Lesson 8
Answers

1) What are the two instruments needed to properly perform the maintenance and troubleshooting tasks for a PV system?

Answer: A digital voltmeter and a dc ammeter.

2) During routine maintenance why is it important to check the voltage and current level at various points in the PV system?

Answer: Checking and recording the voltage and current levels at various points will assist in identifying problems now and can be use for future reference.

3) Where is a good place to check the open-circuit electrical characteristics of the strings in the PV array?

Answer: The best place is a fused combiner box.

4) What are the characteristics that should be measured and recorded in Question 3 and how are they determined?

Answer: Each string’s dc electrical characteristics of open- and closed-circuit voltage should be measured with the digital voltmeter. Most likely the amp connections of the voltmeter can be used to measure the open-and closed-circuit current levels if the amp level is less than 10 amps in the circuit. For current level greater than 10 amps, a dc ammeter will be needed to measure the levels.

5) If you open a disconnect switch while checking the continuity of the grounding system and the ground is broken, what needs to be done and why?

Answer: If the grounding system’s continuity is broken when you open a disconnect switch, the ground wire has been installed improperly. According to the National Electric Code to maintain a safe system, the ground wire can not be broken by any disconnect. The switch needs to be rewired to break only the hot leg in some circuit or both the neutral and the hot legs in other circuits – the equipment ground must remain connected at all times.

6) Give three sources or causes of damage to roof top components of a PV system.

Answer: Damage to roof top PV system component can be caused by the sun, the wind, hailstones, animals, and/or people.

7) During maintenance you discover that one string in the combiner box has a much lower open-circuit current level compared to the other strings from the PV array. Give two possible causes and explain how you would fix each problem.

Answer: Some modules in the series string are defective, i.e they may have defective blocking or bypass diodes of have some internal parallel connections that are broken, loose, or dirty. Replace these modules. Parallel connections between modules in the string may be loose, dirty, or open – clean and connect them tightly. The string may be shaded – remove the shade source. The modules in the string may be dirtier than the other strings in the array – wash off the modules (do all the array while you are at).

8) When checking the array string open-circuit voltages, what are two conditions that would cause a low voltage reading compared to the other strings from the array?

Answer: The wire connecting the modules in the string to each other or to the junction box or combiner box or inverter may by too long or too small for the string’s output current level. Rewire with appropriate sized wire for the length and load. effective blocking or bypass diodes may need to be replaced.

9) If you were measuring the open-circuit current level of a string and the level dropped suddenly, stayed low for 10 seconds or so and then jumped back to the level you first measured, what is the most probable explanation for the event?

Answer: A cloud passing overhead shaded the modules in the string.

10) Why wash the PV modules whenever maintenance is scheduled?

Answer: Washing the modules removes dust, dirt, and other derbies that in effect shade the PV material in the module.

 

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