I have 2 KW implemented of a 3 Kw array of First Solar FS-50 panels, they have been in use for 2 years. In the first year they produced far in excess of their rating.
When first installed I generally saw about 2.25 Kw, with the highwatts being 2687 logged by the MX60, this year I am lucky to see 1.4 Kw, which is only 70% of their rated output. I hope they don't degrade much more. First Solar will not stand behind the power output warranty because they don't sell them in the USA and I was not the original purchaser, however I was the first to implement them. They are CdTE thin film (Cadmium Telluride) so I don't know how their degredation compares to amorphous Si. They are only about 7% efficient light to wire to start, but they are to about 6% now.
Dustin B. Collen
Mad River Wind and Hydro