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MQT 21 Potential-Induced Degradation (PID)

Level: AdvancedActively updated

PID test conditions and pass criteria, plus the mechanisms and prevention of PID

Articles

• PV PID Series #1: High Voltage Difference, the Entry Ticket to PIDWhatever the type, PID needs one precondition, a high voltage difference between the cells and the grounded frame. Using a simplified 30-module string, this article maps cell-to-ground potentials under floating, negative-grounded and positive-grounded systems, and explains why negative grounding has fallen out of use.
• PV PID Series #2: PID-s, PID-p and PID-c, the Root Causes of Three Kinds of PIDWith the same "high voltage difference" ticket, different cells walk through three different doors - sodium piercing the p-n junction, charge throwing off the passivation layer, and electrochemical corrosion leaving permanent damage. This article explains the mechanism, symptoms and reversibility of each type, plus a three-step way to tell them apart.
• PV PID Series #3: Temperature, Humidity, Glass and Encapsulant, the Other Half of What Decides PIDSame voltage, same string position, yet some modules stay healthy for ten years while others degrade in two or three. Starting from "leakage current ≈ voltage difference ÷ loop resistance", this article explains the roles of temperature, humidity, glass, encapsulant and cell coatings, and the three lines of defence against PID at cell, module and system level.
• PV PID Series #4: How Is PID Tested, and How Should You Read a Test Report?How does a lab find out whether a module resists PID? This article explains the chamber and foil methods, the differences between IEC TS 62804-1 (2025 edition), IEC 61215-2 MQT 21 and third-party extended testing, why UV light is being added to tests, six questions to ask of a PID report, and the latest data from the Kiwa PVEL 2026 Scorecard.
• PV PID Series #5 (Finale): Suspected PID in a Plant - How to Investigate, Recover and Prevent ItYields are quietly slipping - is it PID? This article covers three telltale signs (position, time, low light), a four-step field check (data, voltage, infrared, confirmation), four remedies and what to expect from them (night-time recovery, inverter protection, negative grounding, module replacement), an anti-PID checklist for new projects from procurement to O&M, and a recap of the whole PID series.