Methodology

Every number, and where it comes from.

The report is a financial model on public data, not a sales tool. Here is exactly how each figure is produced, so you can check it or argue with it.

Solar production

We use NREL's specific-yield figures, kilowatt-hours produced per kilowatt of panel installed, per year, for your state, derived from NREL PVWatts national runs and the National Solar Radiation Database. That figure is then adjusted for your roof's sun quality (a factor of roughly 0.78 to 1.05). This is a state-level estimate; a per-address run would refine it, and the report says so plainly.

Electricity rate

Your savings depend on the price of the grid power you avoid buying. We look up your specific utility's published residential rate from the OpenEI Utility Rate Database (URDB) and use it when it looks complete; if it isn't available (or lists only the energy charge and understates the true price), we fall back to the EIA average residential rate for your state. The report names which was used.

System size

Your annual usage divided by your roof's adjusted yield, sized to offset roughly 100% of your electricity and bounded to a realistic residential range.

Cost and incentives

• Installed cost: the national residential benchmark of about $3.00 per watt (NREL/SEIA), before incentives. Real quotes vary, this is the yardstick to judge them by.
• Federal tax credit: $0 for a 2026 owned system. The 30% Residential Clean Energy Credit (26 U.S.C. §25D) ended for systems placed in service after December 31, 2025, so the report applies no federal credit to a cash or loan purchase. Only a third-party lease or PPA still captures one. See the federal tax credit guide.
• State incentive: a representative statewide credit or rebate where one clearly exists, from DSIRE. Local utility rebates are often available on top and vary, so the report points you to check DSIRE for your utility.

Payback and savings

We project 25 years, escalating electricity prices about 3% a year and degrading panel output about 0.5% a year, standard planning assumptions, not forecasts. Each year's savings depend on your state's net-metering rules (full retail, partial, California's NEM 3.0 net billing, or utility-specific). Payback is the point where cumulative savings pass your net cost.