NABCEP Solar PV System Design 2 — Questions and Answers
Question 1: When designing a roof-mounted PV system, what is the primary purpose of calculating the roof's dead load capacity?
- To determine inverter placement
- To ensure the structure can support the added weight of the array (Correct answer)
- To calculate the system's energy production
- To size the electrical conduit
Correct answer: To ensure the structure can support the added weight of the array
Dead load capacity determines whether the existing roof structure can safely bear the static weight of the PV modules, racking, and mounting hardware.
Question 2: A PV array has 10 modules in series, each with a Voc of 41.2V at STC. Using NEC temperature correction for a record low of -20°C, what correction factor from Table 690.7 (for -20°C with a temperature coefficient of -0.29%/°C) would be applied?
- 1.12
- 1.25 (Correct answer)
- 1.10
- 1.20
Correct answer: 1.25
At -20°C, the NEC Table 690.7 correction factor is 1.25, accounting for increased Voc at low temperatures to ensure safe conductor and equipment ratings.
Question 3: What does the term 'temperature derating' mean in the context of PV module performance?
- Increasing output at low temperatures
- Reducing rated output due to elevated operating temperatures (Correct answer)
- Adjusting the inverter clipping threshold
- Changing the tilt angle seasonally
Correct answer: Reducing rated output due to elevated operating temperatures
Temperature derating reduces the expected power output of a PV module because higher temperatures decrease cell voltage and therefore total power output.
Question 4: In a string inverter system with three parallel strings of 12 modules each, what is the total number of modules in the array?
- 24
- 36 (Correct answer)
- 48
- 12
Correct answer: 36
Three parallel strings with 12 modules per string equals 3 × 12 = 36 total modules.
Question 5: Which NEC article primarily governs the installation of photovoltaic systems?
- Article 480
- Article 690 (Correct answer)
- Article 705
- Article 702
Correct answer: Article 690
NEC Article 690 specifically covers solar photovoltaic systems, including wiring, equipment, and safety requirements.
Question 6: A designer wants to maximize annual energy production for a fixed-tilt system in Phoenix, AZ (latitude ~33°N). What tilt angle is generally recommended?
- 10°
- 23°
- 33° (Correct answer)
- 45°
Correct answer: 33°
For fixed-tilt arrays optimized for annual energy production, a tilt angle approximately equal to the site's latitude is commonly recommended.
Question 7: What is the purpose of a combiner box in a large PV array?
- To convert DC to AC power
- To combine multiple string circuits into a single DC output (Correct answer)
- To monitor individual module performance
- To provide AC overcurrent protection
Correct answer: To combine multiple string circuits into a single DC output
A combiner box aggregates multiple parallel PV string circuits into one combined DC output, simplifying wiring runs to the inverter.
NABCEP Solar PV System Design 2
When designing a roof-mounted PV system, what is the primary purpose of calculating the roof's dead load capacity?