Estimate how many solar panels you need to meet your home’s electricity demand. Enter your average monthly energy usage in kWh, your location’s peak sun hours, the wattage of your chosen panels and system efficiency to get a panel count, system size and estimated annual production.
Enter your energy usage to calculate.
Solar system sizing starts with your daily energy consumption and local sun availability:
System Size (kW) = Daily kWh ÷ (Peak Sun Hours × System Efficiency)
Panels = System Size (W) ÷ Panel Wattage
Daily usage = monthly kWh bill ÷ 30. System efficiency of 75–85% accounts for inverter losses, wiring resistance, soiling, temperature derating and mismatch losses. A 400W panel in a location with 5 peak sun hours produces roughly 1.6–1.7 kWh per day.
Peak sun hours are not total daylight hours — they represent equivalent hours at 1,000 W/m² solar irradiance. Cloudy, overcast regions have fewer peak sun hours even though daylight lasts the same amount of time.
A typical 2,000 sq ft home uses about 900–1,200 kWh per month. At 5 peak sun hours with 400W panels and 80% system efficiency, that requires approximately 18–24 panels (7.2–9.6 kW system).
A standard 400W residential solar panel is approximately 17.5 sq ft. A 20-panel system requires roughly 350 sq ft of unshaded south-facing roof area.
Use 80% for a standard string inverter system with typical wiring losses. Use 85% for a microinverter or power optimizer system. Use 75% for older or lower-quality equipment.