There are a lot of studies that show the legitimacy of subsidizing renewable energy; however, some mechanisms are defective, and there are problems with the appropriate allocation of funds. Therefore, this paper aims to look at the situation of allocating funds to photovoltaics (PV) micro-installations in Poland through the “My Electricity” program. The article presents the results of analyses aimed at identifying inequalities between provinces in the use of funds available under the “My Electricity” program and verifying whether these inequalities are getting worse and whether the intensity of support should not be territorially conditioned in terms of maximization an electricity production. As part of two editions of the “My Electricity” program (until 1 August 2020), over 64,000 PV micro-installations were created with an average power of approximately 5.7 kWp. The total installed PV capacity was 367.1 MWp (1st edition: 159.3 MWp, 2nd edition: 207.8 MWp). Financial resources (as a whole), in the second edition of “My Electricity” program, were distributed better than in the first edition. In the first edition, as much as 7.60% of funds were allocated inefficiently; in the second edition, it was only 3.88%. Allocation surpluses occur in provinces where the average disposable income is low and where there are a small number of households. There is a potential to introduce a territorial project selection criteria. The analysis shows that the criteria should promote provinces with higher disposable income and a larger number of households.

There are many financial ways to intensify the construction of new renewable energy sources installations, among others: feed in tariff, grants. An example of photovoltaic grant support in Poland is the "Mój Prąd" [My Electricity] program created in 2019. This program, with a budget of PLN 1 billion, is intended for households in which installations with a capacity range of 2-10 kWp have been installed. During its first edition 27,187 application were submitted. Over 98% of installations cost less than PLN 6,000/kWp. The total installed capacity is 151.3 MWp, which gives the average amount of co-funding per unit of power at the level of PLN 884.7/kWp. The average power of the installation on the national scale is 5.57 kWp, the indicator per 1000 inhabitants is 3.94 kWp, and per unit of area is 0.484 kWp/km 2 . These installations will produce around 143.5 GWh of electricity annually, contributing to the reduction of CO 2 emissions by approximately 109,800 Mg per year. Most applications came from the Silesian Province (3855), which translated into the largest installed capacity of 21.82 MWp, as well as 4.81 kWp/1000 inhabitants and 1.77 kWp/km 2 (over 3 times higher than the average in Poland).The installed capacity in the individual province was closely correlated with the population of the province (correlation coefficient -0.95), while the installed capacity indicator per 1,000 inhabitants with insolation (0.80). The highest power ratio per 1000 inhabitants was achieved in the Podkarpackie Province and amounted to 5.05, and the lowest in the West Pomeranian Province (2.41).

The several government subsidies available in Poland contributed to an increased interest in PV installations. Installed PV capacity increased from 100 MW in 2016 up to 2682.7 MW in July 2020. In 2019 alone, 104,000 microinstallations (up to 50 kWp) were installed in Poland. The paper determines the energy gain and the associated reduction of CO2 emissions for two types of solar installation located in Poland. The monofacial solar modules with a power of 5.04 kWp (located in Leki) and bifacial solar modules with a power of 6.1 kWp (located in Bydgoszcz). Both installations use mono-crystalline Si-based 1st generation PV cells. With comparable insolation, a bifacial installation produces approx. 10% (for high insolation) to 28% (for low insolation) more energy than a monofacial PV installation. Avoided annual CO2 emission in relation to the installation capacity ranges from 0.58 to 0.64 Mg/kWp for monofacial and from 0.68 to 0.74 Mg/kWp for bifacial and is on average approx. 16% higher for bifacial installations. Cost-benefit analyses were made. For different electricity prices, the NPV for monofacial and bifacial was determined.

Supervised machine learning and its algorithms are a developing trend in the prediction of rockfill material (RFM) mechanical properties. This study investigates supervised learning algorithms support vector machine (SVM), random forest (RF), AdaBoost, and k-nearest neighbor (KNN) for the prediction of the RFM shear strength. A total of 165 RFM case studies with 13 key material properties for rockfill characterization have been applied to construct and validate the models. The performance of the SVM, RF, AdaBoost, and KNN models are assessed using statistical parameters, including the coefficient of determination (R2), Nash–Sutcliffe efficiency (NSE) coefficient, root mean square error (RMSE), and ratio of the RMSE to the standard deviation of measured data (RSR). The applications for the abovementioned models for predicting the shear strength of RFM are compared and discussed. The analysis of the R2 together with NSE, RMSE, and RSR for the RFM shear strength data set demonstrates that the SVM achieved a better prediction performance with (R2 = 0.9655, NSE = 0.9639, RMSE = 0.1135, and RSR = 0.1899) succeeded by the RF model with (R2 = 0.9545, NSE = 0.9542, RMSE = 0.1279, and RSR = 0.2140), the AdaBoost model with (R2 = 0.9390, NSE = 0.9388, RMSE = 0.1478, and RSR = 0.2474), and the KNN with (R2 = 0.6233, NSE = 0.6180, RMSE = 0.3693, and RSR = 0.6181). Furthermore, the sensitivity analysis result shows that normal stress was the key parameter affecting the shear strength of RFM.

Micro-cogeneration (mCHP) is a promising solution for the generation of heat and electricity in households, it contributes to reducing carbon dioxide emissions in countries where the production of electricity is mainly based on fossil fuels. Its dissemination in Poland faces barriers in the form of high purchase prices in relation to electricity productivity. In this work 1% of the household population in Poland was analyzed using the Monte Carlo method. It was found that for mCHP to become economically profitable for a group of at least 10,000 households, its price should fall from around 18,000 euros (711.5 euros/kWth and 18,000 euros/kWe) to 4800 euros (189.7 euros/kWth and 4800 euros/kWe) and for 100,000 households to 4100 euros (162.1 euros/kWth and 4100 euros/kWe). These calculations were made for fixed gas and electricity prices. The analysis also included cases of various changes in gas and energy prices. Faster growth of electricity prices than gas prices reduce the profitability barrier. In addition, a building located in Lesser Poland region was analyzed, with an above average demand for electricity and heat. Gas micro-cogeneration becomes profitable for this household at a price of 3700 euros (146.2 euros/kWth and 3700 euros/kWe) at fixed gas and electricity prices.

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In Poland, various solar collector systems are used; among them, the most popular are flat plate collectors (FPCs) and evacuated tube collectors (ETCs). The work presents two installations located at a distance of 80 km apart, working in similar external conditions. One of them contains 120 flat plate collectors and works for the preparation of hot water in a swimming pool building; the second one consists of 32 evacuated tube collectors with a heat pipe and supports the preparation of domestic hot water for a multi-family house. During the comparison of the two quite large solar installations, it was confirmed that the use of evacuated tube solar collectors shows a much better solar energy productivity than flat plate collectors for the absorber area. Higher heat solar gains (by 7.9%) were also observed in the case of the gross collector area. The advantages of evacuated tube collectors are observed mainly during colder periods, which allows for a steadier thermal energy production.

In less than a decade, the photovoltaic sector has transformed into a global business. The dynamics of its development vary depending on the country. According to estimates, the value of the photovoltaic micro-installations market in Poland at the end of 2019 exceeded PLN 2.8 billion. In the first half of 2020, the PV sector recorded dynamic growth with a total capacity of the micro-installations of 2.5 GWp. Government subsidies were among the factors contributing to the expansion of the PV sector. In Poland, there are many financial ways to intensify the construction of new renewable energy source installations, among others: feed-in tariff, grants, and loans. An example of photovoltaic grant support in Poland is the "Mój Prąd" [My Electricity] program created in 2019 with a budget of PLN 1.1 billion. The interest in the "My Electricity" program in individual provinces may vary, depending on socio-economic factors, technological and environmental resources, and the level of innovation. The research motivation of this article is a comparison of provinces in Poland according to selected energy, environmental, innovation, and socio-economic indicators and to show how these factors affect individual interest in the "My Electricity" photovoltaic development program in provinces. The highest correlation is for the total installation power under the "My Electricity" program and Gross Domestic Product and Human Developed Index. The highest correlation coefficient from RIS indicators and photovoltaic data programs was achieved for "R&D expenditure in the business sector". The population was closely correlated with the total installation power and the grant value of the "My Electricity" program.