Temperature
The efficiency of solar panels that are exposed to high temperatures may decrease over the years. Increased temperature causes thermal stress on materials, so photovoltaic cells may experience a faster degradation process.
Shade
If the solar panels are partially shaded by trees, buildings, or other objects, the performance of the entire system could be affected. This is because the panels in series are connected to each other, so the performance of one panel affects the others.
Dirt
Dirt, such as dust, leaves, or other debris acts as a barrier that obstructs sunlight and decreases efficiency. If not cleaned regularly, it could stick to the surface, which could cause permanent damage.