This is because a pv solar panel is made up of a string of individual solar cells connected in series with one another.
Burn marks on solar panels.
Mark having solar panels in the sun without a load on them should not damage them.
These have been seen on panels manufactured by smaller suppliers and large distributors alike.
The current output from the whole panel is limited to that passing through the weakest link cell.
Hotspots on panels are mainly caused by badly soldered connections or are a result of a structural defect in the solar cells.
This is a sign of a burnt terminal.
If even a small section of a photovoltaic panel is shaded for example by the branch of a tree there is a very significant drop in power output from the panel.
When you examine the terminal you will more than likely find signs of oxidation.
Typically they are in the same exact place on multiple solar panels.
About half of the panels appear to have burn marks of an unknown origin.
Just like a car battery solar panel system battery terminals can burn out.
You will need to replace all metal parts in the terminal.
As a result the voltage can rise which leads to a hotspot in the soldered points and or a cell.
If you work in the solar panel installation business long enough you ll inevitably come across solar panels with strange brown spots.