PID (Potential Induced Degradation): Causes and Prevention

Quick answer

PID (Potential Induced Degradation) is power loss in PV modules caused by leakage current driven by high voltage between the cells and the grounded frame. Modules are screened for it with the IEC TS 62804-1 test. Designers manage PID risk through module selection, string voltage, inverter grounding and PID-recovery functions, especially in hot, humid sites.

PID Mechanism

High voltage between cells and grounded frame.
Humidity + heat enable ion migration through encapsulant.
Ions accumulate at cell-glass interface.
Shunt resistance decreases → Pmax drops.
Voc drops; FF drops.

Prevention

PID-free / PID-resistant modules: certified per IEC 62804.
Recovery systems: nightly reverse-voltage application (some inverters).
Grounding strategy: PID-N (negative ground), the specific bonding and grounding scheme is what actually gets documented on the module frame bonding detail and the project’s electrical drawing set.
Encapsulant quality: high-quality EVA, POE backsheets.

Detection

IR thermography during operation.
I-V curve tracing.
Power output monitoring (sudden drops).

Why String Position Matters

PID is not evenly distributed across a plant, it concentrates wherever the voltage-to-ground stress is highest, which in a long series string is almost always at the bottom of the string (for negatively grounded systems) or the top (for positively grounded systems).

A 1500V central-inverter design puts far more modules at high voltage-to-ground than a string-inverter layout at 1000V, which is one reason PID risk is a factor in string-sizing decisions and not just a module-datasheet checkbox.

Humid, hot climates accelerate the ion-migration mechanism described above, so the same module and string length that shows negligible PID in a dry climate can lose meaningful output within a couple of operating seasons in a coastal or monsoon-heavy site, this is why field monitoring during the first year, not just the module’s IEC 62804 certificate, is what actually confirms whether PID is under control on a given plant.

Key Takeaways

PID = leakage-current-driven module degradation.
Can cause 20-50% power loss in months on unmanaged systems.
TOPCon and HJT more PID-resistant than PERC.
Specify PID-resistant modules per IEC 62804.
Use PID-recovery systems on long strings in humid/hot climates.

PID losses that go undetected in year one show up later as a gap between modeled and actual generation, which is exactly the risk a bankable yield report is built to price in, see P50 / P90 / P99 in Solar Yield Reports for how uncertainty from module-level effects like PID factors into the exceedance-probability numbers lenders rely on.

Because PID risk is highest in long, high-voltage strings, it’s worth reviewing alongside the degradation rate assumptions used in the underlying yield simulation, since both feed the same 25-year output forecast.

On the electrical side, the grounding scheme chosen to mitigate PID (PID-N or PID-P) has to be documented consistently with the plant’s module frame bonding and grounding details, which is where our Electrical CEIG Drawings work overlaps with module-quality decisions made earlier in procurement.

Frequently Asked Questions

4 commonly searched questions about PID (Potential Induced Degradation).

What causes PID in solar panels?

PID develops when cells sit at a large voltage relative to the grounded frame, typically at the negative end of long strings. Heat and humidity raise leakage current through the glass and encapsulant, letting sodium ions migrate into the cells and shunt them.

How can PID be prevented or reversed?

Prevention starts with modules that pass IEC TS 62804-1 PID testing and quality encapsulant. Some inverters offer negative-pole grounding or night-time PID recovery that applies an offsetting voltage. Early-stage PID is often partly reversible; severe shunting usually is not.

Are TOPCon and HJT modules less prone to PID than PERC?

Generally yes. Many n-type TOPCon and heterojunction modules show lower PID sensitivity than older p-type PERC designs, but susceptibility depends on the specific cell, glass and encapsulant combination. Check the manufacturer's PID test report rather than relying on cell technology alone.

How is PID detected in an operating solar plant?

PID usually shows as falling string output concentrated at the negative end of strings. Electroluminescence imaging reveals darkened shunted cells, and infrared thermography or I-V curve tracing can confirm the pattern. Documented evidence matters if a warranty claim is filed with the module maker.

Need engineering-backed solar designs?

Heaven Designs prepares solar drawings, structural calculations, electrical engineering documents, and project-specific permit plan sets.

Solar 3D Pre-Design Electrical CEIG Drawings

Get a project quote See all services