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The solar PV system troubleshooting checklist

BY SEAN SILVEY • PRODUCT APPLICATION SPECIALIST • FLUKE CORP.

As the demand for solar systems explodes across the country, so does the need for technicians who can troubleshoot PV systems effi ciently and effectively.

Solar system troubleshooting typically focuses on four parts of the system: PV panels, loads, inverters and combiner boxes. Here is a checklist for locating and addressing common problems in those areas.

Troubleshooting PV panels

Before you begin troubleshooting, check the output of the entire system at the metering system or inverter, and record the inverter’s input voltage and current level from the array. One of two conditions is the most likely: either the entire PV system, or a portion of it, is down or not producing power (possibly a problem with the inverter), or the PV system output is less than expected (could be an issue with one of the arrays or modules).

• Trace out the individual branch wiring backward from the concentrator.

Check the entire system visually for any obvious damage or accidental disconnections. Once you fi nd the failed module or array, check all wires, switches, fuses and circuit breakers. Replace blown fuses. Reset the breakers and switches. Watch for loose connections between the

modules and replace or clean broken wires and loose or dirty connections. • Check the combiner box. This is a good place to troubleshoot the system, since the individual wires from the modules come back to it. Each module may have a fuse that you should check with your clamp meter. • Watch for low voltage and check wiring connections. If a module’s output is too low, it may mean that an individual section of cells is bad.

Trace these through the wires, the connections, or potential ground fault issues until you fi nd the problem. • Test the open circuit voltage (Voc). If the polarity is reversed, it may mean that other circuits in the combiner

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box are unintentionally connected in series, resulting in voltages over the maximum inverter input voltage. • Inspect the modules for obstructions.

Although PV modules are usually designed to be maintenance-free for years, they may still need to be cleaned. Contaminants like dirt, pollen or dust, or obstructions like shade on the modules themselves can cause reduced output.

Troubleshooting PV loads

The PV system is used to operate electrical loads, so any problems with the loads will affect the PV system as well.

• Measure voltage on the solar array at the combiner box, load switches, fuses and breakers to see if the proper voltage is present at the load’s connections. • Check the fuses and circuit breakers.

If you fi nd blown fuses or tripped breakers, locate the cause and fi x it, or replace the faulty component. • Check for and repair any ground faults. If any fuses or breakers are blown, there’s a short that you need to locate and repair. • Check for broken wires and loose connections. Replace any broken or damaged wiring and clean all dirty connections.

Troubleshooting inverters

The inverter converts DC power coming from the solar system into AC power for use in a building or connected to the grid, and a failure there can cause problems. If the inverter isn’t producing the right amount of power, it may have a blown fuse, a tripped breaker or broken wires. • First, check and record the inverter’s operating DC input voltage and current level, and then check the inverter’s output voltage and current levels on the AC side. Many systems have a display that indicates current inverter and system performance.

If your meter produces a true-RMS reading, you can use the voltage and current to measure and record the kilowatt output. If possible, use the inverter display to show the current total kilowatt-hours.

You can then record that value and compare it to the one measured during the last inspection. • Use your clamp meter to measure the output/AC side of the inverter.

Confi rm that the output voltage and frequency is correct for the demand. • The inverter may be tied into the local utility. As the AC current output from the inverter fl uctuates with the level of solar input on the array, the inverter maintains the correct output voltage and phase to the utility. Any voltage problems from the utility may cause the inverter to shut down. In that event, contact the utility for repairs.

Troubleshooting combiner boxes

Amperage measurements and calculations are crucial to establishing whether the PV arrays are operating correctly.

• Confi rm that all wiring connections are tight. A loose connection could cause fl uctuating voltage or current output to the inverter. • Validate all fuses in the box.

Check that they have correct resistance and continuity. • Make your calculations. Measure and calculate incoming current and

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voltage from the arrays and validate the combined current and voltage output to the inverter. Measuring current on individual arrays or combining current measurements will help you determine if a cell has malfunctioned.

Troubleshooting PV systems efficiently is about being methodical, thorough and using tools that are rated for the job. As solar systems and loads become bigger and more complex, it’s also about safety. The best all-around tool for working in most areas of a solar installation today is a CAT III 1,500-V rated AC/DC clamp meter with features — such as DC power, audio polarity, visual continuity and a thinner jaw design for tight spaces — that are tailor-made for test and measurement in solar PV applications. SPW

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