February 15, 2020

Fault Busters: A field technician’s guide to troubleshooting solar inverter issues

San Diego – 2/10/20 – You’ve got a fault code or even a whole series of fault codes, and it looks like something has gone wrong with an inverter. Downtime is expensive, so a technician needs to hop in a truck and go fix that faulty inverter pronto, right?

Fault Busters: A field technician’s guide to troubleshooting solar inverter issues

Hold on there. Effective troubleshooters never shoot from the hip. The best field technicians know that those initial fault codes are just the start of a puzzle that requires a measured plan of attack to resolve. Inverters can represent up to one-fifth of the cost of the entire system, but they are the source of 80 percent of the issues when something goes wrong. Getting smarter about fixing those problems can make you a better technician.

This troubleshooting how-to guide can help technicians of all experience levels get the electrons flowing again, ideally with a single truck roll. Whether the repair is needed at a residential PV installation or a utility-scale solar plant, these steps can help fix problems safely and efficiently.

Data Collection and Background Research

First off, document everything from the moment there is any sign of a problem. This holds true at every step of the repair process, including after everything is working smoothly again. Write down or take a picture of everything you learn, see and do. We’ll explain the long-term benefits of all this documentation in the conclusion.

Make full use of any remote monitoring that’s available. Record every fault code and error message. Symptoms may change as you move through the troubleshooting process, but begin building a timeline with those initial signs of trouble.

Don’t assume that every alarm is an additional component issue, but do record all of them. Remote monitors may indicate that a circuit board or a fan has gone bad, but if the first fault code indicated a loss of grid power, there may be nothing wrong with the equipment down the line.

Gather background on each piece of equipment — and each component — that may be involved. Write down model numbers and serial numbers and check whether any of them have been through prior repairs.

Define what every code means. Solar Support’s web portal can help with that, and may even suggest resolutions. Don’t hesitate to reach out to manufacturers, too. They may be able to discuss possible scenarios or even how similar faults have been addressed in the past.

While some manufacturers are good about picking up service calls, some aren’t accessible within reasonable wait times. If you get stuck, equipment specialists like Solar Support with dedicated phone and online services can make all the difference.

And don’t forget to check operating manuals. You may be pleasantly surprised to find answers there.

Prepare for Dispatch


Talk it through. Now you’re ready to prepare a plan of attack, either written or verbal, that you can go over with a colleague. Talking everything through, step by step, is critical to clarifying how you need to prepare.

Build scenarios. Outline what you expect to encounter in the field and how you would respond to each possible scenario.

Safety first. Prepare and discuss a safety plan that anticipates every potential issue and how it can be dealt with. Conduct a job hazard analysis both before dispatch and upon arrival.

Make a list. Determine what tools and possible replacement parts should go to the site with you. For example, is the inverter European? Make sure you take metric tools with you.

Check it twice. Mark off each tool and part as you put them in the truck. Speaking of which, here’s a basic list of tools to get you started.

Tools to Get you Started

  • Standard socket and wrench kit with short and deep sockets
  • Metric socket and wrench kit with short and deep sockets
  • Basic hand tool set (screwdrivers, side cutters, pliers, etc.) electrically rated, preferably up to 1500v
  • A recently calibrated multimeter for up to 1000v works for most systems. You will need a specific type of meter for DC systems in the 1500v range. An amp clamp is mandatory for the multimeter. A multimeter with integrated data logging capabilities is advisable.
  • Torque wrench and marker
  • Flashlight and headlamp
  • Applicable code, standard, AHJ, federal and state compliant safety personal protective equipment (PPE)
  • Pen and paper for documentation
  • Laptop with appropriate software, files, reference manuals, datasheets, service guides, etc.
  • Equipment interface adapters (i.e. RS485, RS232, Ethernet/Cat5, WLAN a/b/c/n, Bluetooth, proprietary connectors or cables, DAQ, etc.)
  • Mechanical probe/reacher/retrieval tool
  • Breaker bar for high torques
  • Megohmmeter (optional, but so useful)
  • Internet/WiFi capable device or hotspot with internet access
  • Camera or photo capability on a smartphone
  • Mobile phone with active and available cellular service (may also satisfy the previous two items)
  • Optional: A live-dead-live device (LDL) also known as a proving unit
  • All five senses
  • And don’t forget the keys for the equipment you will be working on!

On-site Troubleshooting


Safety first, during and after. Know where the power is on and where it is off. Never assume. Conditions are unpredictable in any fault scenario. Go over the job hazard analysis again. Before touching anything, say out loud what you’re going to do.

Document everything. Take plenty of pictures. It’s helpful to know what the site looked like when you got there and how the layout may have changed as you proceed. Go back over your plan of attack, altering it if conditions on-site differ from what you expected.

Use all of your senses. You may be able to follow your nose to a burnt component. Listen — does the troublesome inverter sound different than its counterparts?

Check peripheral connections. Be certain your meter is properly calibrated and rated for the voltage you expect. Bear in mind that what initially appears to be a bad inverter may instead be a symptom of a problem elsewhere.

Measure everything. All of the DC voltages — not just the averages — for each string. Write them down: positive to negative, positive to ground, negative to ground. Measure open circuit and with them connected to the inverter. Do the same with the AC voltages: phase to phase, phase to ground or neutral.

Begin to rule things out. Don’t forget the simple things. Is everything connected properly? Is the wire seated properly in the terminal block? Is the WiFi connection working? Is there metallic dust in the air? Look for Mother Nature’s contributions. Did a squirrel chew through a wire? Did a snake get inside the cabinet?

The Repair

As you hone in on the problem, continue to document everything, including serial numbers both from good parts and bad parts. Double-check your safety plan.

Don’t assume a component is bad just because it’s not working the way it should. That component may perform perfectly after the underlying problem is corrected.

Take pictures of trouble areas before you change anything, and continue to photograph your process as you complete the repair. Changes you make at one point may affect the outcome down the line. Avoid chasing your tail.

Photograph the final repair.

Wrapping Things Up

A successful repair — ideally during a single site visit — isn’t the end of the process. As we hinted earlier, getting your documentation in order is the final step.

As quickly as possible after the repair is finished, go back over all of your material and put it in a format that’s readily accessible to everyone else on your team. Thorough documentation from start to finish separates the experts from the amateurs, making you a much better technician and troubleshooter.

Keep in mind that you may not be the technician called to that site the next time something goes amiss. If each of your colleagues is as conscientious as you have been, you’ll be able to benefit from their previous experience when you are called to an unfamiliar location.

Even veteran technicians benefit from planning ahead, talking things through and documenting throughout. We all can use reminders about what we may need or what we’ve done previously.

Knowing that you’ve seen something before — and being able to look back at exactly what you did you resolve it back then — puts you that much closer to a single truck roll repair.

Auston Taber is CEO of Solar Support. Clifford Myers is the chief engineer of Solar Support. Solar Support is an integrated PV equipment and plant restoration company that combines inverter expertise with construction management to resolve complex issues for utility systems.