Periodic inspection of a photovoltaic system after 5 years of operation – case study
Simply viewing energy yields in the inverter app is not enough – proper energy production does not guarantee the absence of hidden faults. Find out how to perform a professional periodic inspection of a 5-year-old photovoltaic installation in accordance with the EN 62446-1 standard using the Sonel PVM-1021 meter and the Sonel IRM-1.
Why is monitoring the inverter alone not enough?
The large number of photovoltaic systems in Poland means that their subsequent operation and the maintenance of an adequate level of safety and efficiency are becoming increasingly important. While performing a full testing package during the commissioning of a new system is standard practice, in subsequent years of operation, inspection is often reduced merely to monitoring inverter operation and energy yields.
However, it should be remembered that correct energy production does not always signify a sound technical condition of the installation. Insulation degradation, damage to surge protection devices, or deterioration of electrical connection quality can remain undetected for a long time.
Inspection of a 5-year-old photovoltaic system in practice – case study
As part of the case study, a PV system operating at a single-family house was inspected. Photovoltaic modules here were mounted on a ground-based structure, while the inverter was located at a distance of approximately 20–30 m from the PV generator.
The scope of the inspection, based on tests applied during the verification of PV systems in accordance with EN 62446-1, included:
- visual inspection of the installation,
- open circuit voltage measurement (UOC),
- short circuit current measurement (ISC),
- DC side insulation resistance measurement (RISO),
- checking the continuity of protective conductors and equipotential bonding (RCONT),
- recording environmental conditions.
The photovoltaic meter Sonel PVM-1021, operating in cooperation with the solar radiation and temperature meter Sonel IRM-1, was used to perform the measurements.
Stage 1: Visual Inspection and Identification of DC Circuit Parameters
The first stage of the inspection was a detailed visual verification of the installation. Based on the rating plate, LONGi LR4-66HPH-415M modules with a nominal power rating of 415 W were identified.
The installation consisted of 22 modules divided into two strings of 11 modules connected in series. Each string was connected to the inverter via a separate pair of DC cables and tested individually.
During the visual inspection, the following aspects were checked, among others:
- surface and frame condition of the modules,
- mounting of panels to the structure,
- cable routing underneath the modules,
- condition of visible connectors and junction boxes,
- cable protection against friction and sharp edges,
- equipotential bonding of the structure,
- markings and protective devices on the DC side.
Visual inspection result: No mechanical damage to the modules or signs of overheating in cables and connectors were found. The visual inspection of the AC distribution board also concluded with a positive result.
Stage 2: Measurement of protective conductors and equipotential bonding continuity (RCONT)
The next step was measuring the continuity of protective conductors and equipotential bonding. One measurement point was located at the PV installation, and the second in the area of the inverter and main equipotential bonding.
Due to the significant distance, it was necessary to use a 30-meter test lead. Prior to the actual test, auto-nulling was performed, i.e., compensation of the test lead resistance. The Sonel PVM-1021 meter performs the RCONT measurement with a test current of approximately 200 mA.
Obtained measurement results:
- PV frame connection continuity: 0.2 Ω
- Continuity of frame to inverter connection: approximately 0.6 Ω
A great convenience for a field technician is the built-in AutoStart function in the Sonel PVM-1021. It automatically initiates the measurement upon detecting appropriate measurement conditions. This option is available for resistances lower than 21 Ω.
Stage 3: Recording environmental parameters and STC conversion
Environmental parameters used to convert measurement results to STC conditions were transmitted to the Sonel PVM-1021 meter. The solar radiation and temperature meter Sonel IRM-1 was positioned in the same plane as the tested modules so that the irradiance sensor reflected the irradiation conditions of the tested string. A mounting and measurement kit for the IRM-1, equipped with a probe enabling the measurement of both PV module temperature and ambient temperature, was used to attach the meter and measure temperature.
Environmental data was transmitted from the IRM-1 meter to the PVM-1021 in real time via wireless LoRa® radio technology.
The connection status is continuously indicated on the display of the Sonel PVM-1021 (a flashing icon indicates connection initiation, while steady light indicates established stable communication). Thanks to this, the master meter continuously accounts for current irradiance and temperature during STC value calculations.
If radio range is temporarily interrupted during field operation, the reSYNC function comes to the rescue, automatically supplementing results with environmental parameters saved in the memory of the IRM-1 once connection is restored.
Stage 4: Core DC side measurements in AUTO mode
The key part of the inspection was performed in AUTO mode. This is where the Sonel PVM-1021 particularly facilitates the work of the technician - after a single lead connection and pressing the START button, the meter automatically carries out a sequence of three basic DC side tests.
After preparing the installation and disconnecting the tested string from the inverter, the Sonel PVM-1021 was connected via MC4 adapters to the positive and negative leads. The third lead was connected to the grounded mounting structure of the installation.
Before starting the measurement, nominal parameters of the tested module/string and appropriate temperature coefficients α and β were entered in accordance with the manufacturer's documentation.
After setting the parameters and pressing the START button, the meter automatically executed:
- open circuit voltage measurement (UOC),
- short circuit current measurement (ISC),
- insulation resistance measurement (RISO+ and RISO-).
There was no need to switch meter functions or reconnect test leads between consecutive tests. In practice, this means fewer operations performed by the operator, shorter working time at the string, and a lower risk of error when changing the measurement configuration.
The Sonel PVM-1021 measured an open circuit voltage of 510.0 V and a short circuit current of 4.43 A, and thanks to the data received from the IRM-1, it converted the results respectively to 513.3 V and 11.16 A under STC conditions. Simultaneously, insulation resistance measurements were performed: values >300 MΩ for the positive pole and for the negative pole at the 1000 V range. The Sonel PVM-1021 allows selecting the measurement voltage UISO appropriately for the tested installation.
Within the scope of the conducted tests, no irregularities indicating a deterioration of the electrical safety of the installation were found. All measurements were performed within a single automatic sequence, without changing functions and without reconnecting test leads.
At the start of the measurements, irradiance was approximately 430 W/m². During consecutive tests, solar conditions deteriorated, with irradiance periodically dropping to around 380 W/m² and rising to around 410 W/m². Due to the relatively low irradiance level and significant difference between measurement conditions and STC conditions, results converted to STC should be interpreted with increased measurement uncertainty. In case of doubt, it is worth repeating the measurement under higher and more stable irradiance.
Stage 5: Thermal imaging inspection with Sonel KT-525-PRO camera
The final stage of the inspection was a thermal imaging inspection of the PV modules, serving as an excellent complement to the basic range of electrical testing. A Sonel KT-525-PRO thermal imaging camera was used to evaluate temperature distribution on the surface of the modules. The inspection enabled precise analysis of the thermal state of module surfaces and identification of potential anomalies across modules, connectors, and electrical connections.
Thermal diagnostics in photovoltaic installations enables rapid detection of faults such as:
- locally overheating cells,
- irregularities in the operation of individual module sections,
- unwanted activation of bypass diodes,
- overheating junction boxes and electrical connections,
- effects of soiling or partial shading of modules.
Summary: Comprehensive diagnostics is more than yield monitoring
Periodic inspection of a multi-year-old PV installation should include not only evaluating its current operation, but also verifying the technical condition of components that remain outside direct inverter supervision during normal operation.
Measuring the continuity of protective conductors and equipotential bonding, open circuit voltage, short circuit current, and insulation resistance allows evaluating basic electrical parameters of the DC side and detecting irregularities that do not always cause a noticeable drop in energy yield.
Complementing electrical measurements with visual inspection and thermal imaging gives a more complete picture of the installation condition. Thanks to this, the inspection is not limited solely to determining whether the installation produces energy, but also allows pointing out areas requiring further diagnosis.
