Methodology
HomeSolarMath has 25 calculators, checked against 193 worked test cases. This page explains how they are built, where the data comes from and how we keep it current.
How each calculator is built
- Official data first. Prices, production estimates, efficiency standards and other values come from the agency, regulator or national laboratory that publishes them. Each value is stored with the date it applies from and the link to its source.
- One written definition. Every calculator is a versioned definition: its inputs, the values it reads, each calculation step and how results are rounded. The same definition runs on our server and in your browser, so the result on the page and the one you get when you change a value always match.
- Tested before publishing. Each calculator has at least five worked cases calculated independently, including edge cases and invalid inputs. On top of that, hundreds of random inputs are run on the server and in the browser and must give exactly the same result.
- No missing value becomes zero. If a value we need is not available for the date, the calculator says so instead of showing a wrong number.
Official sources in use
Some calculators also use reference figures cited on their own page, such as federal rules, safety guidance or consumer-protection reports.
Updates and corrections
When an agency publishes new data, we load it as a new dated value and the calculators use it from that date. Each page shows when it was last reviewed and keeps a public change log. If you find an error, write to us from the contact page: we review every report.
Limits
Results are estimates for planning. Averages by state or region can differ from your utility, your home and your contract. For a decision with legal, tax, electrical or financial consequences, confirm with a qualified professional.