I can see some browning or yellowing on my solar panel, what is it?
Yellowing or browning is typically caused by an uncontrolled chemical reaction between materials causing the (usually) white plastics to turn yellow or brown.
It has also been known to occur on the surface of the cell, in a chemical reaction between the chemicals on the surface of the silicon cell and the chemicals used to treat the glass. Yellowing and browning usually occurs in the first few years of exposure to sunlight. The jury is still out as to the long term effect on performace when panels have turned yellow or brown, but naturally it's not an attractive look. It is a sign that something uncontrolled is happening. If you had a solar system installed and when you are assessing the panels from time to time, look very closely to make sure there is no evidence of yellowing or browning.
In the photo below, the brown spot is the start of corrosion, due to water penetration in the panel.