The wattage printed on a solar panel is a standard rating used to compare panels. It is not a promise that the panel will produce that exact power throughout a real day.
Real output changes because the sunlight, panel temperature, angle, equipment, and surroundings do not stay fixed.
What does the panel rating tell me?
The rating gives you a consistent starting point. A 400 W panel has a higher rated output than a 200 W panel under the same standard test conditions.
That makes the label useful when describing the array. SunPlanner uses panel count and wattage as part of the configured system. The label alone does not predict daily energy.
Why does output change during the day?
The sun moves, clouds pass, panel temperature changes, and the angle between the light and the panel shifts. A fixed panel may have a useful window in the middle of the day and much weaker output earlier or later.
Daily energy depends on the whole production curve, not one moment near the strongest part of the day.
Where do system losses fit?
Power also moves through wiring, controllers, inverters, and other equipment before it becomes useful energy. Dirt, aging, mismatched equipment, and installation choices can add more difference between the label and the final result.
SunPlanner includes editable efficiency-loss and temperature-derate settings. Those are planning inputs. Use the equipment instructions and measured system information when choosing the values.
Does SunPlanner calculate shade?
No. Sun Finder shows sun geometry and panel direction for a place and date. It does not calculate tree height, terrain shadows, or obstruction shading.
You judge those conditions from the site. If repeated real production stays below the prediction, calibration can learn the consistent gap without claiming which obstruction or equipment loss caused it.
How does calibration help?
Calibration compares the saved prediction with the actual end-of-day production you enter. After three usable readings, the learned factor can begin affecting later forecasts.
That does not turn the forecast into a meter reading. It gives the planning estimate a history tied to the configured system instead of leaving it at the starting assumptions forever.
What number should I plan around?
Use the daily estimate, expected range, confidence, and production history together. The panel rating describes the equipment. The forecast describes what the configured array may produce under the conditions ahead.
If the decision matters, leave room below the highest estimate. The range exists because weather and real installations do not behave like a fixed label.