CSLB C-46 Solar ContractorPhotovoltaic System InstallationMedium
A solar technician is installing an off-grid PV system with a battery bank. To prevent reverse current flow from the battery bank back into the PV array at night, which component is essential and typically integrated into the charge controller or PV combiner box?
- AZener diode
- BBypass diode
- CSchottky diode
- DBlocking diode
Show answer & explanationAnswer & explanation
Correct answer: D. Blocking diode
A blocking diode, also known as an isolation or anti-reverse current diode, is used to prevent current from flowing backward from the battery into the PV array when the array voltage drops below the battery voltage (e.g., at night or during heavy shading). This prevents the battery from discharging through the PV modules.
Why the other options are wrong
- A. Zener diodes are used for voltage regulation, not for blocking reverse current in this context.
- B. Bypass diodes are used within PV modules to shunt current around shaded cells, not to prevent reverse current from the battery to the array.
- C. Schottky diodes are a type of diode known for low forward voltage drop, often used as blocking diodes, but 'blocking diode' is the functional term for its purpose here.
PV Blocking Diode Function
A blocking diode (or isolation diode) in a PV system prevents current from flowing in the reverse direction, specifically from a battery bank back into the PV array, which could discharge the battery at night.
- Prevents battery discharge through PV modules.
- Typically found in charge controllers or combiner boxes for off-grid systems.
- Ensures unidirectional current flow from PV to battery/load.
- Introduces a small voltage drop and power loss.
Memory trick: Blocking Diodes Block Battery Backflow.