Lesson 8
PV System Maintenance

Schedule maintenance twice a year. Around noon on a sunny day is an ideal time to perform maintenance. A homeowner with neither the necessary instrumentation nor the electrical knowledge might consider contracting with an electrician to perform maintenance and inspection of the PV system.

Maintenance Steps

Step 1: At the Inverter
Use a voltmeter and a DC ammeter to check and record the inverter’s operating DC input voltage and current level and on the AC side, and the inverter’s output voltage and current levels. Check that the appropriate LEDs are lit up to indicate proper operation of the inverter. If the inverter can display the total kWh produced since it first started up, record the amount. Use this number to compare the PV system’s production since the last inspection.


Step 2: On the Roof

example of pv array on a house
Rinse the PV array to remove debris.
Image: NREL/PIX 00180
Note and record the condition of the modules. Look for signs of degradation (for example, color changes, fogged glazing, de-lamination, warping, or water leaks), cracked glazing, and bent frames on the modules. Tighten all loose nuts and bolts, holding the modules to the mounting rack and to the mounting clips. Secure any loose wiring under the modules. Check the wiring for signs of chewing by squirrels, and look for cuts, gashes, or worn spots in the wiring’s insulation. Replace any damaged wire runs. Check the frame ground connections between modules and from the modules to the junction box(es). Check to see that the sealants around all building penetrations are in good condition and repair if necessary. Open the junction box(es) and look for and correct any dirty, loose, or broken connections. Test the tightness of each connection and tighten all loose ones. Note any problems that can be corrected at a later time or at the next scheduled inspection time. Close the junctions box(es) and check that all conduit connections are tight.

Remove all sources of shade on the array and rinse the array to remove the accumulated dust, dirt, and other debris. Some debris, such as bird droppings, may need to soak a bit to fully remove it.


Step 3: At the Combiner Box(es)
Open the combiner box(es) and look for any dirty, loose, or broken connections, and correct as necessary. Use a voltmeter and DC ammeter to measure and record the array’s operating voltage and current level on the output side of the combiner box(es). Note the relative sun conditions at the time (i.e., full sun, partly cloudy, heavy overcast). Remove the fuses and then check and record each string’s open circuit voltage and current levels. Note any deviation between strings for future correction. You can also use the open circuit measurements to determine if the array’s output is degrading over time. Return the fuses and close the combiner box(es).


Step 4: Inside
Open all disconnect switches. Use the ohmmeter section of the voltmeter to check the grounding system connections. Greater than 25 ohms indicates that corrosion or a poor connection is present, which must be located and corrected. If opening the disconnect switch breaks the ground, you need to rewire the switch to correct the problem. Check each of the disconnected sections for a ground-fault condition any that are found.


Step 5: Back at the Inverter
Turn the inverter off and check for dirty, loose, or broken wires and connections. Check for and repair any ground faults. Power the system up. Check for normal start up operation and that the inverter produces AC electricity.

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System Troubleshooting

Troubleshooting a PV system usually means:

  1. A load does not operate properly or not at all;
  2. The inverter does not operate properly or not at all; or
  3. The array has low or no voltage or current.

A qualified electrician should check and correct electrical problems in a PV system, since homeowners are unlikely to be qualified to perform such work.


Troubleshooting: Load Problem
The first step is to check all switches. Are they turned off, or in the wrong position? If so, turn them on or put them in the correct position. Also check to see that the load is plugged in. With a voltmeter, check to see that the proper voltage is present at the load’s connection. Next check the fuses and circuit breakers. Are there blown fuses or tripped breakers? If so, locate the cause and fix or replace the faulty component. If there are no blown fuses or tripped breakers and the load is a motor, an internal thermal breaker may be tripped or there may be an open circuit in the motor. Plug in another load and note its operation.

Check for broken wires and any loose connections. Clean all dirty connections and replace all bad wiring. With the power off, check for and repair any ground faults. Replace the fuses and reset the switches. If they blow or trip again, there is a problem short, which must be located and repaired.

If the load does not operate properly, check the system’s voltage at the load’s connection. Low voltage could mean that the wire feeding the circuit is too small and too long and needs to be upgraded to reduce the voltage drop. The load also could be too large for the wire size in the circuit. Reduce the load on the circuit or run larger wire that is sized for the current load.


Troubleshooting: Inverter Problem
A lack of power output from the inverter could be caused by a blown fuse, tripped breaker, a broken wire, a ground fault, or any of the inverter’s internal disconnects (high and low voltage and current). The load on the inverter may have too high of a current demand. Reduce the loads or replace the inverter with one with a larger output.

With the power off, check for and repair any ground faults before starting the inverter again.

The utility’s voltage and frequency are sensed by the inverter, which normally produces AC electricity at the same voltage and frequency. The AC current output from the inverter fluctuates with the level of solar insolation on the array. Low or high utility voltage sensed by the internal disconnects will cause the inverter to shut down. Contact the utility to correct the problem on its side.

Inverter problems could also be caused by a problem on the array side of inverter that trips one of the internal disconnects.


Troubleshooting: Array Problem
Prior to getting on the roof, check and record the inverter’s input voltage and current level from the array. If the array is not producing DC electricity, check all switches, fuses, and circuit breakers. Replace blown fuses and reset the breakers and switches. A spurious surge may have passed through, tripping or blowing the protective devices. Check for broken wires and loose or dirty connections in the inverter. Replace all damaged wires and clean and tighten all connections.

Visually check the array for obvious damage to the modules and wiring. Repair as needed and replace all damaged wiring.

Having a fused combiner box can save a lot of time when checking each module or sub-array string. Remove the fuses and then check and record the open-circuit voltage and current reading for each circuit string.

If the output voltage is low, it could indicate that some modules in the series string are defective or disconnected and need to be replaced. Defective blocking or bypass diodes in the modules may need to be replaced. Low voltage also could be caused by the wrong wiring connecting the modules in the string to the junction box or combiner box or the inverter. The wiring could be either sized too small or the wire run is too long for the string’s output current level. Upgrading the wire size for the current level should correct this problem.

Low current output could be caused by cloudy conditions, a defective blocking or bypass diode, a damaged module, one or more parallel connection between modules in the string is broken, loose, or dirty, or some parallel connections the module are broken, loose, or dirty. Replace a damaged module or one with internal parallel connection problems. Replace defective diodes and clean and tighten all connections. Some of the array may be shaded, significantly reducing the array’s current output. Remove the shade source to regain the string’s full current output.

Dirty modules also could cause reduced current output. Wash the modules to restore the array’s current output.

Questions

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


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


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


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


  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?


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


  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 what could be two causes and how do you fix the problems?


  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?


  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?


  10. Why should you wash the PV modules whenever maintenance is scheduled?

Answers