In Poland, there has been a steady increase in the share of wind-generated energy in the overall energy balance of the country. However, wind power plants belong to unstable energy sources—the amount of generated power is variable in time. Variable generation may cause problems with the quality of energy transmitted in electricity networks. Therefore, this article presents the results of field tests of the impact of the Vestas V90 2 MW wind turbine on selected voltage quality parameters occurring in the grid. Due to the multifaceted influence of the power plant on the parameters of the grid to which it is connected, the article focuses only on four selected parameters: voltage value, zero and reverse asymmetry, and the value of the voltage distortion factor. The research conducted by the authors confirmed the positive influence of the operation of the wind power plant on the quality parameters of the electricity transmitted through the power grid. An increase in the power generated in the tested Vestas V90 power plant resulted in a decrease in the values of both the asymmetry factor (zero and reverse) and the total voltage distortion factor THD_U.

The content of heavy metals in soil should be continuously monitored, especially in organic crops. Exceeding the permissible concentrations of these elements may lead not only to inhibition of plant growth but also to ingestion into the organisms of animals that feed on these plants. Heavy metals usually enter the soil via precipitation or manure. There is a noticeable increase in interest in digestate for fields fertilization. Therefore, the authors decided to test the heavy metal content in substrates (slurry and solid input) and digestate. The 15x3 samples tested showed that only trace amounts of heavy metals were present. The study shows that the content of these elements in the digestate is not the sum of the elements supplied to the digester with the substrates. In most of the samples tested, lead concentrations did not exceed 5 mg‧kg ⁻¹ . The lowest amounts of cadmium (an average of 0.28 mg‧kg ⁻¹ ) were observed in the slurry, and the highest (an average of 0.34 mg‧kg ⁻¹ ) in the solid substrate fed to the digester. Slurry had the lowest mercury and cadmium contents (average 0.012 mg‧kg ⁻¹ and 5.8 mg‧kg ⁻¹ ). The highest concentration of chromium was registered in the digestate (average 3 mg‧kg ⁻¹ ) and this was on average 0.3 mg‧kg ⁻¹ higher than the feedstock and 0.5 mg‧kg ⁻¹ than the slurry

Wind power plants are an increasingly common source of electricity located in rural areas. As a result of the high variability of wind power, and thus the generated power, these sources should be classified as unstable sources. In this paper, the authors attempted to determine the impact of wind turbine operation on the parameters of electricity supplied to farms located near the source. As a result of the conducted field tests, variability courses of the basic parameters describing the supply voltage were obtained. The influence of power plant variability on the values of voltage, frequency, and voltage distortion factor was determined. To estimate the capacity of the transmission lines, the reactive power produced in the power plant and its effect on the value of the power factor were determined. The conducted research and analysis showed that the wind power plant significantly influences voltage fluctuations in its immediate vicinity (the maximum value registered was close to 2%, while the value required by law was 2.5%). Although all the recorded values are within limits specified by the current regulations (e.g., the THD value is four times lower than the required value), wind turbines may cause incorrect operation of loads connected nearby. This applies mainly to cases where consumers sensitive to voltage fluctuations are installed in the direct vicinity of the power plant.

Agricultural biogas plants are not only a place for processing waste resulting from animal husbandry, but also for generating electricity and heat as well as organic fertiliser. In a four-year experiment, pellets were used as organic fertiliser in the establishment of an experiment with fast-growing oxytrees. The study aimed to investigate the growth and stem thickness increment, overwintering in the first and subsequent years of cultivation under the conditions of north-eastern Poland. The dried digestate and the pellets made from it were characterised by a high content of macroelements (N – 1,95%, P2O5 – 1,1%, K2O – 1,3%). The applied pellet from an agricultural biogas plant under oxytree seedlings due to its slow decomposition had a good effect on the growth of oxytrees in the second and third years. The average growth of oxytrees in the second year was 209.7 cm, and in the third year, 246.8 cm. The growth of oxytrees fertilised with pellets made from the digestate of an agricultural biogas plant was 13% higher than that of trees growing on the control strip.

The phenomenon of voltage asymmetry is common in electricity networks and is the cause of many unfavourable phenomena occurring, such as an increase in power and energy losses, as well as the abnormal operation of certain loads. Voltage asymmetry can be caused by several different factors, which include the design of the transmission line (e.g., routing of conductors in relation to each other and the earth), the parameters of consumer circuits (e.g., unequal loading of individual phases), or the design of network equipment (e.g., generators or transformers). An asymmetrical condition also occurs during system disturbances such as single-phase short circuits or lightning. One of the many factors impinging on voltage asymmetry in the electrical network is also the effect of load, but in the case of medium voltage power networks, this effect is neglected in the literature. This paper presents and evaluates the influence of the power consumed by consumers on the values of zero-voltage asymmetry factor indices in medium voltage compensated power networks with the neutral point earthed by an inductance (Petersen coil) operating with wind and photovoltaic power plants.

Over the last few years, a dynamic increase in the installed capacity of distributed energy sources has been observed, with the largest share being photovoltaic sources. The power grid is a system of connected vessels, and changing the structure of electricity production has a specific impact on the operation of this network, which makes it necessary to study the impact of the sources on the power system. The current and projected increase in the number of connected installations will make the issues of interaction and cooperation of distributed sources with the network extremely important. The article presents an analysis of the impact of a photovoltaic farm on selected parameters of the quality of electricity supply. This analysis was made on the basis of simulation results in a computer program and measurement tests carried out on a real photovoltaic farm with a capacity of 1.8 MW connected to the medium voltage power grid. The impact of the farm-generated power on the values of fundamental indicators of the quality of electricity supply, such as voltage deviations, voltage asymmetry factors, and voltage distortions factors, is presented. These relationships were determined based on the correlation and regression analysis of individual electrical quantities.