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Flashcards in PV System Electrical Design Deck (39):
1

Suppose an alternate series three-stage charge controller is available as a backup to a parallel three-stage PV charging source such as a utility-interactive battery-based inverter. Also assume that the PV source is intended to be the dominant charging source. How could one ensure that the PV source is the dominant charging source?

Set the bulk voltage of the PV charging source lower than the float voltage of the alternate controller.

2

The lowest anticipated air temperature must be correct in order to determine what?

The expected maximum PV array voltage

3

When searching for the cause of a PV system failure, at which step would you check the shorted solar cells?

Last step

4

Assume the STC maximum-power voltage of a crystalline silicon PV array is 68.4 V. The irradiance is 800 W/ m2 and the module temperature is 50 degrees C. Assuming the inverter is tracking maximum power with a 1.6% voltage drop between modules and inverter input, what should the inverter input voltage be closest to?

58.9 V

5

What is the formula used to find voltage drop?

V = IR

Volts = Amperes * Resistance

6

A single inverter system requires 9 or 10 modules in series and one or two series strings in parallel. If the southeast roof is large enough for 8 modules and the southwest roof is large enough for 15 modules, what array configuration results in the most efficient use of the PV modules installed?

10 modules on southwest roof and 0 modules on southeast roof

7

Is the DC disconnect between the panel and the inverter?

No

8

What natural factor inhibits higher voltages in PV?

Hot weather

9

What does a self-regulating PV system NOT have?

A charge controller

10

What type of weather does NOT inhibit higher voltages in PV?

Cold weather

11

What happens when the current exceeds that which is determined by the equivalent resistance in the network?

A short circuit

12

To determine the expected maximum PV array voltage, the module voltage at Standard Test Conditions (STC) must be corrected to what?

The lowest anticipated air temperature

13

What is the effect on voltage drop of a higher volt system?

A lower percentage of voltage lost due to resistance

14

What capability of a 500 V DC PV array gives it an advantage over a 48 V DC PV array of the same wattage?

Smaller conductors can be used between the array and inverter

15

During the critical design month in the worst case scenario, what is NOT used to size the PV system?

Total power demand, peak demand, and duty cycle

16

In a PV system, hot weather inhibits what?

Higher voltages in PV

17

The NEC requires what device to be a part of PV systems mounted on residential dwellings?

A ground-fault protection device

18

A utility-interactive PV system with no batteries consists of 15 100 W modules in series that feed a 1500 W inverter. The inverter output power is found to be 780 W when the modules are operating at 50 degrees C with an irradiance level of 800 W/m2. If three modules are observed to be shaded, which conclusion is most likely?

The system is probably functioning properly

19

When does a short circuit happen?

When there is more than the allowable current at maximum power

20

Assume the STC maximum voltage of a crystalline silicon PV array is 68.4 V. The irradiance is 800 W/m2 and the module temperature is 50 degrees C. Assuming the inverter is tracking maximum power with a 1.6 voltage drop between modules and inverter input, will the inverter input voltage be closer to 50 or 100?

50

21

Switching from stand-alone to interactive is the most advisable way to increase what?

Your PV output plan

22

The NEC requires a ground-fault protection device to be part of what?

PV systems mounted on residential dwellings

23

What is the term for when a PV system continues to supply power to the grid even when the grid is down?

Islanding

24

What are some methods to improve the efficiency of producing electricity with a PV system?

Mount modules 6" above the roof

25

Physical damage to the array and wiring presents a greater concern when...

When the PV array rack is mounted at ground level

26

How are other system components affected when a large wire is used to minimize voltage drop in a 12-V PV?

Junction boxes (terminal blocks) and switch boxes must be large enough to house the large wire.

27

What type of PV system operates autonomously?

Stand-alone system

28

The battery bank for a battery backup utility-interactive PV system is located in a harsh environment with temperature and humidity extremes. The system charge controller has a provision for temperature compensation, but it is not connected. What is the most likely result on the battery state of charge?

Undercharged in cold weather and overcharged in hot weather

29

Suppose an alternate series three-stage charger controller is available as a backup to a parallel three-stage PV charging source such as a utility-interactive battery-based inverter. Setting the bulk voltage of the PV charging source lower than the float voltage of the alternate controller will ensure what?

That the PV source is the dominant charging source

30

A PV system is to be selected for a water-pumping operation. The pump will require 300W of PV modules. 12-V and 48-V DC models are available. If both pumps operate at the same power level and voltage drop, how would the resistance of the 48-V pump compare to the resistance of the 12-V pump?

The 48-V would have16x the amount of resistance

31

If V = IR, what is the equation to find R if you are given V and I?

R = V/I

32

What kind of PV system does not operate autonomously?

Interactive system

33

During the critical design month (worst case scenario), the load and ________ are used to size the PV system.

Insolation data

34

What is the most advisable way to increase your PV output plan?

Switch from a stand-alone to interactive system

35

A single inverter system requires 9 or 10 modules in series and one or two series strings in parallel. If the southeast roof is large enough for 8 modules and the southwest roof is large enough for 15 modules, is 10 modules on the southwest roof and 5 modules on the southeast roof the most efficient use of the PV modules?

No, the most efficient configuration would be 10 modules on the southwest roof and 0 modules on the southeast roof.

36

With the PV array rack mounted at ground level, what would normally be of greatest concern?

Physical damage to the array and wiring.

37

A utility-interactive PV system with no batteries consists of 15 100-W modules in series that feed a 1500-W inverter. The inverter output power is found to be 780 W when the modules are operating at 50 degrees C with an irradiance level of 800 W/m2. If three modules are observed to be shaded, is the system functioning properly?

Yes

38

Islanding is when a PV system does what?

Continues to supply power to the grid when the grid is down

39

What effect does cloud cover have on amperage in PV systems?

Cloud cover decreases amperage