What is a solar photovoltaic ground fault?

According to the Photovoltaic Systems textbook (published by NJATC), a solar PV ground fault is “the condition of current flowing through the grounding conductor.”

The cause of this very undesirable current flow is an unintentional electrical connection between a current-carrying conductor in the PV array and the equipment grounding conductor. In other words, the electric current that was supposed to flow to the inverter, or combiner box, flows directly to the ground terminal. Above a certain current threshold, the inverter shuts down entirely for obvious safety reasons.

In this article, we will explore PV ground faults. Further, we will show how to find and mitigate faults using the Z200 PV Analyzer.

Read our high-tech blog post about  “Isolation Resistance” in photovoltaics here.

Z200 PV Analyzer: Ground Fault Locater mode

  • This application is used to measure the isolation of the PV string towards the ground. If poor isolation is found, the instrument will attempt to position the fault.
  • The measurement analysis assumes that modules in the string are producing evenly. If a fault is not found accurately, it may point to additional or other problems. The user is advised to run a String test as well.
  • The test is a very popular feature found in the Z200 suite of testing methods.
  • The analysis algorithm is however a study in itself. The method has been continuously developed to perfection by emazys.

Solar ground fault troubleshooting

Solar ground faults result in PV array shutdown and energy losses. Safety hazards to service technicians are also important to consider. Using the Z200 PV Analyzer, solar PV ground faults can quickly be located and repaired.

The Z200 PV Analyzer is a new type of instrument capable of measuring the position of electrical PV faults. In particular, the instrument is the fastest solution for PV ground fault troubleshooting.

PV system ground faults occur if the isolation resistance Riso drops below a certain value of typically 3 MΩ.

When this happens PV inverters shut down the operation, and the risk is thus massive energy losses if a PV ground fault is not found and corrected. 

Safety to persons and animals becomes an issue when a PV system is not isolated properly.

The Z200 PV Analyzer offers fast PV ground fault analysis. This leads to the exact localization of faults.

Periodic solar panel Riso faults

In some cases, PV ground faults are periodic and intermittent. Typically moisture in the morning will induce the faults. Panel strings are down until the equipment dries up in the sun. This makes PV ground fault troubleshooting difficult and costly.

The Z200 PV Analyzer has a build in ground fault detector. It can measure the position of a ground fault in a solar PV system. The detector has a timer function, which may be used for monitoring also.

The user can simply set a time interval suitable for “catching” the ground fault. hereafter the user let the instrument measure for an extended time period e.g. 24 hours. When the user returns to the instrument, the results may be downloaded and the position of the fault can be read.

Solar PV systems are not maintenance free

The worldwide market for MW-scale O&M is expected to triple over the next years. This development is driven mainly by the big markets in China, the U.S., and Japan.

Solar PV O&M means a lot of things, but basically, it revolves around the following major tasks and activities: 

  • Archive maximum system performance
  • Monitor PV system performance
  • Perform preventive maintenance 
  • Manage PV system alerts 
  • Audit energy production

The tasks all depend on each other, and if one task is avoided, problems tend to build up. Let us consider ground faults as an example. Firstly, ground faults, or earth faults in the PV array, are what apparently take up many field technicians’ time.

Reduce the ground fault troubleshooting costs now!

Many ground fault tools are available on the market today. The most common feature is that the tools help to detect, whether or not a ground fault exists in the PV system. From a maintenance cost point of view, this is not enough. Ideally, a tool also makes it clear where the fault is.

The safety requirements and details can be studied in the IEC 62446-1:2016, Photovoltaic (PV) systems – Requirements for testing, documentation, and maintenance.

For the PV array owner, a PV ground fault has a clear consequence. The fault makes the solar inverter, or combiner box shut down completely. Production is only reestablished if the isolation resistance (Riso) becomes sufficiently high again. Typically Riso must be a minimum of 2 MΩ, but a healthy PV system has a Riso value of more than 40 MΩ.

For a residential PV array, a ground fault typically takes down 2 or 3 strings. The system owner has to pay a local service provider, for hours of troubleshooting, transportation, and scaffolds. Meanwhile, the faulty component is typically a cheap connector or a cable. In some cases, PV ground faults are caused by modules with water intrusion, or by other more rare and exotic faults.

The cost associated with residential ground fault mitigation is often higher than the system owner appreciates. This is especially the case when the return on investment is considered. This is one of the reasons why some residential PV arrays are not properly maintained and serviced.

For utility PV power plants, the ground fault problem is basically the same, but the scale is extended. More technicians have to be involved, and transport costs become essential. Entire PV arrays will be down until the faults are found. For utility-scale PV systems, a ground fault often means that 200-400 modules are not producing while the ground fault persists.

Another cost driver is observed when field technicians are looking for certain inverters, combiners, strings, or modules. While monitoring software can often pinpoint PV arrays on a circuit diagram, no efforts were made to label and map the rows of modules. And even when components are labeled, it still takes time to find the strings, because systems are huge these days – and they are only getting bigger. The Z200 PV Analyzer also has a solution for this problem.

“A photovoltaic array is an investment that is not subject to wear. This hypothesis might have persisted for years, however, this does not make it tenable: even carefully planned and executed arrays need monitoring, an occasional inspection, and, at times, repairs.”

Jochen Siemer
PHOTON International 2016

The above statement from Jochen Heimer seems to be confirmed by almost anyone in the modern solar industry, who has a field-oriented responsibility. A while ago, when solar energy was still a new star in the sky, it was common to hear sales pitches describing solar energy, and how “maintenance free” it was. Nowadays, the solar industry is however more mature and also consolidated in many areas.