Potential-Induced Degradation (PID) in Solar Modules

Accelerated Stress Test (IEC 62804)

System voltage bias -1000 V

Module temperature 60 °C

Relative humidity 85 %

Test speed ×1

Live Readouts

Elapsed stress time

0.0 h

Leakage current

0 µA

Avg. shunt resistance R_sh

3000 Ω

Module power loss

0.0 %

How it works

Potential-Induced Degradation (PID) is a leakage-driven power loss seen in grid-tied c-Si modules. When the array's negative terminal is far below ground (common with transformerless inverters), sodium ions from the soda-lime cover glass drift under the field through the EVA/glass interface toward the grounded aluminum frame — or, for a negatively biased array, migrate from glass into the cell's anti-reflective coating near the frame edge, forming a shunting path that polarizes the cell surface.

The ion front follows a drift-diffusion law from a fixed-concentration boundary at the frame edge, whose classic solution is the complementary error function:

C(d,t) = C0 · erfc( d / (2·√(D·t)) )
D(T)   = D0 · exp(−Ea / (kB·T))     [Arrhenius]
D_eff  = D(T) · (|V|/Vref) · (RH/100)^1.5

Here d is distance from the frame edge, t is elapsed stress time, D(T) is the Arrhenius ion diffusivity (Ea ≈ 0.8 eV, matching reported PID activation energies), and the effective rate is boosted by system voltage (drift field strength) and humidity (surface ionic conduction on the glass, per IEC 62804's damp-heat/bias protocol).

Voltage bias — sets the electric field pulling Na⁺ toward the cells; more negative accelerates the front.
Temperature — enters through the Arrhenius factor; every +10 °C roughly doubles the diffusivity here.
Humidity — raises glass-surface conductivity, supplying more mobile ions.
Cells nearest the grounded frame have the shortest leakage path and degrade first, exactly as PID appears in the field — edge rows go first, the center lags behind.

Consequences modeled: local shunt resistance collapses, module power output drops, and array leakage current (through the encapsulant to the frame) rises — the same three symptoms field technicians measure with a Suns-VOC/EL scan and an insulation-resistance meter.

Healthy cell PID-degraded cell Na⁺ ion

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