Solar Panel Calculator
Find your solar system size, cost & payback period
Frequently Asked Questions
System size (kW) = daily kWh use ÷ (peak sun hours × system efficiency), then divide by panel wattage and round up. A typical US home (900 kWh/month) needs roughly a 6-8 kW system.
The average daily hours of full-strength (1 kW/m²) sunlight at your location — most of the US ranges from 3.5 to 6 hours, with the Southwest highest and the Northeast/Northwest lowest.
Real-world losses from wiring, inverter conversion, heat, dust, and partial shading. NREL's PVWatts tool uses about 80% (a 0.80 derate factor) as a standard planning assumption.
Installed cost ÷ Year 1 electricity savings. The 30% federal solar tax credit (ITC) significantly shortens payback by reducing net cost.