NABCEP Inverter Systems 5

Question 1

What happens to a grid-tied inverter's output when the utility grid voltage rises above the inverter's high-voltage trip threshold?

Accepted Answer

The inverter disconnects from the grid and waits for voltage to return to normal range

Answer

When grid voltage exceeds the high-voltage trip threshold, the inverter disconnects (trips offline) and waits a specified reconnect delay before resynchronizing, protecting both the inverter and connected equipment.

Question 2

In an AC-coupled battery system, the battery inverter synchronizes to the frequency signal from the grid-tied solar inverter. How does the battery inverter signal the solar inverter to reduce output when the battery is full?

Accepted Answer

It slightly raises the AC frequency above 60 Hz, causing the solar inverter to reduce output via frequency-watt droop

Answer

In AC-coupled systems (e.g., Victron + SolarEdge or Enphase), the battery inverter raises AC frequency slightly above 60 Hz, causing the solar inverter's frequency-watt (Freq-Watt) function to curtail output.

Question 3

What does the 'power factor' of a grid-tied inverter output represent?

Accepted Answer

The ratio of real (active) power to apparent power, indicating how much current contributes to useful work

Answer

Power factor is the ratio of real power (watts) to apparent power (volt-amperes); a unity power factor (1.0) means all current contributes to useful work with no reactive component.

Question 4

A homeowner reports their grid-tied solar system stops producing around noon on sunny days despite the panels appearing clean and unshaded. Which inverter issue is most likely?

Accepted Answer

High-temperature thermal derating causing the inverter to reduce output

Answer

Inverters have thermal management systems and will derate (reduce output) or shut down when internal temperatures exceed safe limits, which often occurs at peak solar production on hot days.

Question 5

What is the purpose of the DC disconnect switch (also called PV disconnect or array disconnect) required between the solar array and the inverter?

Accepted Answer

To provide a means for safely de-energizing the DC conductors for maintenance and emergency disconnection

Answer

The DC disconnect provides a manual means to safely isolate the PV array DC conductors from the inverter, required by NEC 690.15 for maintenance, inspection, and emergency de-energization.

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

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

NABCEP Inverter Systems 5