CSLB C-46 Solar ContractorPhotovoltaic System InstallationMedium
A solar installer is configuring a string inverter system for a residential rooftop. The system consists of 18 photovoltaic modules, each with a nominal voltage of 30V and a nominal current of 9A. The selected string inverter has a maximum DC input voltage of 600V and a maximum input current per MPPT tracker of 15A. What is the maximum number of modules that can be connected in series per string without exceeding the inverter's maximum input voltage, assuming standard operating conditions?
- A18 modules
- B12 modules
- C15 modules
- D20 modules
Show answer & explanationAnswer & explanation
Correct answer: D. 20 modules
To determine the maximum number of modules in series, divide the inverter's maximum DC input voltage by the nominal voltage of a single module. 600V / 30V = 20 modules.
Why the other options are wrong
- A. Connecting 18 modules would result in 540V, which is below the maximum but not the maximum possible string length.
- B. This would significantly underutilize the inverter's voltage capacity and is not the maximum.
- C. This would result in a lower total voltage than the inverter's maximum capacity.
PV String Sizing (Voltage)
The process of determining the optimal number of PV modules to connect in series (a string) to match the voltage requirements of a string inverter.
- Total string voltage must not exceed inverter's maximum DC input voltage.
- Total string voltage must be above the inverter's minimum operating voltage.
- Voltage varies with temperature; account for cold weather voltage rise.
Memory trick: Voltage is Vertical, Current is Across, always check both limits!