Methodology & data sources

No black box. Here is exactly how every estimate is built and where the numbers come from.

The formula

We turn your monthly bill into annual kWh using your state’s electricity rate.
We size a system to cover the share of usage you choose, using your state’s solar production factor.
Gross cost = system size × your installed $/W.
Net cost = gross cost − 30% federal credit − any rebate you enter.
Payback = the year your cumulative bill savings overtake that net cost, with power prices rising ~2.5%/yr and panels losing ~0.5%/yr.

Where the data comes from

Electricity rates — average residential prices per state from the U.S. Energy Information Administration (EIA), Electric Power Monthly (~2025). National average in our data: 16.8¢/kWh.
Solar production — annual kWh per kW of panels, a south-facing rooftop ballpark by climate from NREL’s PVWatts. National average: 1330 kWh/kW/yr.
Federal tax credit — the 30% Residential Clean Energy Credit (IRS), in effect through 2032.
State & utility incentives — these change constantly and vary by provider, so we don’t hard-code dollar figures. We link each state page to DSIRE, the authoritative US incentives database, and let you enter any rebate.

What this is — and isn’t

This is a fast, transparent estimate to help you decide whether solar is worth pursuing where you live. It is not a quote, a guarantee, or financial/tax advice. Real costs depend on your roof, shading, equipment and installer, and the federal credit depends on your tax situation. Always get itemised quotes and talk to a tax professional before buying.

Honesty policy

We use state averages and label them as such. We never invent precise rebates, fake “average savings,” or hide the answer behind a lead-capture form. Nothing you type leaves your browser. If a number here is wrong or out of date, that’s a bug — tell us.