The cosine rule
The output readout uses the angle between incoming sunlight and the panel's face. When light hits at an angle, the same beam spreads over more panel area, so output falls with the cosine of that angle. It ignores clouds, temperature and wiring losses, which is why it is shown as a percentage of the best case.
Why farmers are interested
Partial shade can lower plant heat stress and soil water loss in hot, dry places, and panels can give a second income from the same acre. The research is still young: results depend heavily on the crop, the climate and the layout, which is exactly what this model lets you play with.
Look for: with tracking on at midday, output stays near its maximum while the shadow band sits directly under the rows. In early morning, shadows stretch across the gaps.