NABCEP Solar Energy System Design & Installation 5 — Questions and Answers
Question 1: Which type of PV module technology generally has the highest conversion efficiency in standard laboratory and commercial production today?
- Amorphous silicon (a-Si)
- Cadmium telluride (CdTe)
- Monocrystalline silicon (mono-Si) (Correct answer)
- Organic photovoltaic (OPV)
Correct answer: Monocrystalline silicon (mono-Si)
Monocrystalline silicon modules currently achieve the highest commercial conversion efficiencies, typically 20–24% for premium products.
Question 2: What is the purpose of a PV system's 'interconnection agreement' with the utility?
- It sets the net metering rate the utility will pay for exported power
- It establishes technical and contractual terms under which the PV system may connect to and operate in parallel with the grid (Correct answer)
- It certifies that the installer holds a valid electrical contractor license
- It defines the maximum system size allowed by the state renewable portfolio standard
Correct answer: It establishes technical and contractual terms under which the PV system may connect to and operate in parallel with the grid
An interconnection agreement specifies the technical requirements, protective functions, and legal terms governing the parallel operation of a distributed generation system with the utility grid.
Question 3: A homeowner reports that their 6 kW PV system produced 7,200 kWh in its first year. What is the system's capacity factor?
- 8.22%
- 13.7% (Correct answer)
- 16.4%
- 20.0%
Correct answer: 13.7%
Capacity factor = 7,200 kWh / (6 kW × 8,760 hours/year) = 7,200 / 52,560 ≈ 13.7%.
Question 4: Under NEC 690.64, when a PV system is connected to the load side of a service panel, what rule governs the maximum allowed inverter breaker size relative to the bus bar rating?
- The inverter breaker must not exceed 20% of the bus bar rating
- The sum of all supply-side breaker ratings must not exceed 120% of the bus bar rating (Correct answer)
- The inverter breaker must be smaller than the main breaker
- No restriction applies when using load-side connection
Correct answer: The sum of all supply-side breaker ratings must not exceed 120% of the bus bar rating
NEC 690.64(B) allows the sum of all overcurrent device ratings feeding the bus to reach 120% of the panel's bus bar rating when the PV breaker is at the opposite end from the main breaker.
Question 5: What is the main function of a maximum power point tracker (MPPT) in a PV inverter?
- To regulate battery state of charge
- To continuously adjust the electrical operating point of the PV array to extract maximum power under varying conditions (Correct answer)
- To limit the string voltage below the inverter's maximum input rating
- To balance current between parallel strings
Correct answer: To continuously adjust the electrical operating point of the PV array to extract maximum power under varying conditions
An MPPT algorithm dynamically varies the array's operating voltage to find the point on the I-V curve where power output is maximized under current irradiance and temperature.
Question 6: Which of the following best describes the purpose of a 'system design pressure test' for a solar thermal (not PV) collector loop?
- Verifying that the glycol concentration is correct for freeze protection
- Confirming that all piping joints are leak-free by pressurizing the system above operating pressure (Correct answer)
- Testing the flow rate through the collector array at peak solar irradiance
- Calibrating the differential temperature controller setpoints
Correct answer: Confirming that all piping joints are leak-free by pressurizing the system above operating pressure
A pressure test applied above normal operating pressure checks all pipe joints, fittings, and connections for leaks before the system is filled with heat-transfer fluid.
Question 7: When using a string inverter on a roof with multiple orientations, which design approach best minimizes production loss due to mismatched strings?
- Place all strings in series to balance voltages across orientations
- Use a multi-MPPT inverter and connect strings of the same orientation to separate MPPT inputs (Correct answer)
- Increase the number of modules per string to raise string voltage above mismatch losses
- Derate the inverter's nameplate AC rating to match the weakest string
Correct answer: Use a multi-MPPT inverter and connect strings of the same orientation to separate MPPT inputs
A multi-MPPT inverter allows each orientation's string to operate at its own independent maximum power point, preventing a well-exposed string from being dragged down by a shaded or differently oriented string.
NABCEP Solar Energy System Design & Installation 5
Which type of PV module technology generally has the highest conversion efficiency in standard laboratory and commercial production today?