CSLB C-46 Solar ContractorPhotovoltaic System InstallationHard
A solar technician is inspecting a PV array and notices a significant drop in power output from a specific string. Upon testing, they find that the open-circuit voltage (Voc) of the string is normal, but the short-circuit current (Isc) is significantly reduced. Which of the following conditions is the most likely cause?
- AA shorted bypass diode within a module.
- BAn open circuit in one of the series connections.
- CHeavy partial shading on a portion of the string.
- DAn inverter fault causing DC input issues.
Show answer & explanationAnswer & explanation
Correct answer: C. Heavy partial shading on a portion of the string.
Heavy partial shading reduces the current output of the affected cells/modules. While bypass diodes might activate to shunt current, the overall string current will still be significantly reduced, but the open-circuit voltage (Voc) of the string may remain relatively unaffected as long as the circuit is not completely open.
Why the other options are wrong
- A. A shorted bypass diode would likely cause a slight reduction in Voc and Isc, but primarily lead to hot spots, not a significant Isc drop with normal Voc.
- B. An open circuit would result in zero current (Isc = 0) and potentially an interruption of Voc measurement, not just a reduction in Isc.
- D. An inverter fault typically affects the entire system output or causes specific error codes, and might not specifically manifest as normal Voc but reduced Isc at the string level.
PV String Isc Reduction (Shading)
A condition where the short-circuit current of a PV string is significantly lower than expected, often caused by partial shading or module degradation, while open-circuit voltage remains relatively normal.
- Shading primarily impacts current (Isc).
- Open-circuit voltage (Voc) is less affected by shading than Isc.
- Bypass diodes can help, but cannot fully restore current lost to shading.
Memory trick: Voc vs. Isc: Voltage is Open, Current is Short