Solar Panel Savings Calculator
Enter your planned system size, your location's average peak sun hours, and the installed cost, and this calculator estimates how much electricity the array produces each year, what that offsets on your bill, and how long the system takes to pay for itself after the 30% federal tax credit. It is a first-pass screening estimate, not a substitute for a site-specific quote.
System & site
Cost & incentives
First-year bill savings
$1,489.20
8,760 kWh/yr × $0.17/kWh
Payback
8.46 yrs
Net cost after credit
$12,600.00
Cost & savings detail
Cumulative savings vs net cost
How it works
Annual production is estimated as system size (kW) × peak sun hours per day × 365 × a derate factor. Peak sun hours are the number of hours per day the sun delivers 1,000 watts per square meter — they range from roughly 3.5 in the cloudy Northwest to over 6 in the desert Southwest. The derate factor (default 0.8) accounts for real-world losses that nameplate ratings ignore: inverter conversion, wiring resistance, panel soiling, heat, and gradual degradation. NREL's PVWatts model uses a similar system-loss adjustment.
Annual savings equal estimated production multiplied by your retail electricity rate. This is a simplification: it assumes every kilowatt-hour you generate offsets a kilowatt-hour you would otherwise buy at the retail rate, which holds under full net metering but not under time-of-use rates, net-billing, or when production exceeds your usage. The federal residential clean-energy credit (30% of gross cost through 2032 under current law) is subtracted from the system price to give a net cost, and simple payback is net cost divided by annual savings.
The chart tracks your cumulative savings against the net system cost year by year; the point where the line crosses zero is your break-even, or payback, year. The model holds the electricity rate flat, so it is deliberately conservative — real utility rates have historically risen over time, which would shorten payback. It also excludes financing interest, maintenance, inverter replacement, and any state or utility incentives, all of which vary too much to estimate generically.
Frequently asked questions
How accurate is this solar savings estimate?+
Treat it as a screening estimate, not a quote. The two biggest sources of uncertainty are your actual peak sun hours (which depend on latitude, weather, roof orientation, tilt, and shading) and your true retail rate structure (flat vs. time-of-use, and whether your utility offers full retail net metering). A professional installer uses satellite shading analysis, your specific roof geometry, and your utility's exact tariff to produce a bankable number. This tool is best for deciding whether solar is worth investigating, and for sanity-checking a quote you have already received.
What is the 30% federal tax credit and do I qualify?+
The federal Residential Clean Energy Credit lets eligible homeowners claim 30% of a qualifying solar installation's cost as a credit against their federal income taxes, for systems placed in service through 2032 under current law. It is a non-refundable credit, meaning it can reduce your tax liability to zero but the mechanics of carrying forward unused amounts, and your eligibility, depend on your tax situation. This calculator applies the percentage you enter to the gross cost, but it does not constitute tax advice — confirm your eligibility and the current rules with the IRS guidance or a tax professional before relying on the credit.
Why does the calculator assume electricity prices stay flat?+
Holding the rate flat is a conservative modeling choice. US residential electricity prices have trended upward over the long run, so a flat assumption tends to understate lifetime savings and overstate payback time — the opposite of an optimistic sales projection. If you expect rates to rise, your real payback will likely be shorter than shown. We avoid baking in a specific escalation rate because future utility prices are genuinely unknowable and a wrong assumption there can swing the numbers dramatically.