Solar cells are designed to generate an electric current when the sunlight shines upon them.
When the current flows through the solar cell strings within panels, the resistance in cells converts the current into heat losses.
Any imperfection in solar cells, such as cracks, poorly soldered joints, and mismatches, lead to higher resistance and become hot spots in the long run.
The long term effects of hot spots include burnt marks that degrade solar cells and backsheets and may eventually lead to fires if left unchecked.