Solar Payback Calculator
When will solar pay for itself?
About this calculator
Rooftop solar costs a large sum up front and pays it back slowly, through lower electricity bills over the life of the panels. The payback period is how long those savings take to add up to what you paid, and after that point the savings are a gain. Whether solar pays for itself in 8 years or 20 depends on what the system costs, how much sun it gets, what you pay for electricity, and how your utility credits the power you send to the grid. This calculator models those factors year by year and shows when solar pays for itself, along with the net savings and return over the analysis period.
How to use this calculator
Enter the System Size in kilowatts and the Installed Cost per Watt from your quote; many U.S. quotes fall between about $2.50 and $3.50 a watt. Enter any Tax Credit percentage and any State or Utility Rebates. Enter the Annual Production per kW your installer estimates, often 1,200 to 1,500 kWh a year depending on where you live, your Electricity Rate per kWh and the Annual Rate Increase you expect. Under Advanced assumptions you can set Panel Degradation, the Net Metering Share of production credited at the full retail rate, the Export Rate paid for the rest, Annual Maintenance, the Analysis Period and an optional Inverter Replacement in a given year. The page updates as you type and the inputs are saved in the page address.
The method
The cost before incentives is the system size in watts times the cost per watt. Rebates come off first, and the tax credit percentage applies to the cost after rebates; the result is the net cost. In each year, production is the system size times the production per kW, reduced by the degradation rate for every year after the first. The electricity rate grows by the annual increase. The share of production covered by net metering saves the full retail rate; the rest earns the export rate. Maintenance, and the inverter replacement in its year, are subtracted to give the year's savings. Payback is the point at which cumulative savings first reach the net cost, interpolated within that year and shown in years and months. Net savings are total savings over the period minus the net cost; return on investment is net savings divided by the net cost, and the internal rate of return is the yearly rate at which the savings, discounted, exactly repay the net cost.
Worked example using the default values
A 7 kW system at $3.00 a watt costs $21,000. With no tax credit or rebates, the net cost is also $21,000. At 1,300 kWh per kW, it produces 9,100 kWh in the first year, which at $0.17 a kWh saves $1,547. With electricity prices rising 2.5% a year and output falling 0.5% a year, solar pays for itself in 12 years 2 months. Over 25 years the savings add up to $49,472, a net gain of $28,472: a 136% return on the net cost, or an internal rate of return of 7.3% a year. If only 60% of the power were credited at the retail rate and the rest earned $0.05 a kWh, payback would stretch to 16 years 8 months.
Interpreting the results
A shorter payback means less risk, because more of the panels' life is left to earn a gain and less depends on long-range guesses about electricity prices. The internal rate of return is the figure to compare with other uses of the money, such as paying down a mortgage or investing; it accounts for the timing of the savings, which the simple return does not. If the result says solar does not pay for itself within the period, the system costs too much for the power it is likely to save at your rates, or the export rate is too low.
Practical tips
Get at least two or three quotes, and compare them on cost per watt and estimated production, not only on the total price. Ask your utility how it credits exported power; many utilities have moved from full net metering to lower export rates, which makes using solar power during the day, or adding a battery, more valuable. Check for state and local incentives, which vary widely and change often. The federal residential clean energy credit (25D) is not available for systems paid for after December 31, 2025, so it is set to 0% by default. If you might sell the house within a few years, weigh how much of the remaining value a buyer would pay for.
Limitations
The calculator assumes constant yearly rates for price increases and degradation, which real life will not follow. It values savings in nominal dollars without inflation adjustment, and the payback date does not discount future savings. It does not model financing, leases, battery storage, time-of-use rates, monthly net metering true-ups, fixed grid charges, or changes in your electricity use. Production estimates depend on roof direction, shading and local weather; use your installer's estimate where you have one. The tax credit percentage is applied as if it is fully used in the first year.
Frequently Asked Questions
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