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Energies, Volume 6, Issue 11 (November 2013) – 28 articles , Pages 5597-6136

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429 KiB  
Article
A Novel Wind Turbine Concept Based on an Electromagnetic Coupler and the Study of Its Fault Ride-through Capability
by Rui You, Braulio Barahona, Jianyun Chai and Nicolaos A. Cutululis
Energies 2013, 6(11), 6120-6136; https://doi.org/10.3390/en6116120 - 22 Nov 2013
Cited by 21 | Viewed by 7969
Abstract
This paper presents a novel type of variable speed wind turbine with a new drive train different from the variable speed wind turbine commonly used nowadays. In this concept, a synchronous generator is directly coupled with the grid, therefore, the wind turbine transient [...] Read more.
This paper presents a novel type of variable speed wind turbine with a new drive train different from the variable speed wind turbine commonly used nowadays. In this concept, a synchronous generator is directly coupled with the grid, therefore, the wind turbine transient overload capability and grid voltage support capability can be significantly improved. An electromagnetic coupling speed regulating device (EMCD) is used to connect the gearbox high speed shaft and synchronous generator rotor shaft, transmitting torque to the synchronous generator, while decoupling the gearbox side and the synchronous generator, so the synchronous generator torque oscillations during a grid fault are not transmitted to the gearbox. The EMCD is composed of an electromagnetic coupler and a one quadrant operation converter with reduced capability and low cost. A control strategy for the new wind turbine is proposed and a 2 MW wind turbine model is built to study the wind turbine fault ride-through capability. An integrated simulation environment based on the aeroelastic code HAWC2 and software Matlab/Simulink is used to study its fault ride-through capability and the impact on the structural loads during grid three phase and two phase short circuit faults. Full article
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1415 KiB  
Article
Thermal Performance of Motor and Inverter in an Integrated Starter Generator System for a Hybrid Electric Vehicle
by Sung Chul Kim
Energies 2013, 6(11), 6102-6119; https://doi.org/10.3390/en6116102 - 22 Nov 2013
Cited by 27 | Viewed by 15919
Abstract
If the integrated starter generator (ISG) motor and inverter operate under continuously high loading conditions, the system’s performance and durability will decrease and the heat dissipation requirements will increase. Therefore, in this study, we developed two cooling designs for the ISG motor and [...] Read more.
If the integrated starter generator (ISG) motor and inverter operate under continuously high loading conditions, the system’s performance and durability will decrease and the heat dissipation requirements will increase. Therefore, in this study, we developed two cooling designs for the ISG motor and inverter, and then carried out both a model analysis and an experiment on the fluid flow and thermal characteristics of the system under various operating conditions. As the outdoor temperature increased from 25 °C to 95 °C, the coil temperature of the air-cooled motor increased by about 82 °C. Under the harsh-air condition of 95 °C, the coil of the air-cooled motor increased to a maximum temperature of about 158.5 °C. We also determined that the temperature of the metal-oxide-semiconductor field-effect transistor (MOSFET) chip in the liquid-cooled inverter increased to a maximum temperature of about 96.8 °C under a coolant flow rate of 4 L/min and a coolant temperature of 65 °C. The observed thermal performance of the ISG motor and inverter using the proposed cooling structures was found to be sufficient for heat loads under various real driving conditions for a hybrid electric vehicle (HEV). Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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1857 KiB  
Article
Experimental and Numerical Analysis of Thermal and Hygrometric Characteristics of Building Structures Employing Recycled Plastic Aggregates and Geopolymer Concrete
by Francesco Colangelo, Giuseppina De Luca, Claudio Ferone and Alessandro Mauro
Energies 2013, 6(11), 6077-6101; https://doi.org/10.3390/en6116077 - 21 Nov 2013
Cited by 36 | Viewed by 7826
Abstract
The correct estimation of building energy consumptions is assuming an always increasing importance, and a detailed reproduction of building structures, with all the single components involved, is necessary to achieve this aim. In addition, the current ecological development tries to limit the use [...] Read more.
The correct estimation of building energy consumptions is assuming an always increasing importance, and a detailed reproduction of building structures, with all the single components involved, is necessary to achieve this aim. In addition, the current ecological development tries to limit the use of natural raw materials as building components, in favor of alternative (waste) materials, which ensure significant advantages from the economic, energetic and environmental point of views. In this work, dynamic heat and vapor transport in a typical three-dimensional (3D) building structure, involving different types of environmental-friendly concrete mixtures, have been simulated by using finite elements. In particular, the authors propose to substitute part of the aggregates with plastic waste and to use a fly ash based geopolymeric binder for the production of low conductivity concrete, to be employed in eco-efficient buildings. Concrete produced with natural limestone aggregates has been considered as the reference benchmark. The whole characterization of the different types of concrete tested in the present work has been obtained through laboratory experiments. The structure taken into account in the simulations is a 3D thermal bridge, typical of building envelopes. The thermal and hygrometric transient behavior of this structure, employing plastic waste in different percentages and geopolymer concrete, has been analyzed by the authors. Full article
(This article belongs to the Special Issue Energy Efficient Building Design 2013)
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1122 KiB  
Article
Cellular Cycling, Carbon Utilization, and Photosynthetic Oxygen Production during Bicarbonate-Induced Triacylglycerol Accumulation in a Scenedesmus sp.
by Robert D. Gardner, Egan J. Lohman, Keith E. Cooksey, Robin Gerlach and Brent M. Peyton
Energies 2013, 6(11), 6060-6076; https://doi.org/10.3390/en6116060 - 21 Nov 2013
Cited by 20 | Viewed by 7193
Abstract
Microalgae are capable of synthesizing high levels of triacylglycerol (TAG) which can be used as precursor compounds for fuels and specialty chemicals. Algal TAG accumulation typically occurs when cellular cycling is delayed or arrested due to nutrient limitation, an environmental challenge (e.g., pH, [...] Read more.
Microalgae are capable of synthesizing high levels of triacylglycerol (TAG) which can be used as precursor compounds for fuels and specialty chemicals. Algal TAG accumulation typically occurs when cellular cycling is delayed or arrested due to nutrient limitation, an environmental challenge (e.g., pH, light, temperature stress), or by chemical addition. This work is a continuation of previous studies detailing sodium bicarbonate-induced TAG accumulation in the alkaline chlorophyte Scenedesmus sp. WC-1. It was found that upon sodium bicarbonate amendment, bicarbonate is the ion responsible for TAG accumulation; a culture amendment of approximately 15 mM bicarbonate was sufficient to arrest the cellular cycle and switch the algal metabolism from high growth to a TAG accumulating state. However, the cultures were limited in dissolved inorganic carbon one day after the amendment, suggesting additional carbon supplementation was necessary. Therefore, additional abiotic and biotic experimentation was performed to evaluate in- and out-gassing of CO2. Cultures to which 40–50 mM of sodium bicarbonate were added consumed DIC faster than CO2 could ingas during the light hours and total photosynthetic oxygen production was elevated as compared to cultures that did not receive supplemental inorganic carbon. Full article
(This article belongs to the Special Issue Algae Fuel 2013)
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6159 KiB  
Article
Design and Implementation of Real-Time Intelligent Control and Structure Based on Multi-Agent Systems in Microgrids
by Ming-Tse Kuo and Shiue-Der Lu
Energies 2013, 6(11), 6045-6059; https://doi.org/10.3390/en6116045 - 19 Nov 2013
Cited by 31 | Viewed by 9719
Abstract
By consulting various worldwide definitions of microgrids and distributed energy, this study presents a microgrid-structured multi-agent system and uses Matlab/Simulink to construct a circuit with microgrid features, which enables the changes in each electrical source and load in the microgrid to be monitored [...] Read more.
By consulting various worldwide definitions of microgrids and distributed energy, this study presents a microgrid-structured multi-agent system and uses Matlab/Simulink to construct a circuit with microgrid features, which enables the changes in each electrical source and load in the microgrid to be monitored and controlled. This multi-agent system adheres to the Java Agent Development Framework (JADE) platform specifications of the Foundation for Intelligent Physical Agents (FIPA), facilitating communication, information transfers, and the receipt of real-time information regarding the microgrid and each component in the microgrid. Furthermore, the real-time state in the microgrid can be correspondingly controlled, achieving the most efficient real-time monitoring and control for electrical sources and load management in the microgrid. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
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7569 KiB  
Review
Recent Research Progress on Non-aqueous Lithium-Air Batteries from Argonne National Laboratory
by Jun Lu and Khalil Amine
Energies 2013, 6(11), 6016-6044; https://doi.org/10.3390/en6116016 - 18 Nov 2013
Cited by 54 | Viewed by 11303
Abstract
Rechargeable non-aqueous Li-air battery technology offers potential advantages over other existing battery systems in terms of specific energy and energy density, which could enable the driving range of an electric vehicle to be comparable to that of gasoline vehicles. Development of efficient cathode [...] Read more.
Rechargeable non-aqueous Li-air battery technology offers potential advantages over other existing battery systems in terms of specific energy and energy density, which could enable the driving range of an electric vehicle to be comparable to that of gasoline vehicles. Development of efficient cathode catalysts and stable electrolytes for the Li-air battery has been intensively investigated for the past several years, and a number of review articles covering different topics are already available. This review mainly focuses on the research activities on rechargeable non-aqueous Li-air batteries at Argonne National Laboratory, with the emphasis on the gains in understanding of electrolyte decomposition, the structure and magnetic properties of lithium peroxide (Li2O2), development of an air-breathing cathode, and the effect of oxygen crossover on the lithium anode. Insights from this research have led to the improvement of the electrochemical performance of Li-air batteries. Promising paths for future work on rechargeable Li-air batteries are also discussed. Full article
(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)
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793 KiB  
Article
On the Integration of Leadership in Energy and Environmental Design (LEED)® ND Protocol with the Energy Planning and Management Tools in Italy: Strengths and Weaknesses
by Giuliano Dall'O', Annalisa Galante, Nicola Sanna and Karin Miller
Energies 2013, 6(11), 5990-6015; https://doi.org/10.3390/en6115990 - 18 Nov 2013
Cited by 26 | Viewed by 8843
Abstract
Owners and municipalities face the choice to renovate or rebuild buildings in order to improve energy efficiency and sustainability. The process of upgrading the existing building stock can be supported by land management tools, i.e., municipal energy plans (MEP) or sustainable building [...] Read more.
Owners and municipalities face the choice to renovate or rebuild buildings in order to improve energy efficiency and sustainability. The process of upgrading the existing building stock can be supported by land management tools, i.e., municipal energy plans (MEP) or sustainable building codes (BC), that municipalities use to plan, check and monitor actions taken. Many local and regional authorities are involved in the Covenant of Mayors supported by the European Union (EU): the sustainable energy action plan (SEAP) is the key document in which the Covenant signatory outlines how it intends to reach CO2 reduction target by 2020. Sustainability at the urban scale is also supported by voluntary certification schemes such as Leadership in Energy and Environmental Design (LEED)® for neighbourhood development proposed by the United States Green Building Council (USGBC), Building Research Establishment Environmental Assessment Method (BREEAM) Communities proposed by UK Building Research Establishment (BRE) and Comprehensive Assessment System for Built Environment Efficiency (CASBEE) for Urban Development proposed by the Japan GreenBuild Council. The fact that there are so many tools to manage urban sustainability is positive, but what happens when multiple tools are applied to the same territory? Overlap, redundancy, and conflicts in management may be critical elements. The purpose of this article is to analyze these critical issues, highlighting the elements of integration and possible synergies for effective management of sustainability at the local level. Full article
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701 KiB  
Article
Biomass Fuel and Combustion Conditions Selection in a Fixed Bed Combustor
by María E. Arce, Ángeles Saavedra, José L. Míguez, Enrique Granada and Antón Cacabelos
Energies 2013, 6(11), 5973-5989; https://doi.org/10.3390/en6115973 - 18 Nov 2013
Cited by 30 | Viewed by 6456
Abstract
The biomass market has experienced an increase in development, leading to research and development efforts that are focused on determining optimal biofuel combustion conditions. Biomass combustion is a complex process that involves divergent parameters and thus requires the use of advanced analysis methods. [...] Read more.
The biomass market has experienced an increase in development, leading to research and development efforts that are focused on determining optimal biofuel combustion conditions. Biomass combustion is a complex process that involves divergent parameters and thus requires the use of advanced analysis methods. This study proposes combining grey relational analysis (GRA) and error propagation theory (EPT) to select a biofuel and its optimal combustion conditions. This research will study three biofuels that are currently used in a region of South Europe (Spain), and the most important variables that affect combustion are the ignition front propagation speed and the highest temperature that is reached at the fixed bed combustor. The results demonstrate that a combination of both theories for the analysis of solid-state thermochemical phenomena enables a fast and simple way of choosing the best configuration for each fuel. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
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989 KiB  
Article
Thermoelectric Power Generation in a Vacuum Cell of Decomposing Liquid Potassium-Ammonia Solutions
by Jibeom Kim, Kyuchol Shim and Joonhyeon Jeon
Energies 2013, 6(11), 5960-5972; https://doi.org/10.3390/en6115960 - 18 Nov 2013
Cited by 3 | Viewed by 5795
Abstract
This paper describes the design of high-efficiency reversible thermoelectric conversion devices for thermoelectric power generation through liquid potassium-ammonia (K-NH3) solutions. The validity and effectiveness of the proposed design is verified by thermoelectric experiments using two kinds of “U”-shaped vacuum cells with [...] Read more.
This paper describes the design of high-efficiency reversible thermoelectric conversion devices for thermoelectric power generation through liquid potassium-ammonia (K-NH3) solutions. The validity and effectiveness of the proposed design is verified by thermoelectric experiments using two kinds of “U”-shaped vacuum cells with a NH3-gas passageway connecting both legs of “U”, one of which has a waist in the middle of a liquid flow passage. The experimental results show that the gas passageway provides a stable and reliable reaction by preventing an internal pressure imbalance due to NH3 gasification during solution decomposition; hence, long-term, reversible thermoelectric power can be effectively derived by stably inducing two separate phase transitions in the cell. In addition, the effect of the narrow waist in the cell’s middle is verified to cause an increase in thermoelectric conversion efficiency due to improved electric conductivity of liquid in the vacuum cell. Consequently, using these technologies in thermoelectric cell potentially leads to long-time, high-efficiency thermoelectric power generation through liquid K-NH3 solutions. Full article
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842 KiB  
Article
Time Series EROI for Canadian Oil and Gas
by Alexandre Poisson and Charles A. S. Hall
Energies 2013, 6(11), 5940-5959; https://doi.org/10.3390/en6115940 - 15 Nov 2013
Cited by 38 | Viewed by 8872
Abstract
Modern economies are dependent on fossil energy, yet as conventional resources are depleted, an increasing fraction of that energy is coming from unconventional resources such as tar sands. These resources usually require more energy for extraction and upgrading, leaving a smaller fraction available [...] Read more.
Modern economies are dependent on fossil energy, yet as conventional resources are depleted, an increasing fraction of that energy is coming from unconventional resources such as tar sands. These resources usually require more energy for extraction and upgrading, leaving a smaller fraction available to society, and at a higher cost. Here we present a calculation of the energy return on investment (EROI) for all Canadian oil and gas (including tar sands) over the period 1990–2008, and also for tar sands alone (1994–2008). We used energy production and energy use data from Statistics Canada’s Material and Energy Flow Accounts (MEFA). We were able to quantify both direct and indirect energy use, the latter from Statistics Canada’s energy input-output model. We found that since the mid-1990s, total energy used (invested) in the Canadian oil and gas sector increased about 63%, while the energy production (return) increased only 18%, resulting in a decrease in total EROI from roughly 16:1 to 11:1. We also found (although with less certainty) that the EROI for tar sands alone has fluctuated around 4:1 since 1994, with only a slight increasing trend. Finally, we analyzed underlying factors possibly influencing these trends. Full article
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550 KiB  
Review
Review of Microalgae Harvesting via Co-Pelletization with Filamentous Fungus
by Sarman Oktovianus Gultom and Bo Hu
Energies 2013, 6(11), 5921-5939; https://doi.org/10.3390/en6115921 - 12 Nov 2013
Cited by 134 | Viewed by 11461
Abstract
Cultivation of microalgae to utilize CO2 and nutrients in the wastewater to generate biofuel products is a promising research objective. However, the process faces tremendous technical difficulties, especially the harvest of microalgae cells, an economically challenging step. Several researchers recently reported co-culturing [...] Read more.
Cultivation of microalgae to utilize CO2 and nutrients in the wastewater to generate biofuel products is a promising research objective. However, the process faces tremendous technical difficulties, especially the harvest of microalgae cells, an economically challenging step. Several researchers recently reported co-culturing of filamentous fungi with microalgae so that microalgae cells can be co-pelletized in order to facilitate the cell harvest. This algae pelletization via the filamentous fungi represents an innovative approach to address both the cost and sustainability issues in algae biofuel production and also has potential with direct commercial applications. This paper reviews the current research status in this area and some possible drawbacks of this method in order to provide some possible directions for the future research. Full article
(This article belongs to the Special Issue Algae Fuel 2013)
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550 KiB  
Article
Price Forecasting in the Day-Ahead Energy Market by an Iterative Method with Separate Normal Price and Price Spike Frameworks
by Sergey Voronin and Jarmo Partanen
Energies 2013, 6(11), 5897-5920; https://doi.org/10.3390/en6115897 - 12 Nov 2013
Cited by 49 | Viewed by 8618
Abstract
A forecasting methodology for prediction of both normal prices and price spikes in the day-ahead energy market is proposed. The method is based on an iterative strategy implemented as a combination of two modules separately applied for normal price and price spike predictions. [...] Read more.
A forecasting methodology for prediction of both normal prices and price spikes in the day-ahead energy market is proposed. The method is based on an iterative strategy implemented as a combination of two modules separately applied for normal price and price spike predictions. The normal price module is a mixture of wavelet transform, linear AutoRegressive Integrated Moving Average (ARIMA) and nonlinear neural network models. The probability of a price spike occurrence is produced by a compound classifier in which three single classification techniques are used jointly to make a decision. Combined with the spike value prediction technique, the output from the price spike module aims to provide a comprehensive price spike forecast. The overall electricity price forecast is formed as combined normal price and price spike forecasts. The forecast accuracy of the proposed method is evaluated with real data from the Finnish Nord Pool Spot day-ahead energy market. The proposed method provides significant improvement in both normal price and price spike prediction accuracy compared with some of the most popular forecast techniques applied for case studies of energy markets. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
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3572 KiB  
Article
Experimental Analysis of Wireless Power Transmission with Spiral Resonators
by Giovanni Puccetti, Ugo Reggiani and Leonardo Sandrolini
Energies 2013, 6(11), 5887-5896; https://doi.org/10.3390/en6115887 - 11 Nov 2013
Cited by 19 | Viewed by 6217
Abstract
In this paper, a theoretical and experimental analysis of wireless power transfer through a coplanar resonator array is presented. In particular, six identical spiral resonators are used to form an array and transfer power between an emitter and a receiver. All the spiral [...] Read more.
In this paper, a theoretical and experimental analysis of wireless power transfer through a coplanar resonator array is presented. In particular, six identical spiral resonators are used to form an array and transfer power between an emitter and a receiver. All the spiral resonators resonate at about 20 MHz and the emitter and receiver coils are designed with formulas taken from literature. The resonator system is modeled using mutual inductances, being retardation not significant. The transmission coefficient is measured for four different arrangements of the six resonators and the experimental measurements are compared with the theoretical predictions, showing similar trends. The paper shows that the peaks of the transmission coefficient vary slightly for the resonator arrangements considered. Full article
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749 KiB  
Review
Microalgae for Biofuels and Animal Feeds
by John Benemann
Energies 2013, 6(11), 5869-5886; https://doi.org/10.3390/en6115869 - 11 Nov 2013
Cited by 261 | Viewed by 18032
Abstract
The potential of microalgae biomass production for low-cost commodities—biofuels and animal feeds—using sunlight and CO2 is reviewed. Microalgae are currently cultivated in relatively small-scale systems, mainly for high value human nutritional products. For commodities, production costs must be decreased by an order [...] Read more.
The potential of microalgae biomass production for low-cost commodities—biofuels and animal feeds—using sunlight and CO2 is reviewed. Microalgae are currently cultivated in relatively small-scale systems, mainly for high value human nutritional products. For commodities, production costs must be decreased by an order of magnitude, and high productivity algal strains must be developed that can be stably cultivated in large open ponds and harvested by low-cost processes. For animal feeds, the algal biomass must be high in digestible protein and long-chain omega-3 fatty acids that can substitute for fish meal and fish oils. Biofuels will require a high content of vegetable oils (preferably triglycerides), hydrocarbons or fermentable carbohydrates. Many different cultivation systems, algal species, harvesting methods, and biomass processing technologies are being developed worldwide. However, only raceway-type open pond systems are suitable for the production of low-cost commodities. Full article
(This article belongs to the Special Issue Algae Fuel 2013)
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997 KiB  
Review
Recent Approaches to Controlling the Nanoscale Morphology of Polymer-Based Bulk-Heterojunction Solar Cells
by Wasiu Adebayo Hammed, Rosiyah Yahya, Abdulra'uf Lukman Bola and Habibun Nabi Muhammad Ekramul Mahmud
Energies 2013, 6(11), 5847-5868; https://doi.org/10.3390/en6115847 - 8 Nov 2013
Cited by 34 | Viewed by 8157
Abstract
The need for clean, inexpensive and renewable energy has increasingly turned research attention towards polymer photovoltaic cells. However, the performance efficiency of these devices is still low in comparison with silicon-based devices. The recent introduction of new materials and processing techniques has resulted [...] Read more.
The need for clean, inexpensive and renewable energy has increasingly turned research attention towards polymer photovoltaic cells. However, the performance efficiency of these devices is still low in comparison with silicon-based devices. The recent introduction of new materials and processing techniques has resulted in a remarkable increase in power-conversion efficiency, with a value above 10%. Controlling the interpenetrating network morphology is a key factor in obtaining devices with improved performance. This review focuses on the influence of controlled nanoscale morphology on the overall performance of bulk-heterojunction (BHJ) photovoltaic cells. Strategies such as the use of solvents, solvent annealing, polymer nanowires (NWs), and donor–acceptor (D–A) blend ratios employed to control the active-layer morphologies are all discussed. Full article
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450 KiB  
Article
Harmonic Loss Analysis of the Traction Transformer of High-Speed Trains Considering Pantograph-OCS Electrical Contact Properties
by Jin Wang, Zhongping Yang, Fei Lin and Junci Cao
Energies 2013, 6(11), 5826-5846; https://doi.org/10.3390/en6115826 - 7 Nov 2013
Cited by 14 | Viewed by 7413
Abstract
The traction transformer of the traction drive system of a high-speed train is one of the main equipments for energy conversion. The transformer loss will be increased by load harmonics and pantograph arcs at high speed. It is very important to predict losses [...] Read more.
The traction transformer of the traction drive system of a high-speed train is one of the main equipments for energy conversion. The transformer loss will be increased by load harmonics and pantograph arcs at high speed. It is very important to predict losses for the improvement of traction transformer design. In this paper, a dynamic model of the pantograph-catenary system is established using the MSC.Marc software based on the finite element method to analyze disconnection events in different speeds. Then the pantograph arc, traction transformer and four-quadrant converter model is set up. Resistance variations with the change of harmonic frequency have been considered in the calculation formulae of harmonic losses. Traction transformer losses can be calculated based on the harmonic T-equivalent circuit and superposition principle. Considering the harmonic losses variations, the effects of arc voltage on harmonic copper loss and harmonic core loss are analyzed, respectively. The average loss at different disconnection ratios is also calculated. This method could be used to estimate the increment of transformer harmonic losses with poor current conditions at high speed. Full article
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4503 KiB  
Article
Exogenous Measurements from Basic Meteorological Stations for Wind Speed Forecasting
by José Carlos Palomares-Salas, Agustín Agüera-Pérez, Juan José González de la Rosa, José María Sierra-Fernández and Antonio Moreno-Muñoz
Energies 2013, 6(11), 5807-5825; https://doi.org/10.3390/en6115807 - 7 Nov 2013
Cited by 10 | Viewed by 5746
Abstract
This research presents a comparative analysis of wind speed forecasting methods applied to perform 1 h-ahead forecasting. The main significant development has been the introduction of low-quality measurements as exogenous information to improve these predictions. Eight prediction models have been assessed; three of [...] Read more.
This research presents a comparative analysis of wind speed forecasting methods applied to perform 1 h-ahead forecasting. The main significant development has been the introduction of low-quality measurements as exogenous information to improve these predictions. Eight prediction models have been assessed; three of these models [persistence, autoregressive integrated moving average (ARIMA) and multiple linear regression] are used as references, and the remaining five, based on neural networks, are evaluated on the basis of two procedures. Firstly, four quality indices are assessed (the Pearson’s correlation coefficient, the index of agreement, the mean absolute error and the mean squared error). Secondly, an analysis of variance test and multiple comparison procedure are conducted. The findings indicate that a backpropagation network with five neurons in the hidden layer is the best model obtained with respect to the reference models. The pair of improvements (mean absolute-mean squared error) obtained are 29.10%–56.54%, 28.15%–53.99% and 4.93%–14.38%, for the persistence, ARIMA and multiple linear regression models, respectively. The experimental results reported in this paper show that traditional agricultural measurements enhance the predictions. Full article
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4400 KiB  
Article
Methane Gas Hydrate Stability Models on Continental Shelves in Response to Glacio-Eustatic Sea Level Variations: Examples from Canadian Oceanic Margins
by Jacek Majorowicz, Kirk Osadetz and Jan Safanda
Energies 2013, 6(11), 5775-5806; https://doi.org/10.3390/en6115775 - 6 Nov 2013
Cited by 4 | Viewed by 7134
Abstract
We model numerically regions of the Canadian continental shelves during successive glacio-eustatic cycles to illustrate past, current and future marine gas hydrate (GH) stability and instability. These models indicated that the marine GH resource has dynamic features and the formation age and resource [...] Read more.
We model numerically regions of the Canadian continental shelves during successive glacio-eustatic cycles to illustrate past, current and future marine gas hydrate (GH) stability and instability. These models indicated that the marine GH resource has dynamic features and the formation age and resource volumes depend on the dynamics of the ocean-atmosphere system as it responds to both natural (glacial-interglacial) and anthropogenic (climate change) forcing. Our models focus on the interval beginning three million years ago (i.e., Late Pliocene-Holocene). They continue through the current interglacial and they are projected to its anticipated natural end. During the current interglacial the gas hydrate stability zone (GHSZ) thickness in each region responded uniquely as a function of changes in water depth and sea bottom temperature influenced by ocean currents. In general, the GHSZ in the deeper parts of the Pacific and Atlantic margins (≥1316 m) thinned primarily due to increased water bottom temperatures. The GHSZ is highly variable in the shallower settings on the same margins (~400–500 m). On the Pacific Margin shallow GH dissociated completely prior to nine thousand years ago but the effects of subsequent sea level rise reestablished a persistent, thin GHSZ. On the Atlantic Margin Scotian Shelf the warm Gulf Stream caused GHSZ to disappear completely, whereas in shallow water depths offshore Labrador the combination of the cool Labrador Current and sea level rise increased the GHSZ. If future ocean bottom temperatures remain constant, these general characteristics will persist until the current interglacial ends. If the sea bottom warms, possibly in response to global climate change, there could be a significant reduction to complete loss of GH stability, especially on the shallow parts of the continental shelf. The interglacial GH thinning rates constrain rates at which carbon can be transferred between the GH reservoir and the atmosphere-ocean system. Marine GH can destabilize much more quickly than sub-permafrost terrestrial GHs and this combined with the immense marine GH reservoir suggests that GH have the potential to affect the climate-ocean system. Our models show that GH stability reacts quickly to water column pressure effects but slowly to sea bottom temperature changes. Therefore it is likely that marine GH destabilization was rapid and progressive in response to the pressure effects of glacial eustatic sea level fall. This suggests against a catastrophic GH auto-cyclic control on glacial-interglacial climate intervals. It is computationally possible but, unfortunately in no way verifiably, to analyze the interactions and impacts that marine GHs had prior to the current interglacial because of uncertainties in temperature and pressure history constraints. Thus we have the capability, but no confidence that we can contribute currently to questions regarding the relationships among climate, glacio-eustatic sea level fluctuations and marine GH stability without improved local temperature and water column histories. We infer that the possibility for a GH control on climate or oceanic cycles is speculative, but qualitatively contrary to our model results. Full article
(This article belongs to the Special Issue Natural Gas Hydrate 2013)
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417 KiB  
Article
Corn Stover and Wheat Straw Combustion in a 176-kW Boiler Adapted for Round Bales
by René Morissette, Philippe Savoie and Joey Villeneuve
Energies 2013, 6(11), 5760-5774; https://doi.org/10.3390/en6115760 - 4 Nov 2013
Cited by 9 | Viewed by 7672
Abstract
Combustion trials were conducted with corn stover (CS) and wheat straw (WS) round bales in a 176-kW boiler (model Farm 2000). Hot water (80 °C) stored in a 30,000-L water tank was transferred to a turkey barn through a plate exchanger. Gross calorific [...] Read more.
Combustion trials were conducted with corn stover (CS) and wheat straw (WS) round bales in a 176-kW boiler (model Farm 2000). Hot water (80 °C) stored in a 30,000-L water tank was transferred to a turkey barn through a plate exchanger. Gross calorific value measured in the laboratory was 17.0 and 18.9 MJ/kg DM (dry matter) for CS and WS, respectively. Twelve bales of CS (1974 kg DM total, moisture content of 13.6%) were burned over a 52-h period and produced 9.2% ash. Average emissions of CO, NOx and SO2 were 2725, 9.8 and 2.1 mg/m3, respectively. Thermal efficiency was 40.8%. For WS, six bales (940 kg DM total, MC of 15%) were burned over a 28-h period and produced 2.6% ash. Average emissions of CO, NOx and SO2 were 2210, 40.4 and 3.7 mg/m3, respectively. Thermal efficiency was 68.0%. A validation combustion trial performed a year later with 90 CS bales confirmed good heating performance and the potential to lower ash content (6.2% average). Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
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952 KiB  
Article
A Self-Adapting Approach for Forecast-Less Scheduling of Electrical Energy Storage Systems in a Liberalized Energy Market
by Eleonora Riva Sanseverino, Maria Luisa Di Silvestre, Gaetano Zizzo, Roberto Gallea and Ninh Nguyen Quang
Energies 2013, 6(11), 5738-5759; https://doi.org/10.3390/en6115738 - 4 Nov 2013
Cited by 27 | Viewed by 5856
Abstract
In this paper, an original scheduling approach for optimal dispatch of electrical Energy Storage Systems (ESS) in modern distribution networks is proposed. The control system is based on fuzzy rules and does not use forecasts since it repairs the past history according to [...] Read more.
In this paper, an original scheduling approach for optimal dispatch of electrical Energy Storage Systems (ESS) in modern distribution networks is proposed. The control system is based on fuzzy rules and does not use forecasts since it repairs the past history according to the real time data on the electrical energy cost, renewable energy production and load. When the system detects a worsening of performances, the fuzzy logic rule-based control system self-adapts its membership functions using an economic indicator. The common use, in the relevant literature, of forecasted values in such systems can lead to large errors and economic losses. Moreover the speed of calculation guaranteed by the fuzzy control system allows the execution of new calculations even with high frequency. After the Introduction section, where the state of the art on the topic is outlined, the problem formulation is presented and an interesting application of the considered approach to the control on a medium size battery with real world data is proposed. Full article
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1066 KiB  
Article
Probabilistic Approach to Optimizing Active and Reactive Power Flow in Wind Farms Considering Wake Effects
by Jae-Kun Lyu, Jae-Haeng Heo, Jong-Keun Park and Yong-Cheol Kang
Energies 2013, 6(11), 5717-5737; https://doi.org/10.3390/en6115717 - 31 Oct 2013
Cited by 12 | Viewed by 6640
Abstract
This paper presents a novel probabilistic optimization algorithm for simultaneous active and reactive power dispatch in power systems with significant wind power integration. Two types of load and wind-speed uncertainties have been assumed that follow normal and Weibull distributions, respectively. A PV bus [...] Read more.
This paper presents a novel probabilistic optimization algorithm for simultaneous active and reactive power dispatch in power systems with significant wind power integration. Two types of load and wind-speed uncertainties have been assumed that follow normal and Weibull distributions, respectively. A PV bus model for wind turbines and the wake effect for correlated wind speed are used to achieve accurate AC power flow analysis. The power dispatch algorithm for a wind-power integrated system is modeled as a probabilistic optimal power flow (P-OPF) problem, which is operated through fixed power factor control to supply reactive power. The proposed P-OPF framework also considers emission information, which clearly reflects the impact of the energy source on the environment. The P-OPF was tested on a modified IEEE 118-bus system with two wind farms. The results show that the proposed technique provides better system operation performance evaluation, which is helpful in making decisions about power system optimal dispatch under conditions of uncertainty. Full article
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878 KiB  
Article
Measurement of Lipid Droplet Accumulation Kinetics in Chlamydomonas reinhardtii Using Seoul-Fluor
by Jae Woo Park, Sang Cheol Na, Youngjun Lee, Sanghee Lee, Seung Bum Park and Noo Li Jeon
Energies 2013, 6(11), 5703-5716; https://doi.org/10.3390/en6115703 - 31 Oct 2013
Cited by 6 | Viewed by 7165
Abstract
Alternative energy resources have become an important issue due to the limited stocks of petroleum-based fuel. Microalgae, a source of renewable biodiesel, use solar light to convert CO2 into lipid droplets (LDs). Quantification of LDs in microalgae is required for developing and [...] Read more.
Alternative energy resources have become an important issue due to the limited stocks of petroleum-based fuel. Microalgae, a source of renewable biodiesel, use solar light to convert CO2 into lipid droplets (LDs). Quantification of LDs in microalgae is required for developing and optimizing algal bioprocess engineering. However, conventional quantification methods are both time and labor-intensive and difficult to apply in high-throughput screening systems. LDs in plant and mammalian cells can be visualized by staining with various fluorescence probes such as the Nile Red, BODIPY, and Seoul-Fluor (SF) series. This report describes the optimization of LD staining in Chlamydomonas reinhardtii with SF probes via systematic variations of dye concentration, staining time, temperature, and pH. A protocol for quantitative measurement of accumulation kinetics of LDs in C. reinhardtii was developed using a spectrofluorimeter and the accuracy of LD size measurement was confirmed by transmission electron microscopy (TEM). Our results indicate that our spectrofluorimeter-based measurement approach can monitor kinetics of intracellular LDs (in control and nitrogen-source-starved Chlamydomonas reinhardtii) accumulation that has not been possible in the case of conventional imaging-based methods. Our results presented here confirmed that an SF44 can be a powerful tool for in situ monitoring and tracking of intracellular LDs formation. Full article
(This article belongs to the Special Issue Algae Fuel 2013)
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504 KiB  
Article
Microalgal Species Selection for Biodiesel Production Based on Fuel Properties Derived from Fatty Acid Profiles
by Muhammad Aminul Islam, Marie Magnusson, Richard J. Brown, Godwin A. Ayoko, Md. Nurun Nabi and Kirsten Heimann
Energies 2013, 6(11), 5676-5702; https://doi.org/10.3390/en6115676 - 29 Oct 2013
Cited by 293 | Viewed by 13300
Abstract
Physical and chemical properties of biodiesel are influenced by structural features of the fatty acids, such as chain length, degree of unsaturation and branching of the carbon chain. This study investigated if microalgal fatty acid profiles are suitable for biodiesel characterization and species [...] Read more.
Physical and chemical properties of biodiesel are influenced by structural features of the fatty acids, such as chain length, degree of unsaturation and branching of the carbon chain. This study investigated if microalgal fatty acid profiles are suitable for biodiesel characterization and species selection through Preference Ranking Organisation Method for Enrichment Evaluation (PROMETHEE) and Graphical Analysis for Interactive Assistance (GAIA) analysis. Fatty acid methyl ester (FAME) profiles were used to calculate the likely key chemical and physical properties of the biodiesel [cetane number (CN), iodine value (IV), cold filter plugging point, density, kinematic viscosity, higher heating value] of nine microalgal species (this study) and twelve species from the literature, selected for their suitability for cultivation in subtropical climates. An equal-parameter weighted (PROMETHEE-GAIA) ranked Nannochloropsis oculata, Extubocellulus sp. and Biddulphia sp. highest; the only species meeting the EN14214 and ASTM D6751-02 biodiesel standards, except for the double bond limit in the EN14214. Chlorella vulgaris outranked N. oculata when the twelve microalgae were included. Culture growth phase (stationary) and, to a lesser extent, nutrient provision affected CN and IV values of N. oculata due to lower eicosapentaenoic acid (EPA) contents. Application of a polyunsaturated fatty acid (PUFA) weighting to saturation led to a lower ranking of species exceeding the double bond EN14214 thresholds. In summary, CN, IV, C18:3 and double bond limits were the strongest drivers in equal biodiesel parameter-weighted PROMETHEE analysis. Full article
(This article belongs to the Special Issue Algae Fuel 2013)
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895 KiB  
Article
Comparative Study on Different Energy Management Strategies for Plug-In Hybrid Electric Vehicles
by Ximing Wang, Hongwen He, Fengchun Sun, Xiaokun Sun and Henglu Tang
Energies 2013, 6(11), 5656-5675; https://doi.org/10.3390/en6115656 - 29 Oct 2013
Cited by 73 | Viewed by 10991
Abstract
Plug-in hybrid electric vehicles (PHEVs) have a larger battery and can replace a certain amount of conventional fossil fuels with grid electricity, which differs from the traditional hybrid electric vehicles (HEVs). The application of the onboard electrical energy significantly influences the energy utilization [...] Read more.
Plug-in hybrid electric vehicles (PHEVs) have a larger battery and can replace a certain amount of conventional fossil fuels with grid electricity, which differs from the traditional hybrid electric vehicles (HEVs). The application of the onboard electrical energy significantly influences the energy utilization efficiency and thus impacts the fuel economy. In this paper, the basic PHEV operation modes are defined as pure electric driving (PED), hybrid driving charge depleting (HDCD) and hybrid driving charge sustaining (HDCS) based on the battery state of charge (SoC) profile. For a plug-in hybrid electric bus (PHEB), three different energy management strategies, which are combined with two or three of the basic operation modes, are put forward and comparatively examined based on simulation models. If some trip information can be approximately known in advance such as the trip distance and the mean power demand, the PED + HDCD + HDCS strategy comprised optimally of the PED mode, the HDCD mode and the HDCS mode would be the best energy management strategy. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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507 KiB  
Article
Biogas Production from Thin Stillage on an Industrial Scale—Experience and Optimisation
by Jan Moestedt, Sören Nilsson Påledal, Anna Schnürer and Erik Nordell
Energies 2013, 6(11), 5642-5655; https://doi.org/10.3390/en6115642 - 29 Oct 2013
Cited by 38 | Viewed by 13977
Abstract
With the increasing demand for renewable energy and sustainable waste treatment, biogas production is expanding. Approximately four billion litres of bio-ethanol are produced annually for vehicle fuel in Europe, resulting in the production of large amounts of stillage residues. This stillage is energy-rich [...] Read more.
With the increasing demand for renewable energy and sustainable waste treatment, biogas production is expanding. Approximately four billion litres of bio-ethanol are produced annually for vehicle fuel in Europe, resulting in the production of large amounts of stillage residues. This stillage is energy-rich and can be used for biogas production, but is a challenging substrate due to its high levels of nitrogen and sulphate. At the full-scale biogas production plant in Norrköping, Sweden (Svensk Biogas i Linköping AB), thin grain stillage is used as a biogas substrate. This paper describes the plant operation and strategies that have been implemented to digest thin stillage successfully. High ammonia concentrations in the digester have resulted in syntrophic acetate oxidation (SAO) becoming the major pathway for acetate degradation. Therefore, a long hydraulic retention time (HRT) (40–60 days) is used to allow the syntrophic acetate-oxidising bacteria time to grow. The high sulphate levels in thin stillage result in high levels of hydrogen sulphide following degradation of protein and the activity of sulphate-reducing bacteria (SRB), the presence of which has been confirmed by quantitative polymerase chain reaction (qPCR) analysis. To optimise biogas production and maintain a stable process, the substrate is diluted with tap water and co-digested with grain residues and glycerine to keep the ammonium nitrogen (NH4-N) concentration below 6 g L−1. Combined addition of iron, hydrochloric acid and cobalt successfully precipitates sulphides, reduces ammonia toxicity and supplies microorganisms with trace element. Mesophilic temperature (38 °C) is employed to further avoid ammonia toxicity. Together, these measures and doubling the digester volume have made it possible to increase annual biogas production from 27.7 TJ to 69.1 TJ. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
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1026 KiB  
Article
Peukert Revisited—Critical Appraisal and Need for Modification for Lithium-Ion Batteries
by Noshin Omar, Peter Van den Bossche, Thierry Coosemans and Joeri Van Mierlo
Energies 2013, 6(11), 5625-5641; https://doi.org/10.3390/en6115625 - 25 Oct 2013
Cited by 80 | Viewed by 10842
Abstract
The Peukert relationship was originally introduced in 1897 for lead-acid batteries and defines one of the most common parameters for battery performance evaluation. This article assesses its application for lithium-ion batteries. From the performed analysis, we can conclude that the Peukert relationship is [...] Read more.
The Peukert relationship was originally introduced in 1897 for lead-acid batteries and defines one of the most common parameters for battery performance evaluation. This article assesses its application for lithium-ion batteries. From the performed analysis, we can conclude that the Peukert relationship is suitable in a narrow working range such as limited current range and almost constant working temperature. Taking into account however that lithium-ion traction batteries in battery electric vehicle applications operate under strongly variable conditions, a novel relationship has been developed, allowing a more accurate description of the discharge capacity of lithium-ion batteries than the Peukert relationship does. The proposed new relationship has been derived based on comprehensive experimental analysis of the parameters that affect the battery discharge capacity and can be implemented in battery mathematical models. Full article
(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)
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611 KiB  
Article
Cost and CO2 Emission Optimization of Steel Reinforced Concrete Columns in High-Rise Buildings
by Hyo Seon Park, Bongkeun Kwon, Yunah Shin, Yousok Kim, Taehoon Hong and Se Woon Choi
Energies 2013, 6(11), 5609-5624; https://doi.org/10.3390/en6115609 - 25 Oct 2013
Cited by 83 | Viewed by 11723
Abstract
The construction industry is a representative industry that consumes large amounts of energy and produces substantial pollution. The operation of a building accounts for a large portion of its total CO2 emissions. Most efforts are focused on improving the energy efficiency related [...] Read more.
The construction industry is a representative industry that consumes large amounts of energy and produces substantial pollution. The operation of a building accounts for a large portion of its total CO2 emissions. Most efforts are focused on improving the energy efficiency related to the operation of a building. The relative importance of the energy and CO2 emissions from the construction materials increases with the increasing number of low-energy buildings. To minimize the life-cycle energy use of a building, the energy consumed from both materials in the construction phase as well as the energy consumed from the operation of the building must be reduced. In this study, an optimal design method for composite columns in high-rise buildings using a genetic algorithm is proposed to reduce cost and CO2 emissions from the structural materials in the construction phase. The proposed optimal method minimizes the total cost, including the additional cost calculated based on CO2 emissions from composite columns, while satisfying the structural design criteria and constructability conditions. The proposed optimal method is applied to an actual 35-story building, and the effective use of structural materials for the sustainable design of composite columns is investigated. It is shown that using more concrete than steel section and using high-strength materials are economically and environmentally effective methods. Full article
(This article belongs to the Special Issue Energy Efficient Building Design 2013)
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982 KiB  
Article
Modeling the Effects of the Cathode Composition of a Lithium Iron Phosphate Battery on the Discharge Behavior
by Jeongbin Lee, Jaeshin Yi, Chee Burm Shin, Seung Ho Yu and Won Il Cho
Energies 2013, 6(11), 5597-5608; https://doi.org/10.3390/en6115597 - 24 Oct 2013
Cited by 6 | Viewed by 6868
Abstract
This paper reports a modeling methodology to predict the effects on the discharge behavior of the cathode composition of a lithium iron phosphate (LFP) battery cell comprising a LFP cathode, a lithium metal anode, and an organic electrolyte. A one-dimensional model based on [...] Read more.
This paper reports a modeling methodology to predict the effects on the discharge behavior of the cathode composition of a lithium iron phosphate (LFP) battery cell comprising a LFP cathode, a lithium metal anode, and an organic electrolyte. A one-dimensional model based on a finite element method is presented to calculate the cell voltage change of a LFP battery cell during galvanostatic discharge. To test the validity of the modeling approach, the modeling results for the variations of the cell voltage of the LFP battery as a function of time are compared with the experimental measurements during galvanostatic discharge at various discharge rates of 0.1C, 0.5C, 1.0C, and 2.0C for three different compositions of the LFP cathode. The discharge curves obtained from the model are in good agreement with the experimental measurements. On the basis of the validated modeling approach, the effects of the cathode composition on the discharge behavior of a LFP battery cell are estimated. The modeling results exhibit highly nonlinear dependencies of the discharge behavior of a LFP battery cell on the discharge C-rate and cathode composition. Full article
(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)
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