Some of the panels I have in my setup are from the early 80s and they still generate about 90 of their rated output. I have my panels mounted on a pole so I turn them around several times a day to face the sun. this helps with a battery setup because you can get charging for a longer time rather than higher amps for a short time period. I also have to scrape/brush the snow off them (sometimes several times a day).
-James
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