Some commenly found faults during O&M of solar PV projects: Diode failure

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A bypass diode is an electronic device that restricts current flow, primarily to one direction. Bypass diodes are provided in the PV modules to protect the PV cells from overheating. The overheating in the PV cells occurs due to the shading on the cells and a continued shade on the PV cell puts a resistance on the current flow in the cell connected in series with the other cells, which cause overheating in the module at the cell location. The bypass diode will allow the cell string non functional and will protect the cell failure. The Bypass diode also helps in protecting the PV module through the lightning. If any bypass diode in the PV module fails it will lead to the reduced voltage in the PV module  drastically.  If the module is in a 600 V string, the diode failure will lead to the reduced string voltage of the order of 570 V and this will influence the MPPT operating point of other strings and will affect the performance of other strings connected to the single inverter. A bypass is selected based on the current rating of the PV module and should be higher than the PV module max current.



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