One shaded cell can kill your whole panel's output

Solar panels aren’t like a row of buckets filling independently. Most are wired so that one shaded cell drags down the output of the entire string.

Park your RV under a tree for afternoon shade and your 400W array might produce less than 100W — not because of cloud cover, but because three cells are in shadow.

This is why bypass diodes matter, why MPPT controllers outperform PWM in partial shade, and why panel placement deserves more thought than panel wattage.