calcs.homes
calcs.homes
Enter your monthly electricity usage, panel wattage, and average peak sun hours to find how many solar panels you'd need to cover it. Watts, kWh, and sun hours are measured the same way worldwide, so there's no US/EU toggle needed here.
Estimate only — roof space, shading, and panel orientation all affect real-world output.
We divide your monthly usage by 30 to get an average daily kWh target. Each panel's realistic daily output is its wattage ÷ 1,000 (to convert to kW) × peak sun hours × (1 minus your system loss percentage), giving kWh. Dividing daily usage by that one-panel output and rounding up to a whole panel gives the count needed to fully offset your usage.
System losses account for the gap between a panel's rated wattage and what it actually delivers — inverter conversion, wiring resistance, dust, and panel mismatch commonly total around 20%, a figure widely used for solar sizing and planning estimates. Rounding panel count up rather than down ensures the system reaches full offset instead of falling just short of your target.
Peak sun hours aren't daylight hours — they're the equivalent hours of full-intensity (1,000 W/m²) sunlight your location gets in a day. Most of the US averages 4-6 peak sun hours; look up a solar irradiance map for your specific area.
Real systems never convert 100% of sunlight to usable power — inverter efficiency, wiring resistance, dust, and panel mismatch all take a cut. 20% is a common planning assumption for a well-designed system.