Solar panel cost calculatorThis calculator estimates the size and cash price of a home solar system from electricity use, a production factor, a cost per watt, and an incentive percentage. Every line of the result is the formula with your inputs filled in. The default numbers are a worked example: 1,200 kWh a month, a production factor of 1,400 kWh per kW-year, $3 per watt, $0.20 per kWh, and a 0 percent incentive. Those three market-looking inputs are not published benchmarks. Replace them.
On that example, annual use is 1,200 × 12 = 14,400 kWh. System size is 14,400 ÷ 1,400 = 10.29 kW after rounding half up. Gross cost is the unrounded size × 1,000 × 3, which rounds to $30,857.14. Yearly savings at $0.20 per kWh are $2,880. Payback is 30,857.14 ÷ 2,880 = 10.71 years. The 25-year line is 2,880 × 25 − 30,857.14 = $41,142.86. Submit the form to recompute on the server. With JavaScript, the same steps run as you type.
What drives the cost
Three inputs move the cash price. System size scales with how much electricity you are trying to offset and with how many kilowatt-hours each kilowatt of panels produces on that roof. Cost per watt is the installed price in the quote, hardware and labor together. The incentive percent reduces the gross price only to the extent you actually receive it.
A national cost per watt is not printed on this site. Installers in the same city can be far apart once roof work, a main-panel upgrade, and monitoring are in or out of the bid. Type the dollar-per-watt figure from a written quote. If you only have a total price and a system size, divide the price by the size in watts (kilowatts times 1,000) and enter that rate.
The production factor is annual kWh per kW of installed capacity. A shady roof and a south-facing roof should not share a number. This site does not publish a US default. The EPA, using NREL's PVWatts, describes one open-rack example in Kansas City: 1,017.14 kW producing 1,455,726 kWh a year. Dividing those two sourced figures gives about 1,431 kWh per kW-year for that commercial-style array. It is not a home rooftop default. For your house, run PVWatts with your tilt, azimuth, and losses, and paste the specific yield here.
What payback does and does not include
Payback on this page is net cost divided by the first year's savings. Net cost is gross cost minus the incentive you typed. Savings are annual kWh times the electricity rate you typed. If you enter a bill instead of kWh, monthly kWh is the bill divided by the rate. A rate of zero stops that division, and it also makes savings zero, so payback reads "not available" rather than crashing.
The 25-year line repeats year-one savings and subtracts net cost. It assumes no degradation, no repairs, and no rate change. Those costs are unverified here, so they are left out.
Why state incentives matter, and why the menu is off
The federal residential picture is sourced and narrow. The IRS says the residential clean energy credit equals 30 percent of qualified costs for property installed from 2022 through December 31, 2025, and that the credit is not available for property placed in service after that date. The incentive field therefore starts at 0 for a new system in 2026. The historical 30 percent is not typed in for you.
State rebates, sales-tax exemptions, and utility incentives can still change the net price. None of those figures is verified here, for any state. The dropdown stays disabled so an empty menu cannot be mistaken for "your state pays nothing" or for a number we invented. When a state entry is later marked verified, it can appear in the menu without a redesign. Until then, type an incentive percent only from a document you can name.
Typing 30 on the worked example, as a what-if and not as a 2026 entitlement, cuts the gross price to $21,600.00. Payback at $0.20 per kWh falls from 10.71 years to 7.50. That is arithmetic, not a promise.
Roof, shading, and the questions to ask an installer
The production factor hides the roof. Shade from a chimney or a neighbor's tree, a steep pitch, an east-west split, and a vent pipe through the best rafters all change yield. Panel count is a second step: system watts divided by the module watts on the quote. This site does not publish a typical module size. The guide on how many panels you need keeps that division explicit.
Ask the installer for the PVWatts run (city, tilt, azimuth, losses), for costs outside the dollar-per-watt, for who owns the system, and for how exports are credited. The payback formula assumes you pay the net cost and keep the savings.
Read payback explained for the line-by-line version of the formula, and do solar panels pay for themselves for what "pays off" can and cannot mean. If the quote is financed, read loan versus cash versus lease before you compare a monthly payment with the cash payback on this page.
Questions
How is system size calculated?
Monthly kWh times 12 is annual use. Annual use divided by the production factor (kWh per kW per year) is system size in kW. Gross cost is that size times 1,000 times your cost per watt. The page shows each step. It does not round the system size and then multiply, because that would miss the cent on the cost line.
What does payback leave out?
Degradation, inverter replacement, maintenance, insurance, rate changes, and the shape of your utility tariff. A degradation rate is not published here because it is not verified. The 25-year line is annual savings times 25, minus net cost. It is not a forecast.
Does the federal tax credit still apply in 2026?
Not for a new residential system placed in service after December 31, 2025. The IRS says the residential clean energy credit is 30 percent for qualified property installed from 2022 through that date, and that the credit is not available after it. The incentive field starts at 0 for that reason. Type a different percent only if you have a credit or rebate of your own.
Why does my state matter if the menu is off?
Sun, electricity price, and local incentives move the result more than a national slogan does. This site has not verified a rate, a rebate, or a production factor for each state, so the menu stays disabled and no state number is printed. Enter the rate from your bill and a production factor from a PVWatts run for your roof.
How many panels is that?
Divide system watts by the module wattage on the installer quote. This site does not publish a national module size. If a quote uses 400-watt modules and the worked example is 10.29 kW, that is 10,290 watts, or 25.7 modules, which you would round up only as a purchasing choice. The 400-watt figure is the quote in this sentence, not a benchmark.
Does this model a loan?
No. Payback uses the cash net cost. Interest, fees, and a lease payment are outside the formula. A sample loan APR is not published here. Use the cash result as the price you are financing, then ask the lender for the payment.