PV System Design Principles Flashcards
7 cards from real NABCEP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 PV System Design Principles flashcards as text
The purpose of an anti-islanding protection feature in a grid-tied inverter is to:
Answer: Automatically disconnect the PV system when the utility grid goes down
Anti-islanding protection detects grid loss and shuts down the inverter to prevent energizing downed utility lines, protecting utility workers.
Which irradiance condition is used as the standard for rating PV module power output (STC)?
Answer: 1000 W/m² at 25°C cell temperature with AM1.5 spectrum
Standard Test Conditions (STC) are defined as 1000 W/m² irradiance, 25°C cell temperature, and AM1.5 solar spectrum.
Nominal Operating Cell Temperature (NOCT) is used to estimate module temperature under what conditions?
Answer: 800 W/m² irradiance, 20°C ambient, 1 m/s wind speed, open-circuit module
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.
A PV system designer wants to estimate annual energy production. Which data source provides the best site-specific solar resource information for the US?
Answer: NREL's National Solar Radiation Database (NSRDB) or PVWatts
NREL's NSRDB provides high-resolution historical solar irradiance data integrated into tools like PVWatts for accurate US site energy estimates.
In a transformer-less (transformerless) PV inverter, which additional safety concern must the designer address?
Answer: The potential for DC ground faults and leakage current due to lack of galvanic isolation
Transformerless inverters lack galvanic isolation between the DC and AC sides, making DC ground fault detection and leakage current management critical safety concerns.
What is the primary purpose of a PV system's grounding electrode conductor (GEC)?
Answer: To bond the system to earth ground, limiting voltage rise during lightning or fault events
The GEC connects the electrical system to a grounding electrode, dissipating fault and lightning-induced currents safely into the earth.
When evaluating a site for a ground-mounted PV array, inter-row spacing is determined primarily by:
Answer: The sun's lowest elevation angle during the winter solstice to avoid self-shading
Inter-row spacing must be sufficient so that the shadow cast by the front row does not shade the rear row during the worst-case low-sun-angle condition (winter solstice).