In a world where we are seeing the rapid growth of photovoltaic micro-installations, it is essential to not only ensure their proper installation but also to regularly assess their technical condition. The advanced PVM-1021 Pro meter from Sonel S.A. delivers comprehensive, standard-compliant measurements, ensuring both the safety and high operational reliability of PV systems.

Growing Significance of PV System Checks

In 2025, the number of prosumer micro-installations in Poland is expected to reach approximately 1.5 million, with similar large scale investment in other countries. While well designed and properly constructed photovoltaic systems can operate reliably for many years, in practice, installations are not always executed in accordance with the current standards and regulations. It is therefore essential to ensuring the correct implementation of new systems – remembering that it is just as important that regular inspections should be made on existing systems. Only through appropriate visual inspections and electrical tests can you verify that an installation is functioning efficiently and safely, without posing risks of fire or electric shock. The primary legal and technical framework for such inspections is the multi-part standard IEC 62446, which specifies the methodology and scope of safety checks for photovoltaic systems.

Sonel PVM-1021: Successor to a Tried and Tested Solution

Sonel S.A., an established manufacturer of photovoltaic installation measurement instruments, continues to expand its product portfolio with the introduction of the PVM-1021 meter, the successor to the well regarded Sonel PVM-1020 tester. The PVM-1021 features compact housing with a large, easy-to-read display. Measurement functions are selected via a rotary switch, offering an ergonomic interface, while additional settings – such as changing insulation resistance test voltages – are configured using dedicated buttons on the device. Both the buttons and the graphical display are backlit, allowing for operation even in shaded environments, such as under ground-mounted PV panels. The device’s extensive memory streamlines the preparation of measurement documentation, particularly when used with the optional Sonel Reports Plus software. Measurement data from the Sonel PVM-1021 meter can be transferred to a computer via Bluetooth, enabling efficient wireless communication.

Image 1. Sonel PVM-1021 meter

Comprehensive Measurement of Photovoltaic Micro-Installations

The IEC 62446-1 standard classifies tests into Category 1, Category 2, and additional tests. The Sonel PVM-1021 Pro kit supports the complete set of measurements required for the mandatory Category 1 tests. These measurements include:

• measuring the open-circuit voltage U_OC (of a PV panel or chain of panels) up to 1000V DC
• measuring the short-circuit current I_SC (of a PV panel or chain of panels) up to 20A DC
• measuring the operating current of PV panels with external clamps
• polarisation testing performed automatically when measuring U_OC, I_SC or R_ISO PV
• measuring the insulation resistance R_ISO  of PV panels with a measuring voltage of 250, 500 or 1000V DC, simultaneous measurement of two values (plus to earth and minus to earth)
• measuring the resistance of protective and equalising connections R_CONT with ±200 mA.

Image 2. Performing a measurement with the Sonel PVM-1021 meter

In addition to the mandatory Category 1 measurements, the PVM-1021 Pro kit also enables several tests frequently performed in the routine inspections of an electrical test engineer. These include:

• measuring the RMS voltage of the AC mains up to 600V including frequency measurement
• measuring the insulation resistance of AC circuits with a measuring voltage of 250, 500 or 1000V DC
• measuring alternating current (AC)
• measuring active AC/DC power
• measuring resistance with low current with acoustic and visual signalling
• testing diodes at 200 mA with automatic polarity detection
• testing blocking diodes with 1000V DC.

AUTO Mode and Conversion to STC: Fast and Reliable Diagnostics

By measuring key PV installation parameters such as short-circuit current (I_sc) and open-circuit voltage (U_oc), it is possible to quickly verify module integrity, correct polarity, and proper operation within the chain. These measurements can be conducted for either the entire panel chain or an individual module. Notably, the AUTO mode allows the meter to automatically perform measurements of open-circuit voltage (U_OC), short-circuit current (I_SC), and insulation resistance (R_ISO ) of the PV system with a single press of the START button.

To accurately assess the efficiency of the PV panels under test, current and voltage measurements must be converted to Standard Test Conditions (STC), defined as a panel temperature (T_PV) of 25°C, insolation of 1000 W/m², and an air mass factor (AM) of 1.5. These are the conditions under which manufacturers specify the nominal parameters of their modules. The Sonel PVM-1021 makes it possible to automatically convert measurement results to STC, thanks to its integration with the Sonel IRM-1 irradiance and temperature meter.  The two devices communicate over long distances via a LoRa (Long Range) radio link. The IRM-1 meter continuously transmits real-time irradiance data, enabling the PVM-1021 to convert the measured values of short-circuit current and open-circuit voltage to STC. In addition, the Sonel IRM-1 is equipped with a built-in data logger capable of storing up to 5,000 records, greatly enhancing its functionality. This makes it a valuable tool not only during the PV installation design phase but also for diagnosing issues such as panel shading. Measurement data from the IRM-1 can be easily transferred to a computer via a USB connection.

The Sonel IRM-1 insolation and temperature meter measures:

• irradiance (insolation intensity) in W/m² or BTU/ft²h
• PV panel temperature in °C or °F
• ambient temperature in °C or °F
• panel inclination angle
• panel orientation with a built-in compass.

Image 3. Monitoring environmental parameters using the Sonel IRM-1 meter

Safety Standards and the CAT III 1000V Category

The Sonel PVM-1021 meter is housed in a compact casing and fully complys with the CAT III 1000V measurement category. This compliance is crucial, as according to applicable standards such as IEC 61010-2-030, photovoltaic installations are explicitly stated to come under the CAT III overvoltage category.

To ensure safe measurement of PV installations, instruments must meet at least the CAT III category and be rated for the appropriate voltage range. With its CAT III 1000V rating, the Sonel PVM-1021 meets these safety requirements, allowing users to confidently perform measurements on PV systems up to 1000V DC.

Extensive Range of Accessories

In addition to its wide range of measurement functions, the Sonel PVM-1021 Pro set is supplied with a comprehensive array of accessories. These include test leads, alligator clamps, an AC/DC current measuring clamp, MC-4 connector adapters, and an irradiance and temperature meter with a dedicated holder. The entire set is neatly packaged in a durable, portable case that ensures convenient transport and efficient organisation of all the accessories.

Image 4. Sonel PVM-1021 Pro meter with standard accessories

Thanks to its comprehensive accessories and broad measurement capabilities, the Sonel PVM-1021 Pro is an invaluable tool for measurement professionals. It serves as an excellent addition to the toolkit of those who already perform AC-side measurements and wish to expand their capabilities to include the DC side. This model is particularly well-suited for electrical installers involved in the commissioning of photovoltaic installations, where compact size, safety, and equipment reliability are essential.

mgr inż. Marcin Szkudniewski

SONEL S.A.