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Energies, Volume 10, Issue 12 (December 2017)

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Editorial

Jump to: Research, Review, Other

Open AccessEditorial Biomass Chars: Elaboration, Characterization and Applications
Energies 2017, 10(12), 2040; doi:10.3390/en10122040
Received: 28 November 2017 / Revised: 28 November 2017 / Accepted: 1 December 2017 / Published: 3 December 2017
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(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications)

Research

Jump to: Editorial, Review, Other

Open AccessArticle Modeling and Experimental Study of a Small Scale Olive Pomace Gasifier for Cogeneration: Energy and Profitability Analysis
Energies 2017, 10(12), 1930; doi:10.3390/en10121930
Received: 19 September 2017 / Revised: 15 November 2017 / Accepted: 17 November 2017 / Published: 23 November 2017
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Abstract
A thermodynamic model of a combined heat and power (CHP) plant, fed by syngas produced by dry olive pomace gasification is here presented. An experimental study is carried out to inform the proposed model. The plant is designed to produce electric power (200
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A thermodynamic model of a combined heat and power (CHP) plant, fed by syngas produced by dry olive pomace gasification is here presented. An experimental study is carried out to inform the proposed model. The plant is designed to produce electric power (200 kWel) and hot-water by using a cogenerative micro gas turbine (micro GT). Before being released, exhausts are used to dry the biomass from 50% to 17% wb. The ChemCad software is used to model the gasification process, and input data to inform the model are taken from experimental tests. The micro GT and cogeneration sections are modeled assuming data from existing commercial plants. The paper analyzes the whole conversion process from wet biomass to heat and power production, reporting energy balances and costs analysis. The investment profitability is assessed in light of the Italian regulations, which include feed-in-tariffs for biomass based electricity generation. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Effective Loss Minimization and Allocation of Unbalanced Distribution Network
Energies 2017, 10(12), 1931; doi:10.3390/en10121931
Received: 4 September 2017 / Revised: 26 October 2017 / Accepted: 17 November 2017 / Published: 23 November 2017
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Abstract
An efficient distribution network must be able to supply power with good voltage profile. The main objective of the proposed work is to allocate losses of the unbalanced distribution network by the firefly algorithm in regulated and deregulated environments before and after loss
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An efficient distribution network must be able to supply power with good voltage profile. The main objective of the proposed work is to allocate losses of the unbalanced distribution network by the firefly algorithm in regulated and deregulated environments before and after loss minimization. Reconfiguration is one of the methods for loss reduction of unbalanced distribution network. Further, optimal placement of distributed generation and capacitor in the reconfigured unbalanced distribution network can further reduce the loss. The results of reconfigured unbalanced distribution network in regulated environment have already been reported. In this paper reconfiguration of an unbalanced distribution network in a deregulated environment is also carried out using an established Fuzzy Firefly algorithm. Loss sensitivity factor of unbalanced distribution networks is used to get the appropriate location of distributed generation and capacitor to be placed in the unbalanced distribution network. Their ratings have been found out by using bacteria foraging optimization algorithm (BFOA). The suggested loss allocation method using Firefly algorithm is implemented at first on 13 node unbalanced distribution network to check the performance of the proposed loss allocation method when compared to other available method. Finally the proposed method has been implemented on 25 node unbalanced distribution network. Both of the implementations are carried out under MATLAB environment. Full article
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Open AccessArticle Optimization of the Heating Element in a Gas-Gas Heater Using an Integrated Analysis Model
Energies 2017, 10(12), 1932; doi:10.3390/en10121932
Received: 15 October 2017 / Revised: 10 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
Gas-gas heaters (GGHs) are used to reheat gases through desulfurization in coal-fired power plants to reduce low-temperature corrosion and white smoke. Wrinkled heating elements are installed inside the GGH to perform effective heat exchange. An optimization study of the heating element shape was
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Gas-gas heaters (GGHs) are used to reheat gases through desulfurization in coal-fired power plants to reduce low-temperature corrosion and white smoke. Wrinkled heating elements are installed inside the GGH to perform effective heat exchange. An optimization study of the heating element shape was conducted to reduce the differential pressure effectively and improve performance. An integrated analysis model was applied. Based on actual operational data, a computational fluid dynamic analysis was conducted on the L-type heating element and GGH system. The experiments applied the optimal latin hypercube sampling method, and numerical analysis was performed for each sample. Based on the response surface, the result of the sample was optimized through the pointer algorithm. For the integrated analysis model, validation was performed by comparison with the actual operational data, and the thermal-fluid characteristics of the heating element and GGH system were analyzed to set three parameters: plate angle, undulated angle, and pitch 1. From the optimization result, increases in the undulated angle and pitch 1 reduce the pressure drop by widening the heating element cross section. By increasing the plate angle, the heat transfer area is secured and the reduced heat transfer coefficient is compensated, improving the GGH performance. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Design and Performance Analysis of a Coal Bed Gas Drainage Machine Based on Incomplete Non-Circular Gears
Energies 2017, 10(12), 1933; doi:10.3390/en10121933
Received: 16 October 2017 / Revised: 11 November 2017 / Accepted: 17 November 2017 / Published: 23 November 2017
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Abstract
In order to solve the problem of reciprocating motion in no beam supported mining machines, putting energy saving as a starting point in Coal Bed Methane (CBM) exploitation, this paper designs a completely non-circular gear automatic reversing vertical drainage machine based on the
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In order to solve the problem of reciprocating motion in no beam supported mining machines, putting energy saving as a starting point in Coal Bed Methane (CBM) exploitation, this paper designs a completely non-circular gear automatic reversing vertical drainage machine based on the theory of non-circular gear transmission. In the field of CBM exploitation, the use of non-circular gears is an attempt at an innovation. First of all, according to the working conditions of the pump and use requirements, a scheme is established whereby the one-way rotary motion of the motor is changed into reciprocating motion so that it could drive the oil pumping rod to achieve the upper and lower mining. Secondly, this paper has designed a new type non-circular gear reversing box as the core component to replace the traditional four beam linkage mechanism and also provides elaborate calculations. Finally, the movement simulation of the non-circular gear reversing gear system is completed. Comparing the motion simulation results with the theoretical ones, the correctness of our theoretical analysis can be verified. Compared with the traditional devices, the new coal seam gas drainage machine model design has nearly 11% higher efficiency, which has obvious energy saving effects and reduces the cost of mining coal seam gas. Full article
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Open AccessFeature PaperArticle Principal Mismatch Patterns Across a Simplified Highly Renewable European Electricity Network
Energies 2017, 10(12), 1934; doi:10.3390/en10121934
Received: 19 September 2017 / Revised: 17 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
Due to its spatio-temporal variability, the mismatch between the weather and demand patterns challenges the design of highly renewable energy systems. A principal component analysis is applied to a simplified networked European electricity system with a high share of wind and solar power
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Due to its spatio-temporal variability, the mismatch between the weather and demand patterns challenges the design of highly renewable energy systems. A principal component analysis is applied to a simplified networked European electricity system with a high share of wind and solar power generation. It reveals a small number of important mismatch patterns, which explain most of the system’s required backup and transmission infrastructure. Whereas the first principal component is already able to reproduce most of the temporal mismatch variability for a solar dominated system, a few more principal components are needed for a wind dominated system. Due to its monopole structure the first principal component causes most of the system’s backup infrastructure. The next few principal components have a dipole structure and dominate the transmission infrastructure of the renewable electricity network. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Prospects for Increased Energy Recovery from Horse Manure—A Case Study of Management Practices, Environmental Impact and Costs
Energies 2017, 10(12), 1935; doi:10.3390/en10121935
Received: 29 September 2017 / Revised: 3 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
A transition to renewable energy sources and a circular economy has increased interest in renewable resources not usually considered as energy sources or plant nutrient resources. Horse manure exemplifies this, as it is sometimes recycled but not often used for energy purposes. The
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A transition to renewable energy sources and a circular economy has increased interest in renewable resources not usually considered as energy sources or plant nutrient resources. Horse manure exemplifies this, as it is sometimes recycled but not often used for energy purposes. The purpose of this study was to explore horse manure management in a Swedish municipality and prospects for energy recovery. The case study includes a survey of horse manure practices, environmental assessment of horse manure treatment in a biogas plant, including associated transport, compared to on-site unmanaged composting, and finally a simplified economic analysis. It was found that horse manure management was characterized by indoor collection of manure most of the year and storage on concrete slabs or in containers, followed by direct application on arable land. Softwood was predominantly used as bedding, and bedding accounted for a relatively small proportion (13%) of the total mix. Anaerobic digestion was indicated to reduce potential environmental impact in comparison to unmanaged composting, mainly due to biogas substituting use of fossil fuels. The relative environmental impact from transport of manure from horse facilities to anaerobic digestion plant was small. Results also indicate a relatively high cost for horse keepers to change from composting on site to anaerobic digestion in a centralized plant. Full article
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Open AccessArticle Search Improvement Process-Chaotic Optimization-Particle Swarm Optimization-Elite Retention Strategy and Improved Combined Cooling-Heating-Power Strategy Based Two-Time Scale Multi-Objective Optimization Model for Stand-Alone Microgrid Operation
Energies 2017, 10(12), 1936; doi:10.3390/en10121936
Received: 18 October 2017 / Revised: 8 November 2017 / Accepted: 10 November 2017 / Published: 23 November 2017
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Abstract
The optimal dispatching model for a stand-alone microgrid (MG) is of great importance to its operation reliability and economy. This paper aims at addressing the difficulties in improving the operational economy and maintaining the power balance under uncertain load demand and renewable generation,
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The optimal dispatching model for a stand-alone microgrid (MG) is of great importance to its operation reliability and economy. This paper aims at addressing the difficulties in improving the operational economy and maintaining the power balance under uncertain load demand and renewable generation, which could be even worse in such abnormal conditions as storms or abnormally low or high temperatures. A new two-time scale multi-objective optimization model, including day-ahead cursory scheduling and real-time scheduling for finer adjustments, is proposed to optimize the operational cost, load shedding compensation and environmental benefit of stand-alone MG through controllable load (CL) and multi-distributed generations (DGs). The main novelty of the proposed model is that the synergetic response of CL and energy storage system (ESS) in real-time scheduling offset the operation uncertainty quickly. And the improved dispatch strategy for combined cooling-heating-power (CCHP) enhanced the system economy while the comfort is guaranteed. An improved algorithm, Search Improvement Process-Chaotic Optimization-Particle Swarm Optimization-Elite Retention Strategy (SIP-CO-PSO-ERS) algorithm with strong searching capability and fast convergence speed, was presented to deal with the problem brought by the increased errors between actual renewable generation and load and prior predictions. Four typical scenarios are designed according to the combinations of day types (work day or weekend) and weather categories (sunny or rainy) to verify the performance of the presented dispatch strategy. The simulation results show that the proposed two-time scale model and SIP-CO-PSO-ERS algorithm exhibit better performance in adaptability, convergence speed and search ability than conventional methods for the stand-alone MG’s operation. Full article
(This article belongs to the Special Issue Distribution System Operation and Control)
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Open AccessArticle A Cascade Disaster Caused by Geological and Coupled Hydro-Mechanical Factors—Water Inrush Mechanism from Karst Collapse Column under Confining Pressure
Energies 2017, 10(12), 1938; doi:10.3390/en10121938
Received: 23 September 2017 / Revised: 7 November 2017 / Accepted: 17 November 2017 / Published: 23 November 2017
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Abstract
The water inrush from karst collapse column (KCC) is a cascading, vicious cycle disaster caused by geological and mining activities, that can cause serious casualties and property losses. The key to preventing this risk is to study the mechanism of water inrush under
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The water inrush from karst collapse column (KCC) is a cascading, vicious cycle disaster caused by geological and mining activities, that can cause serious casualties and property losses. The key to preventing this risk is to study the mechanism of water inrush under confining pressure. Aiming at the investigationg the characteristics of the KCC named X1 in Chensilou mine, a series of methods, including connectivity experiments, water pressure monitoring tests in two side-walls, and numerical simulations based on plastic damage-seepage (PD-S) theory have been developed. The methods are used to test the security of the 2519 mining area, the damage thickness, pore water pressure, and seepage vector in the X1. The results indicate that the X1 has a certain water blocking capacity. In addition, with the decrease of confining pressure and increase of shear stress, deviatoric stress could cause the increase of permeability, the reduction of strength, and the reduction of pore water pressure in KCC. Therefore the increased effective stress in the rock will force the rock to become more fractured. Conversely, the broken rock could cause the change of stress, and further initiate new plastic strains, damage and pore water pressure until a new equilibrium is reached. This cascading water inrush mechanism will contribute to the exploitation of deep coal resources in complex geological and hydrogeological conditions. Full article
(This article belongs to the Special Issue Mathematical and Computational Modeling in Geothermal Engineering)
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Open AccessArticle Sensorless Control of Late-Stage Offshore DFIG-WT with FSTP Converters by Using EKF to Ride through Hybrid Faults
Energies 2017, 10(12), 1939; doi:10.3390/en10121939
Received: 23 October 2017 / Revised: 19 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
A hybrid fault scenario in a late-stage offshore doubly-fed induction generator (DFIG)-based wind turbine (DFIG-WT) with converter open-circuit fault and position sensor failure is investigated in this paper. An extended Kalman filter (EKF)-based sensorless control strategy is utilized to eliminate the encoder. Based
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A hybrid fault scenario in a late-stage offshore doubly-fed induction generator (DFIG)-based wind turbine (DFIG-WT) with converter open-circuit fault and position sensor failure is investigated in this paper. An extended Kalman filter (EKF)-based sensorless control strategy is utilized to eliminate the encoder. Based on the detailed analysis of the seventh-order dynamic state space model of DFIG, along with the input voltage signals and measured current signals, the EKF algorithm for DFIG is designed to estimate the rotor speed and position. In addition, the bridge arm open circuit in the back-to-back (BTB) power converter of DFIG is taken as a commonly-encountered fault due to the fragility of semiconductor switches. Four-switch three-phase (FSTP) topology-based fault-tolerant converters are employed for post-fault operation by considering the minimization of switching losses and reducing the circuit complexity. Moreover, a simplified space vector pulse width modulation (SVPWM) technique is proposed to reduce the computational burden, and a voltage balancing scheme is put forward to increase the DC-bus voltage utilization rate. Simulation studies are carried out in MATLAB/Simulink2017a (MathWorks, Natick, MA, USA) to demonstrate the validity of the proposed hybrid fault-tolerant strategy for DFIG-WT, with the wind speed fluctuation, measurement noises and grid voltage sag taken into consideration. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle On Hybrid Energy Utilization in Wireless Sensor Networks
Energies 2017, 10(12), 1940; doi:10.3390/en10121940
Received: 8 September 2017 / Revised: 11 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
In a wireless sensor network (WSN), many applications have limited energy resources for data transmission. In order to accomplish a better green communication for WSN, a hybrid energy scheme can supply a more reliable energy source. In this article, hybrid energy utilization—which consists
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In a wireless sensor network (WSN), many applications have limited energy resources for data transmission. In order to accomplish a better green communication for WSN, a hybrid energy scheme can supply a more reliable energy source. In this article, hybrid energy utilization—which consists of constant energy source and solar harvested energy—is considered for WSN. To minimize constant energy usage from the hybrid source, a Markov decision process (MDP) is designed to find the optimal transmission policy. With a finite packet buffer and a finite battery size, an MDP model is presented to define the states, actions, state transition probabilities, and the cost function including the cost values for all actions. A weighted sum of constant energy source consumption and a packet dropping probability (PDP) are adopted as the cost value, enabling us to find the optimal solution for balancing the minimization of the constant energy source utilization and the PDP using a value iteration algorithm. As shown in the simulation results, the performance of optimal solution using MDP achieves a significant improvement compared to solution without its use. Full article
(This article belongs to the Special Issue Industrial Energy Efficiency 2018)
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Open AccessArticle Resilient Prosumer Scenario in a Changing Regulatory Environment—The UniRCon Solution
Energies 2017, 10(12), 1941; doi:10.3390/en10121941
Received: 15 August 2017 / Revised: 30 October 2017 / Accepted: 10 November 2017 / Published: 23 November 2017
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Abstract
Technological developments are pushing for new solutions based upon massive integration of renewable electricity generation in networks already facing many challenges. This paper presents a novel approach to managing the energy transfer towards prosumers making use of smart management of local energy storage.
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Technological developments are pushing for new solutions based upon massive integration of renewable electricity generation in networks already facing many challenges. This paper presents a novel approach to managing the energy transfer towards prosumers making use of smart management of local energy storage. The proposed design (including storage dimensioning) is based on several operating scenarios in which the prosumer might operate as: (i) a “load only” entity (from a grid perspective), thus exhibiting investment resiliency against regulatory changes and high energy efficiency; or (ii) a prosumer, in case regulatory opportunistic profit might be available. This can be realized within a newly proposed Uni-directional Resilient Consumer (UniRCon) architecture. The major aim of the proposed architecture is to achieve optimal self-consumption while avoiding curtailment even in a changing regulatory environment like, for example, the total lack of incentives for generation based on renewable energy sources (RES). One of the major advantages of the proposed architecture consists in the adaptability to changes in the regulatory and market environment. The term resilience is used with multiple meanings: (a) the prosumer’s financial resilience against regulatory changes when investment calculations assume no-grid injections; (b) the prosumer’s technical resilience, with electrical design based on standalone operation; (c) the resilience of clusters of interconnected end-user installations with enabled community-level electricity exchange, independent of the existing main grid supply; (d) the contribution to grid resilience, by enabling AC microgrid (MG) operation in island mode when large portions of the grid are formed by clusters of UniRCon prosumers (the ease of islanding segmentation of the local grid in case of emergencies). For proof of concept, three use-cases are detailed: (i) photovoltaic (PV) installations connected behind the meter; (ii) PV and storage available and controllable behind the meter; and (iii) the UniRCon architecture. The three use-cases are then compared and assessed for four near-future timelines as starting points for the investment. Numerical simulations show the attractiveness of the UniRCon solution in what concerns both system operation costs and supply resilience. Savings are expressed as opportunity savings arising from difference in tariffs while charging and discharging the storage unit and due to the avoidance of curtailment, as well as special taxes for the connection of PV (depending on regulatory environment). An extension of the UniRCon concept is presented also at community scale, with neighbourhood energy exchange inside a resilient cluster. Full article
(This article belongs to the Special Issue Resilience of Energy Systems 2017)
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Open AccessArticle Energy Poverty in China: A Dynamic Analysis Based on a Hybrid Panel Data Decision Model
Energies 2017, 10(12), 1942; doi:10.3390/en10121942
Received: 6 October 2017 / Revised: 14 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
Renewable energy can help to tackle energy poverty issues of the availability of modern energy services and the sustainability of energy supply. Based on the concept of the Energy Development Index, published by International Energy Agency, this paper builds the clean energy development
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Renewable energy can help to tackle energy poverty issues of the availability of modern energy services and the sustainability of energy supply. Based on the concept of the Energy Development Index, published by International Energy Agency, this paper builds the clean energy development index and applies the Grey incidence decision method to analyze regional energy poverty issues in China. A model using panel data investigates the influencing factors that are governing energy poverty alleviation and the relationship between energy poverty and social development. The improved index system not only considers the access to modern energy services, but also addresses the cleanliness of energy supply and the transition to clean energy consumption for cooking. The results indicate that due to insufficient clean energy development, China’s Northeast and West regions have experienced increasing energy poverty problems, while energy poverty in the Southwest region has improved considerably because of its renewable energy development. Urbanization, affordability, and renewable energy development can increase access to modern energy services, contributing to energy poverty alleviation. However, the role of rural household consumption levels in energy poverty alleviation should be considered in rural energy policy. Full article
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Open AccessArticle Charge and Discharge Analyses of a PCM Storage System Integrated in a High-Temperature Solar Receiver
Energies 2017, 10(12), 1943; doi:10.3390/en10121943
Received: 31 October 2017 / Revised: 15 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
Solar Dish Micro Gas Turbine (MGT) systems have the potential to become interesting small-scale power plants in off-grid or mini-grid contexts for electricity or poly-generation production. The main challenging component of such systems is the solar receiver which should operate at high temperatures
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Solar Dish Micro Gas Turbine (MGT) systems have the potential to become interesting small-scale power plants in off-grid or mini-grid contexts for electricity or poly-generation production. The main challenging component of such systems is the solar receiver which should operate at high temperatures with concentrated solar radiations, which strongly vary with time. This paper deals with the design and the analysis of a novel solar receiver integrated with a short-term storage system based on Phase Change Materials to prevent sudden variations in the maximum temperature of the MGT working fluid. Particularly, the charge and discharge behavior of the storage system was analyzed by means of Computational Fluid Dynamic methods to evaluate the potentiality of the concept and the component capabilities. Achieved results were highly satisfactory: the novel solar receiver has a good thermal inertia and can prevent relevant fluctuations in the working fluid temperature for 20–30 min. Full article
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Open AccessArticle Normal Behaviour Models for Wind Turbine Vibrations: Comparison of Neural Networks and a Stochastic Approach
Energies 2017, 10(12), 1944; doi:10.3390/en10121944
Received: 29 October 2017 / Revised: 16 November 2017 / Accepted: 17 November 2017 / Published: 23 November 2017
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Abstract
To monitor wind turbine vibrations, normal behaviour models are built to predict tower top accelerations and drive-train vibrations. Signal deviations from model prediction are labelled as anomalies and are further investigated. In this paper we assess a stochastic approach to reconstruct the 1
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To monitor wind turbine vibrations, normal behaviour models are built to predict tower top accelerations and drive-train vibrations. Signal deviations from model prediction are labelled as anomalies and are further investigated. In this paper we assess a stochastic approach to reconstruct the 1 Hz tower top acceleration signal, which was measured in a wind turbine located at the wind farm Alpha Ventus in the German North Sea. We compare the resulting data reconstruction with that of a model based on a neural network, which has been previously reported as a data-mining algorithm suitable for reconstructing this signal. Our results present evidence that the stochastic approach outperforms the neural network in the high frequency domain (1 Hz). Although neural network retrieves accurate step-forward predictions, with low mean square errors, the stochastic approach predictions better preserve the statistics and the frequency components of the original signal, retaining high accuracy levels. The implementation of our stochastic approach is available as open source code and can easily be adapted for other situations involving stochastic data reconstruction. Based on our findings we argue that such an approach could be implemented in signal reconstruction for monitoring purposes or for abnormal behaviour detection. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Numerical Study on the Acoustic Characteristics of an Axial Fan under Rotating Stall Condition
Energies 2017, 10(12), 1945; doi:10.3390/en10121945
Received: 23 October 2017 / Revised: 17 November 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
Axial fan is an important piece of equipment in the thermal power plant that provides enough air for combustion of coal. This paper focuses on the aerodynamic noise characteristics of an axial fan in the development from stall inception to stall cells. The
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Axial fan is an important piece of equipment in the thermal power plant that provides enough air for combustion of coal. This paper focuses on the aerodynamic noise characteristics of an axial fan in the development from stall inception to stall cells. The aerodynamic noise characteristic of monitoring region in time and frequency domains was simulated employing the large-eddy simulation (LES), with the addition of throttle setting and the Ffowcs Williams-Hawkings (FW-H) noise model. The numerical results show that, under the design condition, the acoustic pressure presents regular periodicity along with the time. The noise energy is concentrated with high energy of the fundamental frequency and high order harmonics. During the stall inception stage, the acoustic pressure amplitude starts fluctuating and discrete frequencies are increased significantly in the low frequency; among them, there are three obvious discrete frequencies: 27.66 Hz, 46.10 Hz and 64.55 Hz. On the rotating stall condition, the fluctuation of the acoustic pressure level and amplitude are more serious than that mentioned above. During the whole evolution process, the acoustic pressure peak is difficult to keep stable all the time, and a sudden increase of the peak value at the 34.5th revolution corresponds to the relative velocity’s first sudden increase at the time when the valve coefficient is 0.780. Full article
(This article belongs to the Special Issue Engineering Fluid Dynamics 2018)
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Open AccessArticle Impacts of Reclassified Brown Coal Reserves on the Energy System and Deep Decarbonisation Target in the Czech Republic
Energies 2017, 10(12), 1947; doi:10.3390/en10121947
Received: 4 September 2017 / Revised: 15 October 2017 / Accepted: 20 November 2017 / Published: 23 November 2017
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Abstract
In 2015, a 24-year-long prohibition of coal mining within some territories in the North Bohemia coal basin was lifted and as a consequence mining a part of the brown coal reserves might well be resumed. This paper analyses the impacts of maintaining the
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In 2015, a 24-year-long prohibition of coal mining within some territories in the North Bohemia coal basin was lifted and as a consequence mining a part of the brown coal reserves might well be resumed. This paper analyses the impacts of maintaining the ban versus three options for a less environmentally stringent policy on the Czech energy system; fuel- and technology-mix, the costs of generating energy, emissions and related external costs up to 2050. We find that overall the effect of lifting the ban, on coal usage, air pollutant emissions and hence externalities is rather small, up to 1–2% compared to the level of keeping the ban. The small difference in the impacts remains even if changes in the prices of fossil fuels and European Emission Allowances or different development in nuclear power usage are assumed. In fact, changing these assumptions will result in more pronounced differences in the impacts than the four policy options might deliver. Maintaining the ban would not achieve the European Energy Roadmap 2050 target and the newly adopted policy and the other two counter-environmental proposals would miss the 80% reduction target to an even greater degree. The environmental and external health costs attributable to emissions of local air pollutants stemming from power generation are in a range of €26–32 billion over the whole period and decline from about 0.5% of gross domestic product in 2015 to 0.1% in 2050. Full article
(This article belongs to the Special Issue Energy Market Transitions)
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Open AccessArticle Internal Combustion Engine Model for Combined Heat and Power (CHP) Systems Design
Energies 2017, 10(12), 1948; doi:10.3390/en10121948
Received: 19 August 2017 / Revised: 20 November 2017 / Accepted: 21 November 2017 / Published: 25 November 2017
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Abstract
A model based, energy focused, quasi-stationary waste heat driven, internal combustion engine (ICE) centred design methodology for cogeneration (heat and electricity) systems is presented. The developed parametric model could be used for system sizing, performance evaluation, and optimization. This paper presents a systematic
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A model based, energy focused, quasi-stationary waste heat driven, internal combustion engine (ICE) centred design methodology for cogeneration (heat and electricity) systems is presented. The developed parametric model could be used for system sizing, performance evaluation, and optimization. This paper presents a systematic approach to model the behaviour of the CHP system using heat recovery prediction methods. The modular, physics based modelling environment shows the power flow between the system components, with a special emphasis on the ICE subsystems, parameter identification, and model validation. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Shale Gas Content Calculation of the Triassic Yanchang Formation in the Southeastern Ordos Basin, China
Energies 2017, 10(12), 1949; doi:10.3390/en10121949
Received: 28 September 2017 / Revised: 15 November 2017 / Accepted: 20 November 2017 / Published: 24 November 2017
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Abstract
Shale gas content is the key parameter for shale gas potential evaluation and favorable area prediction. Therefore, it is very important to determine shale gas content accurately. Generally, we use the US Bureau of Mines (USBM) method for coal reservoirs to calculate the
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Shale gas content is the key parameter for shale gas potential evaluation and favorable area prediction. Therefore, it is very important to determine shale gas content accurately. Generally, we use the US Bureau of Mines (USBM) method for coal reservoirs to calculate the gas content of shale reservoirs. However, shale reservoirs are different from coal reservoirs in depth, pressure, core collection, etc. This method would inevitably cause problems. In order to make the USBM method more suitable for shale reservoirs, an improved USBM method is put forward on the basis of systematic analysis of core pressure history and temperature history during shale gas degassing. The improved USBM method modifies the calculation method of the gas loss time, and determines the temperature balance time of water heating. In addition, we give the calculation method of adsorption gas content and free gas content, especially the new method of calculating the oil dissolved gas content and water dissolved gas content that are easily neglected. We used the direct method (USBM and the improved USBM) and the indirect method (including the calculation of adsorption gas, free gas and the dissolved gas method) to calculate the shale gas content of 16 shale samples of the Triassic Yanchang Formation in the Southeastern Ordos Basin, China. The results of the improved USBM method show that the total shale gas content is high, with an average of 3.97 m3/t, and the lost shale gas content is the largest proportion with an average of 62%. The total shale gas content calculated by the improved USBM method is greater than that of the USBM method. The results of the indirect method show that the total shale gas content is large, with an average of 4.11 m3/t, and the adsorption shale gas content is the largest proportion with an average of 71%. The oil dissolved shale gas content which should be paid attention to accounts for about 7.8%. The discrepancy between the direct method and indirect method is reduced by using the improved USBM method, and the improved USBM method could be more practical and accurate than the USBM method. Full article
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Open AccessArticle Characterization of the Inlet Port Flow under Steady-State Conditions Using PIV and POD
Energies 2017, 10(12), 1950; doi:10.3390/en10121950
Received: 18 October 2017 / Revised: 8 November 2017 / Accepted: 9 November 2017 / Published: 24 November 2017
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Abstract
The current study demonstrates an experimental investigation of the tumble flow structures using Particle Image Velocimetry (PIV) under steady-state conditions considering the central vertical tumble plane. The experiments were carried out on a four-valve, pent-roof Gasoline Direct Injection (GDI) engine head at different
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The current study demonstrates an experimental investigation of the tumble flow structures using Particle Image Velocimetry (PIV) under steady-state conditions considering the central vertical tumble plane. The experiments were carried out on a four-valve, pent-roof Gasoline Direct Injection (GDI) engine head at different valve lifts and with a pressure difference of 150 mmH2O across the intake valves. Furthermore, the Proper Orthogonal Decomposition (POD) analytical technique was applied to PIV-measured velocity vector maps to characterize the flow structures at various valve lifts, and hence the different rig tumble values. The results show that at low valve lifts (1 to 5 mm), 48.9 to 46.6% of the flow energy is concentrated in the large (mode 1) eddies with only 8.4 to 11.46% in mode 2 and 7.2 to 7.5 in mode 3. At high valve lifts, it can be clearly seen that some of the energy in the large eddies of mode 1 is transferred to the smaller flow structures of modes 2 and 3. This can be clearly seen at valve lift 10 mm where the values of the flow energy were 40.6%, 17.3%, and 8.0% for modes 1, 2, and 3, respectively. Full article
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Open AccessArticle Dynamic Equivalent Modeling of a Grid-Tied Microgrid Based on Characteristic Model and Measurement Data
Energies 2017, 10(12), 1951; doi:10.3390/en10121951
Received: 17 October 2017 / Revised: 11 November 2017 / Accepted: 20 November 2017 / Published: 24 November 2017
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Abstract
Microgrids can significantly improve the utilization of distributed generation (DG) and the reliability of the power supply. However, in the grid-tied operational mode, the interaction between the microgrid and the distribution network cannot be ignored. The paper proposes an equivalent modeling method for
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Microgrids can significantly improve the utilization of distributed generation (DG) and the reliability of the power supply. However, in the grid-tied operational mode, the interaction between the microgrid and the distribution network cannot be ignored. The paper proposes an equivalent modeling method for the microgrid under grid-tied mode based on a characteristic model. It can simplify the microgrid model in the numerical simulation of the distribution network. The proposed equivalent model can present the dynamic response of a microgrid but not miss any of its primary characteristics. The characteristic model is represented by a low-order time-varying differential equation with the same characteristics of the original microgrid system. During the modeling process, the voltage and the power exchanged between the microgrid and distribution network are collected as the training data for the identification of model parameters. A recursive damped least squares algorithm (RDLS) is used for the parameter identification. A microgrid system containing different DGs is built to test the proposed modeling method in DIgSILENT, and the results show that the proposed dynamic equivalent modeling method is effective and the characteristic model can present the dynamic behaviors of the detailed model of a microgrid. Full article
(This article belongs to the Special Issue Sustainable and Renewable Energy Systems)
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Open AccessArticle Are Developed Regions in China Achieving Their CO2 Emissions Reduction Targets on Their Own?—Case of Beijing
Energies 2017, 10(12), 1952; doi:10.3390/en10121952
Received: 26 August 2017 / Revised: 12 October 2017 / Accepted: 20 October 2017 / Published: 24 November 2017
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Abstract
The extensive and close economic linkages among different regions of China have effects not only on regional economic growth, but also on CO2 emissions and carbon leakage among regions. Taking Beijing as a study case, we constructed MRIO models for China’s 30
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The extensive and close economic linkages among different regions of China have effects not only on regional economic growth, but also on CO2 emissions and carbon leakage among regions. Taking Beijing as a study case, we constructed MRIO models for China’s 30 provinces and municipalities for 2002, 2007 and 2010, to measure the embodied CO2 emissions in the interregional trade of China on regional and industrial levels to explore their changes over time, and to analyze the driving forces of the final demand-induced interregional CO2 emissions through an SDA model. Results showed that Beijing was a surplus region for embodied carbon and the net input embodied CO2 emissions were in industries with high CO2 emission coefficients, while the net output embodied carbon was in industries with low carbon-emission coefficients. Beijing’s trade with non-Beijing areas led to an increase in the total CO2 emissions in China and a composite effect of Beijing and the efficiency effect of non-Beijing areas were the main effects behind the reduction of Beijing’s input embodied carbon. The results have yielded important implications for China’s CO2 emissions control: first, the embodied CO2 need be taken into consideration when formulating CO2 emissions control measures; second, CO2 emission reduction requirements should be reasonably distributed across the provinces to reduce carbon leakage in interprovincial trade; third, the consumption structure in the production chain needs to be moderately adjusted; and last but not least, financial and technical support for CO2 emissions control in the central and western provinces should be strengthened. Full article
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Open AccessArticle Energy-Efficient Subcarrier Pairing and Power Allocation for DF Relay Networks with an Eavesdropper
Energies 2017, 10(12), 1953; doi:10.3390/en10121953
Received: 13 October 2017 / Revised: 13 November 2017 / Accepted: 17 November 2017 / Published: 24 November 2017
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Abstract
Algorithms for joint subcarrier pairing and power allocation are investigated in order to maximize the worst-case energy efficiency (EE) in dual-hop decode-and-forward (DF) relay networks in the presence of an active eavesdropper. Accordingly, we study the impact of number of subcarriers on the
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Algorithms for joint subcarrier pairing and power allocation are investigated in order to maximize the worst-case energy efficiency (EE) in dual-hop decode-and-forward (DF) relay networks in the presence of an active eavesdropper. Accordingly, we study the impact of number of subcarriers on the trade-off in performance between the EE and the spectrum efficiency (SE). The formulated EE optimization problem is the ratio of the secure SE over the entire power consumption in the network, subject to the constraints of total transmit power and subcarrier pairing. A near-optimal iterative algorithm is proposed to perform the subcarrier pairing and power allocation for achieving the maximum EE in the networks. Furthermore, a suboptimal algorithm is proposed with two-step resource allocation. By considering the subcarrier channel quality of the source-to-relay and relay-to-destination links, the subcarrier pairing is first performed, followed by an energy-efficient iterative power allocation scheme to maximize the EE. Numerical results validate the effectiveness and correctness of the proposed algorithms. Full article
(This article belongs to the Special Issue Energy-Efficient Computing and Networking in the 5G Era)
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Open AccessArticle Force Measurements on a VAWT Blade in Parked Conditions
Energies 2017, 10(12), 1954; doi:10.3390/en10121954
Received: 24 October 2017 / Revised: 17 November 2017 / Accepted: 20 November 2017 / Published: 24 November 2017
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Abstract
The forces on a turbine at extreme wind conditions when the turbine is parked is one of the most important design cases for the survivability of a turbine. In this work, the forces on a blade and its support arms have been measured
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The forces on a turbine at extreme wind conditions when the turbine is parked is one of the most important design cases for the survivability of a turbine. In this work, the forces on a blade and its support arms have been measured on a 12 kW straight-bladed vertical axis wind turbine at an open site. Two cases are tested: one during electrical braking of the turbine, which allows it to rotate slowly, and one with the turbine mechanically fixed with the leading edge of the blade facing the main wind direction. The force variations with respect to wind direction are investigated, and it is seen that significant variations in forces depend on the wind direction. The measurements show that for the fixed case, when subjected to the same wind speed, the forces are lower when the blade faces the wind direction. The results also show that due to the lower forces at this particular wind direction, the average forces for the fixed blade are notably lower. Hence, it is possible to reduce the forces on a turbine blade, simply by taking the dominating wind direction into account when the turbine is parked. The measurements also show that a positive torque is generated from the blade for most wind directions, which causes the turbine to rotate in the electrically-braked case. These rotations will cause increased fatigue loads on the turbine blade. Full article
(This article belongs to the collection Wind Turbines)
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Open AccessArticle Perforated Thermal Mass Shading: An Approach to Winter Solar Shading and Energy, Shading and Daylighting Performance
Energies 2017, 10(12), 1955; doi:10.3390/en10121955
Received: 30 September 2017 / Revised: 10 November 2017 / Accepted: 21 November 2017 / Published: 24 November 2017
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Abstract
Direct solar irradiance may cause thermal discomfort, even in winter when the ambient temperature is low and especially for high-altitude locations with a high intensity of solar radiation. Thus winter solar shading might be required and, if used, must achieve a balance between
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Direct solar irradiance may cause thermal discomfort, even in winter when the ambient temperature is low and especially for high-altitude locations with a high intensity of solar radiation. Thus winter solar shading might be required and, if used, must achieve a balance between the prevention of the transmittance of solar irradiance, the utilization of passive solar heat and the supply of adequate natural daylighting. These considerations render conventional solutions of solar shading inapplicable in the winter. In this paper, a novel approach to perforated thermal mass shading for winter is reported and examined. The impacts of the perforated percentage and the opening positions of this shading device on energy, shading and daylighting performance were assessed for south- and west-facing orientations. A range of perforated percentages and vertical and horizontal positions were tested using simulations by Energyplus and Daysim. Our results indicate that the proposed perforated thermal mass shading is efficient for the integrated performance of shading, daylighting and energy savings in the south-facing orientation, while it achieves acceptable performance in shading and daylighting in the west-facing orientation for a high-altitude cold climate. Full article
(This article belongs to the Special Issue Solar Energy Application in Buildings)
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Open AccessArticle Research on Exergy Flow Composition and Exergy Loss Mechanisms for Waxy Crude Oil Pipeline Transport Processes
Energies 2017, 10(12), 1956; doi:10.3390/en10121956
Received: 19 October 2017 / Revised: 19 November 2017 / Accepted: 21 November 2017 / Published: 24 November 2017
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Abstract
The basic theory of exergy was used to derive the formulae of physical and chemical exergy in the process of pipeline transportation, combined with the effect of wax deposition on the thermodynamic parameters including specific heat, density, chemical potential and concentration gradient. On
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The basic theory of exergy was used to derive the formulae of physical and chemical exergy in the process of pipeline transportation, combined with the effect of wax deposition on the thermodynamic parameters including specific heat, density, chemical potential and concentration gradient. On the basis of this, the expression of various exergy losses were derived, and the exergy balance model was then built in the process. For the case study, a waxy crude oil pipeline in China was selected. The mechanism for how wax deposition affected the physical and chemical exergy loss was studied through analyzing the axial pipeline distribution of pressure, temperature, flow rate and thickness of insulation layer. Finally, under the design flow of 66 × 103 kg·h−1, the orthogonal experimental analysis method was used for comparing the degree of specific factors which could influence the total exergy efficiency. The highest exergy efficiency combination of working conditions was then determined. This research could provide a theoretical basis for guiding safe and economic operation in the actual pipeline transportation process. Full article
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Open AccessArticle Asynchronous Fault Location in Transmission Lines Considering Accurate Variation of the Ground-Mode Traveling Wave Velocity
Energies 2017, 10(12), 1957; doi:10.3390/en10121957
Received: 23 October 2017 / Revised: 17 November 2017 / Accepted: 20 November 2017 / Published: 24 November 2017
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Abstract
This paper proposes a grounding fault location method in transmission lines based on time difference of arrival (TDOA) of ground-mode and aerial-mode traveling waves (TWs). The frequency-dependent characteristics of transmission lines cause different frequencies to have different attenuations and phase lags of different
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This paper proposes a grounding fault location method in transmission lines based on time difference of arrival (TDOA) of ground-mode and aerial-mode traveling waves (TWs). The frequency-dependent characteristics of transmission lines cause different frequencies to have different attenuations and phase lags of different frequency components in traveling waves, which leads to the change of TWs velocities with different propagation distances. Due to these different propagation paths, the wave velocity variations of ground-mode should be considered as a main variable while the velocity of aerial-mode can be seen as a constant factor. A quadratic function that can illustrate the tendency of variation of ground-mode wave velocity is proposed by considering the relation between the wave velocity and fault distance. The least squares method is used to solve the quadratic function of different lines. Combining the quadratic formula and the incident TWs of each mode detected at both terminals of the line, a novel fault location method is proposed. First, according to the maximum and minimum ground-mode velocities, a fault scope can be acquired. Then, more accurate fault scopes and ground-mode velocities can be obtained by iteration computation. Finally, an accurate fault position is acquired when the fault scope is sufficiently small. PSCAD/EMTDC software is used to conduct fault simulations in order to verify the feasibility and accuracy of the method. Full article
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Open AccessArticle Study and Optimization of Design Parameters in Water Loop Heat Pump Systems for Office Buildings in the Iberian Peninsula
Energies 2017, 10(12), 1958; doi:10.3390/en10121958
Received: 24 October 2017 / Revised: 8 November 2017 / Accepted: 20 November 2017 / Published: 24 November 2017
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Abstract
Water loop heat pump (WLHP) air conditioning systems use heat pumps connected to a common water circuit to fulfill the energy demands of different thermal zones in a building. In this study, the energy consumption was analyzed for the air conditioning of an
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Water loop heat pump (WLHP) air conditioning systems use heat pumps connected to a common water circuit to fulfill the energy demands of different thermal zones in a building. In this study, the energy consumption was analyzed for the air conditioning of an office building in the typical climate of four important cities of the Iberian Peninsula. The energy consumption of one water loop heat pump system was compared with a conventional water system. Two design parameters, the range in the control temperatures and the water loop thermal storage size, were tested. Energy redistribution is an important advantage of the WLHP system, but significant savings came from high efficiency parameters in the heat pumps and minor air flow rates in the cooling tower. The low thermal level in the water loop makes this technology appropriate to combine with renewable sources. Using natural gas as the thermal energy source, a mean decrease in CO2 emissions of 8.1% was reached. Simulations showed that the installation of big thermal storage tanks generated small energy savings. Besides, the total annual consumption in buildings with high internal loads can be reduced by keeping the water loop as cool as possible. Full article
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Open AccessArticle Sliding Mode Controller and Lyapunov Redesign Controller to Improve Microgrid Stability: A Comparative Analysis with CPL Power Variation
Energies 2017, 10(12), 1959; doi:10.3390/en10121959
Received: 11 September 2017 / Revised: 13 October 2017 / Accepted: 25 October 2017 / Published: 24 November 2017
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Abstract
To mitigate the microgrid instability despite the presence of dense Constant Power Load (CPL) loads in the system, a number of compensation techniques have already been gone through extensive research, proposed, and implemented around the world. In this paper, a storage based load
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To mitigate the microgrid instability despite the presence of dense Constant Power Load (CPL) loads in the system, a number of compensation techniques have already been gone through extensive research, proposed, and implemented around the world. In this paper, a storage based load side compensation technique is used to enhance stability of microgrids. Besides adopting this technique here, Sliding Mode Controller (SMC) and Lyapunov Redesign Controller (LRC), two of the most prominent nonlinear control techniques, are individually implemented to control microgrid system stability with desired robustness. CPL power is then varied to compare robustness of these two control techniques. This investigation revealed the better performance of the LRC system compared to SMC to retain stability in microgrid with dense CPL load. All the necessary results are simulated in Matlab/Simulink platform for authentic verification. Reasons behind inferior SMC performance and ways to mitigate that are also discussed. Finally, the effectiveness of SMC and LRC systems to attain stability in real microgrids is verified by numerical analysis. Full article
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Open AccessArticle Coupled Thermo-Hydro-Mechanical-Chemical Modeling of Water Leak-Off Process during Hydraulic Fracturing in Shale Gas Reservoirs
Energies 2017, 10(12), 1960; doi:10.3390/en10121960
Received: 9 September 2017 / Revised: 20 November 2017 / Accepted: 21 November 2017 / Published: 24 November 2017
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Abstract
The water leak-off during hydraulic fracturing in shale gas reservoirs is a complicated transport behavior involving thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes. Although many leak-off models have been published, none of the models fully coupled the transient fluid flow
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The water leak-off during hydraulic fracturing in shale gas reservoirs is a complicated transport behavior involving thermal (T), hydrodynamic (H), mechanical (M) and chemical (C) processes. Although many leak-off models have been published, none of the models fully coupled the transient fluid flow modeling with heat transfer, chemical-potential equilibrium and natural-fracture dilation phenomena. In this paper, a coupled thermo-hydro-mechanical-chemical (THMC) model based on non-equilibrium thermodynamics, hydrodynamics, thermo-poroelastic rock mechanics, and non-isothermal chemical-potential equations is presented to simulate the water leak-off process in shale gas reservoirs. The THMC model takes into account a triple-porosity medium, which includes hydraulic fractures, natural fractures and shale matrix. The leak-off simulation with the THMC model involves all the important processes in this triple-porosity medium, including: (1) water transport driven by hydraulic, capillary, chemical and thermal osmotic convections; (2) gas transport induced by both hydraulic pressure driven convection and adsorption; (3) heat transport driven by thermal convection and conduction; and (4) natural-fracture dilation considered as a thermo-poroelastic rock deformation. The fluid and heat transport, coupled with rock deformation, are described by a set of partial differential equations resulting from the conservation of mass, momentum, and energy. The semi-implicit finite-difference algorithm is proposed to solve these equations. The evolution of pressure, temperature, saturation and salinity profiles of hydraulic fractures, natural fractures and matrix is calculated, revealing the multi-field coupled water leak-off process in shale gas reservoirs. The influences of hydraulic pressure, natural-fracture dilation, chemical osmosis and thermal osmosis on water leak-off are investigated. Results from this study are expected to provide a better understanding of the predominant leak-off mechanisms for slickwater fracturing-fluids in hydraulically fractured shale gas reservoirs. Full article
(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries 2018)
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Open AccessArticle A Novel Acoustic Liquid Level Determination Method for Coal Seam Gas Wells Based on Autocorrelation Analysis
Energies 2017, 10(12), 1961; doi:10.3390/en10121961
Received: 28 September 2017 / Revised: 14 November 2017 / Accepted: 21 November 2017 / Published: 24 November 2017
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Abstract
In coal seam gas (CSG) wells, water is periodically removed from the wellbore in order to keep the bottom-hole flowing pressure at low levels, facilitating the desorption of methane gas from the coal bed. In order to calculate gas flow rate and further
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In coal seam gas (CSG) wells, water is periodically removed from the wellbore in order to keep the bottom-hole flowing pressure at low levels, facilitating the desorption of methane gas from the coal bed. In order to calculate gas flow rate and further optimize well performance, it is necessary to accurately monitor the liquid level in real-time. This paper presents a novel method based on autocorrelation function (ACF) analysis for determining the liquid level in CSG wells under intense noise conditions. The method involves the calculation of the acoustic travel time in the annulus and processing the autocorrelation signal in order to extract the weak echo under high background noise. In contrast to previous works, the non-linear dependence of the acoustic velocity on temperature and pressure is taken into account. To locate the liquid level of a coal seam gas well the travel time is computed iteratively with the non-linear velocity model. Afterwards, the proposed method is validated using experimental laboratory investigations that have been developed for liquid level detection under two scenarios, representing the combination of low pressure, weak signal, and intense noise generated by gas flowing and leakage. By adopting an evaluation indicator called Crest Factor, the results have shown the superiority of the ACF-based method compared to Fourier filtering (FFT). In the two scenarios, the maximal measurement error from the proposed method was 0.34% and 0.50%, respectively. The latent periodic characteristic of the reflected signal can be extracted by the ACF-based method even when the noise is larger than 1.42 Pa, which is impossible for FFT-based de-noising. A case study focused on a specific CSG well is presented to illustrate the feasibility of the proposed approach, and also to demonstrate that signal processing with autocorrelation analysis can improve the sensitivity of the detection system. Full article
(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries 2018)
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Open AccessArticle A Novel Fault Early Warning Model Based on Fault Gene Table for Smart Distribution Grids
Energies 2017, 10(12), 1963; doi:10.3390/en10121963
Received: 10 October 2017 / Revised: 16 November 2017 / Accepted: 17 November 2017 / Published: 24 November 2017
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Abstract
Since a smart distribution grid has a diversity of components and complicated topology; it is very hard to achieve fault early warning for each part. A fault early warning model for smart distribution grid combining a back propagation (BP) neural network with a
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Since a smart distribution grid has a diversity of components and complicated topology; it is very hard to achieve fault early warning for each part. A fault early warning model for smart distribution grid combining a back propagation (BP) neural network with a gene sequence alignment algorithm is proposed. Firstly; the operational state of smart distribution grid is divided into four states; and a BP neural network is adopted to explore the operational state from the historical fault data of the smart distribution grid. This obtains the relationship between each state transition time sequence and corresponding fault, and is used to construct the fault gene table. Then; a state transition time sequence is obtained online periodically, which is matched with each gene in fault gene table by an improved Smith–Waterman algorithm. If the maximum match score exceeds the given threshold, the relevant fault will be detected early. Finally, plenty of time domain simulation is performed on the proposed fault early warning model to IEEE-14 bus. The simulation results show that the proposed model can achieve efficient early fault warning of smart distribution grids. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Graphical Diagnosis of Performances in Photovoltaic Systems: A Case Study in Southern Spain
Energies 2017, 10(12), 1964; doi:10.3390/en10121964
Received: 3 November 2017 / Revised: 18 November 2017 / Accepted: 22 November 2017 / Published: 25 November 2017
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Abstract
The starting point of the operation and maintenance tasks in photovoltaic plants is the continuous monitoring and supervision of its components. The great amount of registered data requires a major improvement in the ways this information is processed and analyzed to rapidly detect
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The starting point of the operation and maintenance tasks in photovoltaic plants is the continuous monitoring and supervision of its components. The great amount of registered data requires a major improvement in the ways this information is processed and analyzed to rapidly detect any potential fault, without incurring additional costs. In this paper, a procedure to perform a detailed graphical supported analysis of the operation of photovoltaic installations, based on inverter data, and using a self-developed application, is presented. The program carries out the automated processing of the registered data, providing their access and visualization by means of color maps. These graphs allow a large volume of data set to be simultaneously represented in a readable way, enabling operation and maintenance operators to quickly detect patterns that would require any type of intervention. As a case study, the operation of a grid-connected photovoltaic plant located in southern Spain was studied during a period of three years. The average daily efficiency values of the PV modules and inverters were in the range of 7.6–14.6%, and 73.5–94% respectively. Moreover, the presence of shadings, as well as the hours and days mainly affected by this issue, was easily detected. Full article
(This article belongs to the Special Issue PV System Design and Performance)
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Open AccessArticle Two Stage Analysis of Successful Change Implementation of Knowledge Management Strategies in Energy Companies from Romania
Energies 2017, 10(12), 1965; doi:10.3390/en10121965
Received: 1 November 2017 / Revised: 16 November 2017 / Accepted: 21 November 2017 / Published: 25 November 2017
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Abstract
The purpose of this paper is to emphasize the effects of knowledge management strategies toward organizational change in Romanian companies from the energy sector. This study explored a new vision to implement these types of organizational changes successfully in companies from the Romanian
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The purpose of this paper is to emphasize the effects of knowledge management strategies toward organizational change in Romanian companies from the energy sector. This study explored a new vision to implement these types of organizational changes successfully in companies from the Romanian sector of energy and obtain their early benefits by using knowledge management strategies and also reveal the mediating effect of organizational learning and readiness for change. The results highlighted how energy companies can implement an Enterprise Resource Planning (ERP)-based change effectively through KM strategies. The results are equally valuable for all Romanian organizations that are currently changing their working environment. Full article
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Open AccessArticle Optimal Capacity Configuration for Energy Hubs Considering Part-Load Characteristics of Generation Units
Energies 2017, 10(12), 1966; doi:10.3390/en10121966
Received: 29 September 2017 / Revised: 8 November 2017 / Accepted: 16 November 2017 / Published: 25 November 2017
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Abstract
The simulation model is one of the key points affecting the optimal planning and operation of energy hubs (EHs). Since treating the efficiencies of generation units as constants would significantly simplify the calculation, only a simplified model is investigated in most research works.
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The simulation model is one of the key points affecting the optimal planning and operation of energy hubs (EHs). Since treating the efficiencies of generation units as constants would significantly simplify the calculation, only a simplified model is investigated in most research works. In this paper, aiming at optimizing the capacity configuration of an EH, we present a part-load characteristics-based (PLCB) model, in which the efficiencies of generation units will change with the fluctuating load. Based on the PLCB model, the accuracy of the EH model can be improved. Furthermore, a two-stage planning method is proposed to solve the optimal capacity configuration problem of the EH. Group Search Optimizer (GSO) is used to determine the optimal size in the first stage, and a mathematical programming method is applied to obtain the optimal operation of the EH in the second stage. Comparative studies using the PLCB model and the simplified model are performed to examine the impacts of equipment part-load characteristics on the sizing results. Simulation results indicate that the proposed model appears to have a better economic performance than the simplified model. Full article
(This article belongs to the Special Issue Decentralised Energy Supply Systems)
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Open AccessArticle A Simple and Effective Approach for the Prediction of Turbine Power Production From Wind Speed Forecast
Energies 2017, 10(12), 1967; doi:10.3390/en10121967
Received: 3 November 2017 / Revised: 20 November 2017 / Accepted: 23 November 2017 / Published: 25 November 2017
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Abstract
An accurate forecast of the power generated by a wind turbine is of paramount importance for its optimal exploitation. Several forecasting methods have been proposed either based on a physical modeling or using a statistical approach. All of them rely on the availability
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An accurate forecast of the power generated by a wind turbine is of paramount importance for its optimal exploitation. Several forecasting methods have been proposed either based on a physical modeling or using a statistical approach. All of them rely on the availability of high quality measures of local wind speed, corresponding generated power and on numerical weather forecasts. In this paper, a simple and effective wind power forecast technique, based on the probability distribution mapping of wind speed forecast and observed power data, is presented and it is applied to two turbines located on the island of Borkum (Germany) in the North Sea. The wind speed forecast of the ECMWF model at 100 m from the ground is used as the prognostic meteorological parameter. Training procedures are based entirely on relatively short time series of power measurements. Results show that our approach has skills that are similar or better than those obtained using more standard methods when measured with mean absolute error. Full article
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Open AccessArticle Impact of DC Voltage Enhancement on Partial Discharges in Medium Voltage Cables—An Empirical Study with Defects at Semicon-Dielectric Interface
Energies 2017, 10(12), 1968; doi:10.3390/en10121968
Received: 1 October 2017 / Revised: 20 November 2017 / Accepted: 22 November 2017 / Published: 26 November 2017
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Abstract
A scientific consensus is emerging on the benefits of direct current (DC) distribution in medium voltage (MV) power systems of ships and cities. At least 50% space savings and increased power transfer capacity are estimated with enhanced voltage DC operation of electric cables.
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A scientific consensus is emerging on the benefits of direct current (DC) distribution in medium voltage (MV) power systems of ships and cities. At least 50% space savings and increased power transfer capacity are estimated with enhanced voltage DC operation of electric cables. The goal of this research is to contribute to developing the empirical knowledge on the insulation performance in order to validate the feasibility of such anticipated gains of DC versus alternating current (AC), and to determine the comparative impact of different operational conditions from a component engineering point of view. The partial discharge (PD) activity in cables is measured under AC and DC conditions as an indicator of insulation performance. Specifically, PDs in defects at the semicon-insulation interface are studied in terms of inception voltage, repetition rate and discharge magnitude. Empirical understanding is drawn for operating voltage and frequency dependence of the discharge behavior in such voids in the range of 10 to 20 kV and 0 to 0.1 Hz, respectively. The change in PD activity with void evolution post temperature-induced ageing process is explored. Full article
(This article belongs to the Special Issue Selected Papers from International Workshop of Energy-Open)
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Open AccessArticle The Environmental Burdens of Lead-Acid Batteries in China: Insights from an Integrated Material Flow Analysis and Life Cycle Assessment of Lead
Energies 2017, 10(12), 1969; doi:10.3390/en10121969
Received: 17 October 2017 / Revised: 17 November 2017 / Accepted: 22 November 2017 / Published: 26 November 2017
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Abstract
Lead-acid batteries (LABs), a widely used energy storage equipment in cars and electric vehicles, are becoming serious problems due to their high environmental impact. In this study, an integrated method, combining material flow analysis with life cycle assessment, was developed to analyze the
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Lead-acid batteries (LABs), a widely used energy storage equipment in cars and electric vehicles, are becoming serious problems due to their high environmental impact. In this study, an integrated method, combining material flow analysis with life cycle assessment, was developed to analyze the environmental emissions and burdens of lead in LABs. The environmental burdens from other materials in LABs were not included. The results indicated that the amount of primary lead used in LABs accounted for 77% of the total lead production in 2014 in China. The amount of discharged lead into the environment was 8.54 × 105 tonnes, which was mainly from raw material extraction (57.2%). The largest environmental burden was from the raw materials extraction and processing, which accounted for 81.7% of the total environmental burdens. The environmental burdens of the environmental toxicity potential, human toxicity potential-cancer, human toxicity potential-non-cancer, water footprint and land use accounted for more than 90% at this stage. Moreover, the environmental burdens from primary lead was much more serious than regenerated lead. On the basis of the results, main practical measures and policies were proposed to reduce the lead emissions and environmental burdens of LABs in China, namely establishing an effective LABs recycling system, enlarging the market share of the legal regenerated lead, regulating the production of regenerated lead, and avoiding the long-distance transportation of the waste LABs. Full article
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Open AccessArticle Viscosity Models for Polymer Free CO2 Foam Fracturing Fluid with the Effect of Surfactant Concentration, Salinity and Shear Rate
Energies 2017, 10(12), 1970; doi:10.3390/en10121970
Received: 13 October 2017 / Revised: 15 November 2017 / Accepted: 17 November 2017 / Published: 26 November 2017
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Abstract
High quality polymer free CO2 foam possesses unique properties that make it an ideal fluid for fracturing unconventional shales. In this paper, the viscosity of polymer free fracturing foam and its empirical correlations at high pressure high temperature (HPHT) as a function
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High quality polymer free CO2 foam possesses unique properties that make it an ideal fluid for fracturing unconventional shales. In this paper, the viscosity of polymer free fracturing foam and its empirical correlations at high pressure high temperature (HPHT) as a function of surfactant concentration, salinity, and shear rate are presented. Foams were generated using a widely-used surfactant, i.e., alpha olefin sulfonate (AOS) in the presence of brine and a stabilizer at HPHT. Pressurize foam rheometer was used to find out the viscosity of CO2 foams at different surfactant concentration (0.25–1 wt %) and salinity (0.5–8 wt %) over a wide range of shear rate (10–500 s−1) at 1500 psi and 80 °C. Experimental results concluded that foam apparent viscosity increases noticeably until the surfactant concentration of 0.5 wt %, whereas, the increment in salinity provided a continuous increase in foam apparent viscosity. Nonlinear regression was performed on experimental data and empirical correlations were developed. Power law model for foam viscosity was modified to accommodate for the effect of shear rate, surfactant concentration, and salinity. Power law indices (K and n) were found to be a strong function of surfactant concentration and salinity. The new correlations accurately predict the foam apparent viscosity under various stimulation scenarios and these can be used for fracture simulation modeling. Full article
(This article belongs to the Special Issue Flow and Transport Properties of Unconventional Reservoirs)
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Open AccessArticle A Novel Electricity Transaction Mode of Microgrids Based on Blockchain and Continuous Double Auction
Energies 2017, 10(12), 1971; doi:10.3390/en10121971
Received: 8 October 2017 / Revised: 14 November 2017 / Accepted: 17 November 2017 / Published: 26 November 2017
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Abstract
The installed capacity of distributed generation (DG) based on renewable energy sources has increased continuously in power systems, and its market-oriented transaction is imperative. However, traditional transaction management based on centralized organizations has many disadvantages, such as high operation cost, low transparency, and
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The installed capacity of distributed generation (DG) based on renewable energy sources has increased continuously in power systems, and its market-oriented transaction is imperative. However, traditional transaction management based on centralized organizations has many disadvantages, such as high operation cost, low transparency, and potential risk of transaction data modification. Therefore, a decentralized electricity transaction mode for microgrids is proposed in this study based on blockchain and continuous double auction (CDA) mechanism. A buyer and seller initially complete the transaction matching in the CDA market. In view of the frequent price fluctuation in the CDA market, an adaptive aggressiveness strategy is used to adjust the quotation timely according to market changes. DG and consumer exchange digital certificate of power and expenditure on the blockchain system and the interests of consumers are then guaranteed by multi-signature when DG cannot generate power due to failure or other reasons. The digital certification of electricity assets is replaced by the sequence number with specific tags in the transaction script, and the size of digital certification can be adjusted according to transaction energy quantity. Finally, the feasibility of market mechanism through specific microgrid case and settlement process is also provided. Full article
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Open AccessArticle Experimental and One-Dimensional Mathematical Modeling of Different Operating Parameters in Direct Formic Acid Fuel Cells
Energies 2017, 10(12), 1972; doi:10.3390/en10121972
Received: 15 October 2017 / Revised: 20 November 2017 / Accepted: 23 November 2017 / Published: 27 November 2017
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Abstract
The purpose of this work is to develop a one-dimensional mathematical model for predicting the cell performance of a direct formic acid fuel cell and compare this with experimental results. The predicted model can be applied to direct formic acid fuel cells operated
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The purpose of this work is to develop a one-dimensional mathematical model for predicting the cell performance of a direct formic acid fuel cell and compare this with experimental results. The predicted model can be applied to direct formic acid fuel cells operated with different formic acid concentrations, temperatures, and with various electrolytes. Tafel kinetics at the electrodes, thermodynamic equations for formic acid solutions, and the mass-transport parameters of the reactants are used to predict the effective diffusion coefficients of the reactants (oxygen and formic acid) in the porous gas diffusion layers and the associated limiting current densities to ensure the accuracy of the model. This model allows us to estimate fuel cell polarization curves for a wide range of operating conditions. Furthermore, the model is validated with experimental results from operating at 1–5 M of formic acid feed at 30–80 °C, and with Nafion-117 and silane-crosslinked sulfonated poly(styrene-ethylene/butylene-styrene) (sSEBS) membrane electrolytes reinforced in porous polytetrafluoroethylene (PTFE). The cell potential and power densities of experimental outcomes in direct formic acid fuel cells can be adequately predicted using the developed model. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle Electrical Components for Marine Renewable Energy Arrays: A Techno-Economic Review
Energies 2017, 10(12), 1973; doi:10.3390/en10121973
Received: 1 November 2017 / Revised: 18 November 2017 / Accepted: 21 November 2017 / Published: 27 November 2017
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Abstract
This paper presents a review of the main electrical components that are expected to be present in marine renewable energy arrays. The review is put in context by appraising the current needs of the industry and identifying the key components required in both
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This paper presents a review of the main electrical components that are expected to be present in marine renewable energy arrays. The review is put in context by appraising the current needs of the industry and identifying the key components required in both device and array-scale developments. For each component, electrical, mechanical and cost considerations are discussed; with quantitative data collected during the review made freely available for use by the community via an open access online repository. This data collection updates previous research and addresses gaps specific to emerging offshore technologies, such as marine and floating wind, and provides a comprehensive resource for the techno-economic assessment of offshore energy arrays. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle Market Analysis during the First Year of Korea Emission Trading Scheme
Energies 2017, 10(12), 1974; doi:10.3390/en10121974
Received: 19 October 2017 / Revised: 17 November 2017 / Accepted: 23 November 2017 / Published: 28 November 2017
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Abstract
To derive the supply and demand issues during the first phase of the Korea Emission Trading Scheme (KETS), we investigated the excess or shortage, and the carry-over inflow of carbon emission permits for all of the domestic industries and major corporations. In particular,
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To derive the supply and demand issues during the first phase of the Korea Emission Trading Scheme (KETS), we investigated the excess or shortage, and the carry-over inflow of carbon emission permits for all of the domestic industries and major corporations. In particular, this study explored the supply and future prospects of offset credits, as well as the allocated permits, by forecasting the inflows of offset credits using the amount of certified reduction in domestic boundaries and overseas sources. We observed both the supply and demand of permits and changes in carbon dioxide (CO2) emission levels during the first phase (2015–2017) by comparing the estimated emission levels and the total permit supply. The results showed that permits were either in surplus or insufficient, depending on the sub-sector, and that a surplus in the supply of permits would occur if companies do not carry over more than 70 million tons of permits to the next period. Full article
(This article belongs to the Special Issue Lessons from the Evaluation of Existing Emission Trading Schemes)
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Open AccessArticle Hydropower Bidding Using Linearized Start-Ups
Energies 2017, 10(12), 1975; doi:10.3390/en10121975
Received: 12 November 2017 / Revised: 20 November 2017 / Accepted: 23 November 2017 / Published: 28 November 2017
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Abstract
Hydropower producers must submit bids to electricity market auctions where they state their willingness to produce power. These bids may be determined using a mixed-integer linear stochastic program. However, for large interconnected river systems, this program may be too complex to be solved
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Hydropower producers must submit bids to electricity market auctions where they state their willingness to produce power. These bids may be determined using a mixed-integer linear stochastic program. However, for large interconnected river systems, this program may be too complex to be solved within the time limits set by current market rules. This paper investigates whether a linear approximation to start-ups can be used to reduce the computational burden without significantly degrading the solution quality. In order to investigate the trade-off of time versus solution quality, linear approximation is compared to a formulation that uses binary variables in a case study that simulates the operation of a reservoir system over time. Full article
(This article belongs to the Special Issue Hydropower 2017)
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Open AccessArticle Different Models for Forecasting Wind Power Generation: Case Study
Energies 2017, 10(12), 1976; doi:10.3390/en10121976
Received: 23 October 2017 / Revised: 20 November 2017 / Accepted: 23 November 2017 / Published: 29 November 2017
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Abstract
Generation of electric energy through wind turbines is one of the practically inexhaustible alternatives of generation. It is considered a source of clean energy, but still needs a lot of research for the development of science and technologies that ensures uniformity in generation,
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Generation of electric energy through wind turbines is one of the practically inexhaustible alternatives of generation. It is considered a source of clean energy, but still needs a lot of research for the development of science and technologies that ensures uniformity in generation, providing a greater participation of this source in the energy matrix, since the wind presents abrupt variations in speed, density and other important variables. In wind-based electrical systems, it is essential to predict at least one day in advance the future values of wind behavior, in order to evaluate the availability of energy for the next period, which is relevant information in the dispatch of the generating units and in the control of the electrical system. This paper develops ultra-short, short, medium and long-term prediction models of wind speed, based on computational intelligence techniques, using artificial neural network models, Autoregressive Integrated Moving Average (ARIMA) and hybrid models including forecasting using wavelets. For the application of the methodology, the meteorological variables of the database of the national organization system of environmental data (SONDA), Petrolina station, from 1 January 2004 to 31 March 2017, were used. A comparison among results by different used approaches is also done and it is also predicted the possibility of power and energy generation using a certain kind of wind generator. Full article
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Open AccessArticle On Conceptual Structuration and Coupling Methods of Co-Simulation Frameworks in Cyber-Physical Energy System Validation
Energies 2017, 10(12), 1977; doi:10.3390/en10121977
Received: 31 October 2017 / Revised: 17 November 2017 / Accepted: 22 November 2017 / Published: 29 November 2017
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Abstract
Co-simulation is an emerging method for cyber-physical energy system (CPES) assessment and validation. Combining simulators of different domains into a joint experiment, co-simulation provides a holistic framework to consider the whole CPES at system level. In this paper, we present a systematic structuration
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Co-simulation is an emerging method for cyber-physical energy system (CPES) assessment and validation. Combining simulators of different domains into a joint experiment, co-simulation provides a holistic framework to consider the whole CPES at system level. In this paper, we present a systematic structuration of co-simulation based on a conceptual point of view. A co-simulation framework is then considered in its conceptual, semantic, syntactic, dynamic and technical layers. Coupling methods are investigated and classified according to these layers. This paper would serve as a solid theoretical base for specification of future applications of co-simulation and selection of coupling methods in CPES assessment and validation. 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 A New Control-Oriented Semi-Empirical Approach to Predict Engine-Out NOx Emissions in a Euro VI 3.0 L Diesel Engine
Energies 2017, 10(12), 1978; doi:10.3390/en10121978
Received: 31 October 2017 / Revised: 23 November 2017 / Accepted: 26 November 2017 / Published: 29 November 2017
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Abstract
The present study is focused on the development of a new control-oriented semi-empirical model to predict nitrogen oxide (NOx) emissions in a light-duty diesel engine under both steady-state and transient conditions. The model is based on the estimation of the deviations of NOx
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The present study is focused on the development of a new control-oriented semi-empirical model to predict nitrogen oxide (NOx) emissions in a light-duty diesel engine under both steady-state and transient conditions. The model is based on the estimation of the deviations of NOx emissions, with respect to the nominal engine-calibration map values, as a function of the deviations of the intake oxygen concentration and of the combustion phasing. The model also takes into account the effects of engine speed, total injected quantity, and ambient temperature and humidity. The approach has been developed and assessed on an Fiat Powertrain Technologies (FPT) Euro VI 3.0 L diesel engine for light-duty applications, in the frame of a research project in collaboration with FPT Industrial. The model has also been tested on a rapid prototyping device, and it was shown that it requires a very short computational time, thus being suitable for implementation on the Engine Control Unit (ECU) for real-time NOx control tasks. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessFeature PaperArticle Prospects for Assessing Enhanced Geothermal System (EGS) Basement Rock Flow Stimulation by Wellbore Temperature Data
Energies 2017, 10(12), 1979; doi:10.3390/en10121979
Received: 16 September 2017 / Revised: 9 November 2017 / Accepted: 13 November 2017 / Published: 30 November 2017
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Abstract
We use Matlab 3D finite element fluid flow/transport modelling to simulate localized wellbore temperature events of order 0.05–0.1 °C logged in Fennoscandia basement rock at ~1.5 km depths. The temperature events are approximated as steady-state heat transport due to fluid draining from the
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We use Matlab 3D finite element fluid flow/transport modelling to simulate localized wellbore temperature events of order 0.05–0.1 °C logged in Fennoscandia basement rock at ~1.5 km depths. The temperature events are approximated as steady-state heat transport due to fluid draining from the crust into the wellbore via naturally occurring fracture-connectivity structures. Flow simulation is based on the empirics of spatially-correlated fracture-connectivity fluid flow widely attested by well-log, well-core, and well-production data. Matching model wellbore-centric radial temperature profiles to a 2D analytic expression for steady-state radial heat transport with Peclet number Pe ≡ r0φv0/D (r0 = wellbore radius, v0 = Darcy velocity at r0, φ = ambient porosity, D = rock-water thermal diffusivity), gives Pe ~ 10–15 for fracture-connectivity flow intersecting the well, and Pe ~ 0 for ambient crust. Darcy flow for model Pe ~ 10 at radius ~10 m from the wellbore gives permeability estimate κ ~ 0.02 Darcy for flow driven by differential fluid pressure between least principal crustal stress pore pressure and hydrostatic wellbore pressure. Model temperature event flow permeability κm ~ 0.02 Darcy is related to well-core ambient permeability κ ~ 1 µDarcy by empirical poroperm relation κm ~ κ exp(αmφ) for φ ~ 0.01 and αm ~ 1000. Our modelling of OTN1 wellbore temperature events helps assess the prospect of reactivating fossilized fracture-connectivity flow for EGS permeability stimulation of basement rock. Full article
(This article belongs to the Section Energy Sources)
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Open AccessArticle A Multifunctional Isolated and Non-Isolated Dual Mode Converter for Renewable Energy Conversion Applications
Energies 2017, 10(12), 1980; doi:10.3390/en10121980
Received: 16 October 2017 / Revised: 25 November 2017 / Accepted: 25 November 2017 / Published: 30 November 2017
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Abstract
In this paper, a multifunctional isolated and non-isolated dual-mode low-power converter was designed for renewable energy conversion applications such as photovoltaic power generation to achieve different operating modes under bi-directional electrical conversion. The proposed topology consists of a bidirectional non-isolated DC/DC circuit and
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In this paper, a multifunctional isolated and non-isolated dual-mode low-power converter was designed for renewable energy conversion applications such as photovoltaic power generation to achieve different operating modes under bi-directional electrical conversion. The proposed topology consists of a bidirectional non-isolated DC/DC circuit and an isolated converter with a high-frequency transformer, which merge the advantages of both the conventional isolated converter and non-isolated converter with the combination of the two converter technologies. Compared with traditional converters, the multifunctional converter can not only realize conventional bi-directional functions, but can also be applied for many different operation modes and meet the high output/input ratio demands with the two converter circuits operating together. A novel control algorithm was proposed to achieve the various functions of the proposed converter. An experimental platform based on the proposed circuit was established. Both the simulation and experimental results indicated that the proposed converter could provide isolated and non-isolated modes in different applications, which could meet different practical engineering requirements. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Extremely Efficient Design of Organic Thin Film Solar Cells via Learning-Based Optimization
Energies 2017, 10(12), 1981; doi:10.3390/en10121981
Received: 3 October 2017 / Revised: 21 November 2017 / Accepted: 22 November 2017 / Published: 30 November 2017
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Abstract
Design of efficient thin film photovoltaic (PV) cells require optical power absorption to be computed inside a nano-scale structure of photovoltaics, dielectric and plasmonic materials. Calculating power absorption requires Maxwell’s electromagnetic equations which are solved using numerical methods, such as finite difference time
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Design of efficient thin film photovoltaic (PV) cells require optical power absorption to be computed inside a nano-scale structure of photovoltaics, dielectric and plasmonic materials. Calculating power absorption requires Maxwell’s electromagnetic equations which are solved using numerical methods, such as finite difference time domain (FDTD). The computational cost of thin film PV cell design and optimization is therefore cumbersome, due to successive FDTD simulations. This cost can be reduced using a surrogate-based optimization procedure. In this study, we deploy neural networks (NNs) to model optical absorption in organic PV structures. We use the corresponding surrogate-based optimization procedure to maximize light trapping inside thin film organic cells infused with metallic particles. Metallic particles are known to induce plasmonic effects at the metal–semiconductor interface, thus increasing absorption. However, a rigorous design procedure is required to achieve the best performance within known design guidelines. As a result of using NNs to model thin film solar absorption, the required time to complete optimization is decreased by more than five times. The obtained NN model is found to be very reliable. The optimization procedure results in absorption enhancement greater than 200%. Furthermore, we demonstrate that once a reliable surrogate model such as the developed NN is available, it can be used for alternative analyses on the proposed design, such as uncertainty analysis (e.g., fabrication error). Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Study of a Coil Heat Exchanger with an Ice Storage System
Energies 2017, 10(12), 1982; doi:10.3390/en10121982
Received: 31 October 2017 / Revised: 23 November 2017 / Accepted: 28 November 2017 / Published: 1 December 2017
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Abstract
In this study, a coil heat exchanger with an ice storage system is analyzed by theoretical analysis, numerical analysis, and experimental analysis. The dynamic characteristics of ice thickness variation is studied by means of unstable heat conduction theory in cylindrical coordinates, and the
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In this study, a coil heat exchanger with an ice storage system is analyzed by theoretical analysis, numerical analysis, and experimental analysis. The dynamic characteristics of ice thickness variation is studied by means of unstable heat conduction theory in cylindrical coordinates, and the change rule of the ice layer thickness is obtained. The computational fluid dynamics method is employed to simulate the flow field and ice melting process of the coil heat exchanger. The effect of the agitator height on the flow characteristics and heat transfer characteristics is investigated. The numerical results show that the turbulence intensity of the fluid near the wall of the heat exchanger is the largest with an agitator height of 80 mm. Furthermore, the process of ice melting is analyzed. The ice on the outer side of the evaporator tube close to the container wall melts faster than the inner side and this agrees well with the experimental result. The experimental study on the process of the operational period and deicing of the coil heat exchanger is conducted and the temperature variation curves are obtained by the arrangement of thermocouples. It is found that the temperature of the evaporating tube increases with increasing height in the process of ice storage. Full article
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Open AccessArticle Diurnal Thermal Behavior of Photovoltaic Panel with Phase Change Materials under Different Weather Conditions
Energies 2017, 10(12), 1983; doi:10.3390/en10121983
Received: 16 October 2017 / Revised: 22 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
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Abstract
The electric power generation efficiency of photovoltaic (PV) panels depends on the solar irradiation flux and the operating temperature of the solar cell. To increase the power generation efficiency of a PV system, this study evaluated the feasibility of phase change materials (PCMs)
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The electric power generation efficiency of photovoltaic (PV) panels depends on the solar irradiation flux and the operating temperature of the solar cell. To increase the power generation efficiency of a PV system, this study evaluated the feasibility of phase change materials (PCMs) to reduce the temperature rise of solar cells operating under the climate in Seoul, Korea. For this purpose, two PCMs with different phase change characteristics were prepared and the phase change temperatures and thermal conductivities were compared. The diurnal thermal behavior of PV panels with PCMs under the Seoul climate was evaluated using a 2-D transient thermal analysis program. This paper discusses the heat flow characteristics though the PV cell with PCMs and the effects of the PCM types and macro-packed PCM (MPPCM) methods on the operating temperatures under different weather conditions. Selection of the PCM type was more important than the MMPCM methods when PCMs were used to enhance the performance of PV panels and the mean operating temperature of PV cell and total heat flux from the surface could be reduced by increasing the heat transfer rate through the honeycomb grid steel container for PCMs. Considering the mean operating temperature reduction of 4 °C by PCM in this study, an efficiency improvement of approximately 2% can be estimated under the weather conditions of Seoul. Full article
(This article belongs to the Special Issue Solar Energy Application in Buildings)
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Open AccessArticle Study on Flow in Fractured Porous Media Using Pore-Fracture Network Modeling
Energies 2017, 10(12), 1984; doi:10.3390/en10121984
Received: 30 October 2017 / Revised: 25 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
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Abstract
Microscopic flow in fractured porous media is a typical problem for the exploitation of tight reservoirs. The rapid-flow in the fractured porous-media is of great significance to efficient and continuous oil/gas exploitation. The fractures are expected to enhance flow conductivity and mass transfer
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Microscopic flow in fractured porous media is a typical problem for the exploitation of tight reservoirs. The rapid-flow in the fractured porous-media is of great significance to efficient and continuous oil/gas exploitation. The fractures are expected to enhance flow conductivity and mass transfer between matrix and fractures, and to improve oil displacement during water flooding. However, the fractures may also lead to water channeling under some conditions. The understanding on the mechanism of the microscopic flow in the fractured porous media has been insufficient until now. In this paper, a two-dimensional pore-fracture network model is presented to study the role of fractures in the flow. The effects of two main dimensionless parameters, fracture length to network length lf/l and fracture density Nf/N, on the absolute permeability and the oil displacement efficiency are investigated. The results show that the flow in the matrix plays a controlling role at a low fracture density. Once the fracture density exceeds a certain value, the flow is controlled by fractures. With the increase of the fracture density, the oil displacement efficiency develops into three typical stages: when Nf/N < 0.1, the oil displacement efficiency increases rapidly; when 0.1 < Nf/N < 0.5, the oil displacement efficiency changes slowly; and when Nf/N > 0.5, the oil displacement efficiency decreases rapidly. In the case lf/l > 0.8, the water mainly flows through a concentrated path connected by some fractures, resulting in it bypassing most oil regions, and thus the oil displacement efficiency decreases rapidly, similar to the water channeling. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Large Signal Stabilization of Hybrid AC/DC Micro-Grids Using Nonlinear Robust Controller
Energies 2017, 10(12), 1985; doi:10.3390/en10121985
Received: 13 August 2017 / Revised: 15 October 2017 / Accepted: 25 October 2017 / Published: 1 December 2017
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Abstract
This paper presents a robust nonlinear integrated controller to improve stability of hybrid AC/DC micro-grids under islanding mode. The proposed controller includes two independent controllers where each one is responsible to control one part of the system. First controller will improve the stability
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This paper presents a robust nonlinear integrated controller to improve stability of hybrid AC/DC micro-grids under islanding mode. The proposed controller includes two independent controllers where each one is responsible to control one part of the system. First controller will improve the stability of input DC/DC converter. Using this controller, the voltage of DC bus is fully stabilized such that when a large disturbance occurs, its voltage will become constant without any significant dynamic. The necessity of DC bus regulation which has not been considered in previous studies, is imminent as it not only improves voltage stability of the micro-grid but also protects consumers which are directly connected to the DC bus, against voltage variations. Frequency stability of the micro-grid is provided by the second proposed controller which is applied to output DC/AC converter of the micro-grid. Adaptive method is used to make the controllers proposed in this paper, robust. Duty cycle of converters switches are adjusted such that voltage and frequency of the micro-grid are set on the desired value in minimum possible time under transient disturbances and uncertainty of the loads as well as micro-sources characteristics. Full article
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Open AccessArticle Using a Local Framework Combining Principal Component Regression and Monte Carlo Simulation for Uncertainty and Sensitivity Analysis of a Domestic Energy Model in Sub-City Areas
Energies 2017, 10(12), 1986; doi:10.3390/en10121986
Received: 26 September 2017 / Revised: 19 October 2017 / Accepted: 28 October 2017 / Published: 1 December 2017
PDF Full-text (7792 KB) | HTML Full-text | XML Full-text
Abstract
Domestic energy modelling is complex, in terms of user input and the approach used to define the model; therefore, there is an increase in the sources of uncertainties. Previous efforts to perform sensitivity and uncertainty analyses have focused on national energy models, while
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Domestic energy modelling is complex, in terms of user input and the approach used to define the model; therefore, there is an increase in the sources of uncertainties. Previous efforts to perform sensitivity and uncertainty analyses have focused on national energy models, while in this research, the objective is to extend traditional sensitivity analysis and use a local framework combining principal component regression and Monte Carlo Simulation. Therefore, in our method the total amount of the energy output’s variance is decomposed, in relative terms, according to the contribution of the different predictor parameters. Our framework provides compelling evidence that local area characteristics are important in energy modelling and those national and regional indexes and values may not properly reflect the local conditions, resulting in programmes and interventions that will be sub-optimal. Furthermore, our uncertainty methodology uses a three dimensional integrative taxonomy and a concept map. The concept map identified concrete terminal causes of uncertainty within the taxonomic framework of sources, issues, sub-issues and a further abstraction of those quantities in terms of accuracy and precision. Understanding uncertainties in this way provides a possible framework for modellers, policy makers and data collectors to improve practice in key areas and to reduce uncertainty. Full article
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Open AccessArticle Predictive Maintenance of Power Substation Equipment by Infrared Thermography Using a Machine-Learning Approach
Energies 2017, 10(12), 1987; doi:10.3390/en10121987
Received: 21 October 2017 / Revised: 23 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
PDF Full-text (2774 KB) | HTML Full-text | XML Full-text
Abstract
A variety of reasons, specifically contact issues, irregular loads, cracks in insulation, defective relays, terminal junctions and other similar issues, increase the internal temperature of electrical instruments. This results in unexpected disturbances and potential damage to power equipment. Therefore, the initial prevention measures
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A variety of reasons, specifically contact issues, irregular loads, cracks in insulation, defective relays, terminal junctions and other similar issues, increase the internal temperature of electrical instruments. This results in unexpected disturbances and potential damage to power equipment. Therefore, the initial prevention measures of thermal anomalies in electrical tools are essential to prevent power-equipment failure. In this article, we address this initial prevention mechanism for power substations using a computer-vision approach by taking advantage of infrared thermal images. The thermal images are taken through infrared cameras without disturbing the working operations of power substations. Thus, this article augments the non-destructive approach to defect analysis in electrical power equipment using computer vision and machine learning. We use a total of 150 thermal pictures of different electrical equipment in 10 different substations in operating conditions, using 300 different hotspots. Our approach uses multi-layered perceptron (MLP) to classify the thermal conditions of components of power substations into “defect” and “non-defect” classes. A total of eleven features, which are first-order and second-order statistical features, are calculated from the thermal sample images. The performance of MLP shows initial accuracy of 79.78%. We further augment the MLP with graph cut to increase accuracy to 84%. We argue that with the successful development and deployment of this new system, the Technology Department of Chongqing can arrange the recommended actions and thus save cost in repair and outages. This can play an important role in the quick and reliable inspection to potentially prevent power substation equipment from failure, which will save the whole system from breakdown. The increased 84% accuracy with the integration of the graph cut shows the efficacy of the proposed defect analysis approach. Full article
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Open AccessArticle Day-Ahead Wind Power Forecasting Using a Two-Stage Hybrid Modeling Approach Based on SCADA and Meteorological Information, and Evaluating the Impact of Input-Data Dependency on Forecasting Accuracy
Energies 2017, 10(12), 1988; doi:10.3390/en10121988
Received: 31 October 2017 / Revised: 16 November 2017 / Accepted: 17 November 2017 / Published: 4 December 2017
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Abstract
The power generated by wind generators is usually associated with uncertainties, due to the intermittency of wind speed and other weather variables. This creates a big challenge for transmission system operators (TSOs) and distribution system operators (DSOs) in terms of connecting, controlling and
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The power generated by wind generators is usually associated with uncertainties, due to the intermittency of wind speed and other weather variables. This creates a big challenge for transmission system operators (TSOs) and distribution system operators (DSOs) in terms of connecting, controlling and managing power networks with high-penetration wind energy. Hence, in these power networks, accurate wind power forecasts are essential for their reliable and efficient operation. They support TSOs and DSOs in enhancing the control and management of the power network. In this paper, a novel two-stage hybrid approach based on the combination of the Hilbert-Huang transform (HHT), genetic algorithm (GA) and artificial neural network (ANN) is proposed for day-ahead wind power forecasting. The approach is composed of two stages. The first stage utilizes numerical weather prediction (NWP) meteorological information to predict wind speed at the exact site of the wind farm. The second stage maps actual wind speed vs. power characteristics recorded by SCADA. Then, the wind speed forecast in the first stage for the future day is fed to the second stage to predict the future day’s wind power. Comparative selection of input-data parameter sets for the forecasting model and impact analysis of input-data dependency on forecasting accuracy have also been studied. The proposed approach achieves significant forecasting accuracy improvement compared with three other artificial intelligence-based forecasting approaches and a benchmark model using the smart persistence method. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle Thermal and Electromagnetic Combined Optimization Design of Dry Type Air Core Reactor
Energies 2017, 10(12), 1989; doi:10.3390/en10121989
Received: 28 September 2017 / Revised: 13 November 2017 / Accepted: 17 November 2017 / Published: 1 December 2017
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Abstract
In this paper, taking the minimum metal conductor usage of an air core reactor as optimization goal, the influence of air ducts width and encapsulation number on thermal efficiency and electromagnetic efficiency are analyzed. Combined with the equation constraint conditions for maximum temperature
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In this paper, taking the minimum metal conductor usage of an air core reactor as optimization goal, the influence of air ducts width and encapsulation number on thermal efficiency and electromagnetic efficiency are analyzed. Combined with the equation constraint conditions for maximum temperature rise conservation, inductance conservation and structure function of reactor considering the change of air ducts width and encapsulation number, the thermal and electromagnetic combined optimization curves are formed, and design results are achieved based on the initial design parameters. Meanwhile, the temperature field simulation model of the reactor is established and the results verify the correctness of the optimization method. According to the design results, the proportionality factor of metal conductor usage is only 0.61 compared with the initial design parameters of the reactor, which shows that the proposed comprehensive optimization method can significantly reduce conductor usage, improving the metal conductor utilization ratio. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle H-Shaped Multiple Linear Motor Drive Platform Control System Design Based on an Inverse System Method
Energies 2017, 10(12), 1990; doi:10.3390/en10121990
Received: 11 October 2017 / Revised: 13 November 2017 / Accepted: 21 November 2017 / Published: 1 December 2017
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Abstract
Due to its simple mechanical structure and high motion stability, the H-shaped platform has been increasingly widely used in precision measuring, numerical control machining and semiconductor packaging equipment, etc. The H-shaped platform is normally driven by multiple (three) permanent magnet synchronous linear motors.
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Due to its simple mechanical structure and high motion stability, the H-shaped platform has been increasingly widely used in precision measuring, numerical control machining and semiconductor packaging equipment, etc. The H-shaped platform is normally driven by multiple (three) permanent magnet synchronous linear motors. The main challenges for H-shaped platform-control include synchronous control between the two linear motors in the Y direction as well as total positioning error of the platform mover, a combination of position deviation in X and Y directions. To deal with the above challenges, this paper proposes a control strategy based on the inverse system method through state feedback and dynamic decoupling of the thrust force. First, mechanical dynamics equations have been deduced through the analysis of system coupling based on the platform structure. Second, the mathematical model of the linear motors and the relevant coordinate transformation between dq-axis currents and ABC-phase currents are analyzed. Third, after the main concept of inverse system method being explained, the inverse system model of the platform control system has been designed after defining relevant system variables. Inverse system model compensates the original nonlinear coupled system into pseudo-linear decoupled linear system, for which typical linear control methods, like PID, can be adopted to control the system. The simulation model of the control system is built in MATLAB/Simulink and the simulation result shows that the designed control system has both small synchronous deviation and small total trajectory tracking error. Furthermore, the control program has been run on NI controller for both fixed-loop-time and free-loop-time modes, and the test result shows that the average loop computation time needed is rather small, which makes it suitable for real industrial applications. Overall, it proves that the proposed new control strategy can be used in industrial applications that have high-precision and high real-time performance requirements. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle Dynamic Power Dispatch Considering Electric Vehicles and Wind Power Using Decomposition Based Multi-Objective Evolutionary Algorithm
Energies 2017, 10(12), 1991; doi:10.3390/en10121991
Received: 27 October 2017 / Revised: 17 November 2017 / Accepted: 22 November 2017 / Published: 1 December 2017
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Abstract
The intermittency of wind power and the large-scale integration of electric vehicles (EVs) bring new challenges to the reliability and economy of power system dispatching. In this paper, a novel multi-objective dynamic economic emission dispatch (DEED) model is proposed considering the EVs and
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The intermittency of wind power and the large-scale integration of electric vehicles (EVs) bring new challenges to the reliability and economy of power system dispatching. In this paper, a novel multi-objective dynamic economic emission dispatch (DEED) model is proposed considering the EVs and uncertainties of wind power. The total fuel cost and pollutant emission are considered as the optimization objectives, and the vehicle to grid (V2G) power and the conventional generator output power are set as the decision variables. The stochastic wind power is derived by Weibull probability distribution function. Under the premise of meeting the system energy and user’s travel demand, the charging and discharging behavior of the EVs are dynamically managed. Moreover, we propose a two-step dynamic constraint processing strategy for decision variables based on penalty function, and, on this basis, the Multi-Objective Evolutionary Algorithm Based on Decomposition (MOEA/D) algorithm is improved. The proposed model and approach are verified by the 10-generator system. The results demonstrate that the proposed DEED model and the improved MOEA/D algorithm are effective and reasonable. Full article
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Open AccessArticle Testing for Environmental Kuznets Curve in the EU Agricultural Sector through an Eco-(in)Efficiency Index
Energies 2017, 10(12), 1992; doi:10.3390/en10121992
Received: 1 October 2017 / Revised: 27 October 2017 / Accepted: 26 November 2017 / Published: 1 December 2017
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Abstract
Studies on agricultural production practices advance within international literature and new methods are proposed in order to assess the agricultural sustainability, either at farm or macro level. The present paper builds on these advancements and develops a synthetic Eco-(in)efficiency index by employing a
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Studies on agricultural production practices advance within international literature and new methods are proposed in order to assess the agricultural sustainability, either at farm or macro level. The present paper builds on these advancements and develops a synthetic Eco-(in)efficiency index by employing a directional distance function—data envelopment analysis (DEA) model. This index is used in order to assess the sustainability of the EU agricultural sector for the period 1999–2012 on a country level. Furthermore, Eco-(in)efficiency, together with the energy use and greenhouse gas (GHG) emissions are regressed on the gross domestic product (GDP) of EU countries, in order to check for any environmental Kuznets curve relationship existence. Results signify that efficiency improvements are possible, both towards output development and GHG emissions reduction. In addition, the potential of each country in adopting more sustainable production practices is not totally connected with its economic development, as Eco-(in)efficiency and GDP levels of EU countries seem to be linked with an N-Shaped curve. Full article
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Open AccessArticle Sludge Acts as a Catalyst for Coal during the Co-Combustion Process Investigated by Thermogravimetric Analysis
Energies 2017, 10(12), 1993; doi:10.3390/en10121993
Received: 17 October 2017 / Revised: 16 November 2017 / Accepted: 24 November 2017 / Published: 1 December 2017
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Abstract
Sewage sludge in China has the characteristics of low organic content and low heating value compared with other developed countries. Self-sustaining combustion of Chinese sludge cannot be achieved when the moisture content is high. Co-combusting a small amount of sludge in the existing
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Sewage sludge in China has the characteristics of low organic content and low heating value compared with other developed countries. Self-sustaining combustion of Chinese sludge cannot be achieved when the moisture content is high. Co-combusting a small amount of sludge in the existing coal-fired boilers is a usual sludge disposal method in China. Thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis of a bituminous coal, three different sewage sludges, and their blends have been carried out. Fitted curves by linear calculation and actual curves of blends were compared to study the interaction between sludge and coal in their co-combustion process. The results indicate that the interaction between the two fuels takes place during the devolatilization and combustion period. Sludge acts as a catalyst for coal during the co-combustion process because of the large amount of inorganic salts contained in the sludge. Co-combustion of coal and sludge is more efficient than single burning of the two fuels. Full article
(This article belongs to the collection Bioenergy and Biofuel)
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Open AccessArticle A Novel Semi-Visualizable Experimental Study of a Plate Gravity Heat Pipe at Unsteady State
Energies 2017, 10(12), 1994; doi:10.3390/en10121994
Received: 3 November 2017 / Revised: 24 November 2017 / Accepted: 26 November 2017 / Published: 1 December 2017
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Abstract
An experimental study on a plate gravity heat pipe (PGHP) with inner cavity size of length 100 mm (X), width 2.5 mm (Y), and height 210 mm (Z) with acetone as the working fluid was carried out. The effects of heating power inputs
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An experimental study on a plate gravity heat pipe (PGHP) with inner cavity size of length 100 mm (X), width 2.5 mm (Y), and height 210 mm (Z) with acetone as the working fluid was carried out. The effects of heating power inputs (80–180 W) and fluid filling ratios (25%, 48%, and 55%) on the start-up temperature, start-up time, temperature difference, and relative thermal resistance on the Z-axis of the PGHP in a vacuum of 1 × 10−3 Pa were studied at unsteady state. Furthermore, the gas-liquid two-phase behavior of the interior working fluid of PGHP, and the coupling heat transfer behavior of the boiling liquid and the condensate were observed through a visualizable window under different experimental conditions. The results show that, with the increase of heating power input, the start-up temperature of the PGHP increases and the start-up time is shortened. The start-up temperature of the PGHP was around 33 °C and the start-up time was about 320 s at the heating power input of 120 W and working fluid filling ratio of 55%. The relative thermal resistance and the temperature difference on the Z-axis of the PGHP increase firstly and then decrease with the increase of heating power input at unsteady state. The complex gas-liquid two-phase behavior of the PGHP mainly includes: the formation and growth of bubbles, the merging and break up of bubbles, and the coupling heat transfer between boiling liquid and condensate, which demonstrate that the novel SVPGHP can be used to effectively study the heat transfer process of PGHP. Full article
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Open AccessArticle Studies on an Electromagnetic Transient Model of Offshore Wind Turbines and Lightning Transient Overvoltage Considering Lightning Channel Wave Impedance
Energies 2017, 10(12), 1995; doi:10.3390/en10121995
Received: 12 October 2017 / Revised: 16 November 2017 / Accepted: 24 November 2017 / Published: 1 December 2017
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Abstract
In recent years, with the rapid development of offshore wind turbines (WTs), the problem of lightning strikes has become more and more prominent. In order to reduce the failure rate caused by the transient overvoltage of lightning struck offshore WTs, the influencing factors
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In recent years, with the rapid development of offshore wind turbines (WTs), the problem of lightning strikes has become more and more prominent. In order to reduce the failure rate caused by the transient overvoltage of lightning struck offshore WTs, the influencing factors and the response rules of transient overvoltage are analyzed. In this paper, a new integrated electromagnetic transient model of offshore WTs is established by using the numerical calculation method of the electromagnetic field first. Then, based on the lightning model and considering the impedance of the lightning channel, the transient overvoltage of lightning is analyzed. Last, the electromagnetic transient model of offshore WTs is simulated and analyzed by using the alternative transients program electro-magnetic transient program (ATP-EMTP) software. The influence factors of lightning transient overvoltage are studied. The main influencing factors include the sea depth, the blade length, the tower height, the lightning flow parameters, the lightning strike point, and the blade rotation position. The simulation results show that the influencing factors mentioned above have different effects on the lightning transient overvoltage. The results of the study have some guiding significance for the design of the lightning protection of the engine room. Full article
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Open AccessArticle Assessment of Energy Performance and Emission Control Using Alternative Fuels in Cement Industry through a Process Model
Energies 2017, 10(12), 1996; doi:10.3390/en10121996
Received: 11 October 2017 / Revised: 20 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
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Abstract
Cement manufacturing is one of the most energy intensive processes and is accountable for substantial pollutant emissions. Increasing energy costs compel stakeholders and researchers to search for alternative options to improve energy performance and reduce CO2 emissions. Alternative fuels offer a realistic
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Cement manufacturing is one of the most energy intensive processes and is accountable for substantial pollutant emissions. Increasing energy costs compel stakeholders and researchers to search for alternative options to improve energy performance and reduce CO2 emissions. Alternative fuels offer a realistic solution towards the reduction of the usage of fossil fuels and the mitigation of pollutant emissions. This paper developed a process model of a precalciner kiln system in the cement industry using Aspen Plus software to simulate the effect of five alternative fuels on pollutant emissions and energy performance. The alternatives fuels used were tyre, municipal solid waste (MSW), meat and bone meal (MBM), plastic waste and sugarcane bagasse. The model was developed on the basis of energy and mass balance of the system and was validated against data from a reference cement plant. This study also investigated the effect of these alternative fuels on the quality of the clinker. The results indicated that up to a 4.4% reduction in CO2 emissions and up to a 6.4% reduction in thermal energy requirement could be achieved using these alternative fuels with 20% mix in coal. It was also found that the alternative fuels had minimum influence on the clinker quality except in the case of MSW. Overall, MBM was found to be a better option as it is capable on reducing energy requirement and CO2 emissions more than others. The outcomes of the study offer better understanding of the effects of solid alternative fuels to achieve higher energy performance and on mitigating pollutant emissions in cement industry. Full article
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Open AccessArticle Digital-Control-Based Approximation of Optimal Wave Disturbances Attenuation for Nonlinear Offshore Platforms
Energies 2017, 10(12), 1997; doi:10.3390/en10121997
Received: 20 October 2017 / Revised: 9 November 2017 / Accepted: 22 November 2017 / Published: 1 December 2017
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Abstract
The irregular wave disturbance attenuation problem for jacket-type offshore platforms involving the nonlinear characteristics is studied. The main contribution is that a digital-control-based approximation of optimal wave disturbances attenuation controller (AOWDAC) is proposed based on iteration control theory, which consists of a feedback
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The irregular wave disturbance attenuation problem for jacket-type offshore platforms involving the nonlinear characteristics is studied. The main contribution is that a digital-control-based approximation of optimal wave disturbances attenuation controller (AOWDAC) is proposed based on iteration control theory, which consists of a feedback item of offshore state, a feedforward item of wave force and a nonlinear compensated component with iterative sequences. More specifically, by discussing the discrete model of nonlinear offshore platform subject to wave forces generated from the Joint North Sea Wave Project (JONSWAP) wave spectrum and linearized wave theory, the original wave disturbances attenuation problem is formulated as the nonlinear two-point-boundary-value (TPBV) problem. By introducing two vector sequences of system states and nonlinear compensated item, the solution of introduced nonlinear TPBV problem is obtained. Then, a numerical algorithm is designed to realize the feasibility of AOWDAC based on the deviation of performance index between the adjacent iteration processes. Finally, applied the proposed AOWDAC to a jacket-type offshore platform in Bohai Bay, the vibration amplitudes of the displacement and the velocity, and the required energy consumption can be reduced significantly. Full article
(This article belongs to the Special Issue Marine Energy)
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Open AccessArticle A New Prediction Model for Transformer Winding Hotspot Temperature Fluctuation Based on Fuzzy Information Granulation and an Optimized Wavelet Neural Network
Energies 2017, 10(12), 1998; doi:10.3390/en10121998
Received: 27 October 2017 / Revised: 18 November 2017 / Accepted: 21 November 2017 / Published: 1 December 2017
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Abstract
Winding hotspot temperature is the key factor affecting the load capacity and service life of transformers. For the early detection of transformer winding hotspot temperature anomalies, a new prediction model for the hotspot temperature fluctuation range based on fuzzy information granulation (FIG) and
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Winding hotspot temperature is the key factor affecting the load capacity and service life of transformers. For the early detection of transformer winding hotspot temperature anomalies, a new prediction model for the hotspot temperature fluctuation range based on fuzzy information granulation (FIG) and the chaotic particle swarm optimized wavelet neural network (CPSO-WNN) is proposed in this paper. The raw data are firstly processed by FIG to extract useful information from each time window. The extracted information is then used to construct a wavelet neural network (WNN) prediction model. Furthermore, the structural parameters of WNN are optimized by chaotic particle swarm optimization (CPSO) before it is used to predict the fluctuation range of the hotspot temperature. By analyzing the experimental data with four different prediction models, we find that the proposed method is more effective and is of guiding significance for the operation and maintenance of transformers. Full article
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Open AccessArticle Numerical Simulation Study on Steam-Assisted Gravity Drainage Performance in a Heavy Oil Reservoir with a Bottom Water Zone
Energies 2017, 10(12), 1999; doi:10.3390/en10121999
Received: 19 September 2017 / Revised: 26 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
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Abstract
In the Pikes Peak oil field near Lloydminster, Canada, a significant amount of heavy oil reserves is located in reservoirs with a bottom water zone. The properties of the bottom water zone and the operation parameters significantly affect oil production performance via the
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In the Pikes Peak oil field near Lloydminster, Canada, a significant amount of heavy oil reserves is located in reservoirs with a bottom water zone. The properties of the bottom water zone and the operation parameters significantly affect oil production performance via the steam-assisted gravity drainage (SAGD) process. Thus, in order to develop this type of heavy oil resource, a full understanding of the effects of these properties is necessary. In this study, the numerical simulation approach was applied to study the effects of properties in the bottom water zone in the SAGD process, such as the initial gas oil ratio, the thickness of the reservoir, and oil saturation of the bottom water zone. In addition, some operation parameters were studied including the injection pressure, the SAGD well pair location, and five different well patterns: (1) two corner wells, (2) triple wells, (3) downhole water sink well, (4) vertical injectors with a horizontal producer, and (5) fishbone well. The numerical simulation results suggest that the properties of the bottom water zone affect production performance extremely. First, both positive and negative effects were observed when solution gas exists in the heavy oil. Second, a logarithmical relationship was investigated between the bottom water production ratio and the thickness of the bottom water zone. Third, a non-linear relation was obtained between the oil recovery factor and oil saturation in the bottom water zone, and a peak oil recovery was achieved at the oil saturation rate of 30% in the bottom water zone. Furthermore, the operation parameters affected the heavy oil production performance. Comparison of the well patterns showed that the two corner wells and the triple wells patterns obtained the highest oil recovery factors of 74.71% and 77.19%, respectively, which are almost twice the oil recovery factors gained in the conventional SAGD process (47.84%). This indicates that the optimized SAGD process with the two corner wells and the triple wells pattern is able to improve SAGD production performance in a heavy oil reservoir with a bottom water zone. Full article
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Open AccessArticle A Comparative Study of Energy Performance of Fumed Silica Vacuum Insulation Panels in an Apartment Building
Energies 2017, 10(12), 2000; doi:10.3390/en10122000
Received: 14 October 2017 / Revised: 23 November 2017 / Accepted: 28 November 2017 / Published: 1 December 2017
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Abstract
Building insulation materials has a significant impact on building energy consumptions. However, conventional materials are easily flammable and can cause fire disasters in buildings. Therefore, it is important to select appropriate insulation materials for building energy efficiency and safety and Vacuum Insulation Panels
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Building insulation materials has a significant impact on building energy consumptions. However, conventional materials are easily flammable and can cause fire disasters in buildings. Therefore, it is important to select appropriate insulation materials for building energy efficiency and safety and Vacuum Insulation Panels (VIPs) are increasingly applied to building insulation. Considering this, the present study investigates energy performance of VIPs with design alternatives, such as window systems, infiltration rates, etc., by using energy simulation. Among various VIPs, fumes silica VIPs were chosen. In addition, eight combinations were compared to find the best energy efficient design conditions. The results of the present study showed that building energy performance can be improved with an appropriate combination of design options including fumed silica VIPs. Full article
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Open AccessArticle Wind Speed Forecasting Based on EMD and GRNN Optimized by FOA
Energies 2017, 10(12), 2001; doi:10.3390/en10122001
Received: 13 November 2017 / Revised: 24 November 2017 / Accepted: 28 November 2017 / Published: 1 December 2017
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Abstract
As a kind of clean and renewable energy, wind power is winning more and more attention across the world. Regarding wind power utilization, safety is a core concern and such concern has led to many studies on predicting wind speed. To obtain a
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As a kind of clean and renewable energy, wind power is winning more and more attention across the world. Regarding wind power utilization, safety is a core concern and such concern has led to many studies on predicting wind speed. To obtain a more accurate prediction of the wind speed, this paper adopts a new hybrid forecasting model, combing empirical mode decomposition (EMD) and the general regression neural network (GRNN) optimized by the fruit fly optimization algorithm (FOA). In this new model, the original wind speed series are first decomposed into a collection of intrinsic mode functions (IMFs) and a residue. Next, the inherent relationship (partial correlation) of the datasets is analyzed, and the results are then used to select the input for the forecasting model. Finally, the GRNN with the FOA to optimize the smoothing factor is used to predict each sub-series. The mean absolute percentage error of the forecasting results in two cases are respectively 8.95% and 9.87%, suggesting that the hybrid approach outperforms the compared models, which provides guidance for future wind speed forecasting. Full article
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Open AccessArticle Phase-Inductance-Based Position Estimation Method for Interior Permanent Magnet Synchronous Motors
Energies 2017, 10(12), 2002; doi:10.3390/en10122002
Received: 3 November 2017 / Revised: 23 November 2017 / Accepted: 24 November 2017 / Published: 1 December 2017
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Abstract
This paper presents a phase-inductance-based position estimation method for interior permanent magnet synchronous motors (IPMSMs). According to the characteristics of phase induction of IPMSMs, the corresponding relationship of the rotor position and the phase inductance is obtained. In order to eliminate the effect
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This paper presents a phase-inductance-based position estimation method for interior permanent magnet synchronous motors (IPMSMs). According to the characteristics of phase induction of IPMSMs, the corresponding relationship of the rotor position and the phase inductance is obtained. In order to eliminate the effect of the zero-sequence component of phase inductance and reduce the rotor position estimation error, the phase inductance difference is employed. With the iterative computation of inductance vectors, the position plane is further subdivided, and the rotor position is extracted by comparing the amplitudes of inductance vectors. To decrease the consumption of computer resources and increase the practicability, a simplified implementation is also investigated. In this method, the rotor position information is achieved easily, with several basic math operations and logical comparisons of phase inductances, without any coordinate transformation or trigonometric function calculation. Based on this position estimation method, the field orientated control (FOC) strategy is established, and the detailed implementation is also provided. A series of experiment results from a prototype demonstrate the correctness and feasibility of the proposed method. Full article
(This article belongs to the Section Electrical Power and Energy System)
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