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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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Review

26 pages, 656 KiB  
Review
The Future of the Energy Sector and the Global Economy: Prosumer Capitalism and What Comes Next
by Aleksander Jakimowicz
Energies 2022, 15(23), 9120; https://doi.org/10.3390/en15239120 - 1 Dec 2022
Cited by 8 | Viewed by 3567
Abstract
This paper describes the present and the future of the energy sector in relation to the dominant and constantly evolving form of the global economic system. These considerations have their starting point in transformations of the energy sector in prosumer capitalism, which has [...] Read more.
This paper describes the present and the future of the energy sector in relation to the dominant and constantly evolving form of the global economic system. These considerations have their starting point in transformations of the energy sector in prosumer capitalism, which has dramatically changed the picture of the global economy in recent years. Subsequently, a futuristic approach is applied to determine the role and importance of energy from renewable sources for further human development. The main objective of the paper is to explain the current situation of the energy sector in prosumer capitalism and to extrapolate these relationships for the future, considering the need to enter the path of sustainable development to eliminate the global warming processes and climate changes. A review of the existing scientific literature was applied as the research method. The historical wave concept, proposed by Toffler, was found to be highly useful because of its high potential in futurology, where it enables one to study megatrends. The Fourth Wave was linked to prosumer capitalism, and it provided the base for defining the next ones: the Fifth Wave of Computing (ecosocialism) and the Sixth Wave in the form of technological and energy communism (solar communism). It also turned out that the key to solving mankind’s energy problems lies in the global mean entropy budget. The literature review shows that founding the global energy system on solar radiation is the only known method for eliminating the anthropogenic greenhouse effect, which is the source of global warming and, consequently, of climate change. Therefore, the second law of thermodynamics provides a physical, economic, and logical justification for introducing a new and ultimate management form—solar communism—by 2050. Full article
(This article belongs to the Special Issue Sustainable and Low Carbon Development in the Energy Sector)
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22 pages, 1298 KiB  
Review
Superheated Steam Spray Drying as an Energy-Saving Drying Technique: A Review
by Mariia Sobulska, Pawel Wawrzyniak and Meng Wai Woo
Energies 2022, 15(22), 8546; https://doi.org/10.3390/en15228546 - 15 Nov 2022
Cited by 14 | Viewed by 6031
Abstract
Drying is an extremely energy-intensive process. Superheated steam as a drying medium can improve the energy efficiency of the drying processes. In superheated steam drying, waste heat can be recovered by condensing the exhaust steam or raising its specific enthalpy. Spray drying is [...] Read more.
Drying is an extremely energy-intensive process. Superheated steam as a drying medium can improve the energy efficiency of the drying processes. In superheated steam drying, waste heat can be recovered by condensing the exhaust steam or raising its specific enthalpy. Spray drying is widely used in industry, even though its energy efficiency is often low. Substitution of air by superheated steam as a drying medium in a spray dryer may reduce the energy consumption of the drying process by 20–30%; moreover, if excess steam generated by moisture evaporation is upgraded to a higher temperature level and reused for drying, the energy demand could be decreased by even 80%. A literature review showed that superheated steam spray drying was successfully applied for both thermally resistant and a wide range of thermally sensitive materials. Superheated steam drying gives a number of advantages in terms of product properties, i.e., higher particle porosity due to rapid moisture evaporation results in improved powder rehydration properties. Additionally, steam drying may be applied for in situ particle crystallization. Taking into account the advantages of superheated steam drying and the potential application of this technology in spray drying systems, there is a great need for further research in this field. This literature review aimed to present an energy-saving solution, i.e., superheated steam spray drying process, showing its advantages and potential applications, followed by drying kinetics, providing analysis of the research papers on experimental studies as well as mathematical modeling of this drying technique. Full article
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22 pages, 5146 KiB  
Review
Bioelectrochemical Remediation for the Removal of Petroleum Hydrocarbon Contaminants in Soil
by Md Tabish Noori, Dayakar Thatikayala and Booki Min
Energies 2022, 15(22), 8457; https://doi.org/10.3390/en15228457 - 12 Nov 2022
Cited by 7 | Viewed by 2738
Abstract
Consistent accumulation of petroleum hydrocarbon (PH) in soil and sediments is a big concern and, thus, warrants a static technology to continuously remediate PH-contaminated soil. Bioelectrochemical systems (BESs) can offer the desired solution using the inimitable metabolic response of electroactive microbes without involving [...] Read more.
Consistent accumulation of petroleum hydrocarbon (PH) in soil and sediments is a big concern and, thus, warrants a static technology to continuously remediate PH-contaminated soil. Bioelectrochemical systems (BESs) can offer the desired solution using the inimitable metabolic response of electroactive microbes without involving a physiochemical process. To date, a wide range of BES-based applications for PH bioremediations under different environmental conditions is readily available in the literature. Here, the latest development trend in BESs for PH bioremediation is critically analyzed and discussed. The reactor design and operational factors that affect the performance of BESs and their strategic manipulations such as designing novel reactors to improve anodic reactions, enhancing soil physiology (electrical conductivity, mass diffusion, hydraulic conductivity), electrode modifications, operational conditions, microbial communities, etc., are elaborated to fortify the understanding of this technology for future research. Most of the literature noticed that a low mass diffusion condition in soil restricts the microbes from interacting with the contaminant farther to the electrodes. Therefore, more research efforts are warranted, mainly to optimize soil parameters by specific amendments, electrode modifications, optimizing experimental parameters, integrating different technologies, and conducting life cycle and life cycle cost analysis to make this technology viable for field-scale applications. Full article
(This article belongs to the Special Issue Microbial Electrochemical Technologies for Wastewater Treatment and Bioresource Recovery)
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25 pages, 1339 KiB  
Review
Recent Insights into Low-Surface-Area Catalysts for Hydrogen Production from Ammonia
by Marina Pinzón, Paula Sánchez, Ana Raquel de la Osa, Amaya Romero and Antonio de Lucas-Consuegra
Energies 2022, 15(21), 8143; https://doi.org/10.3390/en15218143 - 1 Nov 2022
Cited by 7 | Viewed by 5857
Abstract
A potential method of storing and transporting hydrogen safely in a cost-effective and practical way involves the utilization of molecules that contain hydrogen in their structure such as ammonia. Because of its high hydrogen content and carbon-free molecular structure, as well as the [...] Read more.
A potential method of storing and transporting hydrogen safely in a cost-effective and practical way involves the utilization of molecules that contain hydrogen in their structure such as ammonia. Because of its high hydrogen content and carbon-free molecular structure, as well as the maturity of related technology (easy liquefaction), ammonia has gained attention as a “hydrogen carrier” for the generation of energy. Unfortunately, hydrogen production from ammonia requires an efficient catalyst to achieve high conversion at low reaction temperatures. Recently, very attractive results have been obtained with low-surface-area materials. This review paper is focused on summarizing and comparing recent advances in novel, economic and active catalysts for this reaction, paying particular attention to materials with low surface area such as silicon carbide (SiC) and perovskites (ABO3 structure). The effects of the supports, the active phase and the addition of promoters in such low-porosity materials have been analyzed in detail. Advances in adequate catalytic systems (including support and active metal) benefit the perspective of ammonia as a hydrogen carrier for the decarbonization of the energy sector and accelerate the “hydrogen economy”. Full article
(This article belongs to the Special Issue Advanced Technologies for Hydrogen Production, Purification and Storage)
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38 pages, 7617 KiB  
Review
Literature Review of Hybrid CO2 Low Salinity Water-Alternating-Gas Injection and Investigation on Hysteresis Effect
by Shijia Ma and Lesley A. James
Energies 2022, 15(21), 7891; https://doi.org/10.3390/en15217891 - 24 Oct 2022
Cited by 9 | Viewed by 2717
Abstract
Low salinity water injection (LSWI) is considered to be more cost-effective and has less environmental impacts over conventional chemical Enhanced Oil Recovery (EOR) methods. CO2 Water-Alternating-Gas (WAG) injection is also a leading EOR flooding process. The hybrid EOR method, CO2 low [...] Read more.
Low salinity water injection (LSWI) is considered to be more cost-effective and has less environmental impacts over conventional chemical Enhanced Oil Recovery (EOR) methods. CO2 Water-Alternating-Gas (WAG) injection is also a leading EOR flooding process. The hybrid EOR method, CO2 low salinity (LS) WAG injection, which incorporates low salinity water into CO2 WAG injection, is potentially beneficial in terms of optimizing oil recovery and decreasing operational costs. Experimental and simulation studies reveal that CO2 LSWAG injection is influenced by CO2 solubility in brine, brine salinity and composition, rock composition, WAG parameters, and wettability. However, the mechanism for increased recovery using this hybrid method is still debatable and the conditions under which CO2 LSWAG injection is effective are still uncertain. Hence, a comprehensive review of the existing literature investigating LSWI and CO2 WAG injection, and laboratory and simulation studies of CO2 LSWAG injection is essential to understand current research progress, highlight knowledge gaps and identify future research directions. With the identified research gap, a core-scale simulation study on hysteresis effect in CO2 LSWAG injection is carried out. The results indicate different changing trend in oil recovery due to the impact of salinity on hysteresis and excluding of hysteresis effect in CO2 LSWAG injection simulation and optimization might lead to significant errors. Full article
(This article belongs to the Special Issue Enhanced Oil Recovery (EOR) Methods)
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40 pages, 10815 KiB  
Review
Overview of the Hydrogen Production by Plasma-Driven Solution Electrolysis
by Sergii Bespalko and Jerzy Mizeraczyk
Energies 2022, 15(20), 7508; https://doi.org/10.3390/en15207508 - 12 Oct 2022
Cited by 11 | Viewed by 5774
Abstract
This paper reviews the progress in applying the plasma-driven solution electrolysis (PDSE), which is also referred to as the contact glow-discharge electrolysis (CGDE) or plasma electrolysis, for hydrogen production. The physicochemical processes responsible for the formation of PDSE and effects occurring at the [...] Read more.
This paper reviews the progress in applying the plasma-driven solution electrolysis (PDSE), which is also referred to as the contact glow-discharge electrolysis (CGDE) or plasma electrolysis, for hydrogen production. The physicochemical processes responsible for the formation of PDSE and effects occurring at the discharge electrode in the cathodic and anodic regimes of the PDSE operation are described. The influence of the PDSE process parameters, especially the discharge polarity, magnitude of the applied voltage, type and concentration of the typical electrolytic solutions (K2CO3, Na2CO3, KOH, NaOH, H2SO4), presence of organic additives (CH3OH, C2H5OH, CH3COOH), temperature of the electrolytic solution, the active length and immersion depth of the discharge electrode into the electrolytic solution, on the energy efficiency (%), energy yield (g(H2)/kWh), and hydrogen production rate (g(H2)/h) is presented and discussed. This analysis showed that in the cathodic regime of PDSE, the hydrogen production rate is 33.3 times higher than that in the anodic regime of PDSE, whereas the Faradaic and energy efficiencies are 11 and 12.5 times greater, respectively, than that in the anodic one. It also revealed the energy yield of hydrogen production in the cathodic regime of PDSE in the methanol–water mixture, as the electrolytic solution is 3.9 times greater compared to that of the alkaline electrolysis, 4.1 times greater compared to the polymer electrolyte membrane electrolysis, 2.8 times greater compared to the solid oxide electrolysis, 1.75 times greater than that obtained in the microwave (2.45 GHz) plasma, and 5.8% greater compared to natural gas steam reforming. Full article
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42 pages, 16861 KiB  
Review
Carbon Nanotube Fiber-Based Wearable Supercapacitors—A Review on Recent Advances
by Kavitha Mulackampilly Joseph, Hunter J. Kasparian and Vesselin Shanov
Energies 2022, 15(18), 6506; https://doi.org/10.3390/en15186506 - 6 Sep 2022
Cited by 22 | Viewed by 4128
Abstract
As wearable electronic devices are becoming an integral part of modern life, there is a vast demand for safe and efficient energy storage devices to power them. While the research and development of microbatteries and supercapacitors (SCs) have significantly progressed, the latter has [...] Read more.
As wearable electronic devices are becoming an integral part of modern life, there is a vast demand for safe and efficient energy storage devices to power them. While the research and development of microbatteries and supercapacitors (SCs) have significantly progressed, the latter has attracted much attention due to their excellent power density, longevity, and safety. Furthermore, SCs with a 1D fiber shape are preferred because of their ease of integration into today’s smart garments and other wearable devices. Fiber supercapacitors based on carbon nanotubes (CNT) are promising candidates with a unique 1D structure, high electrical and thermal conductivity, outstanding flexibility, excellent mechanical strength, and low gravimetric density. This review aims to serve as a comprehensive publication presenting the fundamentals and recent developments on CNT-fiber-based SCs. The first section gives a general overview of the supercapacitor types based on the charge storage mechanisms and electrode configuration, followed by the various fiber fabrication methods. The next section explores the different strategies used to enhance the electrochemical performance of these SCs, followed by a broad study on their stretchability and multifunctionality. Finally, the review presents the current performance and scalability challenges affecting the CNT-based SCs, highlighting their prospects. Full article
(This article belongs to the Topic Electrochemical Energy Storage Materials)
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49 pages, 8420 KiB  
Review
A Review on Heat Extraction Devices for CPVT Systems with Active Liquid Cooling
by Karolina Papis-Frączek and Krzysztof Sornek
Energies 2022, 15(17), 6123; https://doi.org/10.3390/en15176123 - 23 Aug 2022
Cited by 17 | Viewed by 2724
Abstract
Numerous numerical and experimental studies have been conducted regarding the Concentrated Photovoltaic Thermal (CPVT) system because of its significant potential for efficient conversion of solar energy. The overall efficiency of the CPVT system is strongly dependent on the device, which extracts excess heat [...] Read more.
Numerous numerical and experimental studies have been conducted regarding the Concentrated Photovoltaic Thermal (CPVT) system because of its significant potential for efficient conversion of solar energy. The overall efficiency of the CPVT system is strongly dependent on the device, which extracts excess heat from photovoltaic cells. The most efficient cooling technology involves active cooling, which means that heat is collected from the PV cell via the forced flow of heat transfer fluid. This research paper provides an extensive discussion on devices dedicated to active-cooling CPVT systems, taking into account the latest solutions. First, a short introduction regarding CPVT systems and their main components is presented. The second part of this study presents state-of-the-art solutions in the field of heat extraction devices for the active cooling of photovoltaic cells. The available solutions are classified into two main groups depending on the scale of internal channels: macro- and micro-. Each geometry of the heat receiver is juxtaposed with the corresponding concentrating element, photovoltaic cell, concentration ratio, heat transfer fluid, and operating parameters of the specified system. In addition, this paper discusses the advantages and disadvantages of various devices for heat extraction and provides a comparative study of these devices. Finally, a set of recommendations for CPVT cooling devices is provided. Full article
(This article belongs to the Special Issue Energy Performance of the Photovoltaic Systems)
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29 pages, 10208 KiB  
Review
Cooling Techniques in Direct-Drive Generators for Wind Power Application
by Petrica Taras, Reza Nilifard, Zi-Qiang Zhu and Ziad Azar
Energies 2022, 15(16), 5986; https://doi.org/10.3390/en15165986 - 18 Aug 2022
Cited by 8 | Viewed by 5433
Abstract
Direct-drive generators are an attractive candidate for wind power application since they do not need a gearbox, thus increasing operational reliability and reducing power losses. However, this is achieved at the cost of an increased generator size, larger inverter and decreased thermal performance. [...] Read more.
Direct-drive generators are an attractive candidate for wind power application since they do not need a gearbox, thus increasing operational reliability and reducing power losses. However, this is achieved at the cost of an increased generator size, larger inverter and decreased thermal performance. The associated cooling system is therefore crucial to keep the generator and inverter sizes down and to operate within the safe thermal limits. Various cooling techniques suitable for generators are therefore reviewed and analyzed in this paper. The performance and maintenance requirements are unavoidable compromises that need to be investigated together, especially for large generators. The location of the wind turbine is also important and dictates critical issues such as accessibility and maximum size. The key novelty in this paper is the assessment of the cooling methods based on generator size, reliability and maintenance requirements. Full article
(This article belongs to the Special Issue Design and Optimization of High Power/Torque Density Permanent Magnet Machines)
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32 pages, 4976 KiB  
Review
A Review of Using IoT for Energy Efficient Buildings and Cities: A Built Environment Perspective
by Karam M. Al-Obaidi, Mohataz Hossain, Nayef A. M. Alduais, Husam S. Al-Duais, Hossein Omrany and Amirhosein Ghaffarianhoseini
Energies 2022, 15(16), 5991; https://doi.org/10.3390/en15165991 - 18 Aug 2022
Cited by 34 | Viewed by 9516
Abstract
Applications of the Internet of Things (IoT) are rapidly utilized in smart buildings and smart cities to reduce energy consumption. This advancement has caused a knowledge gap in applying IoT effectively by experts in the built environment to achieve energy efficiency. The study [...] Read more.
Applications of the Internet of Things (IoT) are rapidly utilized in smart buildings and smart cities to reduce energy consumption. This advancement has caused a knowledge gap in applying IoT effectively by experts in the built environment to achieve energy efficiency. The study aims to provide an extensive review of IoT applications for energy savings in buildings and cities. This study contributes to the field of IoT by guiding and supporting built environment experts to utilize IoT technologies. This paper performed a thorough study using a systematic review that covered an overview of IoT concepts, models, applications, trends and challenges that can be encountered in the built environment. The findings indicated limitations in developing IoT strategies in buildings and cities by professionals in this field due to insufficient comprehension of technologies and their applied methods. Additionally, the study found an indefinite implementation and constraints on using IoT when integrated into the built environment. Finally, the study provides critical arguments and the next steps to effectively utilize IoT in terms of energy efficiency. Full article
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26 pages, 4693 KiB  
Review
A Review of AC and DC Collection Grids for Offshore Renewable Energy with a Qualitative Evaluation for Marine Energy Resources
by Christoffer Fjellstedt, Md Imran Ullah, Johan Forslund, Erik Jonasson, Irina Temiz and Karin Thomas
Energies 2022, 15(16), 5816; https://doi.org/10.3390/en15165816 - 10 Aug 2022
Cited by 10 | Viewed by 3229
Abstract
Marine energy resources could be crucial in meeting the increased demand for clean electricity. To enable the use of marine energy resources, developing efficient and durable offshore electrical systems is vital. Currently, there are no large-scale commercial projects with marine energy resources, and [...] Read more.
Marine energy resources could be crucial in meeting the increased demand for clean electricity. To enable the use of marine energy resources, developing efficient and durable offshore electrical systems is vital. Currently, there are no large-scale commercial projects with marine energy resources, and the question of how to design such electrical systems is still not settled. A natural starting point in investigating this is to draw on experiences and research from offshore wind power. This article reviews different collection grid topologies and key components for AC and DC grid structures. The review covers aspects such as the type of components, operation and estimated costs of commercially available components. A DC collection grid can be especially suitable for offshore marine energy resources, since the transmission losses are expected to be lower, and the electrical components could possibly be made smaller. Therefore, five DC collection grid topologies are proposed and qualitatively evaluated for marine energy resources using submerged and non-submerged marine energy converters. The properties, advantages and disadvantages of the proposed topologies are discussed, and it is concluded that a suitable electrical system for a marine energy farm will most surely be based on a site-specific techno-economic analysis. Full article
(This article belongs to the Section A3: Wind, Wave and Tidal Energy)
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18 pages, 3829 KiB  
Review
Grid-Forming Converters for Stability Issues in Future Power Grids
by Shahid Aziz Khan, Mengqi Wang, Wencong Su, Guanliang Liu and Shivam Chaturvedi
Energies 2022, 15(14), 4937; https://doi.org/10.3390/en15144937 - 6 Jul 2022
Cited by 42 | Viewed by 7420
Abstract
Historically, the power system has relied on synchronous generators (SGs) to provide inertia and maintain grid stability. However, because of the increased integration of power-electronics-interfaced renewable energy sources, the grid’s stability has been challenged in the last decade due to a lack of [...] Read more.
Historically, the power system has relied on synchronous generators (SGs) to provide inertia and maintain grid stability. However, because of the increased integration of power-electronics-interfaced renewable energy sources, the grid’s stability has been challenged in the last decade due to a lack of inertia. Currently, the system predominantly uses grid-following (GFL) converters, built on the assumption that inertial sources regulate the system stability. Such an assumption does not hold for the low-inertia grids of the future. Grid-forming (GFM) converters, which mimic the traditional synchronous machinery’s functionalities, have been identified as a potential solution to support the low-inertia grids. The performance analysis of GFM converters for small-signal instability can be found in the literature, but large-signal instability is still an open research question. Moreover, various topologies and configurations of GFM converters have been proposed. Still, no comparative study combining all GFC configurations from the perspective of large-signal stability issues can be found. This paper combines and compares all the existing GFM control schemes from the perspective of large-signal stability issues to pave the way for future research and development of GFM converters for large-signal stability analysis and stabilization of the future low-inertia grids. Full article
(This article belongs to the Special Issue Machine Learning Algorithms for Operation and Control of Microgrids with Distributed Energy Sources)
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25 pages, 6544 KiB  
Review
Fatigue Assessment of Wind Turbine Towers: Review of Processing Strategies with Illustrative Case Study
by João Pacheco, Francisco Pimenta, Sérgio Pereira, Álvaro Cunha and Filipe Magalhães
Energies 2022, 15(13), 4782; https://doi.org/10.3390/en15134782 - 29 Jun 2022
Cited by 19 | Viewed by 5098
Abstract
Wind turbines are structures predominantly subjected to dynamic loads throughout their period of life. In that sense, fatigue design plays a central role. Particularly, support structure design might be conservative with respect to fatigue, which may lead to a real fatigue life of [...] Read more.
Wind turbines are structures predominantly subjected to dynamic loads throughout their period of life. In that sense, fatigue design plays a central role. Particularly, support structure design might be conservative with respect to fatigue, which may lead to a real fatigue life of considerably more than 20 years. For these reasons, the implementation of a fatigue monitoring system can be an important advantage for the management of wind farms, providing the following outputs: (i) estimation of the evolution of real fatigue condition; (ii) since the real condition of fatigue damage is known, these results could be an essential element for a decision about extending the lifespan of the structure and the possibility of repowering or overpowering; and (iii) the results of the instrumented wind turbines can be extrapolated to other wind turbines of the same wind farm. This paper reviews the procedures for calculating the fatigue damage of wind turbine towers using strain measurements. The applicability of the described procedures is demonstrated with experimental data acquired in an extensive experimental campaign developed at Tocha Wind Farm, an onshore wind farm located in Portugal, exploring the impact of several user-defined parameters on the fatigue results. The paper also includes the description of the data processing needed to convert raw measurements into bending moments and several validation and calibration steps. Full article
(This article belongs to the Special Issue Wind Turbine Structural Control and Health Monitoring)
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20 pages, 1461 KiB  
Review
Gasification of Solid Fuels (Coal, Biomass and MSW): Overview, Challenges and Mitigation Strategies
by M. Shahabuddin and Tanvir Alam
Energies 2022, 15(12), 4444; https://doi.org/10.3390/en15124444 - 18 Jun 2022
Cited by 24 | Viewed by 7423
Abstract
Currently, hydrogen energy is the most promising energy vector, while gasification is one of the major routes for its production. However, gasification suffers from various issues, including slower carbon conversion, poor syngas quality, lower heating value and higher emissions. Multiple factors affect gasification [...] Read more.
Currently, hydrogen energy is the most promising energy vector, while gasification is one of the major routes for its production. However, gasification suffers from various issues, including slower carbon conversion, poor syngas quality, lower heating value and higher emissions. Multiple factors affect gasification performance, such as the selection of gasifiers, feedstock’s physicochemical properties and operating conditions. In this review, the status of gasification, key gasifier technologies and the effect of solid-fuel (i.e., coal, biomass and MSW) properties on gasification performance are reviewed critically. Based on the current review, the co-gasification of coal, biomass and solid waste, along with a partial utilisation of CO2 as a reactant, are suggested. Furthermore, a technological breakthrough in carbon capture and sequestration is needed to make it industrially viable. Full article
(This article belongs to the Special Issue Recent Progress in Bio-Energy with Carbon Capture and Storage)
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24 pages, 2417 KiB  
Review
Hydrogen Production Cost Forecasts since the 1970s and Implications for Technological Development
by Tomonori Miyagawa and Mika Goto
Energies 2022, 15(12), 4375; https://doi.org/10.3390/en15124375 - 15 Jun 2022
Cited by 11 | Viewed by 3419
Abstract
This study reviews the extant literature on hydrogen production cost forecasts to identify and analyze the historical trend of such forecasts in order to explore the feasibility of wider adoption. Hydrogen is an important energy source that can be used to achieve a [...] Read more.
This study reviews the extant literature on hydrogen production cost forecasts to identify and analyze the historical trend of such forecasts in order to explore the feasibility of wider adoption. Hydrogen is an important energy source that can be used to achieve a carbon-neutral society, but the widespread adoption of hydrogen production technologies is hampered by the high costs. The production costs vary depending on the technology employed: gray, renewable electrolysis, or biomass. The study identifies 174 production cost forecast data points from articles published between 1979 and 2020 and makes a comparative assessment using non-parametric statistical tests. The results show three different cost forecast trends across technologies. First, the production cost of gray hydrogen showed an increasing trend until 2015, but started declining after 2015. Second, the renewable electrolysis hydrogen cost was the highest of all, but has shown a gradual declining trend since 2015. Finally, the biomass hydrogen cost has been relatively cheaper up until 2015, after which it became the highest. Renewable electrolysis and biomass hydrogen will be potential candidates (as principal drivers) to reduce CO2 emissions in the future, but renewable electrolysis hydrogen is more promising in this regard due to its declining production cost trend. Gray hydrogen can also be an alternative candidate to renewable electrolysis hydrogen because it can be equipped with carbon capture storage (CCS) to produce blue hydrogen, although we need to consider additional production costs incurred by the introduction of CCS. The study discusses the technological development and policy implications of the results on hydrogen production costs. Full article
(This article belongs to the Section A5: Hydrogen Energy)
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31 pages, 762 KiB  
Review
Getting Value from Pulp and Paper Industry Wastes: On the Way to Sustainability and Circular Economy
by Mariana S. T. Amândio, Joana M. Pereira, Jorge M. S. Rocha, Luísa S. Serafim and Ana M. R. B. Xavier
Energies 2022, 15(11), 4105; https://doi.org/10.3390/en15114105 - 2 Jun 2022
Cited by 13 | Viewed by 5673
Abstract
The pulp and paper industry is recognized as a well-established sector, which throughout its process, generates a vast amount of waste streams with the capacity to be valorized. Typically, these residues are burned for energy purposes, but their use as substrates for biological [...] Read more.
The pulp and paper industry is recognized as a well-established sector, which throughout its process, generates a vast amount of waste streams with the capacity to be valorized. Typically, these residues are burned for energy purposes, but their use as substrates for biological processes could be a more efficient and sustainable alternative. With this aim, it is essential to identify and characterize each type of waste to determine its biotechnological potential. In this context, this research highlights possible alternatives with lower environmental impact and higher revenues. The bio-based pathway should be a promising alternative for the valorization of pulp and paper industry wastes, in particular for bioproduct production such as bioethanol, polyhydroxyalkanoates (PHA), and biogas. This article focuses on state of the art regarding the identification and characterization of these wastes, their main applied deconstruction technologies and the valorization pathways reported for the production of the abovementioned bioproducts. Full article
(This article belongs to the Special Issue Renewable Resources and Biorefineries 2021)
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30 pages, 4048 KiB  
Review
Plasma and Superconductivity for the Sustainable Development of Energy and the Environment
by Henryka Danuta Stryczewska, Mariusz Adam Stępień and Oleksandr Boiko
Energies 2022, 15(11), 4092; https://doi.org/10.3390/en15114092 - 2 Jun 2022
Cited by 11 | Viewed by 4075
Abstract
The main aim of this review is to present the current state of the research and applications of superconductivity and plasma technologies in the field of energy and environmental protection. An additional goal is to attract the attention of specialists, university students and [...] Read more.
The main aim of this review is to present the current state of the research and applications of superconductivity and plasma technologies in the field of energy and environmental protection. An additional goal is to attract the attention of specialists, university students and readers interested in the state of energy and the natural environment and in how to protect them and ensure their sustainable development. Modern energy systems and the natural environment do not develop in a sustainable manner, thus providing future generations with access to energy that is generated from renewable sources and that does not degrade the natural environment. Most of the energy technologies used today are based on non-renewable sources. Power contained in fuel is irretrievably lost, and the quality of the energy is lowered. It is accompanied by the emissions of fossil fuel combustion products into the atmosphere, which pollutes the natural environment. Environmental problems, such as the production of gaseous and solid pollutants and their emission into the atmosphere, climate change, ozone depletion and acid rains, are discussed. For the problem of air pollution, the effects of combustion products in the form of carbon oxides, sulfur and nitrogen compounds are analyzed. The plasma and superconductivity phenomena, as well as their most important parameters, properties and classifications, are reviewed. In the case of atmospheric pressure plasma generation, basic information about technological gas composition, pressure, discharge type, electromagnetic field specification, electrode geometry, voltage supply systems, etc., are presented. For the phenomenon of superconductivity, attention is mainly paid to the interdependencies between Tc, magnetic flux density Bc and current density Jc parameters. Plasma technologies and superconductivity can offer innovative and energy-saving solutions for power engineering and environmental problems through decreasing the effects of energy production, conversion and distribution for the environment and by reductions in power losses and counteracting energy quality degradation. This paper presents an overview of the application of technologies using plasma and superconductivity phenomena in power engineering and in environmental protection processes. This review of plasma technologies, related to reductions in greenhouse gas emissions and the transformation and valorization of industrial waste for applications in energy and environmental engineering, is carried out. In particular, the most plasma-based approaches for carbon oxides, sulfur and nitrogen compounds removal are discussed. The most common plasma reactors used in fuel reforming technologies, such as dielectric barrier discharge, microwave discharge and gliding-arc discharge, are described. The advantages of solid waste treatment using plasma arc techniques are introduced. Applications of superconductors for energy generation, conversion and transmission can be divided into two main groups with respect to the conducted current (DC and AC) and into three groups with respect to the employed property (zero resistivity, ideal magnetism/flux trapping and quench transition). Among the superconductivity applications of electrical machines, devices for improving energy quality and storage and high field generation are described. An example that combines the phenomena of hot plasma and superconductivity is thermonuclear fusion. It is a hope for solving the world’s energy problems and for creating a virtually inexhaustible, sustainable and waste-free source of energy for many future generations. Full article
(This article belongs to the Section F: Electrical Engineering)
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34 pages, 2432 KiB  
Review
Biological Aspects, Advancements and Techno-Economical Evaluation of Biological Methanation for the Recycling and Valorization of CO2
by Ruggero Bellini, Ilaria Bassani, Arianna Vizzarro, Annalisa Abdel Azim, Nicolò Santi Vasile, Candido Fabrizio Pirri, Francesca Verga and Barbara Menin
Energies 2022, 15(11), 4064; https://doi.org/10.3390/en15114064 - 1 Jun 2022
Cited by 24 | Viewed by 4846
Abstract
Nowadays, sustainable and renewable energy production is a global priority. Over the past decade, several Power-to-X (PtX) technologies have been proposed to store and convert the surplus of renewable energies into chemical bonds of chemicals produced by different processes. CO2 is a [...] Read more.
Nowadays, sustainable and renewable energy production is a global priority. Over the past decade, several Power-to-X (PtX) technologies have been proposed to store and convert the surplus of renewable energies into chemical bonds of chemicals produced by different processes. CO2 is a major contributor to climate change, yet it is also an undervalued source of carbon that could be recycled and represents an opportunity to generate renewable energy. In this context, PtX technologies would allow for CO2 valorization into renewable fuels while reducing greenhouse gas (GHG) emissions. With this work we want to provide an up-to-date overview of biomethanation as a PtX technology by considering the biological aspects and the main parameters affecting its application and scalability at an industrial level. Particular attention will be paid to the concept of CO2-streams valorization and to the integration of the process with renewable energies. Aspects related to new promising technologies such as in situ, ex situ, hybrid biomethanation and the concept of underground methanation will be discussed, also in connection with recent application cases. Furthermore, the technical and economic feasibility will be critically analyzed to highlight current options and limitations for implementing a sustainable process. Full article
(This article belongs to the Special Issue Biomass, Biofuels and Waste)
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26 pages, 789 KiB  
Review
Review of Electric Vehicle Charger Cybersecurity Vulnerabilities, Potential Impacts, and Defenses
by Jay Johnson, Timothy Berg, Benjamin Anderson and Brian Wright
Energies 2022, 15(11), 3931; https://doi.org/10.3390/en15113931 - 26 May 2022
Cited by 42 | Viewed by 32788
Abstract
Worldwide growth in electric vehicle use is prompting new installations of private and public electric vehicle supply equipment (EVSE). EVSE devices support the electrification of the transportation industry but also represent a linchpin for power systems and transportation infrastructures. Cybersecurity researchers have recently [...] Read more.
Worldwide growth in electric vehicle use is prompting new installations of private and public electric vehicle supply equipment (EVSE). EVSE devices support the electrification of the transportation industry but also represent a linchpin for power systems and transportation infrastructures. Cybersecurity researchers have recently identified several vulnerabilities that exist in EVSE devices, communications to electric vehicles (EVs), and upstream services, such as EVSE vendor cloud services, third party systems, and grid operators. The potential impact of attacks on these systems stretches from localized, relatively minor effects to long-term national disruptions. Fortunately, there is a strong and expanding collection of information technology (IT) and operational technology (OT) cybersecurity best practices that may be applied to the EVSE environment to secure this equipment. In this paper, we survey publicly disclosed EVSE vulnerabilities, the impact of EV charger cyberattacks, and proposed security protections for EV charging technologies. Full article
(This article belongs to the Special Issue Cybersecurity Solutions for Photovoltaic Systems, Wind Energy Sites, and Electric Vehicle Chargers)
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21 pages, 6568 KiB  
Review
Techno-Economic Assessment of Half-Cell Modules for Desert Climates: An Overview on Power, Performance, Durability and Costs
by Hamed Hanifi, Bengt Jaeckel, Matthias Pander, David Dassler, Sagarika Kumar and Jens Schneider
Energies 2022, 15(9), 3219; https://doi.org/10.3390/en15093219 - 28 Apr 2022
Cited by 7 | Viewed by 3568
Abstract
Photovoltaic modules in desert areas benefit from high irradiation levels but suffer from harsh environmental stress factors, which influence the Levelized Cost of Electricity by decreasing the lifetime and performance and increasing the maintenance costs. Using optimized half-cell module designs mounted in the [...] Read more.
Photovoltaic modules in desert areas benefit from high irradiation levels but suffer from harsh environmental stress factors, which influence the Levelized Cost of Electricity by decreasing the lifetime and performance and increasing the maintenance costs. Using optimized half-cell module designs mounted in the most efficient orientation according to the plant requirements can lead to reduced production costs, increased energy yield and longer service lives for PV modules in desert areas. In this work, we review the technical advantages of half-cell modules in desert regions and discuss the potential gains in levelized costs of electricity due to reduced material consumption, a higher cell-to-module power ratio, lower module temperatures, better yields, reduced cleaning cycles and finally, reduced fatigue in interconnection due to thermal cycling. We show that half-cell modules are the most cost-effective option for desert areas and are expected to have a relevant lower Levelized Cost of Electricity. Full article
(This article belongs to the Special Issue Frontiers in Photovoltaic Modules)
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16 pages, 893 KiB  
Review
Silicon–Germanium: The Legacy Lives On
by Bruce Cook
Energies 2022, 15(8), 2957; https://doi.org/10.3390/en15082957 - 18 Apr 2022
Cited by 14 | Viewed by 3353
Abstract
Alloy systems comprised of silicon with germanium, lead with tellurium, and bismuth with antimony have constituted a majority of thermoelectric applications during the last half-century. These legacy materials are primarily covalently bonded with a maximum ZT near one. Silicon–germanium alloys have provided the [...] Read more.
Alloy systems comprised of silicon with germanium, lead with tellurium, and bismuth with antimony have constituted a majority of thermoelectric applications during the last half-century. These legacy materials are primarily covalently bonded with a maximum ZT near one. Silicon–germanium alloys have provided the thermal to electrical conversion for many of NASA’s radioisotope thermoelectric generator (RTG) configurations and for nearly all of its deep space and outer planetary flights, such as Pioneer I and II, Voyager I and 11, Ulysses, Galileo, and Cassini. The remarkable success of these materials and their respective devices is evidenced by the fact that there has never been a failure of the RTG systems even after over 1 billion cumulative mission-hours. The history of this alloy system as a thermoelectric conversion material spans over six decades and research to further improve its performance continues to this day. Si-Ge alloys have long been a mainstay of thermoelectric research because of a fortuitous combination of a sufficiently high melting temperature, reasonable energy band gap, high solubility for both n- and p-type dopants, and the fact that this alloy system exhibits complete miscibility in the solid state, which enable tuning of both electrical and thermal properties. This article reviews the history of silicon–germanium as a thermoelectric material and its use in NASA’s RTG programs. Since the device technology is also a critical operational consideration, a brief review of some of the unique challenges imposed by the use in an RTG is also discussed. Full article
(This article belongs to the Special Issue Advanced Thermoelectric Generation Technologies 2022)
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33 pages, 10876 KiB  
Review
Power Electronics Converters for the Internet of Energy: A Review
by Samuele Granata, Marco Di Benedetto, Cristina Terlizzi, Riccardo Leuzzi, Stefano Bifaretti and Pericle Zanchetta
Energies 2022, 15(7), 2604; https://doi.org/10.3390/en15072604 - 2 Apr 2022
Cited by 7 | Viewed by 3860
Abstract
This paper presents a comprehensive review of multi-port power electronics converters used for application in AC, DC, or hybrid distribution systems in an Internet of Energy scenario. In particular, multi-port solid-state transformer (SST) topologies have been addressed and classified according to their isolation [...] Read more.
This paper presents a comprehensive review of multi-port power electronics converters used for application in AC, DC, or hybrid distribution systems in an Internet of Energy scenario. In particular, multi-port solid-state transformer (SST) topologies have been addressed and classified according to their isolation capabilities and their conversion stages configurations. Non-conventional configurations have been considered. A comparison of the most relevant features and design specifications between popular topologies has been provided through a comprehensive and effective table. Potential benefits of SSTs in distribution applications have been highlighted even with reference to a network active nodes usage. This review also highlights standards and technical regulations in force for connecting SSTs to the electrical distribution system. Finally, two case studies of multi-port topologies have been presented and discussed. The first one is an isolated multi-port bidirectional dual active bridge DC-DC converter useful in fast-charging applications. The second case of study deals with a three-port AC-AC multi-level power converter in H-Bridge configuration able to replicate a network active node and capable of routing and controlling energy under different operating conditions. Full article
(This article belongs to the Section A1: Smart Grids and Microgrids)
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24 pages, 9418 KiB  
Review
Automatic Inspection of Photovoltaic Power Plants Using Aerial Infrared Thermography: A Review
by Aline Kirsten Vidal de Oliveira, Mohammadreza Aghaei and Ricardo Rüther
Energies 2022, 15(6), 2055; https://doi.org/10.3390/en15062055 - 11 Mar 2022
Cited by 30 | Viewed by 6248
Abstract
In recent years, aerial infrared thermography (aIRT), as a cost-efficient inspection method, has been demonstrated to be a reliable technique for failure detection in photovoltaic (PV) systems. This method aims to quickly perform a comprehensive monitoring of PV power plants, from the commissioning [...] Read more.
In recent years, aerial infrared thermography (aIRT), as a cost-efficient inspection method, has been demonstrated to be a reliable technique for failure detection in photovoltaic (PV) systems. This method aims to quickly perform a comprehensive monitoring of PV power plants, from the commissioning phase through its entire operational lifetime. This paper provides a review of reported methods in the literature for automating different tasks of the aIRT framework for PV system inspection. The related studies were reviewed for digital image processing (DIP), classification and deep learning techniques. Most of these studies were focused on autonomous fault detection and classification of PV plants using visual, IRT and aIRT images with accuracies up to 90%. On the other hand, only a few studies explored the automation of other parts of the procedure of aIRT, such as the optimal path planning, the orthomosaicking of the acquired images and the detection of soiling over the modules. Algorithms for the detection and segmentation of PV modules achieved a maximum F1 score (harmonic mean of precision and recall) of 98.4%. The accuracy, robustness and generalization of the developed algorithms are still the main issues of these studies, especially when dealing with more classes of faults and the inspection of large-scale PV plants. Therefore, the autonomous procedure and classification task must still be explored to enhance the performance and applicability of the aIRT method. Full article
(This article belongs to the Special Issue Autonomous Monitoring and Analysis of Photovoltaic Systems)
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53 pages, 9473 KiB  
Review
23 Years of Development of the Solar Power Generation Sector in Spain: A Comprehensive Review of the Period 1998–2020 from a Regulatory Perspective
by Sergio Coronas, Jordi de la Hoz, Àlex Alonso and Helena Martín
Energies 2022, 15(4), 1593; https://doi.org/10.3390/en15041593 - 21 Feb 2022
Cited by 9 | Viewed by 4785
Abstract
Spain has become one of the leading countries in the world in promoting electricity generation from renewable energy sources (RES), due to their positive socioeconomic and environmental impacts, through highly favorable regulatory frameworks and public incentives set by Spanish governments mainly during the [...] Read more.
Spain has become one of the leading countries in the world in promoting electricity generation from renewable energy sources (RES), due to their positive socioeconomic and environmental impacts, through highly favorable regulatory frameworks and public incentives set by Spanish governments mainly during the first decade of 2000s, i.e., Royal Decree (RD) 2818/1998, RD 436/2004 and RD 661/2007. Conversely, the highly favorable regime applicable to RES, and specifically to solar power plants during the 1998–2008 promotion period turned into an extremely unfavorable scenario during the 2008–2020 cost-containment stage, characterized by the dismantling of the previous promotion schemes so as to reduce the skyrocketing electricity system tariff deficit, in which regulations such as RD 1578/2008, Royal Decree Law (RDL) 6/2009, RDL 14/2010, RDL 1/2012, Law 15/2012, RDL 9/2013, Law 24/2013 and RD 413/2014 stood out. Nonetheless, the Spanish renewable sector, and especially the solar power sector, has shown great dynamism in its energy policy in the period 1998–2020. This academic contribution provides a comprehensive review of the energy policy evolution for the whole solar power sector in Spain, specifically both solar photovoltaic (PV) and concentrating solar power (CSP) plants, over the last 23 years. Thus, considering both the boom in the solar power sector as well as the solar sector’s bust, a survey of the different legislation in force during the 1998–2020 period, as well as of the existing academic literature dealing with this issue, is conducted to first contextualize and describe, and then carefully assess, the last 23 years of solar energy policy in Spain. In brief, the decisive role of the Spanish government in developing the RES sector, and especially the solar power sector, in recent years has been noted. In this vein, a good planning of the energy development model, the regulatory stability, the simplicity and agility of the corresponding administrative process, the appropriate design of support mechanisms, as well as security and predictability of support levels in the mid and long term, play an important role in providing certainty to all the stakeholders. During the 1998–2008 promotion stage, even with a stable, quite favorable and easily predictable RES support mechanism in place, the Spanish solar system behaved as an open-loop system without any control structure detecting and reacting to problematic situations. The fact that the Spanish government was compelled to implement ex-post measures during the period 2008–2020, seriously jeopardizing the viability of the power plants in operation, as well as compromising the legal–economic stability of the renewable energy sector, clearly indicated a malfunctioning of the energy policy control mechanism. In essence, it is hoped that the lessons extracted from this 23-year comprehensive review of the Spanish solar power sector pathway could be quite useful for other countries either in the initial development stage or fully immersed in the promotion of solar power sector or any other renewable technology. Full article
(This article belongs to the Special Issue Power System Dynamics and Renewable Energy Integration)
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35 pages, 4558 KiB  
Review
A Review of Environmental and Economic Implications of Closing the Nuclear Fuel Cycle—Part One: Wastes and Environmental Impacts
by Robin Taylor, William Bodel, Laurence Stamford and Gregg Butler
Energies 2022, 15(4), 1433; https://doi.org/10.3390/en15041433 - 16 Feb 2022
Cited by 24 | Viewed by 9083
Abstract
Globally, around half a million tonnes of spent nuclear fuel (SNF) will be in dry or wet storage by around 2050. Continued storage is not sustainable, and this SNF must eventually either be disposed (the open nuclear fuel cycle) or recycled (the closed [...] Read more.
Globally, around half a million tonnes of spent nuclear fuel (SNF) will be in dry or wet storage by around 2050. Continued storage is not sustainable, and this SNF must eventually either be disposed (the open nuclear fuel cycle) or recycled (the closed fuel cycle). Many international studies have addressed the advantages and disadvantages of these options. To inform this debate, a detailed survey of the available literature related to environmental assessments of closed and open cycles has been undertaken. Environmental impacts are one of the three pillars that, alongside economic and societal impacts, must be considered for sustainable development. The aims are to provide a critical review of the open literature in order to determine what generic conclusions can be drawn from the broad base of international studies. This review covers the results of life cycle assessments and studies on waste arisings, showing how the management of spent fuels in the open and closed cycles impact the environment, including the use of natural resources, radioactive waste characteristics (heat loading, radiotoxicity and volume) and the size of the geological repository. In the framework of sustainable development, the next part of this review will consider economic impacts. Full article
(This article belongs to the Topic Nuclear Energy Systems)
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27 pages, 1595 KiB  
Review
Building Thermal-Network Models: A Comparative Analysis, Recommendations, and Perspectives
by Abhinandana Boodi, Karim Beddiar, Yassine Amirat and Mohamed Benbouzid
Energies 2022, 15(4), 1328; https://doi.org/10.3390/en15041328 - 11 Feb 2022
Cited by 26 | Viewed by 4290
Abstract
The development of smart buildings, as well as the great need for energy demand reduction, has renewed interest in building energy demand prediction. Intelligent controllers are a solution for optimizing building energy consumption while maintaining indoor comfort. The controller efficiency on the other [...] Read more.
The development of smart buildings, as well as the great need for energy demand reduction, has renewed interest in building energy demand prediction. Intelligent controllers are a solution for optimizing building energy consumption while maintaining indoor comfort. The controller efficiency on the other hand, is mainly determined by the prediction of thermal behavior from building models. Due to the development complexity of the models, these intelligent controllers are not yet implemented on an industrial scale. There are primarily three types of building models studied in the literature: white-box, black-box, and gray-box. The gray-box models are found to be robust, efficient, of low cost computationally, and of moderate modeling complexity. Furthermore, there is no standard model configuration, development method, or operation conditions. These parameters have a significant influence on the model performance accuracy. This motivates the need for this review paper, in which we examined various gray-box models, their configurations, parametric identification techniques, and influential parameters. Full article
(This article belongs to the Section G: Energy and Buildings)
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30 pages, 1332 KiB  
Review
Benchmarking Approaches for Assessing the Performance of Building Control Strategies: A Review
by Clara Ceccolini and Roozbeh Sangi
Energies 2022, 15(4), 1270; https://doi.org/10.3390/en15041270 - 9 Feb 2022
Cited by 6 | Viewed by 2705
Abstract
In the last few decades, researchers have shown that advanced building controllers can reduce energy consumption without negatively impacting occupants’ wellbeing and help to manage building systems, which are becoming increasingly complex. Nevertheless, the lack of benefit awareness and demonstration projects undermines stakeholders’ [...] Read more.
In the last few decades, researchers have shown that advanced building controllers can reduce energy consumption without negatively impacting occupants’ wellbeing and help to manage building systems, which are becoming increasingly complex. Nevertheless, the lack of benefit awareness and demonstration projects undermines stakeholders’ trust, justifying the reluctance to approve new controls in the industry. Therefore, it is necessary to support the development of controls through solid arguments testifying to the performance gain that can be achieved. However, the absence of standardized and systematic testing methods limits the generalization of results and the ability to make fair cross-study comparisons. This study presents an overview of the different benchmarking approaches used to assess control performance. Our goal is to highlight trends, limitations, and controversies through analytics to support the definition of best practices, which remains a widely discussed topic in this research area. We aim to focus on simulation-based benchmarking, which is regarded as a promising solution to overcome the time and cost requirements related to field or hardware-in-the-loop testing. We identify and investigate four key steps relating to virtual benchmarking: defining the key performance indicators, specifying the reference control, characterizing the test scenarios, and post-processing the results. This work confirmed the expected heterogeneity, underlined recurrent features with the help of analytics, and recognized limits and open challenges. Full article
(This article belongs to the Topic Sustainable Built Environment)
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29 pages, 4228 KiB  
Review
Application of Ionic Liquids for the Recycling and Recovery of Technologically Critical and Valuable Metals
by Grace Inman, Ikenna C. Nlebedim and Denis Prodius
Energies 2022, 15(2), 628; https://doi.org/10.3390/en15020628 - 17 Jan 2022
Cited by 34 | Viewed by 5853
Abstract
Population growth has led to an increased demand for raw minerals and energy resources; however, their supply cannot easily be provided in the same proportions. Modern technologies contain materials that are becoming more finely intermixed because of the broadening palette of elements used, [...] Read more.
Population growth has led to an increased demand for raw minerals and energy resources; however, their supply cannot easily be provided in the same proportions. Modern technologies contain materials that are becoming more finely intermixed because of the broadening palette of elements used, and this outcome creates certain limitations for recycling. The recovery and separation of individual elements, critical materials and valuable metals from complex systems requires complex energy-consuming solutions with many hazardous chemicals used. Significant pressure is brought to bear on the improvement of separation and recycling approaches by the need to balance sustainability, efficiency, and environmental impacts. Due to the increase in environmental consciousness in chemical research and industry, the challenge for a sustainable environment calls for clean procedures that avoid the use of harmful organic solvents. Ionic liquids, also known as molten salts and future solvents, are endowed with unique features that have already had a promising impact on cutting-edge science and technologies. This review aims to address the current challenges associated with the energy-efficient design, recovery, recycling, and separation of valuable metals employing ionic liquids. Full article
(This article belongs to the Special Issue Ionic Liquids in Energy and Environment)
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15 pages, 2259 KiB  
Review
Turning Waste Cooking Oils into Biofuels—Valorization Technologies: A Review
by Lucas Nascimento, André Ribeiro, Ana Ferreira, Nádia Valério, Vânia Pinheiro, Jorge Araújo, Cândida Vilarinho and Joana Carvalho
Energies 2022, 15(1), 116; https://doi.org/10.3390/en15010116 - 24 Dec 2021
Cited by 12 | Viewed by 4098
Abstract
In search of a more sustainable society, humanity has been looking to reduce the environmental impacts caused by its various activities. The energy sector corresponds to one of the most impactful activities since most energies produced come from fossil fuels, such as oil [...] Read more.
In search of a more sustainable society, humanity has been looking to reduce the environmental impacts caused by its various activities. The energy sector corresponds to one of the most impactful activities since most energies produced come from fossil fuels, such as oil and coal, which are finite resources. Moreover, their inherent processes to convert energy into electricity emit various pollutants, which are responsible for global warming, eutrophication, and acidification of soil and marine environments. Biofuels are one of the alternatives to fossil fuels, and the raw material used for their production includes vegetable oils, wood and agricultural waste, municipal waste, and waste cooking oils (WCOs). The conventional route for WCO valorization is the production of biodiesel, which, as all recovery technologies, presents advantages and disadvantages that must be explored from a technical and economic perspective. Despite its successful use in the production of biodiesel, it should be noticed that there are other approaches to use WCO. Among them, thermochemical technologies can be applied to produce alternative fuels through cracking or hydrocracking, pyrolysis, and gasification processes. For each technology, the best conditions were identified, and finally, projects and companies that work with this type of technology and use WCO were identified. Full article
(This article belongs to the Special Issue Valorization of Wastes for Energy Production by Thermal and Biological Processes)
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43 pages, 27886 KiB  
Review
Review of the Hydrogen Evolution Reaction—A Basic Approach
by Thomas B. Ferriday, Peter Hugh Middleton and Mohan Lal Kolhe
Energies 2021, 14(24), 8535; https://doi.org/10.3390/en14248535 - 17 Dec 2021
Cited by 29 | Viewed by 9114
Abstract
An increasing emphasis on energy storage has resulted in a surge of R&D efforts into producing catalyst materials for the hydrogen evolution reaction (HER) with emphasis on decreasing the usage of platinum group metals (PGMs). Alkaline water electrolysis holds promise for satisfying future [...] Read more.
An increasing emphasis on energy storage has resulted in a surge of R&D efforts into producing catalyst materials for the hydrogen evolution reaction (HER) with emphasis on decreasing the usage of platinum group metals (PGMs). Alkaline water electrolysis holds promise for satisfying future energy storage demands, however the intrinsic potential of this technology is impeded by sluggish reaction kinetics. Here, we summarize the latest efforts within alkaline HER electrocatalyst design, where these efforts are divided between three catalyst design strategies inspired by the three prevailing theories describing the pH-dependence of the HER activity. Modifying the electronic structure of a host through codoping and creating specific sites for hydrogen/hydroxide adsorption stand out as promising strategies. However, with the vast amount of possible combinations, emphasis on screening parameters is important. The authors predict that creating a codoped catalyst using the first strategy by screening materials based on their hydrogen, hydroxide and water binding energies, and utilizing the second and third strategies as optimization parameters might yield both active and stable HER catalyst materials. This strategy has the potential to greatly advance the current status of alkaline water electrolysis as an energy storage option. Full article
(This article belongs to the Special Issue Recent Advances of Catalysts for Hydrogen Evolution Reaction in Water Splitting)
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18 pages, 14604 KiB  
Review
Solar Energy in the Nordic Built Environment: Challenges, Opportunities and Barriers
by Matteo Formolli, Gabriele Lobaccaro and Jouri Kanters
Energies 2021, 14(24), 8410; https://doi.org/10.3390/en14248410 - 13 Dec 2021
Cited by 22 | Viewed by 4257
Abstract
Within the framework Solar Heating and Cooling Programme of the International Energy Agency Task 51 “Solar Energy in Urban Planning”, case studies from Norway, Sweden, and Denmark were collected and analyzed through a comparative approach. The cases were first classified based on their [...] Read more.
Within the framework Solar Heating and Cooling Programme of the International Energy Agency Task 51 “Solar Energy in Urban Planning”, case studies from Norway, Sweden, and Denmark were collected and analyzed through a comparative approach. The cases were first classified based on their urban characterization (existing and new urban areas) and then compared within the same country or in a cross-country perspective according to three areas of interest (i.e., Scale and planning process, Legislation and planning process, Targets and goals). The comparisons follow a common template of five sections describing the role of the involved stakeholders and highlighting challenges, barriers, and opportunities for the deployment of active solar systems and passive solar strategies. Both technical and non-technical aspects are considered. Among the technical aspects, the focus is on the adoption of solar energy strategies (e.g., solar accessibility, daylighting), the estimation of solar potential and energy generation. Regarding the non-technical aspects, the focus is on identifying barriers and challenges for the adoption of solar systems in relation to national and local legislation. The findings show that municipalities can have a crucial role in facilitating the adoption of solar energy solutions in cities by embracing ambitious visions and storytelling, as well as being directly financially involved as owners or subsidizing bodies. The findings also demonstrate the value of the use of indicators to evaluate the performance of masterplans, the combination of analogue and digital tools in the design process, and the performance of solar simulations from early stages to foster awareness among the involved stakeholders. Despite these positives, the Scandinavian legislation on solar energy utilization in the urban context still displays fragilities, making the creation of guidelines a pressing need. Full article
(This article belongs to the Special Issue Emerging Photovoltaic Technology in Northern Europe)
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17 pages, 1482 KiB  
Review
The Role of Fluorinated Polymers in the Water Management of Proton Exchange Membrane Fuel Cells: A Review
by Marco Mariani, Andrea Basso Peressut, Saverio Latorrata, Riccardo Balzarotti, Maurizio Sansotera and Giovanni Dotelli
Energies 2021, 14(24), 8387; https://doi.org/10.3390/en14248387 - 13 Dec 2021
Cited by 14 | Viewed by 5505
Abstract
As the hydrogen market is projected to grow in the next decades, the development of more efficient and better-performing polymer electrolyte membrane fuel cells (PEMFCs) is certainly needed. Water management is one of the main issues faced by these devices and is strictly [...] Read more.
As the hydrogen market is projected to grow in the next decades, the development of more efficient and better-performing polymer electrolyte membrane fuel cells (PEMFCs) is certainly needed. Water management is one of the main issues faced by these devices and is strictly related to the employment of fluorinated materials in the gas diffusion medium (GDM). Fluorine-based polymers are added as hydrophobic agents for gas diffusion layers (GDL) or in the ink composition of microporous layers (MPL), with the goal of reducing the risk of membrane dehydration and cell flooding. In this review, the state of the art of fluorinated polymers for fuel cells is presented. The most common ones are polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene (FEP), however, other compounds such as PFA, PVDF, PFPE, and CF4 have been studied and reported. The effects of these materials on device performances are analyzed and described. Particular attention is dedicated to the influence of polymer content on the variation of the fuel cell component properties, namely conductivity, durability, hydrophobicity, and porosity, and on the PEMFC behavior at different current densities and under multiple operating conditions. Full article
(This article belongs to the Section D2: Electrochem: Batteries, Fuel Cells, Capacitors)
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25 pages, 631 KiB  
Review
Exploiting the Nutrient Potential of Anaerobically Digested Sewage Sludge: A Review
by Nicola Di Costanzo, Alessandra Cesaro, Francesco Di Capua and Giovanni Esposito
Energies 2021, 14(23), 8149; https://doi.org/10.3390/en14238149 - 5 Dec 2021
Cited by 36 | Viewed by 4381
Abstract
The world is currently witnessing a rapid increase in sewage sludge (SS) production, due to the increased demand for wastewater treatment. Therefore, SS management is crucial for the economic and environmental sustainability of wastewater treatment plants. The recovery of nutrients from SS has [...] Read more.
The world is currently witnessing a rapid increase in sewage sludge (SS) production, due to the increased demand for wastewater treatment. Therefore, SS management is crucial for the economic and environmental sustainability of wastewater treatment plants. The recovery of nutrients from SS has been identified as a fundamental step to enable the transition from a linear to a circular economy, turning SS into an economic and sustainable source of materials. SS is often treated via anaerobic digestion, to pursue energy recovery via biogas generation. Anaerobically digested sewage sludge (ADS) is a valuable source of organic matter and nutrients, and significant advances have been made in recent years in methods and technologies for nutrient recovery from ADS. The purpose of this study is to provide a comprehensive overview, describing the advantages and drawbacks of the available and emerging technologies for recovery of nitrogen (N), phosphorus (P), and potassium (K) from ADS. This work critically reviews the established and novel technologies, which are classified by their ability to recover a specific nutrient (ammonia stripping) or to allow the simultaneous recovery of multiple elements (struvite precipitation, ion exchange, membrane technologies, and thermal treatments). This study compares the described technologies in terms of nutrient recovery efficiency, capital, and operational costs, as well as their feasibility for full-scale application, revealing the current state of the art and future perspectives on this topic. Full article
(This article belongs to the Special Issue Water–Food–Energy Nexus for a Sustainable Use and Management of Natural Resources, Byproducts and Wastes in Agri-Food Systems)
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25 pages, 3366 KiB  
Review
Rotor Position Synchronization in Central-Converter Multi-Motor Electric Actuation Systems
by Cláudio de Andrade Lima, James Cale and Kamran Eftekhari Shahroudi
Energies 2021, 14(22), 7485; https://doi.org/10.3390/en14227485 - 9 Nov 2021
Cited by 2 | Viewed by 2112
Abstract
The aerospace industry is increasingly transitioning from hydraulic and pneumatic drives to power-electronic based drive systems for reduced weight and maintenance. Electromechanical thrust reverse actuation systems (EM-TRAS) are currently being considered as a replacement for mechanical based TRAS for future aircraft. An EM-TRAS [...] Read more.
The aerospace industry is increasingly transitioning from hydraulic and pneumatic drives to power-electronic based drive systems for reduced weight and maintenance. Electromechanical thrust reverse actuation systems (EM-TRAS) are currently being considered as a replacement for mechanical based TRAS for future aircraft. An EM-TRAS consists of one or more power-electronic drives, electrical motors, and gear-trains that extend/retract mechanical members to produce a drag force that decelerates the aircraft upon landing. The use of a single (“central”) power electronic converter to simultaneously control a set of parallel induction machines is a potentially inexpensive and robust method for implementing EM-TRAS. However, because the electrical motors may experience different shaft torques—arising from differences in wind forces and a flexible nacelle—a method to implement rotor position synchronization in central-converter multi-motor (CCMM) architectures is needed. This paper introduces a novel method for achieving position synchronization within CCMM architecture by using closed-loop feedback of variable stator resistances in parallel induction machines. The feasibility of the method is demonstrated in several case studies using electromagnetic transient simulation on a set of parallel induction machines experiencing different load torque conditions, with the central converter implementing both voltage-based and current-based primary control strategies. The key result of the paper is that the CCMM architecture with proposed feedback control strategy is shown in these case studies to dynamically drive the position synchronization error to zero. The initial findings indicate that the CCMM architecture with induction motors may be a viable option for implementing EM-TRAS in future aircraft. Full article
(This article belongs to the Special Issue Modeling and Simulation of Power Systems and Power Electronics)
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16 pages, 2896 KiB  
Review
Economic Evaluation of the Production of Perennial Crops for Energy Purposes—A Review
by Ewelina Olba-Zięty, Mariusz Jerzy Stolarski and Michał Krzyżaniak
Energies 2021, 14(21), 7147; https://doi.org/10.3390/en14217147 - 1 Nov 2021
Cited by 14 | Viewed by 2595
Abstract
Biomass is widely used for the production of renewable energy, which calls for an economic evaluation of its generation. The aim of the present work was to review the literature concerning the economic evaluation of the production of perennial crop biomass for energy [...] Read more.
Biomass is widely used for the production of renewable energy, which calls for an economic evaluation of its generation. The aim of the present work was to review the literature concerning the economic evaluation of the production of perennial crop biomass for energy use. Statistical analysis of the bibliographic data was carried out, as well as an assessment of methods and values of economic indicators of the production of perennial crops for bioenergy. Most of the papers selected for the review were published in the years 2015–2019, which was probably stimulated by the growing interest in sustainable development, particularly after 2015, when the United Nations declared 17 sustainable development goals. The earliest articles concerned the economic analysis of plantations of short rotation coppice; the subsequent ones included the analysis of feedstock production in terms of the net present value and policy. The latest references also investigated transport and sustainability issues. The crops most commonly selected for production cost analysis were willow, poplar, and Miscanthus. The cost of production of willow and poplar were similar, 503 EUR ha−1 year−1 and 557 EUR ha−1 year−1, respectively, while the cost of Miscanthus production was significantly higher, 909 EUR ha−1 year−1 on average. By analogy, the distribution of revenue was similar for willow and poplar, at 236 EUR ha−1 year−1 and 181 EUR ha−1 year−1; Miscanthus production reached the value of 404 EUR ha−1 year−1. The economic conditions of perennial crop production differed in terms of geography; four areas were identified: Canada, the USA, southern Europe, and central and northern Europe. Full article
(This article belongs to the Collection Bio-Energy Reviews)
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21 pages, 2042 KiB  
Review
Review of Renewable Energy Potentials in Indonesia and Their Contribution to a 100% Renewable Electricity System
by Jannis Langer, Jaco Quist and Kornelis Blok
Energies 2021, 14(21), 7033; https://doi.org/10.3390/en14217033 - 27 Oct 2021
Cited by 53 | Viewed by 9909
Abstract
Indonesia has an increasing electricity demand that is mostly met with fossil fuels. Although Indonesia plans to ramp up Renewable Energy Technologies (RET), implementation has been slow. This is unfortunate, as the RET potential in Indonesia might be higher than currently assumed given [...] Read more.
Indonesia has an increasing electricity demand that is mostly met with fossil fuels. Although Indonesia plans to ramp up Renewable Energy Technologies (RET), implementation has been slow. This is unfortunate, as the RET potential in Indonesia might be higher than currently assumed given the archipelago’s size. However, there is no literature overview of RET potentials in Indonesia and to what extent they can meet current and future electricity demand coverage. This paper reviews contemporary literature on the potential of nine RET in Indonesia and analyses their impact in terms of area and demand coverage. The study concludes that Indonesia hosts massive amounts of renewable energy resources on both land and sea. The potentials in the academic and industrial literature tend to be considerably larger than the ones from the Indonesian Energy Ministry on which current energy policies are based. Moreover, these potentials could enable a 100% renewables electricity system and meet future demand with limited impact on land availability. Nonetheless, the review showed that the research topic is still under-researched with three detected knowledge gaps, namely the lack of (i) economic RET potentials, (ii) research on the integrated spatial potential mapping of several RET and (iii) empirical data on natural resources. Lastly, this study provides research and policy recommendations to promote RET in Indonesia. Full article
(This article belongs to the Special Issue BIWAES 2021—Biennial International Workshop Advances in Energy Studies "Empowering Communities, Beyond Energy Scarcity")
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24 pages, 2437 KiB  
Review
A Review on Kinetic Energy Harvesting with Focus on 3D Printed Electromagnetic Vibration Harvesters
by Philipp Gawron, Thomas M. Wendt, Lukas Stiglmeier, Nikolai Hangst and Urban B. Himmelsbach
Energies 2021, 14(21), 6961; https://doi.org/10.3390/en14216961 - 22 Oct 2021
Cited by 12 | Viewed by 3146
Abstract
The increasing amount of Internet of Things (IoT) devices and wearables require a reliable energy source. Energy harvesting can power these devices without changing batteries. Three-dimensional printing allows us to manufacture tailored harvesting devices in an easy and fast way. This paper presents [...] Read more.
The increasing amount of Internet of Things (IoT) devices and wearables require a reliable energy source. Energy harvesting can power these devices without changing batteries. Three-dimensional printing allows us to manufacture tailored harvesting devices in an easy and fast way. This paper presents the development of hybrid and non-hybrid 3D printed electromagnetic vibration energy harvesters. Various harvesting approaches, their utilised geometry, functional principle, power output and the applied printing processes are shown. The gathered harvesters are analysed, challenges examined and research gaps in the field identified. The advantages and challenges of 3D printing harvesters are discussed. Reported applications and strategies to improve the performance of printed harvesting devices are presented. Full article
(This article belongs to the Special Issue Advanced Energy Harvesting Technologies)
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72 pages, 10724 KiB  
Review
Technology for the Recovery of Lithium from Geothermal Brines
by William T. Stringfellow and Patrick F. Dobson
Energies 2021, 14(20), 6805; https://doi.org/10.3390/en14206805 - 18 Oct 2021
Cited by 110 | Viewed by 28738
Abstract
Lithium is the principal component of high-energy-density batteries and is a critical material necessary for the economy and security of the United States. Brines from geothermal power production have been identified as a potential domestic source of lithium; however, lithium-rich geothermal brines are [...] Read more.
Lithium is the principal component of high-energy-density batteries and is a critical material necessary for the economy and security of the United States. Brines from geothermal power production have been identified as a potential domestic source of lithium; however, lithium-rich geothermal brines are characterized by complex chemistry, high salinity, and high temperatures, which pose unique challenges for economic lithium extraction. The purpose of this paper is to examine and analyze direct lithium extraction technology in the context of developing sustainable lithium production from geothermal brines. In this paper, we are focused on the challenges of applying direct lithium extraction technology to geothermal brines; however, applications to other brines (such as coproduced brines from oil wells) are considered. The most technologically advanced approach for direct lithium extraction from geothermal brines is adsorption of lithium using inorganic sorbents. Other separation processes include extraction using solvents, sorption on organic resin and polymer materials, chemical precipitation, and membrane-dependent processes. The Salton Sea geothermal field in California has been identified as the most significant lithium brine resource in the US and past and present efforts to extract lithium and other minerals from Salton Sea brines were evaluated. Extraction of lithium with inorganic molecular sieve ion-exchange sorbents appears to offer the most immediate pathway for the development of economic lithium extraction and recovery from Salton Sea brines. Other promising technologies are still in early development, but may one day offer a second generation of methods for direct, selective lithium extraction. Initial studies have demonstrated that lithium extraction and recovery from geothermal brines are technically feasible, but challenges still remain in developing an economically and environmentally sustainable process at scale. Full article
(This article belongs to the Special Issue Sources and Markets of New Energy Minerals for Renewable Energy Generation and Storage)
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41 pages, 4211 KiB  
Review
Power Quality Phenomena, Standards, and Proposed Metrics for DC Grids
by Andrea Mariscotti
Energies 2021, 14(20), 6453; https://doi.org/10.3390/en14206453 - 9 Oct 2021
Cited by 38 | Viewed by 4046
Abstract
This work addresses the problem of power quality (PQ) metrics (or indexes) suitable for DC grids, encompassing low and medium voltage applications, including electric transports, all-electric ships and aircrafts, electric vehicles, distributed generation and microgrids, modern data centers, etc. The two main pillars [...] Read more.
This work addresses the problem of power quality (PQ) metrics (or indexes) suitable for DC grids, encompassing low and medium voltage applications, including electric transports, all-electric ships and aircrafts, electric vehicles, distributed generation and microgrids, modern data centers, etc. The two main pillars on which such PQ indexes are discussed and built are: (i) the physical justification, so the electric phenomena affecting DC grids and components (PV panels, fuel cells, capacitors, batteries, etc.), causing, e.g., stress of materials, aging, distortion, grid instability; and (ii) the existing standardization framework, pointing out desirable coverage and extension, similarity with AC grids standards, but also inconsistencies. For the first point, each phenomenon is discussed with quantitative conclusions on relevant thresholds: in many cases some percentage of distortion (ripple) is acceptable (stress on capacitors and storage, impact on fuel cells, and PV panels), whereas in other cases, much higher levels may be tolerated (interference to protection and monitoring devices). Standards are reviewed for indications not only of low-order harmonics and voltage fluctuations typical of old DC grid schemes, but also for high-frequency noise, including thus supraharmonics and common-mode disturbance, and filling the gap with the electromagnetic compatibility domain. However, phenomena typical of EMC and electrical safety (such as various types of overvoltages and fast transients) are excluded. Suitable PQ indexes are then reviewed, suggesting integrations and modifications, to cover the relevant phenomena and technological progress, and to better follow the normative exigencies: ripple is considered in time and frequency domain, in particular with a band limited implementation; for transients and pulsed loads, more traditional indexes based on area, energy, and half duration are confronted with indexes evaluating the power trajectory and its derivative. Full article
(This article belongs to the Collection Feature Papers in Smart Grids and Microgrids)
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41 pages, 4095 KiB  
Review
Thermodynamics, Energy Dissipation, and Figures of Merit of Energy Storage Systems—A Critical Review
by Efstathios E. Michaelides
Energies 2021, 14(19), 6121; https://doi.org/10.3390/en14196121 - 26 Sep 2021
Cited by 15 | Viewed by 4193
Abstract
The path to the mitigation of global climate change and global carbon dioxide emissions avoidance leads to the large-scale substitution of fossil fuels for the generation of electricity with renewable energy sources. The transition to renewables necessitates the development of large-scale energy storage [...] Read more.
The path to the mitigation of global climate change and global carbon dioxide emissions avoidance leads to the large-scale substitution of fossil fuels for the generation of electricity with renewable energy sources. The transition to renewables necessitates the development of large-scale energy storage systems that will satisfy the hourly demand of the consumers. This paper offers an overview of the energy storage systems that are available to assist with the transition to renewable energy. The systems are classified as mechanical (PHS, CAES, flywheels, springs), electromagnetic (capacitors, electric and magnetic fields), electrochemical (batteries, including flow batteries), hydrogen and thermal energy storage systems. Emphasis is placed on the magnitude of energy storage each system is able to achieve, the thermodynamic characteristics, the particular applications the systems are suitable for, the pertinent figures of merit and the energy dissipation during the charging and discharging of the systems. Full article
(This article belongs to the Section D: Energy Storage and Application)
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24 pages, 3216 KiB  
Review
Hydraulic Fracturing in Enhanced Geothermal Systems—Field, Tectonic and Rock Mechanics Conditions—A Review
by Rafał Moska, Krzysztof Labus and Piotr Kasza
Energies 2021, 14(18), 5725; https://doi.org/10.3390/en14185725 - 11 Sep 2021
Cited by 35 | Viewed by 6149
Abstract
Hydraulic fracturing (HF) is a well-known stimulation method used to increase production from conventional and unconventional hydrocarbon reservoirs. In recent years, HF has been widely used in Enhanced Geothermal Systems (EGS). HF in EGS is used to create a geothermal collector in impermeable [...] Read more.
Hydraulic fracturing (HF) is a well-known stimulation method used to increase production from conventional and unconventional hydrocarbon reservoirs. In recent years, HF has been widely used in Enhanced Geothermal Systems (EGS). HF in EGS is used to create a geothermal collector in impermeable or poor-permeable hot rocks (HDR) at a depth formation. Artificially created fracture network in the collector allows for force the flow of technological fluid in a loop between at least two wells (injector and producer). Fluid heats up in the collector, then is pumped to the surface. Thermal energy is used to drive turbines generating electricity. This paper is a compilation of selected data from 10 major world’s EGS projects and provides an overview of the basic elements needed to design HF. Authors were focused on two types of data: geological, i.e., stratigraphy, lithology, target zone deposition depth and temperature; geophysical, i.e., the tectonic regime at the site, magnitudes of the principal stresses, elastic parameters of rocks and the seismic velocities. For each of the EGS areas, the scope of work related to HF processes was briefly presented. The most important HF parameters are cited, i.e., fracturing pressure, pumping rate and used fracking fluids and proppants. In a few cases, the dimensions of the modeled or created hydraulic fractures are also provided. Additionally, the current state of the conceptual work of EGS projects in Poland is also briefly presented. Full article
(This article belongs to the Special Issue Sustainable Energy Reviews II)
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45 pages, 12227 KiB  
Review
Redox Flow Batteries: Materials, Design and Prospects
by Igor Iwakiri, Tiago Antunes, Helena Almeida, João P. Sousa, Rita Bacelar Figueira and Adélio Mendes
Energies 2021, 14(18), 5643; https://doi.org/10.3390/en14185643 - 8 Sep 2021
Cited by 37 | Viewed by 9129
Abstract
The implementation of renewable energy sources is rapidly growing in the electrical sector. This is a major step for civilization since it will reduce the carbon footprint and ensure a sustainable future. Nevertheless, these sources of energy are far from perfect and require [...] Read more.
The implementation of renewable energy sources is rapidly growing in the electrical sector. This is a major step for civilization since it will reduce the carbon footprint and ensure a sustainable future. Nevertheless, these sources of energy are far from perfect and require complementary technologies to ensure dispatchable energy and this requires storage. In the last few decades, redox flow batteries (RFB) have been revealed to be an interesting alternative for this application, mainly due to their versatility and scalability. This technology has been the focus of intense research and great advances in the last decade. This review aims to summarize the most relevant advances achieved in the last few years, i.e., from 2015 until the middle of 2021. A synopsis of the different types of RFB technology will be conducted. Particular attention will be given to vanadium redox flow batteries (VRFB), the most mature RFB technology, but also to the emerging most promising chemistries. An in-depth review will be performed regarding the main innovations, materials, and designs. The main drawbacks and future perspectives for this technology will also be addressed. Full article
(This article belongs to the Special Issue Latest Advances in Redox Flow Batteries for Solar Energy Storage)
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28 pages, 3297 KiB  
Review
Comprehensive Review on Fuel Cell Technology for Stationary Applications as Sustainable and Efficient Poly-Generation Energy Systems
by Viviana Cigolotti, Matteo Genovese and Petronilla Fragiacomo
Energies 2021, 14(16), 4963; https://doi.org/10.3390/en14164963 - 13 Aug 2021
Cited by 125 | Viewed by 14113
Abstract
Fuel cell technologies have several applications in stationary power production, such as units for primary power generation, grid stabilization, systems adopted to generate backup power, and combined-heat-and-power configurations (CHP). The main sectors where stationary fuel cells have been employed are (a) micro-CHP, (b) [...] Read more.
Fuel cell technologies have several applications in stationary power production, such as units for primary power generation, grid stabilization, systems adopted to generate backup power, and combined-heat-and-power configurations (CHP). The main sectors where stationary fuel cells have been employed are (a) micro-CHP, (b) large stationary applications, (c) UPS, and IPS. The fuel cell size for stationary applications is strongly related to the power needed from the load. Since this sector ranges from simple backup systems to large facilities, the stationary fuel cell market includes few kWs and less (micro-generation) to larger sizes of MWs. The design parameters for the stationary fuel cell system differ for fuel cell technology (PEM, AFC, PAFC, MCFC, and SOFC), as well as the fuel type and supply. This paper aims to present a comprehensive review of two main trends of research on fuel-cell-based poly-generation systems: tracking the market trends and performance analysis. In deeper detail, the present review will list a potential breakdown of the current costs of PEM/SOFC production for building applications over a range of production scales and at representative specifications, as well as broken down by component/material. Inherent to the technical performance, a concise estimation of FC system durability, efficiency, production, maintenance, and capital cost will be presented. Full article
(This article belongs to the Special Issue Environmental Aspects and Impacts of Hydrogen Technologies)
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21 pages, 6161 KiB  
Review
A Review of the Degradation of Photovoltaic Modules for Life Expectancy
by Jaeun Kim, Matheus Rabelo, Siva Parvathi Padi, Hasnain Yousuf, Eun-Chel Cho and Junsin Yi
Energies 2021, 14(14), 4278; https://doi.org/10.3390/en14144278 - 15 Jul 2021
Cited by 136 | Viewed by 13750
Abstract
Photovoltaic (PV) modules are generally considered to be the most reliable components of PV systems. The PV module has a high probability of being able to perform adequately for 30 years under typical operating conditions. In order to evaluate the long-term performance of [...] Read more.
Photovoltaic (PV) modules are generally considered to be the most reliable components of PV systems. The PV module has a high probability of being able to perform adequately for 30 years under typical operating conditions. In order to evaluate the long-term performance of a PV module under diversified terrestrial conditions, outdoor-performance data should be used. However, this requires a wait of 25 years to determine the module reliability, which is highly undesirable. Thus, accelerated-stress tests performed in the laboratory by mimicking different field conditions are important for understanding the performance of a PV module. In this paper, we discuss PV-module degradation types and different accelerated-stress types that are used to evaluate the PV-module reliability and durability for life expectancy before using them in the real field. Finally, prevention and correction measures are described to minimize economic losses. Full article
(This article belongs to the Collection Review Papers in Solar Energy and Photovoltaic Systems)
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18 pages, 1787 KiB  
Review
Life Cycle Assessment of Bioethanol Production: A Review of Feedstock, Technology and Methodology
by Tahereh Soleymani Angili, Katarzyna Grzesik, Anne Rödl and Martin Kaltschmitt
Energies 2021, 14(10), 2939; https://doi.org/10.3390/en14102939 - 19 May 2021
Cited by 40 | Viewed by 8316
Abstract
So far, a lot of efforts have been put in life cycle assessments (LCA) of bioethanol production. There are many works that have assessed bioethanol production in different points of view to illustrate the environmental impacts. This study reviewed former LCA studies on [...] Read more.
So far, a lot of efforts have been put in life cycle assessments (LCA) of bioethanol production. There are many works that have assessed bioethanol production in different points of view to illustrate the environmental impacts. This study reviewed former LCA studies on bioethanol produced from various biomass resources by considering the effect of methodological components, technical pathways and feedstock provision on the result of LCA studies. The review evaluated 48 papers published 2002–2021 with a focus on studies that included a complete set of environmental impact categories. However, due to lack of harmony among studies, comparing the LCA results was challenging but the review indicated that the final results of studies are influenced by LCA methodological components, such as system boundary, functional unit, etc. Around 80% of the reviewed papers show the reduction in global warming potential, while contrary results have been found about increasing acidification, eutrophication and photochemical oxidant formation impact categories because of the feedstock provision. Regarding technical aspects, results from the review revealed that most of the studies considered the pre-treatment as a crucial step in bioconversion processes. Despite several LCA studies of bioethanol production, there is still low attention given to uncertainty analysis in the publications. Full article
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14 pages, 497 KiB  
Review
Coping with Energy Poverty: Measurements, Drivers, Impacts, and Solutions
by George E. Halkos and Eleni-Christina Gkampoura
Energies 2021, 14(10), 2807; https://doi.org/10.3390/en14102807 - 13 May 2021
Cited by 33 | Viewed by 6108
Abstract
Energy is required for socioeconomic development, and the world’s energy needs have significantly increased in the last decades. The lack of energy can have severe impacts on a person’s well-being; therefore, energy access should be ensured for everyone in the world. Energy poverty [...] Read more.
Energy is required for socioeconomic development, and the world’s energy needs have significantly increased in the last decades. The lack of energy can have severe impacts on a person’s well-being; therefore, energy access should be ensured for everyone in the world. Energy poverty usually refers to a situation where a household cannot be kept adequately warm, but it is a complex issue with many more aspects. This paper aims to present a comprehensive review of the energy poverty problem, particularly presenting various definitions given in the literature that capture the multi-dimensional nature of the problem and analyzing the different ways of measuring energy poverty (expenditure approach and consensual approach). In addition, the impacts of the problem are identified, including health, socioeconomic, and environmental impacts, as well as the drivers that can worsen energy poverty conditions, such as several household characteristics and various socioeconomic and environmental factors. The situation occurring currently in the world is also presented, including studies that focus on different world regions, and the different solutions that can help address the problem are discussed, including changes to the living environments and the use of new technologies. Full article
(This article belongs to the Topic Exergy Analysis and Its Applications)
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24 pages, 5851 KiB  
Review
CdTe-Based Thin Film Solar Cells: Past, Present and Future
by Alessandro Romeo and Elisa Artegiani
Energies 2021, 14(6), 1684; https://doi.org/10.3390/en14061684 - 18 Mar 2021
Cited by 128 | Viewed by 12958
Abstract
CdTe is a very robust and chemically stable material and for this reason its related solar cell thin film photovoltaic technology is now the only thin film technology in the first 10 top producers in the world. CdTe has an optimum band gap [...] Read more.
CdTe is a very robust and chemically stable material and for this reason its related solar cell thin film photovoltaic technology is now the only thin film technology in the first 10 top producers in the world. CdTe has an optimum band gap for the Schockley-Queisser limit and could deliver very high efficiencies as single junction device of more than 32%, with an open circuit voltage of 1 V and a short circuit current density exceeding 30 mA/cm2. CdTe solar cells were introduced at the beginning of the 70s and they have been studied and implemented particularly in the last 30 years. The strong improvement in efficiency in the last 5 years was obtained by a new redesign of the CdTe solar cell device reaching a single solar cell efficiency of 22.1% and a module efficiency of 19%. In this paper we describe the fabrication process following the history of the solar cell as it was developed in the early years up to the latest development and changes. Moreover the paper also presents future possible alternative absorbers and discusses the only apparently controversial environmental impacts of this fantastic technology. Full article
(This article belongs to the Special Issue Photovoltaic Devices)
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23 pages, 2591 KiB  
Review
Review of Multilevel Inverters for PV Energy System Applications
by Ali Bughneda, Mohamed Salem, Anna Richelli, Dahaman Ishak and Salah Alatai
Energies 2021, 14(6), 1585; https://doi.org/10.3390/en14061585 - 12 Mar 2021
Cited by 136 | Viewed by 11235
Abstract
Over the last decade, energy demand from the power grid has increased significantly due to the increasing number of users and the emergence of high-power industries. This has led to a significant increase in global emissions with conventional energy generation. Therefore, the penetration [...] Read more.
Over the last decade, energy demand from the power grid has increased significantly due to the increasing number of users and the emergence of high-power industries. This has led to a significant increase in global emissions with conventional energy generation. Therefore, the penetration of renewable energy resources into the power grid has increased significantly. Photovoltaic systems have become the most popular resources as their protentional is enormous, thus, the worldwide installed PV capacity has increased to more than 635 gigawatts (GW), covering approximately 2% of the global electricity demand. Power electronics are an essential part of photovoltaic generation; the drive for efficient power electronic converters is gaining more and more momentum. Presently, multilevel inverters (MLI) have become more attractive to researchers compared to two-level inverters due to their abilities to provide lower electromagnetic interference, higher efficiency, and larger DC link voltages. This paper reviews multilevel inverters based on their classifications, development, and challenges with practical recommendations in utilizing them in renewable energy systems. Moreover, PV systems with various maximum power point tracking (MPPT) methods have been extensively considered in this paper as well. The importance and the development of a modified multilevel inverter are also highlighted in this review. In general, this paper focuses on utilizing multilevel inverters for PV systems to motivate and guide society to focus on inventing an efficient and economical multilevel inverter that has the combined capabilities of these converters reported in the literature. Full article
(This article belongs to the Special Issue Current Researches on Integrated DC/DC Converters)
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88 pages, 32050 KiB  
Review
Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review
by Muhammad Yaseen, Muhammad Humayun, Abbas Khan, Muhammad Usman, Habib Ullah, Asif Ali Tahir and Habib Ullah
Energies 2021, 14(5), 1278; https://doi.org/10.3390/en14051278 - 25 Feb 2021
Cited by 47 | Viewed by 7611
Abstract
Gold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The [...] Read more.
Gold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The potential catalytic applications and their enhancement upon modification of Au nanostructures have also been discussed in detail. The present analysis also offers brief summaries of the major Au nanomaterials synthetic procedures, such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapor deposition, sonochemical deposition, electrochemical deposition, microwave and laser pyrolysis. Among the various strategies used for improving the catalytic performance of nanostructured Au, the modification and functionalization of nanostructured Au produced better results. Therefore, various synthesis, modification and functionalization methods employed for better catalytic outcomes of nanostructured Au have been summarized in this review. Full article
(This article belongs to the Special Issue Photo(electro)catalytic Water Splitting for H2 Production)
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15 pages, 509 KiB  
Review
Molten Salts for Sensible Thermal Energy Storage: A Review and an Energy Performance Analysis
by Adrián Caraballo, Santos Galán-Casado, Ángel Caballero and Sara Serena
Energies 2021, 14(4), 1197; https://doi.org/10.3390/en14041197 - 23 Feb 2021
Cited by 103 | Viewed by 8847
Abstract
A comprehensive review of different thermal energy storage materials for concentrated solar power has been conducted. Fifteen candidates were selected due to their nature, thermophysical properties, and economic impact. Three key energy performance indicators were defined in order to evaluate the performance of [...] Read more.
A comprehensive review of different thermal energy storage materials for concentrated solar power has been conducted. Fifteen candidates were selected due to their nature, thermophysical properties, and economic impact. Three key energy performance indicators were defined in order to evaluate the performance of the different molten salts, using Solar Salt as a reference for low and high temperatures. The analysis provided evidence that nitrate-based materials are the best choice for the former and chloride-based materials are best for the latter instead of fluoride and carbonate-based candidates, mainly due to their low cost. Full article
(This article belongs to the Section D: Energy Storage and Application)
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