Solar Panel Output Calculator

A 450 W panel in a location with 4.5 peak sun hours and typical 20% system losses produces about 0.45 × 4.5 × 0.8 ≈ 1.6 kWh a day — roughly 590 kWh a year. Output scales with panel size and your local sun: the same panel yields more in sunnier regions and less in cloudy ones.

Daily energy (kWh) = system size (kW) × peak sun hours × performance ratio, where the performance ratio is 1 minus the system losses. A 5 kWp system at 4.5 sun hours and 0.8 performance ratio produces about 18 kWh a day, or around 6,570 kWh a year.

The equivalent number of hours per day of full-strength (1 kW/m²) sunshine your site receives, averaged over the year — most places fall between 3.5 and 6. It is not the same as daylight hours: a 12-hour day may only deliver 5 peak sun hours because morning and evening light is weak.

The rating is measured in laboratory conditions the roof rarely sees. Heat is the big one — panels lose output as they warm — plus dust, wiring and inverter losses, and imperfect orientation. That is the ~20% system loss in the calculation, and why a “5 kW” array rarely shows 5 kW on the meter.

The specific yield — kWh per year per kWp installed — is how installers compare sites. Around 1,000–1,200 kWh/kWp is typical for the cloudier northern states and Pacific Northwest, 1,400–1,700 for sunny regions like the Southwest, Arizona, California and Texas. If your system delivers well below the local norm, look for shading or faults.