NABCEP Solar PV System Design 3 — Questions and Answers
Question 1: What is the minimum required clearance between the bottom of a roof-mounted PV array and the roof surface per most manufacturer and fire code requirements?
- 1 inch
- 3 inches (Correct answer)
- 6 inches
- 12 inches
Correct answer: 3 inches
Most fire codes and manufacturers require at least 3 inches of clearance beneath roof-mounted modules to allow airflow and firefighter access.
Question 2: When sizing a grid-tied inverter for a PV array, what ratio of array STC DC power to inverter AC rated output is commonly called?
- Capacity factor
- DC-to-AC ratio (or clipping ratio) (Correct answer)
- Fill factor
- Irradiance ratio
Correct answer: DC-to-AC ratio (or clipping ratio)
The DC-to-AC ratio (also called inverter loading ratio) compares total array STC wattage to the inverter's rated AC output, typically ranging from 1.1 to 1.3.
Question 3: A PV system designer calculates 8,500 kWh of annual production but the customer uses 10,200 kWh/year. What is the system's offset percentage?
- 120%
- 83% (Correct answer)
- 75%
- 95%
Correct answer: 83%
Offset = (8,500 / 10,200) × 100 ≈ 83%, meaning the system covers approximately 83% of the customer's annual electricity usage.
Question 4: What does MPPT stand for in solar inverter technology?
- Maximum Power Point Tracking (Correct answer)
- Module Power Performance Testing
- Minimum Peak Power Threshold
- Maximum Panel Potential Transfer
Correct answer: Maximum Power Point Tracking
MPPT (Maximum Power Point Tracking) is an algorithm that continuously adjusts electrical operating conditions to extract maximum power from PV modules.
Question 5: In shade analysis for PV system design, what tool is commonly used to assess shading at a specific site?
- Pyranometer
- Solar Pathfinder or SunEye device (Correct answer)
- Clamp meter
- Ground fault interrupter
Correct answer: Solar Pathfinder or SunEye device
Devices like the Solar Pathfinder or Solmetric SunEye capture a hemispherical view of the sky to identify shading obstructions throughout the year.
Question 6: Which of the following best describes 'soiling loss' in a PV system?
- Energy loss from high soil resistivity at the grounding electrode
- Reduction in energy output caused by dirt, dust, or debris on module surfaces (Correct answer)
- Voltage drop from underground conduit runs
- Thermal loss from modules buried in snow
Correct answer: Reduction in energy output caused by dirt, dust, or debris on module surfaces
Soiling loss refers to reduced energy production caused by dust, bird droppings, pollen, or other contaminants blocking sunlight from reaching PV cells.
Question 7: For a roof-mounted system in a high-wind zone (ASCE 7 150 mph), what design aspect becomes especially critical?
- Inverter efficiency rating
- Racking and attachment hardware wind uplift capacity (Correct answer)
- Module temperature coefficient
- String voltage calculation
Correct answer: Racking and attachment hardware wind uplift capacity
In high-wind zones, racking and attachment hardware must be engineered to resist significant wind uplift forces to prevent array detachment.
NABCEP Solar PV System Design 3
What is the minimum required clearance between the bottom of a roof-mounted PV array and the roof surface per most manufacturer and fire code requirements?