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Energies, Volume 14, Issue 15 (August-1 2021) – 329 articles

Cover Story (view full-size image): Analysts typically regard climate change as the existential issue of our time. This laser focuses on just one of many environmental crises belies the broader issue underlying them all: overshoot. We revive this basic ecological concept—taught in ecology courses, applied to humans in Limits to Growth, and once popularized by William Catton’s Overshoot—as holding the key to our survival. We show that so-called renewable energy technologies actually exacerbate overshoot and argue for a radically simple trajectory change: a contraction of the human enterprise back to one-planet living. Shifting from a near-exclusive fixation on material growth to progress of the mind and spirit in harmony with Nature—unlimited frontiers largely untapped at present—is the greatest challenge confronting humanity. View this paper
Overshoot
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Article
The Methodology for Designing Residential Buildings with a Positive Energy Balance—General Approach
Energies 2021, 14(15), 4715; https://doi.org/10.3390/en14154715 - 03 Aug 2021
Cited by 2 | Viewed by 677
Abstract
This a presents an original methodology for designing residential buildings with a positive energy balance. This process is an extremely complex undertaking. So far, no methodology with an open set of decision criteria has been developed that would include the modeling of the [...] Read more.
This a presents an original methodology for designing residential buildings with a positive energy balance. This process is an extremely complex undertaking. So far, no methodology with an open set of decision criteria has been developed that would include the modeling of the decisionmaker’s preferences using statistical surveys of a group of decisionmakers for this purpose. There is also no methodology relating to the interdependence of decision criteria. The present paper presents an original methodology consisting of five stages. The prepared algorithm indicates the need for changes in the classic design of residential buildings, taking into account the decision criteria that show interdependence. The proposed methodology consists in combining three methods of multi-criteria decision support: the DEMATEL method, used to determine the relations between decision criteria; the AHP/ANP method, used to build a model of the decisionmaker’s preferences, and the TOPSIS method, used to create a ranking of permissible and acceptable variants of solutions. The tool, i.e., the DEMATEL method, fulfills the expected function and enables the identification of the relations between the criteria and sub-criteria of evaluation. The AHP/ANP method fulfills the expected function and enables the ranking of evaluation criteria and sub-criteria. Full article
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Article
Development and Validation of Air-to-Water Heat Pump Model for Greenhouse Heating
Energies 2021, 14(15), 4714; https://doi.org/10.3390/en14154714 - 03 Aug 2021
Cited by 2 | Viewed by 765
Abstract
This study proposes a building energy simulation (BES) model of an air-to-water heat pump (AWHP) system integrated with a multi-span greenhouse using the TRNSYS-18 program. The proposed BES model was validated using an experimental AWHP and a multi-span greenhouse installed in Kyungpook National [...] Read more.
This study proposes a building energy simulation (BES) model of an air-to-water heat pump (AWHP) system integrated with a multi-span greenhouse using the TRNSYS-18 program. The proposed BES model was validated using an experimental AWHP and a multi-span greenhouse installed in Kyungpook National University, Daegu, South Korea (latitude 35.53° N, longitude 128.36° E, elevation 48 m). Three AWHPs and a water storage tank were used to fulfill the heat energy requirement of the three-span greenhouse with 391.6 m2 of floor area. The model was validated by comparing the following experimental and simulated results, namely, the internal greenhouse temperature, the heating load of the greenhouse, heat supply from the water storage tank to the greenhouse, heat pumps’ output water temperature, power used by the heat pumps, coefficient of performance (COP) of the heat pump, and water storage tank temperature. The BES model’s performance was evaluated by calculating the root mean square error (RMSE) and the Nash–Sutcliffe efficiency (NSE) coefficient of validation results. The overall results correlated well with the experimental and simulated results and encouraged adopting the BES model. The average calculated COP of the AWHP was 2.2 when the outside temperature was as low as −13 °C. The proposed model was designed simply, and detailed information of each step is provided to make it easy to use for engineers, researchers, and consultants. Full article
(This article belongs to the Special Issue Energy Systems and Applications in Agriculture)
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Article
Calculation of the Shading Factors for Solar Modules with MATLAB
Energies 2021, 14(15), 4713; https://doi.org/10.3390/en14154713 - 03 Aug 2021
Viewed by 849
Abstract
Shadows severely affect the performance of solar photovoltaic (PV) systems. A proper description of this effect is useful for sizing and simulating PV systems when shadows cannot be avoided. Shading factors represent the basis for simulating the effect of shadows on solar modules. [...] Read more.
Shadows severely affect the performance of solar photovoltaic (PV) systems. A proper description of this effect is useful for sizing and simulating PV systems when shadows cannot be avoided. Shading factors represent the basis for simulating the effect of shadows on solar modules. These factors can be used to estimate shading losses, calculate their I-V and P-V curves under shading conditions, or develop new maximum power point tracking (MPPT) techniques. Open-source libraries focused on solar energy have gained popularity in recent years. One of the currently most popular ones is the PV_LIB toolbox initially developed by Sandia Laboratories. PV_LIB significantly facilitates solar energy calculations. However, it currently lacks functions for taking into account shaded conditions. In this paper, a detailed Matlab-based method for calculating the shading factors is provided. The method has been used for elaborating a toolbox for shading calculations. The current work could help extend the functionalities of the PV_LIB toolbox. The results were compared against other currently popular computer programs, namely the System Advisor Model (SAM) and PVsyst. With this method, it is also possible to calculate shading factors with smaller time steps than possible with the mentioned programs. This work also shows the importance of using small time steps and how this can affect the accuracy of the calculated shading factors. The contribution of this work is providing a way of quantifying shadow losses in PV systems with Matlab, allowing for better accuracy, flexibility, and transparency during the calculation. The functions developed in this work can be accessed by contacting the authors. Full article
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Article
Wake Width: Discussion of Several Methods How to Estimate It by Using Measured Experimental Data
Energies 2021, 14(15), 4712; https://doi.org/10.3390/en14154712 - 03 Aug 2021
Cited by 3 | Viewed by 606
Abstract
Several methods of defining and estimating the width of a turbulent wake are presented and tested on the experimental data obtained in the wake past an asymmetric prismatic airfoil NACA 64(3)-618, which is often used as tip profile of the wind turbines. Instantaneous [...] Read more.
Several methods of defining and estimating the width of a turbulent wake are presented and tested on the experimental data obtained in the wake past an asymmetric prismatic airfoil NACA 64(3)-618, which is often used as tip profile of the wind turbines. Instantaneous velocities are measured by using the Particle Image Velocimetry (PIV) technique. All suggested methods of wake width estimation are based on the statistics of a stream-wise velocity component. First, the expansion of boundary layer (BL) thickness is tested, showing that both displacement BL thickness and momentum BL thickness do not represent the width of the wake. The equivalent of 99% BL thickness is used in the literature, but with different threshold value. It is shown that a lower threshold of 50% gives more stable results. The ensemble average velocity profile is fitted by Gauss function and its σ-parameter is used as another definition of wake width. The profiles of stream-wise velocity standard deviation display a two-peak shape; the distance of those peaks serves as wake width for Norberg, while another tested option is to include the widths of such peaks. Skewness (the third statistical moment) of stream-wise velocity displays a pair of sharp peaks in the wake boundary, but their position is heavily affected by the statistical quality of the data. Flatness (the fourth statistical moment) of the stream-wise velocity refers to the occurrence of rare events, and therefore the distance, where turbulent events ejected from the wake become rare and can be considered as another definition of wake width. The repeatability of the mentioned methods and their sensitivity to Reynolds’ number and model quality are discussed as well. Full article
(This article belongs to the Section B2: Wind, Wave and Tidal Energy)
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Article
Online Predictive Maintenance Monitoring Adopting Convolutional Neural Networks
Energies 2021, 14(15), 4711; https://doi.org/10.3390/en14154711 - 03 Aug 2021
Cited by 2 | Viewed by 663
Abstract
Thermal, electrical and mechanical stresses age the electrical insulation systems of high voltage (HV) apparatuses until the breakdown. The monitoring of the partial discharges (PDs) effectively assesses the insulation condition. PDs are both the symptoms and the causes of insulation aging and—in the [...] Read more.
Thermal, electrical and mechanical stresses age the electrical insulation systems of high voltage (HV) apparatuses until the breakdown. The monitoring of the partial discharges (PDs) effectively assesses the insulation condition. PDs are both the symptoms and the causes of insulation aging and—in the long term—can lead to a breakdown, with a burdensome economic loss. This paper proposes the convolutional neural networks (CNNs) to investigate and analyze the aging process of enameled wires, thus predicting the life status of the insulation systems. The CNNs training does not require any kind of assumption of how the factors (e.g., voltage, frequency and temperature) contribute to the life model. The experiments confirm that the proposal obtains better estimations of the life status of twisted pair specimens concerning existing solutions, which are based on strong hypotheses about the life model dependency on the factors. Full article
(This article belongs to the Special Issue Advances in Online Partial Discharge Monitoring Systems)
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Article
The Potential Utilizing of Critical Element from Coal and Combustion Residues
Energies 2021, 14(15), 4710; https://doi.org/10.3390/en14154710 - 03 Aug 2021
Viewed by 718
Abstract
Strategically critical elements are becoming significant for the rising demand of emerging energy-efficient technologies and high-tech applications. These critical elements are mostly geologically dispersed, and mainly recovered from recycled materials. Coal with high concentrations of critical elements is supposed to stable alternative sources. [...] Read more.
Strategically critical elements are becoming significant for the rising demand of emerging energy-efficient technologies and high-tech applications. These critical elements are mostly geologically dispersed, and mainly recovered from recycled materials. Coal with high concentrations of critical elements is supposed to stable alternative sources. The abundances of critical elements in coal varies widely among different deposits and regions. The high concentrations of critical elements are found in many Chinese and Russian coal ores. The global mining potential ratio (MPR) is applied and suggests scandium, hafnium, cesium, yttrium, germanium, gallium, thallium, strontium and rare-earth elements could be potential recovery from coal. A number of benefits are expected with the extraction of critical elements during coal utilization. Full article
(This article belongs to the Special Issue Sustainable Energy from Biomass and Waste)
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Article
A New Multilevel Inverter Topology with Reduced DC Sources
Energies 2021, 14(15), 4709; https://doi.org/10.3390/en14154709 - 03 Aug 2021
Cited by 3 | Viewed by 804
Abstract
The component count for the multilevel inverter has been a research topic for the last few decades. The higher number of power semiconductor devices and sources leads to a higher power loss with the complex control requirement. A new multilevel inverter topology employing [...] Read more.
The component count for the multilevel inverter has been a research topic for the last few decades. The higher number of power semiconductor devices and sources leads to a higher power loss with the complex control requirement. A new multilevel inverter topology employing the concept of half-Bridge modules is suggested in this paper. It requires a lower number of dc sources and power components. The inverter is controlled using a fundamental frequency switching scheme. With the basic unit being able to produce 13 level voltage waveforms with three dc voltage sources, higher-level inverter configuration has also been discussed in the paper. The performance of the topology is analyzed in the aspects of circuit parameters and found better when compared to similar topologies proposed in recent literature. The comparison provided in the paper set the benchmark of the proposed topology in terms of lower component requirements. The topology is also optimized with two voltage fixing algorithms for maximizing the number of levels for the given number of IGBTs, drivers and dc sources, and the observations are presented. The efficiency analysis gives the peak efficiency as 98.5%. The simulations were carried out using the PLECS software tool and validated using a prototype rated at 500 W. The results with several test conditions have been reported and discussed in the paper. Full article
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Article
On-Line Control of Stresses in the Power Unit Pressure Elements Taking Account of Variable Heat Transfer Conditions
Energies 2021, 14(15), 4708; https://doi.org/10.3390/en14154708 - 03 Aug 2021
Cited by 1 | Viewed by 506
Abstract
Coal-fired power units, now balancing power shortages in the power system, must be characterised by increasingly higher flexibility of operation. This means faster start-ups and the capacity for frequent decreases and increases in the power output. These processes cause large temperature gradients in [...] Read more.
Coal-fired power units, now balancing power shortages in the power system, must be characterised by increasingly higher flexibility of operation. This means faster start-ups and the capacity for frequent decreases and increases in the power output. These processes cause large temperature gradients in elements of the power unit and the turbine and lead to an increase in the stress level. At such an operating regime it is impossible to ensure safety based on start-up characteristics only—it becomes necessary to constantly monitor stress levels in critical areas of machinery and equipment elements. The stress level in turbine elements can be monitored on-line using algorithms based on Green’s functions and Duhamel’s integral. This paper presents examples of modifications of stress calculations in turbine valves and casings during start-ups. By modifying basic algorithms, it is possible to take into account the impact of the variability of heat transfer coefficients on the thermal stress level. Additionally, individual Green’s functions and correction factors were determined for specific stages of start-ups. Due to modifications, it is possible to obtain satisfactory agreement with the results obtained from FEM-based calculations for the entire heating process. Equations are also given that enable estimation of values of the heat transfer coefficient in turbine valves. The proposed modification of the algorithm will substantially improve the accuracy of stress modelling in transient states of the turbine operation. On-line stress monitoring will enable an increase in the flexibility of the power unit operation and facilitate operational control, ensuring safety of individual elements at the same time. The stress values calculated in the on-line mode can also be used to estimate fatigue life consumption and forecast the residual lifetime of individual components. Full article
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Review
Adsorbents, Working Pairs and Coated Beds for Natural Refrigerants in Adsorption Chillers—State of the Art
Energies 2021, 14(15), 4707; https://doi.org/10.3390/en14154707 - 03 Aug 2021
Cited by 5 | Viewed by 760
Abstract
Adsorption refrigeration systems are promising, sustainable solutions for many cooling applications. The operating range and the performance of an adsorption cooling cycle are strongly dependent on the properties of adsorbents, adsorbates, and bed coatings. Therefore, further research and analysis may lead to improved [...] Read more.
Adsorption refrigeration systems are promising, sustainable solutions for many cooling applications. The operating range and the performance of an adsorption cooling cycle are strongly dependent on the properties of adsorbents, adsorbates, and bed coatings. Therefore, further research and analysis may lead to improved performance of adsorption coolers. In this paper, studies on working pairs using natural refrigerants and the properties of adsorbent coatings were reviewed. The selected working pairs were then thermodynamically characterised and ranked in terms of refrigerant evaporation temperature values. This was found to be a key parameter affecting the applicability of a given adsorbent/adsorbate pair and the value of SCP (Specific Cooling Power), COP (Coefficient of Performance) parameters, which are now commonly used comparison criteria of adsorption chillers. In the analysis of the coating studies, the focus was on the effect of individual parameters on the performance of the cooling system and the effect of using coated beds compared to packed beds. It was found that a fundamental problem in comparing the performance of different cooling systems is the use of different operating conditions during the tests. Therefore, the analysis compares the performance of the systems along with the most important thermodynamic cycle parameters for the latest studies. Full article
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Article
Deep Reinforcement Learning for Hybrid Energy Storage Systems: Balancing Lead and Hydrogen Storage
Energies 2021, 14(15), 4706; https://doi.org/10.3390/en14154706 - 03 Aug 2021
Cited by 3 | Viewed by 734
Abstract
We address the control of a hybrid energy storage system composed of a lead battery and hydrogen storage. Powered by photovoltaic panels, it feeds a partially islanded building. We aim to minimize building carbon emissions over a long-term period while ensuring that 35% [...] Read more.
We address the control of a hybrid energy storage system composed of a lead battery and hydrogen storage. Powered by photovoltaic panels, it feeds a partially islanded building. We aim to minimize building carbon emissions over a long-term period while ensuring that 35% of the building consumption is powered using energy produced on site. To achieve this long-term goal, we propose to learn a control policy as a function of the building and of the storage state using a Deep Reinforcement Learning approach. We reformulate the problem to reduce the action space dimension to one. This highly improves the proposed approach performance. Given the reformulation, we propose a new algorithm, DDPGαrep, using a Deep Deterministic Policy Gradient (DDPG) to learn the policy. Once learned, the storage control is performed using this policy. Simulations show that the higher the hydrogen storage efficiency, the more effective the learning. Full article
(This article belongs to the Special Issue Machine Learning and Deep Learning for Energy Systems)
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Article
New Circular Challenges in the Development of Take-Away Food Packaging in the COVID-19 Period
Energies 2021, 14(15), 4705; https://doi.org/10.3390/en14154705 - 03 Aug 2021
Cited by 5 | Viewed by 1451
Abstract
The COVID-19 pandemic has set new challenges for the HoReCa industry. Lockdowns have coincided with and strongly impacted the industrial transformation processes that have been taking place for a decade. Among the most important HoReCa transition processes are those related to the rapid [...] Read more.
The COVID-19 pandemic has set new challenges for the HoReCa industry. Lockdowns have coincided with and strongly impacted the industrial transformation processes that have been taking place for a decade. Among the most important HoReCa transition processes are those related to the rapid growth of the delivery-food market and ordering meals via internet platforms. The new delivery-food market requires not only the development of specific distribution channels, but also the introduction of appropriate, very specific food packaging. Food packaging and its functionality are defined by the administrative requirements and standards applicable to materials that have contact with food and principally through the prism of the ecological disaster caused by enormous amounts of plastic waste, mainly attributed to the food packaging. To meet environmental and administrative requirements, new technologies to produce food packaging materials are emerging, ensuring product functionality, low environmental impact, biodegradability, and potential for composting of the final product. However, predominantly, the obtained product should keep the nutritional value of food and protect it against changes in color or shape. Current social transformation has a significant impact on the food packaging sector, on one hand creating a new lifestyle for society all over the world, and on the other, a growing awareness of the negative impact of humans on the environment and increasing responsibility for the planet. The COVID-19 pandemic has highlighted the need to develop a circular economy based on the paradigm of shortening distribution channels, using local raw materials, limiting the consumption of raw materials, energy, water, and above all, minimizing waste production throughout the life cycle of products, all of which are in line with the idea of low-carbon development. Full article
(This article belongs to the Special Issue Economic Aspects of Low Carbon Development)
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Article
Paleovegetational Reconstruction and Implications on Formation of Oil Shale and Coal in the Lower Cretaceous Laoheishan Basin (NE China): Evidence from Palynology and Terpenoid Biomarkers
Energies 2021, 14(15), 4704; https://doi.org/10.3390/en14154704 - 03 Aug 2021
Cited by 2 | Viewed by 511
Abstract
In some cases, the oil shale deposited in shallow lakes may be genetically associated with the coal-bearing successions. Although paleovegetation is an important controlling factor for the formation of oil shale- and coal-bearing successions, few studies have focused on their joint characterization. In [...] Read more.
In some cases, the oil shale deposited in shallow lakes may be genetically associated with the coal-bearing successions. Although paleovegetation is an important controlling factor for the formation of oil shale- and coal-bearing successions, few studies have focused on their joint characterization. In this study, a total of twenty-one oil shale and coal samples were collected from the upper member of the Lower Cretaceous Muling Formation (K1ml2) in the Laoheishan Basin, and investigated for their bulk geochemical, maceral, palynological, and terpenoid biomarker characteristics, in order to reconstruct the paleovegetation and reveal its influence on the formation of oil shale and coal. The K1ml2 is subdivided into lower, middle, and upper units. The studied oil shale samples from the lower and upper units display a high ash yield (Ad), low total organic carbon (TOC) and sulfur (S) contents, and limited hydrocarbon generation potential. The studied coal samples from the middle unit are characterized by low Ad, and high TOC and low S values, and show significant hydrocarbon generation potential. The paleovegetation during the formation of the lower unit was dominated by mire vegetation, such as shrubs (e.g., Lygodiaceae, Schizaeaceae), tree ferns (e.g., Dicksoniaceae/Cyatheaceae), and coniferous trees (e.g., Podocarpaceae). In the middle unit interval, the paleovegetation was represented by highland vegetation (Pinaceae and Araucariaceae) and peat-forming coniferous plants (e.g., Podocarpaceae, Cupressaceae/Taxodiaceae). Various vegetation, such as herbs (e.g., Osmundaceae), shrubs (e.g., Schizaeaceae), and coniferous trees (e.g., Podocarpaceae) was prosperous during the upper unit interval. Coniferous trees could provide abundant hydrogen-rich materials (e.g., resins) to the mire/lake, which may elevate the hydrogen content in peat/lake sediments, and finally result in higher hydrocarbon generation potential in the coal than in the oil shale. Therefore, the influence of paleovegetation on the formation of oil shale and coal should be fully considered when studying oil shale- and coal-bearing successions. The results also provide guidance for further exploration studies on oil shale and coal in northeast China. Full article
(This article belongs to the Special Issue Research and Development Progress in Oil Shale)
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Article
Synthesis of Alkyl Aliphatic Hydrazine and Application in Crude Oil as Flow Improvers
Energies 2021, 14(15), 4703; https://doi.org/10.3390/en14154703 - 03 Aug 2021
Cited by 1 | Viewed by 648
Abstract
In this paper, alkyl aliphatic hydrazine, which is different from traditional polymer fluidity improver, was synthesized from aliphatic hydrazine and cetane bromide, and evaluated as a pour point and viscosity-reducer depressant for crude oil. The evaluation results showed that alkyl aliphatic hydrazone fully [...] Read more.
In this paper, alkyl aliphatic hydrazine, which is different from traditional polymer fluidity improver, was synthesized from aliphatic hydrazine and cetane bromide, and evaluated as a pour point and viscosity-reducer depressant for crude oil. The evaluation results showed that alkyl aliphatic hydrazone fully reduced the pour point and viscosity of crude oil with the increase of crude oil fluidity. The viscosity reduction rate of crude oil in Jinghe oilfield was 79.6%, and the pour point was reduced by about 11.3 °C. The viscosity reduction rate of crude oil in Xinjiang Oilfield was 74.7%, and the pour point was reduced by 8.0 °C. The long alkyl chain is beneficial to the eutectic of wax in crude oil, and the polar group inhibits the crystal growth, resulting in the decrease of pour point and viscosity. The waste oil is fully recycled into oilfield chemicals. Full article
(This article belongs to the Special Issue Experimental and Modeling Study of Waxy Oils)
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Article
Is Secure Communication in the R2I (Robot-to-Infrastructure) Model Possible? Identification of Threats
Energies 2021, 14(15), 4702; https://doi.org/10.3390/en14154702 - 03 Aug 2021
Cited by 2 | Viewed by 534
Abstract
The increase in the role of companion robots in everyday life is inevitable, and their safe communication with the infrastructure is one of the fundamental challenges faced by designers. There are many challenges in the robot’s communication with the environment, widely described in [...] Read more.
The increase in the role of companion robots in everyday life is inevitable, and their safe communication with the infrastructure is one of the fundamental challenges faced by designers. There are many challenges in the robot’s communication with the environment, widely described in the literature on the subject. The threats that scientists believe have the most significant impact on the robot’s communication include denial-of-service (DoS) attacks, satellite signal spoofing, external eavesdropping, spamming, broadcast tampering, and man-in-the-middle attacks. In this article, the authors attempted to identify communication threats in the new robot-to-infrastructure (R2I) model based on available solutions used in transport, e.g., vehicle-to-infrastructure (V2I), taking into account the threats already known affecting the robot’s sensory systems. For this purpose, all threats that may occur in the robot’s communication with the environment were analyzed. Then the risk analysis was carried out, determining, in turn, the likelihood of potential threats occurrence, their consequence, and ability of detection. Finally, specific methods of responding to the occurring threats are proposed, taking into account cybersecurity aspects. A critical new approach is the proposal to use communication and protocols so far dedicated to transport (IEEE 802.11p WAVE, dedicated short-range communications (DSRC)). Then, the companion’s robot should be treated as a pedestrian and some of its sensors as an active smartphone. Full article
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Article
Application of Canonical Variate Analysis to Compare Different Groups of Food Industry Companies in Terms of Financial Liquidity and Profitability
Energies 2021, 14(15), 4701; https://doi.org/10.3390/en14154701 - 03 Aug 2021
Cited by 2 | Viewed by 723
Abstract
Financial liquidity and profitability are two critical phenomena present in the financial economy of a company, whose relations depend on each other and may course in different directions. At the same time, they are an example of the complexity of the problem, which [...] Read more.
Financial liquidity and profitability are two critical phenomena present in the financial economy of a company, whose relations depend on each other and may course in different directions. At the same time, they are an example of the complexity of the problem, which demands a proper approach, allowing one to reconcile two opposing objectives of any enterprise, i.e., maximizing the benefits for the owners and minimizing the risk of losing financial liquidity. Until now, the relationship between liquidity and profitability has not been examined explicitly, using multidimensional methods in particular. Nevertheless, the links between profitability and financial liquidity maintenance ensure the sustainable development of enterprises in different branches. This paper formulates two aims: scientific and practical. The scientific one concerns adopting the canonical variate analysis method to visualize the differences and relationships between food industry companies regarding financial liquidity and profitability. The practical one relates to indicating the relationship between financial liquidity and profitability in different groups of food industry companies. To study the relationships between the selected groups of enterprises and describe them, the liquidity and profitability ratios were utilized, involving canonical variate analysis based on transformation by linear combination and singular value decomposition. The analysis found that the most important feature highlighting the group of the examined entities regarding financial liquidity was the cash conversion cycle. The research results showed the existence of multidirectional relationships between liquidity and profitability. The research indicates that they depend on indicators describing financial dependencies and the industries in which they operate. This led to a much deeper and broader interpretation of the assessment of the financial situation of companies to support their sustainable development. Full article
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Article
Energy Efficiency and Carbon Emission Impact on Competitiveness in the European Energy Intensive Industries
Energies 2021, 14(15), 4700; https://doi.org/10.3390/en14154700 - 03 Aug 2021
Cited by 1 | Viewed by 643
Abstract
Climate change and efforts to mitigate it have given rise to an interest in the relationship between industry competitiveness, energy efficiency, and carbon emissions. A better understanding of this relationship can be essential for economic and environmental decision-makers. This paper presents empirical research [...] Read more.
Climate change and efforts to mitigate it have given rise to an interest in the relationship between industry competitiveness, energy efficiency, and carbon emissions. A better understanding of this relationship can be essential for economic and environmental decision-makers. This paper presents empirical research evaluating industry competitiveness through the factors of energy efficiency and carbon emission in Europe’s most energy-intensive industries. The designed industry competitiveness measure index consists of seven components, grouped into three equally weighted sub-indexes: export performance, energy, and environmental. The export performance of the industry is described by the industry export growth rate, the share of the industry’s export, and the effects on the industry’s competitiveness of changes in a country’s export. The energy intensity of the industry and energy prices are integrated into the energy sub-index. The environmental sub-index consists of the industry’s emissions intensity, and the ratio of freely allocated allowances and verified emissions indicators. The findings indicate that countries with the highest index value also have a positive energy intensity and carbon emission indicator value. The average index value of each industry gradually reduces to zero, and the standard deviation of the index value shows a diminishing trend throughout all sectors, which implies that competitiveness in all sectors is increasing and that all countries are nearing the industry average. The ANOVA results show that: (1) the competitiveness index value was statistically significantly different in the investigated countries; (2) the competitiveness index value was statistically non-significantly different in the investigated industries; (3) there was a significant effect of the interaction between country and industry on the competitiveness index value. These results suggest that the country itself and industry/country interaction significantly affect the competitiveness index. However, it should be mentioned that industry per se does not substantially affect the competitiveness index score. Full article
(This article belongs to the Section I: Energy Economics and Policy)
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Article
A Proposed Guidance for the Economic Assessment of Wave Energy Converters at Early Development Stages
Energies 2021, 14(15), 4699; https://doi.org/10.3390/en14154699 - 03 Aug 2021
Cited by 2 | Viewed by 846
Abstract
Wave energy is one of the most promising renewable energies available with its very large resource. The waves generated by the wind field are steadier than the wind field itself, rendering wave energy more consistent than wind energy. It is also more predictable [...] Read more.
Wave energy is one of the most promising renewable energies available with its very large resource. The waves generated by the wind field are steadier than the wind field itself, rendering wave energy more consistent than wind energy. It is also more predictable than wind and solar. Wave energy is making continuous progress towards commercialisation, and thanks to an increasing number of deployments at sea, the sector is increasing the understanding of the costs and economies of these projects. No wave energy converter has been demonstrated to be commercially viable, and it is yet to be proven that wave energy can contribute to the renewable energy mix. In this context, and in order to find an economically viable solution for exploiting wave energy, it is important to assess the economic potential of a particular concept throughout the entire technological development process. At early development stages, this assessment can be challenging and present large uncertainties. Notwithstanding, it is important to perform the economic assessment already at the early stages in order to identify possible bottlenecks or potential improvements or modifications of a concept. This work presents guidance for the economic evaluation of a wave energy concept at an early development stage by setting up the economic frame based on a target LCoE. It involves the understanding of the entry cost to be achieved for a specific target market and evaluating the breakdown of costs based on a detailed technology agnostic database of costs. The guidance is then applied to a new type of wave energy converter, in which the primary coupling with the waves is through hydrodynamic lift forces. Full article
(This article belongs to the Topic Marine Renewable Energy)
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Article
Harmonics Compensation by Using a Multi-Modular H-Bridge-Based Multilevel Converter
Energies 2021, 14(15), 4698; https://doi.org/10.3390/en14154698 - 03 Aug 2021
Cited by 2 | Viewed by 509
Abstract
This paper presents an active power filter based on a seven-level cascade H-bridge where the main contribution is a control strategy that combines model-based predictive control, the voltage vectors of the converter output levels, the phase shift PWM technique, and suboptimal DC-link voltage [...] Read more.
This paper presents an active power filter based on a seven-level cascade H-bridge where the main contribution is a control strategy that combines model-based predictive control, the voltage vectors of the converter output levels, the phase shift PWM technique, and suboptimal DC-link voltage control. The proposed scheme greatly simplified the overall control system, making it well suited to compensate the current harmonics distortion at the grid side, generated by nonlinear loads connected to the point of common coupling. In addition, the proposed method achieved a balancing of the capacitor voltages of the seven-level cascade H-bridge converter by using the minimum DC-link voltage sensors. This feature significantly reduced the control system complexity and provided a low computational burden. Experimental results confirmed the feasibility and effectiveness of the proposed controller. Full article
(This article belongs to the Special Issue Control Strategies Applied to Active Power Filters)
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Article
Combining Sufficiency, Efficiency and Flexibility to Achieve Positive Energy Districts Targets
Energies 2021, 14(15), 4697; https://doi.org/10.3390/en14154697 - 03 Aug 2021
Cited by 7 | Viewed by 1478
Abstract
Energy efficiency, generation from renewable sources and more recently energy flexibility are key elements of present sustainability policies. However, we are beginning to see a recognition of the need to couple technological solutions with lifestyle and behavioral changes, sometimes labeled under the term [...] Read more.
Energy efficiency, generation from renewable sources and more recently energy flexibility are key elements of present sustainability policies. However, we are beginning to see a recognition of the need to couple technological solutions with lifestyle and behavioral changes, sometimes labeled under the term “sufficiency”. Appropriate policies and design principles are necessary to enable sufficiency options, which in turn reveal that there is a bidirectional influence between the building and the district/city level. In this context, the authors discuss how city and building re-design should be implemented combining energy efficiency, flexibility, production from renewables and sufficiency options for achieving a positive energy balance at the district level even within the constraints of dense cities. Based on a review of recent advances, the paper provides a matrix of interactions between building and district design for use by building designers and city planners. It also compares possible scenarios implementing different strategies at the building and urban level in a case study, in order to evaluate the effect of the proposed integrated approach on the energy balance at yearly and seasonal time scales and on land take. Full article
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Article
Fabrication of a Sensitive and Stable NiO Uric Acid Biosensor Using Ag Nanowires and Reduced Graphene Oxide
Energies 2021, 14(15), 4696; https://doi.org/10.3390/en14154696 - 03 Aug 2021
Viewed by 662
Abstract
How to detect uric acid is an important issue. For the purpose of preparing a potentiometric uric acid biosensor, this research used nickel oxide (NiO) as the sensing film to deposit it onto the substrate by radio frequency sputtering, then modified it with [...] Read more.
How to detect uric acid is an important issue. For the purpose of preparing a potentiometric uric acid biosensor, this research used nickel oxide (NiO) as the sensing film to deposit it onto the substrate by radio frequency sputtering, then modified it with reduced graphene oxide (rGO) and silver (Ag) nanowires. Reduced graphene oxide (rGO) not only has excellent electrical conductivity, but also can make the surface of the film have a larger surface area, while AgNWs have also been proven to improve catalytic activity; hence, these two materials were chosen as sensor modifiers. Finally, the stability and the various characteristics of the uric acid biosensor were investigated using a voltage–time (V–T) system. The results showed that the AgNW–uricase/rGO/NiO uric acid biosensor has average sensitivity with 4.66 mV/(mg/L). In addition, the sensor has good stability. Full article
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Article
A Novel Faulty Phase Selection Method for Single-Phase-to-Ground Fault in Distribution System Based on Transient Current Similarity Measurement
Energies 2021, 14(15), 4695; https://doi.org/10.3390/en14154695 - 03 Aug 2021
Cited by 3 | Viewed by 758
Abstract
In modern electrical power distribution systems, the effective operation of inverter-based arc suppression devices relies on the accuracy of faulty phase selection. In the traditional methods of faulty phase selection for single-phase-to-ground faults (SPGs), power frequency-based amplitude and phase characteristics are used to [...] Read more.
In modern electrical power distribution systems, the effective operation of inverter-based arc suppression devices relies on the accuracy of faulty phase selection. In the traditional methods of faulty phase selection for single-phase-to-ground faults (SPGs), power frequency-based amplitude and phase characteristics are used to identify the faulty phase. In the field, when a high-resistance SPG occurs in the system, traditional methods are difficult for accurately identifying the faulty phase because of the weak fault components and complicated process. A novel realizable and effective method of faulty phase selection based on transient current similarity measurements is presented when SPGs occur in resonantly grounded distribution systems in this paper. An optimized Hausdorff distance matrix (MOHD) is proposed and constructed by the transient currents of three phases’ similarity measurements within a certain time window of our method. This MOHD is used to select the sampling time window adaptively, which allows the proposed method to be applied to any scale of distribution systems. Firstly, when a SPG occurs, the expressions for the transient phase current mutation in the faulty and sound phases are analyzed. Then, the sampling process is segmented into several selection units (SUs) to form the MOHD-based faulty phase selection method. Additionally, the Hausdorff distance algorithm (HD) is used to calculate the waveform similarities of the transient phase current mutation among the three phases to form the HD-based faulty phase selection method. Finally, a practical resonant grounded distribution system is modeled in PSCAD/EMTDC, and the effectiveness and performance of the proposed method is compared and verified under different fault resistances, fault inception angles, system topologies, sampling time windows and rates of data missing. Full article
(This article belongs to the Topic Power Distribution Systems)
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Article
Analysis of Daily Energy Demand for Cooling in Buildings with Different Comfort Categories—Case Study
Energies 2021, 14(15), 4694; https://doi.org/10.3390/en14154694 - 02 Aug 2021
Cited by 1 | Viewed by 669
Abstract
Climate change has a potential impact on the number of hot and torrid days in the summer period. Due to the occupants’ comfort needs, and because of the high heat loads during the summer period, in several European countries, the energy used for [...] Read more.
Climate change has a potential impact on the number of hot and torrid days in the summer period. Due to the occupants’ comfort needs, and because of the high heat loads during the summer period, in several European countries, the energy used for air conditioning in buildings increased. With multiple environmental monitoring systems (Testo Saveris) in two similar offices, having west and east orientation of glazing, 1920 data (internal air, mean radiant temperature) related to operative temperature were collected in order to show the differences between heat loads of rooms with similar geometry in the same building. Data were measured in a 15 min interval. The diffuse and direct solar radiation had been determined for the horizontal and vertical surfaces, using the measured hourly global radiation (Debrecen, Hungary) data for the analyzed days (summer, hot, and torrid days). The local climatic results were compared with other climatic days used in different national standards. The daily energy need for cooling for different building comfort categories was also determined in the case of the representative days. The maximum daily energy need for cooling can be even 2.3 times higher for east orientation in comparison to the west orientation of the facades. Full article
(This article belongs to the Special Issue Energy Consumption in a Smart City)
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Article
Building a Common Support Framework in Differing Realities—Conditions for Renewable Energy Communities in Germany and Bulgaria
Energies 2021, 14(15), 4693; https://doi.org/10.3390/en14154693 - 02 Aug 2021
Cited by 4 | Viewed by 858
Abstract
The revised EU Renewable Energy Directive first introduced renewable energy communities into the EU policy framework and requires Member States to implement a support framework for them. Given the broad scientific evidence showing the benefits of community energy for a just energy transition, [...] Read more.
The revised EU Renewable Energy Directive first introduced renewable energy communities into the EU policy framework and requires Member States to implement a support framework for them. Given the broad scientific evidence showing the benefits of community energy for a just energy transition, a successful implementation across all Member States is essential. However, the preconditions for developing support frameworks differ largely between EU nations, as some countries have long-term experiences with supporting renewable energy communities (i.e., Germany and Denmark), while in other Member States, renewable energy communities are notably non-existent (i.e., Eastern European nations). With the purpose of providing scientific evidence to support the development of a policy framework for renewable energy communities in Eastern European Member States, this article compares key factors for the development of such communities in Bulgaria and Germany, combining a literature review with expert interviews to collect primary information on Bulgaria. A country analysis puts these factors into the contexts of both countries, while a cross-country comparison demonstrates that there are significant gaps in the support framework of Bulgaria, although these gaps are, to a lesser extent, also present in Germany. We discuss these shortcomings, derive policy recommendations and identify further research needs. Full article
(This article belongs to the Special Issue Energy Transition and Social Innovation)
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Article
Analysis of Natural and Power Plant CO2 Emissions in the Mount Amiata (Italy) Volcanic–Geothermal Area Reveals Sustainable Electricity Production at Zero Emissions
Energies 2021, 14(15), 4692; https://doi.org/10.3390/en14154692 - 02 Aug 2021
Viewed by 1071
Abstract
Geothermal energy is a key renewable energy for Italy, with an annual electric production of 6.18 TWh. The future of geothermal energy is concerned with clarity over the CO2 emissions from power plants and geological contexts where CO2 is produced naturally. [...] Read more.
Geothermal energy is a key renewable energy for Italy, with an annual electric production of 6.18 TWh. The future of geothermal energy is concerned with clarity over the CO2 emissions from power plants and geological contexts where CO2 is produced naturally. The Mt. Amiata volcanic–geothermal area (AVGA) is a formidable natural laboratory for investigating the relative roles of natural degassing of CO2 and CO2 emissions from geothermal power plants (GPPs). This research is based on measuring the soil gas flux in the AVGA and comparing the diffuse volcanic soil gas emissions with the emissions from geothermal fields in operation. The natural flux of soil gas is high, independently from the occurrence of GPPs in the area, and the budget for natural diffuse gas flux is high with respect to power plant gas emissions. Furthermore, the CO2 emitted from power plants seems to reduce the amount of natural emissions because of the gas flow operated by power plants. During the GPPs’ life cycle, CO2 emissions in the atmosphere are reduced further because of the reinjection of gas-free aqueous fluids in geothermal reservoirs. Therefore, the currently operating GPPs in the AVGA produce energy at a zero-emission level. Full article
(This article belongs to the Special Issue CO2 Emission in Geothermal Systems and Resources)
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Article
Lyapunov-Function-Based Feedback Linearization Control Strategy of Modular Multilevel Converter–Bidirectional DC–DC Converter for Vessel Integrated Power Systems
Energies 2021, 14(15), 4691; https://doi.org/10.3390/en14154691 - 02 Aug 2021
Cited by 1 | Viewed by 577
Abstract
The modular multilevel converter–bidirectional DC–DC converter (MMC–BDC) has been proposed to be utilized in the vessel integrated power system to interconnect the medium voltage bus and the distributed energy storage elements. In the shipboard applications, MMC–BDC faces unbalanced sub-module power operation because of [...] Read more.
The modular multilevel converter–bidirectional DC–DC converter (MMC–BDC) has been proposed to be utilized in the vessel integrated power system to interconnect the medium voltage bus and the distributed energy storage elements. In the shipboard applications, MMC–BDC faces unbalanced sub-module power operation because of the inconsistent state-of-charge (SOC) of the energy storage elements. Researchers have investigated into the unbalanced operation principle of MMC–BDC and proposed some unbalanced operation control strategies, but these traditional strategies do not perform well in both aspects of operating range and efficiency. Therefore, this paper proposes a novel Lyapunov-function-based feedback linearization control strategy for the independent sub-module voltage control of MMC–BDC, which not only shows wide unbalanced operation range and high efficiency, but also realizes the decoupling and symmetrical control of the sub-module capacitor voltages. Full article
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Review
A Review on Artificial Intelligence Applications for Grid-Connected Solar Photovoltaic Systems
Energies 2021, 14(15), 4690; https://doi.org/10.3390/en14154690 - 02 Aug 2021
Cited by 5 | Viewed by 2771
Abstract
The use of artificial intelligence (AI) is increasing in various sectors of photovoltaic (PV) systems, due to the increasing computational power, tools and data generation. The currently employed methods for various functions of the solar PV industry related to design, forecasting, control, and [...] Read more.
The use of artificial intelligence (AI) is increasing in various sectors of photovoltaic (PV) systems, due to the increasing computational power, tools and data generation. The currently employed methods for various functions of the solar PV industry related to design, forecasting, control, and maintenance have been found to deliver relatively inaccurate results. Further, the use of AI to perform these tasks achieved a higher degree of accuracy and precision and is now a highly interesting topic. In this context, this paper aims to investigate how AI techniques impact the PV value chain. The investigation consists of mapping the currently available AI technologies, identifying possible future uses of AI, and also quantifying their advantages and disadvantages in regard to the conventional mechanisms. Full article
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Article
Comparative Numerical Study of the Influence of Film Hole Location of Ribbed Cooling Channel on Internal and External Heat Transfer
Energies 2021, 14(15), 4689; https://doi.org/10.3390/en14154689 - 02 Aug 2021
Cited by 2 | Viewed by 545
Abstract
The influence of film-hole position on internal and external heat transfer was investigated using Computational Fluid Dynamics (CFD). A simplified geometry of an integrated configuration of a ribbed channel, film hole and mainstream passage is modeled to represent a turbine internal and external [...] Read more.
The influence of film-hole position on internal and external heat transfer was investigated using Computational Fluid Dynamics (CFD). A simplified geometry of an integrated configuration of a ribbed channel, film hole and mainstream passage is modeled to represent a turbine internal and external cooling scheme. The proposed configurations with nine different positions of film holes are parameterized to conduct a series of CFD calculations at a target blowing ratio of 0.8, 1.1 and 1.7. Since the present study is taking a comparative approach, CFX with SST models is applied as a primary tool and the results are compared with Fluent solver for selected cases (total 36 cases). Among the proposed nine positions, the film holes located in the separated flow region of a ribbed channel showed considerable enhancement in film effectiveness with minimum reduction and potential improvement in internal heat transfer. The finding offers a design opportunity to enhance internal as well as external heat transfer. Full article
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Review
Reliability Assessment of Passive Safety Systems for Nuclear Energy Applications: State-of-the-Art and Open Issues
Energies 2021, 14(15), 4688; https://doi.org/10.3390/en14154688 - 02 Aug 2021
Cited by 2 | Viewed by 933
Abstract
Passive systems are fundamental for the safe development of Nuclear Power Plant (NPP) technology. The accurate assessment of their reliability is crucial for their use in the nuclear industry. In this paper, we present a review of the approaches and procedures for the [...] Read more.
Passive systems are fundamental for the safe development of Nuclear Power Plant (NPP) technology. The accurate assessment of their reliability is crucial for their use in the nuclear industry. In this paper, we present a review of the approaches and procedures for the reliability assessment of passive systems. We complete the work by discussing the pending open issues, in particular with respect to the need of novel sensitivity analysis methods, the role of empirical modelling and the integration of passive safety systems assessment in the (static/dynamic) Probabilistic Safety Assessment (PSA) framework. Full article
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Article
Nexus between Economic Policy Uncertainty and Renewable Energy Consumption in BRIC Nations: The Mediating Role of Foreign Direct Investment and Financial Development
Energies 2021, 14(15), 4687; https://doi.org/10.3390/en14154687 - 02 Aug 2021
Cited by 6 | Viewed by 805
Abstract
In recent literature, the impact of economic policy uncertainty (EPU) on macro aspects have been investigated, but the aspect of energy, precisely renewable energy still to explore. The motivation of the study is to produce fresh evidence regarding the nexus between [...] Read more.
In recent literature, the impact of economic policy uncertainty (EPU) on macro aspects have been investigated, but the aspect of energy, precisely renewable energy still to explore. The motivation of the study is to produce fresh evidence regarding the nexus between EPU and renewable energy consumption (REC) with the mediating role of forcing direct investment (FDI) and financial development (FD) in BRIC nations for the period 1997q1–2018q4. The study applied unit root tests following Ng-Perron and Zivot and Andrews for detecting variable’s stationary properties. The long-run cointegration was evaluated by implementing Bayer, Hanck combined the cointegration test, Bound testing approach, and tBDM test. Both linear and non-linear ARDL were implemented to evaluate long-run and short-run shocks, and directional causality was assessed through a non-granger causality test. Furthermore, the study implemented robustness by implementing fully-modified OLS, dynamic OLS, and canonical cointegrating regression (CCR). Unit root test established the variables are stationary after the first difference; moreover, the Bayer and Hanck cointegration test confirmed the long-run association between EPU, FD, FD, and REC in BRIC nations. Accruing to ARDL estimation, adverse effects running from EPU to REC both in the long run and short run. Furthermore, the positive statistically significant linkage revealed for FDI and FD to REC implies that clean energy integration could be augmented with continual inflows of FDI and development of the financial sector. Model estimation with asymmetric assumption, the study documented asymmetric effects running from EPU, FDI, and FD to renewable energy consumption, especially in the long run. Finally, the directional causality revealed unidirectional causality between REC and EPU, whereas the feedback hypothesis was disclosed for FDI and REC] and FD and REC. Study findings postulated that the role of foreign direct investment and financial development is critically significant because technological advancement and capital investment augment clean energy integration through the application of renewable energy. Full article
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Article
Organic-Inorganic Novel Green Cation Exchange Membranes for Direct Methanol Fuel Cells
Energies 2021, 14(15), 4686; https://doi.org/10.3390/en14154686 - 02 Aug 2021
Cited by 5 | Viewed by 921
Abstract
Commercializing direct methanol fuel cells (DMFC) demands cost-effective cation exchange membranes. Herein, a polymeric blend is prepared from low-cost and eco-friendly polymers (i.e., iota carrageenan (IC) and polyvinyl alcohol (PVA)). Zirconium phosphate (ZrPO4) was prepared from the impregnation–calcination method and characterized [...] Read more.
Commercializing direct methanol fuel cells (DMFC) demands cost-effective cation exchange membranes. Herein, a polymeric blend is prepared from low-cost and eco-friendly polymers (i.e., iota carrageenan (IC) and polyvinyl alcohol (PVA)). Zirconium phosphate (ZrPO4) was prepared from the impregnation–calcination method and characterized by energy dispersive X-ray analysis (EDX map), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM), then incorporated as a bonding and doping agent into the polymer blend with different concentrations. The new fabricated membranes were characterized by SEM, FTIR, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and XRD. The results revealed that the membranes’ physicochemical properties (oxidative stability, tensile strength) are enhanced with increasing doping addition, and they realized higher results than Nafion 117 because of increasing numbers of hydrogen bonds fabricated between the polymers and zirconium phosphate. Additionally, the methanol permeability was decreased in the membranes with increasing zirconium phosphate content. The optimum membrane with IC/SPVA/ZrPO4-7.5 provided higher selectivity than Nafion 117. Therefore, it can be an effective cation exchange membrane for DMFCs applications. Full article
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