What are these strange brown spots on my solar panels?

Brown Spots on Solar Panels

What are these strange brown spots on my solar panels?

If you work in the solar panel installation business long enough, you’ll inevitably come across solar panels with strange brown spots. Typically, they are in the same exact place on multiple solar panels. These have been seen on panels manufactured by smaller suppliers and large distributors alike. Unfortunately, the cause for these strange spots has yet to be confirmed, however, there are a few suspects we’ll be discussing in this post. As always, this is for informational purposes only and it is up to you, the installer, to confirm whether or not you will be using these panels on a customer’s home.


It’s possible these could be blemished modules or factory seconds. Blemishes can be visual or electrical related and usually have a sticker on the back identifying which type. Did you get a really good deal on those panels? If you want to be double sure, try to locate that sticker on the back. If you’re not able to, you may want to speak with your supplier directly and ask about the blemished modules. Some speculate these brown spots could simply be soldering burns and will work as expected. If they are indeed blemished modules, they could be factory seconds which you should be informed of.

Multicrystalline Mass Production

The strange brown spots could be the inherent result of the manufacturing process used to mass produce multicrystalline cells. Based on the fact these types of spots haven’t been seen on monocrystalline cells, it may be safe to assume it is directly related to the multicrystalline process. You can read more about the production process here.


Corrosion from water penetration.

Corrosion from water penetration.

Chemical Reaction

Lastly, the browning could be caused by an uncontrolled chemical reaction between materials affecting the white plastics. It’s also been seen 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.

What do I do?

The long term effect on performance is still unknown but naturally, it’s not an attractive look. It’s a sign that something uncontrolled is happening. If you’ve received panels from a supplier/distributor, we recommend checking them thoroughly for any sign of browning/yellowing and contacting them directly if there are any questionable signs.

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