The New York Times published an interesting article about module reliability and degredation problems, quoting several PVPMC members. The article can be seen here: http://nyti.ms/16nXR7p.
One interesting and relevant fact cited is a study by Meteocontrol of 30,000 PV systems in Europe, which found that 80% of these systems are underperforming expectations. This finding indicates to me that predicting module and systems degradation and defects is a critical need in the industry and care should be made to use the best data and models available when predicting PV performance.