Hot Spots on Solar Panels are a really big issue
Hot-spot heating can actually make or literally BREAK your solar panels. This occurs when there is one low current solar cell in a string of at least several high short-circuit current solar cells, as shown in the figure below.
One shaded cell in a string reduces the current through the good cells, causing the good cells to produce higher voltages that can often reverse through the bad cell.
If the operating current of the overall series string reaches the short-circuit current of the "bad" (or shaded) cell, the overall current becomes limited by the bad cell.
The extra current produced by the good cells then forwards their voltage through the good solar cells. If the series string is short-circuited, then the forward bias across all of these cells reverse biases the shaded cell.