They should last for many years. I'd think a lot of the problems are due to weather, storms, snow load, and UV degradation. I don't think there are any internal electronic degradation issues, aside from the UV problem.
Solar panels must withstand heat, cold, rain and hail for many years. Many crystalline silicon module manufacturers offer a warranty that guarantees electrical production for 10 years at 90% of rated power output and 25 years at 80%.
The plastic coating on the cells can turn opaque over the years.
Many natural and synthetic polymers are attacked by ultra-violet radiation and products made using these materials may crack or disintegrate (that is,if they are not UV-stable). The problem is known as UV degradation, and is a common problem in products exposed to sunlight. Continuous exposure is a more serious problem than intermittent exposure, since attack is dependent on the extent and degree of exposure.
Since solar modules have no moving parts, they actually can last a pretty long time. Typically, solar panel manufacturers issue a 20 or 25 year warranty on panels, but most installers say they can endure more than 40 years with proper care.
Andy Black, one of the leading solar financial analysis experts and instructor, recently published his report on the lifespan of solar panels. His analysis showed that the first solar panels manufactured about 40 years ago are still creating power at about 80% of their original power. From that study combined with his other analysis, he concluded that most solar panels will lose about a half percent a year in efficiency.