Frequently Asked Questions
How many solar panels do I need for my home?
It depends on daily consumption, peak sun hours at your location, and the system derate factor. A home using 20 kWh/day at 4.5 PSH with a 0.77 derate needs about 15 panels of 400 W each, or roughly 6 kW of nameplate capacity.
What are peak sun hours and where do I find them?
Peak sun hours (PSH) condense daily irradiance into equivalent hours at 1,000 W/m squared. The U.S. averages 3 to 6 PSH depending on region. Use NREL PVWatts or PVGIS, enter your address, and pull monthly PSH values for accurate sizing.
What derate factor should I use?
NREL PVWatts uses 0.77 as the default total system derate. Drop it to 0.70 for very hot or dusty climates, and push it up to 0.82 for clean, well-ventilated ground arrays in mild weather. The factor covers temperature, wiring, soiling, and inverter losses combined.
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Estimates for informational purposes only.
Important Disclaimer: Estimates for informational purposes only.
This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.