Solar Array Size Calculator: kW From Your Annual Usage
Enter your yearly electricity use and local sun-hours to get a rough solar array size in kW, with the production-per-kW math shown.
size = 10,800 ÷ 1,314 = 8.22 kW
How it works
If you already know your yearly electricity use — the total kilowatt-hours across all twelve bills, often printed on your annual summary — you can size an array in one step. This tool skips the monthly-to-annual conversion and works straight from that number.
The math is the same sizing identity used everywhere in solar: divide annual kWh by the energy one installed kilowatt produces in a year. That per-kW figure is your peak sun-hours times 365 days times a derate factor. At 4.5 sun-hours and a 0.8 derate, one kW makes about 1,314 kWh a year, so a home using 10,800 kWh needs roughly 10,800 ÷ 1,314 ≈ 8.2 kW.
Peak sun-hours come from NREL's solar resource maps and vary with where you live; the derate accounts for the inverter, wiring, heat, and dust losses that separate nameplate DC from delivered AC. Change either input and the size updates live. As with any rule-of-thumb, roof orientation and shading still need a site visit to confirm.
per kW = 4.5 × 365 × 0.80 = 1,314 kWh/yr
size = 10,800 ÷ 1,314 = 8.22 kW