SE Engr. Technical Specifications 3 — Questions and Answers
Question 1: What does the CEC weighted efficiency on an inverter datasheet represent?
- Peak efficiency at 100% load only
- Efficiency averaged over several load levels, weighted to reflect typical operation (Correct answer)
- Efficiency at the lowest MPPT voltage
- Efficiency including transformer losses at night
Correct answer: Efficiency averaged over several load levels, weighted to reflect typical operation
CEC weighted efficiency combines efficiencies at several power levels using weights that reflect how often the inverter typically runs at each level.
Question 2: What does the 'MPPT voltage range' on an inverter datasheet specify?
- The range of AC grid voltages the inverter accepts
- The DC input voltage window in which the inverter can track maximum power (Correct answer)
- The voltage range of battery storage
- The voltage at which the inverter shuts down for rapid shutdown
Correct answer: The DC input voltage window in which the inverter can track maximum power
String Vmp must stay inside the MPPT window across all temperatures for the inverter to harvest full power.
Question 3: A system pairs 12.5 kW DC of modules with a 10 kW AC inverter. What is the DC/AC (inverter loading) ratio?
- 0.80
- 1.00
- 1.25 (Correct answer)
- 2.25
Correct answer: 1.25
12.5 kW DC / 10 kW AC = 1.25.
Question 4: Which maximum DC system voltage is most common in modern US utility-scale PV plants?
- 48 V
- 600 V
- 1000 V
- 1500 V (Correct answer)
Correct answer: 1500 V
Utility-scale plants have standardized on 1500 V DC to allow longer strings and lower balance-of-system costs.
Question 5: Which standard defines interconnection and interoperability requirements for distributed energy resources connected to the US grid?
- IEEE 1547 (Correct answer)
- IEC 61215
- UL 9540
- ASTM E1036
Correct answer: IEEE 1547
IEEE 1547 (2018 revision) sets the performance requirements for DER interconnection, including ride-through and voltage/frequency support.
Question 6: UL 1741 SB certification of an inverter indicates that it:
- Meets module fire classification requirements
- Has been tested for the grid-support functions required by IEEE 1547-2018 (Correct answer)
- Is rated for submersion in water
- Meets battery thermal runaway testing
Correct answer: Has been tested for the grid-support functions required by IEEE 1547-2018
UL 1741 Supplement B certifies inverters against IEEE 1547.1-2020 grid-support function testing.
Question 7: Inverter clipping happens when:
- Available DC power exceeds the inverter's maximum AC output rating (Correct answer)
- Array voltage falls below the MPPT range
- Grid frequency drifts outside limits
- The inverter's ground-fault detector trips
Correct answer: Available DC power exceeds the inverter's maximum AC output rating
When the array produces more DC power than the inverter can convert, output is capped at the AC rating and the excess is lost.
SE Engr. Technical Specifications 3
What does the CEC weighted efficiency on an inverter datasheet represent?