SE Engr. Technical Specifications 4 — Questions and Answers
Question 1: A module has Voc = 40 V and a Voc temperature coefficient of -0.30 %/°C. At a record low of -10°C, what is the maximum Voc of a 12-module string?
- 480.0 V
- 505.2 V
- 530.4 V (Correct answer)
- 556.8 V
Correct answer: 530.4 V
ΔT = -35°C gives a +10.5% increase, so 40 × 1.105 = 44.2 V per module, and 44.2 × 12 = 530.4 V.
Question 2: Under NEC 690.8, maximum PV source-circuit current is calculated as:
- Imp × 1.00
- Isc × 1.25 (Correct answer)
- Isc × 1.56
- Imp × 1.25
Correct answer: Isc × 1.25
Maximum circuit current is 125% of the summed parallel module Isc, and a second 125% factor is applied when sizing conductors and OCPD, for 156% overall.
Question 3: Under NEC 690.12 rapid shutdown, controlled conductors outside the array boundary must be reduced to:
- 80 V within 30 seconds
- 30 V within 30 seconds (Correct answer)
- 0 V within 10 seconds
- 50 V within 60 seconds
Correct answer: 30 V within 30 seconds
Outside the array boundary, conductors must drop to 30 V or less within 30 seconds of initiation; inside the boundary the limit is 80 V.
Question 4: A panel has a 200 A busbar and a 200 A main breaker. Under the NEC 705.12 120% rule, what is the largest PV backfeed breaker allowed at the opposite end of the busbar?
- 20 A
- 40 A (Correct answer)
- 50 A
- 60 A
Correct answer: 40 A
(200 A × 1.2) - 200 A = 40 A.
Question 5: What does the 'maximum series fuse rating' on a module datasheet specify?
- The largest overcurrent device that can protect the module against reverse current (Correct answer)
- The inverter's AC breaker size
- The rapid shutdown device's current limit
- The module's short-circuit current at STC
Correct answer: The largest overcurrent device that can protect the module against reverse current
It is the maximum OCPD rating that keeps reverse fault current from parallel strings within what the module can withstand.
Question 6: What DC voltage-drop target is commonly recommended in PV design to limit losses?
- Under 2% (Correct answer)
- Under 5%
- Under 10%
- Under 15%
Correct answer: Under 2%
Designers commonly target 1-2% DC voltage drop; the NEC sets no mandatory limit, but losses grow quickly above that.
Question 7: On a bifacial module datasheet, the bifaciality factor is defined as:
- Rear-side efficiency (or Pmax) divided by front-side efficiency (Correct answer)
- Total power divided by the front glass area
- Albedo of the ground surface
- The ratio of glass thickness front to back
Correct answer: Rear-side efficiency (or Pmax) divided by front-side efficiency
Bifaciality is the ratio of rear to front performance at STC, typically about 70% for PERC, 80% for TOPCon, and 85-90% for HJT.
SE Engr. Technical Specifications 4
A module has Voc = 40 V and a Voc temperature coefficient of -0.30 %/°C.
At a record low of -10°C, what is the maximum Voc of a 12-module string?