Lifetime of Solar Cells
How long do solar panels last? Long.
25-30 years. 
But, it's really longer. At 0.8% annuaul decrease, they drop to 80% of their capacity after 25 years.
That means, as long as the panels are not physically damaged - they continue producing useful electricity for decades after.
Since 2012, panels have 0.5% annual efficiency drop. 
Thus, after 50 years, they are still 75% of their original efficiency! This is as close to lifetime design as it gets.
Manufacturing energy payback time is about 6 months. 
Panels installed in the 80's are still operational - 
Peak sun hours are defined as the integrated number of kWhrs per day. 
But, it appears peak sun hours are integrated over time - as daily avg in MO as an example is 4.7 kwhr/m2/day. 
Annually - 5kwhr/day *355 is about 1700 kwhr/yr - and you get 2x the sun in the desert than in cold temperate zones.