In one line
Power loss caused by leakage currents driven by the voltage difference between cells and the grounded module frame — capable of costing 20% or more of array output within a few years.
What it means
In a long string, modules at the ends sit at a large potential relative to the grounded frame — up to ±1,500 V in modern systems. That potential drives sodium-ion migration from the glass through the encapsulant to the cell surface, shunting the emitter and destroying the cell's ability to separate charge. Heat and humidity accelerate the process dramatically, which is why PID surfaces first in tropical and coastal installations. The good news is that PID is both preventable and often reversible: PID-resistant cell and encapsulant designs are now standard from tier-one manufacturers, and applying a positive voltage overnight with a PID-recovery device can restore much of the lost output if caught early. Diagnosis is by I-V tracing (shunt-type distortion) confirmed with electroluminescence imaging, which shows characteristic dark cells near the frame.
Worth knowing
- Driven by system voltage, so worst at string ends — a spatial pattern that aids diagnosis.
- Heat and humidity accelerate it sharply.
- Often partially reversible with overnight voltage recovery.
- Modern PID-resistant designs and negative grounding largely prevent it.
Field notes
- 1Check whether losses correlate with position in the string — a gradient from one end is the PID signature.
- 2Confirm with electroluminescence: PID-affected cells appear dark, typically starting at cell edges nearest the frame.
- 3Ask suppliers for IEC TS 62804 test results rather than accepting a marketing claim of 'PID-free'.
Common mistakes
- Attributing PID losses to normal degradation and quietly accepting years of lost yield.
- Ignoring inverter grounding topology, which determines whether the array sits at positive or negative potential.
Frequently asked
What causes potential induced degradation?
Leakage current driven by the voltage difference between the cells and the grounded frame, which moves sodium ions from the glass into the cell surface and shunts it. High temperature, high humidity and high system voltage all accelerate the mechanism.
Can PID be reversed?
Frequently, yes. Applying a positive voltage to the array overnight with a PID-recovery device can restore a substantial share of the lost output, provided the degradation is caught before it becomes permanent.
Sources
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