REP Solar Energy Systems 3 — Questions and Answers
Question 1: Soiling losses on PV panels are primarily caused by which of the following?
- High ambient temperature
- Dust, dirt, bird droppings, and other surface deposits (Correct answer)
- Shading from nearby trees
- UV degradation of the encapsulant
Correct answer: Dust, dirt, bird droppings, and other surface deposits
Soiling refers to the accumulation of contaminants on the panel surface that block incoming light and reduce output power.
Question 2: What is the typical temperature coefficient of power (Pmax) for a standard crystalline silicon PV module?
- +0.5% per °C
- -0.5% per °C (Correct answer)
- -0.05% per °C
- +0.05% per °C
Correct answer: -0.5% per °C
Most crystalline silicon modules lose approximately 0.3–0.5% of rated power for every degree Celsius above 25°C (STC).
Question 3: In solar thermal systems, what does the 'stagnation temperature' refer to?
- Operating temperature at peak efficiency
- Maximum temperature reached when there is no fluid flow (Correct answer)
- Ambient temperature at the installation site
- Temperature of the storage tank at night
Correct answer: Maximum temperature reached when there is no fluid flow
Stagnation temperature is the highest temperature a collector can reach when fluid circulation stops and all absorbed heat remains in the collector.
Question 4: Which PV cell technology generally has the highest commercial module efficiency?
- 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 achieve the highest commercial efficiencies, typically 20–23%, due to their highly ordered crystal structure.
Question 5: What is 'net metering' in the context of a grid-tied solar PV system?
- Measuring total system losses
- A billing arrangement where excess solar energy is credited against grid consumption (Correct answer)
- A method of grounding the PV array
- Monitoring inverter efficiency in real time
Correct answer: A billing arrangement where excess solar energy is credited against grid consumption
Net metering allows customers to send surplus PV energy to the grid and receive a credit on their utility bill, effectively running the meter backward.
Question 6: Which interconnection standard governs the technical requirements for distributed energy resources connected to the electric grid in the US?
- NFPA 70E
- IEEE 1547 (Correct answer)
- UL 1741
- ANSI C84.1
Correct answer: IEEE 1547
IEEE 1547 establishes requirements for the interconnection and interoperability of distributed energy resources with the electric power system.
Question 7: A PV system's performance ratio (PR) is calculated as which of the following?
- Actual energy output divided by rated module power
- Actual energy output divided by theoretical energy output based on irradiance (Correct answer)
- Array peak power divided by inverter rated power
- Total irradiation divided by system capacity
Correct answer: Actual energy output divided by theoretical energy output based on irradiance
Performance ratio compares actual kWh produced to the kWh theoretically possible given the irradiance received, indicating overall system quality.
REP Solar Energy Systems 3
Soiling losses on PV panels are primarily caused by which of the following?