Potential Induced Degradation (PID) in PV plants


Most PV modules are typically connected in series to form a string to match with the inverter voltage. The typical voltage at module level is about 30V and at Inverter level is about 300-700V and accordingly the number of panels in series and parallel are decided. Potential Induced Degradation (PID) is the degradation of modules due to the leakage current between the solar cells and panel frame surface. PID is more prone to the cells having the negative potential. In a typical string the cells are at a voltage level of -200V at the negative end o fthe string and +200V at the positive end of the string. The aluminium frame of the panel is grounded due to security reasons, and the high potential difference between the module frame and the negative cell voltage causes the leakage current flow from the cell surface to the module frame and subsequent to the ground, which results in the degradation of the cell as well as reduced generation.

To prevent PID, the solar cells must not have a negative voltage relative to their surroundings. Grounding the negative pole of the PV array resolves this problem. A PV Offset Box can be used for transformerless inverters that cannot be grounded.PID

String potential

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4 responses to “Potential Induced Degradation (PID) in PV plants

  1. Conventional crystalline silicon-based modules have typically have been PID tested for 5-7 days at 65 – 85 degrees Celsius and up to 85% relative humidity using the standard 1,000 volts of system voltage bias.

  2. Panasonic’s high-performance ‘HIT’ PV modules have shown no sign of being affected by potential induced degradation (PID) characteristics after testing took place at the Fraunhofer Center for Silicon-Photovoltaics (CSP).

    A special PID testing regime was developed by the Fraunhofer CSP to account for Panasonic’s unique HIT solar modules. The test developed included both negative and positive voltages, whereby 5 modules were subjected to +1,000 volts for 48 hours at a temperature of 50 degrees Celsius with 50% relative humidity and 5 modules at -1,000 volts over 48 hours. According to the company, no evidence of PID was observed.

    The Panasonic HIT photovoltaic modules exhibited no sign of degradation under such conditions. Of the ten modules used for the test, five were subjected to +1,000 volts, and the other five to -1,000 volts over 48 hours. The results show no evidence of PID.
    http://www.pv-tech.org/news/panasonic_hit_solar_modules_pid_tested_by_fraunhofer

  3. You can also prevent PID via the Off Set Box which will generate “over Night” a field 600-1000V DC between
    Minus and Frame or Positive and Frame .
    Power will be back after several days/Nightsessions but of course it should be prevented at Module / Waferlevel
    if possible.

    Cheers
    Andreas

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