Recurrent inverter failures at a utility-scale solar plant, published forensic analysis

What happened

A peer-reviewed engineering paper published in June 2025 documented a forensic investigation into repeated catastrophic inverter failures at a utility-scale solar plant in northern Europe. The study combined controlled laboratory reproduction of DC-side short circuit scenarios, with particular attention to faults at the negative DC input terminal, with waveform analysis of failure events recorded at the site. In the laboratory work the initiating faults escalated into multi-phase short circuits and sustained ground fault arcs.

Field waveforms from several separate inverter failures at the site showed comparable signatures, which the authors treated as field validation of the laboratory results. The paper is an open access engineering analysis of utility-scale PV inverter failure modes, and its findings bear on inverter design, protection coordination and operator inspection programmes at sites using inverters of similar protection architecture.

Contributing factors

As stated in the published analysis, the failure sequence ran as follows: a DC-side fault initiated, typically at a negative DC input terminal, with insulation degradation, moisture ingress or mechanical damage identified as possible initiators; internal inverter protection did not interrupt the fault before semiconductor damage occurred; power electronics components then failed under fault currents above their interruption capability; protection relay operating time allowed a ground fault arc to be sustained at high energy during the delay window; and the fault propagated into a multi-phase short circuit within the inverter. The authors note that the laboratory reproduction of the field signatures supports their proposed mechanism and mitigations. Site climate and system configuration form part of the specific context, but the authors describe the underlying failure mechanism as generic to inverters of similar architecture.

Lessons learned

1. Check inverter internal protection and plant relays for DC-side short circuit interruption before semiconductor damage occurs.
2. Inspect negative DC input terminals for insulation degradation, moisture ingress and mechanical damage at sites with similar inverters.
3. Review protection relay operating times against DC fault dynamics to limit sustained ground fault arc energy.

More lessons on electrical protection and isolation, from every incident on the register.

Not yet known

• Inverter manufacturer and model
• Plant name and exact location
• Duration of outages
• Cost of repairs and replacements

This entry is updated when these are reported. Get an alert for the next one like it.

Source

ncbi.nlm.nih.gov