Free Solar and Battery Calculators

Our calculators are built for one job: helping you check a solar or battery decision with numbers you can see. They do not ask for your address, phone number or email, and they never route you to a salesperson.

How the calculators work

Every tool runs client-side, which means the math happens in your browser. When you change a field, the page recalculates instantly without contacting our server. That keeps your bill details private and makes the tools work even on a slow connection once the page has loaded.

Each tool page has the same structure:

1. The calculator, with a state picker that fills typical rates and sunshine where that applies.
2. How to use it, field by field.
3. How the calculation works, including the formula written out and every assumption.
4. A worked example using the default inputs, so you can check our math by hand.
5. Limits, an honest list of what the tool does not capture.

Where the defaults come from

Defaults are starting points, not predictions. We choose them from public data and say so on each page:

• Electricity rates start from the US Energy Information Administration's retail price data. The national default is 17.5¢ per kWh; EIA reported a US residential average of about 18.2¢ for January through July 2026 in its Electric Power Monthly (opens in a new tab). State presets use state averages.
• Solar output uses yearly kWh per kW of panels from NREL PVWatts (opens in a new tab), with 1,350 kWh per kW as the national default and higher values for sunny states.
• Degradation defaults to 0.5% per year, near the median NREL research reports.
• Installed cost defaults to $3.00 per watt as a documented example. We sanity-check it against Lawrence Berkeley National Laboratory's Tracking the Sun data, but your own quotes are always the better input.
• Federal credit defaults to none, because the 25D credit ended for installations completed after 2025.

Limits you should know

The tools simplify on purpose. They use yearly or monthly averages rather than hourly utility data, they cannot see shade on your roof, and they do not model every tariff detail such as fixed charges, minimum bills or demand charges. Results are educational estimates, not financial, tax or engineering advice.

Popular starting points

• How many solar panels do I need sizes a system from your bill.
• Solar savings calculator estimates first-year and 25-year savings.
• Solar payback calculator finds your break-even year.
• NEM 3.0 calculator and net metering calculator show what exports are worth.
• Solar battery size calculator and battery backup runtime calculator help with storage.
• Solar lease vs buy calculator compares ownership options.

Want the background first? Our guide on whether solar panels are worth it explains how the numbers fit together. Read our methodology for the full sourcing rules.