Solar Calculators and Tools
Free calculators for sizing a system, laying out strings and rows, checking wire, and working out what solar costs, saves and earns. Plus PDF tools for quotes, parts lists, service plans, warranties, leads and stock. No sign-up.
These calculators use real data, not rules of thumb. Type in a ZIP code and you get the sun for your area, your state’s electricity price and what homes there paid for solar.
Everything runs in your browser. What you type isn’t sent to us. Pick a tool below, change the numbers and the answer updates as you go. The tools for quotes, parts lists, maintenance, warranties, leads and stock make a PDF and remember your last entries on your own device.
System sizing
How many panels, how big an inverter and how much battery a system needs.
Wiring and electrical
How many panels fit in a string, and the wire size for each run, checked against the standard tables.
Array layout
The best tilt for your location, and how far apart to set the rows.
Cost and savings
What a system costs, what it saves, when it pays back, and what an install earns the installer.
Quotes and paperwork
For installers: quotes and parts lists you can print as a PDF.
Maintenance and warranty
Service dates and warranty end dates, kept in your own browser.
Business tools
Simple lead and stock lists for small solar companies.
Where the data comes from
Sun and temperature data comes from NASA POWER, averaged over 20 years for each 3-digit ZIP area. Electricity prices come from the Energy Information Administration (EIA). Installed prices come from Berkeley Lab’s Tracking the Sun, a record of systems that homeowners really bought.
The energy model behind the panel, output, savings and tilt tools was checked against NREL’s PVWatts at eight places across the country. Every tool page lists its sources and the date of the data. We refresh the data once a year.
These are planning tools. Your roof, shade, equipment and utility rules decide the final numbers, so treat a quote from a licensed installer as the last word.
Questions
Are the solar calculators free?
Yes. There’s no sign-up and no limit on use.
Where do my numbers go?
Nowhere. The tools run in your browser, and what you type stays on your device. The quote, parts list, maintenance, warranty, lead and stock tools also keep your last entries in your browser’s storage on that device, so they’re there when you return. Each has a button that clears them.
How accurate are the results?
They’re good for planning. The energy model was checked against NREL’s PVWatts and matched it within about 6% at the places tested. Real systems vary with shade, weather and equipment, so get a written quote before you buy.
How often is the data updated?
Once a year. Each tool page shows the date of the data it uses.
I’m a solar installer. Can I use these with customers?
Yes. Use them for a first estimate, then confirm with a site visit and your own design software.
Want a real price for your home?
Send one short form and get quotes from solar companies that work in your area.