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

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.

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.

1. Review inverter platforms specifically for DC-side fault interruption capability, and check that inverter internal protection, plant protection and inspection practice are coordinated rather than assumed to be.
2. Include negative DC input terminal condition, moisture ingress and mechanical damage in scheduled inverter inspections, as this is a documented initiation point.
3. Check protection relay settings and operating times against the actual dynamics of DC-side inverter faults, since the delay window influences both the survival of the unit and the energy released.
4. Treat repeated failures of the same equipment type at one site as a possible systemic issue and commission a combined laboratory and field investigation, rather than handling each failure as a stand-alone replacement.
5. Retain high-resolution waveform records from inverter failure events, as matching field signatures against reproduced faults is what allows a mechanism to be identified.
6. Use published engineering literature on inverter failure modes alongside vendor technical bulletins when setting inspection and protection policy.

ncbi.nlm.nih.gov/pmc/articles/PMC12197166