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.
Divide monthly usage by 30 for daily usage in kWh. Each panel's real-world daily output is its wattage × peak sun hours × (1 minus system losses), converted to kWh. Dividing daily usage by one panel's output — and rounding up — gives the panel count needed to offset your electricity use.
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.