I don´t think orientation is any problem as this is fixed I mean sun is always same place and panels also so is predictable. It may be weather and shadow from the clouds one of the problem but this is also kind of statistically predictable for a fixed place.
In my opinion main problem is cleaning, as it decreases a lot the efficiency and it is very costly to clean the panels frequently.
About the quality of the solar panels use to be warrant and the loss of efficiency predicted and inset on the financial calculus. So after 10 years maybe the efficiency of the panels is low because of silicon degradation but as this loss of eficiency is predicted on the financial plan when the investment is done is not a problem. the problem is more the dirt on the panels that maybe is not predicted on the financial model.