Methodology
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.
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.
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.
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.
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.
What this is not: a quote, a guarantee, or tax advice. It's an unbiased baseline built from the same public data an honest engineer would use. Confirm the tax credit with a professional and net-metering with your utility.
