CSLB C-46 Solar ContractorPhotovoltaic System InstallationMedium
A solar installer is connecting a ground-mounted PV array to a central inverter. The array is located a significant distance from the inverter, and the installer is concerned about potential reverse current flow from the inverter back into the array at night or during fault conditions. Which component is specifically designed to prevent this reverse current flow?
- ASurge protector
- BArc-fault circuit interrupter (AFCI)
- CBypass diode
- DBlocking diode
Show answer & explanationAnswer & explanation
Correct answer: D. Blocking diode
A blocking diode (also known as a series diode) is placed in series with a PV string or array to prevent current from flowing backward from the battery bank or inverter into the PV modules when the array voltage is lower than the system voltage (e.g., at night or during shading/faults).
Why the other options are wrong
- A. Surge protectors protect against voltage spikes, not reverse current flow.
- B. AFCI detects and interrupts arc faults, not reverse current.
- C. Bypass diodes shunt current around shaded or faulty modules within a string, they don't prevent reverse current from the system.
Blocking Diode
A semiconductor device placed in series with a PV string or array to prevent reverse current flow from the load (e.g., battery, inverter) back into the PV modules, which could cause damage or discharge.
- Ensures one-way current flow.
- Prevents module discharge at night.
- Protects against reverse current during faults.
Memory trick: Blocking stops the backflow, bypass jumps the shade.