The article explains about the cause & effect of Potential Induced Degradation, Snail Trail & Long Time Damp Heat as quality issues in solar PV modules.

1.
3
Common
Solar
Module
Quality
Issues
to
Understand
&
Act
On
Potential Induced Degradation -
Potential Induced Degradation (PID) occurs when the module’s voltage potential
and leakage current drive ion mobility within the module between the
semiconductor material and other elements of the module (e.g. glass, mount and
frame), thus causing the module’s power output capacity to degrade. The ion
mobility accelerates with humidity, temperature and voltage potential.
To bring down the effect caused by PID, manufacturers need to improve the
insulation of EVA and refractive index of silicon nitride layer of solar cell. Some
suppliers ignore PID-free demand of solar cell, and partially pursue module’s high
efficiency.
Snail Trail -
Snail Trail is caused by solar cell grid discolour and till now the mechanism is still
unknown. Main reason is that moisture transmits through the back sheet, EVA
and solar cell, and reacts with silver on cell grid and EVA. Choosing the back
sheet with low moisture transmission could prevent Snail Trail.
Also, the back sheet will turn yellow if the front EVA lets UV transmit. We should
strictly control light transmission in EVA selection.
Long Time Damp Heat -
Solar panel power output will degrade after long-time damp heat (DH). After DH,
heat spots might appear in the corresponding position of cell back-electrode in
short-circuit condition, which can even cause 70% power degradation.
Manufacturers ignore the importance of back electrode, to lower cost at the
expense of using little silver. In current IEC standard, module power degradation
must be less than 10% after module is subjected to long time damp heat of 1000
Hours.