Free Solar Panel Calculator
Sizing a solar system starts with your electric bill. This free solar panel calculator turns your monthly bill into a system size in kilowatts, a panel count, an installed cost estimate, and a 25-year savings figure, all in one pass.
This free solar panel calculator estimates your system size, panel count, installed cost, and long-term savings from your monthly electric bill. For example, a $150 monthly bill with 5 peak sun hours and 400-watt panels points to about a 7.3 kW system (roughly 19 panels), costing around $21,400 before incentives, with about $65,600 in 25-year savings and a payback near 12 years. Results are estimates; get installer quotes for exact pricing.
Estimates only. Costs are before federal and state incentives and vary by installer, roof condition, and local rates. Not financial advice.
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How solar sizing math works
The calculator starts with your monthly bill and divides it by a typical residential electricity rate of 17 cents per kilowatt-hour, which converts the bill into the kilowatt-hours your home uses each year.
Annual usage is then divided by your area's peak sun hours times 365 days times a 0.80 derate factor for real-world losses from heat, shade, wiring, and inverter efficiency. The result is your system size in kilowatts.
Panel count is the system size divided by your panel wattage, rounded up. Installed cost multiplies system watts by a default of $2.95 per watt. Twenty-five-year savings assume electricity rates rise 3 percent a year, which is conservative against the last decade of utility rate increases.
Solar panel calculator questions
How many solar panels do I need?
Divide your annual kilowatt-hours by (peak sun hours x 365 x 0.80), then divide by panel wattage and round up. A home using 10,600 kWh a year with 5 sun hours needs about a 7.3 kW system, which is 19 panels at 400 watts. The calculator above runs this math from your electric bill.
How much do solar panels cost in 2026?
A typical residential install runs about $2.50 to $3.50 per watt before incentives, so a 7.3 kW system costs roughly $18,000 to $25,500. The federal solar tax credit can cut the net cost substantially; check current IRS rules for the current rate.
How long until solar panels pay for themselves?
Most US systems pay back in 8 to 14 years, depending on sun hours, electricity rates, and installed cost. Higher utility rates and sunnier locations shorten the payback. After payback, the electricity the system produces is nearly free for the remaining life of the panels.
Do solar panels work on cloudy days?
Yes, at reduced output. Panels produce roughly 25 to 40 percent of their rated power under heavy cloud cover, which the calculator's 0.80 derate factor and your sun-hours setting already account for. Snow usually slides off tilted panels quickly.