PV System Electrical Design

Question 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?

Answer 1

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

Question 2

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

Answer 2

The expected maximum PV array voltage

Question 3

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

Answer 3

Last step

Question 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?

Answer 4

58.9 V

Question 5

What is the formula used to find voltage drop?

Answer 5

V = IR

Volts = Amperes * Resistance

Question 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?

Answer 6

10 modules on southwest roof and 0 modules on southeast roof

Question 7

Is the DC disconnect between the panel and the inverter?

Answer 7

No

Question 8

What natural factor inhibits higher voltages in PV?

Answer 8

Hot weather

Question 9

What does a self-regulating PV system NOT have?

Answer 9

A charge controller

Question 10

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

Answer 10

Cold weather

Question 11

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

Answer 11

A short circuit

Question 12

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

Answer 12

The lowest anticipated air temperature

Question 13

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

Answer 13

A lower percentage of voltage lost due to resistance

Question 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?

Answer 14

Smaller conductors can be used between the array and inverter

Question 15

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

Answer 15

Total power demand, peak demand, and duty cycle

Question 16

In a PV system, hot weather inhibits what?

Answer 16

Higher voltages in PV

Question 17

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

Answer 17

A ground-fault protection device

Question 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?

Answer 18

The system is probably functioning properly

Question 19

When does a short circuit happen?

Answer 19

When there is more than the allowable current at maximum power

Question 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?

Answer 20

50

Question 21

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

Answer 21

Your PV output plan

Question 22

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

Answer 22

PV systems mounted on residential dwellings

Question 23

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

Answer 23

Islanding

Question 24

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

Answer 24

Mount modules 6” above the roof

Question 25

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

Answer 25

When the PV array rack is mounted at ground level

Question 26

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

Answer 26

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

Question 27

What type of PV system operates autonomously?

Answer 27

Stand-alone system

Question 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?

Answer 28

Undercharged in cold weather and overcharged in hot weather

Question 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?

Answer 29

That the PV source is the dominant charging source

Question 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?

Answer 30

The 48-V would have16x the amount of resistance

Question 31

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

Answer 31

R = V/I

Question 32

What kind of PV system does not operate autonomously?

Answer 32

Interactive system

Question 33

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

Answer 33

Insolation data

Question 34

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

Answer 34

Switch from a stand-alone to interactive system

Question 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?

Answer 35

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

Question 36

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

Answer 36

Physical damage to the array and wiring.

Question 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?

Answer 37

Yes

Question 38

Islanding is when a PV system does what?

Answer 38

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

Question 39

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

Answer 39

Cloud cover decreases amperage