Troubleshooting Photovoltaic Systems

Troubleshooting Photovoltaic Systems

Solutions to three common problems you might find in the field

Make energy while the sun shines — that’s what we expect of a photovoltaic (PV) system (see Components of a PV System). So if the sun is out but the system isn’t producing to capacity, there’s a problem. Like other energy systems, a PV system requires troubleshooting on occasion. The strategy you choose for identifying the trouble source is key to your success. Look for three causes: an array problem, inverter problem, or load problem. We all like to take advantage of the summer’s sunny days. By focusing on common troubleshooting problems and solutions, you can make sure your PV system does too.

Troubleshooting an 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 might 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.

Many combiner boxes have fuses for each module or sub-array string. These can save you time when troubleshooting. Remove the fuses, and record the open-circuit voltage and current reading for each circuit string. If the output voltage is low, it could indicate some modules in the series string are defective or disconnected and need to be replaced. Defective blocking or bypass diodes in the modules might need to be replaced. Low voltage could also be caused by the wrong wiring connecting the modules in the string to the junction box, combiner box, or the inverter. The wiring could either be 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, or a damaged module. One or more parallel connections between modules in the string might be broken, loose, or dirty — or some parallel connections in the module might be 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 might be shaded, significantly reducing its current output. Remove the shade source to regain the string’s full current output.

Dirty modules could also cause reduced current output. Wash the modules to restore the array’s current output; then check it again.

Troubleshooting an inverter problem

Use a volt meter and DC ammeter to check and record the inverter’s operating DC input voltage and current level. On the AC side, check the inverter’s output voltage and current level. A lack of power output from the inverter could be caused by a blown fuse, a tripped breaker, or broken wires.

Many PV inverters have LED displays as indicators. Check that the appropriate LEDs are lit up to indicate proper inverter operation.

If your volt meter is of the true-rms reading type, you can use the voltage and current to measure and record the kilowatt output. If the inverter can display the total kilowatt hours produced since it first started up, record the amount. Use this number to compare the PV system’s production since the last inspection.

Also take measurements on the AC load side of the inverter, as load on the inverter might have too high of a current demand. In this case, you might need to reduce the loads or replace the inverter with one that has a larger output.

With the power off, check for and repair any ground faults before starting the inverter again. The electric 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 input on the array. Low or high electric utility voltage sensed by the internal disconnects will cause the inverter to shut down. If this problem exists, then contact the electric utility to correct the problem. Inverter problems could also be caused by a problem on the array side of the inverter, which trips one of the internal disconnects.

Troubleshooting a load problem

First, check all load switches. Are they turned off or placed in the wrong position? Check to make sure that the load is plugged in. Next, check the fuses and circuit breakers. If there are blown fuses or tripped breakers, 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 might be tripped, or there might be an open circuit in the motor. In this case, 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 voltage at the load’s connection point. Low voltage could mean that the wire feeding the circuit is too small/too long and needs to be upgraded to reduce the voltage drop. The load could also 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 circuit.

Auvil is the owner of High Performance Mechanical Training (HIPMT), a training consulting firm in Rock Hill, S.C. He is also a technical author for Fluke Corp., Everett, Wash.

Components of a PV System

Cells, modules, and arrays — A typical PV cell produces a small electrical output (between 0.5W and 2W). Because these devices are electrical, they can be connected in series and parallel strings to boost the overall output level. Connecting PV cells in this manner forms what is called a module. Some manufacturers now produce “power modules,” which can produce 190W or more. A 190W module connected to a load might produce 27V at around 7A when exposed to full sun conditions. Modules are commonly connected in series and parallel strings to form what is called an
“array.” The output of an array can be designed to meet almost any electric requirement — large or small.

Combiner box — As noted above, modules are commonly connected into an electrical string to produce the desired voltage and amperage. The resulting wires from each string are routed to the combiner box. In this box, all the strings are combined into one electrical output, which is then fed to the inverter.

Inverter — Depending on the application, a PV system might need to provide DC or AC. Because the cells produce DC, an inverter is required to switch it to AC, as desired. Inverters that are connected to the electric utility grid produce AC that is identical to the power produced by the electric utility. These inverters sense the electric utility’s generated voltage and waveform characteristics and produce AC of the same form.

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