Solar Panel Calculator

Your details

Look at a recent utility bill. The U.S. average home uses roughly 900 kWh per month (EIA RECS 2024).
kWh/month
Average daily hours of full-strength (1 kW/m2) sunlight at your location. Most of the U.S. is 3.5-6. See the reference table below.
hrs/day
Rated power of a single panel. Over 97% of U.S. residential panels sold in 2026 are 400 W or higher.
W
Real-world losses from wiring, inverter, heat, dust and shading. NREL PVWatts uses about 80% (a 0.80 derate factor).
%
Percentage of your annual electricity use to cover with solar. Set to 100-150% if you have an EV or heat pump.
%
Currency
System size neededLarge system
8.2kW
Number of panels21
Annual production (Year 1)11,045kWh/yr
Roof area needed588sq ft (with setbacks)
Annual CO2 offset9,090lbs/yr
Annual production (kWh)11,045
CO2 offset (lbs/yr)9,090

You need about a 8.2 kW array, roughly 21 panels.

  • At 400 W each, those panels should generate about 11,045 kWh in Year 1 and cover your target usage.
  • Your 4.5 peak sun hours drive this result the most. A sunnier site needs fewer panels for the same annual output.
  • The array needs about 588 sq ft of usable south-facing roof (including fire-code setbacks).
  • This offset replaces roughly 9,090 lbs (4.1 t) of CO2 per year, equivalent to planting about 189 trees annually (EPA estimate).

Next stepTurn on "Estimate cost and savings" to see your payback period and 25-year net return.

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