SE Engr. Technical Specifications 2 — Questions and Answers
Question 1: Which set of conditions defines Standard Test Conditions (STC) for PV module ratings?
- 1000 W/m², 25°C cell temperature, AM1.5 spectrum (Correct answer)
- 800 W/m², 20°C ambient temperature, 1 m/s wind
- 1000 W/m², 25°C ambient temperature, AM1.0 spectrum
- 1200 W/m², 45°C cell temperature, AM1.5 spectrum
Correct answer: 1000 W/m², 25°C cell temperature, AM1.5 spectrum
STC specifies 1000 W/m² irradiance, 25°C cell temperature, and an AM1.5 spectrum.
Question 2: NOCT (Nominal Operating Cell Temperature) is measured under which conditions?
- 1000 W/m², 25°C ambient, no wind
- 800 W/m², 20°C ambient, 1 m/s wind, open-rack mounting (Correct answer)
- 800 W/m², 25°C cell, 2 m/s wind, roof-mounted
- 500 W/m², 20°C ambient, still air
Correct answer: 800 W/m², 20°C ambient, 1 m/s wind, open-rack mounting
NOCT uses 800 W/m² irradiance, 20°C ambient air, 1 m/s wind, and open-rack mounting, and typically gives cell temperatures around 41-46°C.
Question 3: A typical crystalline silicon module datasheet lists a Pmax temperature coefficient of about:
- +0.05 %/°C
- -0.10 %/°C
- -0.35 %/°C (Correct answer)
- -1.5 %/°C
Correct answer: -0.35 %/°C
Crystalline silicon modules usually lose about 0.29-0.40% of their power for each °C above 25°C.
Question 4: How is a PV module's fill factor calculated?
- (Voc × Isc) / (Vmp × Imp)
- (Vmp × Imp) / (Voc × Isc) (Correct answer)
- Pmax / (Area × 1000 W/m²)
- Vmp / Voc
Correct answer: (Vmp × Imp) / (Voc × Isc)
Fill factor is the maximum power (Vmp × Imp) divided by the product of Voc and Isc.
Question 5: A module datasheet lists a power tolerance of '0/+5 W'. What does this mean?
- Delivered modules can be up to 5 W below the rated power
- Delivered modules will measure at or above nameplate power, by up to 5 W (Correct answer)
- Power varies by ±5 W with temperature
- Output degrades by up to 5 W in the first year
Correct answer: Delivered modules will measure at or above nameplate power, by up to 5 W
A positive-only tolerance means flash-tested power is never below the nameplate rating.
Question 6: How does a module's open-circuit voltage (Voc) behave on a very cold, sunny morning?
- It drops below the STC value
- It stays equal to the STC value
- It rises above the STC value (Correct answer)
- It falls to zero until the module warms up
Correct answer: It rises above the STC value
Voc has a negative temperature coefficient, so it rises at cell temperatures below 25°C, which is why maximum system voltage is calculated at the coldest expected temperature.
Question 7: A 400 W module has an area of 2.0 m². What is its efficiency at STC?
- 18%
- 20% (Correct answer)
- 22%
- 40%
Correct answer: 20%
Efficiency = 400 W / (2.0 m² × 1000 W/m²) = 20%.
SE Engr. Technical Specifications 2
Which set of conditions defines Standard Test Conditions (STC) for PV module ratings?