Solar Panel Calculator with real city data
Every generic solar calculator assumes the same sun hours for the whole country. This one uses satellite-reanalysis irradiance for your actual city — from 3.48 peak sun hours in Seattle to 5.84 in Phoenix.
Your system in
—panels
—system size (kWp)
—peak sun hours/day
—annual output (kWh)
—bill offset
—roof area needed
Month-by-month production
Calculated from real satellite irradiance for this city, so summer and winter differ the way they actually do on site.
How this was calculated
- Daily load = monthly kWh ÷ 30.
- Array kW = daily load ÷ (peak sun hours × 0.826 efficiency × roof factor).
- Panels = array kW ÷ panel wattage, rounded up.
- Annual output uses each month's real irradiance value.
- System efficiency follows the NREL PVWatts defaults: 14% system losses and 96% inverter efficiency.
Why city-level data changes the answer
Two cities 300 miles apart can differ by more than 40% in annual solar energy. A calculator that assumes "5 peak sun hours" everywhere oversells panels in the north and undersells them in the desert. These are the real measured values for each city we cover.
| City | State | Peak sun hours/day | Annual irradiance (kWh/m²) |
|---|