Energies

20 pages, 4552 KiB

Open AccessArticle

Do Tense Geopolitical Factors Drive Crude Oil Prices?

by Fen Li, Zhehao Huang, Junhao Zhong and Khaldoon Albitar

Energies 2020, 13(16), 4277; https://doi.org/10.3390/en13164277 - 18 Aug 2020

Cited by 22 | Viewed by 5334

Geopolitical factors are considered a crucial factor that makes a difference in crude oil prices. Over the last three decades, many political events occurred frequently, causing short-term fluctuations in crude oil prices. This paper aims to examine the dynamic correlation and causal link [...] Read more.

Geopolitical factors are considered a crucial factor that makes a difference in crude oil prices. Over the last three decades, many political events occurred frequently, causing short-term fluctuations in crude oil prices. This paper aims to examine the dynamic correlation and causal link between geopolitical factors and crude oil prices based on data from June 1987 to February 2020. By using a time-varying copula approach, it is shown that the correlation between geopolitical factors and crude oil prices is strong during periods of political tensions. The GPA (geopolitical acts) index, as the real factor, drives the rise in prices of crude oil. Moreover, the dynamic correlation between geopolitical factors and crude oil prices shows strong volatility over time during periods of political tensions. We also found unidirectional causality running from geopolitical factors to crude oil prices by using the Granger causality test. Full article

(This article belongs to the Special Issue Global Market for Crude Oil)

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9 pages, 1697 KiB

Open AccessArticle

Blue-Light Levels Emitted from Portable Electronic Devices Compared to Sunlight

by David Baeza Moyano, Yolanda Sola and Roberto Alonso González-Lezcano

Energies 2020, 13(16), 4276; https://doi.org/10.3390/en13164276 - 18 Aug 2020

Cited by 23 | Viewed by 6921

Abstract

Over recent years, a technological revolution has taken place in which conventional lighting has been replaced by light emitting diodes (LEDs). Some studies have shown the possibility that blue light from these artificial sources could have deleterious effects on the retina. Considering that [...] Read more.

Over recent years, a technological revolution has taken place in which conventional lighting has been replaced by light emitting diodes (LEDs). Some studies have shown the possibility that blue light from these artificial sources could have deleterious effects on the retina. Considering that people spend a non-negligible time in front of screens from computers and mobile phones, the eyes receive blue light of different intensities depending on the source. Nevertheless, any study about the visual and non-visual effects of blue light must consider precise measurements taken from actual artificial sources. For this reason, we have analyzed the spectral emission of 10 different electronic devices and weighted them according to the hazard caused by blue light to the eyes, comparing the results with solar radiation simulated with a radiative transfer model. The maximum spectral irradiance of the measured electronic devices at 10 cm from the detector was located between 440 nm and 460 nm. The irradiance for blue light hazard ranged from 0.008 to 0.230 Wm⁻² depending on the particular characteristics of each electronic device. In contrast, the solar radiances in the same spectral range are larger both under clear and cloudy conditions. Full article

(This article belongs to the Special Issue Technology Evolution and Power Quality Issues in Designing Future Lighting Systems)

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17 pages, 7939 KiB

Open AccessArticle

Manufacturing Challenges of a Modular Transverse Flux Alternator for Aerospace

by Mehmet C. Kulan, Nick J. Baker and Simon Turvey

Energies 2020, 13(16), 4275; https://doi.org/10.3390/en13164275 - 18 Aug 2020

Cited by 12 | Viewed by 3370

Abstract

This paper presents the manufacturing challenges of a transverse flux alternator for an aerospace application. For fault tolerance, four independent isolated phases are required to deliver a specific power at low speeds, whilst at over speed, there is a strict limit on the [...] Read more.

This paper presents the manufacturing challenges of a transverse flux alternator for an aerospace application. For fault tolerance, four independent isolated phases are required to deliver a specific power at low speeds, whilst at over speed, there is a strict limit on the short circuit current. A transverse flux machine (TFM) was selected due to its high inductance combined with the modular nature of separate phases lending itself to fault tolerance. The stator consists of pressed soft magnetic composite (SMC) segments. The authors explore the electromagnetic, mechanical, and assembly design challenges of the machine. It is shown that mechanical design aspects of the segments are of equal importance to the electromagnetic design and optimization. Simple design choices have allowed the same component to be used as all the stator segments, despite the requirement of a 90° electrical phase difference between phases and a tooth offset of 180° electrical within each phase. Full article

(This article belongs to the Special Issue Modular (Segmented) Electrical Machines)

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23 pages, 7660 KiB

Open AccessArticle

Temperature Analysis of the Stand-Alone and Building Integrated Photovoltaic Systems Based on Simulation and Measurement Data

by Adam Idzkowski, Karolina Karasowska and Wojciech Walendziuk

Energies 2020, 13(16), 4274; https://doi.org/10.3390/en13164274 - 18 Aug 2020

Cited by 7 | Viewed by 3255

Abstract

Sunlight is converted into electrical energy due to the photovoltaic effect in photovoltaic cells. Energy yield of photovoltaic systems depends on the solar array location, orientation, tilt, tracking and local weather conditions. In order to determine the amount of energy produced in a [...] Read more.

Sunlight is converted into electrical energy due to the photovoltaic effect in photovoltaic cells. Energy yield of photovoltaic systems depends on the solar array location, orientation, tilt, tracking and local weather conditions. In order to determine the amount of energy produced in a photovoltaic system, it is important to analyze the operation of the photovoltaic (PV) arrays in real operating conditions and take into account the impact of external factors such as irradiance, ambient temperature or the speed of blowing wind, which is the natural coolant of PV panels. The analysis was carried out based on mathematical models and actual measurement data, regarding the dependence of the average temperature of PV arrays on variable and difficult to predict ambient conditions. The analysis used standard (nominal operating cell temperature (NOCT)), King, Skoplaki, Faiman and Mattei thermal models and the standard model for flat-plate photovoltaic arrays. Photovoltaic installations PV1, PV2a and PV2b, being part of the hybrid power plant of the Bialystok University of Technology, Poland, were the objects of the research. In the case of a free-standing solar system, the Skoplaki model proved to be the best method for determining the average temperatures of the PV arrays. For building-integrated PV systems, a corrected value of the mounting coefficient in the Skoplaki model was proposed, and the original results were compared. The comparison of the accuracy measures of the average operating temperatures for three micro-power plants, differently mounted and located, is presented. Full article

(This article belongs to the Special Issue Innovations-Sustainability-Modernity-Openness in Energy Research 2020)

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45 pages, 3149 KiB

Open AccessReview

Reviewing the Modeling Aspects and Practices of Shallow Geothermal Energy Systems

by Paul Christodoulides, Ana Vieira, Stanislav Lenart, João Maranha, Gregor Vidmar, Rumen Popov, Aleksandar Georgiev, Lazaros Aresti and Georgios Florides

Energies 2020, 13(16), 4273; https://doi.org/10.3390/en13164273 - 18 Aug 2020

Cited by 15 | Viewed by 5206

Abstract

Shallow geothermal energy systems (SGES) may take different forms and have recently taken considerable attention due to energy geo-structures (EGS) resulting from the integration of heat exchange elements in geotechnical structures. Still, there is a lack of systematic design guidelines of SGES. Hence, [...] Read more.

Shallow geothermal energy systems (SGES) may take different forms and have recently taken considerable attention due to energy geo-structures (EGS) resulting from the integration of heat exchange elements in geotechnical structures. Still, there is a lack of systematic design guidelines of SGES. Hence, in order to contribute towards that direction, the current study aims at reviewing the available SGES modeling options along with their various aspects and practices. This is done by first presenting the main analytical and numerical models and methods related to the thermal behavior of SGES. Then, the most important supplementary factors affecting such modeling are discussed. These include: (i) the boundary conditions, in the form of temperature variation or heat flow, that majorly affect the predicted thermal behavior of SGES; (ii) the spatial dimensions that may be crucial when relaxing the infinite length assumption for short heat exchangers such as energy piles (EP); (iii) the determination of SGES parameters that may need employing specific techniques to overcome practical difficulties; (iv) a short-term vs. long-term analysis depending on the thermal storage characteristics of GHE of different sizes; (v) the influence of groundwater that can have a moderating effect on fluid temperatures in both heating and cooling modes. Subsequently, thermo-mechanical interactions modeling issues are addressed that may be crucial in EGS that exhibit a dual functioning of heat exchangers and structural elements. Finally, a quite lengthy overview of the main software tools related to thermal and thermo-hydro-mechanical analysis of SGES that may be useful for practical applications is given. A unified software package incorporating all related features of all SGES may be a future aim. Full article

(This article belongs to the Special Issue Computational Geothermal Energy Applications)

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14 pages, 4365 KiB

Open AccessArticle

Performance Comparison of PD Data Acquisition Techniques for Condition Monitoring of Medium Voltage Cables

by Muhammad Shafiq, Ivar Kiitam, Kimmo Kauhaniemi, Paul Taklaja, Lauri Kütt and Ivo Palu

Energies 2020, 13(16), 4272; https://doi.org/10.3390/en13164272 - 18 Aug 2020

Cited by 10 | Viewed by 3047

Abstract

Already installed cables are aging and the cable network is growing rapidly. Improved condition monitoring methods are required for greater visibility of insulation defects in the cable networks. One of the critical challenges for continuous monitoring is the large amount of partial discharge [...] Read more.

Already installed cables are aging and the cable network is growing rapidly. Improved condition monitoring methods are required for greater visibility of insulation defects in the cable networks. One of the critical challenges for continuous monitoring is the large amount of partial discharge (PD) data that poses constraints on the diagnostic capabilities. This paper presents the performance comparison of two data acquisition techniques based on phase resolved partial discharge (PRPD) and pulse acquisition (PA). The major contribution of this work is to provide an in-depth understanding of these techniques considering the perspective of randomness of the PD mechanism and improvements in the reliability of diagnostics. Experimental study is performed on the medium voltage (MV) cables in the laboratory environment. It has been observed that PRPD based acquisition not only requires a significantly larger amount of data but is also susceptible to losing the important information especially when multiple PD sources are being investigated. On the other hand, the PA technique presents improved performance for PD diagnosis. Furthermore, the use of the PA technique enables the efficient practical implementation of the continuous PD monitoring by reducing the amount of data that is acquired by extracting useful signals and discarding the silent data intervals. Full article

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

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23 pages, 12524 KiB

Open AccessArticle

Kinematics Measurement and Power Requirements of Fruitflies at Various Flight Speeds

by Hao Jie Zhu and Mao Sun

Energies 2020, 13(16), 4271; https://doi.org/10.3390/en13164271 - 18 Aug 2020

Cited by 13 | Viewed by 3720

Abstract

Energy expenditure is a critical characteristic in evaluating the flight performance of flying insects. To investigate how the energy cost of small-sized insects varies with flight speed, we measured the detailed wing and body kinematics in the full speed range of fruitflies and [...] Read more.

Energy expenditure is a critical characteristic in evaluating the flight performance of flying insects. To investigate how the energy cost of small-sized insects varies with flight speed, we measured the detailed wing and body kinematics in the full speed range of fruitflies and computed the aerodynamic forces and power requirements of the flies. As flight speed increases, the body angle decreases and the stroke plane angle increases; the wingbeat frequency only changes slightly; the geometrical angle of attack in the middle upstroke increases; the stroke amplitude first decreases and then increases. The mechanical power of the fruitflies at all flight speeds is dominated by aerodynamic power (inertial power is very small), and the magnitude of aerodynamic power in upstroke increases significantly at high flight speeds due to the increase of the drag and the flapping velocity of the wing. The specific power (power required for flight divided by insect weigh) changes little when the advance ratio is below about 0.45 and afterwards increases sharply. That is, the specific power varies with flight speed according to a J-shaped curve, unlike those of aircrafts, birds and large-sized insects which vary with flight speed according to a U-shaped curve. Full article

(This article belongs to the Section A4: Bio-Energy)

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18 pages, 5672 KiB

Open AccessArticle

AC–DC Flyback Dimmable LED Driver with Low-Frequency Current Ripple Reduced and Power Dissipation in BJT Linearly Proportional to LED Current

by Yeu-Torng Yau, Kuo-Ing Hwu and Kun-Jie Liu

Energies 2020, 13(16), 4270; https://doi.org/10.3390/en13164270 - 18 Aug 2020

Cited by 5 | Viewed by 3490

Abstract

In this paper, a dimmable light-emitting diode (LED) driver, along with the low-frequency current ripple decreased and the bipolar junction transistor (BJT) power dissipation reduced, is developed. This driver is designed based on a single-stage flyback converter. On the one hand, the low-frequency [...] Read more.

In this paper, a dimmable light-emitting diode (LED) driver, along with the low-frequency current ripple decreased and the bipolar junction transistor (BJT) power dissipation reduced, is developed. This driver is designed based on a single-stage flyback converter. On the one hand, the low-frequency output current ripple reduction is based on the physical behavior of the linear current regulator. On the other hand, when the voltage across the LED string is decreased/increased due to dimming or temperature, the output voltage of the flyback converter will be automatically regulated down/up, thereby making the power dissipation in the BJT linearly proportional to the LED current. By doing so, not only the power loss in the linear current regulator will be decreased as the LED current is decreased or the LED temperature rises, but also the output current ripple can be reduced. Furthermore, the corresponding power factor (PF) is almost not changed, and the total harmonic distortion (THD) is improved slightly. In addition, the LED dimming is based on voltage division. Eventually, a 30 W LED driver, with an input voltage range from 85 to 295 V_rms and with 24 LEDs in series used as a load, is developed, and accordingly, the feasibility of the proposed LED driver is validated by experimental results. Full article

(This article belongs to the Special Issue Technology Evolution and Power Quality Issues in Designing Future Lighting Systems)

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21 pages, 7211 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Power and Wind Shear Implications of Large Wind Turbine Scenarios in the US Central Plains

by Rebecca J. Barthelmie, Tristan J. Shepherd, Jeanie A. Aird and Sara C. Pryor

Energies 2020, 13(16), 4269; https://doi.org/10.3390/en13164269 - 18 Aug 2020

Cited by 22 | Viewed by 4993

Abstract

Continued growth of wind turbine physical dimensions is examined in terms of the implications for wind speed, power and shear across the rotor plane. High-resolution simulations with the Weather Research and Forecasting model are used to generate statistics of wind speed profiles for [...] Read more.

Continued growth of wind turbine physical dimensions is examined in terms of the implications for wind speed, power and shear across the rotor plane. High-resolution simulations with the Weather Research and Forecasting model are used to generate statistics of wind speed profiles for scenarios of current and future wind turbines. The nine-month simulations, focused on the eastern Central Plains, show that the power scales broadly as expected with the increase in rotor diameter (D) and wind speeds at hub-height (H). Increasing wind turbine dimensions from current values (approximately H = 100 m, D = 100 m) to those of the new International Energy Agency reference wind turbine (H = 150 m, D = 240 m), the power across the rotor plane increases 7.1 times. The mean domain-wide wind shear exponent (α) decreases from 0.21 (H = 100 m, D = 100 m) to 0.19 for the largest wind turbine scenario considered (H = 168 m, D = 248 m) and the frequency of extreme positive shear (α > 0.2) declines from 48% to 38% of 10-min periods. Thus, deployment of larger wind turbines potentially yields considerable net benefits for both the wind resource and reductions in fatigue loading related to vertical shear. Full article

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

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16 pages, 2143 KiB

Open AccessArticle

Structural Vector Autoregressive Approach to Evaluate the Impact of Electricity Generation Mix on Economic Growth and CO₂ Emissions in Iran

by Bahareh Oryani, Yoonmo Koo and Shahabaldin Rezania

Energies 2020, 13(16), 4268; https://doi.org/10.3390/en13164268 - 18 Aug 2020

Cited by 19 | Viewed by 2965

Abstract

This research attempts to evaluate the impact of renewable electricity generation mix on economic growth and CO₂ emissions in Iran from 1980 to 2016. In this regard, by using EViews 10, the Structural Vector Autoregressive model (SVAR) is estimated by imposing the [...] Read more.

This research attempts to evaluate the impact of renewable electricity generation mix on economic growth and CO₂ emissions in Iran from 1980 to 2016. In this regard, by using EViews 10, the Structural Vector Autoregressive model (SVAR) is estimated by imposing the Blanchard and Quah long-run restrictions. The yearly data on real Gross Domestic Production (GDP), the share of electricity generation from renewable sources, and carbon dioxide emissions (CO₂) caused by liquid, solid, and gaseous fuels were used. The positive impact of one standard deviation shock of increasing the share of renewable electricity on economic growth was confirmed by using Impulse Response Function (IRF). Contrary to the expectation, the share of renewable electricity in the energy mix is not at a desirable level to lower CO₂ emissions, which partly could be explained by the dominant role of fossil fuel in Iran (as an energy-driven country). Moreover, the findings of Variance Decomposition (VD) verified the low share of electricity generated by renewable energy in explaining forecast error variations in economic growth and CO₂ emissions. It indicates that in this stage of development, increasing the share of renewable electricity could not be considered as an appropriate strategy to control environmental issues. Therefore, initiating and implementing environmental policies could be considered as the most proper policies to lower CO₂ emissions and to achieve the goal of sustainable development. Full article

(This article belongs to the Section B: Energy and Environment)

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19 pages, 2435 KiB

Open AccessArticle

The Influence of Power Sources for Charging the Batteries of Electric Cars on CO₂ Emissions during Daily Driving: A Case Study from Poland

by Łukasz Sobol and Arkadiusz Dyjakon

Energies 2020, 13(16), 4267; https://doi.org/10.3390/en13164267 - 18 Aug 2020

Cited by 24 | Viewed by 12399

Abstract

The main sources of greenhouse gas emissions and air pollution from the transport sector are diesel- and gasoline-powered passenger cars. The combustion of large amounts of conventional fuels by cars contributes to a significant release of various compounds into the atmosphere, such as [...] Read more.

The main sources of greenhouse gas emissions and air pollution from the transport sector are diesel- and gasoline-powered passenger cars. The combustion of large amounts of conventional fuels by cars contributes to a significant release of various compounds into the atmosphere, such as solid particles, nitrogen oxides, carbon monoxide, and carbon dioxide. In order to reduce these pollutants in places of their high concentration (especially in urban agglomerations), the use of ecological means of transport for daily driving is highly recommended. Electric vehicles (EV) are characterized by ecological potential due to their lack of direct emissions and low noise. However, in Poland and many other countries, electricity production is still based on fossil fuels which can significantly influence the indirect emissions of carbon dioxide into the atmosphere associated with battery charging. Thus, indirect emissions from electric cars may be comparable or even higher than direct emissions related to the use of traditional cars. Therefore, the aim of the work was to analyze the amount of carbon dioxide emissions associated with the use of electric vehicles for daily driving (City, Sedan, SUV) and their impact on the environment on a local and global scale. Based on the assumed daily number of kilometers driven by the vehicle and the collected certified catalog data (Car Info Nordic AB), the direct emissions generated by the internal combustion engines (ICE) were calculated for specific cars. These values were compared to the indirect emissions related to the source of electricity generation, for the calculation of which the CO₂ emission coefficient for a particular energy source and energy mix was used, as well as reference values of electricity generation efficiency in a given combustion installation, in accordance with the KOBiZE (The National Centre for Emissions Management) and European Union regulation. Indirect emissions generated from non-renewable fuels (lignite, hard coal, natural gas, diesel oil, heating oil, municipal waste) and renewable emissions (wind energy, solar energy, hydro energy, biomass, biogas) were considered. The results indicated that for the Polish case study, indirect carbon dioxide emission associated with the daily driving of EV (distance of 26 km) ranges 2.49–3.28 kgCO₂∙day⁻¹. As a result, this indirect emission can be even higher than direct emissions associated with ICE usage (2.55–5.64 kgCO₂∙day⁻¹). Full article

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

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31 pages, 1194 KiB

Open AccessReview

An Overview of Demand Response in Smart Grid and Optimization Techniques for Efficient Residential Appliance Scheduling Problem

by Amit Shewale, Anil Mokhade, Nitesh Funde and Neeraj Dhanraj Bokde

Energies 2020, 13(16), 4266; https://doi.org/10.3390/en13164266 - 18 Aug 2020

Cited by 61 | Viewed by 6865

Abstract

Smart grid (SG) is a next-generation grid which is responsible for changing the lifestyle of modern society. It avoids the shortcomings of traditional grids by incorporating new technologies in the existing grids. In this paper, we have presented SG in detail with its [...] Read more.

Smart grid (SG) is a next-generation grid which is responsible for changing the lifestyle of modern society. It avoids the shortcomings of traditional grids by incorporating new technologies in the existing grids. In this paper, we have presented SG in detail with its features, advantages, and architecture. The demand side management techniques used in smart grid are also presented. With the wide usage of domestic appliances in homes, the residential users need to optimize the appliance scheduling strategies. These strategies require the consumer’s flexibility and awareness. Optimization of the power demand for home appliances is a challenge faced by both utility and consumers, particularly during peak hours when the consumption of electricity is on the higher side. Therefore, utility companies have introduced various time-varying incentives and dynamic pricing schemes that provides different rates of electricity at different times depending on consumption. The residential appliance scheduling problem (RASP) is the problem of scheduling appliances at appropriate periods considering the pricing schemes. The objectives of RASP are to minimize electricity cost (EC) of users, minimize the peak-to-average ratio (PAR), and improve the user satisfaction (US) level by minimizing waiting times for the appliances. Various methods have been studied for energy management in residential sectors which encourage the users to schedule their appliances efficiently. This paper aims to give an overview of optimization techniques for residential appliance scheduling. The reviewed studies are classified into classical techniques, heuristic approaches, and meta-heuristic algorithms. Based on this overview, the future research directions are proposed. Full article

(This article belongs to the Special Issue Optimization Models to Foster Demand Response in Power Systems)

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24 pages, 3093 KiB

Open AccessArticle

Solution of Optimal Power Flow Using Non-Dominated Sorting Multi Objective Based Hybrid Firefly and Particle Swarm Optimization Algorithm

by Abdullah Khan, Hashim Hizam, Noor Izzri Abdul-Wahab and Mohammad Lutfi Othman

Energies 2020, 13(16), 4265; https://doi.org/10.3390/en13164265 - 18 Aug 2020

Cited by 22 | Viewed by 3232

Abstract

In this paper, a multi-objective hybrid firefly and particle swarm optimization (MOHFPSO) was proposed for different multi-objective optimal power flow (MOOPF) problems. Optimal power flow (OPF) was formulated as a non-linear problem with various objectives and constraints. Pareto optimal front was obtained by [...] Read more.

In this paper, a multi-objective hybrid firefly and particle swarm optimization (MOHFPSO) was proposed for different multi-objective optimal power flow (MOOPF) problems. Optimal power flow (OPF) was formulated as a non-linear problem with various objectives and constraints. Pareto optimal front was obtained by using non-dominated sorting and crowding distance methods. Finally, an optimal compromised solution was selected from the Pareto optimal set by applying an ideal distance minimization method. The efficiency of the proposed MOHFPSO technique was tested on standard IEEE 30-bus and IEEE 57-bus test systems with various conflicting objectives. Simulation results were also compared with non-dominated sorting based multi-objective particle swarm optimization (MOPSO) and different optimization algorithms reported in the current literature. The achieved results revealed the potential of the proposed algorithm for MOOPF problems. Full article

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

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22 pages, 3456 KiB

Open AccessFeature PaperArticle

Process Modelling and Simulation of Waste Gasification-Based Flexible Polygeneration Facilities for Power, Heat and Biofuels Production

by Chaudhary Awais Salman and Ch Bilal Omer

Energies 2020, 13(16), 4264; https://doi.org/10.3390/en13164264 - 18 Aug 2020

Cited by 24 | Viewed by 4247

Abstract

There is increasing interest in the harnessing of energy from waste owing to the increase in global waste generation and inadequate currently implemented waste disposal practices, such as composting, landfilling or dumping. The purpose of this study is to provide a modelling and [...] Read more.

There is increasing interest in the harnessing of energy from waste owing to the increase in global waste generation and inadequate currently implemented waste disposal practices, such as composting, landfilling or dumping. The purpose of this study is to provide a modelling and simulation framework to analyze the technical potential of treating municipal solid waste (MSW) and refuse-derived fuel (RDF) for the polygeneration of biofuels along with district heating (DH) and power. A flexible waste gasification polygeneration facility is proposed in this study. Two types of waste—MSW and RDF—are used as feedstock for the polygeneration process. Three different gasifiers—the entrained flow gasifier (EFG), circulating fluidized bed gasifier (CFBG) and dual fluidized bed gasifier (DFBG)—are compared. The polygeneration process is designed to produce DH, power and biofuels (methane, methanol/dimethyl ether, gasoline or diesel and ammonia). Aspen Plus is used for the modelling and simulation of the polygeneration processes. Four cases with different combinations of DH, power and biofuels are assessed. The EFG shows higher energy efficiency when the polygeneration process provides DH alongside power and biofuels, whereas the DFBG and CFBG show higher efficiency when only power and biofuels are produced. RDF waste shows higher efficiency as feedstock than MSW in polygeneration process. Full article

(This article belongs to the Special Issue The Potential Role of Renewable Energy Sources (RES) in Combined Heat and Power (CHP) and Polygeneration Systems)

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15 pages, 15383 KiB

Open AccessArticle

VSG Control Strategy Incorporating Voltage Inertia and Virtual Impedance for Microgrids

by Zipeng Ke, Yuxing Dai, Zishun Peng, Guoqiang Zeng, Jun Wang, Minying Li and Yong Ning

Energies 2020, 13(16), 4263; https://doi.org/10.3390/en13164263 - 18 Aug 2020

Cited by 6 | Viewed by 2767

Abstract

Virtual synchronous generator (VSG) control lacks voltage inertia and powerful decoupling capabilities. The voltage of the distributed generator (DG) unit controlled by the VSG will be easily affected by power fluctuations and high-frequency noise, and the DG coupling usually makes the VSG control [...] Read more.

Virtual synchronous generator (VSG) control lacks voltage inertia and powerful decoupling capabilities. The voltage of the distributed generator (DG) unit controlled by the VSG will be easily affected by power fluctuations and high-frequency noise, and the DG coupling usually makes the VSG control effect unsatisfactory. In order to effectively reduce power fluctuations, the influence of high-frequency noise on voltage, the influence of coupling on the power regulation, and effectively improve the economy of the economic system, the improved VSG control that combines voltage inertia and virtual impedance is proposed in this paper. The second-order inertia in the proposed VSG control strategy can minimize the voltage change rate and filter high-frequency noise from the excitation and virtual impedance. The virtual impedance in the proposed VSG control strategy can simulate the actual impedance to change the line characteristics, so the coupling of the DG unit can be reduced. Experimental results based on the microgrid platform prove the feasibility of improving the VSG control. Full article

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

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15 pages, 5354 KiB

Open AccessArticle

Development of Greener D-Metal Inorganic Crosslinkers for Polymeric Gels Used in Water Control in Oil and Gas Applications

by Hassan I. Nimir, Ahmed Hamza and Ibnelwaleed A. Hussein

Energies 2020, 13(16), 4262; https://doi.org/10.3390/en13164262 - 18 Aug 2020

Cited by 5 | Viewed by 2379

Abstract

Crosslinkable polymers, such as polyacrylamide (PAM), are widely applied for water control in oil and gas reservoirs. Organic and inorganic crosslinkers are used to formulate a gel with PAM. Although chromium has a high level of toxicity, it has been implemented as an [...] Read more.

Crosslinkable polymers, such as polyacrylamide (PAM), are widely applied for water control in oil and gas reservoirs. Organic and inorganic crosslinkers are used to formulate a gel with PAM. Although chromium has a high level of toxicity, it has been implemented as an effective crosslinker combined with carboxylates because of the controllability of crosslinking time at low temperatures. The objective of this work was to develop greener d-metal inorganic crosslinkers based on cobalt, copper, and nickel to replace chromium for application at reservoir conditions. The obtained results showed that the gelation chemistry of the developed systems depends on the metal charge density. The gelation of PAM with d-metals depends on pH and temperature for low- and high-charge density, respectively. Cobalt (II) acetate (CoAc) was effective at high temperatures (130–150 °C) and forms (4% CoAc + 9%PAM) stable, and strong gels at a pH > 7 with a storage modulus exceeding 4300 Pa. However, Nickel Acetate and Cupper Acetate formed stable weak gels at low temperatures (50–70 °C) and a pH > 6 and gel decomposition was observed upon increasing the temperature. The developed formulations were compatible with low-salinity water (1000 ppm NaCl). Full article

(This article belongs to the Special Issue CO2 EOR and Sequestration: Conventional and Unconventional Reservoirs)

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31 pages, 5651 KiB

Open AccessArticle

Electricity Generation from Renewable Energy Sources in Poland as a Part of Commitment to the Polish and EU Energy Policy

by Józef Paska, Tomasz Surma, Paweł Terlikowski and Krzysztof Zagrajek

Energies 2020, 13(16), 4261; https://doi.org/10.3390/en13164261 - 18 Aug 2020

Cited by 37 | Viewed by 7984

Abstract

The aim of this paper is to present the state of development of renewable energy sources (RES) in Poland in accordance with the obligations of European Union energy policy. The EU Member States are obliged to adopt different support mechanisms for the development [...] Read more.

The aim of this paper is to present the state of development of renewable energy sources (RES) in Poland in accordance with the obligations of European Union energy policy. The EU Member States are obliged to adopt different support mechanisms for the development of renewable energy sources, and in consequence to achieve their Directive’s targets. Poland, being a Member State of the EU since 2004, has accepted a target of a 15% share of energy generated from renewable energy sources in final energy consumption, including 19.3% from renewable electricity until 2020. Due to the difficulties with target achievement, the authors found it reasonable to analyze the challenge of RES development in Poland. The article presents energy policy in the EU, as well as the review of measures implemented for renewable energy development. The current state of and perspectives on using renewable energy sources in Poland and in the EU are also depicted. In the article, the authors analyze the relation between reference prices at dedicated RES auctions in Poland and the levelized cost of electricity (LCOE). The paper also provides a description of the renewable energy sources’ development in three areas: electricity, heat and transport biofuels. Its main content, though, refers to the generation of electricity from renewable energy sources. Full article

(This article belongs to the Special Issue Sustainable Energy Technologies for Power System Transformation)

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26 pages, 7743 KiB

Open AccessArticle

Fault Ride through Capability Analysis (FRT) in Wind Power Plants with Doubly Fed Induction Generators for Smart Grid Technologies

by Aphrodis Nduwamungu, Etienne Ntagwirumugara, Francis Mulolani and Waqar Bashir

Energies 2020, 13(16), 4260; https://doi.org/10.3390/en13164260 - 17 Aug 2020

Cited by 11 | Viewed by 4865

Abstract

Faults in electrical networks are among the key factors and sources of network disturbances. Control and automation strategies are among the key fault clearing techniques responsible for the safe operation of the system. Several researchers have revealed various constraints of control and automation [...] Read more.

Faults in electrical networks are among the key factors and sources of network disturbances. Control and automation strategies are among the key fault clearing techniques responsible for the safe operation of the system. Several researchers have revealed various constraints of control and automation strategies such as a slow dynamic response, the inability to switch the network on and off remotely, a high fault clearing time and loss minimization. For a system with wind energy technologies, if the power flow of a wind turbine is perturbed by a fault, the intermediate circuit voltage between the machine side converter and line side converter will rise to unacceptably high values due to the accumulation of energy in the DC link capacitor. To overcome the aforementioned issues, this paper used MATLAB simulations and experiments to analyze and validate the results. The results revealed that fault ride through capability with Supervisory Control and Data Acquisition (SCADA) viewer software, Active Servo software and wind sim packages are more adaptable to the variations of voltage sag, voltage swell and wind speed and avoid loss of synchronism and improve power quality. Furthermore, for protection purposes, a DC chopper and a crowbar should be incorporated into the management of excess energy during faults and a ferrite device included for the reduction of the electromagnetic field. Full article

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

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16 pages, 3415 KiB

Open AccessArticle

Measurement-Based Distribution Grid Harmonic Impedance Models and Their Uncertainties

by Ravi Shankar Singh, Vladimir Ćuk and Sjef Cobben

Energies 2020, 13(16), 4259; https://doi.org/10.3390/en13164259 - 17 Aug 2020

Cited by 9 | Viewed by 2801

Abstract

Aggregated Norton’s equivalent models, with parallel impedance and current injection at different harmonic frequencies are used to model the distribution grid in harmonic studies. These models are derived based on measurements and/or prior knowledge about the grid. The measurement-based distribution (sub-)grid impedance estimation [...] Read more.

Aggregated Norton’s equivalent models, with parallel impedance and current injection at different harmonic frequencies are used to model the distribution grid in harmonic studies. These models are derived based on measurements and/or prior knowledge about the grid. The measurement-based distribution (sub-)grid impedance estimation method uses harmonic phasors of 3-phase current and voltage measurements to capture the response of the distribution (sub-)grid before and after an event in the utility side of the grid. However, due to increasing non-linear components in the grid, knowledge about uncertainty in parameters of such equivalent models which intrinsically describe a linear grid becomes important. The aim of this paper is to present two novel methods to calculate the uncertainty of the measurement-based Norton’s equivalent harmonic model of the distribution (sub-)grids as seen from the utility side at the Point of Common Coupling (PCC). The impedance and the uncertainty calculations are demonstrated on a simulated network. Full article

(This article belongs to the Special Issue Harmonics and Quality of Power)

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23 pages, 4103 KiB

Open AccessArticle

Single Column Model Simulations of Icing Conditions in Northern Sweden: Sensitivity to Surface Model Land Use Representation

by Erik Janzon, Heiner Körnich, Johan Arnqvist and Anna Rutgersson

Energies 2020, 13(16), 4258; https://doi.org/10.3390/en13164258 - 17 Aug 2020

Cited by 2 | Viewed by 2531

Abstract

In-cloud ice mass accretion on wind turbines is a common challenge that is faced by energy companies operating in cold climates. On-shore wind farms in Scandinavia are often located in regions near patches of forest, the heterogeneity length scales of which are often [...] Read more.

In-cloud ice mass accretion on wind turbines is a common challenge that is faced by energy companies operating in cold climates. On-shore wind farms in Scandinavia are often located in regions near patches of forest, the heterogeneity length scales of which are often less than the resolution of many numerical weather prediction (NWP) models. The representation of these forests—including the cloud water response to surface roughness and albedo effects that are related to them—must therefore be parameterized in NWP models used as meteorological input in ice prediction systems, resulting in an uncertainty that is poorly understood and, to the present date, not quantified. The sensitivity of ice accretion forecasts to the subgrid representation of forests is examined in this study. A single column version of the HARMONIE-AROME three-dimensional (3D) NWP model is used to determine the sensitivity of the forecast of ice accretion on wind turbines to the subgrid forest fraction. Single column simulations of a variety of icing cases at a location in northern Sweden were examined in order to investigate the impact of vegetation cover on ice accretion in varying levels of solar insolation and wind magnitudes. In mid-winter cases, the wind speed response to surface roughness was the primary driver of the vegetation effect on ice accretion. In autumn cases, the cloud water response to surface albedo effects plays a secondary role in the impact of in-cloud ice accretion, with the wind response to surface roughness remaining the primary driver for the surface vegetation impact on icing. Two different surface boundary layer (SBL) forest canopy subgrid parameterizations were tested in this study that feature different methods for calculating near-surface profiles of wind, temperature, and moisture, with the ice mass accretion again following the wind response to surface vegetation between both of these schemes. Full article

(This article belongs to the Special Issue Recent Advances in Wind Power Meteorology)

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16 pages, 1259 KiB

Open AccessArticle

Thermophilic Co-Fermentation of Wood Wastes and High in Nitrogen Animal Manures into Bio-Methane with the Aid of Fungi and its Potential in the USA

by John G. Ingersoll

Energies 2020, 13(16), 4257; https://doi.org/10.3390/en13164257 - 17 Aug 2020

Cited by 6 | Viewed by 2816

Abstract

A novel process is proposed whereby wood wastes from forest tree mortalities and improved forest management are co-digested with high in nitrogen content animal manures to yield bio-methane along with nitrogen, phosphorous, and potassium bio-fertilizers. The process mimics the well-known wood conversion to [...] Read more.

A novel process is proposed whereby wood wastes from forest tree mortalities and improved forest management are co-digested with high in nitrogen content animal manures to yield bio-methane along with nitrogen, phosphorous, and potassium bio-fertilizers. The process mimics the well-known wood conversion to methane process in lower termites but relies on thermophilic fungi, bacteria, and archaea instead. It is based on the modified state-of-the art two-step, hyperthermophilic (70 °C) hydrolysis and thermophilic (55 °C) fermentation, dry (30% TS), anaerobic digestion technology with a high organic loading and shortened retention time. The process is augmented with the thermophilic fermentation of carbon dioxide in the biogas into secondary bio-methane by employing hydrogen produced via wind-powered electrolysis. The entire process comprised of five distinct steps is designated as “Wood to Methane 3 + 2”. An industrial type, standardized plant unit has been developed that can be employed in a modular fashion. The implementation of these plant units across the US, utilizing the estimated waste wood potential along with 3/4 of the produced poultry and pig manure, would generate the equivalent of 2/3 of transportation fuel consumption and would supply about 11% of current US energy use per annum. The produced bio-methane can be cost-competitive only if it is employed as a transportation fuel to replace fossil gasoline and diesel fuels. The required annual investment over a 20-year period is well within the means of the US economy in a public–private development partnership. Full article

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19 pages, 3115 KiB

Open AccessArticle

Innovative Hydrodynamic Disintegrator Adjusted to Agricultural Substrates Pre-treatment Aimed at Methane Production Intensification—CFD Modelling and Batch Tests

by Monika Zubrowska-Sudol, Aleksandra Dzido, Agnieszka Garlicka, Piotr Krawczyk, Michał Stępień, Katarzyna Umiejewska, Justyna Walczak, Marcin Wołowicz and Katarzyna Sytek-Szmeichel

Energies 2020, 13(16), 4256; https://doi.org/10.3390/en13164256 - 17 Aug 2020

Cited by 17 | Viewed by 2736

Abstract

The study objective was to adjust the hydrodynamic disintegrator dedicated to sewage sludge pre-treatment (HDS) to work with agricultural substrate. This involved the development and implementation of a mathematical model of flow via the device’s domain. An innovative disintegrator (HAD—hydrodynamic disintegrator for agriculture) [...] Read more.

The study objective was to adjust the hydrodynamic disintegrator dedicated to sewage sludge pre-treatment (HDS) to work with agricultural substrate. This involved the development and implementation of a mathematical model of flow via the device’s domain. An innovative disintegrator (HAD—hydrodynamic disintegrator for agriculture) was designed, built, and tested based on the obtained results. The main improvements to the HDS include the implementation of shredding knives in order to overcome clogging by crushed substrate, and the application of ribs in the recirculation zone, contributing to the development of an additional structure damage zone. The challenge of this study was also to determine the operating parameters of the HDA that would provide for an increase in methane production with positive energy balance. The testing procedures, for which maize silage was selected, involved batch disintegration tests and biochemical methane potential tests. No clogging of rotor or spontaneous shutting off of the device, in other words, problems that had occurred in the HDS, were observed. The applied pre-treatment method permitted an increase in the methane potential of maize silage by 34.4%, 27.0%, and 21.6%, respectively for samples disintegrated at energy densities of 10 kJ/L, 20 kJ/L, and 35 kJ/L with net energy profit. Full article

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

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10 pages, 2297 KiB

Open AccessCommunication

Simulating Power Generation from Photovoltaics in the Polish Power System Based on Ground Meteorological Measurements—First Tests Based on Transmission System Operator Data

by Jakub Jurasz, Marcin Wdowikowski and Mariusz Figurski

Energies 2020, 13(16), 4255; https://doi.org/10.3390/en13164255 - 17 Aug 2020

Cited by 3 | Viewed by 2813

Abstract

The Polish power system is undergoing a slow process of transformation from coal to one that is renewables dominated. Although coal will remain a fundamental fuel in the coming years, the recent upsurge in installed capacity of photovoltaic (PV) systems should draw significant [...] Read more.

The Polish power system is undergoing a slow process of transformation from coal to one that is renewables dominated. Although coal will remain a fundamental fuel in the coming years, the recent upsurge in installed capacity of photovoltaic (PV) systems should draw significant attention. Owning to the fact that the Polish Transmission System Operator recently published the PV hourly generation time series in this article, we aim to explore how well those can be modeled based on the meteorological measurements provided by the Institute of Meteorology and Water Management. The hourly time series of PV generation on a country level and irradiation, wind speed, and temperature measurements from 23 meteorological stations covering one month are used as inputs to create an artificial neural network. The analysis indicates that available measurements combined with artificial neural networks can simulate PV generation on a national level with a mean percentage error of 3.2%. Full article

(This article belongs to the Special Issue Computational Intelligence for Modeling, Control, Optimization, Forecasting and Diagnostics in Photovoltaic Applications)

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27 pages, 4969 KiB

Open AccessArticle

Sustainable Development and Industry 4.0: A Bibliometric Analysis Identifying Key Scientific Problems of the Sustainable Industry 4.0

by Bożena Gajdzik, Sandra Grabowska, Sebastian Saniuk and Tadeusz Wieczorek

Energies 2020, 13(16), 4254; https://doi.org/10.3390/en13164254 - 17 Aug 2020

Cited by 63 | Viewed by 5889

Abstract

The main aim of the manuscript is the identification of key research problems in the field of sustainable development, in the era of implementing the Industry 4.0 concept. The manuscript presents results of the bibliometric analysis in the subject: “Sustainable Industry 4.0”. The [...] Read more.

The main aim of the manuscript is the identification of key research problems in the field of sustainable development, in the era of implementing the Industry 4.0 concept. The manuscript presents results of the bibliometric analysis in the subject: “Sustainable Industry 4.0”. The bibliometric analysis was realized in three segments: Sustainability, Industry 4.0 and Sustainable Industry 4.0. In the analysis, the following databases were used: Web of Science (WoS), Scopus, Google Scholar. The main purpose of the analysis was to outline the dynamics of publications in the categories: citation, author, country, type document, science field, research area. The review of sources carried out in this way allowed us to identify key research areas and confirm the research thesis adopted in the manuscript. The research thesis: Sustainable Industry 4.0 allows the integration of the Industry 4.0 concept with sustainable development goals. The article is dedicated especially to scientists looking for still unsolved research problems in the implementation of sustainable Industry 4.0. Furthermore, the manuscript could be an inspiration for scientists, stakeholders, practitioners and governments to complete today’s knowledge about the problems of sustainability in Industry 4.0. Full article

(This article belongs to the Special Issue Integrated Approaches for Enterprise Sustainability)

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22 pages, 4085 KiB

Open AccessArticle

Analysis of Gas Recirculation Influencing Factors of a Double Reheat 1000 MW Unit with the Reheat Steam Temperature under Control

by Meng Yue, Guoqian Ma and Yuetao Shi

Energies 2020, 13(16), 4253; https://doi.org/10.3390/en13164253 - 17 Aug 2020

Cited by 3 | Viewed by 3455

Abstract

In this paper, the simulation software EBSILON is used to simulate the reheat units, and the reheat temperature control mode is deeply explored. In the benchmark system, the influence of different load intermediate point temperature on the flue gas recirculation (FGR) is analyzed. [...] Read more.

In this paper, the simulation software EBSILON is used to simulate the reheat units, and the reheat temperature control mode is deeply explored. In the benchmark system, the influence of different load intermediate point temperature on the flue gas recirculation (FGR) is analyzed. Then, the effects of load, coal quality, excess air factor, and feed water temperature on FGR are studied under the premise of intermediate point temperature as design value, and the cause for FGR change is analyzed by comparing the cutoff bypass flue (CBF) system. The results show that under any load, the FGR decreases with the increase of the intermediate point temperature, while under low load, the change of the intermediate point temperature has a greater impact on the FGR rate. When the intermediate point temperature remains constant, the FGR plunge has an increase of load at low load and is almost unchanged at high load; the FGR rate of coal with low calorific value and high moisture content is low and the coal with low volatile and high ash content has great influence on reheat steam temperature; and the excess air factor and feed water temperature are inversely proportional to the flue gas recirculation rate. In the CBF system, the change trend is similar to the reference system, but under the same working condition, the FGR rate is higher than the latter. Full article

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22 pages, 7066 KiB

Open AccessArticle

Impacts of Investment Cost, Energy Prices and Carbon Tax on Promoting the Combined Cooling, Heating and Power (CCHP) System of an Amusement Park Resort in Shanghai

by Liting Zhang, Weijun Gao, Yongwen Yang and Fanyue Qian

Energies 2020, 13(16), 4252; https://doi.org/10.3390/en13164252 - 17 Aug 2020

Cited by 9 | Viewed by 3218

Abstract

Poor economic performance has limited the diffusion of the combined cooling, heating, and power (CCHP) system. Various factors influence the economic performance of the CCHP system. To analyze the impacts of these different factors and promote the CCHP system, this study evaluated its [...] Read more.

Poor economic performance has limited the diffusion of the combined cooling, heating, and power (CCHP) system. Various factors influence the economic performance of the CCHP system. To analyze the impacts of these different factors and promote the CCHP system, this study evaluated its comprehensive performance through a multi-criteria method, using an amusement park resort in Shanghai as a research case. First, three CCHP systems with different penetration rates were presented and simulated in a transient simulation model for comparison. The economic and environmental performance of these different penetration CCHP systems were evaluated based on the dynamic payback period and carbon dioxide emissions. The impacts of investment cost, energy prices, investment subsidy and a carbon tax on the economic performance of the three systems were discussed, and a sensitivity analysis was used to compare these factors. The results show that the current subsidy can reduce the economic gap between the CCHP system and the conventional system, but it still needs to be increased by 1.71 times to achieve market competitiveness of the CCHP system with 100% penetration under the current investment cost and energy prices. In addition, the introduction of a carbon tax could accelerate the promotion of the CCHP system. When the carbon tax reaches 25 $/ton, the CCHP system becomes the best choice of energy supply system. Full article

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26 pages, 8059 KiB

Open AccessArticle

Willow Biomass Crops Are a Carbon Negative or Low-Carbon Feedstock Depending on Prior Land Use and Transportation Distances to End Users

by Sheng Yang, Timothy A. Volk and Marie-Odile P. Fortier

Energies 2020, 13(16), 4251; https://doi.org/10.3390/en13164251 - 17 Aug 2020

Cited by 20 | Viewed by 4747

Abstract

Few life cycle assessments (LCAs) on willow biomass production have investigated the effects of key geographically specific parameters. This study uses a spatial LCA model for willow biomass production to determine spatially explicit greenhouse gas (GHG) emissions and energy return on investment (EROI), [...] Read more.

Few life cycle assessments (LCAs) on willow biomass production have investigated the effects of key geographically specific parameters. This study uses a spatial LCA model for willow biomass production to determine spatially explicit greenhouse gas (GHG) emissions and energy return on investment (EROI), including land use conversion from pasture and cropland or grassland. There were negative GHG emissions on 92% of the land identified as suitable for willow biomass production, indicating this system’s potential for climate change mitigation. For willow planted on cropland or pasture, life cycle GHG emissions ranged from −53.2 to −176.9 kg CO_2eq Mg^-1. When willow was grown on grassland the projected decrease in soil organic carbon resulted in a slightly positive GHG balance. Changes in soil organic carbon (SOC) associated with land use change, transportation distance, and willow yield had the greatest impacts on GHG emissions. Results from the uncertainty analysis exhibited large variations in GHG emissions between counties arising from differences in these parameters. The average EROI across the entire region was 19.2. Willow biomass can be a carbon negative or low-carbon energy source with a high EROI in regions with similar infrastructure, transportation distances, and growing conditions such as soil characteristics, land cover types, and climate. Full article

(This article belongs to the Special Issue Renewable Energy Production from Energy Crops and Agricultural Residues)

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27 pages, 5950 KiB

Open AccessReview

Halide Perovskite Single Crystals: Optoelectronic Applications and Strategical Approaches

by Yurou Zhang, Miaoqiang Lyu, Tengfei Qiu, Ekyu Han, Il Ku Kim, Min-Cherl Jung, Yun Hau Ng, Jung-Ho Yun and Lianzhou Wang

Energies 2020, 13(16), 4250; https://doi.org/10.3390/en13164250 - 17 Aug 2020

Cited by 22 | Viewed by 6956

Abstract

Halide perovskite is one of the most promising semiconducting materials in a variety of fields such as solar cells, photodetectors, and light-emitting diodes. Lead halide perovskite single crystals featuring long diffusion length, high carrier mobility, large light absorption coefficient and low defect density, [...] Read more.

Halide perovskite is one of the most promising semiconducting materials in a variety of fields such as solar cells, photodetectors, and light-emitting diodes. Lead halide perovskite single crystals featuring long diffusion length, high carrier mobility, large light absorption coefficient and low defect density, have been attracting increasing attention. Fundamental study of the intrinsic nature keeps revealing the superior optoelectrical properties of perovskite single crystals over their polycrystalline thin film counterparts, but to date, the device performance lags behind. The best power conversion efficiency (PCE) of single crystal-based solar cells is 21.9%, falling behind that of polycrystalline thin film solar cells (25.2%). The oversized thickness, defective surfaces, and difficulties in depositing functional layers, hinder the application of halide perovskite single crystals in optoelectronic devices. Efforts have been made to synthesize large-area single crystalline thin films directly on conductive substrates and apply defect engineering approaches to improve the surface properties. This review starts from a comprehensive introduction of the optoelectrical properties of perovskite single crystals. Then, the synthesis methods for high-quality bulk crystals and single-crystalline thin films are introduced and compared, followed by a systematic review of their optoelectronic applications including solar cells, photodetectors, and X-ray detectors. The challenges and strategical approaches for high-performance applications are summarized at the end with a brief outlook on future work. Full article

(This article belongs to the Special Issue Advanced Polymer and Perovskite Solar Cells)

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14 pages, 3665 KiB

Open AccessArticle

Investigation and Control Technology on Excessive Ammonia-Slipping in Coal-Fired Plants

by Xuan Yao, Man Zhang, Hao Kong, Junfu Lyu and Hairui Yang

Energies 2020, 13(16), 4249; https://doi.org/10.3390/en13164249 - 17 Aug 2020

Cited by 10 | Viewed by 2836

Abstract

After the implementation of the ultra-low emissions regulation on the coal-fired power plants in China, the problem of the excessive ammonia-slipping from selective catalytic reduction (SCR) seems to be more severe. This paper analyzes the operating statistics of the coal-fired plants including 300 [...] Read more.

After the implementation of the ultra-low emissions regulation on the coal-fired power plants in China, the problem of the excessive ammonia-slipping from selective catalytic reduction (SCR) seems to be more severe. This paper analyzes the operating statistics of the coal-fired plants including 300 MW/600 MW/1000-MW units. Statistics data show that the phenomenon of the excessive ammonia-slipping is widespread. The average excessive rate is over 110%, while in the small units the value is even higher. A field test data of nine power plants showed that excessive ammonia-slipping at the outlet of SCR decreased following the flue-gas process. After most ammonia reduced by the dust collector and the wet flue-gas desulfurization (FGD), the ammonia emission at the stack was extremely low. At same time, a method based on probability distribution is proposed in this paper to describe the relationship between the NH₃/NOX distribution deviation and the De–NOX efficiency/ammonia-slipping. This paper also did some original work to solve the ammonia-slipping problem. A real-time self-feedback ammonia injection technology using neural network algorithm to predict and moderate the ammonia distribution is proposed to decrease the NH₃/NOX deviation and excessive ammonia-slipping. The technology is demonstrated in a 600-MW unit and works successfully. The excessive ammonia-slipping problem is well controlled after the implementation of the technology. Full article

(This article belongs to the Special Issue Coal Conversion Processes)

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25 pages, 1857 KiB

Open AccessArticle

How Much Electricity Sharing Will Electric Vehicle Owners Allow from Their Battery? Incorporating Vehicle-to-Grid Technology and Electricity Generation Mix

by Kyuho Maeng, Sungmin Ko, Jungwoo Shin and Youngsang Cho

Energies 2020, 13(16), 4248; https://doi.org/10.3390/en13164248 - 17 Aug 2020

Cited by 13 | Viewed by 3282

Abstract

Global trends and prospects of environmentally friendly transportation have helped to popularize electric vehicles (EVs). With the spread of EVs, vehicle-to-grid (V2G) technology is gaining importance for its role in connecting the electricity stored in the battery of EVs to a grid-like energy [...] Read more.

Global trends and prospects of environmentally friendly transportation have helped to popularize electric vehicles (EVs). With the spread of EVs, vehicle-to-grid (V2G) technology is gaining importance for its role in connecting the electricity stored in the battery of EVs to a grid-like energy storage system (ESS). Electricity generation mix and battery for V2G energy storage have a decisive effect on the stabilization of a V2G system, but no attempt has been made. Therefore, this study analyzes consumer preference considering the electricity generation mix and battery for the V2G. We conduct a conjoint survey of a 1000 South Koreans and employ the multiple discrete-continuous extreme value model. The results show that drivers prefer plug-in hybrid- and battery EVs to other vehicles. Additionally, findings show that driver’s utility changes at 27.9% of the battery allowance for V2G system and it becomes positive after 55.7%. Furthermore, we conduct a scenario analysis considering the electricity generation mix (more traditional vs. renewable) and battery allowance. Based on this analysis, we suggest some policies and corporate strategies to support the success of the V2G market depending on energy policies and battery allowance level. Full article

(This article belongs to the Special Issue Smart Electric Vehicles: Optimization, Security and Privacy Issues)

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Energies, Volume 13, Issue 16 (August-2 2020) – 239 articles

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