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.
If you work in the solar panel installation business long enough you ll inevitably come across solar panels with strange brown spots.
As a result the voltage can rise which leads to a hotspot in the soldered points and or a cell.
The current output from the whole panel is limited to that passing through the weakest link cell.
About half of the panels appear to have burn marks of an unknown origin.
When you use a charge controller that is what it is doing anytime the battery bank is full tapering off the.
Typically they are in the same exact place on multiple solar panels.
This is a sign of a burnt terminal.
You will need to replace all metal parts in the terminal.
Hotspots on panels are mainly caused by badly soldered connections or are a result of a structural defect in the solar cells.
These have been seen on panels manufactured by smaller suppliers and large distributors alike.
A burnt terminal can be cause by wiring too many panels to one 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.