Arc Fault Detection in Solar Power Systems
When a break occurs in a power cable, it can sometimes result in sparking. In an AC (alternating current) cable, this is usually not a major issue—circuit breakers in the fuse box will typically trip and shut off power to the affected circuit. In other words, the fuse blows (actually the residual-current device trips), making the system safe.
However, in a DC (direct current) cable, this does not work the same way. Damage to a DC cable can lead to what is known as an 'arc fault'—a continuous flow of energy between the broken cable ends, generating heat. As long as electricity flows through the cable, the arc fault persists, which can cause the cable insulation to melt and potentially lead to a fire if flammable materials are nearby.
Flammable Materials
Fortunately, in most cases, there are no flammable materials nearby. The arc fault will continue to erode the cable ends until the gap becomes too large to sustain it. At that point, the current stops flowing, eliminating the fire risk. The system owner will notice that the inverter is no longer producing power and call a technician for an inspection.
However, in the Netherlands, there have been a few cases where flammable materials were present near DC wiring, likely causing fires. This has happened with 'in-roof' solar systems, where panels are integrated into the roof rather than mounted on top. In some instances, DC cables inside the roof came into contact with (flammable) insulation materials.
A DC-connector between solar panels that has endured an arc fault for a while and partially melted as a result
Automatic Detection
To address the fire risks associated with faulty DC wiring, some inverter manufacturers have implemented 'arc fault detection.' A sophisticated detection system in the inverter monitors the system for arc faults and generates alerts if one is detected. But how does this system actually work?
An arc fault detector continuously monitors and analyzes the current and voltage waveforms in the electrical circuit, searching for irregularities. When an unusual pattern is detected, the system responds by either sending an alert to the system owner or automatically shutting down the inverter.
error message on SolarEdge inverter indicating an arc fault in the system
False Positives
Recognizing an abnormal pattern is more challenging than it sounds. It is difficult for a detector to distinguish between a normal waveform and one indicating a potential arc fault. As a result, arc fault detection systems often produce 'false positives'—triggering alarms even when no actual problem exists. These false alarms can have costly consequences, as they may lead to unnecessary system shutdowns or dispatching service technicians for no reason. In practice, many arc fault detection systems are disabled after installation, making them a questionable investment.
If the detection system remains active, what happens when an alarm is triggered? In some cases, the PV system owner receives a notification; in others, the inverter shuts down automatically. If the inverter is off, the DC circuit is interrupted, stopping current flow and extinguishing the arc fault. Before restarting the system, a technician must inspect the wiring to determine whether the alarm was a false positive or if a damaged cable needs repair.
False Security or Skilled Installation?
New inverters from manufacturers like SolarEdge and SMA now include arc fault detection functionality. SMA adheres to the latest IEC standards for arc detection in solar power systems: a lot of detailed information can be found in this document. Some insurers now require (especially for larger PV installations on flammable roofs) that inverters have this functionality
The most important thing however, is to pay extra attention to proper DC cable connections during installation, instead of relying solely on the false security of arc fault detection. It's also important to note that only 0.006% of all solar power systems have experienced fires due to the presence of solar panels. The risk of fire is extremely low, and at Zonnefabriek, we can confirm this: In over 15 years and after thousands of installations, we have never encountered a fire in a functional PV installation. The best way to ensure a safe system is through professional installation by experienced experts—like Zonnefabriek.
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