The slow city concept is associated with great care for the protection of the natural environment and the use of renewable energy sources. Thus, the study aimed to discuss the potential of the slow city model and the actual role of Cittaslow local governments in deploying renewable energy, based on the case study of the Polish Cittaslow Network. To achieve this aim, we carried out qualitative and quantitative data analyses, based on literature review and data for all 35 Polish Cittaslow municipalities, retrieved from: (i) development strategies (ii) a survey (iii) the Local Data Bank of Statistics Poland, (iv) the Quality of Life Synthetic Index (QLI). To process the data, we applied descriptive statistics, the Shapiro-Wilk test, the non-parametric Kruskal-Wallis test, and the Spearman’s rank test. Findings showed that the support for renewable energy deployment was not at a high level and did not correlate with the goals set in the Cittaslow development strategies. This was the result... [more]

Previous analyses of the PV market (and the impact of the pandemic on it) have focused on the market as a whole. The literature does not contain analyses of selected services sectors (e.g., catering, hotel services) in terms of the use of photovoltaics. There are no studies that would show in which segments the demand profile for electricity most closely matches the production from photovoltaic installations (not to mention the impact of the pandemic). The authors analyzed selected service sectors (catering and hotel) in terms of the use of photovoltaics before and during the COVID-19 pandemic. The paper proposes a comparative methodology for the use of photovoltaics for self-consumption, including statistical analyses and calculations of the self-consumption index for representatives of various selected services sectors. The highest value of the self-consumption ratio at the level of 52% was shown for cafes and restaurants (during the pandemic). Surprisingly, in the pandemic, the self... [more]

The aim of this design was to improve the heat transfer performance significantly due to larger turbulent region and much vortices formed by tube inserted. In this article, the BSL k-ω model was chosen as turbulence model to simulate the thermohydraulic performance of the proposed tubes inserted with rectangular winglet vortex generators (RWVGs) when the Re was set as 5000 to 15,000. The reliability of the simulation results was obtained by comparing with the empirical formulas and experimental results. By means of numerical simulation, the influence mechanism of geometric parameters of RWVGs on thermal-hydraulic performance in tubes was analyzed. And the impact of three configurational parameters on the thermal performance was studied, namely the angle α, the height H and the number N of the RWVGs, respectively. The results revealed that the capacity of heat transfer in tubes with RWVG inserts was obviously larger than that in ordinary circular tube. In addition, it could be seen... [more]

The determination of methane content of coal seams is conducted in hard coal mines in order to assess the state of methane hazard but also to evaluate gas resources in the deposit. In the world’s mining industry, natural gas content in coal determination is usually based on direct methods. It remains the basic method in Poland as well. An important element in the determination procedure is the gas loss that occurs while collecting a sample for testing in underground conditions. In the method developed by the authors, which is a Polish standard, based on taking a sample in the form of drill cuttings, this loss was established at a level of 12%. Among researchers dealing with the methane content of coal, there are doubts related to the procedures adopted for coal sampling and the time which passes from taking a sample to enclosing it in a sealed container. Therefore, the studies were designed to evaluate the degree of degassing of the sample taken in the form of drill cuttings according... [more]

Supercritical water gasification (SCWG) is a promising technology for the valorization of wet biomass with a high-water content, which has attracted increasing interest. Many experimental studies have been carried out using conventional heating equipment at lab scale, where researchers try to obtain insight into the process. However, heat transfer from the energy source to the fluid stream entering the reactor may be ineffective, so slow heating occurs that produces a series of undesirable reactions, especially char formation and tar formation. This paper reviews the limitations due to different factors affecting heat transfer, such as low Reynolds numbers or laminar flow regimes, unknown real fluid temperature as this is usually measured on the tubing surface, the strong change in physical properties of water from subcritical to supercritical that boosts a deterioration in heat transfer, and the insufficient mixing, among others. In addition, some troubleshooting and new perspectives... [more]

Poland is dynamically changing its energy mix. As a result of this process, solar energy is increasing its share in energy production. The development of the solar energy market is determined by numerous factors. This paper aims to develop a roadmap for further development of the photovoltaic (PV) energy market in Poland. The scope of the research covers five areas of PV technology and market development in Poland: (i) technology; (ii) power grids; (iii) law; (iv) economic conditions; and (v) social conditions. With the use of a Technology Roadmapping Methodology (TRM), for each of the determined areas, several factors were analyzed, and their development paths were described. In addition, the article focuses on technological challenges (regarding PV cells, modules, components, power conversion and monitoring and management system, optimizers, batteries, and other energy storage systems), grid efficiency, recycling, production costs, subsidies, public awareness and education, and the e... [more]

Recent trends in the photovoltaic (PV) technology industry are moving towards utilizing bifacial PV panels. Unlike traditional PV panels, bifacial PV panels can yield energy from both sides of the panel. Manufacturers specify that bifacial PV panels can harness up to 30% more energy than traditional PV panels. Hence, bifacial PV panels are becoming a common approach at low solar irradiance conditions to yield more energy. However, a bifacial PV panel increases PV inverter loading. The PV inverter is the most unreliable component in the entire PV system. This results in a negative impact on PV system reliability and cost. Hence, it is necessary to anticipate the inverter’s reliability when used in bifacial PV panels. This paper analyzes the reliability, i.e., lifetime, of PV inverters, considering both monofacial and bifacial PV panels for the analysis. Results showed that the increase in bifacial energy yield could significantly affect PV inverter reliability performance, especially in... [more]

An investigation of the effects of wind gusts on the directly interconnected wind generators is reported, and techniques toward the mitigation of the wind gust negative influences have been proposed. Using a directly interconnected system approach, wind turbine generators are connected to a single synchronous bus or collection grid without the use of power converters on each turbine. This bus can then be transformed for transmission onshore using High Voltage Alternating Current, Low-Frequency Alternating Current or High Voltage Direct Current techniques with shared power conversion resources onshore connecting the farm to the grid. Analysis of the potential for instability in transient conditions on the wind farm, for example, caused by wind gusts is the subject of this paper. Gust magnitude and rise time/fall time are investigated. Using pitch control and the natural damping of the high inertial offshore system, satisfactory overall system performance and stability can be achieved du... [more]

In this paper, a two-bladed medium-sized floating wind turbine with variable speed and power regulation by stall is studied. For floating offshore wind turbines, the major challenges are related to the dynamical behavior of the system in response to combined wind and wave loading. Especially for smaller systems, the coupling of aerodynamic and wave forces may lead to large amplitude motions. Coupled aero-hydro-servo-elastic simulations are carried out in OpenFAST. The goal of the study is to investigate the global dynamic response of the hypothetical wind turbine with stall regulation. Stall regulation concept is proposed and the structural loads are computed and results are presented and discussed.

From the environmental perspective, wooden structures are favorable insulators that are suitable for carbon fixation and wooden-related products are considered the most sustainable material. Research has indicated that wooden structures have superior energy-saving performance compared to reinforced concrete (RC) structures. In this study, a CLT-based hybrid structure system that potentially improves the efficiency of energy consumption is proposed. The proposed hybrid structure system, which preserved original RC beams, columns and replaced CLT floors and walls, has less building weight compared to the original RC building. Additionally, less energy required for the manufacturing of building materials in the renovation of the aged building is achieved, compared to building a new CLT building. The energy consumptions for buildings with heights of 10 stories were compared. CLT and RC were selected as benchmark building materials to compare the energy-saving efficiencies with the proposed... [more]

In order to deepen the understanding of rotating effects on internal cooling, the flow and heat transfer characteristics of 2-pass rotating rectangular smooth/ribbed channels are investigated by Reynolds-Averaged Navier-Stokes (RANS) simulation. Three rotating numbers (Ro = 0.10, 0.25, and 0.40) are simulated, and the maximum buoyancy parameter (Bo) reaches 5.0. The results show that the rotating buoyancy has significant effects on the flow and heat transfer under high Bo conditions. When Bo > 1.0, rotating buoyancy inducts flow separation near the leading edge (LE) in the first passage, while the air flow in the second passage shows a double-peak profile. With increased Bo, the heat transfer in the first passage is greatly increased, and the maximum growth rate occurs at Bo = 0.6~1.0. However, the heat transfer in the second passage has no obvious changes due to a strong turn effect. In the ribbed channel, rotating effects are much weaker than those in the smooth channel. This researc... [more]

Ground source heat pumps (GSHPs), a high-efficiency and energy-saving air-conditioning technology that utilizes shallow geothermal resources for both heating and cooling, are a vital green energy system for residential and commercial buildings. Improving the performance of such a system was the focus of the current research. As soil temperature and thermal radius are two important aspects that affect the performance of ground source heat pump systems, we conducted a new numerical simulation to capture the changes in sensitive factors and propose the optimized paths. The numerical simulation analyzed the thermal characteristics of a borefield under different pre-cooling times and soil types. The results indicated the following: (1) The rate of the ground temperature change with pre-cooling during the discharging period had a faster rise than in the case without pre-cooling. The longer the precooling time was, the smaller the thermal radius became. In particular, when the precooling time... [more]

Short-term load forecasting is an important part of load forecasting, which is of great significance to the optimal power flow and power supply guarantee of the power system. In this paper, we proposed the load series reconstruction method combined improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) with sample entropy (SE). The load series is decomposed by ICEEMDAN and is reconstructed into a trend component, periodic component, and random component by comparing with the sample entropy of the original series. Extreme learning machine optimized by salp swarm algorithm (SSA-ELM) is used to predict respectively, and the final prediction value is obtained by superposition of the prediction results of the three components. Then, the prediction error of the training set is divided into four load intervals according to the predicted value, and the kernel probability density is estimated to obtain the error distribution of the training set. Combining the pre... [more]

In this paper, a new application of Bonobo (BO) metaheuristic optimizer is presented for PV parameter extraction. Its processes depict a reproductive approach and the social conduct of Bonobos. The BO algorithm is employed to extract the parameters of both the single diode and double diode model. The good performance of the BO is experimentally investigated on three commercial PV modules (STM6-40 and STP6-120/36) and an R.T.C. France silicon solar cell under various operating circumstances. The algorithm is easy to implement with less computational time. BO is extensively compared to other state of the art algorithms, manta ray foraging optimization (MRFO), artificial bee colony (ABO), particle swarm optimization (PSO), flower pollination algorithm (FPA), and supply-demand-based optimization (SDO) algorithms. Throughout the 50 runs, the BO algorithm has the best performance in terms of minimal simulation time for the R.T.C. France silicon, STM6-40/36 and STP6-120/36 modules. The fitnes... [more]

Geothermal energy is a resource that has the potential for development in many countries around the world. Despite its versatility and economic viability, this resource faces numerous obstacles that hinder its deployment and capacity for achieving a similar market share as other renewable and clean energy sources. Both technical and non-technical barriers can be highly detrimental to the implementation of geothermal projects. A social license to operate (SLO) is a tool that can help the deployment of geothermal energy. As a new concept, SLO is little developed in the business literature but is still being adopted in many industries. Its main challenges reside in its context-dependence and the lack of clear frameworks to utilize it. This paper introduces, in a first known attempt, through a qualitative approach, a conceptual model of the social license to operate in the geothermal energy sector. For its development, three case studies, working group discussion and surveying were conduct... [more]

The Republic of Djibouti has untapped potential in terms of renewable energy resources, such as geothermal, wind, and solar energy. This study examines the economic feasibility of green hydrogen production by water electrolysis using wind and geothermal energy resources in the Asal−Ghoubbet Rift (AG Rift), Republic of Djibouti. It is the first study in Africa that compares the cost per kg of green hydrogen produced by wind and geothermal energy from a single site. The unit cost of electricity produced by the wind turbine (0.042 $/kWh) is more competitive than that of a dry steam geothermal plant (0.086 $/kWh). The cost of producing hydrogen with a suitable electrolyzer powered by wind energy ranges from $0.672/kg H2 to $1.063/kg H2, while that produced by the high-temperature electrolyzer (HTE) powered by geothermal energy ranges from $3.31/kg H2 to $4.78/kg H2. Thus, the AG Rift area can produce electricity and green hydrogen at low-cost using wind energy compared to geothermal energy... [more]

Currently, fossil fuels are still the primary fuel source and reducing agent in the steel industries. The utilization of fossil fuels is strongly associated with CO2 emissions. Therefore, an alternative solution for green steel production is highly recommended, with the use of biomass as a source of fuel and a reducing agent. Biomass’s growth consumes carbon dioxide from the atmosphere, which may be stored for variable amounts of time (carbon dioxide removal, or CDR). The pellets used in this study were prepared from a mixture of low-grade iron ore and palm kernel shells (PKS). The reducing reactivity of the pellets was investigated by combining thermogravimetric analysis (TGA) and laboratory experiments. In the TGA, the heating changes stably from room temperature to 950 °C with 5−15 °C/min heating rate. The laboratory experiments’ temperature and heating rate variations were 600−900 °C and 10−20 °C/min, respectively. Additionally, the reduction mechanism was observed based on the X-r... [more]

The article presents tests on the possibility of using ultrasonic transducers for accurate distance measurement in hard coal mines. In order to check the impact of selected disturbing factors on the measurement results, test stands were built, and then a full cycle of measurements with the use of different transducers (AR30 and AR41), which were selected and pre-tested in previous research projects, was realized. The impact of such disturbing factors as airborne dust (coal, stone, lime and mixed dust), changes in temperature and humidity on the propagation of ultrasonic waves, amplitude and measurement accuracy was investigated. The tests were preceded by theoretical analysis. It was found that the transducers selected for the tests had a sufficient accuracy and range, so they can be used in the devices planned to be designed, allowing for the determining of the location of a roadheader in hard coal mine roadways, taking into account technical and legal restrictions. It was also specif... [more]

With the rapid expansion of renewable energy, the penetration rate of behind-the-meter (BTM) solar photovoltaic (PV) generators is increasing in South Korea. The BTM solar PV generation is not metered in real-time, distorts the electric load and increases the errors of load forecasting. In order to overcome the problems caused by the impact of BTM solar PV generation, an extreme gradient boosting (XGBoost) load forecasting algorithm is proposed. The capacity of the BTM solar PV generators is estimated based on an investigation of the deviation of load using a grid search. The influence of external factors was considered by using the fluctuation of the load used by lighting appliances and data filtering based on base temperature, as a result, the capacity of the BTM solar PV generators is accurately estimated. The distortion of electric load is eliminated by the reconstituted load method that adds the estimated BTM solar PV generation to the electric load, and the load forecasting is co... [more]

Poland has great potential for the development of renewable energy sources. The implementation of support systems dedicated to renewable sources has resulted in the installation of over 10,500 MW of installed capacity. At present, with high electricity prices, stimulated by the costs of CO2 emissions and the costs of fuel purchase, renewable energy sources are of particular importance in the transformation of the Polish power industry. The RES auction system and the My Electricity Program contributed to the growth of entrepreneurship and the development of the economy. Energy consumers, from passive ones, have become active market participants—prosumers. The RES auction system alone contributed to the creation of approx. 5 GWp of installed capacity of photovoltaics (PV) sources in 2016−2021, while the My Electricity Program contributed to the creation of approx. 2 GWp of installed capacity in PV installations in 2019−2021. The aim of the study is to compare the economic and social cost... [more]

To reach effective monitoring and control, a physical power grid couples with a communication network and evolves into cyber−physical power systems (CPPS), but this cyber−physical interdependence may exacerbate failure on the physical/cyber side and may turn into a cascading failure. Furthermore, distributed generators (DGs) and plug-in hybrid electric vehicles (PHEVs) introduced into CPPS add uncertainties to both the supply side and demand side of power energy. In this paper, we detail the model of CPPS and its coupling mechanism in operation and discuss the propagation mechanism of cascading failure within and across a physical power grid and a communication network. For uncertainties of power energy in the supply and demand sides, the generation and load of each day are divided into 24 time segments for modeling. In the case study, the well-being criteria and reliability indexes are employed to analyze the effect of DGs and cyber−physical interdependence on the reliability of CPPS... [more]

In search of a more sustainable society, humanity has been looking to reduce the environmental impacts caused by its various activities. The energy sector corresponds to one of the most impactful activities since most energies produced come from fossil fuels, such as oil and coal, which are finite resources. Moreover, their inherent processes to convert energy into electricity emit various pollutants, which are responsible for global warming, eutrophication, and acidification of soil and marine environments. Biofuels are one of the alternatives to fossil fuels, and the raw material used for their production includes vegetable oils, wood and agricultural waste, municipal waste, and waste cooking oils (WCOs). The conventional route for WCO valorization is the production of biodiesel, which, as all recovery technologies, presents advantages and disadvantages that must be explored from a technical and economic perspective. Despite its successful use in the production of biodiesel, it shoul... [more]

Currently, ensuring the correct functioning of the electrical grid is an important issue in terms of maintaining the normative voltage parameters and local line overloads. The unpredictability of Renewable Energy Sources (RES), the occurrence of the phenomenon of peak demand, as well as exceeding the voltage level above the nominal values in a smart grid makes it justifiable to conduct further research in this field. The article presents the results of simulation tests and experimental laboratory tests of an electricity management system in order to reduce excessively high grid load or reduce excessively high grid voltage values resulting from increased production of prosumer RES. The research is based on the Elastic Energy Management (EEM) algorithm for smart appliances (SA) using IoT (Internet of Things) technology. The data for the algorithm was obtained from a message broker that implements the Message Queue Telemetry Transport (MQTT) protocol. The complexity of selecting power set... [more]

The overcoming of the issues on energy crisis and inequality have become the priorities as far developing as developed countries are concerned. Moreover, energy inequality has increased due to the shortage of natural gas and rising energy prices in retaliation to the economic recovery affected by the COVID-19 pandemic. This study aims to verify the linkage between the growth of renewable energy consumption and the country’s economic advancement. In this context, this paper determines the main driving forces of renewable energy consumption in European countries during 2000−2018. The annual data for panel regression analysis are retrieved from the OECD. Stat and World Bank Open Data. This empirical analysis employed a set of estimation procedures such as the panel unit root test (Levin, Lin & Chu; Im, Pesaran, Shin W-Stat; ADF-Fisher Chi-square; and PP-Fisher Chi-square methods), the Pearson correlation, fixed- and random-effects models, generalized method of moments (GMM), Hausman and t... [more]

The paper aims to detect the differences in stock market performance between companies from the alternative energy sector and main stock market sectors in the first and second years of the COVID-19 pandemic. We used Global Industry Classification Standard to analyse eleven main stock market sectors and the alternative energy sector. Based on the one-factor variance analysis—ANOVA, we reveal the statistically significant differences between the analysed stock market sectors in both 2020 and 2021. The analysis implied that the performance of stock market companies during COVID-19 is sector-specific. Tukey’s Honestly Significant Difference (HSD) test for pairwise comparison indicates that the alternative energy sector shows the most differentiation. Its average rate of return in 2020 is the highest and is significantly different for all eleven stock market sectors, while the top constituents from the conventional energy and financial sectors suffered the most. In 2021, a reverse trend in... [more]