Solar Panel Output Calculator
Estimate daily, monthly, and yearly solar energy output from your panel array.
Estimates are for planning purposes only. Actual output depends on shading, panel orientation, local climate, and equipment specifications. Consult a qualified solar installer before purchasing or installing a system.
How it works
- 1Enter the panel wattage, average peak sun hours, panel count, and system derate %.
- 2The calculator multiplies watts × sun hours × count × derate ÷ 1000 for kWh per day.
- 3Monthly and yearly estimates and the total array size in kW are shown alongside.
Use cases
- Sizing a rooftop solar install to cover a household electricity bill.
- Comparing how panel count changes with location and peak sun hours.
- Estimating annual kWh for a feed-in tariff or net-metering application.
Frequently asked questions
What is the derate factor?
Derate (~75–80%) covers inverter efficiency, wiring, dust, and temperature losses. A 400 W panel in 5 sun hours at 75% derate makes 400 × 5 × 0.75 ÷ 1000 = 1.5 kWh/day.
What are peak sun hours?
The hours per day when irradiance averages 1000 W/m². They vary by location and season — deserts may see 6–7 h, cloudy climates 3–4 h.
Why is output below the nameplate rating?
Ratings are at lab Standard Test Conditions. In the field, heat, shading, and inverter losses reduce output — the derate factor rolls these into one adjustment.
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