NABCEP Solar Energy System Design & Installation 3 — Questions and Answers
Question 1: What type of roof penetration sealant is recommended for PV mounting hardware to ensure a weatherproof installation?
- Standard silicone caulk applied externally
- Flashing kits with code-compliant waterproofing integrated into the mount (Correct answer)
- Roofing tar applied around the base of each mount
- No sealant is needed if lag bolts are used
Correct answer: Flashing kits with code-compliant waterproofing integrated into the mount
Approved flashing kits integrate waterproofing into the mount assembly, meeting roofing standards and preventing leaks around penetrations.
Question 2: A string of 10 modules each with Voc of 40V is installed in a climate with a minimum design temperature of -10°F. Using the IEC 60364-7-712 method, if the voltage correction factor at -10°F is 1.25, what is the maximum string Voc?
- 400V
- 450V
- 500V (Correct answer)
- 312V
Correct answer: 500V
Maximum Voc = 10 modules × 40V × 1.25 correction factor = 500V, which must not exceed the inverter's maximum input voltage.
Question 3: Which tool is most commonly used during commissioning to verify that each PV module in a string is producing power and to identify failed modules?
- Thermal infrared camera (Correct answer)
- Digital multimeter only
- Clamp ammeter measuring AC output
- Power quality analyzer
Correct answer: Thermal infrared camera
An infrared camera reveals hot spots, failed bypass diodes, and shading effects that indicate underperforming modules during commissioning.
Question 4: What is the purpose of a module-level power electronics (MLPE) device such as a microinverter or DC optimizer?
- To increase the open-circuit voltage of each module
- To mitigate shading and mismatch losses by independently maximizing each module's power output (Correct answer)
- To convert AC power back to DC for battery storage
- To reduce the number of required overcurrent protection devices
Correct answer: To mitigate shading and mismatch losses by independently maximizing each module's power output
MLPEs perform per-module maximum power point tracking, reducing losses caused by partial shading, soiling, or module mismatch.
Question 5: Which of the following is a key design consideration when using transformerless inverters in a PV system?
- They require a higher minimum string voltage than transformer-based inverters
- The PV array must not have a grounded conductor under NEC 690.35 conditions (Correct answer)
- They are incompatible with string configurations exceeding 600V
- They cannot be used with thin-film modules due to leakage current
Correct answer: The PV array must not have a grounded conductor under NEC 690.35 conditions
Transformerless inverters typically require an ungrounded PV array because they lack galvanic isolation, and NEC 690.35 addresses ungrounded PV system requirements.
Question 6: What does the term 'specific yield' refer to in PV system performance analysis?
- The ratio of DC nameplate capacity to AC output capacity
- Annual AC energy production per unit of installed DC capacity (kWh/kWp/year) (Correct answer)
- The percentage of sunlight hours in a given location
- The ratio of actual to theoretical irradiance on a tilted surface
Correct answer: Annual AC energy production per unit of installed DC capacity (kWh/kWp/year)
Specific yield normalizes a system's annual energy production by its DC nameplate capacity, enabling comparison across different system sizes and locations.
Question 7: In a residential battery storage system connected to an existing PV array, what is typically required to ensure the battery can charge from the grid independently of the PV system?
- A separate AC-coupled inverter/charger with its own utility connection (Correct answer)
- Larger DC conductors between the PV array and the battery
- An additional PV string dedicated solely to battery charging
- A higher-voltage battery bank matching the string Voc
Correct answer: A separate AC-coupled inverter/charger with its own utility connection
An AC-coupled inverter/charger with a utility connection allows the battery to charge from the grid when PV production is insufficient.
NABCEP Solar Energy System Design & Installation 3
What type of roof penetration sealant is recommended for PV mounting hardware to ensure a weatherproof installation?