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Energies, Volume 7, Issue 4 (April 2014), Pages 1852-2739

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Open AccessArticle Development and Field Test of a Real-Time Database in the Korean Smart Distribution Management System
Energies 2014, 7(4), 1852-1875; doi:10.3390/en7041852
Received: 24 November 2013 / Revised: 16 March 2014 / Accepted: 21 March 2014 / Published: 25 March 2014
Cited by 2 | PDF Full-text (2918 KB) | HTML Full-text | XML Full-text
Abstract
Recently, a distribution management system (DMS) that can conduct periodical system analysis and control by mounting various applications programs has been actively developed. In this paper, we summarize the development and demonstration of a database structure that can perform real-time system analysis [...] Read more.
Recently, a distribution management system (DMS) that can conduct periodical system analysis and control by mounting various applications programs has been actively developed. In this paper, we summarize the development and demonstration of a database structure that can perform real-time system analysis and control of the Korean smart distribution management system (KSDMS). The developed database structure consists of a common information model (CIM)-based off-line database (DB), a physical DB (PDB) for DB establishment of the operating server, a real-time DB (RTDB) for real-time server operation and remote terminal unit data interconnection, and an application common model (ACM) DB for running application programs. The ACM DB for real-time system analysis and control of the application programs was developed by using a parallel table structure and a link list model, thereby providing fast input and output as well as high execution speed of application programs. Furthermore, the ACM DB was configured with hierarchical and non-hierarchical data models to reflect the system models that increase the DB size and operation speed through the reduction of the system, of which elements were unnecessary for analysis and control. The proposed database model was implemented and tested at the Gochaing and Jeju offices using a real system. Through data measurement of the remote terminal units, and through the operation and control of the application programs using the measurement, the performance, speed, and integrity of the proposed database model were validated, thereby demonstrating that this model can be applied to real systems. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle Economic Scheduling of Residential Plug-In (Hybrid) Electric Vehicle (PHEV) Charging
Energies 2014, 7(4), 1876-1898; doi:10.3390/en7041876
Received: 13 January 2014 / Revised: 19 March 2014 / Accepted: 19 March 2014 / Published: 25 March 2014
Cited by 3 | PDF Full-text (303 KB) | HTML Full-text | XML Full-text
Abstract
In the past decade, plug-in (hybrid) electric vehicles (PHEVs) have been widely proposed as a viable alternative to internal combustion vehicles to reduce fossil fuel emissions and dependence on petroleum. Off-peak vehicle charging is frequently proposed to reduce the stress on the [...] Read more.
In the past decade, plug-in (hybrid) electric vehicles (PHEVs) have been widely proposed as a viable alternative to internal combustion vehicles to reduce fossil fuel emissions and dependence on petroleum. Off-peak vehicle charging is frequently proposed to reduce the stress on the electric power grid by shaping the load curve. Time of use (TOU) rates have been recommended to incentivize PHEV owners to shift their charging patterns. Many utilities are not currently equipped to provide real-time use rates to their customers, but can provide two or three staggered rate levels. To date, an analysis of the optimal number of levels and rate-duration of TOU rates for a given consumer demographic versus utility generation mix has not been performed. In this paper, we propose to use the U.S. National Household Travel Survey (NHTS) database as a basis to analyze typical PHEV energy requirements. We use Monte Carlo methods to model the uncertainty inherent in battery state-of-charge and trip duration. We conclude the paper with an analysis of a different TOU rate schedule proposed by a mix of U.S. utilities. We introduce a centralized scheduling strategy for PHEV charging using a genetic algorithm to accommodate the size and complexity of the optimization. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle Conditional Methods in Modeling CO2 Capture from Coal Syngas
Energies 2014, 7(4), 1899-1916; doi:10.3390/en7041899
Received: 29 October 2013 / Revised: 10 February 2014 / Accepted: 5 March 2014 / Published: 27 March 2014
Cited by 1 | PDF Full-text (871 KB) | HTML Full-text | XML Full-text
Abstract
Gasification of coal or biomass with in-situ CO2 capture is an emerging technology aiming to address the problem of climate change. Development of a CO2 sorbent with desirable properties and understanding the behavior of such a material in carbonation/calcination reactions [...] Read more.
Gasification of coal or biomass with in-situ CO2 capture is an emerging technology aiming to address the problem of climate change. Development of a CO2 sorbent with desirable properties and understanding the behavior of such a material in carbonation/calcination reactions is an important part of developing the technology. In this paper, we report experimental results describing the carbonation behavior of three synthetic CaO-based sorbents. We also present a physically-based model of the reactive transport processes in sorbent particles, which have complicated pore structures. This modeling is based on the conditional approach (i.e., conditional moment closure (CMC)), which has proven to be successful in modeling reactive transport phenomena in porous media. The model predictions are in good agreement with the experimental data. Full article
(This article belongs to the Special Issue Coal Combustion and Gasification)
Open AccessArticle Influence of Three Dynamic Predictive Clothing Insulation Models on Building Energy Use, HVAC Sizing and Thermal Comfort
Energies 2014, 7(4), 1917-1934; doi:10.3390/en7041917
Received: 25 January 2014 / Revised: 5 March 2014 / Accepted: 19 March 2014 / Published: 27 March 2014
Cited by 3 | PDF Full-text (1270 KB) | HTML Full-text | XML Full-text
Abstract
In building energy simulation, indoor thermal comfort condition, energy use and equipment size are typically calculated based on the assumption that the clothing insulation is equal to a constant value of 0.5 clo during the cooling season and 1.0 clo during the [...] Read more.
In building energy simulation, indoor thermal comfort condition, energy use and equipment size are typically calculated based on the assumption that the clothing insulation is equal to a constant value of 0.5 clo during the cooling season and 1.0 clo during the heating season. The assumption is not reflected in practice and thus it may lead to errors. In reality, occupants frequently adjust their clothing depending on the thermal conditions, as opposed to the assumption of constant clothing values above, indicating that the clothing insulation variation should be captured in building simulation software to obtain more reliable and accurate results. In this study, the impact of three newly developed dynamic clothing insulation models on the building simulation is quantitatively assessed using the detailed whole-building energy simulation program, EnergyPlus version 6.0. The results showed that when the heating ventilation and air conditioning system (HVAC) is controlled based on indoor temperature the dynamic clothing models do not affect indoor operative temperatures, energy consumption and equipment sizing. When the HVAC is controlled based on the PMV model the use of a fixed clothing insulation during the cooling (0.5 clo) and heating (1.0 clo) season leads to the incorrect estimation of the indoor operative temperatures, energy consumption and equipment sizing. The dynamic clothing models significantly (p < 0.0001) improve the ability of energy simulation tools to assess thermal comfort. The authors recommend that the dynamic clothing models should be implemented in dynamic building energy simulation software such as EnergyPlus. Full article
(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)
Open AccessArticle Short-Term Electrical Peak Demand Forecasting in a Large Government Building Using Artificial Neural Networks
Energies 2014, 7(4), 1935-1953; doi:10.3390/en7041935
Received: 7 February 2014 / Revised: 14 March 2014 / Accepted: 24 March 2014 / Published: 27 March 2014
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Abstract
The power output capacity of a local electrical utility is dictated by its customers’ cumulative peak-demand electrical consumption. Most electrical utilities in the United States maintain peak-power generation capacity by charging for end-use peak electrical demand; thirty to seventy percent of an [...] Read more.
The power output capacity of a local electrical utility is dictated by its customers’ cumulative peak-demand electrical consumption. Most electrical utilities in the United States maintain peak-power generation capacity by charging for end-use peak electrical demand; thirty to seventy percent of an electric utility’s bill. To reduce peak demand, a real-time energy monitoring system was designed, developed, and implemented for a large government building. Data logging, combined with an application of artificial neural networks (ANNs), provides short-term electrical load forecasting data for controlled peak demand. The ANN model was tested against other forecasting methods including simple moving average (SMA), linear regression, and multivariate adaptive regression splines (MARSplines) and was effective at forecasting peak building electrical demand in a large government building sixty minutes into the future. The ANN model presented here outperformed the other forecasting methods tested with a mean absolute percentage error (MAPE) of 3.9% as compared to the SMA, linear regression, and MARSplines MAPEs of 7.7%, 17.3%, and 7.0% respectively. Additionally, the ANN model realized an absolute maximum error (AME) of 8.2% as compared to the SMA, linear regression, and MARSplines AMEs of 26.2%, 45.1%, and 22.5% respectively. Full article
(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)
Open AccessArticle Experimental Study on Influence of Pitch Motion on the Wake of a Floating Wind Turbine Model
Energies 2014, 7(4), 1954-1985; doi:10.3390/en7041954
Received: 25 December 2013 / Revised: 14 February 2014 / Accepted: 5 March 2014 / Published: 27 March 2014
Cited by 6 | PDF Full-text (5743 KB) | HTML Full-text | XML Full-text
Abstract
Wind tunnel experiments were performed, where the development of the wake of a model wind turbine was measured using stereo Particle Image Velocimetry to observe the influence of platform pitch motion. The wakes of a classical bottom fixed turbine and a streamwise [...] Read more.
Wind tunnel experiments were performed, where the development of the wake of a model wind turbine was measured using stereo Particle Image Velocimetry to observe the influence of platform pitch motion. The wakes of a classical bottom fixed turbine and a streamwise oscillating turbine are compared. Results indicate that platform pitch creates an upward shift in all components of the flow and their fluctuations. The vertical flow created by the pitch motion as well as the reduced entrainment of kinetic energy from undisturbed flows above the turbine result in potentially higher loads and less available kinetic energy for a downwind turbine. Experimental results are compared with four wake models. The wake models employed are consistent with experimental results in describing the shapes and magnitudes of the streamwise velocity component of the wake for a fixed turbine. Inconsistencies between the model predictions and experimental results arise in the floating case particularly regarding the vertical displacement of the velocity components of the flow. Furthermore, it is found that the additional degrees of freedom of a floating wind turbine add to the complexity of the wake aerodynamics and improved wake models are needed, considering vertical flows and displacements due to pitch motion. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
Open AccessArticle Large-Scale Land Use for Construction and Energy Consumption after the New Millennium with Their Impact on Total-Factor Efficiency Change in China’s Regional Economy
Energies 2014, 7(4), 1986-2003; doi:10.3390/en7041986
Received: 7 February 2014 / Revised: 17 March 2014 / Accepted: 17 March 2014 / Published: 27 March 2014
Cited by 3 | PDF Full-text (329 KB) | HTML Full-text | XML Full-text
Abstract
The rapid economic growth after the new millennium could be characterized by the reappearance of heavy industrialization and land urbanization. In the literatures, extensive studies have examined the impact of energy and emissions on the growth quality during the heavy industrialization process, [...] Read more.
The rapid economic growth after the new millennium could be characterized by the reappearance of heavy industrialization and land urbanization. In the literatures, extensive studies have examined the impact of energy and emissions on the growth quality during the heavy industrialization process, but few have paid attention to the land dimension. This paper aims at studying the role of land use in changing the total-factor efficiency (TFE) in China’s regional economy, together with the energy factors. The basic conclusions obtained are as follows: (1) the land and energy factors do have a statistically significant influence on the total-factor integrated efficiency (TFIE), leading to a much lower and not improved efficiency performance in the sample period. The integrated efficiency is dominated by the land factor rather than energy ones; and (2) the total-factor land efficiency (TFLE) is lower than the energy efficiency and has more room to improve. The land factor has a statistically significant influence on the total-factor energy efficiency (TFEE) but not vice versa. As compared to single-factor efficiency, the total-factor energy/land efficiency provides us a more precise measure of factor efficiency in China. Full article
(This article belongs to the Special Issue Large Scale LUCC, Surface Energy Fluxes and Energy Use)
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Open AccessArticle Sodium Silicate Behavior in Porous Media Applied for In-Depth Profile Modifications
Energies 2014, 7(4), 2004-2026; doi:10.3390/en7042004
Received: 17 January 2014 / Revised: 10 March 2014 / Accepted: 17 March 2014 / Published: 31 March 2014
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Abstract
This paper addresses alkaline sodium silicate (Na-silicate) behavior in porous media. One of the advantages of the Na-silicate system is its water-like injectivity during the placement stage. Mixing Na-silicate with saline water results in metal silicate precipitation as well as immediate gelation. [...] Read more.
This paper addresses alkaline sodium silicate (Na-silicate) behavior in porous media. One of the advantages of the Na-silicate system is its water-like injectivity during the placement stage. Mixing Na-silicate with saline water results in metal silicate precipitation as well as immediate gelation. This work demonstrated that low salinity water (LSW, sea water diluted 25 times) could be used as a pre-flush in flooding operations. A water override phenomenon was observed during gel formation which is caused by gravity segregation. Dynamic adsorption tests in the sand-packed tubes showed inconsiderable adsorbed silicon density (about 8.5 × 10−10 kg/cm3 for a solution with 33 mg/L silicon content), which is less than the estimated mono-layer adsorption density of 1.4 × 10−8 kg/cm3. Na-silicate enhanced water sweep efficiency after application in a dual-permeability sand-pack system, without leak off into the oil-bearing low permeability (LP) zone. Field-scale numerical sensitivity studies in a layered reservoir demonstrated that higher permeability and viscosity contrasts and lower vertical/horizontal permeability ratio result in lower Na-silicate leakoff into the matrix. The length of the mixing zone between reservoir water and the injected Na-silicate solution, which is formed by low salinity pre-flush, acts as a buffer zone. Full article
Open AccessArticle Stochastic Modeling and Optimization in a Microgrid: A Survey
Energies 2014, 7(4), 2027-2050; doi:10.3390/en7042027
Received: 7 February 2014 / Revised: 25 March 2014 / Accepted: 25 March 2014 / Published: 31 March 2014
Cited by 26 | PDF Full-text (565 KB) | HTML Full-text | XML Full-text
Abstract
The future smart grid is expected to be an interconnected network of small-scale and self-contained microgrids, in addition to a large-scale electric power backbone. By utilizing microsources, such as renewable energy sources and combined heat and power plants, microgrids can supply electrical [...] Read more.
The future smart grid is expected to be an interconnected network of small-scale and self-contained microgrids, in addition to a large-scale electric power backbone. By utilizing microsources, such as renewable energy sources and combined heat and power plants, microgrids can supply electrical and heat loads in local areas in an economic and environment friendly way. To better adopt the intermittent and weather-dependent renewable power generation, energy storage devices, such as batteries, heat buffers and plug-in electric vehicles (PEVs) with vehicle-to-grid systems can be integrated in microgrids. However, significant technical challenges arise in the planning, operation and control of microgrids, due to the randomness in renewable power generation, the buffering effect of energy storage devices and the high mobility of PEVs. The two-way communication functionalities of the future smart grid provide an opportunity to address these challenges, by offering the communication links for microgrid status information collection. However, how to utilize stochastic modeling and optimization tools for efficient, reliable and economic planning, operation and control of microgrids remains an open issue. In this paper, we investigate the key features of microgrids and provide a comprehensive literature survey on the stochastic modeling and optimization tools for a microgrid. Future research directions are also identified. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle Priority-Based Hierarchical Operational Management for Multiagent-Based Microgrids
Energies 2014, 7(4), 2051-2078; doi:10.3390/en7042051
Received: 7 February 2014 / Revised: 17 March 2014 / Accepted: 25 March 2014 / Published: 31 March 2014
Cited by 1 | PDF Full-text (6358 KB) | HTML Full-text | XML Full-text
Abstract
Electricity consumption in the world is constantly increasing, making our lives become more and more dependent on electricity. There are several new paradigms proposed in the field of power grids. In Japan, especially after the Great East Japan Earthquake in March 2011, [...] Read more.
Electricity consumption in the world is constantly increasing, making our lives become more and more dependent on electricity. There are several new paradigms proposed in the field of power grids. In Japan, especially after the Great East Japan Earthquake in March 2011, the new power grid paradigms are expected to be more resilient to survive several difficulties during disasters. In this paper, we focus on microgrids and propose priority-based hierarchical operational management for multiagent-based microgrids. The proposed management is a new multiagent-based load shedding scheme and multiagent-based hierarchical architecture to realize such resilient microgrids. We developed a prototype system and performed an evaluation of the proposed management using the developed system. The result of the evaluation shows the effectiveness of our proposal in power shortage situations, such as disasters. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle An Experimental Investigation on the Influence of Temperature on the Normal Impact of Fine Particles with a Plane Surface
Energies 2014, 7(4), 2079-2094; doi:10.3390/en7042079
Received: 20 December 2013 / Revised: 23 March 2014 / Accepted: 25 March 2014 / Published: 31 March 2014
Cited by 1 | PDF Full-text (1323 KB) | HTML Full-text | XML Full-text
Abstract
This study investigated the rebound behavior of SiO2 particles normally impacting a planar surface under different temperature conditions. The system has been characterized for an aerosol inlet temperature range of 20–190 °C, flow velocities of 0–20 ms−1, and an [...] Read more.
This study investigated the rebound behavior of SiO2 particles normally impacting a planar surface under different temperature conditions. The system has been characterized for an aerosol inlet temperature range of 20–190 °C, flow velocities of 0–20 ms−1, and an impaction surface temperature range of 20–140 °C. For the first time, while keeping the same temperature gradient from the high- to low-temperature regions, the influences of varying temperature on the rebound behavior of SiO2 particles normally impacting a plane surface were examined. At increased temperatures, the plastic deformation increases and the coefficient of restitution reduces. The critical velocity is between 0.542 and 0.546 m/s under condition 1 (the carrier gas temperature (Tg) and the impaction surface temperature (TW) remain at room temperature of 20 °C), which increases to between 0.829 and 0.847 m/s under condition 4 (Tg and TW remain at temperatures of 190 °C and 140 °C, respectively). The experimental results show that the critical velocity increases with increasing temperature. Full article
Open AccessArticle Transesterification Kinetics of Waste Vegetable Oil in Supercritical Alcohols
Energies 2014, 7(4), 2095-2106; doi:10.3390/en7042095
Received: 5 January 2014 / Revised: 11 March 2014 / Accepted: 17 March 2014 / Published: 1 April 2014
Cited by 1 | PDF Full-text (340 KB) | HTML Full-text | XML Full-text
Abstract
The kinetic analysis method using the non-isothermal technique was proposed to determine the kinetic parameters for the transesterification reaction of waste vegetable oil (WVO) in supercritical alcohols. To investigate the transesterification of WVO, experiments have been carried out with WVO and alcohols [...] Read more.
The kinetic analysis method using the non-isothermal technique was proposed to determine the kinetic parameters for the transesterification reaction of waste vegetable oil (WVO) in supercritical alcohols. To investigate the transesterification of WVO, experiments have been carried out with WVO and alcohols at three molar ratios of 1:6, 1:12 and 1:18 for both supercritical ethanol (SCE) and supercritical methanol (SCM) at temperatures between 210 °C and 350 °C in a 25 mL batch reactor. The products were analyzed by gas chromatography mass spectrometry (GC-MS). To verify the effectiveness of the proposed kinetic analysis method, the experimental values were compared with the values calculated using the kinetic parameters obtained from this work. It was found that the proposed kinetic analysis method gave reliable kinetic parameters for the transesterification of WVO in supercritical alcohols. It was also seen that SCM was a better solvent than SCE for the transesterification of WVO. Full article
Open AccessArticle Energy and Exergy Analysis of High Temperature Agent Gasification of Biomass
Energies 2014, 7(4), 2107-2122; doi:10.3390/en7042107
Received: 21 January 2014 / Revised: 6 March 2014 / Accepted: 18 March 2014 / Published: 1 April 2014
Cited by 8 | PDF Full-text (614 KB) | HTML Full-text | XML Full-text
Abstract
A chemical equilibrium model was developed to predict the product composition of a biomass gasification system using highly preheated air and steam. The advantages and limitations of this system were discussed from a thermodynamic viewpoint. The first and second law analyses have [...] Read more.
A chemical equilibrium model was developed to predict the product composition of a biomass gasification system using highly preheated air and steam. The advantages and limitations of this system were discussed from a thermodynamic viewpoint. The first and second law analyses have been conducted for various preheating temperatures and steam/biomass mass (S/B) ratios. The results demonstrated that the chemical energy output of the produced syngas is highest when the S/B ratio is 1.83 under the conditions used in this study. However, higher S/B ratios have a negative effect on the energy and exergy efficiencies. Higher preheating temperatures increase the chemical energy of the produced syngas and the two efficiencies. The peak values for the energy and exergy efficiencies are 81.5% and 76.2%, respectively. Based on the calculated limitation values, where the highest chemical energy (exergy) of the produced syngas and maximum achievable efficiencies are determined, a thermodynamically possible operating region is suggested. Full article
Open AccessArticle Effects of Degree of Superheat on the Running Performance of an Organic Rankine Cycle (ORC) Waste Heat Recovery System for Diesel Engines under Various Operating Conditions
Energies 2014, 7(4), 2123-2145; doi:10.3390/en7042123
Received: 26 January 2014 / Revised: 18 March 2014 / Accepted: 18 March 2014 / Published: 1 April 2014
Cited by 9 | PDF Full-text (2100 KB) | HTML Full-text | XML Full-text
Abstract
This study analyzed the variation law of engine exhaust energy under various operating conditions to improve the thermal efficiency and fuel economy of diesel engines. An organic Rankine cycle (ORC) waste heat recovery system with internal heat exchanger (IHE) was designed to [...] Read more.
This study analyzed the variation law of engine exhaust energy under various operating conditions to improve the thermal efficiency and fuel economy of diesel engines. An organic Rankine cycle (ORC) waste heat recovery system with internal heat exchanger (IHE) was designed to recover waste heat from the diesel engine exhaust. The zeotropic mixture R416A was used as the working fluid for the ORC. Three evaluation indexes were presented as follows: waste heat recovery efficiency (WHRE), engine thermal efficiency increasing ratio (ETEIR), and output energy density of working fluid (OEDWF). In terms of various operating conditions of the diesel engine, this study investigated the variation tendencies of the running performances of the ORC waste heat recovery system and the effects of the degree of superheat on the running performance of the ORC waste heat recovery system through theoretical calculations. The research findings showed that the net power output, WHRE, and ETEIR of the ORC waste heat recovery system reach their maxima when the degree of superheat is 40 K, engine speed is 2200 r/min, and engine torque is 1200 N·m. OEDWF gradually increases with the increase in the degree of superheat, which indicates that the required mass flow rate of R416A decreases for a certain net power output, thereby significantly decreasing the risk of environmental pollution. Full article
(This article belongs to the Special Issue Waste Heat Recovery—Strategy and Practice)
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Open AccessArticle Sensitivity Analysis of Parameters Governing the Recovery of Methane from Natural Gas Hydrate Reservoirs
Energies 2014, 7(4), 2148-2176; doi:10.3390/en7042148
Received: 27 November 2013 / Revised: 3 March 2014 / Accepted: 13 March 2014 / Published: 1 April 2014
Cited by 1 | PDF Full-text (2528 KB) | HTML Full-text | XML Full-text
Abstract
Naturally occurring gas hydrates are regarded as an important future source of energy and considerable efforts are currently being invested to develop methods for an economically viable recovery of this resource. The recovery of natural gas from gas hydrate deposits has been [...] Read more.
Naturally occurring gas hydrates are regarded as an important future source of energy and considerable efforts are currently being invested to develop methods for an economically viable recovery of this resource. The recovery of natural gas from gas hydrate deposits has been studied by a number of researchers. Depressurization of the reservoir is seen as a favorable method because of its relatively low energy requirements. While lowering the pressure in the production well seems to be a straight forward approach to destabilize methane hydrates, the intrinsic kinetics of CH4-hydrate decomposition and fluid flow lead to complex processes of mass and heat transfer within the deposit. In order to develop a better understanding of the processes and conditions governing the production of methane from methane hydrates it is necessary to study the sensitivity of gas production to the effects of factors such as pressure, temperature, thermal conductivity, permeability, porosity on methane recovery from naturally occurring gas hydrates. A simplified model is the base for an ensemble of reservoir simulations to study which parameters govern productivity and how these factors might interact. Full article
(This article belongs to the Special Issue Natural Gas Hydrate 2013)
Open AccessArticle An Asymmetrical Fuzzy-Logic-Control-Based MPPT Algorithm for Photovoltaic Systems
Energies 2014, 7(4), 2177-2193; doi:10.3390/en7042177
Received: 14 February 2014 / Revised: 17 March 2014 / Accepted: 20 March 2014 / Published: 1 April 2014
Cited by 13 | PDF Full-text (1349 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a fuzzy-logic-control (FLC) based maximum power point tracking (MPPT) algorithm for photovoltaic (PV) systems is proposed. The power variation and output voltage variation are chosen as inputs of the proposed FLC, which simplifies the calculation. Compared with the conventional [...] Read more.
In this paper, a fuzzy-logic-control (FLC) based maximum power point tracking (MPPT) algorithm for photovoltaic (PV) systems is proposed. The power variation and output voltage variation are chosen as inputs of the proposed FLC, which simplifies the calculation. Compared with the conventional perturb and observe (P&O) method, the proposed FLC-based MPPT can simultaneously improve the dynamic and steady state performance of the PV system. To further improve the performance of the proposed method, an asymmetrical membership function (MF) concept is also proposed. Two design procedures are proposed to determine the universe of discourse (UOD) of the input MF. Comparing with the proposed symmetrical FLC-based MPPT method, the transient time and the MPPT tracking accuracy are further improved by 42.8% and 0.06%, respectively. Full article
Open AccessArticle Spatial Variation of Surface Energy Fluxes Due to Land Use Changes across China
Energies 2014, 7(4), 2194-2206; doi:10.3390/en7042194
Received: 22 January 2014 / Revised: 13 March 2014 / Accepted: 1 April 2014 / Published: 8 April 2014
Cited by 1 | PDF Full-text (866 KB) | HTML Full-text | XML Full-text
Abstract
We estimate the heat flux changes caused by the projected land transformation over the next 40 years across China to improve the understanding of the impacts of land dynamics on regional climate. We use the Weather Research and Forecasting (WRF) model to [...] Read more.
We estimate the heat flux changes caused by the projected land transformation over the next 40 years across China to improve the understanding of the impacts of land dynamics on regional climate. We use the Weather Research and Forecasting (WRF) model to investigate these impacts in four representative land transformation zones, where reclamation, overgrazing, afforestation, and urbanization dominates the land use and land cover changes in each zone respectively. As indicated by the significant variance of albedo due to different land use and cover changes, different surface properties cause great spatial variance of the surface flux. From the simulation results, latent heat flux increases by 2 and 21 W/m2 in the reclamation and afforestation regions respectively. On the contrary, overgrazing and urban expansion results in decrease of latent heat flux by 5 and 36 W/m2 correspondingly. Urban expansion leads to an average increase of 40 W/m2 of sensible heat flux in the future 40 years, while reclamation, afforestation, as well as overgrazing result in the decrease of sensible heat flux. Results also show that reclamation and overgrazing lead to net radiation decrease by approximately 4 and 7 W/m2 respectively, however, afforestation and urbanization lead to net radiation increase by 6 and 3 W/m2 respectively. The simulated impacts of projected HLCCs on surface energy fluxes will inform sustainable land management and climate change mitigation. Full article
(This article belongs to the Special Issue Large Scale LUCC, Surface Energy Fluxes and Energy Use)
Open AccessArticle Analysis of the Energy Balance of Shale Gas Development
Energies 2014, 7(4), 2207-2227; doi:10.3390/en7042207
Received: 26 November 2013 / Revised: 27 March 2014 / Accepted: 30 March 2014 / Published: 8 April 2014
Cited by 5 | PDF Full-text (1628 KB) | HTML Full-text | XML Full-text
Abstract
Interest has rapidly grown in the use of unconventional resources to compensate for depletion of conventional hydrocarbon resources (“easy hydrocarbon”) that are produced at relatively low cost from oil and gas fields with large proven reserves. When one wants to ensure the [...] Read more.
Interest has rapidly grown in the use of unconventional resources to compensate for depletion of conventional hydrocarbon resources (“easy hydrocarbon”) that are produced at relatively low cost from oil and gas fields with large proven reserves. When one wants to ensure the prospects for development of unconventional resources that are potentially vast in terms of their energy potential, it is essential to determine the quality of that energy. Here we consider the development of shale gas, an unconventional energy resource of particularly strong interest of late, through analysis of its energy return on investment (EROI), a key indicator for qualitative assessment of energy resources. We used a Monte Carlo approach for the carbon footprint of U.S. operations in shale gas development to estimate expected ranges of EROI values by incorporating parameter variability. We obtained an EROI of between 13 and 23, with a mean of approximately 17 at the start of the pipeline. When we incorporated all the costs required to bring shale gas to the consumer, the mean value of EROI drops from about 17 at the start of the pipeline to 12 when delivered to the consumer. The shale gas EROI values estimated in the present study are in the initial stage of shale gas exploitation where the quality of that resource may be considerably higher than the mean and thus the careful and continuous investigation of change in EROI is needed, especially as production moves off the initial “sweet spots”. Full article
Open AccessArticle Taxing Strategies for Carbon Emissions: A Bilevel Optimization Approach
Energies 2014, 7(4), 2228-2245; doi:10.3390/en7042228
Received: 26 January 2014 / Revised: 4 April 2014 / Accepted: 4 April 2014 / Published: 9 April 2014
Cited by 4 | PDF Full-text (483 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a quantitative and computational method to determine the optimal tax rate among generating units. To strike a balance between the reduction of carbon emission and the profit of energy sectors, the proposed bilevel optimization model can be regarded as [...] Read more.
This paper presents a quantitative and computational method to determine the optimal tax rate among generating units. To strike a balance between the reduction of carbon emission and the profit of energy sectors, the proposed bilevel optimization model can be regarded as a Stackelberg game between the government agency and the generation companies. The upper-level, which represents the government agency, aims to limit total carbon emissions within a certain level by setting optimal tax rates among generators according to their emission performances. The lower-level, which represents decision behaviors of the grid operator, tries to minimize the total production cost under the tax rates set by the government. The bilevel optimization model is finally reformulated into a mixed integer linear program (MILP) which can be solved by off-the-shelf MILP solvers. Case studies on a 10-unit system as well as a provincial power grid in China demonstrate the validity of the proposed method and its capability in practical applications. Full article
(This article belongs to the Special Issue Energy Transitions and Economic Change)
Open AccessArticle Balancing Power Output and Structural Fatigue of Wave Energy Converters by Means of Control Strategies
Energies 2014, 7(4), 2246-2273; doi:10.3390/en7042246
Received: 25 December 2013 / Revised: 11 March 2014 / Accepted: 19 March 2014 / Published: 9 April 2014
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Abstract
In order to reduce the cost of electricity produced by wave energy converters (WECs), the benefit of selling electricity as well as the investment costs of the structure has to be considered. This paper presents a methodology for assessing the control strategy [...] Read more.
In order to reduce the cost of electricity produced by wave energy converters (WECs), the benefit of selling electricity as well as the investment costs of the structure has to be considered. This paper presents a methodology for assessing the control strategy for a WEC with respect to both energy output and structural fatigue loads. Different active and passive control strategies are implemented (proportional (P) controller, proportional-integral (PI) controller, proportional-integral-derivative with memory compensation (PID) controller, model predictive control (MPC) and maximum energy controller (MEC)), and load time-series resulting from numerical simulations are used to design structural parts based on fatigue analysis using rain-flow counting, Stress-Number (SN) curves and Miner’s rule. The objective of the methodology is to obtain a cost-effective WEC with a more comprehensive analysis of a WEC based on a combination of well known control strategies and standardised fatigue methods. The presented method is then applied to a particular case study, the Wavestar WEC, for a specific location in the North Sea. Results, which are based on numerical simulations, show the importance of balancing the gained power against structural fatigue. Based on a simple cost model, the PI controller is shown as a viable solution. Full article
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Open AccessArticle Failure Test and Finite Element Simulation of a Large Wind Turbine Composite Blade under Static Loading
Energies 2014, 7(4), 2274-2297; doi:10.3390/en7042274
Received: 9 December 2013 / Revised: 26 March 2014 / Accepted: 27 March 2014 / Published: 10 April 2014
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Abstract
This study presented a failure analysis of a 52.3 m composite wind turbine blade under static loading. Complex failure characteristics exhibited at the transition region of the blade were thoroughly examined and typical failure modes were indentified. In order to predict multiple [...] Read more.
This study presented a failure analysis of a 52.3 m composite wind turbine blade under static loading. Complex failure characteristics exhibited at the transition region of the blade were thoroughly examined and typical failure modes were indentified. In order to predict multiple failure modes observed in the tests and gain more insights into the failure mechanisms of the blade, a Finite Element (FE) simulation was performed using a global-local modeling approach and Progressive Failure Analysis (PFA) techniques which took into account material failure and property degradation. Failure process and failure characteristics of the transition region were satisfactorily reproduced in the simulation, and it was found that accumulated delamination in spar cap and shear web failure at the transition region were the main reasons for the blade to collapse. Local buckling played an important role in the failure process by increasing local out-of-plane deformation, while the Brazier effect was found not to be responsible for the blade failure. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
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Open AccessArticle Spatiotemporal Variability of Carbon Flux from Different Land Use and Land Cover Changes: A Case Study in Hubei Province, China
Energies 2014, 7(4), 2298-2316; doi:10.3390/en7042298
Received: 23 January 2014 / Revised: 26 March 2014 / Accepted: 3 April 2014 / Published: 10 April 2014
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Abstract
Carbon sources and sinks as a result of land use and land cover changes (LUCC) are significant for global climate change. This paper aims to identify and analyze the temporal and spatial changes of land use-based carbon emission in the Hubei Province [...] Read more.
Carbon sources and sinks as a result of land use and land cover changes (LUCC) are significant for global climate change. This paper aims to identify and analyze the temporal and spatial changes of land use-based carbon emission in the Hubei Province in China. We use a carbon emission coefficient to calculate carbon emissions in different land use patterns in Hubei Province from 1998 to 2009. The results indicate that regional land use is facing tremendous pressure from rapid carbon emission growth. Source:sink ratios and average carbon emission intensity values of urban land are increasing, while slow-growing carbon sinks fail to offset the rapidly expanding carbon sources. Overall, urban land carbon emissions have a strong correlation with the total carbon emissions, and will continue to increase in the future mainly due to the surge of industrialization and urbanization. Furthermore, carbon emission in regions with more developed industrial structures is much higher than in regions with less advanced industrial structures. Lastly, carbon emission per unit of GDP has declined since 2004, indicating that a series of reform measures i.e., economic growth mode transformation and land-use structure optimization, has initiated the process of carbon emission reduction. Full article
(This article belongs to the Special Issue Large Scale LUCC, Surface Energy Fluxes and Energy Use)
Open AccessArticle Pricing Energy and Ancillary Services in a Day-Ahead Market for a Price-Taker Hydro Generating Company Using a Risk-Constrained Approach
Energies 2014, 7(4), 2317-2342; doi:10.3390/en7042317
Received: 13 October 2013 / Revised: 24 March 2014 / Accepted: 8 April 2014 / Published: 11 April 2014
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Abstract
This paper analyzes a price-taker hydro generating company which participates simultaneously in day-ahead energy and ancillary services markets. An approach for deriving marginal cost curves for energy and ancillary services is proposed, taking into consideration price uncertainty and opportunity cost of water, [...] Read more.
This paper analyzes a price-taker hydro generating company which participates simultaneously in day-ahead energy and ancillary services markets. An approach for deriving marginal cost curves for energy and ancillary services is proposed, taking into consideration price uncertainty and opportunity cost of water, which can later be used to determine hourly bid curves. The proposed approach combines an hourly conditional value-at-risk, probability of occurrence of automatic generation control states and an opportunity cost of water to determine energy and ancillary services marginal cost curves. The proposed approach is in a linear constraint form and is easy to implement in optimization problems. A stochastic model of the hydro-economic river basin is presented, based on the actual Vinodol hydropower system in Croatia, with a complex three-dimensional relationship between the power produced, the discharged water, and the head of associated reservoir. Full article
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Open AccessArticle Summer and Winter Effect of Innovative Cool Roof Tiles on the Dynamic Thermal Behavior of Buildings
Energies 2014, 7(4), 2343-2361; doi:10.3390/en7042343
Received: 30 January 2014 / Revised: 27 March 2014 / Accepted: 9 April 2014 / Published: 14 April 2014
Cited by 27 | PDF Full-text (1695 KB) | HTML Full-text | XML Full-text
Abstract
Cool roofs represent an acknowledged passive cooling technique to reduce building energy consumption for cooling and to mitigate urban heat island effects. This paper concerns the evaluation of the dynamic effect of new cool roof clay tiles on building thermal performance in [...] Read more.
Cool roofs represent an acknowledged passive cooling technique to reduce building energy consumption for cooling and to mitigate urban heat island effects. This paper concerns the evaluation of the dynamic effect of new cool roof clay tiles on building thermal performance in summer and winter conditions. To this end, these properties have been analyzed on traditional roof brick tiles through an indoor and outdoor two-year long continuous monitoring campaign set up in a residential building located in central Italy. The analysis and the cooperation with industrial companies producing brick tiles and reflective coatings allowed the production of a new tile with notable “cool roof” properties through the traditional industrial manufacturing path of such tiles. Notable results show that during summer the high reflection tiles are able to decrease the average external roof surface temperature by more than 10 °C and the indoor operative temperature by more than 3 °C. During winter the average external surface temperature is lower with high reflection tiles by about 1 °C. Singular optic-thermal phenomena are registered while evaluating the dynamics of the cool roof effect. Interesting findings show how the sloped cool roof application could suggest further considerations about the dynamic effect of cool roofs. Full article
(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)
Open AccessArticle Window Material Daylighting Performance Assessment Algorithm: Comparing Radiosity and Split-Flux Methods
Energies 2014, 7(4), 2362-2376; doi:10.3390/en7042362
Received: 2 March 2014 / Revised: 2 April 2014 / Accepted: 8 April 2014 / Published: 14 April 2014
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Abstract
Windows are the primary aperture to introduce solar radiation to the interior space of a building. This experiment explores the use of EnergyPlus software for analyzing the illuminance level on the floor of a room with reference to its distance from the [...] Read more.
Windows are the primary aperture to introduce solar radiation to the interior space of a building. This experiment explores the use of EnergyPlus software for analyzing the illuminance level on the floor of a room with reference to its distance from the window. For this experiment, a double clear glass window has been used. The preliminary modelling in EnergyPlus showed a consistent result with the experimentally monitored data in real time. EnergyPlus has two mainly used daylighting algorithms: DElight method employing radiosity technique and Detailed method employing split-flux technique. Further analysis for illuminance using DElight and Detailed methods showed significant difference in the results. Finally, we compared the algorithms of the two analysis methods in EnergyPlus. Full article
(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)
Open AccessArticle Modeling of Clostridium tyrobutyricum for Butyric Acid Selectivity in Continuous Fermentation
Energies 2014, 7(4), 2421-2435; doi:10.3390/en7042421
Received: 14 January 2014 / Revised: 27 March 2014 / Accepted: 4 April 2014 / Published: 17 April 2014
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Abstract
A mathematical model was developed to describe batch and continuous fermentation of glucose to organic acids with Clostridium tyrobutyricum. A modified Monod equation was used to describe cell growth, and a Luedeking-Piret equation was used to describe the production of butyric [...] Read more.
A mathematical model was developed to describe batch and continuous fermentation of glucose to organic acids with Clostridium tyrobutyricum. A modified Monod equation was used to describe cell growth, and a Luedeking-Piret equation was used to describe the production of butyric and acetic acids. Using the batch fermentation equations, models predicting butyric acid selectivity for continuous fermentation were also developed. The model showed that butyric acid production was a strong function of cell mass, while acetic acid production was a function of cell growth rate. Further, it was found that at high acetic acid concentrations, acetic acid was metabolized to butyric acid and that this conversion could be modeled. In batch fermentation, high butyric acid selectivity occurred at high initial cell or glucose concentrations. In continuous fermentation, decreased dilution rate improved selectivity; at a dilution rate of 0.028 h−1, the selectivity reached 95.8%. The model and experimental data showed that at total cell recycle, the butyric acid selectivity could reach 97.3%. This model could be used to optimize butyric acid production using C. tyrobutyricum in a continuous fermentation scheme. This is the first study that mathematically describes batch, steady state, and dynamic behavior of C. tyrobutyricum for butyric acid production. Full article
Open AccessArticle Dynamic Response of a 50 kW Organic Rankine Cycle System in Association with Evaporators
Energies 2014, 7(4), 2436-2448; doi:10.3390/en7042436
Received: 29 January 2014 / Revised: 23 March 2014 / Accepted: 9 April 2014 / Published: 17 April 2014
Cited by 12 | PDF Full-text (334 KB) | HTML Full-text | XML Full-text
Abstract
The influences of various evaporators on the system responses of a 50 kW ORC system using R-245fa are investigated in this study. First the effect of the supplied hot water flowrate into the evaporator is examined and the exit superheat on the [...] Read more.
The influences of various evaporators on the system responses of a 50 kW ORC system using R-245fa are investigated in this study. First the effect of the supplied hot water flowrate into the evaporator is examined and the exit superheat on the system performance between plate and shell-and-tube evaporator is also reported. Test results show that the effect of hot water flowrate on the evaporator imposes a negligible effect on the transient response of the ORC system. These results prevail even for a 3.5-fold increase of the hot water flowrate and the system shows barely any change subject to this drastic hot water flowrate change. The effect of exit superheat on the ORC system depends on the type of the evaporator. For the plate evaporator, an exit superheat less than 10 °C may cause ORC system instability due to considerable liquid entrainment. To maintain a stable operation, the corresponding Jakob number of the plate heat evaporator must be above 0.07. On the other hand, by employing a shell and tube heat evaporator connected to the ORC system, no unstable oscillation of the ORC system is observed for exit superheats ranging from 0 to 17 °C. Full article
(This article belongs to the Special Issue Waste Heat Recovery—Strategy and Practice)
Open AccessArticle Optimal Charging Scheduling of Electric Vehicles in Smart Grids by Heuristic Algorithms
Energies 2014, 7(4), 2449-2475; doi:10.3390/en7042449
Received: 30 January 2014 / Revised: 10 April 2014 / Accepted: 14 April 2014 / Published: 17 April 2014
Cited by 6 | PDF Full-text (1108 KB) | HTML Full-text | XML Full-text
Abstract
Transportation electrification has become an important issue in recent decades and the large scale deployment of electric vehicles (EVs) has yet to be achieved. The smart coordination of EV demand addresses an improvement in the flexibility of power systems and reduces the [...] Read more.
Transportation electrification has become an important issue in recent decades and the large scale deployment of electric vehicles (EVs) has yet to be achieved. The smart coordination of EV demand addresses an improvement in the flexibility of power systems and reduces the costs of power system investment. The uncertainty in EV drivers’ behaviour is one of the main problems to solve to obtain an optimal integration of EVs into power systems. In this paper, an optimisation algorithm to coordinate the charging of EVs has been developed and implemented using a Genetic Algorithm (GA), where thermal line limits, the load on transformers, voltage limits and parking availability patterns are taken into account to establish an optimal load pattern for EV charging-based reliability. This methodology has been applied to an existing residential low-voltage system. The results indicate that a smart charging schedule for EVs leads to a flattening of the load profile, peak load shaving and the prevention of the aging of power system elements. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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Open AccessArticle Design of a Control Scheme for Distribution Static Synchronous Compensators with Power-Quality Improvement Capability
Energies 2014, 7(4), 2476-2497; doi:10.3390/en7042476
Received: 15 February 2014 / Revised: 6 April 2014 / Accepted: 16 April 2014 / Published: 22 April 2014
Cited by 3 | PDF Full-text (1076 KB) | HTML Full-text | XML Full-text
Abstract
Electric power systems are among the greatest achievements of the last century. Today, important issues, such as an ever-increasing demand, the flexible and reliable integration of distributed generation or a growth in disturbing loads, must be borne in mind. In this context, [...] Read more.
Electric power systems are among the greatest achievements of the last century. Today, important issues, such as an ever-increasing demand, the flexible and reliable integration of distributed generation or a growth in disturbing loads, must be borne in mind. In this context, smart grids play a key role, allowing better efficiency of power systems. Power electronics provides solutions to the aforementioned matters, since it allows various energy sources to be integrated into smart grids. Nevertheless, the design of the various control schemes that are necessary for the correct operation of the power-electronic interface is a very important issue that must always be taken into consideration. This paper deals with the design of the control system of a distribution static synchronous compensator (DSTATCOM) based on flying-capacitor multilevel converters. The control system is tailored to compensate for both voltage sags by means of reactive-power injection and voltage imbalances caused by unbalanced loads. The design of the overall control is carried out by using the root-locus and frequency-response techniques, improving both the transient response and the steady-state error of the closed-loop system. Simulation results obtained using PSCADTM/EMTDCTM (Manitoba Hydro International Ltd., Commerce Drive, Winnipeg, MB, Canada) show the resultant voltage regulation. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle Compact Design of 10 kW Proton Exchange Membrane Fuel Cell Stack Systems with Microcontroller Units
Energies 2014, 7(4), 2498-2514; doi:10.3390/en7042498
Received: 13 December 2013 / Revised: 18 February 2014 / Accepted: 21 March 2014 / Published: 22 April 2014
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Abstract
In this study, fuel, oxidant supply and cooling systems with microcontroller units (MCU) are developed in a compact design to fit two 5 kW proton exchange membrane fuel cell (PEMFC) stacks. At the initial stage, the testing facility of the system has [...] Read more.
In this study, fuel, oxidant supply and cooling systems with microcontroller units (MCU) are developed in a compact design to fit two 5 kW proton exchange membrane fuel cell (PEMFC) stacks. At the initial stage, the testing facility of the system has a large volume (2.0 m × 2.0 m × 1.5 m) with a longer pipeline and excessive control sensors for safe testing. After recognizing the performance and stability of stack, the system is redesigned to fit in a limited space (0.4 m × 0.5 m × 0.8 m). Furthermore, the stack performance is studied under different hydrogen recycling modes. Then, two similar 5 kW stacks are directly coupled with diodes to obtain a higher power output and safe operation. The result shows that the efficiency of the 5 kW stack is 43.46% with a purge period of 2 min with hydrogen recycling and that the hydrogen utilization rate µf is 66.31%. In addition, the maximum power output of the twin-coupled module (a power module with two stacks in electrical cascade/parallel arrangement) is 9.52 kW. Full article
(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells)
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Open AccessArticle Wetland Changes and Their Responses to Climate Change in the “Three-River Headwaters” Region of China since the 1990s
Energies 2014, 7(4), 2515-2534; doi:10.3390/en7042515
Received: 23 January 2014 / Revised: 6 March 2014 / Accepted: 31 March 2014 / Published: 22 April 2014
Cited by 13 | PDF Full-text (1765 KB) | HTML Full-text | XML Full-text
Abstract
The wetland ecosystem in the “Three-River Headwaters” (TRH) region plays an irreplaceable role in water source conservation, run-off adjustment and biodiversity maintenance. In recent years, assessment of wetland resources affected by climate changes has aroused enormous attention, since it can further protect [...] Read more.
The wetland ecosystem in the “Three-River Headwaters” (TRH) region plays an irreplaceable role in water source conservation, run-off adjustment and biodiversity maintenance. In recent years, assessment of wetland resources affected by climate changes has aroused enormous attention, since it can further protect wetland resources and provide a scientific basis for decision makers. In this study, wetland changes and its response to climate changes in the TRH region from the early 1990s to 2012 were analyzed by remote sensing (RS) image interpretation and climate change trend analysis. The results showed that wetlands occupied 6.3% of the total land area in 2012, and swamps, streams & rivers and lakes were the dominant wetland types in the TRH region. Since the early 1990s, wetlands have undergone great changes, and total wetland area increased by 260.57 km2 (1.17%). Lakes, reservoir & ponds took on continuous increasing trend, but swamps, streams & rivers had a continuous decreasing trend. On the other hand, the wetland area in the Yangtze River basin showed an overall increasing trend, while in the Yellow River and Langcang River basins, it decreased in general. The climate turned from Warm-Dry to Warm-Wet. The average temperature and precipitation increased by 0.91 °C and 101.99 mm, respectively, from 1990 to 2012, and the average humidity index (HI) increased by 0.06 and showing an upward trend and a shifting of the dividing line towards the northwest in both the areas of semi-humid and semi-arid zone. The correlation analysis of wetland changes with meteorological factors from 1990 to 2012 indicated that the regional humidity differences and the interannual variation trend, caused by the change of precipitation and evaporation, was the main driving factor for the dynamic variation of wetland change in the TRH region. In the general, the increase of HI in the THR region since the 1990s, especially in the western TRH region, contributed to wetland increase continuously. The conclusions of this study will provide some scientific references for the management and protection of wetlands in the TRH region, especially for restoration, reconstruction and conservation of degradation wetland. Full article
(This article belongs to the Special Issue Large Scale LUCC, Surface Energy Fluxes and Energy Use)
Open AccessArticle Energy-Efficient Power Allocation Using Probabilistic Interference Model for OFDM-Based Green Cognitive Radio Networks
Energies 2014, 7(4), 2535-2557; doi:10.3390/en7042535
Received: 20 January 2014 / Revised: 8 April 2014 / Accepted: 9 April 2014 / Published: 22 April 2014
Cited by 3 | PDF Full-text (348 KB) | HTML Full-text | XML Full-text
Abstract
We study the energy-efficient power allocation techniques for OFDM-based cognitive radio (CR) networks, where a CR transmitter is communicating with CR receivers on a channel borrowed from licensed primary users (PUs). Due to non-orthogonality of the transmitted signals in the adjacent bands, [...] Read more.
We study the energy-efficient power allocation techniques for OFDM-based cognitive radio (CR) networks, where a CR transmitter is communicating with CR receivers on a channel borrowed from licensed primary users (PUs). Due to non-orthogonality of the transmitted signals in the adjacent bands, both the PU and the cognitive secondary user (SU) cause mutual-interference. We assume that the statistical channel state information between the cognitive transmitter and the primary receiver is known. The secondary transmitter maintains a specified statistical mutual-interference limits for all the PUs communicating in the adjacent channels. Our goal is to allocate subcarrier power for the SU so that the energy efficiency metric is optimized as well as the mutual-interference on all the active PU bands are below specified bounds. We show that the green power loading problem is a fractional programming problem. We use Charnes-Cooper transformation technique to obtain an equivalent concave optimization problem for what the solution can be readily obtained. We also propose iterative Dinkelbach method using parametric objective function for the fractional program. Numerical results are given to show the effect of different interference parameters, rate and power thresholds, and number of PUs. Full article
(This article belongs to the Special Issue Green IT and IT for Smart Energy Savings)
Open AccessArticle Geometric Characteristics of Three Dimensional Reconstructed Anode Electrodes of Lithium Ion Batteries
Energies 2014, 7(4), 2558-2572; doi:10.3390/en7042558
Received: 25 February 2014 / Revised: 31 March 2014 / Accepted: 1 April 2014 / Published: 22 April 2014
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Abstract
The realistic three dimensional (3D) microstructure of lithium ion battery (LIB) electrode plays a key role in studying the effects of inhomogeneous microstructures on the performance of LIBs. However, the complexity of realistic microstructures imposes a significant computational cost on numerical simulation [...] Read more.
The realistic three dimensional (3D) microstructure of lithium ion battery (LIB) electrode plays a key role in studying the effects of inhomogeneous microstructures on the performance of LIBs. However, the complexity of realistic microstructures imposes a significant computational cost on numerical simulation of large size samples. In this work, we used tomographic data obtained for a commercial LIB graphite electrode to evaluate the geometric characteristics of the reconstructed electrode microstructure. Based on the analysis of geometric properties, such as porosity, specific surface area, tortuosity, and pore size distribution, a representative volume element (RVE) that retains the geometric characteristics of the electrode material was obtained for further numerical studies. In this work, X-ray micro-computed tomography (CT) with 0.56 μm resolution was employed to capture the inhomogeneous porous microstructures of LIB anode electrodes. The Sigmoid transform function was employed to convert the initial raw tomographic images to binary images. Moreover, geometric characteristics of an anode electrode after 2400 cycles at the charge/discharge rate of 1 C were compared with those of a new anode electrode to investigate morphological change of the electrode. In general, the cycled electrode shows larger porosity, smaller tortuosity, and similar specific surface area compared to the new electrode. Full article
(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)
Open AccessArticle Implications of Spatial Variability in Heat Flow for Geothermal Resource Evaluation in Large Foreland Basins: The Case of the Western Canada Sedimentary Basin
Energies 2014, 7(4), 2573-2594; doi:10.3390/en7042573
Received: 13 February 2014 / Revised: 28 March 2014 / Accepted: 10 April 2014 / Published: 22 April 2014
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Abstract
Heat flow and geothermal gradient of the sedimentary succession of the Western Canada Sedimentary Basin (WCSB) are mapped based on a large thermal database. Heat flow in the deep part of the basin varies from 30 mW/m2 in the south to [...] Read more.
Heat flow and geothermal gradient of the sedimentary succession of the Western Canada Sedimentary Basin (WCSB) are mapped based on a large thermal database. Heat flow in the deep part of the basin varies from 30 mW/m2 in the south to high 100 mW/m2 in the north. As permeable strata are required for a successful geothermal application, the most important aquifers are discussed and evaluated. Regional temperature distribution within different aquifers is mapped for the first time, enabling a delineation of the most promising areas based on thermal field and aquifer properties. Results of previous regional studies on the geothermal potential of the WCSB are newly evaluated and discussed. In parts of the WCSB temperatures as high as 100–210 °C exist at depths of 3–5 km. Fluids from deep aquifers in these “hot” regions of the WCSB could be used in geothermal power plants to produce electricity. The geothermal resources of the shallower parts of the WCSB (>2 km) could be used for warm water provision (>50 °C) or district heating (>70 °C) in urban areas. Full article
Open AccessArticle A Wide-Area Measurement Systems-Based Adaptive Strategy for Controlled Islanding in Bulk Power Systems
Energies 2014, 7(4), 2631-2657; doi:10.3390/en7042631
Received: 13 December 2013 / Revised: 25 March 2014 / Accepted: 2 April 2014 / Published: 23 April 2014
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Abstract
Controlled islanding is the last countermeasure for a bulk power system when it suffers from severe cascading contingencies. The objective of controlled islanding is to maintain the stability of each island and to keep the total loss of loads of the whole [...] Read more.
Controlled islanding is the last countermeasure for a bulk power system when it suffers from severe cascading contingencies. The objective of controlled islanding is to maintain the stability of each island and to keep the total loss of loads of the whole system to a minimum. This paper presents a novel integrated wide-area measurement systems (WAMS)-based adaptive controlled islanding strategy, which depends on the dynamic post-fault trajectories under different failure modes. We first utilize an improved Laplacian eigenmap algorithm (ILEA) to identify the coherent generators and use the slow coherency grouping algorithm to guarantee coherent stability within an island. Using the identification result, we then define the minimum coherent generator virtual nodes to reduce the searching space in a graph and utilize the k-way partitioning (KWP) algorithm to obtain a preliminary partition of the simplified graph. Based on the preliminary partition, we consider the direction of power flow and propose a variable neighborhood heuristic searching algorithm to search the optimal separation surfaces so that the net imbalanced power of islands is minimized. Finally, the bidirectional power flow tracing algorithm and PQ decomposition power flow analysis are utilized to determine the corrective controls within each island. The test results with the New England 39-bus system and the IEEE 118-bus system show that the proposed integrated controlled islanding strategy can automatically adapt to different fault modes through generator coherency identification and effectively group the different coherent generators into different islands. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle Fault Detection and Location by Static Switches in Microgrids Using Wavelet Transform and Adaptive Network-Based Fuzzy Inference System
Energies 2014, 7(4), 2658-2675; doi:10.3390/en7042658
Received: 7 February 2014 / Revised: 4 April 2014 / Accepted: 9 April 2014 / Published: 23 April 2014
Cited by 2 | PDF Full-text (660 KB) | HTML Full-text | XML Full-text
Abstract
Microgrids are a highly efficient means of embedding distributed generation sources in a power system. However, if a fault occurs inside or outside the microgrid, the microgrid should be immediately disconnected from the main grid using a static switch installed at the [...] Read more.
Microgrids are a highly efficient means of embedding distributed generation sources in a power system. However, if a fault occurs inside or outside the microgrid, the microgrid should be immediately disconnected from the main grid using a static switch installed at the secondary side of the main transformer near the point of common coupling (PCC). The static switch should have a reliable module implemented in a chip to detect/locate the fault and activate the breaker to open the circuit immediately. This paper proposes a novel approach to design this module in a static switch using the discrete wavelet transform (DWT) and adaptive network-based fuzzy inference system (ANFIS). The wavelet coefficient of the fault voltage and the inference results of ANFIS with the wavelet energy of the fault current at the secondary side of the main transformer determine the control action (open or close) of a static switch. The ANFIS identifies the faulty zones inside or outside the microgrid. The proposed method is applied to the first outdoor microgrid test bed in Taiwan, with a generation capacity of 360.5 kW. This microgrid test bed is studied using the real-time simulator eMegaSim developed by Opal-RT Technology Inc. (Montreal, QC, Canada). The proposed method based on DWT and ANFIS is implemented in a field programmable gate array (FPGA) by using the Xilinx System Generator. Simulation results reveal that the proposed method is efficient and applicable in the real-time control environment of a power system. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle An Approach to Determine the Weibull Parameters for Wind Energy Analysis: The Case of Galicia (Spain)
Energies 2014, 7(4), 2676-2700; doi:10.3390/en7042676
Received: 19 February 2014 / Revised: 21 March 2014 / Accepted: 21 March 2014 / Published: 23 April 2014
Cited by 5 | PDF Full-text (588 KB) | HTML Full-text | XML Full-text
Abstract
The Weibull probability density function (PDF) has mostly been used to fit wind speed distributions for wind energy applications. The goodness of fit of the results depends on the estimation method that was used and the wind type of the analyzed area. [...] Read more.
The Weibull probability density function (PDF) has mostly been used to fit wind speed distributions for wind energy applications. The goodness of fit of the results depends on the estimation method that was used and the wind type of the analyzed area. In this paper, a study on a particular area (Galicia) was performed to test the performance of several fitting methods. The goodness of fit was evaluated by well-known indicators that use the wind speed or the available wind power density. However, energy production must be a critical parameter in wind energy applications. Hence, a fitting method that accounts for the power density distribution is proposed. To highlight the usefulness of this method, indicators that use energy production values are also presented. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
Open AccessArticle Optimal Time to Invest Energy Storage System under Uncertainty Conditions
Energies 2014, 7(4), 2701-2719; doi:10.3390/en7042701
Received: 8 February 2014 / Revised: 16 April 2014 / Accepted: 18 April 2014 / Published: 24 April 2014
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Abstract
This paper proposes a model to determine the optimal investment time for energy storage systems (ESSs) in a price arbitrage trade application under conditions of uncertainty over future profits. The adoption of ESSs can generate profits from price arbitrage trade, which are [...] Read more.
This paper proposes a model to determine the optimal investment time for energy storage systems (ESSs) in a price arbitrage trade application under conditions of uncertainty over future profits. The adoption of ESSs can generate profits from price arbitrage trade, which are uncertain because the future marginal prices of electricity will change depending on supply and demand. In addition, since the investment is optional, an investor can delay adopting an ESS until it becomes profitable, and can decide the optimal time. Thus, when we evaluate this investment, we need to incorporate the investor’s option which is not captured by traditional evaluation methods. In order to incorporate these aspects, we applied real option theory to our proposed model, which provides an optimal investment threshold. Our results concerning the optimal time to invest show that if future profits that are expected to be obtained from arbitrage trade become more uncertain, an investor needs to wait longer to invest. Also, improvement in efficiency of ESSs can reduce the uncertainty of arbitrage profit and, consequently, the reduced uncertainty enables earlier ESS investment, even for the same power capacity. Besides, when a higher rate of profits is expected and ESS costs are higher, an investor needs to wait longer. Also, by comparing a widely used net present value model to our real option model, we show that the net present value method underestimates the value for ESS investment and misleads the investor to make an investment earlier. Full article
Open AccessArticle Downscaling the Impacts of Large-Scale LUCC on Surface Temperature along with IPCC RCPs: A Global Perspective
Energies 2014, 7(4), 2720-2739; doi:10.3390/en7042720
Received: 31 January 2014 / Revised: 12 April 2014 / Accepted: 17 April 2014 / Published: 24 April 2014
Cited by 7 | PDF Full-text (959 KB) | HTML Full-text | XML Full-text
Abstract
This study focuses on the potential impacts of large-scale land use and land cover changes (LUCC) on surface temperature from a global perspective. As important types of LUCC, urbanization, deforestation, cultivated land reclamation, and grassland degradation have effects on the climate, the [...] Read more.
This study focuses on the potential impacts of large-scale land use and land cover changes (LUCC) on surface temperature from a global perspective. As important types of LUCC, urbanization, deforestation, cultivated land reclamation, and grassland degradation have effects on the climate, the potential changes of the surface temperature caused by these four types of large-scale LUCC from 2010 to 2050 are downscaled, and this issue analyzed worldwide along with Representative Concentration Pathways (RCPs) of the Intergovernmental Panel on Climate Change (IPCC). The first case study presents some evidence of the effects of future urbanization on surface temperature in the Northeast megalopolis of the United States of America (USA). In order to understand the potential climatological variability caused by future forest deforestation and vulnerability, we chose Brazilian Amazon region as the second case study. The third selected region in India as a typical region of cultivated land reclamation where the possible climatic impacts are explored. In the fourth case study, we simulate the surface temperature changes caused by future grassland degradation in Mongolia. Results show that the temperature in built-up area would increase obviously throughout the four land types. In addition, the effects of all four large-scale LUCC on monthly average temperature change would vary from month to month with obviously spatial heterogeneity. Full article
(This article belongs to the Special Issue Large Scale LUCC, Surface Energy Fluxes and Energy Use)

Review

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Open AccessReview Strategies for Power Line Communications Smart Metering Network Deployment
Energies 2014, 7(4), 2377-2420; doi:10.3390/en7042377
Received: 7 February 2014 / Revised: 21 March 2014 / Accepted: 24 March 2014 / Published: 15 April 2014
Cited by 10 | PDF Full-text (775 KB) | HTML Full-text | XML Full-text
Abstract
Smart Grids are becoming a reality all over the world. Nowadays, the research efforts for the introduction and deployment of these grids are mainly focused on the development of the field of Smart Metering. This emerging application requires the use of technologies [...] Read more.
Smart Grids are becoming a reality all over the world. Nowadays, the research efforts for the introduction and deployment of these grids are mainly focused on the development of the field of Smart Metering. This emerging application requires the use of technologies to access the significant number of points of supply (PoS) existing in the grid, covering the Low Voltage (LV) segment with the lowest possible costs. Power Line Communications (PLC) have been extensively used in electricity grids for a variety of purposes and, of late, have been the focus of renewed interest. PLC are really well suited for quick and inexpensive pervasive deployments. However, no LV grid is the same in any electricity company (utility), and the particularities of each grid evolution, architecture, circumstances and materials, makes it a challenge to deploy Smart Metering networks with PLC technologies, with the Smart Grid as an ultimate goal. This paper covers the evolution of Smart Metering networks, together with the evolution of PLC technologies until both worlds have converged to project PLC-enabled Smart Metering networks towards Smart Grid. This paper develops guidelines over a set of strategic aspects of PLC Smart Metering network deployment based on the knowledge gathered on real field; and introduces the future challenges of these networks in their evolution towards the Smart Grid. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Figures

Open AccessReview Wind Turbine Condition Monitoring: State-of-the-Art Review, New Trends, and Future Challenges
Energies 2014, 7(4), 2595-2630; doi:10.3390/en7042595
Received: 14 February 2014 / Revised: 23 March 2014 / Accepted: 24 March 2014 / Published: 22 April 2014
Cited by 27 | PDF Full-text (943 KB) | HTML Full-text | XML Full-text
Abstract
As the demand for wind energy continues to grow at exponential rates, reducing operation and maintenance (OM) costs and improving reliability have become top priorities in wind turbine (WT) maintenance strategies. In addition to the development of more highly evolved WT designs [...] Read more.
As the demand for wind energy continues to grow at exponential rates, reducing operation and maintenance (OM) costs and improving reliability have become top priorities in wind turbine (WT) maintenance strategies. In addition to the development of more highly evolved WT designs intended to improve availability, the application of reliable and cost-effective condition-monitoring (CM) techniques offers an efficient approach to achieve this goal. This paper provides a general review and classification of wind turbine condition monitoring (WTCM) methods and techniques with a focus on trends and future challenges. After highlighting the relevant CM, diagnosis, and maintenance analysis, this work outlines the relationship between these concepts and related theories, and examines new trends and future challenges in the WTCM industry. Interesting insights from this research are used to point out strengths and weaknesses in today’s WTCM industry and define research priorities needed for the industry to meet the challenges in wind industry technological evolution and market growth. Full article
(This article belongs to the Special Issue Wind Turbines 2014)

Other

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Open AccessCorrection Correction: Márquez-Domínguez, S.; Sørensen, J.D. Fatigue Reliability and Calibration of Fatigue Design Factors for Offshore Wind Turbines. Energies 2012, 5, 1816–1834
Energies 2014, 7(4), 2146-2147; doi:10.3390/en7042146
Received: 29 January 2014 / Accepted: 26 February 2014 / Published: 1 April 2014
PDF Full-text (131 KB) | HTML Full-text | XML Full-text
Abstract The authors wish to make the following correction to this paper [1]. [...] Full article
(This article belongs to the Special Issue Wind Turbines)

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