NABCEP PV System Design Principles 5

Question 1

The purpose of an anti-islanding protection feature in a grid-tied inverter is to:

Accepted Answer

Automatically disconnect the PV system when the utility grid goes down

Answer

Anti-islanding protection detects grid loss and shuts down the inverter to prevent energizing downed utility lines, protecting utility workers.

Question 2

Which irradiance condition is used as the standard for rating PV module power output (STC)?

Accepted Answer

1000 W/m² at 25°C cell temperature with AM1.5 spectrum

Answer

Standard Test Conditions (STC) are defined as 1000 W/m² irradiance, 25°C cell temperature, and AM1.5 solar spectrum.

Question 3

Nominal Operating Cell Temperature (NOCT) is used to estimate module temperature under what conditions?

Accepted Answer

800 W/m² irradiance, 20°C ambient, 1 m/s wind speed, open-circuit module

Answer

NOCT is measured at 800 W/m², 20°C ambient temperature, 1 m/s wind, and open-circuit electrical conditions to represent typical outdoor operating conditions.

Question 4

A PV system designer wants to estimate annual energy production. Which data source provides the best site-specific solar resource information for the US?

Accepted Answer

NREL's National Solar Radiation Database (NSRDB) or PVWatts

Answer

NREL's NSRDB provides high-resolution historical solar irradiance data integrated into tools like PVWatts for accurate US site energy estimates.

Question 5

In a transformer-less (transformerless) PV inverter, which additional safety concern must the designer address?

Accepted Answer

The potential for DC ground faults and leakage current due to lack of galvanic isolation

Answer

Transformerless inverters lack galvanic isolation between the DC and AC sides, making DC ground fault detection and leakage current management critical safety concerns.

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

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

NABCEP PV System Design Principles 5