Analysing anomalies in a photovoltaic system requires a shift from reactive maintenance to preventive diagnostics of power quality phenomena. Seemingly isolated symptoms, such as inverter resets, nuisance tripping, and brief shutdowns, often conceal voltage variations, voltage sags, or harmonic pollution. Implementing active protection systems stabilises output, reduces downtime, and extends the service life of power components.
WHY ELECTRICAL TROUBLESHOOTING IN A PV SYSTEM MEANS MORE THAN JUST FINDING THE FAULT
The traditional approach to photovoltaic system maintenance focuses on replacing the damaged component. Effective PV troubleshooting, by contrast, requires an understanding of the grid dynamics that lead to degradation or service interruption. Identifying the root cause of a malfunction prevents the same damage from recurring, shifting the focus from emergency response to optimisation of the electrical architecture.
A structured investigation maps the interference between the distribution grid, the non-linear loads within the facility, and the power electronics of the solar installation. This approach is especially relevant today, as the growing integration of renewable sources introduces new and specific challenges for voltage stability and power quality.
ARERA Data: according to data published in document 287/2019/R/EEL, in 2017 each user connected to the Italian MV grid experienced an average of approximately 100.97 voltage sags over the course of the year. A statistically significant phenomenon, often invisible to a superficial inspection, yet capable of generating resets, shutdowns, and production losses, particularly in continuous manufacturing processes and sensitive loads such as photovoltaic inverters.
Business Driver: Operational continuity (O&M).
Expected impact: reduction of unplanned plant downtime by up to 30% and stabilisation of the LCOE (Levelised Cost of Energy) through elimination of systemic faults.
THE 7 RECURRING ELECTRICAL SYMPTOMS TO MONITOR
The presence of power quality anomalies manifests through specific signals affecting power electronics and distribution panels. Below are the seven most common operational symptoms, together with their technical interpretation.
1. REPEATED TRIPPING OR ALARMS WITHOUT APPARENT CAUSE
The operation of MCB or RCD protection devices in the absence of evident overloads often indicates the presence of high-frequency leakage currents or harmonic distortion. The circuit breaker interprets these waveform alterations as a fault and interrupts supply as a self-protection measure.
Correct diagnosis requires distinguishing between a local anomaly (loose connection, degraded insulation) and an upstream electrical disturbance affecting the entire distribution chain. If the same event recurs across separate panels at similar times, the cause is almost certainly systemic and should be traced back to the quality of the supply voltage.
2. SUDDEN RESETS OF INVERTERS, CONTROLS, OR AUXILIARY DEVICES
Uncommanded restarts of conversion systems or PLC control boards signal a momentary loss of supply. Voltage sags, even lasting only a few milliseconds, bring the voltage below the electronics’ tolerance threshold, forcing a shutdown and restart cycle.
Technical note.V_POD Mechanism: In prosumer installations (combining passive load and PV generation), the voltage at the point of delivery (V_POD) is not fixed. When loads prevail, V_POD drops; when the generator dominates, V_POD rises. The simplified formula is: V_POD = V_S ± ΔV, where ΔV depends on the current flowing through the line impedance Z. On a ‘weak grid’ (high impedance), even moderate changes in current generate large voltage fluctuations, sufficient to trigger the inverter’s over- or under-voltage protection. This is not an inverter fault, but its correct response to an abnormal electrical condition. Normative reference: CEI EN 50160 (limits Vn ±10%).
3. IRREGULAR PV OUTPUT INCONSISTENT WITH ENVIRONMENTAL CONDITIONS
Abnormal dips in the efficiency curve, not justified by shading or irradiance drops, indicate inverter derating. The unit autonomously reduces the power fed into the grid to protect itself from phase imbalances, sustained overvoltages, or instability on the AC side.
Same irradiance, same temperature, but significantly different output compared with the previous day: this scenario is the most direct signal that the problem does not lie in the modules, but in the electrical conditions of the installation.
4. SPORADIC DISCONNECTIONS OR TEMPORARY PV SYSTEM SHUTDOWNS
Disconnection of the photovoltaic system via the Interface Protection System (IPS) occurs when grid parameters, voltage and frequency, fall outside normative limits. Sudden fluctuations caused by nearby large industrial loads generate temporary disconnections that halt production for several minutes before automatic recovery.
A distinction must be drawn between a protection-triggered shutdown (correct: the device is operating as designed) and an actual loss of continuity. In the former case, the solution lies upstream, in the stabilisation of the grid voltage at the system’s point of connection.
5. ABNORMAL OVERHEATING OF ELECTRICAL COMPONENTS
Excessive heat generated by transformers, cabling, and power-factor correction capacitors is the primary symptom of harmonic pollution. Harmonic currents, adding their frequency to the fundamental component, increase the Joule effect and accelerate thermal degradation of plastic insulation.
Abnormal thermal behaviour in components correctly rated for nominal loads is almost always attributable to the presence of non-linear loads, such as inverters, variable-frequency drives, and UPSs, which inject harmonic currents into the network.
6. INCONSISTENT BEHAVIOUR ACROSS SIMILAR DAYS OR SHIFTS
The variability of faults according to production schedules indicates an interaction between the PV system and the internal loads of the facility. Start-up of large motors, compressors, or arc furnaces modifies the grid impedance, generating cyclic voltage drops that affect solar energy injection.
On bank holidays or during night-time hours the grid is generally ‘high’ (fewer voltage drops because fewer active loads). At full production, with PV generation at maximum and heavy loads running, the V_POD can oscillate in both directions. This explains why the same installation exhibits radically different behaviour at different times of day or week.
7. BRIEF EVENTS THAT LEAVE NO OBVIOUS TRACE BUT CAUSE DISRUPTION
Rapid transients (voltage spikes) damage semiconductors over time without causing immediate shutdowns. The most insidious phenomena are the briefest, invisible to a superficial inspection, yet sufficient to trigger the control electronics.
ARERA data (Table A2.17, source: document 287/2019/R/EEL, 2017 data) shows the duration distribution of voltage sags recorded on the Italian MV grid:
| Sag Duration | Avg. Events (2017) | % of Total | Operational Perception |
| 10–200 ms | 84.02 | 83.2% | Invisible, but critical |
| 200–500 ms | 14.04 | 13.9% | Barely perceptible |
| 500 ms–1 s | 1.78 | 1.8% | Brief interruption |
| 1–5 s | 0.83 | 0.8% | Clearly perceived |
| 5–60 s | 0.30 | 0.3% | Evident interruption |
| Total | 100.97 | 100% | MV user average/year |
The vast majority of events (over 97%) last less than 500 ms, too brief to be noticed by operators, but more than enough to force a reset of the control electronics or a disconnection of the IPS. Monitoring these anomalies requires dedicated diagnostic platforms, not a simple visual inspection.
HOW TO DISTINGUISH AN OCCASIONAL SYMPTOM FROM A POWER QUALITY ANOMALY
Identifying a structural problem requires the categorisation of events recorded by industrial data loggers. Not all symptoms carry the same diagnostic urgency.
| Symptom Type | Event Frequency | Impact on Inverter | Recommended Action |
| Occasional | < once a month | Log entry, no restart | Passive monitoring |
| Severe transient | Linked to storms or grid faults | IPS disconnection, surge arrester activation | Visual inspection of components |
| Systemic (voltage sags) | Weekly or daily | Frequent resets, loss of production data | Installation of voltage compensators |
| Structural degradation (harmonics) | Continuous | Overheating, premature wear of transformers & cables | Instrumental analysis, active filters |
The most reliable discriminating criterion is repeatability: if the same symptom occurs under the same operating conditions (same shift, same load combination, same irradiance), the problem is structural and requires instrumental analysis. Correlation with production schedules is the second key indicator.
WHAT ELECTRICAL CAUSES MAY LIE BEHIND THESE SIGNALS
The symptoms described above stem from physical alterations in the quality of the energy supplied. There are four main categories of cause.
VOLTAGE VARIATIONS AND SAGS
Voltage sags are temporary reductions in voltage, even as little as 10–30% below the nominal value, lasting from a few milliseconds to a few seconds. They are caused by faults on the medium-voltage grid or by the energisation of large nearby loads, and they deprive inverters of the energy needed for synchronisation with the grid.
TRANSIENT OVERVOLTAGES
Often linked to switching operations in distribution panels or atmospheric events, transient overvoltages stress the galvanic insulation of components. They do not always cause immediate failure, but accelerate insulation degradation over time, increasing the risk of catastrophic fault.
HARMONIC POLLUTION
Produced by PV inverters themselves or by variable-speed drives in the facility, harmonic pollution distorts the sinusoidal waveform of voltage and current. It generates eddy currents in transformers, increases Joule losses, and causes abnormal overheating.
INTERACTIONS WITH INDUSTRIAL LOADS AND THE GRID
The start-up of high-inertia motors, insertion/disconnection cycles of arc furnaces or hydraulic presses instantaneously alter the system impedance. This generates voltage fluctuations that interact with the PV system’s IPS, causing the sporadic disconnections described in Symptom 4.
Normative Note. Reference limits for voltage quality on low- and medium-voltage networks are defined by CEI EN 50160. The standard requires that the supply voltage remains within Vn ±10% for 95% of the time over any given week. Exceeding these limits, documented by instrumental analysis, provides the technical basis for initiating a corrective intervention. Additional reference: CEI 0-21 for the connection of PV systems to the low-voltage grid.
WHEN TO MOVE FROM TROUBLESHOOTING TO SYSTEM PROTECTION
The diagnostic investigation has fulfilled its purpose once the problem has been isolated and measured. Continuing to manually restore machines after each anomaly incurs unsustainable operational costs and undermines the return on investment of the photovoltaic asset.
The transition to protective action becomes necessary when data confirm the recurrent nature of the disturbance. Three concrete operational thresholds:
Voltage sags cause multiple production stoppages in a month: the lost energy exceeds the cost of a compensator.
Harmonic distortion exceeds 5% THD (Total Harmonic Distortion) on voltage, or 20% on current: the thresholds of CEI EN 50160 have been exceeded and accelerated component degradation is at risk.
Recurring inverter derating reduces average output by more than 3–5% compared with plan: the revenue loss is quantifiable and justifies a technical intervention.
In all these cases, troubleshooting has fulfilled its function: it has turned a vague symptom into a measurement. The next step is the selection of the most appropriate protective technology.
ORTEA NEXT SOLUTIONS FOR IMPROVED STABILITY AND CONTINUITY
Implementing power quality technologies resolves the electrical symptoms identified at their root, protects sensitive equipment, and optimises system performance. The architectures engineered by Ortea Next cover the full spectrum of grid anomalies.
BIDIRECTIONAL VOLTAGE STABILISERS – SLOW FLUCTUATIONS
Voltage stabilisers (Orion, Sirius, Odyssey series) compensate for slow grid variations, maintaining the supply within the optimal parameters for conversion electronics to a precision of ±0.5%, in compliance with CEI 0-21. Designed to operate in prosumer installations without special variants, they correctly manage both the flow of energy from loads towards the grid and the reverse flow from PV generation towards loads.
OXYGEN AND OXYGEN ZERO COMPENSATORS (VOLTAGE SAGS AND MICRO-INTERRUPTIONS)
To address rapid transient phenomena (voltage sags and micro-interruptions), those responsible for the majority of inverter resets, the Oxygen and Oxygen Zero series compensators intervene by injecting the missing energy to prevent inverter reset and the consequent disconnection of industrial loads. The range covers outputs from 200 to 2,500 kVA.
ACTIVE FILTERS (HARMONIC POLLUTION)
Against abnormal overheating and nuisance tripping caused by harmonics, the ACTIVEmatic FA40 and VARYX FILTER active filters analyse the waveform in real time and generate counter-phase currents, cancelling harmonic distortion at source. They operate across a range of 60 to 300 A and integrate with any existing installation configuration.
ISOLATION TRANSFORMERS (GALVANIC ISOLATION)
To protect inverters and storage systems from overvoltages and overcurrents originating on the grid, Ortea Next isolation transformers (up to 2,000 kVA) create a galvanic barrier between the PV side and the grid side, preventing the propagation of disturbances in both directions.
The value does not lie in the individual product, but in the correct diagnosis. Without an accurate reading of the symptoms, even the best technology risks being oversized or ill-suited. Ortea Next integrates analytical expertise, customised design, and post-installation technical support to ensure that the adopted solution responds precisely to the nature of the disturbance identified.
FAQ
WHAT ARE THE MOST COMMON ELECTRICAL SYMPTOMS IN A PV SYSTEM?
The most frequent operational signals include sudden inverter resets, tripping of RCD protections in the absence of overloads, frequent disconnection of the Interface Protection System (IPS), and abnormal overheating of cables or transformers in switchrooms. In the vast majority of cases, the root cause is attributable to power quality phenomena, not physical component failures.
HOW TO DETERMINE WHETHER THE PROBLEM ORIGINATES FROM THE SUPPLY VOLTAGE?
Voltage-related anomalies typically manifest as sudden dips in power fed into the grid, instantaneous shutdowns and restarts of industrial control boards, or through specific alarms (Overvoltage / Undervoltage) systematically recorded in the inverter logs. Correlation between the timing of events and load peaks within the facility is a fundamental diagnostic indicator.
DOES AN OCCASIONAL INVERTER RESET REQUIRE IMMEDIATE ACTION?
If the event occurs less than once a month and coincides with extreme weather conditions, it falls within normal operating parameters. If it is more frequent, or occurs under apparently stable grid conditions, an instrumental inspection specifically targeting voltage sags is required. ARERA data indicates that the Italian MV grid records an average of approximately 101 voltage sags per year per user: the statistical probability that an industrial PV installation is affected is far from negligible.
CAN VOLTAGE SAGS CAUSE TEMPORARY PRODUCTION STOPPAGES?
Yes. Voltage sags drastically reduce the energy available to the inverter’s control circuits. If the event exceeds the system’s millisecond tolerance threshold, the machine enters protective lockout, requiring several minutes to safely complete the restart and synchronisation cycle. For continuous-production installations, even five monthly stoppages of ten minutes each represent a significant and quantifiable loss of generated energy.
WHEN IS AN IN-DEPTH POWER QUALITY ANALYSIS NECESSARY?
Instrumental measurement becomes an indispensable action when recurring failures of electronic boards are recorded, when thermal protection devices operate systematically, or when calculated production losses cannot be correlated with actual solar irradiance data. Monitoring with certified data loggers (compliant with IEC 61000-4-30 Class S) makes it possible to classify disturbances precisely and to correctly size the protective intervention.
CONTACT AND TECHNICAL SUPPORT – ORTEA NEXT
If any of the symptoms described in this guide recur over time in your installation, it is advisable to investigate whether voltage disturbances or electrical continuity issues are at the root cause. A structured technical analysis makes it possible to identify the nature of the disturbance and the most appropriate solution -without oversizing and without guesswork.
