PID and LID degradation in solar panels: what they are and how to prevent

You buy a 410 W panel. After 1 year it produces 397 W. After 25 years: 330 W. That's degradation, and it has two distinct modes: LID (fast) and PID (slow and dangerous).

LID: Light Induced Degradation

First hours/days of sun exposure reorganize silicon crystal defects. Loss 1-3% in month one. Stabilizes after. The 'fine print': 410 W panel quickly becomes 400-405 W real.

PID: Potential Induced Degradation

Much more dangerous. Voltage between cells and metal frame causes ion migration (sodium from glass into silicon). Bad conditions: up to 30% loss in 5-10 years. Hard to repair.

What causes PID

Three combined factors: 1) high panel-frame voltage (>600 V typical on long string). 2) High humidity (>80%). 3) Heat (>104 °F). Tropical and coastal climates worst-affected. Inland: very low PID.

How to prevent PID

1) Buy 'PID-resistant' panels (all modern Tier 1 are). 2) Ground the negative pole of the array (some inverters do automatically). 3) Avoid too-long strings (>20 panels).

How to recover PID if already happened

Apply reverse voltage to panel (24-48h): ions migrate back. Commercial devices exist (Fronius Eco-PID, SMA SC PID Box) doing it automatically every night. 5+ years with the problem: partially irreversible.

Typical degradation rates

Tier 1 mono PERC: -0.5%/year. TOPCon: -0.4%/year. HJT: -0.25%/year. Typical warranty: 80-87% power at 25 years. Yours loses more: PID or defect. Measure with multimeter, compare to year one.

To detect issues, read hot spots on panels.