Long term degradation and manufacturer warranty for such is indeed a factor. There's a number of poly and monocrystalline Si 156mm cell based PV modules now which are warranted for something like 83% of their original STC rated output after 25 years. Of course you have to also believe that the manufacturer will still be around in the same corporate form in 25 years and able to honor its warranty.

This certainly may not be the case if you follow PV industry news and are aware of how many PV panel manufacturers have formed as startups and gone bankrupt in the last 8 to 14 years.

edit: the other reply here in the thread asks:

> but can be replaced as a layer every, say, 5 years or so? It's not trivial maintenance, but you have to do some maintenance on the panels anyway

Typical mass market PV panels are cells permanently encapsulated behind glass sandwiched with a back sheet, it is not practical or possible to replace a layer or modify the cells once they're assembled into a panel. The only maintenance done on a series of ground or roof mounted typical PV panels is to wash them.