About SolarSpan
SolarSpan is the homeowner's pre-quote arithmetic: how big a system your bill implies, how many panels that takes, and when it pays for itself.
SolarSpan exists because solar quotes arrive aspackages — "10.4 kW, $31k, trust us" — with the assumptions buried. The underlying math (sun-hours, derate, incentives) is public. Seeing it first changes the conversation from price to design.
Every calculator on SolarSpan shows its formula and its assumptions on the page, so you can check the math, reproduce it in a spreadsheet, or argue with it. Inputs are processed entirely in your browser — nothing is sent to a server, and there are no accounts.
SolarSpan is an independent, ad-supported project. We are not affiliated with any lender, brand, agency, or the sources we cite (DOE and EPA public efficiency guidance). If a number looks wrong, the contact page reaches a human who fixes it.
What makes SolarSpan different
- Your numbers never leave your browser. Every calculator on SolarSpan runs entirely on your device. We never see, store, or transmit the figures you enter — there are no accounts and no server-side processing of your inputs.
- Published methodology. Each calculator page explains the exact formula it uses and the assumptions behind it, so you can check our work or reproduce it in a spreadsheet.
- Free, forever, without a paywall. SolarSpan is supported by advertising. There is no premium tier, no email gate, and no upsell.
Independence
SolarSpan is an independent educational project. We are not affiliated with, endorsed by, or acting on behalf of any government agency, lender, insurer, or the organizations whose formulas and public data we reference (such as DOE and EPA public efficiency guidance). All trademarks and referenced standards belong to their respective owners.
Questions, corrections, or suggestions are genuinely welcome — get in touch.