NABCEP Solar PV Fundamentals 5 — Questions and Answers
Question 1: In a grid-tied PV system, what component is responsible for converting DC power from the array into AC power synchronized with the utility grid?
- Charge controller
- Battery management system (BMS)
- Grid-tied inverter (Correct answer)
- Transformer-coupled rectifier
Correct answer: Grid-tied inverter
A grid-tied inverter converts DC from the PV array to AC at the correct voltage, frequency, and phase to match and feed into the utility grid.
Question 2: What is the purpose of anti-islanding protection in a grid-tied PV inverter?
- To prevent the inverter from operating when cloud cover reduces irradiance below 20%
- To shut down the inverter when grid power is lost, preventing energizing de-energized utility lines (Correct answer)
- To isolate individual PV strings experiencing faults from the rest of the array
- To disconnect modules from the inverter during high-temperature events
Correct answer: To shut down the inverter when grid power is lost, preventing energizing de-energized utility lines
Anti-islanding protection shuts the inverter down during grid outages to protect utility workers from energized lines and ensure safe reconnection.
Question 3: A PV module has a rated power of 400W at STC. If the system's combined derating factors (temperature, soiling, wiring, inverter efficiency) equal 0.78, what is the estimated AC output power?
- 400 W
- 312 W (Correct answer)
- 400 W × 1.78 = 712 W
- 78 W
Correct answer: 312 W
Derated AC power = 400W × 0.78 = 312W, accounting for all system losses from STC rated power to actual AC output.
Question 4: What does the term 'specific yield' (or 'specific production') of a PV system represent?
- The ratio of AC energy output to DC nameplate capacity, expressed in kWh/kWp (Correct answer)
- The power output per unit area of the array in W/m²
- The ratio of actual energy to maximum theoretically possible energy
- The efficiency of the inverter expressed as a percentage
Correct answer: The ratio of AC energy output to DC nameplate capacity, expressed in kWh/kWp
Specific yield (kWh/kWp) normalizes annual energy production by system nameplate capacity, enabling comparison of systems in different locations or sizes.
Question 5: Which of the following best describes the difference between 'irradiance' and 'insolation' in solar energy terminology?
- Irradiance is the cumulative energy over a time period (kWh/m²); insolation is the instantaneous power (W/m²)
- Irradiance is instantaneous solar power per unit area (W/m²); insolation is cumulative solar energy over time (kWh/m²) (Correct answer)
- Irradiance applies to diffuse light only; insolation applies to direct beam radiation
- Irradiance and insolation are interchangeable terms for solar resource measurement
Correct answer: Irradiance is instantaneous solar power per unit area (W/m²); insolation is cumulative solar energy over time (kWh/m²)
Irradiance is the instantaneous rate of solar energy per unit area (W/m²), while insolation is the total energy accumulated over time (kWh/m²).
Question 6: What is the primary function of an MPPT (Maximum Power Point Tracker) in a PV system?
- To regulate battery state of charge and prevent overcharging
- To continuously adjust the operating voltage of the PV array to extract maximum available power (Correct answer)
- To synchronize the inverter output with the utility grid frequency
- To monitor module-level performance and detect faults
Correct answer: To continuously adjust the operating voltage of the PV array to extract maximum available power
MPPT algorithms dynamically adjust the electrical load seen by the array to keep it operating at the voltage-current combination that delivers maximum power.
Question 7: When sizing a PV array for a given load, what term describes the ratio of total array output energy to total load energy demand over a given period?
- System efficiency
- Performance ratio (PR)
- Solar fraction (Correct answer)
- Capacity factor
Correct answer: Solar fraction
The solar fraction indicates what portion of total energy demand is met by the PV system, with the remainder supplied by the grid or backup source.
NABCEP Solar PV Fundamentals 5
In a grid-tied PV system, what component is responsible for converting DC power from the array into AC power synchronized with the utility grid?