CSLB C-46 Solar ContractorPhotovoltaic System InstallationMedium
A solar technician is performing an open-circuit voltage (Voc) test on a PV array string. They measure 450V, but the inverter specification requires a maximum Voc of 400V. Which of the following is the most appropriate action to take to bring the string within the inverter's specifications?
- AIncrease the number of parallel strings connected to the inverter.
- BReplace the inverter with one that has a lower maximum Voc rating.
- CDecrease the number of modules in series in the string.
- DIncrease the number of modules in series in the string.
Show answer & explanationAnswer & explanation
Correct answer: C. Decrease the number of modules in series in the string.
Open-circuit voltage (Voc) is directly proportional to the number of modules connected in series. To reduce the string Voc, the number of series-connected modules must be decreased.
Why the other options are wrong
- A. Increasing parallel strings affects current (Isc), not Voc.
- B. Replacing the inverter with a lower Voc rating would worsen the problem; a higher Voc rating inverter would be needed if the string couldn't be modified.
- D. Increasing series modules would further increase Voc, exceeding the inverter's limit.
PV String Voltage Sizing
The process of selecting the correct number of PV modules in series to match the voltage operating window of a specific inverter or charge controller.
- Open-circuit voltage (Voc) is additive in series.
- Voltage must stay within inverter's min/max operating range.
- Temperature significantly affects Voc (Voc increases at colder temperatures).
Memory trick: Series = Voltage, Parallel = Current