REP Solar Energy Systems 4 — Questions and Answers
Question 1: Which type of solar concentrating technology uses a parabolic dish to focus sunlight onto a Stirling engine at the focal point?
- Parabolic trough
- Power tower (central receiver)
- Dish-Stirling system (Correct answer)
- Linear Fresnel reflector
Correct answer: Dish-Stirling system
Dish-Stirling systems use a parabolic dish concentrator to focus sunlight onto a Stirling heat engine mounted at the focal point for electricity generation.
Question 2: What is the main advantage of a microinverter over a string inverter in a residential PV installation?
- Lower upfront cost per watt
- Module-level MPPT that reduces shading and mismatch losses (Correct answer)
- Higher peak efficiency at full load
- Simpler wiring because it uses AC strings
Correct answer: Module-level MPPT that reduces shading and mismatch losses
Microinverters perform MPPT at each individual panel, so shading or soiling on one panel does not significantly reduce the output of other panels.
Question 3: In NEC Article 690, what is the significance of the 'maximum system voltage' rating for PV equipment?
- It defines the minimum wire gauge for DC circuits
- Equipment must be rated for voltages at or above the highest voltage that can appear in the system under any conditions (Correct answer)
- It sets the maximum allowable AC output voltage of the inverter
- It determines the minimum number of strings per inverter
Correct answer: Equipment must be rated for voltages at or above the highest voltage that can appear in the system under any conditions
NEC 690 requires that all PV system components be rated for the maximum system voltage, which includes the open-circuit voltage corrected for the lowest expected temperature.
Question 4: A 10 kW PV system produces 14,000 kWh annually at a site with 1,750 peak sun hours per year. What is the system's capacity factor?
- 8%
- 12%
- 16% (Correct answer)
- 20%
Correct answer: 16%
Capacity factor = actual output ÷ (rated capacity × 8,760 h) = 14,000 ÷ (10 × 8,760) ≈ 16%.
Question 5: What is the primary purpose of grounding the DC negative conductor in a transformerless PV inverter system?
- Improve power factor
- Prevent potential-induced degradation (PID) in the modules (Correct answer)
- Reduce inverter switching losses
- Stabilize the AC output voltage
Correct answer: Prevent potential-induced degradation (PID) in the modules
Grounding the negative rail in a transformerless system reduces the potential difference between the module frame and cells, mitigating potential-induced degradation.
Question 6: Which solar thermal collector type is best suited for high-temperature industrial process heat applications (above 150°C)?
- Flat-plate collector
- Evacuated tube collector
- Unglazed pool heating collector
- Parabolic trough collector (Correct answer)
Correct answer: Parabolic trough collector
Parabolic trough collectors concentrate sunlight onto an absorber tube, achieving fluid temperatures above 150°C, making them suitable for industrial process heat and power generation.
Question 7: What does 'specific yield' (kWh/kWp) measure in a solar PV project?
- Cost per kilowatt-hour of energy produced
- Annual energy output per kilowatt of installed peak capacity (Correct answer)
- Ratio of AC to DC power at the inverter
- Energy stored per kilowatt-hour of battery capacity
Correct answer: Annual energy output per kilowatt of installed peak capacity
Specific yield normalizes annual energy production by installed capacity, allowing fair comparison of PV system performance across different locations and sizes.
REP Solar Energy Systems 4
Which type of solar concentrating technology uses a parabolic dish to focus sunlight onto a Stirling engine at the focal point?