Solar ROI Calculator
Solar panels are an investment that pays back through avoided electricity purchases. This calculator works out three figures that matter most: annual electricity savings, simple payback period in years, and lifetime return on investment as a percentage. You supply the gross system cost, any rebate or tax credit, annual energy production in kilowatt-hours, your electricity rate, and the expected system lifespan. Every empirical figure is a user-editable input because costs, rates, and local sun all vary, so the answer reflects your real situation rather than a national average.
Solar ROI formula
Net cost = gross cost - rebate
Annual savings = annual kWh * rate per kWh
Payback years = net cost / annual savings
Lifetime savings = annual savings * lifespan
Lifetime ROI % = (lifetime savings - net cost) / net cost * 100
The model uses simple, undiscounted cash flows. It does not apply a discount rate, electricity price inflation, or panel degradation, so it gives a clear baseline rather than a finance-grade net present value.
What drives solar returns
- Net cost is what you actually pay after the federal Residential Clean Energy Credit and any state or utility rebate.
- Annual production depends on system size and local sun; the DOE PVWatts tool estimates it by address.
- The U.S. Energy Information Administration publishes average residential electricity rates by state.
- Higher local rates shorten payback because each kWh produced avoids a larger bill.
- Most residential systems are warrantied for 25 years; real output declines gradually over that period.
Solar ROI: frequently asked questions
How is solar payback period calculated?
Payback period is the net system cost (gross cost minus any rebate or tax credit you enter) divided by the annual savings. Annual savings is the kilowatt-hours produced per year multiplied by the electricity rate you pay per kWh. The result is the number of years until accumulated savings equal what you paid.
What electricity rate should I enter?
Use your own utility rate per kilowatt-hour, found on your electricity bill. The U.S. Energy Information Administration also publishes average residential rates by state. Because rates vary widely and change over time, this is a user-editable input rather than an assumed figure.
How do I estimate annual production?
Annual kWh is system size in kW multiplied by your local specific yield in kWh per kW per year. The U.S. Department of Energy PVWatts tool gives a location-specific yield. Enter your own estimate; typical U.S. yields fall between 1,000 and 1,800 kWh per kW per year depending on sun and tilt.
Does this account for rate inflation or panel degradation?
This calculator uses a flat annual saving for a clear baseline. Real returns are usually higher because electricity prices tend to rise, and slightly lower because panels degrade by roughly half a percent per year. For a first-pass payback estimate the flat model is a reasonable, conservative starting point.
What does lifetime ROI mean here?
Lifetime ROI is total savings over the system lifespan minus the net cost, expressed as a percentage of the net cost. It answers: for every dollar invested after incentives, how many dollars of electricity savings does the system return across its working life?
Official sources
- U.S. Department of Energy: PVWatts production estimator (NREL).
- U.S. Energy Information Administration: Electric Power Monthly average rates.
- U.S. Department of Energy: Residential Clean Energy Credit guide.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.