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Energies, Volume 11, Issue 11 (November 2018)

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Open AccessArticle Comparison of NARX and Dual Polarization Models for Estimation of the VRLA Battery Charging/Discharging Dynamics in Pulse Cycle
Energies 2018, 11(11), 3160; https://doi.org/10.3390/en11113160 (registering DOI)
Received: 22 October 2018 / Revised: 7 November 2018 / Accepted: 11 November 2018 / Published: 14 November 2018
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Abstract
The following work presents the model-assisted research on Valve-Regulated Lead-Acid (VRLA) Absorbent Glass Mat (AGM) battery in pulse operation cycle. The experimental research was conducted for a constant value of State of Charge (SOC) of the battery, for values ranging from 0.2 to
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The following work presents the model-assisted research on Valve-Regulated Lead-Acid (VRLA) Absorbent Glass Mat (AGM) battery in pulse operation cycle. The experimental research was conducted for a constant value of State of Charge (SOC) of the battery, for values ranging from 0.2 to 0.8. Based on the conducted test stand research, the parameters of the battery were identified, which were later used to model the battery using the equivalent circuit based on dual polarization (DP) model with double Resistive-Capacitive (RC) loop. Simulations were performed for the identified parameters of the battery which are described by the general form of the polynomial. The second part contains the research on utilization of Nonlinear AutoRegressive eXogenous (NARX) recurrent neural network to predict SOC and a terminal voltage of the battery. Obtained validation results with the use of the identified parameters of the double RC loop and NARX model were discussed in the following work. The article also features the advantages and disadvantages of NARX model and DP model utilization for the use of in Battery Managements Systems (BMS) and micro-installations based on renewable energy sources. Furthermore, the advantages of the addition of more RC loops to describe the dynamic states of batteries in pulse states were discussed in the article. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessFeature PaperArticle Hardware in the Loop Real-Time Simulation for Heating Systems: Model Validation and Dynamics Analysis
Energies 2018, 11(11), 3159; https://doi.org/10.3390/en11113159 (registering DOI)
Received: 26 October 2018 / Revised: 7 November 2018 / Accepted: 8 November 2018 / Published: 14 November 2018
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Abstract
Heating systems such as heat pumps and combined heat and power cycle systems (CHP) represent a key component in the future smart grid. Their capability to couple the electricity and heat sector promises a massive contribution to the energy transition. Hence, these systems
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Heating systems such as heat pumps and combined heat and power cycle systems (CHP) represent a key component in the future smart grid. Their capability to couple the electricity and heat sector promises a massive contribution to the energy transition. Hence, these systems are continuously studied numerically and experimentally to quantify their potential and develop optimal control methods. Although numerical simulations provide time and cost-effective solutions for system development and optimization, they are exposed to several uncertainties. Hardware in the loop (HiL) approaches enable system validation and evaluation under different real-life dynamic constraints and boundary conditions. In this paper, a HiL system of a heat pump testbed is presented. It is used to present two case studies. In the first case, the conventional heat pump testbed operation method is compared to the HiL operation method. Energetic and dynamic analyses are performed to quantify the added value of the HiL and its necessity for dynamics analysis. In the second case, the HiL testbed is used to validate a model of a single family house with a heat pump participating in a local energy market. The energetic analysis indicates a deviation of 2% and 5% for heat generation and electricity consumption of the heat pump model, respectively. The model dynamics emphasized its capability to present the dynamics of a real system with a temporal distortion of 3%. Full article
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Open AccessFeature PaperArticle Numerical Investigation of an OxyfuelNon-Premixed CombustionUsing a Hybrid Eulerian Stochastic Field/Flamelet Progress Variable Approach: Effects of H2/CO2Enrichment and Reynolds Number
Energies 2018, 11(11), 3158; https://doi.org/10.3390/en11113158 (registering DOI)
Received: 2 October 2018 / Revised: 2 November 2018 / Accepted: 13 November 2018 / Published: 14 November 2018
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Abstract
In the present paper, the behaviour of an oxy-fuel non-premixed jet flame is numerically investigated by using a novel approach which combines a transported joint scalar probability density function (T-PDF) following the Eulerian Stochastic Field methodology (ESF) and a Flamelet Progress Variable (FPV)
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In the present paper, the behaviour of an oxy-fuel non-premixed jet flame is numerically investigated by using a novel approach which combines a transported joint scalar probability density function (T-PDF) following the Eulerian Stochastic Field methodology (ESF) and a Flamelet Progress Variable (FPV) turbulent combustion model under consideration of detailed chemical reaction mechanism. This hybrid ESF/FPV approach overcomes the limitations of the presumed- probability density function (P-PDF) based FPV modelling along with the solving of associated additional modelled transport equations while rendering the T-PDF computationally less demanding. In Reynolds Averaged Navier-Stokes (RANS) context, the suggested approach is first validated by assessing its general prediction capability in reproducing the flame and flow properties of a simple piloted jet flame configuration known as Sandia Flame D. Second, its feasibility in capturing CO2addition effect on the flame behaviour is demonstrated while studying a non-premixed oxy-flame configuration. This consists of an oxy-methane flame characterized by a high CO2 amount in the oxidizer and a significant content of H2 in the fuel stream, making it challenging for combustion modelling. Comparisons of numerical results with experimental data show that the complete model reproduces the major properties of the flame cases investigated and allows achieving the best agreement for the temperature and different species mass fractions once compared to the classical presumed PDF approach. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics (CFD) 2018)
Open AccessReview A Review of the Energy Performance and Life-Cycle Assessment of Building-Integrated Photovoltaic (BIPV) Systems
Energies 2018, 11(11), 3157; https://doi.org/10.3390/en11113157 (registering DOI)
Received: 7 October 2018 / Revised: 27 October 2018 / Accepted: 9 November 2018 / Published: 14 November 2018
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Abstract
Building integrated photovoltaic (BIPV) technology provides an aesthetical, economic, and technical solution for electricity self-sufficiency in buildings. As one of the most promising technologies for solar energy harvesting in urban areas, BIPV technology provides multiple benefits for buildings, including power generation from renewable
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Building integrated photovoltaic (BIPV) technology provides an aesthetical, economic, and technical solution for electricity self-sufficiency in buildings. As one of the most promising technologies for solar energy harvesting in urban areas, BIPV technology provides multiple benefits for buildings, including power generation from renewable energy resources, the replacement of traditional wall cladding, daytime lighting, heating/cooling load reduction, etc. This paper systematically reviews the progress of recent research on the electrical, thermal, optical, and overall energy performances of BIPV systems. Furthermore, based on the literature review on the energy payback time and the greenhouse-gas emission of various BIPV technologies, the research progress of the life-cycle assessment of BIPV systems is also discussed. It is anticipated that the review results can provide meaningful reference and support for the research and development of BIPV technology. Full article
(This article belongs to the Special Issue 10 Years Energies - Horizon 2028)
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Open AccessArticle Switched-Capacitor Boost Converter for Low Power Energy Harvesting Applications
Energies 2018, 11(11), 3156; https://doi.org/10.3390/en11113156 (registering DOI)
Received: 19 October 2018 / Revised: 8 November 2018 / Accepted: 13 November 2018 / Published: 14 November 2018
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Abstract
The paper presents a Switched-Capacitor Boost DC-DC Converter (SC-BC) which can be used in energy harvesting applications using thermoelectric generators (TEGs) with low output voltage, low power and a significant internal resistance. It consists of a switching capacitor circuit, where MOSFETs are used
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The paper presents a Switched-Capacitor Boost DC-DC Converter (SC-BC) which can be used in energy harvesting applications using thermoelectric generators (TEGs) with low output voltage, low power and a significant internal resistance. It consists of a switching capacitor circuit, where MOSFETs are used as switches, and a boost stage. The converter is a modification of a previously presented scheme in which diodes are used in the switched capacitor stage. A higher voltage gain and an increased efficiency can thus be achieved. The model of the converter was developed considering the internal resistance of the TEG and boost stage inductor. A comparison with the diode based converter is shown, with consideration of the TEG internal resistance. Calculation is presented of the main passive components. A control algorithm is also proposed and evaluated. It is based on a linearization approach, and designed for output voltage and inductor current control. The operation of both converter and control are verified with the simulation and experimental results. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle An Efficient Power Scheduling in Smart Homes Using Jaya Based Optimization with Time-of-Use and Critical Peak Pricing Schemes
Energies 2018, 11(11), 3155; https://doi.org/10.3390/en11113155 (registering DOI)
Received: 30 September 2018 / Revised: 30 October 2018 / Accepted: 5 November 2018 / Published: 14 November 2018
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Abstract
Presently, the advancements in the electric system, smart meters, and implementation of renewable energy sources (RES) have yielded extensive changes to the current power grid. This technological innovation in the power grid enhances the generation of electricity to meet the demands of industrial,
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Presently, the advancements in the electric system, smart meters, and implementation of renewable energy sources (RES) have yielded extensive changes to the current power grid. This technological innovation in the power grid enhances the generation of electricity to meet the demands of industrial, commercial and residential sectors. However, the industrial sectors are the focus of power grid and its demand-side management (DSM) activities. Neglecting other sectors in the DSM activities can deteriorate the total performance of the power grid. Hence, the notion of DSM and demand response by way of the residential sector makes the smart grid preferable to the current power grid. In this circumstance, this paper proposes a home energy management system (HEMS) that considered the residential sector in DSM activities and the integration of RES and energy storage system (ESS). The proposed HEMS reduces the electricity cost through scheduling of household appliances and ESS in response to the time-of-use (ToU) and critical peak price (CPP) of the electricity market. The proposed HEMS is implemented using the Earliglow based algorithm. For comparative analysis, the simulation results of the proposed method are compared with other methods: Jaya algorithm, enhanced differential evolution and strawberry algorithm. The simulation results of Earliglow based optimization method show that the integration of RES and ESS can provide electricity cost savings up to 62.80% and 20.89% for CPP and ToU. In addition, electricity cost reduction up to 43.25% and 13.83% under the CPP and ToU market prices, respectively. Full article
(This article belongs to the Special Issue Energy Performance and Indoor Climate Analysis in Buildings)
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Open AccessArticle Poly(imide-co-siloxane) as a Thermo-Stable Binder for a Thin Layer Cathode of Thermal Batteries
Energies 2018, 11(11), 3154; https://doi.org/10.3390/en11113154 (registering DOI)
Received: 23 October 2018 / Accepted: 10 November 2018 / Published: 14 November 2018
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Abstract
The polymer binder, poly(imide-co-siloxane) (PIS), was synthesized and applied to form a thin cathode layer of composites for a thermal battery that has an unusually high operating temperature of 450 °C. The PIS was prepared through cross-linking of the polyimide with
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The polymer binder, poly(imide-co-siloxane) (PIS), was synthesized and applied to form a thin cathode layer of composites for a thermal battery that has an unusually high operating temperature of 450 °C. The PIS was prepared through cross-linking of the polyimide with polysiloxane. The morphology of FeS2/PIS composites showed that FeS2 particles was coated with the PIS cross-linked gel. The FeS2/PIS composites enabled to fabricate mechanically stable thin cathode layer that was 10–20% of the thickness of a conventional pellet-type cathode. The FeS2/PIS composites were stable up to 400 °C and maintained their morphology at this temperature. PIS coating layers decomposed at 450 °C, and a new residue was generated, which was observed by transmission electron microscopy, and the compositional change was analyzed. The FeS2/PIS composites showed enhanced thermal stability over that of FeS2 in thermogravimetric analysis. The thermal battery with the PIS polymer binder showed a 20% discharge capacity increase when compared to a conventional pellet-type cathode. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessReview Technology Evolution in Membrane-Based CCS
Energies 2018, 11(11), 3153; https://doi.org/10.3390/en11113153 (registering DOI)
Received: 17 October 2018 / Revised: 7 November 2018 / Accepted: 11 November 2018 / Published: 14 November 2018
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Abstract
In recent years, many CO2 capture technologies have been developed due to growing awareness about the importance of reducing greenhouse gas emissions. In this paper, publications from the last decade addressing this topic were analyzed, paying special attention to patent status to
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In recent years, many CO2 capture technologies have been developed due to growing awareness about the importance of reducing greenhouse gas emissions. In this paper, publications from the last decade addressing this topic were analyzed, paying special attention to patent status to provide useful information for policymakers, industry, and businesses and to help determine the direction of future research. To show the most current patent activity related to carbon capture using membrane technology, we collected 2749 patent documents and 572 scientific papers. The results demonstrated that membranes are a developing field, with the number of applications growing at a steady pace, exceeding 100 applications per year in 2013 and 2014. North American assignees were the main contributors, with the greatest number of patents owned by companies such as UOP LLC, Kilimanjaro Energy Inc., and Membrane Technology and Research Inc., making up 26% of the total number of published patents. Asian countries (China, Japan, and Korea) and international offices were also important knowledge sources, providing 29% and 24% of the documents, respectively. Furthermore, this paper highlights 10 more valuable patents regarding their degree of innovation and citations, classified as Y02C 10/10 according to the Cooperative Patent Classification (CPC) criteria. Full article
(This article belongs to the Section Sustainable Energy)
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Open AccessArticle A Grid-Supporting Photovoltaic System Implemented by a VSG with Energy Storage
Energies 2018, 11(11), 3152; https://doi.org/10.3390/en11113152 (registering DOI)
Received: 24 October 2018 / Revised: 6 November 2018 / Accepted: 8 November 2018 / Published: 14 November 2018
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Abstract
Conventional photovoltaic (PV) systems interfaced by grid-connected inverters fail to support the grid and participate in frequency regulation. Furthermore, reduced system inertia as a result of the integration of conventional PV systems may lead to an increased frequency deviation of the grid for
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Conventional photovoltaic (PV) systems interfaced by grid-connected inverters fail to support the grid and participate in frequency regulation. Furthermore, reduced system inertia as a result of the integration of conventional PV systems may lead to an increased frequency deviation of the grid for contingencies. In this paper, a grid-supporting PV system, which can provide inertia and participate in frequency regulation through virtual synchronous generator (VSG) technology and an energy storage unit, is proposed. The function of supporting the grid is implemented in a practical PV system through using the presented control scheme and topology. Compared with the conventional PV system, the grid-supporting PV system, behaving as an inertial voltage source like synchronous generators, has the capability of participating in frequency regulation and providing inertia. Moreover, the proposed PV system can mitigate autonomously the power imbalance between generation and consumption, filter the PV power, and operate without the phase-locked loop after initial synchronization. Performance analysis is conducted and the stability constraint is theoretically formulated. The novel PV system is validated on a modified CIGRE benchmark under different cases, being compared with the conventional PV system. The verifications demonstrate the grid support functions of the proposed PV system. Full article
(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems)
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Open AccessArticle Computational Fluid Dynamics Modelling and Simulation of an Inclined Horizontal Axis Hydrokinetic Turbine
Energies 2018, 11(11), 3151; https://doi.org/10.3390/en11113151 (registering DOI)
Received: 2 August 2018 / Revised: 25 October 2018 / Accepted: 30 October 2018 / Published: 14 November 2018
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Abstract
In this contribution, unsteady three-dimensional numerical simulations of the water flow through a horizontal axis hydrokinetic turbine (HAHT) of the Garman type are performed. This study was conducted in order to estimate the influence of turbine inclination with respect to the incoming flow
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In this contribution, unsteady three-dimensional numerical simulations of the water flow through a horizontal axis hydrokinetic turbine (HAHT) of the Garman type are performed. This study was conducted in order to estimate the influence of turbine inclination with respect to the incoming flow on turbine performance and forces acting on the rotor, which is studied using a time-accurate Reynolds-averaged Navier-Stokes (RANS) commercial solver. Changes of the flow in time are described by a physical transient model based on two domains, one rotating and the other stationary, combined with a sliding mesh technique. Flow turbulence is described by the well-established Shear Stress Transport (SST) model using its standard and transitional versions. Three inclined operation conditions have been analyzed for the turbine regarding the main stream: 0° (SP configuration, shaft parallel to incoming velocity), 15° (SI15 configuration), and 30° (SI30 configuration). It was found that the hydrodynamic efficiency of the turbine decreases with increasing inclination angles. Besides, it was obtained that in the inclined configurations, the thrust and drag forces acting on rotor were lower than in the SP configuration, although in the former cases, blades experience alternating loads that may induce failure due to fatigue in the long term. Moreover, if the boundary layer transitional effects are included in the computations, a slight increase in the power coefficient is computed for all inclination configurations. Full article
(This article belongs to the Section Sustainable Energy)
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Open AccessArticle Design and Implementation of Novel Multi-Converter-Based Unified Power Quality Conditioner for Low-Voltage High-Current Distribution System
Energies 2018, 11(11), 3150; https://doi.org/10.3390/en11113150 (registering DOI)
Received: 30 September 2018 / Revised: 3 November 2018 / Accepted: 11 November 2018 / Published: 14 November 2018
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Abstract
This paper introduces a novel multi-converter-based unified power quality conditioner (MCB-UPQC). Three optimization methods are proposed based on the traditional UPQC: (1) The shunt converter is substituted with multi-modular parallel converters. Hence, the reactive power and harmonic currents can be increased greatly, which
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This paper introduces a novel multi-converter-based unified power quality conditioner (MCB-UPQC). Three optimization methods are proposed based on the traditional UPQC: (1) The shunt converter is substituted with multi-modular parallel converters. Hence, the reactive power and harmonic currents can be increased greatly, which are suitable for low-voltage high-current distribution systems. (2) The series converters consist of three H-bridge inverters, and each of the H-bridge inverters is controlled separately. The control strategy is easier to achieve and can improve the control performance of voltage regulation under unbalanced voltage sag or swell. (3) A three-phase four-leg (3P4L) converter is connected to the common DC bus of the proposed UPQC to connect the renewable energy and energy storage system. The detailed mathematical models of shunt and series converters are analyzed, respectively. A multi-proportional resonant (PR) controller is presented in the voltage regulation and reactive power compensation control algorithms. The simulation results verify the feasibility of the control algorithms. Finally, the experimental platform is established, and the experimental results are presented to verify the validity and superiority of the proposed topology and algorithms. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Economic Feasibility of Wave Energy Farms in Portugal
Energies 2018, 11(11), 3149; https://doi.org/10.3390/en11113149 (registering DOI)
Received: 22 September 2018 / Revised: 3 November 2018 / Accepted: 6 November 2018 / Published: 14 November 2018
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Abstract
This paper develops a methodology to determine the economic feasibility of implementing offshore wave energy farms on the Portuguese continental coast. This methodology follows several phases: the geographic phase, the energy phase, the economic phase, and the restrictions phase. First, in the geographic
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This paper develops a methodology to determine the economic feasibility of implementing offshore wave energy farms on the Portuguese continental coast. This methodology follows several phases: the geographic phase, the energy phase, the economic phase, and the restrictions phase. First, in the geographic phase, the height and the period of the waves, the bathymetry, the distance from the farm to the shore, from farm to shipyard, and from farm to port, are calculated. In the energy phase the energy produced by each wave energy converter is determined, and in the economic phase, the parameters calculated in the previous phases are used as input to find the economic parameters. Finally, in the restrictions phase, a limitation by the bathymetry will be added to the economic maps, whose value will be different depending on the floating offshore wave energy converter (WEC). In this study, three wave energy converters have been considered, Pelamis, AquaBuOY, and Wave Dragon, and several scenarios for electric tariffs have been taken into account. The results obtained indicate what the best WEC is for this study in terms of its levelized cost of energy (LCOE), internal rate of return (IRR), and net present value (NPV), and where the best area is to install wave energy farms. Full article
(This article belongs to the Special Issue Wave and Tidal Energy)
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Open AccessArticle Modelling the Dynamics of Fuel and EU Allowance Prices during Phase 3 of the EU ETS
Energies 2018, 11(11), 3148; https://doi.org/10.3390/en11113148 (registering DOI)
Received: 4 October 2018 / Revised: 5 November 2018 / Accepted: 9 November 2018 / Published: 14 November 2018
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Abstract
This article studies the relationship between the prices of fuel and EU Allowances (EUA) for carbon emissions during Phase 3 of the European Union Emissions Trading System. We find that the forward prices of EUA, coal, gas and Brent oil are jointly determined
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This article studies the relationship between the prices of fuel and EU Allowances (EUA) for carbon emissions during Phase 3 of the European Union Emissions Trading System. We find that the forward prices of EUA, coal, gas and Brent oil are jointly determined in equilibrium. The existence of such a long-run relationship entails a permanent-transitory decomposition for the series of EUA and fuel prices that reveals the short- and long-term causal influence of the EUA market in shaping the joint dynamics of fuel prices. This result complements the literature that suggests that EUA prices are driven by the dynamics of fuel prices. Interestingly, we do not find an equilibrium relationship in the spot market. EUA and fuel spot prices are driven by independent unit root processes. The differences between spot and forward markets are attributed to the tradability of forward prices that are used for speculation and hedging in financial markets. In contrast, spot prices are mainly driven by supply and demand in energy markets. Full article
(This article belongs to the Special Issue Energy Markets and Economics)
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Open AccessArticle Combustion Inhibition of Aluminum–Methane–Air Flames by Fine NaCl Particles
Energies 2018, 11(11), 3147; https://doi.org/10.3390/en11113147 (registering DOI)
Received: 11 October 2018 / Revised: 10 November 2018 / Accepted: 12 November 2018 / Published: 14 November 2018
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Abstract
The effect of NaCl as an extinguishing agent on metal dust fires require further exploration. This paper reports the results of an experimental study on the performance of micron-sized NaCl powders on hybrid aluminum–methane–air flames. NaCl particles with sub-10 μm sizes were newly
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The effect of NaCl as an extinguishing agent on metal dust fires require further exploration. This paper reports the results of an experimental study on the performance of micron-sized NaCl powders on hybrid aluminum–methane–air flames. NaCl particles with sub-10 μm sizes were newly fabricated via a simple solution/anti-solvent method. The combustion characteristics of aluminum combustion in a methane-air flame were investigated prior to the particle inhibition study to verify the critical aluminum concentration that enables conical aluminum-powder flame formation. To study the inhibition effectiveness, the laminar burning velocity was measured for the established aluminum–methane–air flames with the added NaCl using a modified nozzle burner over a range of dust concentrations. The results were also compared to flames with quartz sand and SiC particles. It is shown that the inhibition performance of NaCl considerably outperformed the sand and SiC particles by more rapidly decreasing the burning velocity. The improved performance can be attributed to contributions from both dilution and thermal effects. In addition, the dynamic behavior of the NaCl particles in the laminar aluminum–methane–air flame was investigated based on experimental observations. The experimental data provided quantified the capabilities of NaCl for metal fire suppression on a fundamental level. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Physicochemical, Performance, Combustion and Emission Characteristics of Melaleuca Cajuputi Oil-Refined Palm Oil Hybrid Biofuel Blend
Energies 2018, 11(11), 3146; https://doi.org/10.3390/en11113146 (registering DOI)
Received: 13 September 2018 / Revised: 25 September 2018 / Accepted: 28 September 2018 / Published: 14 November 2018
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Abstract
To reduce the economic impact caused by the fossil fuel crisis and avoid relying on existing biofuels, it is important to seek locally available and renewable biofuel throughout the year. In the present work, a new light biofuel—Melaleuca Cajuputi oil (MCO)—was introduced to
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To reduce the economic impact caused by the fossil fuel crisis and avoid relying on existing biofuels, it is important to seek locally available and renewable biofuel throughout the year. In the present work, a new light biofuel—Melaleuca Cajuputi oil (MCO)—was introduced to blend with refined palm oil (RPO). The physicochemical properties, combustion characteristics, engine performance, and exhaust emissions were comprehensively examined. It was found that the higher the percentage of MCO, the lower the viscosity and density of the blends obtained. Calorific value (CV) was increased with the increase of MCO fraction in the blend. Regression analysis has suggested that the blend of 32% (v/v) of RPO and 68% (v/v) of MCO (RPO32MCO68) is optimal to obtain viscosity and density in accordance with ASTM 6751/EN 14214 standards. The experimental results show that the in-cylinder pressure, brake torque, and brake power of the optimal blend were slightly lower than those of baseline diesel fuel. Brake specific fuel consumption (BSFC), carbon monoxide (CO), and unburnt hydrocarbon (HC) were found to be slightly higher compared to diesel fuel. Notably, nitrogen oxides (NOx) and smoke opacity were found to be decreased over the entire range of the test. Overall, the optimal blend of RPO32MCO68 has shown a decent result which marks it as a potential viable source of biofuel. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle A University Building Test Case for Occupancy-Based Building Automation
Energies 2018, 11(11), 3145; https://doi.org/10.3390/en11113145 (registering DOI)
Received: 7 October 2018 / Revised: 28 October 2018 / Accepted: 9 November 2018 / Published: 14 November 2018
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Abstract
Heating, ventilation and air-conditioning (HVAC) units in buildings form a system-of-subsystems entity that must be accurately integrated and controlled by the building automation system to ensure the occupants’ comfort with reduced energy consumption. As control of HVACs involves a standardized hierarchy of high-level
[...] Read more.
Heating, ventilation and air-conditioning (HVAC) units in buildings form a system-of-subsystems entity that must be accurately integrated and controlled by the building automation system to ensure the occupants’ comfort with reduced energy consumption. As control of HVACs involves a standardized hierarchy of high-level set-point control and low-level Proportional-Integral-Derivative (PID) controls, there is a need for overcoming current control fragmentation without disrupting the standard hierarchy. In this work, we propose a model-based approach to achieve these goals. In particular: the set-point control is based on a predictive HVAC thermal model, and aims at optimizing thermal comfort with reduced energy consumption; the standard low-level PID controllers are auto-tuned based on simulations of the HVAC thermal model, and aims at good tracking of the set points. One benefit of such control structure is that the PID dynamics are included in the predictive optimization: in this way, we are able to account for tracking transients, which are particularly useful if the HVAC is switched on and off depending on occupancy patterns. Experimental and simulation validation via a three-room test case at the Delft University of Technology shows the potential for a high degree of comfort while also reducing energy consumption. Full article
(This article belongs to the Special Issue Optimisation Models and Methods in Energy Systems)
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Open AccessArticle A Centralized Smart Decision-Making Hierarchical Interactive Architecture for Multiple Home Microgrids in Retail Electricity Market
Energies 2018, 11(11), 3144; https://doi.org/10.3390/en11113144 (registering DOI)
Received: 3 October 2018 / Revised: 6 November 2018 / Accepted: 10 November 2018 / Published: 14 November 2018
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Abstract
The principal aim of this study is to devise a combined market operator and a distribution network operator structure for multiple home-microgrids (MH-MGs) connected to an upstream grid. Here, there are three distinct types of players with opposite intentions that can participate as
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The principal aim of this study is to devise a combined market operator and a distribution network operator structure for multiple home-microgrids (MH-MGs) connected to an upstream grid. Here, there are three distinct types of players with opposite intentions that can participate as a consumer and/or prosumer (as a buyer or seller) in the market. All players that are price makers can compete with each other to obtain much more possible profitability while consumers aim to minimize the market-clearing price. For modeling the interactions among partakers and implementing this comprehensive structure, a multi-objective function problem is solved by using a static, non-cooperative game theory. The propounded structure is a hierarchical bi-level controller, and its accomplishment in the optimal control of MH-MGs with distributed energy resources has been evaluated. The outcome of this algorithm provides the best and most suitable power allocation among different players in the market while satisfying each player’s goals. Furthermore, the amount of profit gained by each player is ascertained. Simulation results demonstrate 169% increase in the total payoff compared to the imperialist competition algorithm. This percentage proves the effectiveness, extensibility and flexibility of the presented approach in encouraging participants to join the market and boost their profits. Full article
(This article belongs to the Special Issue Communications in Microgrids)
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Open AccessArticle Dynamic Daylight Metrics for Electricity Savings in Offices: Window Size and Climate Smart Lighting Management
Energies 2018, 11(11), 3143; https://doi.org/10.3390/en11113143
Received: 20 July 2018 / Revised: 7 November 2018 / Accepted: 10 November 2018 / Published: 13 November 2018
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Abstract
Daylight performance metrics provide a promising approach for the design and optimization of lighting strategies in buildings and their management. Smart controls for electric lighting can reduce power consumption and promote visual comfort using different control strategies, based on affordable technologies and low
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Daylight performance metrics provide a promising approach for the design and optimization of lighting strategies in buildings and their management. Smart controls for electric lighting can reduce power consumption and promote visual comfort using different control strategies, based on affordable technologies and low building impact. The aim of this research is to assess the energy efficiency of these smart controls by means of dynamic daylight performance metrics, to determine suitable solutions based on the geometry of the architecture and the weather conditions. The analysis considers different room dimensions, with variable window size and two mean surface reflectance values. DaySim 3.1 lighting software provides the simulations for the study, determining the necessary quantification of dynamic metrics to evaluate the usefulness of the proposed smart controls and their impact on energy efficiency. The validation of dynamic metrics is carried out by monitoring a mesh of illuminance-meters in test cells throughout one year. The results showed that, for most rooms more than 3.00 m deep, smart controls achieve worthwhile energy savings and a low payback period, regardless of weather conditions and for worst-case situations. It is also concluded that dimming systems provide a higher net present value and allow the use of smaller window size than other control solutions. Full article
(This article belongs to the Section Sustainable Energy)
Open AccessReview A Survey of Real-Time Optimal Power Flow
Energies 2018, 11(11), 3142; https://doi.org/10.3390/en11113142
Received: 24 September 2018 / Revised: 3 November 2018 / Accepted: 8 November 2018 / Published: 13 November 2018
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Abstract
There has been a strong increase of penetration of renewable energies into power systems. However, the renewables pose new challenges for the operation of the networks. Particularly, wind power is intermittently fluctuating, and, therefore, the network operator has to fast update the operations
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There has been a strong increase of penetration of renewable energies into power systems. However, the renewables pose new challenges for the operation of the networks. Particularly, wind power is intermittently fluctuating, and, therefore, the network operator has to fast update the operations correspondingly. This task should be performed by an online optimization. Therefore, real-time optimal power flow (RT-OPF) has become an attractive topic in recent years. This paper presents an overview of recent studies on RT-OPF under wind energy penetration, offering a critical review of the major advancements in RT-OPF. It describes the challenges in the realization of the RT-OPF and presents available approaches to address these challenges. The paper focuses on a number of topics which are reviewed in chronological order of appearance: offline energy management systems (EMSs) (deterministic and stochastic approaches) and real-time EMSs (constraint satisfaction-based and OPF-based methods). The particular challenges associated with the incorporation of battery storage systems in the networks are explored, and it is concluded that the current research on RT-OPF is not sufficient, and new solution approaches are needed. Full article
(This article belongs to the Special Issue Energy Systems Engineering)
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Open AccessArticle Use of Hydrogen in Off-Grid Locations, a Techno-Economic Assessment
Energies 2018, 11(11), 3141; https://doi.org/10.3390/en11113141
Received: 4 October 2018 / Revised: 5 November 2018 / Accepted: 8 November 2018 / Published: 13 November 2018
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Abstract
Diesel generators are currently used as an off-grid solution for backup power, but this causes CO2 and GHG emissions, noise emissions, and the negative effects of the volatile diesel market influencing operating costs. Green hydrogen production, by means of water electrolysis, has
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Diesel generators are currently used as an off-grid solution for backup power, but this causes CO2 and GHG emissions, noise emissions, and the negative effects of the volatile diesel market influencing operating costs. Green hydrogen production, by means of water electrolysis, has been proposed as a feasible solution to fill the gaps between demand and production, the main handicaps of using exclusively renewable energy in isolated applications. This manuscript presents a business case of an off-grid hydrogen production by electrolysis applied to the electrification of isolated sites. This study is part of the European Ely4off project (n° 700359). Under certain techno-economic hypothesis, four different system configurations supplied exclusively by photovoltaic are compared to find the optimal Levelized Cost of Electricity (LCoE): photovoltaic-batteries, photovoltaic-hydrogen-batteries, photovoltaic-diesel generator, and diesel generator; the influence of the location and the impact of different consumptions profiles is explored. Several simulations developed through specific modeling software are carried out and discussed. The main finding is that diesel-based systems still allow lower costs than any other solution, although hydrogen-based solutions can compete with other technologies under certain conditions. Full article
(This article belongs to the Special Issue Sustainable Hydrogen Production, Storage and Utilization)
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Open AccessArticle Active and Reactive Power Compensation Control Strategy for VSC-HVDC Systems under Unbalanced Grid Conditions
Energies 2018, 11(11), 3140; https://doi.org/10.3390/en11113140
Received: 23 October 2018 / Revised: 5 November 2018 / Accepted: 8 November 2018 / Published: 13 November 2018
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Abstract
This paper presents a power compensation strategy to suppress the double frequency power ripples of Voltage source converter high-voltage direct current (VSC-HVDC) systems under unbalanced grid voltage conditions. The mathematical control equations of the double frequency ripple power of VSC under unbalanced operating
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This paper presents a power compensation strategy to suppress the double frequency power ripples of Voltage source converter high-voltage direct current (VSC-HVDC) systems under unbalanced grid voltage conditions. The mathematical control equations of the double frequency ripple power of VSC under unbalanced operating conditions are firstly derived and established, where the dynamic behaviors of the double frequency ripples in active and reactive power are regarded as being driven by current-relevant components and voltage-relevant components, respectively. Based on the equations, a power compensation control strategy of VSC-HVDC is proposed via the passivity-based control with disturbance observer to suppress both the current-relevant and voltage-relevant components in the power ripples. With this control strategy, the double frequency ripples in active and reactive power are suppressed simultaneously and system performance is significantly enhanced with the implementation of the disturbance observer in the passivity-based control. Theoretical stability analysis and simulation cases show the effectiveness and superiority of the proposed strategy. Full article
(This article belongs to the Special Issue HVDC/FACTS for Grid Services in Electric Power Systems)
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Open AccessArticle Exergy As a Measure of Sustainable Retrofitting of Buildings
Energies 2018, 11(11), 3139; https://doi.org/10.3390/en11113139
Received: 14 October 2018 / Revised: 3 November 2018 / Accepted: 10 November 2018 / Published: 13 November 2018
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Abstract
This study presents a novel optimization methodology for choosing optimal building retrofitting strategies based on the concept of exergy analysis. The study demonstrates that the building exergy analysis may open new opportunities in the design of an optimal retrofit solution despite being a
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This study presents a novel optimization methodology for choosing optimal building retrofitting strategies based on the concept of exergy analysis. The study demonstrates that the building exergy analysis may open new opportunities in the design of an optimal retrofit solution despite being a theoretical approach based on the high performance of a Carnot reverse cycle. This exergy-based solution is different from the one selected through traditional efficient retrofits where minimizing energy consumption is the primary selection criteria. The new solution connects the building with the reference environment, which acts as “an unlimited sink or unlimited sources of energy”, and it adapts the building to maximize the intake of energy resources from the reference environment. The building hosting the School of Architecture at the University of Navarra has been chosen as the case study building. The unique architectural appearance and bespoke architectural characteristics of the building limit the choices of retrofitting solutions; therefore, retrofitting solutions on the façade, roof, roof skylight and windows are considered in multi-objective optimization using the jEPlus package. It is remarkable that different retrofitting solutions have been obtained for energy-driven and exergy-driven optimization, respectively. Considering the local contexts and all possible reference environments for the building, three “unlimited sinks or unlimited sources of energy” are selected for the case study building to explore exergy-driven optimization: the external air, the ground in the surrounding area and the nearby river. The evidence shows that no matter which reference environment is chosen, an identical envelope retrofitting solution has been obtained. Full article
(This article belongs to the Section Sustainable Energy)
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Open AccessArticle Design of an Emergency Energy System for a City Assisted by Renewable Energy, Case Study: Latakia, Syria
Energies 2018, 11(11), 3138; https://doi.org/10.3390/en11113138
Received: 18 October 2018 / Revised: 8 November 2018 / Accepted: 10 November 2018 / Published: 13 November 2018
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Abstract
Electrical energy is one of the most important daily needs. Shortage of energy can be very dangerous for any society. This can affect the standard of living and quality of life of the people and even endanger the lives of those in hospitals,
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Electrical energy is one of the most important daily needs. Shortage of energy can be very dangerous for any society. This can affect the standard of living and quality of life of the people and even endanger the lives of those in hospitals, and so forth. Developed countries do not face such risks in general because they have well organized electrical systems and high energy security. The developing countries are faced daily with electric system collapses, especially in the case of wars, where many parts of the electrical grid in the country can be damaged and fuel transmission lines for generators cut off. Urban areas in developing countries should have a strategic plan to deal with any unexpected occurrence of energy shortages using any available renewable energy sources. City of Latakia is located in the region which has been suffering from the consequences of war for more than six years. The fact that a high number of migrants from other cities have come to Latakia along with a lack of fuel makes the energy shortage in the city worse. An emergency system could use the cheapest available renewable energy sources in addition to few big portable generators to provide an acceptable energy supply for the most needed requirements of daily life. Full article
(This article belongs to the Section Sustainable Energy)
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Open AccessArticle The Effects of the Downstream Contraction Ratio of Organ-Pipe Nozzle on the Pressure Oscillations of Self-Resonating Waterjets
Energies 2018, 11(11), 3137; https://doi.org/10.3390/en11113137
Received: 18 October 2018 / Revised: 6 November 2018 / Accepted: 8 November 2018 / Published: 13 November 2018
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Abstract
Self-resonating waterjets (SRWJs) are being widely used in the fields of energy exploitation, due to the significantly increased penetration rate of roller bits in deep-hole drilling. To further improve the impact and erosion abilities of SRWJs, the effects of the downstream contraction ratio
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Self-resonating waterjets (SRWJs) are being widely used in the fields of energy exploitation, due to the significantly increased penetration rate of roller bits in deep-hole drilling. To further improve the impact and erosion abilities of SRWJs, the effects of the downstream contraction ratio of organ-pipe nozzle on the axial pressure oscillations were experimentally studied. The axial pressure oscillation peak and amplitude were used to evaluate the effects under two inlet pressures and various standoff distances. The results show that the downstream contraction ratio can affect the development trends of the pressure oscillations and determines the values of the peaks and amplitudes. Under the experimental conditions, 2.5 is the ratio that leads to the maximum peaks and amplitudes at almost all the testing standoff distances, while the ratio of 2 always results in the minimum ones. The development trend of the pressure oscillation peak for the ratio of 3.5 has a great change at an inlet pressure of 20 MPa. Generally, the relative pressure oscillations are more violent at an inlet pressure of 10 MPa, which is regardless of the contraction ratio. This study helps provide a guideline for determining the physical parameters required in the fabrication of organ-pipe nozzles used for deep-hole drilling. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle CO2 and CH4 Adsorption Behavior of Biomass-Based Activated Carbons
Energies 2018, 11(11), 3136; https://doi.org/10.3390/en11113136
Received: 25 July 2018 / Revised: 5 November 2018 / Accepted: 8 November 2018 / Published: 13 November 2018
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Abstract
The aim of the present work is to study the effect of different activation methods for the production of a biomass-based activated carbon on the CO2 and CH4 adsorption. The influence of the activation method on the adsorption uptake was studied
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The aim of the present work is to study the effect of different activation methods for the production of a biomass-based activated carbon on the CO 2 and CH 4 adsorption. The influence of the activation method on the adsorption uptake was studied using three activated carbons obtained by different activation methods (H 3 PO 4 chemical activation and H 2 O and CO 2 physical activation) of olive stones. Methane and carbon dioxide pure gas adsorption experiments were carried out at two working temperatures (303.15 and 323.15 K). The influence of the activation method on the adsorption uptake was studied in terms of both textural properties and surface chemistry. For the three adsorbents, the CO 2 adsorption was more important than that of CH 4 . The chemically-activated carbon presented a higher specific surface area and micropore volume, which led to a higher adsorption capacity of both CO 2 and CH 4 . For methane adsorption, the presence of mesopores facilitated the diffusion of the gas molecules into the micropores. In the case of carbon dioxide adsorption, the presence of more oxygen groups on the water vapor-activated carbon enhanced its adsorption capacity. Full article
(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications Ⅱ)
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Open AccessArticle Dynamic Study of a Rooftop Vertical Axis Wind Turbine Tower Based on an Automated Vibration Data Processing Algorithm
Energies 2018, 11(11), 3135; https://doi.org/10.3390/en11113135
Received: 3 July 2018 / Revised: 29 July 2018 / Accepted: 6 August 2018 / Published: 13 November 2018
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Abstract
When constructed on tall building rooftops, the vertical axis wind turbine (VAWT) has the potential of power generation in highly urbanized areas. In this paper, the ambient dynamic responses of a rooftop VAWT were investigated. The dynamic analysis was based on ambient measurements
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When constructed on tall building rooftops, the vertical axis wind turbine (VAWT) has the potential of power generation in highly urbanized areas. In this paper, the ambient dynamic responses of a rooftop VAWT were investigated. The dynamic analysis was based on ambient measurements of the structural vibration of the VAWT (including the supporting structure), which resides on the top of a 24-story building. To help process the ambient vibration data, an automated algorithm based on stochastic subspace identification (SSI) with a fast clustering procedure was developed. The algorithm was applied to the vibration data for mode identification, and the results indicate interesting modal responses that may be affected by the building vibration, which have significant implications for the condition monitoring strategy for the VAWT. The environmental effects on the ambient vibration data were also investigated. It was found that the blade rotation speed contributes the most to the vibration responses. Full article
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Open AccessArticle Power Control of Direct Interconnection Technique for Airborne Wind Energy Systems
Energies 2018, 11(11), 3134; https://doi.org/10.3390/en11113134
Received: 15 October 2018 / Revised: 7 November 2018 / Accepted: 11 November 2018 / Published: 13 November 2018
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In this paper, an offshore airborne wind energy (AWE) farm consisting of three non-reversing pumping mode AWE systems is modelled and simulated. The AWE systems employ permanent magnet synchronous generators (PMSG). A direct interconnection technique is developed and implemented for AWE systems. This
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In this paper, an offshore airborne wind energy (AWE) farm consisting of three non-reversing pumping mode AWE systems is modelled and simulated. The AWE systems employ permanent magnet synchronous generators (PMSG). A direct interconnection technique is developed and implemented for AWE systems. This method is a new approach invented for interconnecting offshore wind turbines with the least number of required offshore-based power electronic converters. The direct interconnection technique can be beneficial in improving the economy and reliability of marine airborne wind energy systems. The performance and interactions of the directly interconnected generators inside the energy farm internal power grid are investigated. The results of the study conducted in this paper, show the directly interconnected AWE systems can exhibit a poor load balance and significant reactive power exchange which must be addressed. Power control strategies for controlling the active and reactive power of the AWE farm are designed, implemented, and promising results are discussed in this paper. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessFeature PaperArticle Growth Mechanism of Siliceous Cement in Tight Sandstone and Its Influence on Reservoir Physical Properties
Energies 2018, 11(11), 3133; https://doi.org/10.3390/en11113133
Received: 9 October 2018 / Revised: 2 November 2018 / Accepted: 9 November 2018 / Published: 13 November 2018
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Abstract
To investigate the effect of siliceous cementation on the densification of sandstone and the forming process of tight sandstone, based on cathodoluminescence, scanning electron microscopy and thin section analysis, the growth mechanism and characteristics of quartz particles in tight sandstone formations are explored.
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To investigate the effect of siliceous cementation on the densification of sandstone and the forming process of tight sandstone, based on cathodoluminescence, scanning electron microscopy and thin section analysis, the growth mechanism and characteristics of quartz particles in tight sandstone formations are explored. Meanwhile, combined with conventional core analysis and X-ray diffraction experiments, the factors affecting the crystallization of quartz particles, including the chlorite content, grain size and clay mineral, are analyzed, respectively. The entire siliceous cementation is divided into two processes. The first part is the process in which the weathered and rounded particles in the formation are restored to the hexagonal dipyramid crystal by siliceous cementation. The second part is the process of coaxial growth that the hexagonal dipyramid crystal continues to increase with the form of micro-quartz film. As siliceous cements continue to increase, the petrological characteristics of sandstones are constantly changing. The tight sandstone developed in the study area is composed of lithic sandstone and quartz lithic sandstone. Based on the analysis results, 2D and 3D evolution models are established for densification of two different lithic sandstones. When the content of siliceous cement in the study area is less than 17%, the porosity of tight sandstone increases with the increase of cement. When the content of cement is more than 17%, the porosity of tight sandstone is negatively correlated with the content of cement. When the cement content is greater than 10%, the reservoir permeability is negatively correlated with it. Furthermore, the particle size mainly affects the permeability of reservoir, and the particle size is negatively correlated with the permeability of tight sandstone. The most high-quality tight sandstone reservoir in the study area is in the first cementation stage when siliceous cements are distributed in porphyritic texture with the content of 10–15% and a grain size of 0.2–0.3 mm. In addition, the relatively high-quality reservoir is the one developing clay mineral film with a content of cementation about 5–12%. Full article
(This article belongs to the Special Issue Nanotech for Oil and Gas 2019)
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Open AccessFeature PaperArticle Improvement of Tubular Permanent Magnet Machine Performance Using Dual-Segment Halbach Array
Energies 2018, 11(11), 3132; https://doi.org/10.3390/en11113132
Received: 15 October 2018 / Revised: 29 October 2018 / Accepted: 8 November 2018 / Published: 13 November 2018
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Abstract
In this paper, a modification of the dual-segment permanent magnet (PM) Halbach array is investigated to improve the performance of the tubular linear machine, in terms of flux density and output power. Instead of a classical Halbach array with only radial and axial
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In this paper, a modification of the dual-segment permanent magnet (PM) Halbach array is investigated to improve the performance of the tubular linear machine, in terms of flux density and output power. Instead of a classical Halbach array with only radial and axial PMs, the proposed model involves the insertion of mig-magnets, which have a magnetized angle shifted from the reference magnetized angles of axial and radial PMs. This structure leads to the elimination of flux leakage and the concentration of flux linkage in middle of the coil; therefore, the output power is increased by 13.2%. Full article
(This article belongs to the Special Issue Electrical Machine Design)
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Open AccessArticle Energy Performance Assessment of Waste Materials for Buildings in Extreme Cold and Hot Conditions
Energies 2018, 11(11), 3131; https://doi.org/10.3390/en11113131
Received: 21 September 2018 / Revised: 7 October 2018 / Accepted: 19 October 2018 / Published: 13 November 2018
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In this article, thermal performance of different waste materials and by-products of industrial processes is investigated experimentally. A geopolymer concrete block with 7.5 cm thickness and cross-sectional area of 5 × 5 cm was considered as a reference model to measure heat transmission
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In this article, thermal performance of different waste materials and by-products of industrial processes is investigated experimentally. A geopolymer concrete block with 7.5 cm thickness and cross-sectional area of 5 × 5 cm was considered as a reference model to measure heat transmission across the two opposite surfaces while all four remnant surfaces were perfectly insulated. For all other samples, a sandwich concrete block was developed by taking two pieces of the geopolymer concrete with 2.5 cm thickness each on either side and insulation material of 2.5 cm thickness in between. The sandwich materials investigated were air cavity, expanded polystyrene foam, polyurethane foam, rubber tire, date palm, PCM-30, and PCM-42. Experimental investigations revealed that the investigated green materials and industrial by-products have comparable insulation performance with respect to the traditional insulations such as expanded polystyrene foam. It is found that polyurethane foam and date palm can reduce indoor cooling demand by 46.6% each in hot conditions while rubber tire can reduce indoor heating demand by 59.2% in cold climatic conditions at the maximum. The research results confirm and encourage the effective utilization of waste materials in building walls for reducing indoor air-conditioning demand in the extreme climatic conditions. Full article
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