They lose their rated output after 25 supposedly, the problem with solar pv right now is that manufacturers might not be around that long as so many companies are pumping them out and the cards haven't fallen yet on who will still be in business in a couple decades.

The same thing happens in the lighting industry, cfls, LEDs, any hot technology has a bunch of manufacturers enter the industry and after a while most close their doors leaving the customer with a useless warranty