Solar output comes down to one relation: Energy = Array size × Efficiency × Sunlight × Performance ratio. The array and panel efficiency are yours to set; sunlight (irradiation) comes from long-run climate averages for the chosen location; the performance ratio folds in the everyday losses — heat, wiring, inverter conversion, dust — that keep a real system below its theoretical maximum.
A 6 kW residential array in a sunny climate might see 5.5 peak-sun-hours a day. At a typical 80% performance ratio, that's roughly 6 × 5.5 × 0.8 ≈ 26 kWh a day — about 9,600 kWh a year, before accounting for winter/summer swing or shading.
Panels generate the most power when sunlight hits them close to perpendicular. A due-south array (in the northern hemisphere) tilted near the local latitude catches the most sun over a year; east/west-facing or flat arrays trade some annual total for a flatter output curve across the day.
The fraction of a system's theoretical output it actually delivers once every real-world loss is accounted for — heat derating, wiring resistance, inverter conversion, soiling, and small mismatches between panels. A well-installed system typically lands around 75–85%.
This tool uses baked-in long-run climate averages, not live weather, satellite imagery, or site-specific shading. A tree, a chimney, or an unusually cloudy year can shift real output meaningfully above or below the estimate — which is exactly why installers run a proper site survey before quoting.
Mostly through irradiation — how much sunlight a location receives on average — and secondarily through temperature, since panel efficiency drops slightly as they heat up. Two identically sized systems in different climates can have meaningfully different annual yields.