NABCEP Solar PV Fundamentals 2 — Questions and Answers
Question 1: What is the term for the voltage a PV module produces under open-circuit conditions with no load connected?
- Maximum power point voltage (Vmp)
- Open-circuit voltage (Voc) (Correct answer)
- Short-circuit voltage (Vsc)
- Nominal operating voltage (Vnom)
Correct answer: Open-circuit voltage (Voc)
Open-circuit voltage (Voc) is the maximum voltage a module produces when no current is flowing through it.
Question 2: Which semiconductor material is used in the majority of commercially installed crystalline silicon PV modules?
- Cadmium telluride (CdTe)
- Copper indium gallium selenide (CIGS)
- Amorphous silicon (a-Si)
- Monocrystalline or polycrystalline silicon (Correct answer)
Correct answer: Monocrystalline or polycrystalline silicon
Monocrystalline and polycrystalline silicon dominate the commercial PV market due to high efficiency and established manufacturing.
Question 3: How does increasing cell temperature affect the power output of a crystalline silicon PV module?
- Power increases because electrons gain energy
- Power decreases primarily due to reduced Voc (Correct answer)
- Power stays the same because Isc compensates
- Power increases only at very high temperatures
Correct answer: Power decreases primarily due to reduced Voc
Higher temperatures reduce Voc more than they increase Isc, resulting in a net decrease in module power output.
Question 4: What is the standard test condition (STC) irradiance value used to rate PV module output?
- 800 W/m²
- 900 W/m²
- 1000 W/m² (Correct answer)
- 1200 W/m²
Correct answer: 1000 W/m²
STC specifies 1000 W/m² irradiance, 25°C cell temperature, and an AM1.5 solar spectrum.
Question 5: In a PV I-V curve, where does the module operate to deliver maximum power?
- At Voc where current is zero
- At Isc where voltage is zero
- At the knee of the curve where the product V×I is maximized (Correct answer)
- At the midpoint between Voc and Isc
Correct answer: At the knee of the curve where the product V×I is maximized
The maximum power point (MPP) is located at the knee of the I-V curve where the product of voltage and current is greatest.
Question 6: What does the term 'fill factor' (FF) indicate about a PV module?
- The percentage of the module surface covered by active cells
- How closely the module's power output approaches the product of Voc and Isc (Correct answer)
- The ratio of monocrystalline to polycrystalline cells in the module
- The fraction of sunlight converted to electricity at STC
Correct answer: How closely the module's power output approaches the product of Voc and Isc
Fill factor is Pmax divided by (Voc × Isc), indicating how 'square' the I-V curve is and the quality of the module.
Question 7: Which condition causes bypass diodes in a PV module to conduct current?
- When the module is producing more power than rated
- When one or more cells are shaded or underperforming (Correct answer)
- When irradiance exceeds 1000 W/m²
- When module temperature drops below 25°C
Correct answer: When one or more cells are shaded or underperforming
Bypass diodes activate when shaded cells would otherwise become reverse-biased and dissipate power as heat, creating a hot spot.
NABCEP Solar PV Fundamentals 2
What is the term for the voltage a PV module produces under open-circuit conditions with no load connected?