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Energies, Volume 11, Issue 10 (October 2018)

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Cover Story (view full-size image) The importance of iodide as an anion in room-temperature ionic liquids (RTILs) is established as an [...] Read more.
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Open AccessArticle Oil Prices and Global Stock Markets: A Time-Varying Causality-In-Mean and Causality-in-Variance Analysis
Energies 2018, 11(10), 2848; https://doi.org/10.3390/en11102848 (registering DOI)
Received: 12 August 2018 / Revised: 15 October 2018 / Accepted: 16 October 2018 / Published: 21 October 2018
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Abstract
This study examines the Granger-causal relationships between oil price movements and global stock returns by using time-varying Granger-causality tests in mean and in variance. We use the daily returns from Morgan Stanley Capital International (MSCI) G7 and the MSCI Emerging Stock Market Indexes
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This study examines the Granger-causal relationships between oil price movements and global stock returns by using time-varying Granger-causality tests in mean and in variance. We use the daily returns from Morgan Stanley Capital International (MSCI) G7 and the MSCI Emerging Stock Market Indexes to distinguish between the effects of daily oil price movements on G7 countries’ and emerging market countries’ stock markets. We further divide the emerging markets into two groups as oil-exporting and oil-importing countries. For the oil market, we use both the West Texas Intermediate (WTI) and Brent oil daily price movements. While the Granger-causality-in-mean tests indicate a causal link from WTI oil prices and G7 countries’ stock returns to MSCI emerging countries’ stock returns, the Granger-causality-in-variance tests suggest no causal link from global oil market prices to stock market returns. Nonetheless, a causal link from the G7 countries’ stock returns to the MSCI emerging countries’ stock returns is detected. In addition, G7 countries’ stock market volatility is found to Granger-cause Brent oil price volatility. The time-varying Granger-causality-in-mean and Granger-causality-in-variance tests present new and further insights. A causal relationship between oil price changes and G7 countries’ stock returns is found for some periods during and after the global financial crisis. Time-varying Granger-causality-in-variance test results indicate evidence of causal linkages among oil prices and global stock market returns that are specific only to certain time periods. We also find that there might be a difference between the movements in Brent and WTI oil prices with respect to their Granger-causal effects on oil-importing emerging markets’ stock returns—especially after the global financial crisis. Our results provide further evidence that the effects of oil price movements on stock returns might be different depending on the volatility in the stock markets. Full article
(This article belongs to the Special Issue Energy Markets and Economics)
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Open AccessArticle Legal and Regulatory Development of Nuclear Energy in Bangladesh
Energies 2018, 11(10), 2847; https://doi.org/10.3390/en11102847 (registering DOI)
Received: 4 September 2018 / Revised: 5 October 2018 / Accepted: 19 October 2018 / Published: 21 October 2018
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Abstract
The adequacy of legal and regulatory framework relating to nuclear energy in Bangladesh has sparked many questions since the government took the formal decision to establish a nuclear power plant (NPP) at Rooppur. Consequently, the government has taken some measures to make a
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The adequacy of legal and regulatory framework relating to nuclear energy in Bangladesh has sparked many questions since the government took the formal decision to establish a nuclear power plant (NPP) at Rooppur. Consequently, the government has taken some measures to make a comprehensive and robust framework to ensure safe and secure nuclear energy production in the country. Even though these initiatives are highly appreciable, there remain certain regulatory concerns which this paper has attempted to reflect. Therefore, the objective of this paper is to showcase the recent legal and regulatory development of Bangladesh in relation to nuclear energy and to recommend further developments. The study was based on secondary sources where a doctrinal research was carried out to solve particular research questions. The safety and security of the Rooppur Nuclear Power Plant will frankly rely on how the government of Bangladesh plans and learns to implement, design, safeguard, exchange and further develop nuclear energy related knowledge and talent around the country. Full article
(This article belongs to the Special Issue 10 Years Energies - Horizon 2028)
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Open AccessArticle Preliminary Performance Tests and Simulation of a V-Shape Roof Guide Vane Mounted on an Eco-Roof System
Energies 2018, 11(10), 2846; https://doi.org/10.3390/en11102846 (registering DOI)
Received: 27 August 2018 / Revised: 4 October 2018 / Accepted: 16 October 2018 / Published: 21 October 2018
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Abstract
The technical and economic features of a patented V-shape roof guide vane (VRGV) with a solar and wind power generation system mounted on an eco-roof system are presented in this paper. Moreover, this innovative VRGV was investigated on for the purpose of improving
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The technical and economic features of a patented V-shape roof guide vane (VRGV) with a solar and wind power generation system mounted on an eco-roof system are presented in this paper. Moreover, this innovative VRGV was investigated on for the purpose of improving the performance of a vertical axis wind turbine (VAWT), which was installed on an eco-roof system to solve the low-efficiency power generation problem of the wind turbines under the condition of a low wind speed. This paper proposes a preliminary study for the performance of the VAWT with the VRGV on a building. This research used a mock-up building with a double slope roof, where a five straight-bladed VAWT was mounted and tested under two conditions, with and without the VRGV. From the comparative experiments, the self-starting performance and rotational speed of the VAWT mounted above a double slope roof with the VRGV have been significantly improved compared to the VAWT without the VRGV. Further, the power coefficient (Cp) of the VAWT can be augmented to about 71.2% increment due to the VRGV design. In addition, numerical simulations by computational fluid dynamics (CFD) were proposed to verify the augmented effect of the Cp of the VAWT under the influence of the VRGV in the experiment. Besides, economic estimation of the VRGV was conducted. Full article
(This article belongs to the Section Sustainable Energy)
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Open AccessArticle Intensification of Continuous Biodiesel Production from Waste Cooking Oils Using Shockwave Power Reactor: Process Evaluation and Optimization through Response Surface Methodology (RSM)
Energies 2018, 11(10), 2845; https://doi.org/10.3390/en11102845 (registering DOI)
Received: 27 July 2018 / Revised: 5 October 2018 / Accepted: 18 October 2018 / Published: 21 October 2018
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Abstract
This research aims to develop an optimal continuous process to produce fatty acid methyl esters (biodiesel) from waste cooking oil using a series of shockwave power reactors. Response surface methodology (RSM) based on central composite design (CCD) was used to design the experiment
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This research aims to develop an optimal continuous process to produce fatty acid methyl esters (biodiesel) from waste cooking oil using a series of shockwave power reactors. Response surface methodology (RSM) based on central composite design (CCD) was used to design the experiment and to analyze five operating parameters: ratio of rotor diameter to stator diameter (Dr/Ds), ratio of cavity diameter to rotor diameter (Dc/Dr), ratio of cavity depth to gap between rotor and stator (dc/∆r), rotational speed of rotor (N), and Residence time (Tr). The optimum conditions were determined to be Dr/Ds = 0.73, Dc/Dr = 0.06, dc/∆r = 0.50, 25,510.55 rpm rotational speed of rotor, and 30.10 s residence times under this condition. Regarding the results, the most important parameter in shockwave power reactor (SPR) reactors was ratio of rotor diameter to stator diameter (Dr/Ds). The optimum predicted and actual FAME yield was 98.53% and 96.62%, respectively, which demonstrates that RSM is a reliable method for modeling the current procedure. Full article
Open AccessReview A Review on the Fundamentals and Practical Implementation Details of Strongly Coupled Magnetic Resonant Technology for Wireless Power Transfer
Energies 2018, 11(10), 2844; https://doi.org/10.3390/en11102844 (registering DOI)
Received: 13 September 2018 / Revised: 12 October 2018 / Accepted: 18 October 2018 / Published: 21 October 2018
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Abstract
Users are increasing their demands on the home appliances they utilize by requiring them to be powered anywhere and anytime. In order to satisfy this need, wireless power transfer helps transfer energy between objects without conductors. For domestic scenarios, strongly magnetic resonant technology
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Users are increasing their demands on the home appliances they utilize by requiring them to be powered anywhere and anytime. In order to satisfy this need, wireless power transfer helps transfer energy between objects without conductors. For domestic scenarios, strongly magnetic resonant technology offers a method to enable wireless power transfer, even when there exist intermediate non-metallic objects between the wireless power source and the load. This paper reviews this technology with a comprehensive explanation about its fundamentals and physical principles. Some practical issues are also analyzed in this work. Particularly, how the control can be designed and how the coils are built. Finally, this paper also addresses the study about the features of other technologies to power home appliances without conductors. They can be foreseen as the technological competitors of strongly coupled magnetic resonant systems. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Experimental Investigation on Microscopic Residual Oil Distribution During CO2 Huff-and-Puff Process in Tight Oil Reservoirs
Energies 2018, 11(10), 2843; https://doi.org/10.3390/en11102843 (registering DOI)
Received: 30 September 2018 / Revised: 14 October 2018 / Accepted: 18 October 2018 / Published: 21 October 2018
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Abstract
The determination of microscopic residual oil distribution is beneficial for exploiting reservoirs to their maximum potential. In order to investigate microscopic residual oil during the carbon dioxide (CO2) huff-and-puff process in tight oil reservoirs, several CO2 huff-and-puff tests with tight
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The determination of microscopic residual oil distribution is beneficial for exploiting reservoirs to their maximum potential. In order to investigate microscopic residual oil during the carbon dioxide (CO2) huff-and-puff process in tight oil reservoirs, several CO2 huff-and-puff tests with tight sandstone cores were conducted at various conditions. Then, nuclear magnetic resonance (NMR) was used to determine the microscopic residual oil distribution of the cores. The experiments showed that the oil recovery factor increased from 27.22% to 52.56% when injection pressure increased from 5 MPa to 13 MPa. The oil recovery was unable to be substantially enhanced as the injection pressure further increased beyond the minimum miscible pressure. The lower limit of pore distribution where the oil was recoverable corresponded to relaxation times of 2.68 ms, 1.29 ms, and 0.74 ms at an injection pressure of 5 MPa, 11 MPa, and 16 MPa, respectively. Longer soaking time also increased the lower limit of the oil-recoverable pore distribution. However, more cycles had no obvious effect on expanding the interval of oil-recoverable pore distribution. Therefore, higher injection pressure and longer soaking time convert the residual oil in smaller and blind pores into recoverable oil. This investigation provides some technical ideas for oilfields in design development programs for optimizing the production parameters during the CO2 huff-and-puff process. Full article
(This article belongs to the Special Issue CO2 EOR and CO2 Storage in Oil Reservoirs)
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Open AccessArticle Effects of Aerodynamic Interactions of Closely-Placed Vertical Axis Wind Turbine Pairs
Energies 2018, 11(10), 2842; https://doi.org/10.3390/en11102842 (registering DOI)
Received: 1 July 2018 / Revised: 16 October 2018 / Accepted: 18 October 2018 / Published: 21 October 2018
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Abstract
In this study, a numerical model was developed to study the effects of aerodynamic interactions between a pair of counter-rotating vertical axis wind turbines (VAWTs) in close proximity. In this model, the rotor rotation is not prescribed as a constant as in most
[...] Read more.
In this study, a numerical model was developed to study the effects of aerodynamic interactions between a pair of counter-rotating vertical axis wind turbines (VAWTs) in close proximity. In this model, the rotor rotation is not prescribed as a constant as in most other studies, but is determined by the moment of inertia and the total torque of the rotor, including the aerodynamic torque, generator torque, and a torque representing friction. This model enables study of the behavior of the rotor under an arbitrary ambient wind profile. The model was applied to an isolated rotor with five straight J-blades and pairs of identical rotors placed in close proximity. Compared with an isolated rotor, the aerodynamic interactions between the pair of rotors enhance the aerodynamic torques on the rotors and significantly increase the turbine power output on a per unit basis. The enhancement in turbine power output due to aerodynamic enhancement decreases with the distance between the pair of rotors. Full article
Open AccessArticle Comprehensive Performance Assessment on Various Battery Energy Storage Systems
Energies 2018, 11(10), 2841; https://doi.org/10.3390/en11102841 (registering DOI)
Received: 20 August 2018 / Revised: 3 September 2018 / Accepted: 5 September 2018 / Published: 20 October 2018
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Abstract
With the increasing development of renewable resources-based electricity generation and the construction of wind-photovoltaic-energy storage combination exemplary projects, the intermittent and fluctuating nature of renewable resources exert great challenges for the power grid to supply electricity reliably and stably. An energy storage system
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With the increasing development of renewable resources-based electricity generation and the construction of wind-photovoltaic-energy storage combination exemplary projects, the intermittent and fluctuating nature of renewable resources exert great challenges for the power grid to supply electricity reliably and stably. An energy storage system (ESS) is deemed to be the most valid solution to deal with these challenges. Considering the various types of ESSs, it is necessary to develop a comprehensive assessment framework for selecting appropriate energy storage techniques in establishing exemplary projects combining renewable resources-based electricity generation and an ESS. This paper proposes a multi-criteria decision making (MCDM) model combining a fuzzy-Delphi approach to establish the comprehensive assessment indicator system, the entropy weight determination method, and the best-worst method (BWM) to calculate weights of all sub-criteria, and a Vlsekriterijumska Optimizacija I Kompromisno Resenje (VIKOR) comprehensive evaluation model to choose the optimal battery ESS. In accordance with the comprehensive evaluation results, the Li-ion battery is the optimal battery ESS to apply to wind-photovoltaic-energy storage combination exemplary projects. Based on the discussion on the comprehensive evaluation results, policy implications are suggested to improve the applicability of battery ESSs and provide some references for decision makers in related fields. Full article
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Open AccessArticle Densities for Ternary System of CaCl2–H2O–CO2 at Elevated P-T: An Experimental and Modeling Approach
Energies 2018, 11(10), 2840; https://doi.org/10.3390/en11102840 (registering DOI)
Received: 6 September 2018 / Revised: 3 October 2018 / Accepted: 8 October 2018 / Published: 20 October 2018
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Abstract
Very few thermodynamic models exist for estimation of density alteration due to solution of CO2 in a pure H2O and CaCl2–H2O system. All of these models require density of CaCl2 solution to estimate density of
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Very few thermodynamic models exist for estimation of density alteration due to solution of CO2 in a pure H2O and CaCl2–H2O system. All of these models require density of CaCl2 solution to estimate density of CaCl2–H2O–CO2 system. Similarly, models presented to calculate CaCl2 solution density need pure H2O density in advance. The main approach to model density of CaCl2–H2O–CO2 system is based on estimation of density alteration of CaCl2–H2O system due to the solution of CO2 mole fraction. Hence, to estimate CO2–CaCl2–H2O system density, density of CaCl2 solution is necessary, and to estimate density of CaCl2–H2O system, density of pure H2O is required in advance. Firstly in this paper, density of 0, 1.91, and 4.85 mol/kg CaCl2 solutions saturated with CO2 at 328.15 to 375.15 °K and 68.9 to 206.8 Bar were measured through laboratory experiments. Then, a new model is developed to estimate the density of CaCl2 solutions containing CO2 based on the experiments conducted in this study. The average and maximum absolute deviations of the new model from the experimental data are 0.0047 and 0.0177, respectively. Hence, the new model combined with other existing models to separately calculate density of the CaCl2 solution can be used to accurately predict density of the CaCl2–H2O–CO2 system in a wide range of P-T applicable for subsurface reservoirs. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Estimation of Cement Thermal Properties through the Three-Phase Model with Application to Geothermal Wells
Energies 2018, 11(10), 2839; https://doi.org/10.3390/en11102839 (registering DOI)
Received: 24 August 2018 / Revised: 28 September 2018 / Accepted: 16 October 2018 / Published: 20 October 2018
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Abstract
Geothermal energy has been used by mankind since ancient times. Given the limited geographical distribution of the most favorable resources, exploration efforts have more recently focused on unconventional geothermal systems targeting greater depths to reach sufficient temperatures. In these systems, geothermal well performance
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Geothermal energy has been used by mankind since ancient times. Given the limited geographical distribution of the most favorable resources, exploration efforts have more recently focused on unconventional geothermal systems targeting greater depths to reach sufficient temperatures. In these systems, geothermal well performance relies on efficient heat transfer between the working fluid, which is pumped from surface, and the underground rock. Most of the wells designed for such environments require that the casing strings used throughout the well construction process be cemented in place. The overall heat transfer around the wellbore may be optimized through accurate selection of cement recipes. This paper presents the application of a three-phase analytical model to estimate the cement thermal properties. The results show that cement recipes can be designed to enhance or minimize heat transfer around wellbore, extending the application of geothermal exploitation. Full article
(This article belongs to the Special Issue Geothermal Energy: Utilization and Technology)
Open AccessArticle Optimization of Control Variables and Design of Management Strategy for Hybrid Hydraulic Vehicle
Energies 2018, 11(10), 2838; https://doi.org/10.3390/en11102838 (registering DOI)
Received: 24 September 2018 / Revised: 14 October 2018 / Accepted: 16 October 2018 / Published: 20 October 2018
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Abstract
The article deals with optimization of control variables and design of management strategy for a hybrid hydraulic vehicle in parallel configuration. Conventionally driven delivery truck with experimentally verified data from the previous research is taken as a starting base and benchmark for comparison
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The article deals with optimization of control variables and design of management strategy for a hybrid hydraulic vehicle in parallel configuration. Conventionally driven delivery truck with experimentally verified data from the previous research is taken as a starting base and benchmark for comparison of the benefits of hybridization. Optimization of control variables is carried out using dynamic programming (DP) algorithm to gain insight into optimum operation of the driveline and minimum possible fuel consumption for five different driving cycles. Two rule based management strategies are given and compared, one of which is improved and innovative, based on the knowledge gained from DP results. Hybrid driveline can reduce fuel consumption from 5% to 30% depending on the driving cycle. More dynamic cycles with lot of "stop-and-go" events score greater reduction. Innovative management strategy has achieved a similar distribution of internal combustion engine (ICE) operating points as DP optimization but this did not result in a consistent reduction of fuel consumption compared to basic management strategy for all cycles. That is explained by the state of charge (SoC) behaviour and reducing the potential for recovery of regenerative braking energy. Full article
(This article belongs to the Special Issue 10 Years Energies - Horizon 2028)
Open AccessArticle Consequences of the National Energy Strategy in the Mexican Energy System: Analyzing Strategic Indicators with an Optimization Energy Model
Energies 2018, 11(10), 2837; https://doi.org/10.3390/en11102837 (registering DOI)
Received: 28 August 2018 / Revised: 16 October 2018 / Accepted: 16 October 2018 / Published: 20 October 2018
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Abstract
This paper presents an approach to the assessment of the Mexican energy system’s evolution under the climate and energy objectives set by the National Climate Change Strategy using an energy optimization model. Some strategic indicators have been chosen to analyze the performance of
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This paper presents an approach to the assessment of the Mexican energy system’s evolution under the climate and energy objectives set by the National Climate Change Strategy using an energy optimization model. Some strategic indicators have been chosen to analyze the performance of three integration elements: sustainability, efficiency, and energy security. Two scenarios have been defined in the medium and long-term: the business as usual scenario, with no energy or climate targets, and the National Climate Change Strategy scenario, where clean energy technologies and CO2 emissions objectives are considered. The aim of this work is the analysis of some of those strategic indicators’ evolution using the EUROfusion Times Model. Results show that reaching the strategy targets leads to improvements in the integration elements in the medium and long term. Besides, meeting the CO2 emission limits is achievable in terms of technologies and resources availability but at a high cost, while clean technologies targets are met with no extra costs even in the business as usual scenario. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Evaluation of Displacement Effects of Different Injection Media in Tight Oil Sandstone by Online Nuclear Magnetic Resonance
Energies 2018, 11(10), 2836; https://doi.org/10.3390/en11102836 (registering DOI)
Received: 13 September 2018 / Revised: 29 September 2018 / Accepted: 19 October 2018 / Published: 20 October 2018
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Abstract
In order to evaluate the displacement effect of four kinds of injection media in tight oil sandstone, water, active water, CO2, N2 flooding experiments were carried out in laboratory. Online Nuclear Magnetic Resonance (NMR) spectrometers combine the advantages of NMR
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In order to evaluate the displacement effect of four kinds of injection media in tight oil sandstone, water, active water, CO2, N2 flooding experiments were carried out in laboratory. Online Nuclear Magnetic Resonance (NMR) spectrometers combine the advantages of NMR technology and core displacement experiments. In the displacement experiment, NMR data of different injection volumes were obtained and magnetic resonance imaging (MRI) was carried out. The results showed that micro and sub-micropores provided 62–97% of the produced crude oil. The enhanced oil recovery ratio of active water flooding was higher than that of conventional water flooding up to 10%. The recovery ratio of gas flooding in micro and sub-micropores was 60–70% higher than that of water flooding. The recovery ratio of CO2 flooding was 10% higher than that of N2 flooding. The remaining oil was mainly distributed in pores larger than 0.1 μm. Under the same permeability level, the remaining oil saturation of cores after gas flooding was 10–25% lower than water flooding. From MRI images, the displacement effects from good to bad were as follows: CO2 flooding, N2 flooding, active water flooding, and conventional water flooding. Full article
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Open AccessArticle Influence of Input Climatic Data on Simulations of Annual Energy Needs of a Building: EnergyPlus and WRF Modeling for a Case Study in Rome (Italy)
Energies 2018, 11(10), 2835; https://doi.org/10.3390/en11102835 (registering DOI)
Received: 4 September 2018 / Revised: 11 October 2018 / Accepted: 16 October 2018 / Published: 20 October 2018
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Abstract
The simulation of the energy consumptions in an hourly regime is necessary in order to perform calculations on residential buildings of particular relevance for volume or for architectural features. In such cases, the simplified methodology provided by the regulations may be inadequate, and
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The simulation of the energy consumptions in an hourly regime is necessary in order to perform calculations on residential buildings of particular relevance for volume or for architectural features. In such cases, the simplified methodology provided by the regulations may be inadequate, and the use of software like EnergyPlus is needed. To obtain reliable results, usually, significant time is spent on the meticulous insertion of the geometrical inputs of the building, together with the properties of the envelope materials and systems. Less attention is paid to the climate database. The databases available on the EnergyPlus website refer to airports located in rural areas near major cities. If the building to be simulated is located in a metropolitan area, it may be affected by the local heat island, and the database used as input to the software should take this phenomenon into account. To this end, it is useful to use a meteorological model such as the Weather Research and Forecasting (WRF) model to construct an appropriate input climate file. A case study based on a building located in the city center of Rome (Italy) shows that, if the climatic forcing linked to the heat island is not considered, the estimated consumption due to the cooling is underestimated by 35–50%. In particular, the analysis and the seasonal comparison between the energy needs of the building simulated by EnergyPlus, with the climatic inputs related to two airports in the rural area of Rome and with the inputs provided by the WRF model related to the center of Rome, show discrepancies of about (i) WRF vs. Fiumicino (FCO): Δ = −3.48% for heating, Δ = 49.25% for cooling; (ii) WRF vs. Ciampino (CIA): Δ = −7.38% for heating, Δ = +35.52% for cooling. Full article
(This article belongs to the Section Sustainable Energy)
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Open AccessArticle Hierarchical Energy Management for the MultiEnergy Carriers System with Different Interest Bodies
Energies 2018, 11(10), 2834; https://doi.org/10.3390/en11102834 (registering DOI)
Received: 30 September 2018 / Revised: 18 October 2018 / Accepted: 18 October 2018 / Published: 20 October 2018
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Abstract
Multi-energy carriers system (MECS), in which diverse energy carriers and different energy systems interact together, has drawn the interest of many researchers in recent years. However, the optimal economic operational model of the MECS is a nonlinear, multi-variable, and multi-period problem, of which
[...] Read more.
Multi-energy carriers system (MECS), in which diverse energy carriers and different energy systems interact together, has drawn the interest of many researchers in recent years. However, the optimal economic operational model of the MECS is a nonlinear, multi-variable, and multi-period problem, of which it is difficult to find the solution because several different energy flows are integrated in the system. To this end, three interest bodies in the MECS were investigated, which included the energy provider, the energy facilitator, and the energy consumer, and a hierarchical optimal economic operation strategy was then presented. A hybrid optimization strategy combining the swarm intelligence algorithm and interior point method was developed taking advantage of the merits of each method. Case studies were conducted to verify the effectiveness of the proposed hierarchical optimal economic operation strategy, whereby demonstrating that the proposed strategy can achieve rational energy allocation and decrease the energy cost in the MECS compared with traditional energy systems. Full article
Open AccessArticle Co-Optimization of Energy and Reserve Capacity Considering Renewable Energy Unit with Uncertainty
Energies 2018, 11(10), 2833; https://doi.org/10.3390/en11102833 (registering DOI)
Received: 24 July 2018 / Revised: 2 October 2018 / Accepted: 15 October 2018 / Published: 20 October 2018
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Abstract
This paper proposes a system model for optimal dispatch of the energy and reserve capacity considering uncertain load demand and unsteady power generation. This implicates uncertainty in managing the power demand along with the consideration of utility, user and environmental objectives. The model
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This paper proposes a system model for optimal dispatch of the energy and reserve capacity considering uncertain load demand and unsteady power generation. This implicates uncertainty in managing the power demand along with the consideration of utility, user and environmental objectives. The model takes into consideration a day-ahead electricity market that involves the varying power demand bids and generates a required amount of energy in addition with reserve capacity. The lost opportunity cost is also considered and incorporated within the context of expected load not served. Then, the effects of combined and separate dispatching the energy and reserve are investigated. The nonlinear cost curves have been addressed by optimizing the objective function using robust optimization technique. Finally, various cases in accordance with underlying parameters have been considered in order to conduct and evaluate numerical results. Simulation results show the effectiveness of proposed scheduling model in terms of reduced cost and system stability. Full article
Open AccessArticle Framework for Microgrid Design Using Social, Economic, and Technical Analysis
Energies 2018, 11(10), 2832; https://doi.org/10.3390/en11102832 (registering DOI)
Received: 2 August 2018 / Revised: 1 September 2018 / Accepted: 17 October 2018 / Published: 20 October 2018
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Abstract
Microgrids are emerging as feasible solutions to handle local energy systems. Several factors influence the development of such systems, such as technical, economic, social, legal, and regulatory issues. These important aspects need to be addressed to design appropriate microscale projects that take into
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Microgrids are emerging as feasible solutions to handle local energy systems. Several factors influence the development of such systems, such as technical, economic, social, legal, and regulatory issues. These important aspects need to be addressed to design appropriate microscale projects that take into consideration adequate technology without underestimating local characteristics. This article aims to propose a framework design for microgrid optimization using technical, social, and economic analysis. The framework is presented through a small island case study that shows each step of the method. As a contribution, this work provides a multi-objective optimization framework with different criteria consideration, such as the inhabitants’ cost of living and inter-cultural aspects, instead of traditional technical and economic analysis. The results show the applicability of the proposed framework showing better alternatives when compared with actual or future improvements in the study case scenario. Full article
(This article belongs to the Special Issue Microgrids-2018)
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Open AccessFeature PaperArticle Sensitivity Assessment of Microgrid Investment Options to Guarantee Reliability of Power Supply in Rural Networks as an Alternative to Underground Cabling
Energies 2018, 11(10), 2831; https://doi.org/10.3390/en11102831 (registering DOI)
Received: 30 August 2018 / Revised: 20 September 2018 / Accepted: 26 September 2018 / Published: 19 October 2018
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Abstract
Microgrids could be utilized to improve the distribution network resiliency against weather-related network outages and increase the security of power supply of rural electricity consumers. Whereas underground cabling is expensive for the distribution system operator (DSO), an alternative microgrid investment could benefit the
[...] Read more.
Microgrids could be utilized to improve the distribution network resiliency against weather-related network outages and increase the security of power supply of rural electricity consumers. Whereas underground cabling is expensive for the distribution system operator (DSO), an alternative microgrid investment could benefit the DSO and consumer, provided the necessary changes were made in the network regulation. A rural detached house customer microgrid is analysed in comparison to underground cabling, considering the uncertainties in the calculation parameters through a sensitivity analysis. Adequacy of the microgrid power supply during unexpected network outage for a reasonably long duration is assessed, as well as the economics of the feasible microgrid setup consisting of variable generation, controllable generation, and electric storage. The total costs and benefits for the DSO and consumer/prosumer are considered. A microgrid would likely be a more cost-efficient option overall, but not as-is for the consumer. The battery energy storage system (BESS)-related cost-sharing strategies are suggested in this paper in order to assess possible break-even investment solutions for the related parties. The sensitivities of the microgrid and cabling investments were considered in particular. Cost-sharing strategies under network regulatory framework would need to be developed further in order for both the consumer and DSO to benefit from the solution as a whole. Full article
(This article belongs to the Special Issue Methods and Concepts for Designing and Validating Smart Grid Systems)
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Open AccessArticle Hierarchical Scheduling Scheme for AC/DC Hybrid Active Distribution Network Based on Multi-Stakeholders
Energies 2018, 11(10), 2830; https://doi.org/10.3390/en11102830 (registering DOI)
Received: 4 September 2018 / Revised: 16 October 2018 / Accepted: 17 October 2018 / Published: 19 October 2018
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Abstract
This paper presents a hierarchical multi-stage scheduling scheme for the AC/DC hybrid active distribution network (ADN). The load regulation center (LRC) is considered in the developed scheduling strategy, as well as the AC and DC sub-network operators. They are taken to be different
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This paper presents a hierarchical multi-stage scheduling scheme for the AC/DC hybrid active distribution network (ADN). The load regulation center (LRC) is considered in the developed scheduling strategy, as well as the AC and DC sub-network operators. They are taken to be different stakeholders. To coordinate the interests of all stakeholders, a two-level optimization model is established. The flexible loads are dispatched by LRC in the upper-level optimization model, the objective of which is minimizing the loss of the entire distribution network. The lower-level optimization is divided into two sub-optimal models, and they are carried out to minimize the operating costs of the AC/DC sub-network operators respectively. This two-level model avoids the difficulty of solving multi-objective optimization and can clarify the role of various stakeholders in the system scheduling. To solve the model effectively, a discrete wind-driven optimization (DWDO) algorithm is proposed. Then, considering the combination of the proposed DWDO algorithm and the YALMIP toolbox, a hierarchical optimization algorithm (HOA) is developed. The HOA can obtain the overall optimization result of the system through the iterative optimization of the upper and lower levels. Finally, the simulation results verify the effectiveness of the proposed scheduling scheme. Full article
(This article belongs to the Special Issue Optimization Methods Applied to Power Systems)
Open AccessArticle Wind Power Consumption Research Based on Green Economic Indicators
Energies 2018, 11(10), 2829; https://doi.org/10.3390/en11102829
Received: 28 September 2018 / Revised: 18 October 2018 / Accepted: 18 October 2018 / Published: 19 October 2018
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Abstract
As a representative form of new energy generation, wind power has effectively alleviated environmental pollution and energy shortages. This paper constructs a green economic indicator to measure the degree of coordinated development of environmental and social benefits. To increase the amount of wind
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As a representative form of new energy generation, wind power has effectively alleviated environmental pollution and energy shortages. This paper constructs a green economic indicator to measure the degree of coordinated development of environmental and social benefits. To increase the amount of wind power consumption, an economic dispatch model based on the coordinated operation of cogeneration units and electric boilers was established; we also introduced the green certificate transaction cost, which effectively meets the strategic needs of China’s energy low-carbon transformation top-level system design. Wind power output has instability and volatility, so it puts higher requirements on the stable operation of thermal power units. To solve the stability problem, this paper introduces the output index of the thermal power unit and rationally plans the unit combination strategy, as well as introducing the concept of chance-constrained programming due to the uncertainty of load and wind power in the model. Uncertainty factors are transformed into load forecasting errors and wind power prediction errors for processing. Based on the normal distribution theory, the uncertainty model is transformed into a certain equivalence class model, and the improved disturbance mutated particle swarm optimization algorithm is used to solve the problem. Finally, the validity and feasibility of the proposed model are verified based on the IEEE30 node system. Full article
Open AccessArticle Parallel Control Method Based on the Consensus Algorithm for the Non-Isolated AC/DC Charging Module
Energies 2018, 11(10), 2828; https://doi.org/10.3390/en11102828
Received: 9 September 2018 / Revised: 10 October 2018 / Accepted: 16 October 2018 / Published: 19 October 2018
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Abstract
A high-power charging station for electric vehicles usually adopts a parallel structure of multiple power modules. However, due to the parameter differences among power modules, a parallel system always has circulating current issues. This paper takes a non-isolated AC/DC charging module as the
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A high-power charging station for electric vehicles usually adopts a parallel structure of multiple power modules. However, due to the parameter differences among power modules, a parallel system always has circulating current issues. This paper takes a non-isolated AC/DC charging module as the research object and proposes a current sharing control strategy for multiple power modules based on the consensus algorithm. By constructing a sparse communication network with the CAN (Controller Area Network) protocol and exchanging current information, accurate current sharing among power modules is realized. Firstly, the zero-sequence circulating current issue is analyzed through a parallel model of the three-phase rectifier, with an improved circulating current restraint strategy proposed based on the zero-sequence voltage compensation. Then, the principle of the consensus algorithm is explained, which is applied to the current sharing control of multiple power modules. Finally, the proposal is tested by the designed simulation and experimental cases. From the obtained results, it can be seen that the proposed control strategy can effectively realize accurate current sharing among multiple power modules and well restrain the zero-sequence circulating current at the input side. Full article
(This article belongs to the Special Issue Power Electronics for Energy Storage)
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Open AccessReview Fungi-Based Microbial Fuel Cells
Energies 2018, 11(10), 2827; https://doi.org/10.3390/en11102827
Received: 2 October 2018 / Revised: 15 October 2018 / Accepted: 16 October 2018 / Published: 19 October 2018
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Abstract
Fungi are among the microorganisms able to generate electricity as a result of their metabolic processes. Throughout the last several years, a large number of papers on various microorganisms for current production in microbial fuel cells (MFCs) have been published; however, fungi still
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Fungi are among the microorganisms able to generate electricity as a result of their metabolic processes. Throughout the last several years, a large number of papers on various microorganisms for current production in microbial fuel cells (MFCs) have been published; however, fungi still lack sufficient evaluation in this regard. In this review, we focus on fungi, paying special attention to their potential applicability to MFCs. Fungi used as anodic or cathodic catalysts, in different reactor configurations, with or without the addition of an exogenous mediator, are described. Contrary to bacteria, in which the mechanism of electron transfer is pretty well known, the mechanism of electron transfer in fungi-based MFCs has not been studied intensively. Thus, here we describe the main findings, which can be used as the starting point for future investigations. We show that fungi have the potential to act as electrogens or cathode catalysts, but MFCs based on bacteria–fungus interactions are especially interesting. The review presents the current state-of-the-art in the field of MFC systems exploiting fungi. Full article
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Open AccessArticle Energy Efficiency Analysis Carried Out by Installing District Heating on a University Campus. A Case Study in Spain
Energies 2018, 11(10), 2826; https://doi.org/10.3390/en11102826
Received: 27 September 2018 / Revised: 11 October 2018 / Accepted: 16 October 2018 / Published: 19 October 2018
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Abstract
This article analyses the reduction of energy consumption following the installation of district heating (DH) in the Miguel Delibes campus at the University of Valladolid (Spain), in terms of historical consumption and climate variables data. In order to achieve this goal, consumption models
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This article analyses the reduction of energy consumption following the installation of district heating (DH) in the Miguel Delibes campus at the University of Valladolid (Spain), in terms of historical consumption and climate variables data. In order to achieve this goal, consumption models are carried out for each building, enabling the comparison of actual data with those foreseen in the model. This paper shows the statistical method used to accept these models, selecting the most influential climate variables data obtained by the models from the consumption baselines in the buildings at the Miguel Delibes campus through to the linear regression equations with a confidence level of 95%. This study shows that the best variables correlated with consumption are the degree-days for 58% of buildings and the average temperature for the remaining 42%. The savings obtained to date with this third generation network have been significantly higher than the 21% average for 33% of the campus buildings. In the case of 17% of the buildings, there was a significant increase in consumption of 20%, and in the case of the remaining 50% of the buildings, no significant differences were found between consumption before and after installation of district heating. Full article
(This article belongs to the Special Issue District Heating and Cooling Networks)
Open AccessArticle Hydrogen as a Long-Term Large-Scale Energy Storage Solution to Support Renewables
Energies 2018, 11(10), 2825; https://doi.org/10.3390/en11102825
Received: 21 September 2018 / Revised: 12 October 2018 / Accepted: 16 October 2018 / Published: 19 October 2018
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Abstract
This paper presents a case study of using hydrogen for large-scale long-term storage application to support the current electricity generation mix of South Australia state in Australia, which primarily includes gas, wind and solar. For this purpose two cases of battery energy storage
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This paper presents a case study of using hydrogen for large-scale long-term storage application to support the current electricity generation mix of South Australia state in Australia, which primarily includes gas, wind and solar. For this purpose two cases of battery energy storage and hybrid battery-hydrogen storage systems to support solar and wind energy inputs were compared from a techno-economical point of view. Hybrid battery-hydrogen storage system was found to be more cost competitive with unit cost of electricity at $0.626/kWh (US dollar) compared to battery-only energy storage systems with a $2.68/kWh unit cost of electricity. This research also found that the excess stored hydrogen can be further utilised to generate extra electricity. Further utilisation of generated electricity can be incorporated to meet the load demand by either decreasing the base load supply from gas in the present scenario or exporting it to neighbouring states to enhance economic viability of the system. The use of excess stored hydrogen to generate extra electricity further reduced the cost to $0.494/kWh. Full article
(This article belongs to the Special Issue Solar Energy Harvesting, Storage and Utilization)
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Open AccessArticle Assessing the Macro-Economic Benefit of Installing a Farm of Oscillating Water Columns in Scotland and Portugal
Energies 2018, 11(10), 2824; https://doi.org/10.3390/en11102824
Received: 14 August 2018 / Revised: 27 September 2018 / Accepted: 16 October 2018 / Published: 19 October 2018
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Abstract
The nascent wave energy sector has the potential to contribute significantly to global renewables targets, yet at present there are no proven commercially viable technologies. Macro-economic assessment is seldom used to assess wave energy projects, yet can provide insightful information on the wider
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The nascent wave energy sector has the potential to contribute significantly to global renewables targets, yet at present there are no proven commercially viable technologies. Macro-economic assessment is seldom used to assess wave energy projects, yet can provide insightful information on the wider economic benefits and can be used in conjunction with techno-economic analysis to inform policy makers, investors and funding bodies. Herein, we present a coupled techno–macro-economic model, which is used to assess the macro-economic benefit of installing a 5.25 MW farm of oscillating water column wave energy devices at two locations: Orkney in Scotland and Leixoes in Portugal. Through an input-output analysis, the wide-reaching macro-economic benefit of the prospective projects is highlighted; evidenced by the finding that all 29 industry sectors considered are either directly or indirectly stimulated by the project for both locations. Peak annual employment is expected to be 420 and 190 jobs in Portugal and Scotland respectively during the combined installation and manufacturing stage, with an associated peak annual GVA of over €16.6 m and €12.8 m. The discrepancies between the two locations is concluded to largely be a result of the site-specific attributes of the farm locations: specifically, increased water depth and distance to shore for the Portuguese site, resulting in higher costs associated with mooring and electrical cables and vessels. The insights gained through the presented results demonstrate the merit of macro-economic analysis for understanding the wider economic benefit of wave energy projects, while providing an understanding over key physical factors which will dominate estimated effects. Full article
(This article belongs to the Special Issue Offshore Renewable Energy: Ocean Waves, Tides and Offshore Wind)
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Open AccessBrief Report Wind Turbine Wake Characterization for Improvement of the Ainslie Eddy Viscosity Wake Model
Energies 2018, 11(10), 2823; https://doi.org/10.3390/en11102823
Received: 3 July 2018 / Revised: 13 September 2018 / Accepted: 11 October 2018 / Published: 19 October 2018
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Abstract
This paper presents a modified version of the Ainslie eddy viscosity wake model and its accuracy by comparing it with selected exiting wake models and wind tunnel test results. The wind tunnel test was performed using a 1.9 m rotor diameter wind turbine
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This paper presents a modified version of the Ainslie eddy viscosity wake model and its accuracy by comparing it with selected exiting wake models and wind tunnel test results. The wind tunnel test was performed using a 1.9 m rotor diameter wind turbine model operating at a tip speed ratio similar to that of modern megawatt wind turbines. The control algorithms for blade pitch and generator torque used for below and above rated wind speed regions similar to those for multi-MW wind turbines were applied to the scaled wind turbine model. In order to characterize the influence of the wind turbine operating conditions on the wake, the wind turbine model was tested in both below and above rated wind speed regions at which the thrust coefficients of the rotor varied. The correction of the Ainslie eddy viscosity wake model was made by modifying the empirical equation of the original model using the wind tunnel test results with the Nelder-Mead simplex method for function minimization. The wake prediction accuracy of the modified wake model in terms of wind speed deficit was found to be improved by up to 6% compared to that of the original model. Comparisons with other existing wake models are also made in detail. Full article
(This article belongs to the Special Issue Solar and Wind Energy Forecasting)
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Open AccessArticle Short-Term Electric Power Forecasting Using Dual-Stage Hierarchical Wavelet- Particle Swarm Optimization- Adaptive Neuro-Fuzzy Inference System PSO-ANFIS Approach Based On Climate Change
Energies 2018, 11(10), 2822; https://doi.org/10.3390/en11102822
Received: 15 September 2018 / Revised: 5 October 2018 / Accepted: 17 October 2018 / Published: 19 October 2018
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Abstract
Analyzing electrical power generation for a wind turbine has associated inaccuracies due to fluctuations in environmental factors, mechanical alterations of wind turbines, and natural disaster. Thus, development of a highly reliable prediction model based on climatic conditions is crucial in forecasting electrical power
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Analyzing electrical power generation for a wind turbine has associated inaccuracies due to fluctuations in environmental factors, mechanical alterations of wind turbines, and natural disaster. Thus, development of a highly reliable prediction model based on climatic conditions is crucial in forecasting electrical power for proper management of energy demand and supply. This is essential because early forecasting systems will enable an energy supplier to schedule and manage resources efficiently. In this research, we have put forward a novel electrical power prediction model using wavelet and particle swarm optimization based dual-stage adaptive neuro-fuzzy inference system (dual-stage Wavelet-PSO-ANFIS) for precise estimation of electrical power generation based on climatic factors. The first stage is used to project wind speed based on meteorological data available, while the second stage took the output wind speed prediction to predict electrical power based on actual supervisory control and data acquisition (SCADA). Furthermore, influence of data dependence on the forecasting accuracy for both stages is analyzed using a subset of data as input to predict the wind power which was also compared with other existing electrical power forecasting techniques. This paper defines the basic framework and the performance evaluation of a dual-stage Wavelet-PSO-ANFIS based electrical power forecasting system using a practical implementation. Full article
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Open AccessArticle PLDAD—An Algorihm to Reduce Data Center Energy Consumption
Energies 2018, 11(10), 2821; https://doi.org/10.3390/en11102821
Received: 1 August 2018 / Revised: 10 September 2018 / Accepted: 17 September 2018 / Published: 19 October 2018
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Abstract
Due to the demands of new technologies such as social networks, e-commerce and cloud computing, more energy is being consumed in order to store all the produced data. While these new technologies require high levels of availability, a reduction in the cost and
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Due to the demands of new technologies such as social networks, e-commerce and cloud computing, more energy is being consumed in order to store all the produced data. While these new technologies require high levels of availability, a reduction in the cost and environmental impact is also expected. The present paper proposes a power balancing algorithm (power load distribution algorithm-depth (PLDA-D)) to optimize the energy distribution of data center electrical infrastructures. The PLDA-D is based on the Bellman and Ford–Fulkerson flow algorithms that analyze energy-flow models (EFM). EFM computes the power efficiency, sustainability and cost metrics of data center infrastructures. To demonstrate the applicability of the proposed strategy, we present a case study that analyzes four power infrastructures. The results obtained show about a 3.8% reduction in sustainability impact and operational costs. Full article
(This article belongs to the Special Issue Optimization Methods Applied to Power Systems)
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Open AccessArticle Distribution Network Congestion Dispatch Considering Time-Spatial Diversion of Electric Vehicles Charging
Energies 2018, 11(10), 2820; https://doi.org/10.3390/en11102820
Received: 5 September 2018 / Revised: 11 October 2018 / Accepted: 17 October 2018 / Published: 19 October 2018
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Abstract
With the popularization of electric vehicles, free charging behaviors of electric vehicle owners can lead to uncertainty about charging in both time and space. A time-spatial dispatching strategy for the distribution network guided by electric vehicle charging fees is proposed in this paper,
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With the popularization of electric vehicles, free charging behaviors of electric vehicle owners can lead to uncertainty about charging in both time and space. A time-spatial dispatching strategy for the distribution network guided by electric vehicle charging fees is proposed in this paper, which aims to solve the network congestion problem caused by the unrestrained and free charging behaviors of large numbers of electric vehicles. In this strategy, congestion severity of different lines is analyzed and the relationship between the congested lines and the charging stations is clarified. A price elastic matrix is introduced to reflect the degree of owners’ response to the charging prices. A pricing scheme for optimal real-time charging fees for multiple charging stations is designed according to the congestion severity of the lines and the charging power of the related charging stations. Charging price at different charging station at different time is different, it can influence the charging behaviors of vehicle owners. The simulation results confirmed that the proposed congestion dispatching strategy considers the earnings of the operators, charging cost to the owners and the satisfaction of the owners. Moreover, the strategy can influence owners to make judicious charging plans that help to solve congestion problems in the network and improve the safety and economy of the power grid. Full article
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Open AccessFeature PaperArticle Islanding Detection of Synchronous Distributed Generator Based on the Active and Reactive Power Control Loops
Energies 2018, 11(10), 2819; https://doi.org/10.3390/en11102819
Received: 4 October 2018 / Revised: 15 October 2018 / Accepted: 16 October 2018 / Published: 19 October 2018
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Abstract
There has been a considerable importance for the islanding detection due to the growing integration of distributed generations (DGs) in the modern power grids. This paper proposes a novel active islanding detection scheme for synchronous DGs, considering two additional compensators and a positive
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There has been a considerable importance for the islanding detection due to the growing integration of distributed generations (DGs) in the modern power grids. This paper proposes a novel active islanding detection scheme for synchronous DGs, considering two additional compensators and a positive feedback for each of active and reactive power control loops. The added blocks are designed using the small gain theorem and stability margins definition considering characteristics of open loop transfer functions of synchronous DG control loops. Islanding can be detected using the proposed method even where there is an exact match between generation and local load without sacrificing power quality. In addition, the performance of the proposed method can be retained even with high penetration of motor loads. The proposed scheme improves the stability and power quality of the grid, when the synchronous DG is subjected to the grid-connected disturbances. Furthermore, this method augments the stability margins of the system in the grid-connected conditions to enhance the disturbances ride-through capability of the system and reduce the negative impact of the active methods on the power quality. Simultaneous advantages of the proposed scheme are demonstrated by modeling a test system in MATLAB software and time-domain simulation achieved by PSCAD. Full article
(This article belongs to the Section Electrical Power and Energy System)
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