Environment & Energy

There are 5 solar installations in Switzerland that are still producing after 30 years.

https://www.chemistryworld.com/news/30-year-old-solar-panels-still-going-strong/4022052.article

Solar panels lose less than 0.5% a year which is why the warranty for a good quality panel is 80% output after 25 years.

For a commercial solar farm there would come a point where they would be replaced. It's after they have been fully depreciated and new technology (just like flat screen TV's - they are on a constant improvement cycle) makes that investment a no brainer. It would be really simple - unlike upgrading a wind farm - because new panels would probably be the same size. New windmills are bigger so the spacing would be different.

edited to add:

From asking Google - specs from solar panels from 30 years ago

Solar panels from 30 years ago, circa the early 1990s, typically had lower efficiency ratings, around 14-15%, and lower wattage, with panels often in the range of 150-200 watts or less, compared to modern 22-24% efficient, 400-500+ watt panels. While still reliable and capable of functioning, their performance degradation rate was around 0.5-0.8% annually, and their higher cost per watt compared to today's panels made them a significant investment.