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Abstract:The paper presents selected isotropic and anisotropic mathematical models to calculate the distribution of solar radiation on the photovoltaic module plane with any spatial orientation. A comparison of solar radiation models for Poland is based on measured data and received from the Institute of Meteorology and Water Management. Power density of solar radiation for different angular positions, especially for representative days of each month, was calculated. Based on the statistical analysis of the percentage root-mean-square error (RMSE%), mean-bias error (MBE%) and the Pearson correlation coefficient of an individual mathematical model, our own correction factor for diffuse radiation was proposed. A modified Liu-Jordan model was compared with six common mathematical models showing better agreement of measured and calculated values of solar radiation density. The presented analysis explains which mathematical model is the most suitable for central Poland (Poznań, 52°25' N, 16°56' E) and shows the validity of applying the modified model to improve the accuracy of determination of the radiation power density for a given elevation and azimuth angle using values for a horizontal plane.

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Abstract. The paper presents the methodology of minimisation of the unit cost of production of energy generated in the hybrid system compatible with the lead-acid battery, and used to power a load with the known daily load curve. For this purpose, the objective function in the form of the LCOE and the genetic algorithm method were used. Simulation tests for three types of load with set daily load characteristics were performed. By taking advantage of the legal regulations applicable in the territory of Poland, regarding the energy storing in the power system, the optimal structure of the prosumer solar-wind system including the lead-acid battery, which meets the condition of maximum rated power, was established. An assumption was made that the whole solar energy supplied to the load would be generated in the optimised system.

Abstract.One of the methods of renewable energy production is biogas plant. Products of anaerobic digestion are biogas and residual material called digested pulp or digestate. This material is commonly used as a fertilizer. One of a new possibility of digested pulp management is solid biofuels production after separation. This paper presents the calculation of cost for production of briquettes from digested pulp. The performed economic analysis proves that the production of briquettes from digested solid fraction (DSF) can be profitable and provide additional income for the biogas plant.

Abstract. The paper presents a physical construction of a measurement stand consisting of a photovoltaic module operating in a fixed optimal configuration and in a solar tracking with a modified astronomical positioning. In order to reduce the electric energy consumption by two direct current linear motors system is positioned three times a day during winter months. Prepared energy balance, using annual measurements, confirmed the legitimacy of using twoaxis Sun tracking units for central Poland. Basing on the daily and monthly electricity production and solar irradiance for both photovoltaic units a mathematical formula with proposed correction factors is presented to calculate with good accuracy monthly electric energy generation for a fixed photovoltaic installation. The results of calculations were compared with measurements showing good correlation.

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Abstract. The paper presents the most representative -from the three-year measurement time periodcharacteristics of daily and monthly electricity production from a photovoltaic conversion using modules installed in a fixed and 2-axis tracking construction. Results are presented for selected summer, autumn, spring and winter days. Analyzed measuring stand is located on the roof of the Faculty of Electrical Engineering Poznan University of Technology building. The basic parameters of the statistical analysis like mean value, standard deviation, skewness, kurtosis, median, range, or coefficient of variation were used. It was found that the asymmetry factor can be useful in the analysis of the daily electricity production from a photovoltaic conversion. In order to determine the repeatability of monthly electricity production, occurring between the summer, and summer and winter months, a non-parametric Mann-Whitney U test was used as a statistical solution. In order to analyze the repeatability of daily peak hours, describing the largest value of the hourly electricity production, a non-parametric Kruskal-Wallis test was applied as an extension of the Mann-Whitney U test. Based on the analysis of the electric energy distribution from a prepared monitoring system it was found that traditional forecasting methods of the electricity production from a photovoltaic conversion, like multiple regression models, should not be the preferred methods of the analysis.