A bypass diode is a small component built into your panels. Its job is to route current around a shaded group of cells so that shade doesn’t bottleneck the whole string.

The problem comes when a fixed obstruction puts the same shadow in the same place every day. The diode keeps activating, the heat builds, and eventually it can fail. A failed diode either causes permanent partial output loss, or creates a hotspot that poses a fire risk. Sustained hard shading can also void your panel warranty.