Energies

13 pages, 4136 KiB

Open AccessEditor’s ChoiceArticle

An Electric Vehicle Charge Scheduling Approach Suited to Local and Supplying Distribution Transformers

by Teguh Kurniawan, Craig A. Baguley, Udaya K. Madawala, Suwarno, Nanang Hariyanto and Yuana Adianto

Energies 2020, 13(13), 3486; https://doi.org/10.3390/en13133486 - 6 Jul 2020

Cited by 9 | Viewed by 3647

Abstract

Distribution networks with high electric vehicle (EV) penetration levels can experience transformer overloading and voltage instability issues. A charge scheduling approach is proposed to mitigate against these issues that suits smart home settings in residential areas. It comprises measurement systems located at distribution [...] Read more.

Distribution networks with high electric vehicle (EV) penetration levels can experience transformer overloading and voltage instability issues. A charge scheduling approach is proposed to mitigate against these issues that suits smart home settings in residential areas. It comprises measurement systems located at distribution transformers that communicate directly with fuzzy logic controller (FLC) systems embedded within EV supply equipment (EVSE). This realizes a reduction in data processing requirements compared to more centralized control approaches, which is advantageous for distribution networks with large numbers of transformers and EV scheduling requests. A case study employing the proposed approach is presented. Realistic driver behavior patterns, EV types, and multivariate probabilistic modeling were used to estimate EV charging demands, daily travel mileage, and plug-in times. A Monte Carlo simulation approach was developed to obtain EV charging loads. The effectiveness of mitigation in terms of reducing distribution transformer peak load levels and losses, as well as improving voltage stability is demonstrated for a distribution network in Jakarta, Indonesia. Full article

(This article belongs to the Special Issue Bidirectional Energy Transfer Technologies for Vehicle-to-Grid and Other Vehicle-to-X Applications, and Solutions to Issues Caused by High Electric Vehicle Penetration Rates)

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27 pages, 3232 KiB

Open AccessEditor’s ChoiceArticle

Life Cycle Assessment of Classic and Innovative Batteries for Solar Home Systems in Europe

by Federico Rossi, Maria Laura Parisi, Sarah Greven, Riccardo Basosi and Adalgisa Sinicropi

Energies 2020, 13(13), 3454; https://doi.org/10.3390/en13133454 - 3 Jul 2020

Cited by 22 | Viewed by 5973

Abstract

This paper presents an environmental sustainability assessment of residential user-scale energy systems, named solar home systems, encompassing their construction, operation, and end of life. The methodology adopted is composed of three steps, namely a design phase, a simulation of the solar home systems’ [...] Read more.

This paper presents an environmental sustainability assessment of residential user-scale energy systems, named solar home systems, encompassing their construction, operation, and end of life. The methodology adopted is composed of three steps, namely a design phase, a simulation of the solar home systems’ performance and a life cycle assessment. The analysis aims to point out the main advantages, features, and challenges of lithium-ion batteries, considered as a benchmark, compared with other innovative devices. As the environmental sustainability of these systems is affected by the solar radiation intensity during the year, a sensitivity analysis is performed varying the latitude of the installation site in Europe. For each site, both isolated and grid-connected solar home systems have been compared considering also the national electricity mix. A general overview of the results shows that, regardless of the installation site, solid state nickel cobalt manganese and nickel cobalt aluminium lithium-ion batteries are the most suitable choices in terms of sustainability. Remarkably, other novel devices, like sodium-ion batteries, are already competitive with them and have great potential. With these batteries, the solar home systems’ eco-profile is generally advantageous compared to the energy mix, especially in on-grid configurations, with some exceptions. Full article

(This article belongs to the Special Issue Life Cycle Assessment of Sustainable Energy System)

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14 pages, 3346 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Dependencies for Determining the Thermal Conductivity of Moist Capillary-Porous Materials

by Abdrahman Alsabry, Beata Backiel-Brzozowska and Vadzim I. Nikitsin

Energies 2020, 13(12), 3211; https://doi.org/10.3390/en13123211 - 20 Jun 2020

Cited by 5 | Viewed by 2396

Abstract

A method of determining the effective thermal conductivity of moist capillary-porous materials has been proposed, in which calculations are carried out while taking into account all components of the system (solid, liquid and gas) at once. The method makes it easy to take [...] Read more.

A method of determining the effective thermal conductivity of moist capillary-porous materials has been proposed, in which calculations are carried out while taking into account all components of the system (solid, liquid and gas) at once. The method makes it easy to take into account the way water is distributed in the pore space of the material, either as isolated inclusions (drops) or as a continuous component, depending on the moisture content of the material. In the analysis of heat transport in moist capillary-porous materials, the theory of generalized conductivity is used and the structure of moist material is modeled using an ordered geometric structure consisting of identical unit cells in the form of a cube. An equation is obtained for calculating the effective conductivity of capillary-porous materials with isolated and continuous liquid inclusions, with adiabatic and isothermal division of the unit cell. The proposed method is compared to the previously proposed method of determining the effective thermal conductivity of moist materials, in which the three-component system is gradually reduced to a binary system, showing disadvantages of this method compared to the currently proposed. It has been shown that the proposed formulas grant the possibility of a sufficiently accurate prediction of experimental results using the experimental results of the thermal conductivity of moist aerated concrete. Full article

(This article belongs to the Section G: Energy and Buildings)

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37 pages, 7221 KiB

Open AccessEditor’s ChoiceArticle

Waste to Energy: Solid Fuel Production from Biogas Plant Digestate and Sewage Sludge by Torrefaction-Process Kinetics, Fuel Properties, and Energy Balance

by Kacper Świechowski, Martyna Hnat, Paweł Stępień, Sylwia Stegenta-Dąbrowska, Szymon Kugler, Jacek A. Koziel and Andrzej Białowiec

Energies 2020, 13(12), 3161; https://doi.org/10.3390/en13123161 - 18 Jun 2020

Cited by 14 | Viewed by 4835

Abstract

Sustainable solutions are needed to manage increased energy demand and waste generation. Renewable energy production from abundant sewage sludge (SS) and digestate (D) from biogas is feasible. Concerns about feedstock contamination (heavy metals, pharmaceuticals, antibiotics, and antibiotic-resistant bacteria) in SS and D limits [...] Read more.

Sustainable solutions are needed to manage increased energy demand and waste generation. Renewable energy production from abundant sewage sludge (SS) and digestate (D) from biogas is feasible. Concerns about feedstock contamination (heavy metals, pharmaceuticals, antibiotics, and antibiotic-resistant bacteria) in SS and D limits the use (e.g., agricultural) of these carbon-rich resources. Low temperature thermal conversion that results in carbonized solid fuel (CSF) has been proposed as sustainable waste utilization. The aim of the research was to investigate the feasibility of CSF production from SS and D via torrefaction. The CSF was produced at 200~300 °C (interval of 20 °C) for 20~60 min (interval 20 min). The torrefaction kinetics and CSF fuel properties were determined. Next, the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of SS and D torrefaction were used to build models of energy demand for torrefaction. Finally, the evaluation of the energy balance of CSF production from SS and D was completed. The results showed that torrefaction improved the D-derived CSF’s higher heating value (HHV) up to 11% (p < 0.05), whereas no significant HHV changes for SS were observed. The torrefied D had the highest HHV of 20 MJ∙kg⁻¹ under 300 °C and 30 min, (the curve fitted value from the measured time periods) compared to HHV = 18 MJ∙kg⁻¹ for unprocessed D. The torrefied SS had the highest HHV = 14.8 MJ∙kg⁻¹ under 200 °C and 20 min, compared to HHV 14.6 MJ∙kg⁻¹ for raw SS. An unwanted result of the torrefaction was an increase in ash content in CSF, up to 40% and 22% for SS and D, respectively. The developed model showed that the torrefaction of dry SS and D could be energetically self-sufficient. Generating CSF with the highest HHV requires raw feedstock containing ~15.4 and 45.9 MJ∙kg⁻¹ for SS and D, respectively (assuming that part of feedstock is a source of energy for the process). The results suggest that there is a potential to convert biogas D to CSF to provide renewable fuel for, e.g., plants currently fed/co-fed with municipal solid waste. Full article

(This article belongs to the Special Issue Materials Recycling and Energy Use of Waste)

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20 pages, 4936 KiB

Open AccessEditor’s ChoiceArticle

A Real-Time Dynamic Fuel Cell System Simulation for Model-Based Diagnostics and Control: Validation on Real Driving Data

by Daniel Ritzberger, Christoph Hametner and Stefan Jakubek

Energies 2020, 13(12), 3148; https://doi.org/10.3390/en13123148 - 17 Jun 2020

Cited by 18 | Viewed by 4733

Abstract

Fuel cell systems are regarded as a promising candidate in replacing the internal combustion engine as a renewable and emission free alternative in automotive applications. However, the operation of a fuel cell stack fulfilling transient power-demands poses significant challenges. Efficiency is to be [...] Read more.

Fuel cell systems are regarded as a promising candidate in replacing the internal combustion engine as a renewable and emission free alternative in automotive applications. However, the operation of a fuel cell stack fulfilling transient power-demands poses significant challenges. Efficiency is to be maximized while adhering to critical constraints, avoiding adverse operational conditions (fuel starvation, membrane flooding or drying, etc.) and mitigating degradation as to increase the life-time of the stack. Owing to this complexity, advanced model-based diagnostic and control methods are increasingly investigated. In this work, a real time stack model is presented and its experimental parameterization is discussed. Furthermore, the stack model is integrated in a system simulation, where the compressor dynamics, the feedback controls for the hydrogen injection and back-pressure valve actuation, and the purging strategy are considered. The resulting system simulation, driven by the set-point values of the operating strategy is evaluated and validated on experimental data obtained from a fuel cell vehicle during on-road operation. It will be shown how the internal states of the fuel cell simulation evolve during the transient operation of the fuel cell vehicle. The measurement data, for which this analysis is conducted, stem from a fuel cell research and demonstrator vehicle, developed by a consortium of several academic and industrial partners under the lead of AVL List GmbH. Full article

(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cell Systems)

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21 pages, 16732 KiB

Open AccessEditor’s ChoiceArticle

Partial Discharge Behaviour of a Protrusion in Gas-Insulated Systems under DC Voltage Stress

by Thomas Götz, Hannah Kirchner and Karsten Backhaus

Energies 2020, 13(12), 3102; https://doi.org/10.3390/en13123102 - 16 Jun 2020

Cited by 12 | Viewed by 3999

Abstract

High reliability, independence from environmental conditions, and the compact design of gas-insulated systems will lead to a wide application in future high voltage direct current (HVDC) transmission systems. Reliable operation of these assets can be ensured by applying meaningful and robust partial discharge [...] Read more.

High reliability, independence from environmental conditions, and the compact design of gas-insulated systems will lead to a wide application in future high voltage direct current (HVDC) transmission systems. Reliable operation of these assets can be ensured by applying meaningful and robust partial discharge diagnosis during development tests, acceptance tests, or operation. Therefore, the discharge behavior must be well understood. This paper aims to contribute to this understanding by investigating the partial discharge behavior of a distorted weakly inhomogeneous electrode arrangement in sulfur hexafluoride (SF₆) and synthetic air under high DC voltage stress. In order to get a better understanding, the partial discharge current is measured under the variation of the insulation gas pressure, the gas type, the electric field strength, and the voltage polarity. Derived from this, a classification of the different discharge types is performed. As a result, four different discharge types can be categorized depending on the experimental parameters: discharge impulses, discharge impulses with superimposed pulseless discharges, discharge impulses with superimposed pulseless discharges, and subsequent smaller discharges and pulseless discharges. Concluding suggestions for partial discharge measurements under DC voltage stress are given: recommendations for the necessary measurement time, the applied voltage and polarity, and useful measurement techniques. Full article

(This article belongs to the Special Issue Outdoor Insulation and Gas Insulated Switchgears)

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33 pages, 7279 KiB

Open AccessEditor’s ChoiceArticle

Unlocking the Effects of Fluid Optimization on Remaining Oil Saturation for the Combined Sulfate-Modified Water and Polymer Flooding

by Muhammad Tahir, Rafael E. Hincapie and Leonhard Ganzer

Energies 2020, 13(12), 3049; https://doi.org/10.3390/en13123049 - 12 Jun 2020

Cited by 7 | Viewed by 3135

Abstract

Interfacial interactions and wettability alteration remain as the main recovery mechanism when modified water is applied seeking to obtain higher oil recoveries. Fluid-fluid interaction could lead to the development of the called viscoelastic layer at the interface in oil-brine systems. This interfacial layer [...] Read more.

Interfacial interactions and wettability alteration remain as the main recovery mechanism when modified water is applied seeking to obtain higher oil recoveries. Fluid-fluid interaction could lead to the development of the called viscoelastic layer at the interface in oil-brine systems. This interfacial layer stabilizes thanks to the slow chemical interaction between oil polar compounds and salts in the brine. This study investigates the role of sulfate presence in injection brine that could possible lead to develop the interfacial viscoelastic layer and hence to contribute to the higher oil recovery. Furthermore, polymer flooding is performed in tertiary mode after brine flood to investigate/unlock the synergies and potential benefits of the hybrid enhanced oil recovery. Brine optimization is performed using the composition of two formation brines and four injection brines. Moreover, interfacial tension measurements and oil drop snap-off volume measurements are performed in parallel with the core flooding experiments to define the role of interfacial viscoelasticity as the recovery mechanism other than wettability alteration. Synthetic seawater spiked with double amount of sulfate depicted potential results of interfacial viscoelastic layer development and hence to contribute the higher oil recovery. Total oil recovery after secondary-mode using sulfate-modified water and tertiary-mode polymer flood was higher than the combination of seawater brine in secondary-mode and polymer flood in tertiary-mode. Nevertheless, experiments helped us concluding that the amount of sulfate added is a critical factor to obtain maximum oil recovery and to avoid pore-plugging problems. We, therefore, demonstrate that executing a detailed fluid optimization leads to promising laboratory results, potentially linked with an improvement in the economics of the field applications. Full article

(This article belongs to the Special Issue Enhanced Oil Recovery 2020)

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11 pages, 1809 KiB

Open AccessEditor’s ChoiceArticle

An Aqueous CaCl₂ Solution in the Condenser/Evaporator Instead of Pure Water: Application for the New Adsorptive Cycle “Heat from Cold”

by Ilya Girnik and Yuri Aristov

Energies 2020, 13(11), 2904; https://doi.org/10.3390/en13112904 - 5 Jun 2020

Cited by 5 | Viewed by 3582

Abstract

This paper addresses the analysis of the applicability of water as a working fluid for the new adsorptive heat transformation (AHT) cycle "Heat from Cold" (HeCol). The cycle proposed for cold countries operates at the ambient temperature below 0 °C. In this work, [...] Read more.

This paper addresses the analysis of the applicability of water as a working fluid for the new adsorptive heat transformation (AHT) cycle "Heat from Cold" (HeCol). The cycle proposed for cold countries operates at the ambient temperature below 0 °C. In this work, an aqueous solution of calcium chloride is proposed instead of liquid water to prevent the ice formation in the evaporator and condenser. The proposed water-based cycle is compared with the common methanol-based HeCol one in terms of the specific useful heat generated per cycle. The effect of the CaCl₂ solution on the cycle boundary pressures and its useful heat is studied both theoretically and experimentally. This approach can be extended to other adsorptive heat transformation cycles working at an evaporator or condenser temperature below 0 °C. Full article

(This article belongs to the Special Issue Adsorptive Systems for Heat Transformation and Heat Storage Applications)

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17 pages, 5197 KiB

Open AccessEditor’s ChoiceArticle

Comparative Building Energy Simulation Study of Static and Thermochromically Adaptive Energy-Efficient Glazing in Various Climate Regions

by Daniel Mann, Cindy Yeung, Roberto Habets, Zeger Vroon and Pascal Buskens

Energies 2020, 13(11), 2842; https://doi.org/10.3390/en13112842 - 3 Jun 2020

Cited by 33 | Viewed by 7112

Abstract

The building sector contributes approximately one third of the total energy consumption worldwide. A large part of this energy is used for the heating and cooling of buildings, which can be drastically reduced by use of energy-efficient glazing. In this study, we performed [...] Read more.

The building sector contributes approximately one third of the total energy consumption worldwide. A large part of this energy is used for the heating and cooling of buildings, which can be drastically reduced by use of energy-efficient glazing. In this study, we performed building energy simulations on a prototypical residential building, and compared commercially available static (low-e, solar IR blocking) to newly developed adaptive thermochromic glazing systems for various climate regions. The modeling results show that static energy-efficient glazing is mainly optimized for either hot climates, where low solar heat gain can reduce cooling demands drastically, or cold climates, where low-e properties have a huge influence on heating demands. For intermediate climates, we demonstrate that adaptive thermochromic glazing in combination with a low-e coating is perfectly suited. The newly developed thermochromic glazing can lead to annual energy consumption improvement of up to 22% in comparison to clear glass, which exceeds all other glazing systems. Furthermore, we demonstrate that in the Netherlands the use of this new glazing system can lead to annual cost savings of EU 638 per dwelling (172 m², 25% window façade), and to annual nationwide CO₂ savings of 4.5 Mt. Ergo, we show that further development of thermochromic smart windows into market-ready products can have a huge economic, ecological and societal impact on all intermediate climate region in the northern hemisphere. Full article

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30 pages, 3790 KiB

Open AccessEditor’s ChoiceReview

Wireless Power Transfer for Implanted Medical Application: A Review

by Yujing Zhou, Chunhua Liu and Yongcan Huang

Energies 2020, 13(11), 2837; https://doi.org/10.3390/en13112837 - 2 Jun 2020

Cited by 102 | Viewed by 11875

Abstract

With ever-increasing concerns on health and environmental safety, there is a fast-growing interest in new technologies for medical devices and applications. Particularly, wireless power transfer (WPT) technology provides reliable and convenient power charging for implant medical devices without additional surgery. For those WPT [...] Read more.

With ever-increasing concerns on health and environmental safety, there is a fast-growing interest in new technologies for medical devices and applications. Particularly, wireless power transfer (WPT) technology provides reliable and convenient power charging for implant medical devices without additional surgery. For those WPT medical systems, the width of the human body restricts the charging distance, while the specific absorption rate (SAR) standard limits the intensity of the electromagnetic field. In order to develop a high-efficient charging strategy for medical implants, the key factors of transmission distance, coil structure, resonant frequency, etc. are paid special attention. In this paper, a comprehensive overview of near-field WPT technologies in medical devices is presented and discussed. Also, future development is discussed for the prediction of different devices when embedded in various locations of the human body. Moreover, the key issues including power transfer efficiency and output power are addressed and analyzed. All concerning characteristics of WPT links for medical usage are elaborated and discussed. Thus, this review provides an in-depth investigation and the whole map for WPT technologies applied in medical applications. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 1275 KiB

Open AccessEditor’s ChoiceArticle

Machine Learning Modeling of Horizontal Photovoltaics Using Weather and Location Data

by Christil Pasion, Torrey Wagner, Clay Koschnick, Steven Schuldt, Jada Williams and Kevin Hallinan

Energies 2020, 13(10), 2570; https://doi.org/10.3390/en13102570 - 19 May 2020

Cited by 25 | Viewed by 5384

Abstract

Solar energy is a key renewable energy source; however, its intermittent nature and potential for use in distributed systems make power prediction an important aspect of grid integration. This research analyzed a variety of machine learning techniques to predict power output for horizontal [...] Read more.

Solar energy is a key renewable energy source; however, its intermittent nature and potential for use in distributed systems make power prediction an important aspect of grid integration. This research analyzed a variety of machine learning techniques to predict power output for horizontal solar panels using 14 months of data collected from 12 northern-hemisphere locations. We performed our data collection and analysis in the absence of irradiation data—an approach not commonly found in prior literature. Using latitude, month, hour, ambient temperature, pressure, humidity, wind speed, and cloud ceiling as independent variables, a distributed random forest regression algorithm modeled the combined dataset with an R² value of 0.94. As a comparative measure, other machine learning algorithms resulted in R² values of 0.50–0.94. Additionally, the data from each location was modeled separately with R² values ranging from 0.91 to 0.97, indicating a range of consistency across all sites. Using an input variable permutation approach with the random forest algorithm, we found that the three most important variables for power prediction were ambient temperature, humidity, and cloud ceiling. The analysis showed that machine learning potentially allowed for accurate power prediction while avoiding the challenges associated with modeled irradiation data. Full article

(This article belongs to the Section A2: Solar Energy and Photovoltaic Systems)

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24 pages, 2029 KiB

Open AccessEditor’s ChoiceArticle

A Coordination Mechanism For Reducing Price Spikes in Distribution Grids

by Shantanu Chakraborty, Remco Verzijlbergh, Kyri Baker, Milos Cvetkovic, Laurens De Vries and Zofia Lukszo

Energies 2020, 13(10), 2500; https://doi.org/10.3390/en13102500 - 15 May 2020

Cited by 3 | Viewed by 3203

Abstract

Recently, given the increased integration of renewables and growing uncertainty in demand, the wholesale market price has become highly volatile. Energy communities connected to the main electricity grid may be exposed to this increasing price volatility. Additionally, they may also be exposed to [...] Read more.

Recently, given the increased integration of renewables and growing uncertainty in demand, the wholesale market price has become highly volatile. Energy communities connected to the main electricity grid may be exposed to this increasing price volatility. Additionally, they may also be exposed to local network congestions, resulting in price spikes. Motivated by this problem, in this paper, we present a coordination mechanism between entities at the distribution grid to reduce price volatility. The mechanism relies on the concept of duality theory in mathematical programming through which explicit constraints can be imposed on the local electricity price. Constraining the dual variable related to price enables the quantification of the demand-side flexibility required to guarantee a certain price limit. We illustrate our approach with a case study of a congested distribution grid and an energy storage system as the source of the required demand-side flexibility. Through detailed simulations, we determine the optimal size and operation of the storage system required to constrain prices. An economic evaluation of the case study shows that the business case for providing the contracted flexibility with the storage system depends strongly on the chosen price limit. Full article

(This article belongs to the Special Issue Flexibility in Distribution Systems from EVs and Batteries)

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24 pages, 4098 KiB

Open AccessEditor’s ChoiceArticle

The Role of Powertrain Electrification in Achieving Deep Decarbonization in Road Freight Transport

by Juan C. González Palencia, Van Tuan Nguyen, Mikiya Araki and Seiichi Shiga

Energies 2020, 13(10), 2459; https://doi.org/10.3390/en13102459 - 13 May 2020

Cited by 33 | Viewed by 5126

Abstract

Decarbonizing road freight transport is difficult due to its reliance on fossil fuel internal combustion engine vehicles (ICEVs). The role of powertrain electrification in achieving deep decarbonization in road freight transport was studied using a vehicle stock turnover model, focusing on Japan. Twelve [...] Read more.

Decarbonizing road freight transport is difficult due to its reliance on fossil fuel internal combustion engine vehicles (ICEVs). The role of powertrain electrification in achieving deep decarbonization in road freight transport was studied using a vehicle stock turnover model, focusing on Japan. Twelve vehicle types were considered; combining four powertrains, ICEV, hybrid electric vehicle (HEV), battery electric vehicle (BEV) and fuel cell electric vehicle (FCEV); and three vehicle size classes, normal, compact and mini-sized vehicles. A scenario-based approach was used; considering a Base scenario, and three alternative scenarios targeting powertrain electrification. Between 2012 and 2050, tank to wheel CO₂ emissions decrease 42.8% in the Base scenario, due to the reduction of vehicle stock, the improvement of vehicle fuel consumption and the adoption of HEVs. Diffusion of FCEVs in normal vehicles and BEVs in compact and mini-sized vehicles achieves the largest tank to wheel CO₂ emissions reductions, up to 44.6% compared with the 2050 baseline value. The net cash flow is positive over the whole time horizon, peaking at 6.7 billion USD/year in 2049 and reaching 6.6 billion USD/year by 2050. Powertrain electrification is not enough to achieve any of the CO₂ emissions reduction targets in road freight transport. Full article

(This article belongs to the Special Issue Electric Systems for Transportation)

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19 pages, 5463 KiB

Open AccessEditor’s ChoiceArticle

The Application of Hierarchical Clustering to Power Quality Measurements in an Electrical Power Network with Distributed Generation

by Michał Jasiński, Tomasz Sikorski, Zbigniew Leonowicz, Klaudiusz Borkowski and Elżbieta Jasińska

Energies 2020, 13(9), 2407; https://doi.org/10.3390/en13092407 - 11 May 2020

Cited by 17 | Viewed by 3824

Abstract

This article presents the application of data mining (DM) to long-term power quality (PQ) measurements. The Ward algorithm was selected as the cluster analysis (CA) technique to achieve an automatic division of the PQ measurement data. The measurements were conducted in an electrical [...] Read more.

This article presents the application of data mining (DM) to long-term power quality (PQ) measurements. The Ward algorithm was selected as the cluster analysis (CA) technique to achieve an automatic division of the PQ measurement data. The measurements were conducted in an electrical power network (EPN) of the mining industry with distributed generation (DG). The obtained results indicate that the application of the Ward algorithm to PQ data assures the division with regards to the work of the distributed generation, and also to other important working conditions (e.g., reconfiguration or high harmonic pollution). The presented analysis is conducted for the area-related approach—all measurement point data are connected at an initial stage. The importance rate was proposed in order to indicate the parameters that have a high impact on the classification of the data. Another element of the article was the reduction of the size of the input database. The reduction of input data by 57% assured the classification with a 95% agreement when compared to the complete database classification. Full article

(This article belongs to the Special Issue Signal Analysis in Power Systems)

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27 pages, 752 KiB

Open AccessEditor’s ChoiceReview

Synergies and Trade-Offs Between Sustainable Development and Energy Performance of Exterior Lighting

by Annika K. Jägerbrand

Energies 2020, 13(9), 2245; https://doi.org/10.3390/en13092245 - 3 May 2020

Cited by 24 | Viewed by 4242

Abstract

The aim of this review was to map synergies and trade-offs between sustainable development and energy efficiency and savings regarding exterior lighting. Exterior lighting, such as public road and street lighting, requires significant amounts of energy and hinders sustainable development through its increasing [...] Read more.

The aim of this review was to map synergies and trade-offs between sustainable development and energy efficiency and savings regarding exterior lighting. Exterior lighting, such as public road and street lighting, requires significant amounts of energy and hinders sustainable development through its increasing of light pollution, ecological impact, and global climate change. Interlinkages between indicators in sustainability and energy that have positive interactions will lead to a mutual reinforcement in the decision-making process, and vice versa, interlinkages between trade-offs may lead to unwanted and conflicting effects. Very few studies have presented a clear vision of how exterior lighting should be contributing to, and not counteracting, the sustainable development of our planet. This study was conducted through a theoretical and systematic analysis that examined the interactions between sustainable development and energy performance based on a framework using indicators and variables, and by reviewing the current literature. Additionally, 17 indicators of energy efficiency and energy savings were identified and used in the analysis. Most interactions between variables for sustainable development and energy performance (52%) were found to be synergistic. The synergistic interactions were mostly found (71%) in the ecological and environmental dimension showing that environmental and ecological sustainability goes hand in hand with energy efficiency and savings. Trade-offs were found only in the economic and social dimensions accounting for 18% of the interactions identified. This review shows that the interactions between sustainable development and energy performance can be used to establish more efficient policies for decision-making processes regarding exterior lighting. Full article

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20 pages, 1494 KiB

Open AccessEditor’s ChoiceArticle

Energy Vision Strategies for the EU Green New Deal: A Case Study of European Cities

by David Maya-Drysdale, Louise Krog Jensen and Brian Vad Mathiesen

Energies 2020, 13(9), 2194; https://doi.org/10.3390/en13092194 - 2 May 2020

Cited by 34 | Viewed by 6032

Abstract

There are three strategic levels for successful energy planning in cities: 1) Integration strategy for integrating energy planning into urban planning institutions; 2) Practice strategy for developing suitable energy planning practices in urban planning institutions, and 3) Vision strategy for the creation and [...] Read more.

There are three strategic levels for successful energy planning in cities: 1) Integration strategy for integrating energy planning into urban planning institutions; 2) Practice strategy for developing suitable energy planning practices in urban planning institutions, and 3) Vision strategy for the creation and integration of energy visions and scenarios required for long-term decarbonisation. The vision strategy is critical but not well researched and is the focus of this article. Using Strategic Energy Planning (SEP) as an analytical framework, the vision strategy of eight forerunner European cities are analysed. Some critical elements of SEP include the use of long-term targets, holistic energy system thinking, and retention of scenarios. The results indicate that the level of understanding and practice of the vision strategy is still deficient in the cities. Cities often use the practice of urban planning, which does not fit very well with energy planning, particularly with the vision strategy. The energy planning in the cities mostly focuses on shorter-term goals and actions, and they often abandon energy scenarios once extracted. However, through trial and error, some cities are finding ways forward. The article concludes with several recommendations, particularly that cities need to see scenarios as retainable long-term servants providing information desired by the planner, rather than serving as a guide to the planner. Full article

(This article belongs to the Special Issue Municipal Energy System Planning: New Approaches, Applications and Future Research Needs)

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18 pages, 3037 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Application of Molten Salt Energy Storage to Advance the Transition from Coal to Green Energy Power Systems

by Wojciech Kosman and Andrzej Rusin

Energies 2020, 13(9), 2222; https://doi.org/10.3390/en13092222 - 2 May 2020

Cited by 20 | Viewed by 3734

Abstract

The paper presents technical solutions for a power grid that undergoes the elimination of a significant number of coal-based power generating units. The purpose of the solutions is to adapt the existing machines with sufficient lifespans to the new operating conditions. In particular [...] Read more.

The paper presents technical solutions for a power grid that undergoes the elimination of a significant number of coal-based power generating units. The purpose of the solutions is to adapt the existing machines with sufficient lifespans to the new operating conditions. In particular these include steam turbines. The steam turbines’ cycles may be extended with energy storage systems based on a molten salt. This allows to increase the flexibility of the power generating units while maintaining the largest possible efficiency of the power generation. The solutions presented here allow to connect the steam turbines cycles to renewable energy sources and reduce the overall number of the units that create the fundamental layer of the power grid. The analysis of the solutions involves numerical modeling. The paper describes the assumptions and the results of the modeling for chosen cases of the modernization. The researched considered a number of options that differed in the investment costs and the resulting performance. Full article

(This article belongs to the Special Issue Advanced Mathematical Modeling Technology for Heat Storage and Conversion Systems)

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18 pages, 3616 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Renewable and Nuclear Energy Consumption on Decoupling Economic Growth from CO₂ Emissions in Spain

by Mariola Piłatowska, Andrzej Geise and Aneta Włodarczyk

Energies 2020, 13(9), 2124; https://doi.org/10.3390/en13092124 - 25 Apr 2020

Cited by 79 | Viewed by 7045

Abstract

This study examines the relationship between renewable and nuclear energy consumption, carbon dioxide emissions and economic growth by using the Granger causality and non-linear impulse response function in a business cycle in Spain. We estimate the threshold vector autoregression (TVAR) model on the [...] Read more.

This study examines the relationship between renewable and nuclear energy consumption, carbon dioxide emissions and economic growth by using the Granger causality and non-linear impulse response function in a business cycle in Spain. We estimate the threshold vector autoregression (TVAR) model on the basis of annual data from the period 1970–2018, which are disaggregated into quarterly data to obtain robust empirical results through avoiding a sample size problem. Our analysis reveals that economic growth and CO₂ emissions are positively correlated during expansions but not during recessions. Moreover, we find that rising nuclear energy consumption leads to decreased CO₂ emissions during expansions, while the impact of increasing renewable energy consumption on emissions is negative but insignificant. In addition, there is a positive feedback between nuclear energy consumption and economic growth, but unidirectional positive causality running from renewable energy consumption to economic growth in upturns. Our findings do indicate that both nuclear and renewable energy consumption contribute to a reduction in emissions; however, the rise in economic activity, leading to a greater increase in emissions, offsets this positive impact of green energy. Therefore, a decoupling of economic growth from CO₂ emissions is not observed. These results demand some crucial changes in legislation targeted at reducing emissions, as green energy alone is insufficient to reach this goal. Full article

(This article belongs to the Section C: Energy Economics and Policy)

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25 pages, 7419 KiB

Open AccessEditor’s ChoiceArticle

Wave Power Absorption by Arrays of Wave Energy Converters in Front of a Vertical Breakwater: A Theoretical Study

by Dimitrios N. Konispoliatis and Spyridon A. Mavrakos

Energies 2020, 13(8), 1985; https://doi.org/10.3390/en13081985 - 17 Apr 2020

Cited by 23 | Viewed by 3568

Abstract

The present paper deals with the theoretical evaluation of the efficiency of an array of cylindrical Wave Energy Converters (WECs) having a vertical symmetry axis and placed in front of a reflecting vertical breakwater. Linear potential theory is assumed, and the associated diffraction [...] Read more.

The present paper deals with the theoretical evaluation of the efficiency of an array of cylindrical Wave Energy Converters (WECs) having a vertical symmetry axis and placed in front of a reflecting vertical breakwater. Linear potential theory is assumed, and the associated diffraction and motion radiation problems are solved in the frequency domain. Axisymmetric eigenfunction expansions of the velocity potential are introduced into properly defined ring-shaped fluid regions surrounding each body of the array. The potential solutions are matched at the boundaries of adjacent fluid regions by enforcing continuity of the hydrodynamic pressures and redial velocities. A theoretical model for the evaluation of the WECs’ performance is developed. The model properly accounts for the effect of the breakwater on each body’s hydrodynamic characteristics and the coupling between the bodies’ motions and the power take-off mechanism. Numerical results are presented and discussed in terms of the expected power absorption. The results show how the efficiency of the array is affected by (a) the distance between the devices and the wall, (b) the shape of the WEC array configuration, as well as (c) the angle of the incoming incident wave. Full article

(This article belongs to the Section A3: Wind, Wave and Tidal Energy)

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17 pages, 2005 KiB

Open AccessEditor’s ChoiceArticle

Experimental Assessment of Flow, Performance, and Loads for Tidal Turbines in a Closely-Spaced Array

by Donald R. Noble, Samuel Draycott, Anup Nambiar, Brian G. Sellar, Jeffrey Steynor and Aristides Kiprakis

Energies 2020, 13(8), 1977; https://doi.org/10.3390/en13081977 - 16 Apr 2020

Cited by 34 | Viewed by 6031

Abstract

Tidal stream turbines are subject to complex flow conditions, particularly when installed in staggered array configurations where the downstream turbines are affected by the wake and/or bypass flow of upstream turbines. This work presents, for the first time, methods for and results from [...] Read more.

Tidal stream turbines are subject to complex flow conditions, particularly when installed in staggered array configurations where the downstream turbines are affected by the wake and/or bypass flow of upstream turbines. This work presents, for the first time, methods for and results from the physical testing of three 1/15 scale instrumented turbines configured in a closely-spaced staggered array, and demonstrates experimentally that increased power extraction can be achieved through reduced array separation. A comprehensive set of flow measurements was taken during several weeks testing in the FloWave Ocean Energy Research Facility, with different configurations of turbines installed in the tank in a current of

0.8

m/s, to understand the effect that the front turbines have on flow through the array and on the inflow to the centrally placed rearmost turbine. Loads on the turbine structure, rotor, and blade roots were measured along with the rotational speed of the rotor to assess concurrently in real-time the effects of flow and array geometry on structural loading and performance. Operating in this closely-spaced array was found to improve the power delivered by the rear turbine by 5.7–10.4% with a corresponding increase in the thrust loading on the rotor of 4.8–7.3% around the peak power operating point. The experimental methods developed and results arising from this work will also be useful for further scale-testing elsewhere, validating numerical models, and for understanding the performance and loading of full-scale tidal stream turbines in arrays. Full article

(This article belongs to the Section A3: Wind, Wave and Tidal Energy)

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16 pages, 2492 KiB

Open AccessEditor’s ChoiceArticle

Thermochromic Paints on External Surfaces: Impact Assessment for a Residential Building through Thermal and Energy Simulation

by Vasco Granadeiro, Margarida Almeida, Tiago Souto, Vítor Leal, João Machado and Adélio Mendes

Energies 2020, 13(8), 1912; https://doi.org/10.3390/en13081912 - 14 Apr 2020

Cited by 22 | Viewed by 7278

Abstract

This work addresses the effect of using thermochromic paints in residential buildings. Two different thermochromic paint types were considered: One that changes properties through a step transition at a certain temperature, and another that changes properties in a gradual/linear manner throughout a temperature [...] Read more.

This work addresses the effect of using thermochromic paints in residential buildings. Two different thermochromic paint types were considered: One that changes properties through a step transition at a certain temperature, and another that changes properties in a gradual/linear manner throughout a temperature range. The studied building was a two-floor villa, virtually simulated through a digital model with and without thermal insulation, and considering thermochromic paints applied both on external walls and on the roof. The performance assessment was done through the energy use for heating and cooling (in conditioned mode), as well as in terms of the indoor temperature (in free-floating mode). Three different cities/climates were considered: Porto, Madrid, and Abu Dhabi. Results showed that energy savings up to 50.6% could be reached if the building is operated in conditioned mode. Conversely, when operated in free-floating mode, optimally selected thermochromic paints enable reductions up to 11.0 °C, during summertime, and an increase up to 2.7 °C, during wintertime. These results point out the great benefits of using optimally selected thermochromic paints for obtaining thermal comfort, and also the need to further develop stable and cost-effective thermochromic pigments for outdoor applications, as well as to test physical models in a real environment. Full article

(This article belongs to the Special Issue Buildings Energy Efficiency and Innovative Energy Systems)

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10 pages, 1031 KiB

Open AccessFeature PaperEditor’s ChoiceCommentary

Will Electric Vehicles Be Killed (again) or Are They the Next Mobility Killer App?

by Christian Thiel, Anastasios Tsakalidis and Arnulf Jäger-Waldau

Energies 2020, 13(7), 1828; https://doi.org/10.3390/en13071828 - 10 Apr 2020

Cited by 26 | Viewed by 7292

Abstract

Electric vehicles (EVs) have been around for more than a hundred years. Nevertheless, their deployment has not been a sustainable success up until now. Many scientists, engineers and policymakers argue that EVs are a promising, maybe even indispensable option to achieve ambitious decarbonization [...] Read more.

Electric vehicles (EVs) have been around for more than a hundred years. Nevertheless, their deployment has not been a sustainable success up until now. Many scientists, engineers and policymakers argue that EVs are a promising, maybe even indispensable option to achieve ambitious decarbonization goals, if powered by electricity from renewable energy sources. At the moment, the EVs market is gaining a lot of momentum and we may be near the point of no return for a sustained mass market deployment of electric vehicles. Many papers exist that describe future prospects of EVs. In our commentary we try to provide a bigger picture view and look at market and societal aspects. We analyze why previous generations of EVs were not successful and how current electric vehicles could become a sustainable success. We perform a semi-quantitative Strengths, Weaknesses, Opportunities, Threats (SWOT) analysis and find that current electric vehicle designs are technologically on par with or better than conventional alternatives. Car buyers go electric when the economics make sense to them. We conclude that incentives are needed for electric vehicles until battery costs lower—as much as to allow EVs to become cheaper—from a total cost of ownership (TCO) perspective, than other alternatives. Other policy measures are needed to overcome remaining barriers, especially in supporting the setup and operation of publicly accessible recharging points to overcome range anxiety. EVs in isolation may not be the next mobility killer app. The real next mobility killer app may emerge as an autonomous shared EV in a world where the border between public and private transport will cease to exist. The findings of our commentary are relevant for scientists, policymakers and industry. Full article

(This article belongs to the Section E: Electric Vehicles)

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11 pages, 3677 KiB

Open AccessEditor’s ChoiceArticle

Recursive State of Charge and State of Health Estimation Method for Lithium-Ion Batteries Based on Coulomb Counting and Open Circuit Voltage

by Alejandro Gismero, Erik Schaltz and Daniel-Ioan Stroe

Energies 2020, 13(7), 1811; https://doi.org/10.3390/en13071811 - 9 Apr 2020

Cited by 80 | Viewed by 5896

Abstract

The state of charge (SOC) and state of health (SOH) are two crucial indicators needed for a proper and safe operation of the battery. Coulomb counting is one of the most adopted and straightforward methods to calculate the SOC. Although it can be [...] Read more.

The state of charge (SOC) and state of health (SOH) are two crucial indicators needed for a proper and safe operation of the battery. Coulomb counting is one of the most adopted and straightforward methods to calculate the SOC. Although it can be implemented for all kinds of applications, its accuracy is strongly dependent on the operation conditions. In this work, the behavior of the batteries at different current and temperature conditions is analyzed in order to adjust the charge measurement according to the battery efficiency at the specific operating conditions. The open-circuit voltage (OCV) is used to reset the SOC estimation and prevent the error accumulation. Furthermore, the SOH is estimated by evaluating the accumulated charge between two different SOC using a recursive least squares (RLS) method. The SOC and SOH estimations are verified through an extensive test in which the battery is subjected to a dynamic load profile at different temperatures. Full article

(This article belongs to the Special Issue Energy Storage Systems for Electric Vehicles)

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18 pages, 6085 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Electric Vehicle–Grid Integration with Voltage Regulation in Radial Distribution Networks

by Chong Cao, Zhouquan Wu and Bo Chen

Energies 2020, 13(7), 1802; https://doi.org/10.3390/en13071802 - 8 Apr 2020

Cited by 26 | Viewed by 3879

Abstract

In this paper, a vehicle–grid integration (VGI) control strategy for radial power distribution networks is presented. The control schemes are designed at both microgrid level and distribution level. At the VGI microgrid level, the available power capacity for electric vehicle (EV) charging is [...] Read more.

In this paper, a vehicle–grid integration (VGI) control strategy for radial power distribution networks is presented. The control schemes are designed at both microgrid level and distribution level. At the VGI microgrid level, the available power capacity for electric vehicle (EV) charging is optimally allocated for charging electric vehicles to meet charging requirements. At the distribution grid level, a distributed voltage compensation algorithm is designed to recover voltage violation when it happens at a distribution node. The voltage compensation is achieved through a negotiation between the grid-level agent and VGI microgrid agents using the alternating direction method of multipliers. In each negotiation round, individual agents pursue their own objectives. The computation can be carried out in parallel for each agent. The presented VGI control schemes are simulated and verified in a modified IEEE 37 bus distribution system. The simulation results are presented to show the effectiveness of the VGI control algorithms and the effect of algorithm parameters on the convergence of agent negotiation. Full article

(This article belongs to the Special Issue Electric Systems for Transportation)

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22 pages, 8785 KiB

Open AccessEditor’s ChoiceArticle

Single-Solution-Based Vortex Search Strategy for Optimal Design of Offshore and Onshore Natural Gas Liquefaction Processes

by Muhammad Abdul Qyyum, Muhammad Yasin, Alam Nawaz, Tianbiao He, Wahid Ali, Junaid Haider, Kinza Qadeer, Abdul-Sattar Nizami, Konstantinos Moustakas and Moonyong Lee

Energies 2020, 13(7), 1732; https://doi.org/10.3390/en13071732 - 5 Apr 2020

Cited by 26 | Viewed by 5161

Abstract

Propane-Precooled Mixed Refrigerant (C3MR) and Single Mixed Refrigerant (SMR) processes are considered as optimal choices for onshore and offshore natural gas liquefaction, respectively. However, from thermodynamics point of view, these processes are still far away from their maximum achievable energy efficiency due to [...] Read more.

Propane-Precooled Mixed Refrigerant (C3MR) and Single Mixed Refrigerant (SMR) processes are considered as optimal choices for onshore and offshore natural gas liquefaction, respectively. However, from thermodynamics point of view, these processes are still far away from their maximum achievable energy efficiency due to nonoptimal execution of the design variables. Therefore, Liquefied Natural Gas (LNG) production is considered as one of the energy-intensive cryogenic industries. In this context, this study examines a single-solution-based Vortex Search (VS) approach to find the optimal design variables corresponding to minimal energy consumption for LNG processes, i.e., C3MR and SMR. The LNG processes are simulated using Aspen Hysys and then linked with VS algorithm, which is coded in MATLAB. The results indicated that the SMR process is a potential process for offshore sites that can liquefy natural gas with 16.1% less energy consumption compared with the published base case. Whereas, for onshore LNG production, the energy consumption for the C3MR process is reduced up to 27.8% when compared with the previously published base case. The optimal designs of the SMR and C3MR processes are also found via distinctive well-established optimization approaches (i.e., genetic algorithm and particle swarm optimization) and their performance is compared with that of the VS methodology. The authors believe this work will greatly help the process engineers overcome the challenges relating to the energy efficiency of LNG industry, as well as other mixed refrigerant-based cryogenic processes. Full article

(This article belongs to the Section A: Sustainable Energy)

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23 pages, 9502 KiB

Open AccessEditor’s ChoiceArticle

Analysis of the Use of Electric Drive Systems for Crew Transfer Vessels Servicing Offshore Wind Farms

by Andrzej Łebkowski

Energies 2020, 13(6), 1466; https://doi.org/10.3390/en13061466 - 20 Mar 2020

Cited by 16 | Viewed by 6846

Abstract

The article presents issues related to the possibility of using electric propulsion systems in units used to transport crews servicing wind towers at sea. Offshore wind energy issues are discussed. Proposals for electric propulsion systems that could be used on units for transporting [...] Read more.

The article presents issues related to the possibility of using electric propulsion systems in units used to transport crews servicing wind towers at sea. Offshore wind energy issues are discussed. Proposals for electric propulsion systems that could be used on units for transporting crews servicing offshore wind farms are presented. The possibility of using purely electrical drive systems or hybrid drive systems operating in a diesel-electric configuration is analyzed. By observing the motion of real CTV units, based on the data from the MarineTraffic service, a mathematical simulation model was developed, for which a number of simulations were carried out in the Modelica environment. The developed mathematical model takes into account the dynamic loads acting on the ship’s hull, hydrodynamic resistances, electric and diesel propulsion systems’ properties together with their individual elements’ characteristics. The tests of the electric propulsion system showed reduced fuel consumption (approx. 60%) and harmful gas emissions to the atmosphere (approximately 70%) in relation to conventional, internal combustion engine propulsion. Full article

(This article belongs to the Section D: Energy Storage and Application)

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20 pages, 5943 KiB

Open AccessEditor’s ChoiceArticle

Geological and Thermodynamic Analysis of Low Enthalpy Geothermal Resources to Electricity Generation Using ORC and Kalina Cycle Technology

by Michał Kaczmarczyk, Barbara Tomaszewska and Leszek Pająk

Energies 2020, 13(6), 1335; https://doi.org/10.3390/en13061335 - 13 Mar 2020

Cited by 23 | Viewed by 6292

Abstract

The article presents an assessment of the potential for using low enthalpy geothermal resources for electricity generation on the basis of the Małopolskie Voivodeship (southern Poland). Identification the locations providing the best prospects with the highest efficiency and possible gross power output. Thermodynamic [...] Read more.

The article presents an assessment of the potential for using low enthalpy geothermal resources for electricity generation on the basis of the Małopolskie Voivodeship (southern Poland). Identification the locations providing the best prospects with the highest efficiency and possible gross power output. Thermodynamic calculations of power plants were based on data from several geothermal wells: the Bańska PGP-1, Bańska IG-1, Bańska PGP-3 and Chochołów PIG-1 which are working wells located in one of the best geothermal reservoirs in Poland. As the temperature of geothermal waters from the wells does not exceed 86 °C, considerations include the use of binary technologies—the Organic Rankine Cycle (ORC) and Kalina Cycle. The potential gross capacity calculated for existing geothermal wells will not exceed 900 kW for ORC and 1.6 MW for Kalina Cycle. In the case of gross electricity, the total production will not exceed 3.3 GWh/year using the ORC, and will not exceed 6.3 GWh/year for the Kalina Cycle. Full article

(This article belongs to the Special Issue Assessment, Management and Treatment of Waters and Geothermal Systems)

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14 pages, 3829 KiB

Open AccessEditor’s ChoiceArticle

Prediction of Performance Variation Caused by Manufacturing Tolerances and Defects in Gas Diffusion Electrodes of Phosphoric Acid (PA)–Doped Polybenzimidazole (PBI)-Based High-Temperature Proton Exchange Membrane Fuel Cells

by Vladimir Gurau and Emory S. De Castro

Energies 2020, 13(6), 1345; https://doi.org/10.3390/en13061345 - 13 Mar 2020

Cited by 4 | Viewed by 3814

Abstract

The automated process of coating catalyst layers on gas diffusion electrodes (GDEs) for high-temperature proton exchange membrane fuel cells results inherently into a number of defects. These defects consist of agglomerates in which the platinum sites cannot be accessed by phosphoric acid and [...] Read more.

The automated process of coating catalyst layers on gas diffusion electrodes (GDEs) for high-temperature proton exchange membrane fuel cells results inherently into a number of defects. These defects consist of agglomerates in which the platinum sites cannot be accessed by phosphoric acid and which are the consequence of an inconsistent coating, uncoated regions, scratches, knots, blemishes, folds, or attached fine particles—all ranging from μm to mm size. These electrochemically inactive spots cause a reduction of the effective catalyst area per unit volume (cm²/cm³) and determine a drop in fuel cell performance. A computational fluid dynamics (CFD) model is presented that predicts performance variation caused by manufacturing tolerances and defects of the GDE and which enables the creation of a six-sigma product specification for Advent phosphoric acid (PA)-doped polybenzimidazole (PBI)-based membrane electrode assemblies (MEAs). The model was used to predict the total volume of defects that would cause a 10% drop in performance. It was found that a 10% performance drop at the nominal operating regime would be caused by uniformly distributed defects totaling 39% of the catalyst layer volume (~0.5 defects/μm²). The study provides an upper bound for the estimation of the impact of the defect location on performance drop. It was found that the impact on the local current density is higher when the defect is located closer to the interface with the membrane. The local current density decays less than 2% in the presence of an isolated defect, regardless of its location along the active area of the catalyst layer. Full article

(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells 2019)

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26 pages, 10513 KiB

Open AccessEditor’s ChoiceArticle

Low Enthalpy Geothermal Systems in Structural Controlled Areas: A Sustainability Analysis of Geothermal Resource for Heating Plant (The Mondragone Case in Southern Appennines, Italy)

by Marina Iorio, Alberto Carotenuto, Alfonso Corniello, Simona Di Fraia, Nicola Massarotti, Alessandro Mauro, Renato Somma and Laura Vanoli

Energies 2020, 13(5), 1237; https://doi.org/10.3390/en13051237 - 6 Mar 2020

Cited by 19 | Viewed by 5062

Abstract

In this study, the sustainability of low-temperature geothermal field exploitation in a carbonate reservoir near Mondragone (CE), Southern Italy, is analyzed. The Mondragone geothermal field has been extensively studied through the research project VIGOR (Valutazione del potenzIale Geotermico delle RegiOni della convergenza). From [...] Read more.

In this study, the sustainability of low-temperature geothermal field exploitation in a carbonate reservoir near Mondragone (CE), Southern Italy, is analyzed. The Mondragone geothermal field has been extensively studied through the research project VIGOR (Valutazione del potenzIale Geotermico delle RegiOni della convergenza). From seismic, geo-electric, hydro-chemical and groundwater data, obtained through the experimental campaigns carried out, physiochemical features of the aquifers and characteristics of the reservoir have been determined. Within this project, a well-doublet open-loop district heating plant has been designed to feed two public schools in Mondragone town. The sustainability of this geothermal application is analyzed in this study. A new exploration well (about 300 m deep) is considered to obtain further stratigraphic and structural information about the reservoir. Using the derived hydrogeological model of the area, a numerical analysis of geothermal exploitation was carried out to assess the thermal perturbation of the reservoir and the sustainability of its exploitation. The effect of extraction and reinjection of fluids on the reservoir was evaluated for 60 years of the plant activity. The results are fundamental to develop a sustainable geothermal heat plant and represent a real case study for the exploitation of similar carbonate reservoir geothermal resources. Full article

(This article belongs to the Special Issue Geothermal Energy Utilization and Technologies 2020)

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14 pages, 2195 KiB

Open AccessEditor’s ChoiceArticle

Logistics Design for Mobile Battery Energy Storage Systems

by Hassan S. Hayajneh and Xuewei Zhang

Energies 2020, 13(5), 1157; https://doi.org/10.3390/en13051157 - 4 Mar 2020

Cited by 20 | Viewed by 4650

Abstract

Currently, there are three major barriers toward a greener energy landscape in the future: (a) Curtailed grid integration of energy from renewable sources like wind and solar; (b) The low investment attractiveness of large-scale battery energy storage systems; and, (c) Constraints from the [...] Read more.

Currently, there are three major barriers toward a greener energy landscape in the future: (a) Curtailed grid integration of energy from renewable sources like wind and solar; (b) The low investment attractiveness of large-scale battery energy storage systems; and, (c) Constraints from the existing electric infrastructure on the development of charging station networks to meet the increasing electrical transportation demands. A new conceptual design of mobile battery energy storage systems has been proposed in recent studies to reduce the curtailment of renewable energy while limiting the public costs of battery energy storage systems. This work designs a logistics system in which electric semi-trucks ship batteries between the battery energy storage system and electric vehicle charging stations, enabling the planning and operation of power grid independent electric vehicle charging station networks. This solution could be viable in many regions in the United States (e.g., Texas) where there are plenty of renewable resources and little congestion pressure on the road networks. With Corpus Christi, Texas and the neighboring Chapman Ranch wind farm as the test case, this work implement such a design and analyze its performance based on the simulation of its operational processes. Further, we formulate an optimization problem to find design parameters that minimize the total costs. The main design parameters include the number of trucks and batteries. The results in this work, although preliminary, will be instrumental for potential stakeholders to make investment or policy decisions. Full article

(This article belongs to the Special Issue Integration of Electric Vehicles and Battery Storage Systems)

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21 pages, 1893 KiB

Open AccessEditor’s ChoiceArticle

Addressing Abrupt PV Disturbances, and Mitigating Net Load Profile’s Ramp and Peak Demands, Using Distributed Storage Devices

by Roshan Sharma and Masoud Karimi-Ghartemani

Energies 2020, 13(5), 1024; https://doi.org/10.3390/en13051024 - 25 Feb 2020

Cited by 24 | Viewed by 3860

Abstract

At high penetration level of photovoltaic (PV) generators, their abrupt disturbances (caused by moving clouds) cause voltage and frequency perturbations and increase system losses. Meanwhile, the daily irradiation profile increases the slope in the net-load profile, for example, California duck curve, which imposes [...] Read more.

At high penetration level of photovoltaic (PV) generators, their abrupt disturbances (caused by moving clouds) cause voltage and frequency perturbations and increase system losses. Meanwhile, the daily irradiation profile increases the slope in the net-load profile, for example, California duck curve, which imposes the challenge of quickly bringing on-line conventional generators in the early evening hours. Accordingly, this paper presents an approach to achieve two objectives: (1) address abrupt disturbances caused by PV generators, and (2) shape the net load profile. The approach is based on employing battery energy storage (BES) systems coupled with PV generators and equipped with proper controls. The proposed BES addresses these two issues by realizing flexible power ramp-up and ramp-down rates by the combined PV and BES. This paper presents the principles, modeling and control design aspects of the proposed system. A hybrid dc/ac study system is simulated and the effectiveness of the proposed BES in reducing the impacts of disturbances on both the dc and ac subsystems is verified. It is then shown that the proposed PV-BES modifies the daily load profile to mitigate the required challenge for quickly bringing on-line synchronous generators. Full article

(This article belongs to the Special Issue Grid-Connected PV Plants)

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18 pages, 3790 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of Temporal Complexity Reduction Techniques Applied to Storage Expansion Planning in Power System Models

by Oriol Raventós and Julian Bartels

Energies 2020, 13(4), 988; https://doi.org/10.3390/en13040988 - 22 Feb 2020

Cited by 14 | Viewed by 3724

Abstract

The growing share of renewable energy makes the optimization of power flows in power system models computationally more complicated, due to the widely distributed weather-dependent electricity generation. This article evaluates two methods to reduce the temporal complexity of a power transmission grid model [...] Read more.

The growing share of renewable energy makes the optimization of power flows in power system models computationally more complicated, due to the widely distributed weather-dependent electricity generation. This article evaluates two methods to reduce the temporal complexity of a power transmission grid model with storage expansion planning. The goal of the reduction techniques is to accelerate the computation of the linear optimal power flow of the grid model. This is achieved by choosing a small number of representative time periods to represent one whole year. To select representative time periods, a hierarchical clustering is used to aggregate either adjacent hours chronologically or independently distributed coupling days into clusters of time series. The aggregation efficiency is evaluated by means of the error of the objective value and the computational time reduction. Further, both the influence of the network size and the efficiency of parallel computation in the optimization process are analysed. As a test case, the transmission grid of the northernmost German federal state of Schleswig-Holstein with a scenario corresponding to the year 2035 is considered. The considered scenario is characterized by a high share of installed renewables. Full article

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37 pages, 7120 KiB

Open AccessEditor’s ChoiceArticle

by Jarosław Brodny and Magdalena Tutak

Energies 2020, 13(4), 913; https://doi.org/10.3390/en13040913 - 18 Feb 2020

Cited by 106 | Viewed by 9823

Abstract

The European Union (EU) countries, as one of the most economically developed regions in the world, are taking increasingly decisive actions to reduce the emission of harmful substances into the natural environment. This can be exemplified by a new climate strategy referred to [...] Read more.

The European Union (EU) countries, as one of the most economically developed regions in the world, are taking increasingly decisive actions to reduce the emission of harmful substances into the natural environment. This can be exemplified by a new climate strategy referred to as “The European Green Deal”. Its basic assumption is that the EU countries will have achieved climate neutrality by 2050. To do so, it is necessary to make an energy transition involving the widest possible use of renewable energy sources (RES) for energy production. However, activities in this area should be preceded by analyses due to the large diversity of the EU countries in terms of economic development, the number of inhabitants and their wealth as well as geographical location and area. The results of such analyses should support the implementation of adopted strategies. In order to assess the current state of the energy sector in the EU and indicate future directions of activities, research was carried out to analyze the structure and volume of energy production from RES in the EU countries. The aim of the study was to divide the EU countries into similar groups by the structure and volume of energy production from RES. This production was compared with the number of inhabitants of each EU country, its area and the value of Gross Domestic Product (GDP). This approach allows a new and broader view of the structure of energy production from RES and creates an opportunity to take into account additional factors when developing and implementing new climate strategies. The k-means algorithm was used for the analysis. The presented analyses and obtained results constitute a new approach to studying the diversified energy market in the EU. The results should be used for the development of a common energy and climate policy and economic integration of the EU countries. Full article

(This article belongs to the Special Issue 100% Renewable Energy Transition: Pathways and Implementation II)

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17 pages, 2127 KiB

Open AccessEditor’s ChoiceArticle

An Investigation of an Adaptive Neuro-Fuzzy Inference System to Predict the Relationship among Energy Intensity, Globalization, and Financial Development in Major ASEAN Economies

by Hafezali Iqbal Hussain, Beata Slusarczyk, Fakarudin Kamarudin, Hassanudin Mohd Thas Thaker and Katarzyna Szczepańska-Woszczyna

Energies 2020, 13(4), 850; https://doi.org/10.3390/en13040850 - 15 Feb 2020

Cited by 63 | Viewed by 5132

Abstract

The enhancement of the financial sector significantly drives a nation’s economy and thereby increase energy intensity. Considering this situation, the current study aims to examine the link between globalization and financial advancements with the energy intensity of the top 5 ASEAN (Association of [...] Read more.

The enhancement of the financial sector significantly drives a nation’s economy and thereby increase energy intensity. Considering this situation, the current study aims to examine the link between globalization and financial advancements with the energy intensity of the top 5 ASEAN (Association of Southeast Asian Nations) economies. The development structure of the ASEAN region is considered significant for having stable growth. The authors used the annual data from 1990 to 2018 for five of the largest ASEAN economies: Singapore, Malaysia, Thailand, Indonesia, and the Philippines. The present study used novel methodology, the Adaptive Neuro-Fuzzy Inference System (ANFIS), to examine the nonlinear behaviour among globalization, financial development, and energy intensity in the top 5 ASEAN countries. The study results using ANFIS confirm that globalization and financial development are positively correlated and have a significant impact on the energy intensity level in the top ASEAN countries. The results further suggest that globalization and financial development increase the level of energy intensity more in the countries that are developed relative to their peers in the top ASEAN countries. Moreover, the outcomes of ANFIS also suggest that those countries, which are more globalized and financially developed, have more potential to increase the level of energy intensity. Therefore, the government needs to focus more on projects that involve renewable energy and are environmentally friendly. Full article

(This article belongs to the Special Issue Management and Technology for Energy Efficiency Development)

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34 pages, 19966 KiB

Open AccessEditor’s ChoiceArticle

Low Temperature District Heating: An Expert Opinion Survey

by Alessandro Guzzini, Marco Pellegrini, Edoardo Pelliconi and Cesare Saccani

Energies 2020, 13(4), 810; https://doi.org/10.3390/en13040810 - 13 Feb 2020

Cited by 17 | Viewed by 4139

Abstract

Among the available solutions for building heating and cooling, district heating (DH) and district cooling (DC) systems are considered some of the best options since they can ensure a better control of pollutant emissions and greater efficiency than individual systems. Nevertheless, improvements are [...] Read more.

Among the available solutions for building heating and cooling, district heating (DH) and district cooling (DC) systems are considered some of the best options since they can ensure a better control of pollutant emissions and greater efficiency than individual systems. Nevertheless, improvements are needed to increase their sustainability and reliability. The so-called “low temperature district heating” (LTDH) concept has been introduced in recent years in an attempt (i) to reduce the distribution heat losses through a temperature decrease in the DH network, (ii) to favor the integration with renewable energy sources, and (iii) to create the conditions required for the development of future smart energy systems. However, many concerns have been raised about its implementation in both existing and new systems. For this reason, this paper aims to identify the stakeholders’ ranking of the barriers against LTDH system development and implementation over the next few years. Aiming to this, a questionnaire was designed, including an analysis of current gaps and strengths, and then submitted to more than 50 Italian and international experts in the field of DH. An in-depth analysis of the received answers was performed, focusing in particular on the Italian experts’ answers. Comments and suggestions on how to promote the transition to the new LTDH approach are reported. Full article

(This article belongs to the Section A1: Smart Grids and Microgrids)

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17 pages, 10575 KiB

Open AccessEditor’s ChoiceArticle

Self-Powered Autonomous Wireless Sensor Node by Using Silicon-Based 3D Thermoelectric Energy Generator for Environmental Monitoring Application

by Jong-Pil Im, Jeong Hun Kim, Jae Woo Lee, Ji Yong Woo, Sol Yee Im, Yeriaron Kim, Yong-Sung Eom, Won Chul Choi, Jun Soo Kim and Seung Eon Moon

Energies 2020, 13(3), 674; https://doi.org/10.3390/en13030674 - 4 Feb 2020

Cited by 18 | Viewed by 5056

Abstract

In this paper, we present the results of a preliminary study on the self-powered autonomous wireless sensor node by using thermoelectric energy generator based on Silicon (Si) thermoelectric legs, energy management integrated circuit (EMIC), Radio Frequency (RF) module with a temperature and humidity [...] Read more.

In this paper, we present the results of a preliminary study on the self-powered autonomous wireless sensor node by using thermoelectric energy generator based on Silicon (Si) thermoelectric legs, energy management integrated circuit (EMIC), Radio Frequency (RF) module with a temperature and humidity sensor, etc. A novel thermoelectric module structure is designed as an energy generator module, which consists of 127 pairs of Silicon legs and this module is fabricated and tested to demonstrate the feasibility of generating electrical power under the temperature gradient of 70K. EMIC has three key features besides high efficiency, which are maximum power point tracking (MPPT), cold start, and complete self-power operation. EMIC achieved a cold start voltage of 200 mV, peak efficiency of 78.7%, MPPT efficiency 99.4%, and an output power of 34 mW through only the Thermoelectric Generator (TEG) source. To assess the capability of the device as a small scale power source for internet of things (IoT) service, we also tested energy conversion and storage experiments. Finally, the proposed sensor node system which can transmit and monitor the information from the temperature and humidity sensor through the RF module in real time demonstrates the feasibility for variable applications. Full article

(This article belongs to the Section F: Electrical Engineering)

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21 pages, 4346 KiB

Open AccessEditor’s ChoiceArticle

Improving the Efficiency of PEM Electrolyzers through Membrane-Specific Pressure Optimization

by Fabian Scheepers, Markus Stähler, Andrea Stähler, Edward Rauls, Martin Müller, Marcelo Carmo and Werner Lehnert

Energies 2020, 13(3), 612; https://doi.org/10.3390/en13030612 - 1 Feb 2020

Cited by 88 | Viewed by 17255

Abstract

Hydrogen produced in a polymer electrolyte membrane (PEM) electrolyzer must be stored under high pressure. It is discussed whether the gas should be compressed in subsequent gas compressors or by the electrolyzer. While gas compressor stages can be reduced in the case of [...] Read more.

Hydrogen produced in a polymer electrolyte membrane (PEM) electrolyzer must be stored under high pressure. It is discussed whether the gas should be compressed in subsequent gas compressors or by the electrolyzer. While gas compressor stages can be reduced in the case of electrochemical compression, safety problems arise for thin membranes due to the undesired permeation of hydrogen across the membrane to the oxygen side, forming an explosive gas. In this study, a PEM system is modeled to evaluate the membrane-specific total system efficiency. The optimum efficiency is given depending on the external heat requirement, permeation, cell pressure, current density, and membrane thickness. It shows that the heat requirement and hydrogen permeation dominate the maximum efficiency below 1.6 V, while, above, the cell polarization is decisive. In addition, a pressure-optimized cell operation is introduced by which the optimum cathode pressure is set as a function of current density and membrane thickness. This approach indicates that thin membranes do not provide increased safety issues compared to thick membranes. However, operating an N212-based system instead of an N117-based one can generate twice the amount of hydrogen at the same system efficiency while only one compressor stage must be added. Full article

(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells and Electrolyzers)

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17 pages, 2388 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optimization of Isolated Hybrid Microgrids with Renewable Energy Based on Different Battery Models and Technologies

by Yimy E. García-Vera, Rodolfo Dufo-López and José L. Bernal-Agustín

Energies 2020, 13(3), 581; https://doi.org/10.3390/en13030581 - 26 Jan 2020

Cited by 43 | Viewed by 5756

Abstract

Energy supply in remote areas (mainly in developing countries such as Colombia) has become a challenge. Hybrid microgrids are local and reliable sources of energy for these areas where access to the power grid is generally limited or unavailable. These systems generally include [...] Read more.

Energy supply in remote areas (mainly in developing countries such as Colombia) has become a challenge. Hybrid microgrids are local and reliable sources of energy for these areas where access to the power grid is generally limited or unavailable. These systems generally include a diesel generator, solar modules, wind turbines, and storage devices such as batteries. Battery life estimation is an essential factor in the optimization of a hybrid microgrid since it determines the system’s final costs, including future battery replacements. This article presents a comparison of different technologies and battery models in a hybrid microgrid. The optimization is achieved using the iHOGA software, based on data from a real microgrid in Colombia. The simulation results allowed the comparison of prediction models for lifespan calculation for both lead–acid and lithium batteries in a hybrid microgrid, showing that the most accurate models are more realistic in predicting battery life by closely estimating real lifespans that are shorter, unlike other simplified methods that obtain much longer and unrealistic lifetimes. Full article

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17 pages, 6431 KiB

Open AccessEditor’s ChoiceReview

Review of Time and Space Harmonics in Multi-Phase Induction Machine

by Vladimir Kindl, Radek Cermak, Zelmira Ferkova and Bohumil Skala

Energies 2020, 13(2), 496; https://doi.org/10.3390/en13020496 - 19 Jan 2020

Cited by 28 | Viewed by 8299

Abstract

Modern multiphase electric machines take advantage of additional degrees of freedom for various purposes, including harmonic current injection to increase torque per ampere. This new approach introduces a non-sinusoidal air gap flux density distribution causing additional technical problems and so the conventional assumptions [...] Read more.

Modern multiphase electric machines take advantage of additional degrees of freedom for various purposes, including harmonic current injection to increase torque per ampere. This new approach introduces a non-sinusoidal air gap flux density distribution causing additional technical problems and so the conventional assumptions need to be revised. The paper presents a methodology for synthesis of air gap magnetic field generated by a symmetrically distributed multiphase windings including the rotor field reaction due to the machine’s load. The proposed method is suitable either for single-layer or double layer windings and can be adopted either for full-pitched or chorded winding including slots effects. The article analyses the air gap flux density harmonic content and formulates conclusions important to multiphase induction motors. It also discusses effects of time harmonic currents and illustrates the principle of changing number of pole-pairs typical for harmonic currents being injected to increase torque. Full article

(This article belongs to the Special Issue Advances in Rotating Electric Machines)

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24 pages, 8844 KiB

Open AccessEditor’s ChoiceArticle

Energy End-Use Categorization and Performance Indicators for Energy Management in the Engineering Industry

by Fayas Malik Kanchiralla, Noor Jalo, Simon Johnsson, Patrik Thollander and Maria Andersson

Energies 2020, 13(2), 369; https://doi.org/10.3390/en13020369 - 12 Jan 2020

Cited by 21 | Viewed by 4295

Abstract

Energy efficiency (EE) improvement is one of the most crucial elements in the decarbonization of industry. EE potential within industries largely remains untapped due to the lack of information regarding potential EE measures (EEM), knowledge regarding energy use, and due to the existence [...] Read more.

Energy efficiency (EE) improvement is one of the most crucial elements in the decarbonization of industry. EE potential within industries largely remains untapped due to the lack of information regarding potential EE measures (EEM), knowledge regarding energy use, and due to the existence of some inconsistencies in the evaluation of energy use. Classification of energy end-using processes would increase the understanding of energy use, which in turn would increase the detection and deployment of EEMs. The study presents a novel taxonomy with hierarchical levels for energy end-use in manufacturing operations for the engineering industry, analyzes processes in terms of energy end-use (EEU) and CO₂ emissions, and scrutinizes energy performance indicators (EnPIs), as well as proposing potential new EnPIs that are suitable for the engineering industry. Even though the study has been conducted with a focus on the Swedish engineering industry, the study may be generalizable to the engineering industry beyond Sweden. Full article

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21 pages, 1690 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Thermal Energy Storage for Grid Applications: Current Status and Emerging Trends

by Diana Enescu, Gianfranco Chicco, Radu Porumb and George Seritan

Energies 2020, 13(2), 340; https://doi.org/10.3390/en13020340 - 10 Jan 2020

Cited by 124 | Viewed by 9999

Abstract

Thermal energy systems (TES) contribute to the on-going process that leads to higher integration among different energy systems, with the aim of reaching a cleaner, more flexible and sustainable use of the energy resources. This paper reviews the current literature that refers to [...] Read more.

Thermal energy systems (TES) contribute to the on-going process that leads to higher integration among different energy systems, with the aim of reaching a cleaner, more flexible and sustainable use of the energy resources. This paper reviews the current literature that refers to the development and exploitation of TES-based solutions in systems connected to the electrical grid. These solutions facilitate the energy system integration to get additional flexibility for energy management, enable better use of variable renewable energy sources (RES), and contribute to the modernisation of the energy system infrastructures, the enhancement of the grid operation practices that include energy shifting, and the provision of cost-effective grid services. This paper offers a complementary view with respect to other reviews that deal with energy storage technologies, materials for TES applications, TES for buildings, and contributions of electrical energy storage for grid applications. The main aspects addressed are the characteristics, parameters and models of the TES systems, the deployment of TES in systems with variable RES, microgrids, and multi-energy networks, and the emerging trends for TES applications. Full article

(This article belongs to the Section A: Sustainable Energy)

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23 pages, 5780 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Sizing and Allocation of Battery Energy Storage Systems in Åland Islands for Large-Scale Integration of Renewables and Electric Ferry Charging Stations

by Jagdesh Kumar, Chethan Parthasarathy, Mikko Västi, Hannu Laaksonen, Miadreza Shafie-Khah and Kimmo Kauhaniemi

Energies 2020, 13(2), 317; https://doi.org/10.3390/en13020317 - 9 Jan 2020

Cited by 39 | Viewed by 6463

Abstract

The stringent emission rules set by international maritime organisation and European Directives force ships and harbours to constrain their environmental pollution within certain targets and enable them to employ renewable energy sources. To this end, harbour grids are shifting towards renewable energy sources [...] Read more.

The stringent emission rules set by international maritime organisation and European Directives force ships and harbours to constrain their environmental pollution within certain targets and enable them to employ renewable energy sources. To this end, harbour grids are shifting towards renewable energy sources to cope with the growing demand for an onshore power supply and battery-charging stations for modern ships. However, it is necessary to accurately size and locate battery energy storage systems for any operational harbour grid to compensate the fluctuating power supply from renewable energy sources as well as meet the predicted maximum load demand without expanding the power capacities of transmission lines. In this paper, the equivalent circuit battery model of nickel–cobalt–manganese-oxide chemistry has been utilised for the sizing of a lithium-ion battery energy storage system, considering all the parameters affecting its performance. A battery cell model has been developed in the Matlab/Simulink platform, and subsequently an algorithm has been developed for the design of an appropriate size of lithium-ion battery energy storage systems. The developed algorithm has been applied by considering real data of a harbour grid in the Åland Islands, and the simulation results validate that the sizes and locations of battery energy storage systems are accurate enough for the harbour grid in the Åland Islands to meet the predicted maximum load demand of multiple new electric ferry charging stations for the years 2022 and 2030. Moreover, integrating battery energy storage systems with renewables helps to increase the reliability and defer capital cost investments of upgrading the ratings of transmission lines and other electrical equipment in the Åland Islands grid. Full article

(This article belongs to the Section F: Electrical Engineering)

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13 pages, 1710 KiB

Open AccessEditor’s ChoiceArticle

Thermal Gradients with Sintered Solid State Electrolytes in Lithium-Ion Batteries

by Robert Bock, Morten Onsrud, Håvard Karoliussen, Bruno G. Pollet, Frode Seland and Odne S. Burheim

Energies 2020, 13(1), 253; https://doi.org/10.3390/en13010253 - 3 Jan 2020

Cited by 18 | Viewed by 5054

Abstract

The electrolyte is one of the three essential constituents of a Lithium-Ion battery (LiB) in addition to the anode and cathode. During increasingly high power and high current charging and discharging, the requirement for the electrolyte becomes more strict. Solid State Electrolyte (SSE) [...] Read more.

The electrolyte is one of the three essential constituents of a Lithium-Ion battery (LiB) in addition to the anode and cathode. During increasingly high power and high current charging and discharging, the requirement for the electrolyte becomes more strict. Solid State Electrolyte (SSE) sees its niche for high power applications due to its ability to suppress concentration polarization and otherwise stable properties also related to safety. During high power and high current cycling, heat management becomes more important and thermal conductivity measurements are needed. In this work, thermal conductivity was measured for three types of solid state electrolytes: Li

_{7}

La

_{3}

Zr

_{2}

O

_{12}

(LLZO), Li

_{1.5}

Al

_{0.5}

Ge

_{1.5}

(PO

_{4}

)

_{3}

(LAGP), and Li

_{1.3}

Al

_{0.3}

Ti

_{1.7}

(PO

_{4}

)

_{3}

(LATP) at different compaction pressures. LAGP and LATP were measured after sintering, and LLZO was measured before and after sintering the sample material. Thermal conductivity for the sintered electrolytes was measured to 0.470 ± 0.009 WK

^{- 1}

m

^{- 1}

, 0.5 ± 0.2 WK

^{- 1}

m

^{- 1}

and 0.49 ± 0.02 WK

^{- 1}

m

^{- 1}

for LLZO, LAGP, and LATP respectively. Before sintering, LLZO showed a thermal conductivity of 0.22 ± 0.02 WK

^{- 1}

m

^{- 1}

. An analytical temperature distribution model for a battery stack of 24 cells shows temperature differences between battery center and edge of 1–2 K for standard liquid electrolytes and 7–9 K for solid state electrolytes, both at the same C-rate of four. Full article

(This article belongs to the Special Issue Smart and Functional Materials for Lithium-Ion Battery)

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15 pages, 12461 KiB

Open AccessEditor’s ChoiceArticle

Fault Analysis and Design of a Protection System for a Mesh Power System with a Co-Axial HTS Power Cable

by Thai-Thanh Nguyen, Woon-Gyu Lee, Hak-Man Kim and Hyung Suk Yang

Energies 2020, 13(1), 220; https://doi.org/10.3390/en13010220 - 2 Jan 2020

Cited by 7 | Viewed by 3657

Abstract

The uses of high-temperature superconducting (HTS) cables pose a challenge of power system protection since the impedance of the HTS cable is varied during fault conditions. The protection systems should be designed properly to ensure the reliability and stability of the whole system. [...] Read more.

The uses of high-temperature superconducting (HTS) cables pose a challenge of power system protection since the impedance of the HTS cable is varied during fault conditions. The protection systems should be designed properly to ensure the reliability and stability of the whole system. This paper presents a fault analysis of the co-axial HTS cable in the mesh system and proposes a coordinated protection system. In the proposed protection system, the main protection is the differential current relay whereas the backup protections are the overcurrent and directional overcurrent relays. The normal and abnormal relay operations are considered to analyze the transient fault current in the HTS cable and evaluate the performance of the proposed coordinated protection system. Characteristics of cable impedances and temperatures under various fault conditions are presented. The proposed protection scheme is validated by the simulation in the PSCAD/EMTDC program. Simulation results show that the coordinated protection scheme could successfully protect the HTS cables in both normal and abnormal relay operations. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2019)

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38 pages, 11685 KiB

Open AccessEditor’s ChoiceArticle

Modelling of Passive Heat Removal Systems: A Review with Reference to the Framatome BWR Reactor KERENA: Part II

by René Manthey, Frances Viereckl, Amirhosein Moonesi Shabestary, Yu Zhang, Wei Ding, Dirk Lucas, Christoph Schuster, Stephan Leyer, Antonio Hurtado and Uwe Hampel

Energies 2020, 13(1), 109; https://doi.org/10.3390/en13010109 - 24 Dec 2019

Cited by 8 | Viewed by 5757

Abstract

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventions and are solely driven by thermal gradients and gravitational force. This brings up new needs for performance and [...] Read more.

Passive safety systems are an important feature of currently designed and constructed nuclear power plants. They operate independent of external power supply and manual interventions and are solely driven by thermal gradients and gravitational force. This brings up new needs for performance and reliably assessment. This paper provides a review on fundamental approaches to model and analyze the performance of passive heat removal systems exemplified for the passive heat removal chain of the KERENA boiling water reactor concept developed by Framatome. We discuss modeling concepts for one-dimensional system codes such as ATHLET, RELAP and TRACE and furthermore for computational fluid dynamics codes. Part I dealt with numerical and experimental methods for modeling of condensation inside the emergency condenser and on the containment cooling condenser. This second part deals with boiling and two-phase flow instabilities. Full article

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26 pages, 5930 KiB

Open AccessEditor’s ChoiceArticle

A Model-Based Design Approach for Stability Assessment, Control Tuning and Verification in Off-Grid Hybrid Power Plants

by Lennart Petersen, Florin Iov and German Claudio Tarnowski

Energies 2020, 13(1), 49; https://doi.org/10.3390/en13010049 - 20 Dec 2019

Cited by 14 | Viewed by 7160

Abstract

This paper proposes detailed and practical guidance on applying model-based design (MBD) for voltage and frequency stability assessments, control tuning and verification of off-grid hybrid power plants (HPPs) comprising both grid-forming and grid-feeding inverter units and synchronous generation. First, the requirement specifications are [...] Read more.

This paper proposes detailed and practical guidance on applying model-based design (MBD) for voltage and frequency stability assessments, control tuning and verification of off-grid hybrid power plants (HPPs) comprising both grid-forming and grid-feeding inverter units and synchronous generation. First, the requirement specifications are defined by means of system, functional and model requirements. Secondly, a modular approach for state-space modelling of the distributed energy resources (DERs) is presented. Flexible merging of subsystems by properly defining input and output vectors is highlighted to describe the dynamics of the HPP during various operating states. Eigenvalue (EV) and participation factor (PF) analyses demonstrate the necessity of assessing small-signal stability over a wide range of operational scenarios. A sensitivity analysis shows the impact of relevant system parameters on critical EVs and enables one to finally design and tune the central HPP controller (HPPC). The rapid control prototyping and control verification stages are accomplished by means of discrete-time domain models being used in both off-line simulation studies and real-time hardware-in-the-loop (RT-HIL) testing. The outcome of this paper is targeted at off-grid HPP operators seeking to achieve a proof-of-concept on stable voltage and frequency regulation. Nonetheless, the overall methodology is applicable to on-grid HPPs, too. Full article

(This article belongs to the Special Issue Microgrids: Planning, Protection and Control)

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17 pages, 6719 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Endurance of Polymeric Insulation Foil Exposed to DC-Biased Medium-Frequency Rectangular Pulse Voltage Stress

by Raphael Färber, Thomas Guillod, Florian Krismer, Johann W. Kolar and Christian M. Franck

Energies 2020, 13(1), 13; https://doi.org/10.3390/en13010013 - 18 Dec 2019

Cited by 25 | Viewed by 4897

Abstract

The endurance of polymeric insulation foil is investigated under a mixed medium-voltage stress (DC + medium-frequency rectangular pulse) by means of accelerated lifetime testing. A dedicated setup is used that allows us to selectively eliminate the known risk factors for premature insulation failure [...] Read more.

The endurance of polymeric insulation foil is investigated under a mixed medium-voltage stress (DC + medium-frequency rectangular pulse) by means of accelerated lifetime testing. A dedicated setup is used that allows us to selectively eliminate the known risk factors for premature insulation failure under medium-frequency pulse voltage stress: partial discharges (PDs) during pulse transitions, excessive dielectric heating, and systemic overvoltages. The obtained results on polyethylenterephtalat (PET) insulation foil suggest that the adequate consideration of these factors is sufficient for eliminating the adverse effects of the pulse modulation under the investigated conditions. Indeed, if all mentioned risk factors are eliminated, the time to failure observed under a pure DC stress is shorter than with a superimposed pulse (keeping the same peak voltage). There is then no indication of an additional detrimental “per pulse” degradation process (i.e., the time to failure is not dependent on pulse frequency). In contrast, when repetitive PDs are present, the lifetime under combined DC + rectangular pulse stress strongly decreases with increasing pulse switching frequency. PD erosion of the foil is quantified by means of confocal microscopy, and the applicability of the streamer criterion for predicting PD inception is discussed. Full article

(This article belongs to the Special Issue Advances in Electric Insulating Materials for Components of Power System)

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42 pages, 6173 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Finite Control Set Model Predictive Control of Six-Phase Asymmetrical Machines—An Overview

by Pedro Gonçalves, Sérgio Cruz and André Mendes

Energies 2019, 12(24), 4693; https://doi.org/10.3390/en12244693 - 10 Dec 2019

Cited by 75 | Viewed by 6183

Abstract

Recently, the control of multiphase electric drives has been a hot research topic due to the advantages of multiphase machines, namely the reduced phase ratings, improved fault tolerance and lesser torque harmonics. Finite control set model predictive control (FCS-MPC) is one of the [...] Read more.

Recently, the control of multiphase electric drives has been a hot research topic due to the advantages of multiphase machines, namely the reduced phase ratings, improved fault tolerance and lesser torque harmonics. Finite control set model predictive control (FCS-MPC) is one of the most promising high performance control strategies due to its good dynamic behaviour and flexibility in the definition of control objectives. Although several FCS-MPC strategies have already been proposed for multiphase drives, a comparative study that assembles all these strategies in a single reference is still missing. Hence, this paper aims to provide an overview and a critical comparison of all available FCS-MPC techniques for electric drives based on six-phase machines, focusing mainly on predictive current control (PCC) and predictive torque control (PTC) strategies. The performance of an asymmetrical six-phase permanent magnet synchronous machine is compared side-by-side for a total of thirteen PCC and five PTC strategies, with the aid of simulation and experimental results. Finally, in order to determine the best and the worst performing control strategies, each strategy is evaluated according to distinct features, such as ease of implementation, minimization of current harmonics, tuning requirements, computational burden, among others. Full article

(This article belongs to the Special Issue Advances in Rotating Electric Machines)

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26 pages, 4962 KiB

Open AccessEditor’s ChoiceArticle

Future Hydrogen Markets for Transportation and Industry: The Impact of CO₂ Taxes

by Simonas Cerniauskas, Thomas Grube, Aaron Praktiknjo, Detlef Stolten and Martin Robinius

Energies 2019, 12(24), 4707; https://doi.org/10.3390/en12244707 - 10 Dec 2019

Cited by 57 | Viewed by 10420

Abstract

The technological lock-in of the transportation and industrial sector can be largely attributed to the limited availability of alternative fuel infrastructures. Herein, a countrywide supply chain analysis of Germany, spanning until 2050, is applied to investigate promising infrastructure development pathways and associated hydrogen [...] Read more.

The technological lock-in of the transportation and industrial sector can be largely attributed to the limited availability of alternative fuel infrastructures. Herein, a countrywide supply chain analysis of Germany, spanning until 2050, is applied to investigate promising infrastructure development pathways and associated hydrogen distribution costs for each analyzed hydrogen market. Analyzed supply chain pathways include seasonal storage to balance fluctuating renewable power generation with necessary purification, as well as trailer- and pipeline-based hydrogen delivery. The analysis encompasses green hydrogen feedstock in the chemical industry and fuel cell-based mobility applications, such as local buses, non-electrified regional trains, material handling vehicles, and trucks, as well as passenger cars. Our results indicate that the utilization of low-cost, long-term storage and improved refueling station utilization have the highest impact during the market introduction phase. We find that public transport and captive fleets offer a cost-efficient countrywide renewable hydrogen supply roll-out option. Furthermore, we show that, at comparable effective carbon tax resulting from the current energy tax rates in Germany, hydrogen is cost-competitive in the transportation sector by the year 2025. Moreover, we show that sector-specific CO₂ taxes are required to provide a cost-competitive green hydrogen supply in both the transportation and industrial sectors. Full article

(This article belongs to the Section A5: Hydrogen Energy)

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18 pages, 9401 KiB

Open AccessEditor’s ChoiceArticle

Large-Eddy Simulation of Yawed Wind-Turbine Wakes: Comparisons with Wind Tunnel Measurements and Analytical Wake Models

by Mou Lin and Fernando Porté-Agel

Energies 2019, 12(23), 4574; https://doi.org/10.3390/en12234574 - 30 Nov 2019

Cited by 36 | Viewed by 5516

Abstract

In this study, we validated a wind-turbine parameterisation for large-eddy simulation (LES) of yawed wind-turbine wakes. The presented parameterisation is modified from the rotational actuator disk model (ADMR), which takes account of both thrust and tangential forces induced by a wind turbine based [...] Read more.

In this study, we validated a wind-turbine parameterisation for large-eddy simulation (LES) of yawed wind-turbine wakes. The presented parameterisation is modified from the rotational actuator disk model (ADMR), which takes account of both thrust and tangential forces induced by a wind turbine based on the blade-element theory. LES results using the yawed ADMR were validated with wind-tunnel measurements of the wakes behind a stand-alone miniature wind turbine model with different yaw angles. Comparisons were also made with the predictions of analytical wake models. In general, LES results using the yawed ADMR are in good agreement with both wind-tunnel measurements and analytical wake models regarding wake deflections and spanwise profiles of the mean velocity deficit and the turbulence intensity. Moreover, the power output of the yawed wind turbine is directly computed from the tangential forces resolved by the yawed ADMR, in contrast with the indirect power estimation used in the standard actuator disk model. We found significant improvement in the power prediction from LES using the yawed ADMR over the simulations using the standard actuator disk without rotation, suggesting a good potential of the yawed ADMR to be applied in LES studies of active yaw control in wind farms. Full article

(This article belongs to the Special Issue Fluid Mechanics and Turbulence in Wind Farms)

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