What is a solar savings calculator?
A solar savings calculator estimates how long a solar system takes to pay for itself and how much it could save over its lifetime. Enter a system size and install cost, and it returns annual energy production, annual savings, payback period, and projected long-term savings.
This is useful as a first-pass check before requesting quotes from installers, or for comparing how a quoted system size and price stacks up against a typical payback period for your area. Pages for individual states pre-fill the production estimate with real solar resource data so you do not need to research irradiance figures yourself.
Key inputs
Three numbers drive the estimate. System size and cost are usually available from a quote; the electricity rate can come from a recent bill.
| Input | What to enter |
|---|---|
| System size | Total panel capacity in kilowatts (kW), from a quote or system spec sheet |
| Install cost | Either the total project cost in dollars, or a cost per watt — switch the unit to match how your quote is presented |
| Electricity rate | Cost per kilowatt-hour, used to value the energy the system offsets, pre-filled with your state's average |
What the calculator returns
Once your inputs are entered, the calculator produces a complete production and savings breakdown.
Annual savings, payback period, and 25-year net savings, so you can see whether a quoted system is likely to pay for itself within a reasonable timeframe.
Estimated annual energy production in kilowatt-hours (kWh), based on your system size and local solar resource data.
The total install cost and electricity rate used in the calculation, so you can confirm they match your own quote and utility bill.
How to use this calculator
- 1
Enter your system size
Use the size from an installer's quote, typically between 5 and 10 kW for a residential rooftop system.
- 2
Enter the install cost
Switch between total cost and cost per watt depending on how your quote presents pricing, and enter the value either way.
- 3
Confirm the electricity rate
The rate is pre-filled with your state's average. Edit it if your utility bill shows a different rate — this directly changes how much each kWh of solar production is worth.
- 4
Review payback period and savings
Check the payback period against how long you plan to stay in the home, and review the 25-year net savings for a longer-term view.
Factors that affect real-world production
The production estimate is based on regional solar resource data, but actual output from a specific roof depends on several site-specific factors.
Roof orientation and tilt
South-facing roofs in the northern hemisphere typically produce the most energy. East- or west-facing roofs can still work well, usually at a moderate reduction in output.
Shading
Trees, chimneys, and neighboring structures that shade panels during peak sun hours can meaningfully reduce production, even if the roof itself is well-oriented.
Panel degradation over time
Most panels lose a small percentage of output capacity each year. This calculator's 25-year projection does not adjust for that gradual decline, so actual long-term production is somewhat lower than a flat estimate.
Weather and seasonal variation
Cloud cover, snow, and seasonal changes in day length cause production to vary month to month. Annual totals smooth this out, but monthly savings will not be even across the year.
Practical tips and limitations
Tax credits and incentives are not included
Many regions offer rebates or tax credits that reduce the effective install cost. This calculator uses the cost you enter as-is, so subtract any incentives from your quote before entering it for a more accurate payback period.
Financing changes the real payback picture
If the system is financed rather than paid for upfront, loan interest affects the true breakeven point. This calculator assumes a cash purchase.
Electricity rates can change over time
The 25-year projection assumes a flat rate. If electricity prices rise over time, as they often do, actual savings could be higher than this estimate.
Use it as a starting point, not a final quote
Actual production depends on roof-specific factors an installer's site assessment will capture more precisely than a state-level average.
Frequently asked questions
How is solar payback period calculated?
▾
Payback period is the total install cost divided by annual savings. Annual savings come from multiplying estimated yearly production by your electricity rate. This calculator handles both steps automatically.
What is a typical payback period for solar?
▾
It varies widely by location, system cost, and electricity rates, but many residential systems in the US fall somewhere in the range of 6 to 12 years. Areas with high electricity rates and strong sun exposure tend to pay back faster.
Does this calculator include tax credits or rebates?
▾
No. Enter your install cost after subtracting any incentives you plan to claim for a more accurate payback estimate, since this calculator uses the cost figure exactly as entered.
Where does the production estimate come from?
▾
State pages are pre-filled with solar resource data from the National Renewable Energy Laboratory (NREL), reflecting typical solar irradiance for that region. Actual production also depends on your specific roof.
Why does the 25-year savings number not account for panel aging?
▾
This calculator projects a flat annual savings figure across 25 years for simplicity. In reality, panels gradually lose some output capacity over time, so real long-term savings are typically somewhat lower than this straight-line projection.