Module discoloration

[pv_n00b]

There are a number of processes that can cause discoloration over time that do not impact production. I've heard from a couple of PV contractors over the years about a customer who wanted modules replaced because of discoloration and that is just not covered by the module warranty.
If the production is impacted enough to qualify for a warranty replacement go that route, otherwise I would not do anything but monitor it.

 

[PWDickerson]

The way the two circular marks are perfectly spaced from centerline of the module indicates it is from manufacturing. I hear you saying that it is definitely under the glass, but I am still suspicious that it might be surface mineral deposits. Did you try vinegar?