21 Operations, Maintenance & Troubleshooting Practice Questions & Answers

1. 1. A technician compares a home system's measured AC output on a clear day against the output expected from irradiance measured in the plane of the array. Which statement best describes a healthy grid-tied system?

   • A.Measured output reaches the nameplate rating once the modules warm up
   • B.Measured output matches the nameplate rating whenever the sky is clear
   • C.Measured output sits below the nameplate rating even under clear skies✓ Answer
   • D.Measured output exceeds the nameplate rating through most of a sunny day

   Nameplate ratings come from standard test conditions, which combine full reference irradiance with a cool cell temperature that a working rooftop array almost never sees at the same moment. In the field, hot cells, less than full plane-of-array irradiance, soiling, wiring losses and inverter conversion losses all subtract, so system health is judged by comparing measured output with output modelled from the measured irradiance, not with the nameplate figure.

   Source: NABCEP PV Associate job task analysis, performance parameters — standard test conditions versus field operating conditionsReport a problem with this question

2. 2. Every string on an inverter shows normal open-circuit voltage, but operating current is about 20% lower than it was on a comparable day last year at similar measured irradiance. Which explanation fits the measurements best?

   • A.Cell temperature well above normal, because heat reduces module current sharply
   • B.A bypass diode failed in one module, because diodes carry the whole array current
   • C.A loose grid connection at the service panel, because it throttles DC current
   • D.Soiling accumulated across the array, because current tracks irradiance nearly proportionally✓ Answer

   Module current is very nearly proportional to the light reaching the cells, while open-circuit voltage barely moves with irradiance and instead follows cell temperature. Normal voltage on every string with current depressed on every string therefore points to something uniformly blocking light, and soiling is the common cause; heat would show up as reduced voltage, and a diode or grid-side problem would not lower current identically across all strings.

   Source: Dunlop, Photovoltaic Systems (ATP) — effect of irradiance and temperature on module current and voltageReport a problem with this question

3. 3. At which site would soiling losses most likely be worst between rainfalls?

   • A.A low-tilt array at a lakeside home where afternoon storms are frequent
   • B.A low-tilt array beside unpaved farm roads where dry seasons are long✓ Answer
   • C.A steeply tilted array in a coastal region with rain through the year
   • D.A steeply tilted array in a suburb with regular rain and no bare soil

   Soiling builds up when a site supplies dust and the weather does not rinse it away. Unpaved roads and field work generate airborne dust, a long dry season removes natural washing, and a shallow tilt lets particles settle and stay instead of running off with the rain that does fall.

   Source: NREL/SunSpec best practices for operation and maintenance of photovoltaic systems — soiling lossesReport a problem with this question

4. 4. A rooftop system in a cold climate produced nothing for three days in midwinter and then returned to normal on the fourth day, with no service visit. What does this pattern indicate?

   • A.A blown combiner fuse cleared itself once the array cooled down
   • B.A module's bypass diode opened in the cold and reset when warmed
   • C.Snow covered the modules and then slid or melted off the glass✓ Answer
   • D.Snow loading tripped the inverter's ground-fault protection for three days

   An outage that ends by itself with no intervention is a production loss driven by conditions, not a hardware failure. Snow blocks light completely and then slides or melts off; a fuse that has opened stays open and a failed diode stays failed, so neither restores production on its own.

   Source: NREL/SunSpec best practices for operation and maintenance of photovoltaic systems — snow and weather-related production lossesReport a problem with this question

5. 5. An owner reports that output dips by several percent every spring and recovers after the first heavy rain, year after year. What is the most reasonable interpretation?

   • A.Pollen and field dust settle on the glass and wash off with rain✓ Answer
   • B.Inverter capacitors weaken in spring and recover in wet weather
   • C.String wiring resistance rises in spring and falls after a rain
   • D.Module degradation accelerates each spring and reverses in summer

   A loss that repeats on the same seasonal schedule and reverses as soon as rain washes the glass is a soiling loss, and pollen and agricultural dust are the classic spring sources. Degradation is permanent and component failures do not undo themselves with the weather, so the repeating and self-correcting pattern is what identifies soiling.

   Source: NREL/SunSpec best practices for operation and maintenance of photovoltaic systems — seasonal soiling and cleaning intervalsReport a problem with this question

6. 6. Monitoring shows a shallow dip in the production curve each afternoon; over three summers the dip has become deeper and has begun earlier in the day. What does this trend most likely indicate?

   • A.The array's fuses have weakened and open partially during hot afternoons
   • B.The inverter has begun clipping output during part of each afternoon
   • C.The trees near the array have grown and now shade it earlier each afternoon✓ Answer
   • D.The modules have degraded steadily and now lose more power every year

   Shading from a fixed obstruction appears as a dip at the same time of day, because it follows the sun's path past that object. When the dip deepens and starts earlier season after season, the obstruction itself is getting bigger, which is what vegetation does; degradation would lower the whole daily curve rather than carve a growing notch into one part of it.

   Source: NABCEP PV Associate job task analysis, deviations from expected performance — shading analysis and vegetation managementReport a problem with this question

7. 7. Annual production has fallen by roughly half a percent per year since the system was installed, and this year output dropped by 12% from one week to the next. How should a technician read these two observations?

   • A.The slow decline reflects meter drift; the sudden drop reflects slow inverter aging
   • B.The slow decline reflects a wiring fault; the sudden drop reflects normal module aging
   • C.The slow decline reflects seasonal weather; the sudden drop reflects gradual soiling
   • D.The slow decline reflects normal aging; the sudden drop points to a discrete failure✓ Answer

   Crystalline silicon modules lose a small fraction of a percent of their output per year, so a slow, steady decline over many years is expected aging and needs only trending. A step change from one week to the next cannot be aging, because aging does not happen in a week; something discrete failed or changed, such as an open fuse, a failed module-level device, a tripped breaker or new shading, and it should be traced.

   Source: NREL/SunSpec best practices for operation and maintenance of photovoltaic systems — performance trending and module degradationReport a problem with this question

8. 8. In a combiner box on a sunny morning, seven strings read about 380 V open-circuit while the eighth reads near zero volts between its own two conductors. What does the eighth reading indicate?

   • A.The string has a shorted bypass diode in one of its modules
   • B.The string is shaded now and will recover as the sun moves
   • C.The string is producing normally but has an oversized fuse
   • D.The string is open somewhere along its series circuit✓ Answer

   Series-connected modules develop open-circuit voltage whenever any light reaches them, so even a heavily shaded string still reads substantial voltage. Essentially zero volts between that string's own conductors means the series path is interrupted — an unseated or damaged connector, a broken conductor, or a module removed from the circuit — and the break has to be located along the string.

   Source: Dunlop, Photovoltaic Systems (ATP) — troubleshooting series-connected PV source circuitsReport a problem with this question

9. 9. A string shows normal open-circuit voltage but produces less power than its neighbours, and a thermal scan shows one connector pair much hotter than the surrounding wiring. What does this combination indicate?

   • A.An oversized string fuse, which lets the connector run above its rated current
   • B.A high-resistance connection there, which drops voltage and gives off heat under load✓ Answer
   • C.A ground fault in that section, which forces current through the connector body
   • D.A shorted bypass diode nearby, which pushes extra current into the connector

   A poor joint only reveals itself when current flows: the resistance develops a voltage across the joint, and that voltage times the current is dissipated as heat, which is why the connector glows on a thermal image while the open-circuit voltage, measured at no current, still looks normal. Such a connection is also a potential series-arc source and must be repaired rather than monitored.

   Source: NREL/SunSpec best practices for operation and maintenance of photovoltaic systems — infrared inspection of terminations and connectorsReport a problem with this question

10. 10. A string is dead and its modules and conductors look intact from the ground. What is the most efficient way to locate the break?

    • A.Measure the inverter output against the neighbouring inverter
    • B.Measure at the combiner and replace the warmest module found
    • C.Measure at the midpoint, then halve the suspect half again✓ Answer
    • D.Measure at each connector starting from the first module

    Splitting the circuit in half at each step tells the technician which half still contains the fault, so the suspect length shrinks quickly and a long string is resolved in a handful of measurements. Walking connector by connector reaches the same answer but takes far more time on the roof, and replacing parts before measuring guesses at the cause.

    Source: Dunlop, Photovoltaic Systems (ATP) — systematic troubleshooting procedure for PV source circuitsReport a problem with this question

11. 11. One string fuse in a combiner box is found open. What is the correct response?

    • A.Replace it with the next larger rating to stop nuisance opening
    • B.Replace it with a solid link until the bad module is found
    • C.Replace it at the next annual visit, since one string is minor
    • D.Replace it with the same rating after finding why it opened✓ Answer

    A fuse opens because current exceeded its rating, and that current came from somewhere — a short circuit, a ground fault, reverse current fed from the other strings, or a wiring error. Replacing the fuse without finding the cause only repeats the event, and fitting a larger fuse or a solid link removes the protection the conductors and modules were sized to depend on.

    Source: NFPA 70, National Electrical Code — principle of overcurrent protection for PV source circuitsReport a problem with this question

12. 12. With the meter's red lead on each string's positive conductor and the black lead on its negative, seven strings read about +380 V and one reads about −380 V. What does this indicate?

    • A.The string's modules are wired in parallel, so its voltage adds in reverse polarity
    • B.The string's fuse is open, so the meter reports the reading as negative
    • C.The string's polarity is reversed, so it opposes the others and cuts output✓ Answer
    • D.The string's bypass diodes are conducting, so its voltage reads inverted

    A full-magnitude reading of the opposite sign, with the leads placed the same way on every string, means that string's conductors are landed backwards. Paralleled onto a common bus, a reversed string opposes the others instead of adding to them, which sharply reduces array output and can drive current backwards through that string, so the wiring must be corrected before the array is returned to service.

    Source: Dunlop, Photovoltaic Systems (ATP) — series and parallel PV circuit polarity and combiner wiringReport a problem with this question

13. 13. An inverter reports a ground-fault or low insulation-resistance alarm that clears on dry days and returns after rain. What does the alarm indicate?

    • A.The array's output is exceeding the inverter's rated input current
    • B.A series break in a conductor is drawing an arc inside a junction box
    • C.The utility voltage is drifting outside the inverter's allowed window
    • D.Insulation has been damaged and lets current reach a grounded surface when wet✓ Answer

    Ground-fault and insulation-resistance monitoring watches for current leaking from the array's current-carrying conductors to grounded metal or earth. Damaged insulation — a conductor abraded on a roof surface, a pinched wire, a cracked enclosure — often conducts only when water bridges the damage, which is exactly why such an alarm appears after rain and clears once things dry out.

    Source: IEC standard for grid-connected PV system testing and maintenance — insulation resistance of PV arraysReport a problem with this question

14. 14. A DC arc-fault detection function in an inverter has shut the array down twice. Which condition is that function designed to detect?

    • A.A grid outage that leaves the inverter without a voltage reference
    • B.A break in a current-carrying conductor, like a loose connector✓ Answer
    • C.A short between a live conductor and a grounded metal surface
    • D.A string current running above the module's series fuse rating

    Arc-fault detection listens for the high-frequency electrical signature of an arc sustained across a gap in the current path — typically a loose, corroded, damaged or cross-mated connector, or a conductor broken inside a raceway. That is a series fault, and it is a different phenomenon from a ground fault, where current escapes from the intended path to grounded metal.

    Source: NFPA 70, National Electrical Code — purpose of DC arc-fault circuit protection for PV systemsReport a problem with this question

15. 15. A system's ground-fault protection trips again within a day of being reset, and the cause has not been found. What is the correct course of action?

    • A.Leave the fault alone and file a module warranty claim with the maker
    • B.Leave the array running and reset the protection each morning remotely
    • C.Leave the array shut down and have a qualified person find the fault✓ Answer
    • D.Leave the protection disabled so the system can run until the next visit

    Protective devices operate to prevent shock and fire, so repeated tripping is evidence of a real fault that is still present. The array has to stay out of service until someone qualified to work on energized PV equipment traces and corrects it; defeating the protection or resetting it over and over leaves a live fault energized on the roof.

    Source: NFPA 70E, standard for electrical safety in the workplace — response to repeated protective device operationReport a problem with this question

16. 16. During a neighbourhood power outage on a sunny day, a grid-tied inverter without battery backup produces nothing. How should the technician read this?

    • A.The inverter is mis-programmed, since its grid settings are clearly too narrow
    • B.The inverter is behaving correctly, since it must not energize a dead grid✓ Answer
    • C.The inverter is of low capacity, since it cannot carry the home's load alone
    • D.The inverter is faulted internally, since sunlight alone should keep it running

    Grid-interactive inverters are required to stop exporting when the utility supply is absent or outside its allowed voltage and frequency limits, so that they cannot back-feed lines that line crews may be working on. Without storage and islanding capability, an inverter that goes quiet during an outage and restarts after the utility returns is doing exactly what it is designed to do.

    Source: IEEE standard for interconnection of distributed energy resources with electric power systems — anti-islanding requirementReport a problem with this question

17. 17. A thermal scan taken at midday under strong sun shows one cell in a module much hotter than the cells around it. Which explanation is most consistent with that image?

    • A.That cell is bonded to the frame and carries stray ground current
    • B.That cell is newer than the others and runs at higher efficiency
    • C.That cell is cracked or shaded and dissipates power instead of making it✓ Answer
    • D.That cell is receiving far more sunlight than the cells around it

    Cells in a series string all carry the same current, so a cell that is cracked, soiled or shaded cannot generate that current and instead becomes a load, turning the power the healthy cells produce into heat. That is why hot spots only appear when the string is carrying current under good irradiance, and why the finding calls for inspecting the cell, its shading and its bypass diode.

    Source: NABCEP PV Associate job task analysis, deviations from expected performance — infrared thermography and hot-spot causesReport a problem with this question

18. 18. A string of 20 identical modules measures roughly the open-circuit voltage of only 19 of them, while its operating current is normal. What is the most likely cause?

    • A.One module is wired in parallel with the rest of the string
    • B.One module is bypassed by a shorted diode or is disconnected✓ Answer
    • C.One module is heavily soiled and produces no voltage at all
    • D.One module is running hot and has lost most of its current output

    Voltages add in a series string, so a shortfall equal to about one module's open-circuit voltage means one module is no longer contributing to the chain while the circuit still carries current. A shorted bypass diode conducting around that module, or a module bridged out or dropped from the circuit, produces exactly that signature; soiling or heat would change current or lower voltage across the whole string instead.

    Source: Dunlop, Photovoltaic Systems (ATP) — bypass diode function in series stringsReport a problem with this question

19. 19. A module is found with a browned, delaminated area and a scorched junction box, while the rest of the array looks sound. What should the associate do?

    • A.Document it, swap in any spare module of a different make and wattage
    • B.Document it, take the module out of service and file a warranty claim✓ Answer
    • C.Document it, seal the junction box with tape and put it back in service
    • D.Document it, clean the browned area and leave the module in service

    Delamination, cell browning and a scorched junction box are module-level failures that cannot be repaired in the field, and a burned junction box is an active fire and shock hazard because the module's leads stay energized in daylight. The correct path is to photograph and record the condition, remove the module from service, and pursue replacement through the manufacturer's warranty process with an electrically compatible module.

    Source: NREL/SunSpec best practices for operation and maintenance of photovoltaic systems — module visual defects and warranty claimsReport a problem with this question

20. 20. During a scheduled maintenance visit, a technician finds that the array has one more string than the as-built drawing shows. What is the appropriate action?

    • A.Record the as-found configuration and have the documentation corrected and reissued✓ Answer
    • B.Record the difference but assume the drawing is right and the array is wrong
    • C.Record nothing, because as-built drawings are only used during permitting
    • D.Record the change and disconnect the extra string to match the drawing

    As-built documentation is what the next technician, the inspector and the emergency responder rely on to know what is installed and how to shut it down, so a mismatch is itself a defect that has to be resolved on paper. The system is not altered to fit an outdated drawing; the technician records what is actually installed and has the drawings and labels updated to match.

    Source: NABCEP PV Associate job task analysis, maintenance of PV systems — as-built documentation and record keepingReport a problem with this question

21. 21. Before separating the DC connectors of one module in an energized array on a sunny afternoon, what must be done?

    • A.Open the DC disconnect only, since the modules then stop producing
    • B.Open the DC disconnect after separating the connectors, not before
    • C.Open the DC disconnect, cover the module, and verify it is dead✓ Answer
    • D.Open the AC disconnect only, since that removes the array's voltage

    A module is a source, not a load: its leads are energized whenever light falls on the glass, and no switch downstream changes that. Opening the DC disconnect isolates the circuit from the inverter, an opaque cover over the module collapses its output, and verifying with a meter that the leads are de-energized before touching them is what makes the work safe, because pulling a connector while current flows draws a sustained DC arc.

    Source: NFPA 70E and PV module manufacturer instructions — safe isolation of PV source circuits energized by daylightReport a problem with this question

Practice questions based on the published knowledge domains of the NABCEP PV Associate Job Task Analysis and on standard photovoltaic engineering and safety references. NABCEP is not affiliated with this site and does not endorse it. Answers here deliberately avoid code dimensions, manufacturer specifications, incentive rules and prices, all of which change and vary by jurisdiction — always apply the electrical and building codes adopted by the authority having jurisdiction, the equipment manufacturer's instructions, and your employer's safety program. Confirm current exam requirements with NABCEP before testing. About the NABCEP Associate program →