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Energies, Volume 15, Issue 7 (April-1 2022) – 407 articles

Cover Story (view full-size image): As the energy crisis goes on and carbon-neutral goals are established, the exploration of new green energy production routes is becoming a necessity. Therefore, quantum dot photovoltaic devices (solar cells) are entering the spotlight as a novel 3rd-generation solar cell. Like other semiconductor devices, quantum dot solar cells also need to be properly doped in order to achieve a high performance. Scientists have been using various techniques to tune the doping of colloidal quantum dots, such as synthesis, stoichiometry tuning, post-treatment ion exchange, remote doping, and ligand exchange. The resulting doped quantum dots will alter the band structure and accomplish band alignment, extended depletion region, and homo/heterojunctions to effectively retrieve carriers. View this paper
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Article
Environmental Impact Analysis of Portland Cement (CEM1) Using the Midpoint Method
Energies 2022, 15(7), 2708; https://doi.org/10.3390/en15072708 - 06 Apr 2022
Cited by 1 | Viewed by 744
Abstract
The cement industry confronts significant challenges in raw materials, energy demands, and CO2 emissions reduction, which are global and local environmental concerns. Life cycle assessment (LCA) has been used in many studies to assess the environmental impact of cement production and investigate [...] Read more.
The cement industry confronts significant challenges in raw materials, energy demands, and CO2 emissions reduction, which are global and local environmental concerns. Life cycle assessment (LCA) has been used in many studies to assess the environmental impact of cement production and investigate ways to improve environmental performance. This study aims to analyse the environmental impact of Portland cement (CEM I) on the South African cement industry using the life cycle impact assessment (LCIA), based on the Recipe 2016 v 1.04 midpoint method. The study was conducted using data modeled after the South African cement plant, considered a cradle-to-gate system boundary, starting from the extraction of the raw material to the cement production process that produces cement as the main product. The data were obtained from the Ecoinvent database v3.7.1, integrated with SimaPro 9.1.1. software, used to assess the impact categories. For simplicity, the study merged the entire production process into five processes, i.e., raw materials usage, fuel consumption, clinker production, transportation and electricity. The impact categories of the five production stages were assessed using the LCA methodology. The impact categories investigated were classified into three categories: atmospheric, resource depletion and toxicity categories. According to the results, clinker production and electricity usage stages contribute the most to atmospheric impact (global warming, which causes climatic change due to high CO2 emissions), followed by raw materials and fuel consumption, contributing to the toxicity and resource depletion impact category. These stages contribute more than 76% of CO2 eq. and 93% of CFC-11 eq. In the midpoint method, CO2 is the most significant pollutant released. Therefore, replacing fossil fuels with alternative fuels can reduce fossil fuel use and the atmospheric impact of cement kilns. Full article
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Article
Data Screening Based on Correlation Energy Fluctuation Coefficient and Deep Learning for Fault Diagnosis of Rolling Bearings
Energies 2022, 15(7), 2707; https://doi.org/10.3390/en15072707 - 06 Apr 2022
Cited by 1 | Viewed by 477
Abstract
The accuracy of the intelligent diagnosis of rolling bearings depends on the quality of its vibration data and the accuracy of the state identification model constructed accordingly. Aiming at the problem of “poor quality” of data and “difficult to select” structural parameters of [...] Read more.
The accuracy of the intelligent diagnosis of rolling bearings depends on the quality of its vibration data and the accuracy of the state identification model constructed accordingly. Aiming at the problem of “poor quality” of data and “difficult to select” structural parameters of the identification model, a method is proposed to integrate data cleaning in order to select effective learning samples and optimize the selection of the structural parameters of the deep belief network (DBN) model. First, by calculating the relative energy fluctuation value of the finite number of intrinsic function components using the variational modal decomposition of the rolling bearing vibration data, the proportion of each component containing the fault component is characterized. Then, high-quality learning samples are obtained through screening and reconstruction to achieve the effective cleaning of vibration data. Second, the improved particle swarm algorithm (IPSO) is used to optimize the number of nodes in each hidden layer of the DBN model in order to obtain the optimal structural parameters of the intelligent diagnosis model. Finally, the high-quality learning samples obtained from data cleaning are used as input to construct an intelligent identification model for rolling bearing faults. The results showed that the proposed method not only screens out the intrinsic mode function components that contain the fault effective components in the rolling bearing vibration data, but also finds the optimal solution for the number of nodes in the DBN hidden layer, which improves bearing state identification accuracy by 3%. Full article
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Article
Distributed Active Power Optimal Dispatching of Wind Farm Cluster Considering Wind Power Uncertainty
Energies 2022, 15(7), 2706; https://doi.org/10.3390/en15072706 - 06 Apr 2022
Viewed by 526
Abstract
With the large-scale volatility and uncertainty of the centralized grid connection of wind power, the dimensionality disaster problem of wind farm cluster (WFC) scheduling optimization calculation becomes more and more significant. In view of these challenges, a distributed active power optimal dispatch model [...] Read more.
With the large-scale volatility and uncertainty of the centralized grid connection of wind power, the dimensionality disaster problem of wind farm cluster (WFC) scheduling optimization calculation becomes more and more significant. In view of these challenges, a distributed active power optimal dispatch model for WFC based on the alternating direction multiplier method (ADMM) is proposed, and the analytical description of the distribution characteristics of the active power output of wind farms is introduced into the proposed model. Firstly, based on the wake effect, the Weibull distribution of wind speed is transformed by the impulse function to establish an analytical model of the active output distribution of the wind farm. Secondly, the optimization goal is to minimize the expected sum of the deviations of the dispatch instructions and the output probability density function of each wind farm, constructing a WFC active power optimal dispatch model considering uncertainty. Finally, the proposed model is decoupled in space and time into sub-optimization problems, and the ADMM is improved to construct an efficient solution algorithm that can iterate in parallel and decouple a large number of decision variables at the same time. The model is compared with other current classical models through the evaluation of multiple recommendation evaluation metrics, and the experimental results show that the model has a 3–7% reduction in dispatched power shortfalls and a 4–21% improvement in wind power utilization. The optimization algorithm for model construction has extremely high computational efficiency and good convergence. The results show that when the update step size is three, the convergence is the fastest, and when the update step size is six, the convergence is the slowest; in addition, when the number of wind farms is greater than eight, the distributed computing efficiency has an incomparable advantage over the centralized one. It plays a helpful role in wind power consumption and the efficient calculation of the power grid and effectively improves the reliability of the power grid. Full article
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Article
Servitization of Energy Sector: Emerging Service Business Models and Startup’s Participation
Energies 2022, 15(7), 2705; https://doi.org/10.3390/en15072705 - 06 Apr 2022
Viewed by 733
Abstract
Changing asset ownership models in the energy sector is spurring established companies and startups to implement customer-centric smart services. In this sense, startups are pioneers of innovative business models, and unbundle the energy value chain to provide various services to final customers. Although [...] Read more.
Changing asset ownership models in the energy sector is spurring established companies and startups to implement customer-centric smart services. In this sense, startups are pioneers of innovative business models, and unbundle the energy value chain to provide various services to final customers. Although service business models have received large attention in the energy sector, the role of startups in service business model innovation (S-BMI) is not fully understood in the literature. To put this into perspective, the proposed work analyzes the six most practiced energy service categories, specifically, Comfort and Heating, Flexibility and Trading, Energy Efficiency and Management, Solar and Microgrid, Charging and Battery, and Energy Software Solutions are taken into account, accompanying service business model archetypes in the energy sector. Data from two different company databases are combined, and a list of 432 startups dealing with energy services are analyzed. The operating revenue, stakeholders, investors, and funding are considered as the main indicators to compare the service categories. The top two categories in terms of the number of startups are Solar and Microgrid (38.1%) alongside Energy Efficiency and Management (20.1%). The analysis suggests that X-as-a-service (XaaS) and platform-based business models are becoming the center-of-attention for investors and shareholders. Digital marketplaces are also evolving in the energy sector. In fact, the current study found that startups associated with XaaS, platforms, and marketplace activities are attracting the majority of investors and funding programs. From a theoretical point of view, the study has provided the main motivations and enablers behind the energy sector servitization. The findings could serve as an initial methodological framework to analyze services in the energy sector, putting service business models and startups into focus. Full article
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Article
Fuel Cell Electrical Vehicles as Mobile Coupled Heat and Power Backup-Plant in Neighbourhoods
Energies 2022, 15(7), 2704; https://doi.org/10.3390/en15072704 - 06 Apr 2022
Viewed by 570
Abstract
Fuel cell electric vehicles (FCEVs) can be used during idle times to convert hydrogen into electricity in a decentralised manner, thus ensuring a completely renewable energy supply. In addition to the electric power, waste heat is generated in the fuel cell stack that [...] Read more.
Fuel cell electric vehicles (FCEVs) can be used during idle times to convert hydrogen into electricity in a decentralised manner, thus ensuring a completely renewable energy supply. In addition to the electric power, waste heat is generated in the fuel cell stack that can also be used. This paper investigates how the energy demand of a compiled German neighbourhood can be met by FCEVs and identifies potential technical problems. For this purpose, energy scenarios are modelled in the Open Energy System Modelling Framework (oemof). An optimisation simulation finds the most energetically favourable solution for the 10-day period under consideration. Up to 49% of the heat demand for heating and hot water can be covered directly by the waste heat of the FCEVs. As the number of battery electric vehicles (BEVs) to be charged increases, so does this share. 5 of the 252 residents must permanently provide an FCEV to supply the neighbourhood. The amount of hydrogen required was identified as a problem. If the vehicles cannot be supplied with hydrogen in a stationary way, 15 times more vehicles are needed than required in terms of performance due to the energy demand. Full article
(This article belongs to the Topic Distributed Generation and Storage in Power Systems)
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Article
Cumulative Emissions of CO2 for Electric and Combustion Cars: A Case Study on Specific Models
Energies 2022, 15(7), 2703; https://doi.org/10.3390/en15072703 - 06 Apr 2022
Cited by 1 | Viewed by 1263
Abstract
This work includes calculations of the cumulative CO2 emissions of two comparable cars—the VW Golf VII—one with a combustion engine and the other with an electric motor. Calculation of CO2 emissions was performed, taking into account the stages of production, utilization [...] Read more.
This work includes calculations of the cumulative CO2 emissions of two comparable cars—the VW Golf VII—one with a combustion engine and the other with an electric motor. Calculation of CO2 emissions was performed, taking into account the stages of production, utilization and use of the above-mentioned vehicles. For the use phase, it was assumed that the total mileage of the car will be 150,000 km over 10 years. For the electric vehicle, calculations were made assuming five different sources of electricity (from coal only, from natural gas only, from PV and wind turbines, an average mix of European power sources and an average mix of Polish power sources; W1–W5 designations, respectively). For individual sources of electricity, cumulative CO2 emissions were taken into account, that is, resulting both from the production of electricity and the use of the resources (for example, technical service per 1 kWh of electricity produced). The obtained results of the analysis show that for the adopted assumptions regarding operation, for variants W2–W5, the use of an electric car results in lower cumulative CO2 emission than a the use of a combustion car. For a combustion car, the value was 37,000 kg-CO2, and for an electric car, depending on the variant, the value was 43, 31, 16, 23 and 34 thousand kg-CO2 for variants W1 to W5, respectively. Based on the emissions results obtained for individual stages of the use of selected vehicles, a comparative analysis of cumulative CO2 emissions was performed. The purpose of this analysis was to determine whether the replacement of an existing combustion car (that has already been manufactured; therefore, this part of the analysis does not include CO2 emissions in the production stage) with a new electric car, which has to be manufactured, therefore associated with additional CO2 emissions, would reduce cumulative CO2 emissions. Considering three adopted average annual car mileages (3000, 7500 and 15,000 km) and the previously described power options (W1–W5), we sought an answer as to whether the use of a new electric car would be burdened with lower cumulative CO2 emissions. In this case we assumed an analysis time of 15 years. For the worst variant from the point of view of CO2 emissions (W1, electricity from coal power sources only), further use of a combustion car is associated with lower cumulative CO2 emissions than the purchase of a new electric car over the entire analyzed period of 15 years. In turn, for the most advantageous variant (W3, electricity from PV or wind power sources) with an annual mileage of 3000 km, the purchase of a new electric car results in higher cumulative CO2 emissions throughout the analyzed period, whereas for an annual milage of 7500 or 15,000 km, replacing the car with an electric car “pays back” in terms of cumulative CO2 emissions after 8.5 or 4 years, respectively. Full article
(This article belongs to the Section E: Electric Vehicles)
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Article
Smart Energy Management System: Design of a Smart Grid Test Bench for Educational Purposes
Energies 2022, 15(7), 2702; https://doi.org/10.3390/en15072702 - 06 Apr 2022
Cited by 5 | Viewed by 1063
Abstract
The presented article aims to design an educational test bench setup for smart grids and renewable energies with multiple features and techniques used in a microgrid. The test bench is designed for students, laboratory engineers, and researchers, which enables electrical microgrid system studies [...] Read more.
The presented article aims to design an educational test bench setup for smart grids and renewable energies with multiple features and techniques used in a microgrid. The test bench is designed for students, laboratory engineers, and researchers, which enables electrical microgrid system studies and testing of new, advanced control algorithms to optimize the energy efficiency. The idea behind this work is to design hybrid energy sources, such as wind power, solar photovoltaic power, hydroelectric power, hydrogen energy, and different types of energy storage systems such as batteries, pumped storage, and flywheel, integrating different electrical loads. The user can visualize the state of the components of each emulated scenario through an open-source software that interacts and communicates using OPC Unified Architecture protocol. The researchers can test and validate new solutions to manage the energy behavior in the grid using machine learning and optimization algorithms integrated in the software in form of blocks that can be modified and improved, and then simulate the results. A model-based system of engineering is provided, which describes the different requirements and case studies of the designed test bench, respecting the open-source software and the frugal innovation features in which there is use of low-cost hardware and open-source software. The users obtain the opportunity to add new sources and new loads, change software platforms, and communicate with other simulators and equipment. The students can understand the different features of smart grids, such as defect classification, energy forecasting, energy optimization, and basics of production, transmission, and consumption. Full article
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Article
Location and Technical Requirements for Photovoltaic Power Stations in Poland
Energies 2022, 15(7), 2701; https://doi.org/10.3390/en15072701 - 06 Apr 2022
Cited by 1 | Viewed by 538
Abstract
The objective of Poland’s energy policy is to guarantee energy security while enhancing economic competitiveness and energy efficiency, thus minimizing the power sector’s environmental impact and optimizing the use of energy resources in the country. Poland is not the only European country to [...] Read more.
The objective of Poland’s energy policy is to guarantee energy security while enhancing economic competitiveness and energy efficiency, thus minimizing the power sector’s environmental impact and optimizing the use of energy resources in the country. Poland is not the only European country to rely on coal for power generation. Historical factors and large coal deposits act as natural barriers to increasing the share of renewable energy in the Polish power sector. Yet, today, environmental concerns and climate change are prompting many countries to move away from fossil fuels. Renewable energy sources, such as solar and wind energy, are an alternative to traditional energy generated from fossil fuels. However, investors developing solar and wind farms in Poland encounter numerous problems at each stage of the project. These difficulties are associated mainly with the location, technical requirements, infrastructure and formal and legal documents. This study aimed to identify the key factors that influence the development of photovoltaic power stations in Poland, with special emphasis on the choice of location and technical aspects of the investment process. The demand for clean energy and the renewable energy prospects for Poland are discussed based on the example of solar farms. Sixty-seven prospective farm locations were analyzed, and the results of the analysis were used to identify the main barriers and opportunities for renewable energy development in Poland. The option of connecting solar farms to the existing power grid was also examined. This study demonstrates that the development of solar farms in Poland is inhibited mainly by technical barriers, in particular the lack of options for connecting farms to the power grid, as well as the absence of support mechanisms and dedicated legislative solutions, rather than environmental obstacles. Full article
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Article
Analogies in the Analysis of the Thermal Status of Batteries and Internal Combustion Engines for Mobility
Energies 2022, 15(7), 2700; https://doi.org/10.3390/en15072700 - 06 Apr 2022
Viewed by 449
Abstract
Thermal management is an important research area for the automotive sector in order to make high-efficiency and low-impact future vehicles. The transition from internal combustion engines to battery systems in the automotive field requires new skills to be achieved in the shortest possible [...] Read more.
Thermal management is an important research area for the automotive sector in order to make high-efficiency and low-impact future vehicles. The transition from internal combustion engines to battery systems in the automotive field requires new skills to be achieved in the shortest possible time. The well-consolidated knowledge of thermal management of engine systems can be rearranged to face new challenges regarding the thermal control of batteries. The present work aims to show the analogies between the thermal behavior of an engine component, such as the piston, and of a battery. The thermodynamic processes involved during the operation are described, experimentally investigated, and modeled. The external temperature of the piston window is measured once per cycle with a K-type sheathed thermocouple, while the surface temperature of the battery is detected via infrared imaging. An almost-fixed stabilization time of 500 s is observed for the engine while it varies with the current load for the battery ranging from 1800 s to 3000 s, for the tested cases. Different temperature increments are also observed. Two mono-dimensional (1D) models of heat transfer are built using the finite-difference method. Good agreement with the experimental data is quantitatively demonstrated by a Normalize Root Mean Square Error lower than 0.07 for all the test cases and systems, except for the battery charging phase. The analysis of the temperature provides an estimation of the heat losses for the two systems, spanning from 15% to 27% for the engine and from 6% to 10% for the battery. The analysis carried out in this work can provide a methodology to understand and improve the thermal management of the new mobility system. Full article
(This article belongs to the Special Issue Thermal Management of Internal Combustion Engines)
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Review
Key Features of TEMPO-Containing Polymers for Energy Storage and Catalytic Systems
Energies 2022, 15(7), 2699; https://doi.org/10.3390/en15072699 - 06 Apr 2022
Viewed by 791
Abstract
The need for environmentally benign portable energy storage drives research on organic batteries and catalytic systems. These systems are a promising replacement for commonly used energy storage devices that rely on limited resources such as lithium and rare earth metals. The redox-active TEMPO [...] Read more.
The need for environmentally benign portable energy storage drives research on organic batteries and catalytic systems. These systems are a promising replacement for commonly used energy storage devices that rely on limited resources such as lithium and rare earth metals. The redox-active TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl) fragment is a popular component of organic systems, as its benefits include remarkable electrochemical performance and decent physical properties. TEMPO is also known to be an efficient catalyst for alcohol oxidation, oxygen reduction, and various complex organic reactions. It can be attached to various aliphatic and conductive polymers to form high-loading catalysis systems. The performance and efficiency of TEMPO-containing materials strongly depend on the molecular structure, and thus rational design of such compounds is vital for successful implementation. We discuss synthetic approaches for producing electroactive polymers based on conductive and non-conductive backbones with organic radical substituents, fundamental aspects of electrochemistry of such materials, and their application in energy storage devices, such as batteries, redox-flow cells, and electrocatalytic systems. We compare the performance of the materials with different architectures, providing an overview of diverse charge interactions for hybrid materials, and presenting promising research opportunities for the future of this area. Full article
(This article belongs to the Collection Review Papers in Energy and Environment)
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Article
A New Wind Speed Scenario Generation Method Based on Principal Component and R-Vine Copula Theories
Energies 2022, 15(7), 2698; https://doi.org/10.3390/en15072698 - 06 Apr 2022
Viewed by 467
Abstract
The intermittent and uncertain properties of wind power have presented enormous obstacles to the planning and steady operation of power systems. In this context, as an effective technique to study wind power uncertainty, the development of an accurate wind speed scenario generation method [...] Read more.
The intermittent and uncertain properties of wind power have presented enormous obstacles to the planning and steady operation of power systems. In this context, as an effective technique to study wind power uncertainty, the development of an accurate wind speed scenario generation method is of great significance for evaluating the impact of wind power in the power system. In the case of several wind farms, accurate scenario generation involves precise acquisition of the correlation between wind speeds and the greatest retention of statistical properties of wind speed data. Under this goal, this research provided a new method for scenario development based on principle component (PC) and R-vine copula theories that incorporates the spatiotemporal correlation of wind speeds. By integrating with PC theory, this strategy avoids the dimension disaster induced by employing R-vine copula alone while taking benefit of its flexibility. The simulation results utilizing the historical wind speeds of three adjacent wind farms as samples showed that the method described in this article could effectively preserve the statistical properties of wind speed data. Eight evaluation indicators covering three facets of the scenario generation method were used to compare the proposed method holistically to two other commonly used scenario generation methods. The results indicated that this method’s accuracy was increased further. Additionally, the validity and necessity of applying R-vine copula in this model was demonstrated through comparisons to C-vine and D-vine copulas. Full article
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Review
Integration of Waste to Bioenergy Conversion Systems: A Critical Review
Energies 2022, 15(7), 2697; https://doi.org/10.3390/en15072697 - 06 Apr 2022
Cited by 1 | Viewed by 521
Abstract
Sustainable biofuel production is the most effective way to mitigate greenhouse gas emissions associated with fossil fuels while preserving food security and land use. In addition to producing bioenergy, waste biorefineries can be incorporated into the waste management system to solve the future [...] Read more.
Sustainable biofuel production is the most effective way to mitigate greenhouse gas emissions associated with fossil fuels while preserving food security and land use. In addition to producing bioenergy, waste biorefineries can be incorporated into the waste management system to solve the future challenges of waste disposal. Biomass waste, on the other hand, is regarded as a low-quality biorefinery feedstock with a wide range of compositions and seasonal variability. In light of these factors, biomass waste presents limitations on the conversion technologies available for value addition, and therefore more research is needed to enhance the profitability of waste biorefineries. Perhaps, to keep waste biorefineries economically and environmentally sustainable, bioprocesses need to be integrated to process a wide range of biomass resources and yield a diverse range of bioenergy products. To achieve optimal integration, the classification of biomass wastes to match the available bioprocesses is vital, as it minimizes unnecessary processes that may increase the production costs of the biorefinery. Based on biomass classification, this study discusses the suitability of the commonly used waste-to-energy conversion methods and the creation of integrated biorefineries. In this study, the integration of waste biorefineries is discussed through the integration of feedstocks, processes, platforms, and the symbiosis of wastes and byproducts. This review seeks to conceptualize a framework for identifying and integrating waste-to-energy technologies for the varioussets of biomass wastes. Full article
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Editorial
Collective Action Initiatives as a Tool for a Peaceful Energy Transition
Energies 2022, 15(7), 2696; https://doi.org/10.3390/en15072696 - 06 Apr 2022
Viewed by 365
Abstract
In recent years, collective action initiatives in the energy field, such as energy communities and cooperatives, have been gaining relevance both in the policy and in the social research domains as primary actors of energy transition. [...] Full article
(This article belongs to the Special Issue Energy Transition and Social Innovation)
Article
Impact of Educational Attainment on Renewable Energy Use: Evidence from Emerging Market Economies
Energies 2022, 15(7), 2695; https://doi.org/10.3390/en15072695 - 06 Apr 2022
Cited by 1 | Viewed by 468
Abstract
Renewable energy has become a crucial factor for circular economies, sustainable development, and the environment given the limited non-renewable energy reserves and global environmental degradation mainly resulting from non-renewable energy use. This study explores the effect of educational attainment and economic growth on [...] Read more.
Renewable energy has become a crucial factor for circular economies, sustainable development, and the environment given the limited non-renewable energy reserves and global environmental degradation mainly resulting from non-renewable energy use. This study explores the effect of educational attainment and economic growth on renewable energy use in a sample of selected emerging markets over the 2000–2018 period through causality and cointegration analyses. Causality analysis points out a significant unidirectional causality from indicators of educational attainment and economic growth to renewable energy use. In other words, educational attainment indicators and economic growth are significant determinants of renewable energy in the short run. Furthermore, the cointegration analysis ascertains a positive influence of indicators of educational attainment and economic growth on renewable energy use in the long run. The findings of both analyses indicate that educational attainment and economic growth have a significant impact on renewable energy use in the short and long term. Therefore, the policies fostering educational attainment can be used as instruments to increase the share of renewable energy use in total energy consumption. Full article
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Article
Two Channels Opto-Isolation Circuit for Measurements of the Differential Voltage of Voltage Transformers and Dividers
Energies 2022, 15(7), 2694; https://doi.org/10.3390/en15072694 - 06 Apr 2022
Viewed by 338
Abstract
In this paper the design of the two channel opto-isolation circuit for measurements of the differential voltage is presented. It is used to ensure high impedance of the measuring channel(s) in the differential system to ensure the rated operation of connected voltage divider(s). [...] Read more.
In this paper the design of the two channel opto-isolation circuit for measurements of the differential voltage is presented. It is used to ensure high impedance of the measuring channel(s) in the differential system to ensure the rated operation of connected voltage divider(s). Its conversion accuracy tests are oriented to determine the ratio and phase errors introduced by a tested device under three test conditions. The opto-isolation circuit is tested for the internal noise at various levels of common voltage. In the next step the calibration of the zero output voltage at zero differential voltage is tested. In the last step of the testing procedure, the values of conversion ratio and phase errors are determined. In the first case the analysis is performed during an operation with an additional common voltage divider when both inputs ensure high impedance. In the second case the values of the conversion ratio and phase errors are tested in conditions when only one input ensures high impedance. In this paper the application of the opto-isolation circuit to determine the values of the composite error of the tested voltage divider with the rated voltage ratios equal to 15 kV:100 V, 10 kV:100 V, 5 kV:100 V is presented. Moreover, its usage to determine the values of the composite error of the inductive voltage transformer with voltage ratio (15 kV/√3)/(100 V/√3) is shown. Full article
(This article belongs to the Special Issue Development of Voltage and Current Transformers in Power System)
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Article
Emission of Methane and Carbon Dioxide during Soil Freezing without Permafrost
Energies 2022, 15(7), 2693; https://doi.org/10.3390/en15072693 - 06 Apr 2022
Viewed by 546
Abstract
Research on methane and carbon dioxide emissions mainly focuses on industrial emissions, cultivated land, and wetlands, while few studies have studied freezing-related emissions. This paper presents field experiments conducted during soil freezing to measure carbon dioxide and methane concentrations in the air, near [...] Read more.
Research on methane and carbon dioxide emissions mainly focuses on industrial emissions, cultivated land, and wetlands, while few studies have studied freezing-related emissions. This paper presents field experiments conducted during soil freezing to measure carbon dioxide and methane concentrations in the air, near the soil surface, and in the soil. In addition, the influence of precipitation, snowfall, air temperature, and depth of freezing on gas emissions was analyzed. We observed increased concentrations of methane and carbon dioxide in soil and air at soil freezing and snow cover growth. For the first time, an increase in gas flux during soil freezing was found in the absence of permafrost. Full article
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Article
Relationships between the Petrographic and Abrasive Properties of Sandstones in the Aspect of Their Cutting
Energies 2022, 15(7), 2692; https://doi.org/10.3390/en15072692 - 06 Apr 2022
Viewed by 470
Abstract
The research described in this article was carried out on samples of sandstone obtained from the underground excavations of four hard coal mines that operate in the region of Poland with the highest energy resources, i.e., Upper Silesia. The majority of underground tunnel [...] Read more.
The research described in this article was carried out on samples of sandstone obtained from the underground excavations of four hard coal mines that operate in the region of Poland with the highest energy resources, i.e., Upper Silesia. The majority of underground tunnel excavations are mainly drilled using roadheaders, the organs of which are equipped with conical picks. The selection of pick type is usually based on rock compressive strength. However, sandstones often cause more problems during cutting compared to other waste rocks because of their variety. This article’s primary purpose is to emphasize the importance of researching various properties of waste rock in addition to uniaxial compression strength, which is crucial in the selection of both the appropriate cutting method and appropriate cutting tools. Accordingly, relations between mineralogical, petrographic, physical and mechanical properties were examined in this study, with special attention paid to the abrasive properties that comprise rock abrasivity. Sandstones from the regions of Upper Silesia are characterized by a heterogeneity of mineralogical and petrographic features that strongly affect the physical and mechanical properties of these rocks, especially their abrasive properties. The determined correlations can aid understanding of the behavior of rocks during their mechanical cutting and facilitate the selection of appropriate cutting tools. Full article
(This article belongs to the Special Issue Volume II: Mining Innovation)
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Article
FEM Strength Analysis of Circumferential Compensation with Integrated Lips in Gear Pumps
Energies 2022, 15(7), 2691; https://doi.org/10.3390/en15072691 - 06 Apr 2022
Viewed by 443
Abstract
Currently, gear pumps are developed with a aim to increase their efficiency, reduce internal leaks, and increase their working pressures. This development direction requires new solutions which would compensate backlash while ensuring an optimal size of the gaps for the entire range of [...] Read more.
Currently, gear pumps are developed with a aim to increase their efficiency, reduce internal leaks, and increase their working pressures. This development direction requires new solutions which would compensate backlash while ensuring an optimal size of the gaps for the entire range of working pressures. One of the solutions intended to meet this demand is to design circumferential compensation with the so-called integrated lips. The presented backlash compensation method is the result of research performed as part of a project named Designing High-Pressure Gear Pumps. The project was granted funding under path A of the Applied Research Program, contract No. PBS3/A6/22/2015. The research works were performed in the Laboratory of Hydraulic Drives and Vibroacoustics of Machines at Wrocław University of Science and Technology, and in cooperation with Hydrotor SA. Full article
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Article
Economic and Environmental Aspects of Engine Selection in Cargo Transportation
Energies 2022, 15(7), 2690; https://doi.org/10.3390/en15072690 - 06 Apr 2022
Viewed by 477
Abstract
A company’s productivity and success measure its effectiveness. This article presents the problem of economic efficiency and aspects related to environmental protection. The basic parameters analysed were the engine type and how it affects the environment. Over three months, the analysis was carried [...] Read more.
A company’s productivity and success measure its effectiveness. This article presents the problem of economic efficiency and aspects related to environmental protection. The basic parameters analysed were the engine type and how it affects the environment. Over three months, the analysis was carried out and used the data envelopment analysis. As a result of the research carried out, the comparison of the amount of fuel used with the amount of transported goods should answer the following questions: What type of engine should be ordered for new trucks to show the best efficiency during operation? What is the efficiency of the currently used engines? How do they affect the environment? The method proposed in the article makes it possible to define the initial requirements for the definition of truck units, which is included in the conclusions of this paper. Full article
(This article belongs to the Special Issue Energy Transportation Visualization)
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Article
A Comparative Study and Optimization of Switching Functions for Sliding-Mode Observer in Sensorless Control of PMSM
Energies 2022, 15(7), 2689; https://doi.org/10.3390/en15072689 - 06 Apr 2022
Cited by 1 | Viewed by 522
Abstract
The sensorless control of the permanent magnet synchronous motor (PMSM) has attracted wide attention due to its high reliability, economic and safety benefits. A fast and high-precision rotor-position estimation is inevitable for the implementation of sensorless control. Sliding-mode observer (SMO) is a preferred [...] Read more.
The sensorless control of the permanent magnet synchronous motor (PMSM) has attracted wide attention due to its high reliability, economic and safety benefits. A fast and high-precision rotor-position estimation is inevitable for the implementation of sensorless control. Sliding-mode observer (SMO) is a preferred solution for sensorless control by many industrial companies. This article addresses the comparison of different switching functions employed in the control structure of sensorless field-oriented control with SMO. The switching functions are classified and their influence on the performance of the PMSM is verified for different shaping coefficients (SC). In addition, a statistical evaluation of the switching functions is provided to find the optimal values of SC. An experimental and statistical evaluation validated the substitutability of signum and hyperbolic switching functions and optimal values of SC have been found. Full article
(This article belongs to the Special Issue Applications of Modern Methods to Control of Electric Drives)
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Article
Deeper Understanding of Ternary Eutectic Carbonates/Ceria-Based Oxide Composite Electrolyte through Thermal Cycling
Energies 2022, 15(7), 2688; https://doi.org/10.3390/en15072688 - 06 Apr 2022
Viewed by 472
Abstract
Due to a high conductivity of about 0.1 S·cm−1, Li-Na-K carbonate eutectic and Sm-doped ceria composite material is a good electrolyte candidate for hybrid fuel cells operating between 500 °C and 600 °C. The present paper aims at a deeper understanding [...] Read more.
Due to a high conductivity of about 0.1 S·cm−1, Li-Na-K carbonate eutectic and Sm-doped ceria composite material is a good electrolyte candidate for hybrid fuel cells operating between 500 °C and 600 °C. The present paper aims at a deeper understanding of the species and mechanisms involved in the ionic transport through impedance spectroscopy and thermal analyses, in oxidizing and reducing atmospheres, wet and dry, and during two heating/cooling cycles. Complementary structural analyses of post-mortem phases allowed us to evidence the irreversible partial transformation of molten carbonates into hydrogenated species, when water and/or hydrogen are added in the surrounding atmospheres. Furthermore, this modification was avoided by adding CO2 in anodic and/or cathodic compartments. Finally, a mechanistic model of such composite electrical behavior is suggested, according to the surrounding atmospheres used. It leads to the conclusions that cells based on this kind of electrolyte would preferably operate in molten carbonate fuel cell conditions, than in solid oxide fuel cell conditions, and confirms the name of “Hybrid Fuel Cells” instead of Intermediate Temperature (or even Low Temperature) Solid Oxide Fuel Cells. Full article
(This article belongs to the Special Issue Solid Oxide Cells: Technology, Design and Applications)
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Article
Parameter Studies on Hydraulic Fracturing in Brittle Rocks Based on a Modified Hydromechanical Coupling Model
Energies 2022, 15(7), 2687; https://doi.org/10.3390/en15072687 - 06 Apr 2022
Viewed by 384
Abstract
In this paper, we present a numerical study of hydraulic fracturing in brittle rock by using particle flow simulation. The emphasis is put on the influence of in situ stress, differential stress, fluid injection rate, fluid viscosity and borehole size on hydraulic fracturing [...] Read more.
In this paper, we present a numerical study of hydraulic fracturing in brittle rock by using particle flow simulation. The emphasis is put on the influence of in situ stress, differential stress, fluid injection rate, fluid viscosity and borehole size on hydraulic fracturing behavior. To this end, an improved hydromechanical coupling model is first introduced to better describe fluid flow and local deformation of particle-based rocks. A series of parameter sensitivity studies are then conducted under the framework of particle flow simulation. Modelling results suggest that the breakdown pressure and time to fracture both linearly increase with confining stress, and hydraulic fracturing patterns present a distinct transition from brittle to ductile. Fluid injection rate and fluid viscosity have similar influences on hydraulic fracturing propagation, their value decrease leads to borehole pressure decrement and time to fracture prolongation. However, the former mainly controls the time to initial cracking, while the latter largely decides the duration of fracturing propagation. As for borehole radius, its increases can directly enhance the fluid diffusion zone, which further intensifies the nonlinear property of borehole pressure, leads to breakdown pressure decrease, prolongs time to fracture and forms more complex hydraulic fractures. Full article
(This article belongs to the Special Issue Geomechanics of Hydraulic Fracturing)
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Article
An Iterative Algorithm for the Estimation of Thermal Boundary Conditions Varying in Both Time and Space
Energies 2022, 15(7), 2686; https://doi.org/10.3390/en15072686 - 06 Apr 2022
Viewed by 349
Abstract
The presented survey of the up-to-date state of knowledge indicates that despite the great number of works devoted to the issue in question, there is no simple method that allows the use of commercial programs for the identification of the transient thermal state [...] Read more.
The presented survey of the up-to-date state of knowledge indicates that despite the great number of works devoted to the issue in question, there is no simple method that allows the use of commercial programs for the identification of the transient thermal state in elements with a simple or complex shape. This paper presents an inverse method developed to estimate the convective heat transfer coefficient varying both in time and space on a vertical plate during its cooling. Despite the smaller number of measurement points and larger disturbance of measured temperatures compared to the data presented in the available literature, comparable results are obtained. The developed iterative algorithm is also applied to estimate the time- and space-dependent heat flux and the convective heat transfer coefficient in the steam boiler membrane waterwall. The analysed component has the form of the non-simply connected and complex shape domain Ω. Temperature-dependent thermophysical properties are used. Calculations are performed for the unknown heat flux or heat transfer coefficient distribution on the domain boundary based on measured temperature transients disturbed with a random error of 0.5 °C. To reduce oscillations, the number of future time steps of NF = 20 is selected. The number of iterations in each time step ranges between 1 and 8. The estimated boundary conditions are close to the exact values. In this work, the ANSYS software using the FEM is applied. Full article
(This article belongs to the Section J1: Heat and Mass Transfer)
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Review
State of the Art, Perspective and Obstacles of Ground-Source Heat Pump Technology in the European Building Sector: A Review
Energies 2022, 15(7), 2685; https://doi.org/10.3390/en15072685 - 06 Apr 2022
Cited by 1 | Viewed by 708
Abstract
In the European Union, 40% of the overall final energy consumption is attributable to the buildings sector. A reason for such data may be found considering that the great majority of the building stock is more than 40 years old. According to the [...] Read more.
In the European Union, 40% of the overall final energy consumption is attributable to the buildings sector. A reason for such data may be found considering that the great majority of the building stock is more than 40 years old. According to the European Commission, an interesting potential lies in the refurbishment of the building sector, and heat pump technology has been recognized as one of the most cost-effective solutions to tackle the environmental issue of this sector. Regarding heat pump technology, ground-source heat pumps (GSHPs) have been proven to be the most efficient solution on equal boundary conditions. Despite this, in most EU states’ markets, GSHPs hold only a small market share with respect to air-source heat pumps. In this paper, the state of art and possible future developments of GSHP technology have been reviewed together with a focus on the potential of such technology, most of all on the refurbishment of existing buildings, and on the obstacles to its spread. The state of art of borehole heat exchangers has been studied, focusing on the parameters characterizing the outside pipe and the pipe itself, i.e., pipe and grout materials. Moreover, an overview on the last developments involving refrigerants and secondary fluids is given. Finally, the design and control strategies of GSHPs have been reviewed. Full article
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Article
Study on the Causes of Water Blocking Damage and Its Solutions in Gas Reservoirs with Microfluidic Technology
Energies 2022, 15(7), 2684; https://doi.org/10.3390/en15072684 - 06 Apr 2022
Viewed by 462
Abstract
The water blocking damage to the reservoir caused by the invasion of external fluid is one of the main factors that affect the efficient development of tight sandstone gas reservoirs. In this paper, microfluidic chip technology is used to explore the causes of [...] Read more.
The water blocking damage to the reservoir caused by the invasion of external fluid is one of the main factors that affect the efficient development of tight sandstone gas reservoirs. In this paper, microfluidic chip technology is used to explore the causes of water blocking damage in porous media and find suitable recovery solutions. The research results show that reducing the gas-liquid capillary pressure can effectively reduce the rate and quantity of spontaneous speed of cores. After chemical treatment, the liquid phase fluidity of the non-fractured matrix core is increased by 1.72 times, and that of the fractured core is increased by 2.13 times. In water wetting porous media, there are mainly four types of liquid hold-up: (1) Liquid hold-up in the dead volume of a non-connected pore; (2) The water phase in the pore throat with a small inner diameter cannot be driven away due to its larger capillary pressure; (3) Adsorption viscous force, the wetting phase is adsorbed on the surface of the solid phase; (4) Reservoir heterogeneity. The water blocking damage can be removed to a certain extent by changing the gas injection pressure, the gas injection method, or adding a wetting modifier. Full article
(This article belongs to the Special Issue Shale Oil and Gas Accumulation Mechanism)
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Review
Membrane and Electrochemical Based Technologies for the Decontamination of Exploitable Streams Produced by Thermochemical Processing of Contaminated Biomass
Energies 2022, 15(7), 2683; https://doi.org/10.3390/en15072683 - 06 Apr 2022
Viewed by 656
Abstract
Phytoremediation is an emerging concept for contaminated soil restoration via the use of resilient plants that can absorb soil contaminants. The harvested contaminated biomass can be thermochemically converted to energy carriers/chemicals, linking soil decontamination with biomass-to-energy and aligning with circular economy principles. Two [...] Read more.
Phytoremediation is an emerging concept for contaminated soil restoration via the use of resilient plants that can absorb soil contaminants. The harvested contaminated biomass can be thermochemically converted to energy carriers/chemicals, linking soil decontamination with biomass-to-energy and aligning with circular economy principles. Two thermochemical conversion steps of contaminated biomass, both used for contaminated biomass treatment/exploitation, are considered: Supercritical Water Gasification and Fast Pyrolysis. For the former, the vast majority of contaminants are transferred into liquid and gaseous effluents, and thus the application of purification steps is necessary prior to further processing. In Fast Pyrolysis, contaminants are mainly retained in the solid phase, but a part appears in the liquid phase due to fine solids entrainment. Contaminants include heavy metals, particulate matter, and hydrogen sulfide. The purified streams allow the in-process re-use of water for the Super Critical Water Gasification, the sulfur-free catalytic conversion of the fuel-rich gaseous stream of the same process into liquid fuels and recovery of an exploitable bio-oil rich stream from the Fast Pyrolysis. Considering the fundamental importance of purification/decontamination to exploit the aforementioned streams in an integrated context, a review of available such technologies is conducted, and options are shortlisted. Technologies of choice include polymeric-based membrane gas absorption for desulfurization, electrooxidation/electrocoagulation for the liquid product of Supercritical Water Gasification and microfiltration via ceramic membranes for fine solids removal from the Fast Pyrolysis bio-oil. Challenges, risks, and suitable strategies to implement these options in the context of biomass-to-energy conversion are discussed and recommendations are made. Full article
(This article belongs to the Special Issue Biofuel Value Chains: Innovations and Sustainability)
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Article
Osmotic Membrane Distillation Crystallization of NaHCO3
Energies 2022, 15(7), 2682; https://doi.org/10.3390/en15072682 - 06 Apr 2022
Cited by 1 | Viewed by 736
Abstract
A new crystallization process for sodium bicarbonate (NaHCO3) was studied, proposing the use of osmotic membrane distillation crystallization. Crystallization takes place due to the saturation of the feed solution after water evaporation on the feed side, permeating through the membrane pores [...] Read more.
A new crystallization process for sodium bicarbonate (NaHCO3) was studied, proposing the use of osmotic membrane distillation crystallization. Crystallization takes place due to the saturation of the feed solution after water evaporation on the feed side, permeating through the membrane pores to the osmotic side. The process operational parameters, i.e., feed and osmotic velocities, feed concentration, and temperature were studied to determine the optimal operating conditions. Regarding the feed and osmotic velocities, values of 0.038 and 0.0101 m/s, respectively, showed the highest transmembrane flux, i.e., 4.4 × 10−8 m3/m2·s. Moreover, study of the temperature variation illustrated that higher temperatures have a positive effect on the size and purity of the obtained crystals. The purity of the crystals obtained varied from 96.4 to 100% In addition, the flux changed from 2 × 10−8 to 7 × 10−8 m3/m2·s with an increase in temperature from 15 to 40 °C. However, due to heat exchange between the feed and the osmotic solutions, the energy loss in osmotic membrane distillation crystallization is higher at higher temperatures. Full article
(This article belongs to the Special Issue Thermal Performance of Membrane Distillation)
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Article
Polyhumous Dystrophic Pit Lakes: Hydrographic and Hydrochemical Characteristics on the Example of Reservoirs in the Włoszczowska Basin, Central Poland
Energies 2022, 15(7), 2681; https://doi.org/10.3390/en15072681 - 06 Apr 2022
Viewed by 387
Abstract
The article presents the hydrographic and hydrochemical characteristics of post-exploitation reservoirs formed in peat excavations. Two natural bog lakes were selected as the control objects for the study. The research indicated that both the waters of post-exploitation peat reservoirs and natural bog lakes [...] Read more.
The article presents the hydrographic and hydrochemical characteristics of post-exploitation reservoirs formed in peat excavations. Two natural bog lakes were selected as the control objects for the study. The research indicated that both the waters of post-exploitation peat reservoirs and natural bog lakes show low electrolytic conductivity (<100 µS/cm) and acidic water reaction (pH < 5.5). The concentration of major cations and anions is also very low. The concentration of calcium and magnesium does not exceed a few mg/L. Hydrochemically, all post-exploitation peat reservoirs are bi-ionic sulphate–calcium (SO42−-Ca2+). This distinguishes post-exploitation peat reservoirs from natural bog lakes in which multi-ion waters were found, for example, sulphate–chloride–calcium (SO42−-Cl-Ca2+) and sulphate–calcium–sodium (SO42−-Ca2+-Na+). The calculated water humic state index (HSI) allowed the classifying of the examined reservoirs as polyhumous. The value of this index, in all reservoirs, was >50. Based on the calculated hydrochemical dystrophy index (HDI), it was found that all post-exploitation peat reservoirs are dystrophic. So far, no such hydrochemical type has been found in other post-exploitation peat reservoirs. Therefore, the examined objects should be classified as unique post-exploitation peat reservoirs. Full article
(This article belongs to the Special Issue Impact of Mine Activity on Water Environment)
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Article
Determining the Burning Rate of Fine-Grained Propellants in Closed Vessel Tests
Energies 2022, 15(7), 2680; https://doi.org/10.3390/en15072680 - 06 Apr 2022
Viewed by 442
Abstract
This paper presents the method of determining the burning rate of fine-grained propellants based on the results of closed vessel tests. It is shown that in the case of fine-grained propellants, the standard methods of determining the burning rate fail. There are two [...] Read more.
This paper presents the method of determining the burning rate of fine-grained propellants based on the results of closed vessel tests. It is shown that in the case of fine-grained propellants, the standard methods of determining the burning rate fail. There are two reasons for this: imperfections of the grain shapes and the prolonged process of ignition due to a more developed surface than that of coarse grains at the same mass of the propellant. The value of the exponent in the burning law is estimated by the use of the so-called experimental form–function. The upper and lower limits of the value of the coefficient in the burning law are estimated. The accuracy of the proposed method is analyzed. Its validity is assessed by comparing the results of closed vessel tests analysis with accessible literature data. Full article
(This article belongs to the Special Issue Ignition and Combustion of Energetic Materials)
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Article
Survey Results on Using Nudges for Choice of Green-Energy Supplier
Energies 2022, 15(7), 2679; https://doi.org/10.3390/en15072679 - 06 Apr 2022
Cited by 1 | Viewed by 505
Abstract
One of the most important climate change mitigation strategies is to exploit the potential of individual behavioral changes in order to reduce greenhouse gas (GHG) emissions, and the insights of behavioral economics are proving helpful in this regard. This contributes to improving traditional [...] Read more.
One of the most important climate change mitigation strategies is to exploit the potential of individual behavioral changes in order to reduce greenhouse gas (GHG) emissions, and the insights of behavioral economics are proving helpful in this regard. This contributes to improving traditional instruments, developing new ones related to choice architecture (nudges), and combining them within behavioral decarbonization intervention strategies. It is important, in terms of their effectiveness and efficiency, whether the instruments of such interventions are supported by citizens. This paper presents the results of a survey of Polish respondents’ (n = 1064) reactions to hypothetical nudges regarding the choice of a “green energy” supplier. The main research questions of the study are: how much civic support do these behavioral intervention tools have, and what is the importance of selected factors for their acceptance? The aim of the study is to present nudges as one of the strategies of pro-environmental behavioral change and to analyze selected factors of acceptance of these instruments by the Polish society. There are two main conclusions of the research: (1) Poles’ support for the green nudges analyzed is comparatively high, like in other European countries; (2) statistically significant differences in support for one of them are age and individual political party preferences. Full article
(This article belongs to the Special Issue Energy Decision Making: Problems, Methods, and Tools)
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