NABCEP Commissioning and Troubleshooting 2

Question 1

During PV system commissioning, you measure an open-circuit voltage significantly higher than the STC-rated Voc. What is the most likely cause?

Accepted Answer

Ambient temperature is much lower than 25°C STC

Answer

PV module Voc increases as temperature decreases below 25°C STC, so cold conditions yield higher-than-rated Voc readings.

Question 2

A string of 10 modules shows an Isc that is 15% lower than expected while all other strings test normally. What is the first diagnostic step?

Accepted Answer

Inspect each module in the string for shading or soiling

Answer

A proportionally low Isc in a single string commonly points to shading, soiling, or a failing module reducing current generation.

Question 3

When commissioning a battery-based off-grid system, what parameter must be verified to ensure the charge controller protects the battery bank?

Accepted Answer

Maximum PV array open-circuit voltage vs. charge controller input rating

Answer

The PV array Voc at minimum temperature must not exceed the charge controller's maximum input voltage rating to prevent damage.

Question 4

An inverter repeatedly faults with an 'AC voltage high' error during afternoon peak. What is the most probable cause?

Accepted Answer

Utility grid voltage rises above the inverter's upper trip threshold

Answer

Backfeed from distributed generation during low-load periods can raise local utility voltage, triggering AC overvoltage faults.

Question 5

During commissioning, an IR thermal scan of a module shows one cell running 20°C hotter than surrounding cells. What does this indicate?

Accepted Answer

A localized cell defect such as a crack or hot spot

Answer

An isolated hot cell in an IR scan is a classic sign of a cracked or defective cell creating a resistive hot spot.

(NABCEP) Certified North American Board of Certified Energy Practitioners Specialist Practice Test