One shaded panel drags down the string

Shade doesn't reduce solar output proportionally. It's worse than that, and how you wire matters enormously.

Series means current flows through every panel. Shade one and it becomes a bottleneck. One branch across one corner can cost far more than its share.

Bypass diodes limit the damage. Modern panels have them built in: they route current around a shaded section. Partial shade costs you that section rather than the entire panel. Helps a lot — doesn't make shade free.

Parallel is more shade-tolerant. Each panel does its own thing, so a shaded one only costs you that panel. The tradeoff is higher current and thicker wire.

What this means practically:

On a rig, where shade moves constantly, parallel wiring or per-panel optimization is more forgiving. It's also why "park in the shade to stay cool" and "get good solar" are in direct conflict.

On a fixed site, survey shade across the whole year before mounting. December sun angle is dramatically lower than June.