Solar panel surface goes foggy over time [+solution]

[kni]

Not a moteino issue, but I am sure some of you have experienced this.

Back in the winter of 2017, I deployed a couple of solar powered moteino projects.
These projects were powered by inexpensive panels you can buy off Amazon and EBay.

After just a year, the surface of these cheap panels has gone foggy, so much so that it no longer provides sufficient power. No doubt the protective surface is not UV resistant.  Here is a photo to show you what I mean:



Yeah, you get what you pay for, but what I'd really like to learn is what feature to look for in a solar panel to avoid this problem.
Can anyone speak to this?

For the time being, I am using these:
https://www.amazon.com/gp/product/B07DJCPKQF/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

They seem to be lasting, come with mounting hardware, and also regulate their voltage to < 5.25 volts which is nice. At $25 a pop though, it is hard to justify these for some of my smaller projects.

[Felix]

This is similar to the yellowing on plastic headlights on various cars. There are chemical+abrasive solutions to fix that.
Out of curiosity - have you tried to polish away the top layer and see if it becomes clear again? I wonder if all the material is degraded or just a top layer to a certain depth.

[ChemE]

This is similar to the yellowing on plastic headlights on various cars. There are chemical+abrasive solutions to fix that.

I just did this project on my 15 year old Kia actually.  A luxmeter confirms that I'm now getting 3x the luminous intensity as prior to polishing and they look brand new.  All I did was wet sand with 400 grit sandpaper, followed by 600/1000/3000/5000/7000/3M Scratch Remover.  Wet sanding is as simple as spray a bunch of water and sand.  The sandpaper should be suctioned to the lens by the water.

[Lavenoh]

Are there any chemical/abrasive solutions that you would recommend over others? Or do they all generally do a fairly good job. Looking to clean mine.

[kni]

Found this article when I was looking for something else:
https://www.instructables.com/id/Repairing-Polymer-Degradation-on-Solar-Cells/