simple payback (17.5 to 19.3), while using more of the output at home (running daytime loads while the panels produce) brings it in: at 80% self-use instead of 70%, simple payback is 16.5 years. Utilities set and change their own export rates, so check the current tariff and ask whether it is locked for your system.

Solar panel return on investment, over the life of the panels

Counting 25 years, the example saves $44,810 on a $23,000 cost: $21,810 more than it cost. But a dollar saved decades from now is worth less than a dollar spent today. Discounting each year’s savings at an illustrative 4% (what the money might earn elsewhere), the savings are worth $26,643 in today’s money, so the net present value is $3,643. It still beats the discount rate in this example, by a much narrower margin than the undiscounted total suggests.

Inverter replacement, roof work under the panels and any effect on resale value are not counted; add them to the cost if they apply to you.

Solar on a loan: payback is not monthly cash flow

A short payback does not mean a loan pays for itself month by month. Borrowing the $23,000 at an illustrative 7.99% over 15 years costs $219.67 a month, against $109.53 a month of savings in year one. That is $110.13 a month out of pocket at the start, and $16,540 of interest over the loan. With savings growing 2.49% a year, the monthly savings would not reach the payment for about 28 years, after this loan is paid off. On a loan, the useful questions are the monthly gap and the total interest, alongside the payback.

How these were calculated

Net cost is the installed price per watt times the system size plus extra work, less rebates and credits (none in this example). First-year value is the kWh used at home at the retail rate plus the kWh exported at the export credit. Payback with rising prices and aging panels treats savings as growing by a constant rate each year and finds the point where cumulative savings equal the cost. Present value discounts each year’s savings to today. The loan is a fixed-rate, fully amortizing loan with level monthly payments.

Every figure on this page was computed twice: once by the code behind the calculator pack below, and once by an independent implementation written for this page (savings added up year by year, payback found by searching that running total rather than from a formula, and the loan payment found by trial). The two agree to the cent before anything is published. All prices, production figures, rates and credits are illustrative examples, not quotes or forecasts. This is not financial or tax advice; check irs.gov, your state energy office and a tax professional before counting any incentive.

If you want to run the cost, production, both kinds of payback, the loan and the export-credit test on your own quote and bill, the spreadsheet pack below has each one as an editable sheet with the formulas visible.