There are two factors that can affect the performance of a solar panel. They are
- Internal faults
- External disturbances
They occur due to the shorting of the modules that make up a panel. This causes a dip in the current and voltage readings leaading to less overall power output.
They are a result of naturally occuring external factors that lessen the intensity of sunlight(irradiance) that falls on the surface of the solar panels. This also causes dips in the current and voltage values again resulting in a dip in overall power output.
The change in readings due to internal faults can often be confused with that of external disturbances. It is the internal faults only that need attention. The external disturbances can be ignored as it may just be a passing cloud for example and should not be detected as a fault which requires attention.
To identify only the internal (Line-to-Line or LL) faults that can occur in a panel and be able to ignore the reduction in power output due to external (shading) disturbances.