CSLB C-46 Solar ContractorPhotovoltaic System InstallationMedium
A solar installer is connecting a ground-mounted PV array to a central inverter. The array consists of multiple strings, each protected by an individual string fuse. Before connecting to the inverter's DC input, these strings are combined in a combiner box. What is the primary function of the blocking diode in this combiner box, if present?
- ATo convert DC power from the strings into AC power.
- BTo prevent reverse current flow from other strings or the battery into a shaded string.
- CTo regulate the voltage output of the entire array.
- DTo prevent overcurrent from flowing to the inverter.
Show answer & explanationAnswer & explanation
Correct answer: B. To prevent reverse current flow from other strings or the battery into a shaded string.
Blocking diodes, also known as isolation diodes, prevent current from flowing backward from higher-voltage strings or a battery bank into lower-voltage (e.g., shaded or faulty) strings, which could cause damage or power loss.
Why the other options are wrong
- A. Converting DC to AC is the function of an inverter, not a blocking diode.
- C. Voltage regulation is typically handled by charge controllers or the inverter's MPPT, not blocking diodes.
- D. Overcurrent protection is typically handled by fuses or circuit breakers, not blocking diodes.
PV Blocking Diode Function
A diode placed in series with a PV string or array to prevent reverse current flow from other strings, the inverter, or a battery bank into a specific string, especially when shaded or underperforming.
- Also known as isolation diodes.
- Protects strings from becoming a load.
- Common in multi-string systems and battery-based systems.
Memory trick: Diodes Direct Current