What is PID?
Potential Induced Degradation (PID) is due to a high potential difference between the semiconductor material (cell) and other parts of the module (glass, mount or aluminium frame). This potential difference creates a current leakage, resulting in the migration of negative and positive ions. Negative ions flow out via the aluminium frame, whilst positive ions (sodium ions) migrate to the cell surface. These “pollute” the cell by reducing its photovoltaic effect, leading to power losses. PID effects can be responsible for power losses of up to 20% and the effects are not immediately noticeable – it can take several months to a few years.
Causes of PID
The PID is closely linked to environmental factors (humidity, temperature) and the configuration of the PV system (grounding, module and cell type).
Environmental factors : The ion mobility accelerates with humidity and temperature, increasing the PID effect. However, these are parameters that cannot be influenced.
System configuration : The voltage potential and sign of the module have an impact on the PID occurrence. It depends on the position of the panel in the array and the system earthing. Most of the time, PID is related to a negative voltage potential to earth, the more negative panel will be the panel at most risk.
Module composition : Recent research has shown that the chemical composition of glass, encapsulating material or anti-reflective coating, has a considerable impact on the occurrence of PID. For example the sodium contained in the glass is a cause of PID. The resistance to moisture of the used material is also a determining factor since it increases conductivity and therefore, ion migration.
By Clément Vinet, Asset Manager