Photovoltaic installations - analysis of basic parameters recorded with the PQM-707 analyzer
Renewable energy sources such as photovoltaics, wind or geothermal energy constitute an increasing share in energy production in the modern world.
A roof covered by photovoltaic panels or a landscape with wind turbines are normal views for us now. It is worth noting that the total installed capacity of photovoltaic installations used in the whole world at the end of 2020, depending on the data source, was between 713 GW[1] and 759 GW[2]. The growing share of electricity production from RES, in particular from photovoltaic installations, prompts a deeper reflection on the efficiency of devices and components used in photovoltaic systems. For future investors, the zero-emission awareness and efficiency of a given installation are equally important. In case of a PV installation, its high ability to transform solar energy into electricity translates into a positive economic calculation in the later stages of operation. Producers are increasingly interested in the quality and durability of the equipment. The apparent savings in the initial phase of the investment are of less importance. The growing requirements for companies offering services in the field of renewable energy sources require an increase in the competences of employees as well as the quality and accuracy of measuring equipment in order to meet the customer's needs.
Fig. 1 Ground-mounted photovoltaic plant in Lubawka (material published with the consent of ECOGRID Bartosz Choromański).
The basic elements of a photovoltaic installation include: photovoltaic modules (PV modules), an inverter, system protective devices the DC (primary) and AC (secondary) side, and a bidirectional meter. The task of PV modules is to convert the energy of solar radiation photons directly into direct current. This current is converted into alternating current in the inverter and then it is used for own needs of the installation, producer or transferred to the power grid. Correct parameters of the power grid (grid voltage and frequency) are very important for the proper operation of the inverter. Any problem in the operation of the PV installation may be analysed with Sonel PQM-707 power quality analyzer, which allows the user to check whether the problem is attributable to the electricity distributor or producer.
Measurement of alternating voltage on the distributor's side is very important, as the operating range of inverters sold and installed in many countries around the world must comply with the requirements of IEC 60038 [3] standard, allowing the maximum deviation of ±10% from the rated mains voltage in a given country. If the power grid distributor does not provide the appropriate conditions, i.e. the grid voltage is outside the permissible range, the inverter will automatically switch off and the photovoltaic installation will stop its electricity production. It is extremely important from the point of view of power generation, as the crucial parameter for investors is the amount of electricity produced by the photovoltaic installation, which translates directly into finances.
Sonel PQM-707 analyzer, with its inverter efficiency measurement function, allows user to check whether the values displayed by the inverter are in line with reality.
Fig. 2 Layout of the auxiliary screen for connecting the PQM-707 analyzer to the inverter
Figure 2 shows the diagram of connecting the meter to the tested inverter. The meter may be used to measure both single-phase and three-phase inverters connection systems. The meter, apart from the instantaneous efficiency of the inverter, also enables the measurement of parameters on the DC side, such as voltage, current, active power and active energy. These parameters are also measured on the AC side for individual phases.
The software of Sonel PQM-707 analyzer has been designed to guide the user step-by-step through the correct configuration of the recording process and appropriate connection of the instrument to the tested object. The mechanism of signalling the correct connection of the analyzer informs the user about the correct or potentially problematic configuration or connection of the analyzer. This ensures a high standard and quality of measurements, as well as safety of the user, because the device notifies the user on any detected irregularities. Measurements performed with PQM-707 are very convenient thanks to its 7-inch touch display, which shows all the available options along with the visualization of the connected test leads and measuring clamps. The device may be provided with a memory card up to 32 GB, ensuring a long-term recording of many advanced parameters. At the same time, during the recording, the analyzer provides the option of viewing the gathered results in real time and saving the screenshots.
The operator of the device may assign names to individual measurements, indicating their date and time, which is a great convenience, as it provides the history of measurements and material for analysing changes over time. With the function of performing the analysis directly on the device, it is not necessary to connect the instrument to a computer in order to remediate the detected irregularities. Measurement reports may be prepared in the office or in a car, as the device is provided with adapter powered from the car cigarette lighter socket.
The results of measurements provided by Sonel PQM-707 power quality analyzer are very important for owners or managers of a photovoltaic installation. The device has defined configurations in accordance with the requirements of standards applicable in many countries. These features ensure that the measurement results may be presented in the form of a protocol, almost without any additional work of the user. The functions of the device include recording for compliance with the EN 50160 [4] standard specifying the parameters of power supply voltage in public power networks. Advanced analytical functions of the meter may be used to analyse the recorded data. For example, the energy cost calculator is a suitable tool for calculating energy costs according to the tariff data by the user, facilitating the proper selection of electricity tariff. Recorded events such as voltage dips, swells and interruptions, which are network disturbances (their effective voltage significantly differs from the nominal value), may be used to set threshold values, in order to analyse incorrect operation of devices and components of the photovoltaic installation. Sonel PQM-707 provides the quality control of the PV installations immediately after system commissioning, during subsequent inspection tests and after the expansion (modification) of the PV system. Another useful option of PQM-707 is the function of the energy loss calculator, which uses currently measured parameters to estimate active power losses and related costs caused by poor power quality. The meter presents these losses for the hour, day, month and year, as shown in figure 3.
Fig. 3 Energy losses calculator in Sonel PQM-707
Changes in the law and in electricity billing methods draw the attention of entrepreneurs and private consumers towards a deeper analysis of the quality of their networks. Depending on the local law in a given country, in addition to the active power charges, which are the main part of the electricity bill, there are also components such as inductive and capacitive reactive energy charges. Using the network quality analyzer, you can measure how much reactive power has been consumed by the receiver and take steps to minimize the costs associated with it.
As the topic of reactive power compensation and the method of changes in metering by power network distributors is currently extremely important, we will focus on it in subsequent articles devoted to the analysis of the quality of networks with connected photovoltaic installations.
Fig. 4 Recording configuration screen of Sonel PQM-707 for setting parameters of energy and power factors
Network quality, analysis of its parameters and the growing number of components to be billed for electricity are the reasons for using the professional Sonel PQM-707 analyzer. The obtained accurate measurement results for parameters such as AC/DC amperage and voltage, losses caused by poor power quality as well as values of active, reactive and apparent power enable the user to prevent failures and save time and money usually spent on repairs and electricity bills. PQM-707 analyzer used for measurements is a convenient, professional and practical device that has been tested all over the world. It will definitely facilitate the work of every measurement and installation company.
Bibliography:
[1] IRENA (2021), Renewable capacity statistics 2021 International Renewable Energy Agency (IRENA), Abu Dhabi.
[2] IEA PVPS (2021), Report IEA-PVPS T1-39:2021, April 2021.
[3] IEC 60038. IEC standard voltages
[4] EN 50160:2010. Voltage characteristics of electricity supplied by public electricity networks
