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Energies, Volume 7, Issue 1 (January 2014), Pages 1-497

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Research

Open AccessArticle Evaluation of Biofuel Cells with Hemoglobin as Cathodic Electrocatalysts for Hydrogen Peroxide Reduction on Bare Indium-Tin-Oxide Electrodes
Energies 2014, 7(1), 1-12; doi:10.3390/en7010001
Received: 1 November 2013 / Revised: 9 December 2013 / Accepted: 13 December 2013 / Published: 20 December 2013
PDF Full-text (967 KB) | HTML Full-text | XML Full-text
Abstract
A biofuel cell (BFC) cathode has been developed based on direct electron transfer (DET) of hemoglobin (Hb) molecules with an indium-tin-oxide (ITO) electrode and their electrocatalysis for reduction of hydrogen peroxide (H2O2). In this study, the ITO-coated glass plates
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A biofuel cell (BFC) cathode has been developed based on direct electron transfer (DET) of hemoglobin (Hb) molecules with an indium-tin-oxide (ITO) electrode and their electrocatalysis for reduction of hydrogen peroxide (H2O2). In this study, the ITO-coated glass plates or porous glasses were prepared by using a chemical vapor deposition (CVD) method and examined the electrochemical characteristics of the formed ITO in pH 7.4 of phosphate buffered saline (PBS) solutions containing and not containing Hb. In half-cell measurements, the reduction current of H2O2 due to the electrocatalytic activity of Hb increased with decreasing electrode potential from around 0.1 V versus Ag|AgCl|KCl(satd.) in the PBS solution. The practical open-circuit voltage (OCV) on BFCs utilizing H2O2 reduction at the Hb-ITO cathode with a hydrogen (H2) oxidation anode at a platinum (Pt) electrode was expected to be at least 0.74 V from the theoretical H2 oxidation potential of −0.64 V versus Ag|AgCl|KCl(satd.) in pH 7.4. The assembled single cell using the ITO-coated glass plate showed the OCV of 0.72 V and the maximum power density of 3.1 µW cm−2. The maximum power per single cell was recorded at 21.5 µW by using the ITO-coated porous glass. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
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Open AccessArticle Product Yields and Characteristics of Corncob Waste under Various Torrefaction Atmospheres
Energies 2014, 7(1), 13-27; doi:10.3390/en7010013
Received: 23 October 2013 / Revised: 10 December 2013 / Accepted: 13 December 2013 / Published: 20 December 2013
Cited by 8 | PDF Full-text (337 KB) | HTML Full-text | XML Full-text
Abstract
Biomass is a promising energy source due to its abundant, carbon-fixing, and carbon-neutral properties. Torrefaction can be employed to improve the properties of biomass in an oxygen-free or nitrogen atmosphere. This study investigates the product yields and the solid product characteristics from corncob
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Biomass is a promising energy source due to its abundant, carbon-fixing, and carbon-neutral properties. Torrefaction can be employed to improve the properties of biomass in an oxygen-free or nitrogen atmosphere. This study investigates the product yields and the solid product characteristics from corncob waste torrefaction at the temperatures of 250 °C and 300 °C for 1 h. Nitrogen, carbon dioxide, and a gas mixture of air and carbon dioxide are employed as the carrier gases. The solid product characteristics approach those of coal at the higher temperature, regardless of what the carrier gases are. The fixed carbon, higher heating value, and solid and energy yields using carbon dioxide as a carrier gas at 300 °C are close to those using nitrogen. The product safety and storage properties before and after torrefaction are revealed by the measurements of ignition temperature and hygroscopicity. A higher torrefaction temperature leads to a higher ignition temperature of treated biomass, except using the mixture of air and carbon dioxide as the carrier gas. Carbon dioxide is a better carrier gas than nitrogen for biomass torrefaction, from the storage and transportation points of view. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
Open AccessArticle Optimum Settings for a Compound Parabolic Concentrator with Wings Providing Increased Duration of Effective Temperature for Solar-Driven Systems: A Case Study for Tokyo
Energies 2014, 7(1), 28-42; doi:10.3390/en7010028
Received: 22 October 2013 / Revised: 11 December 2013 / Accepted: 17 December 2013 / Published: 24 December 2013
Cited by 2 | PDF Full-text (842 KB) | HTML Full-text | XML Full-text
Abstract
We designed a compound parabolic concentrator (CPC) with wings angled toward the east and west. Normally, solar collectors are straight, facing south, and the effective temperature is only achieved for a short period of time at midday. In the proposed design, the collector
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We designed a compound parabolic concentrator (CPC) with wings angled toward the east and west. Normally, solar collectors are straight, facing south, and the effective temperature is only achieved for a short period of time at midday. In the proposed design, the collector is divided into three parts, with the ends angled and tilted at different orientations. The objective was to increase the duration of the effective temperature period by capturing the maximum solar energy in the morning and afternoon without tracking by the collector. A simulation model was developed to evaluate the performance of the proposed CPC. The tilt and bending angles of the CPC wings were optimized for year-round operation in Tokyo, Japan. A 35° tilt for the south-facing central part of the CPC and a 45° tilt for the wings with 50° angles toward the east and west were found to be optimal. Analyses were conducted at these optimum settings with temperatures of 70, 80, and 90 °C as minimum requirements. The effective duration increased by up to 2 h in the winter and up to 2.53 h in the summer using the proposed CPC. The proposed CPC will improve the efficiency of solar-driven systems by providing useful heat for longer periods of time with the same collector length and without the need for tracking. Full article
Open AccessArticle An Experimental and Numerical Investigation of Fluidized Bed Gasification of Solid Waste
Energies 2014, 7(1), 43-61; doi:10.3390/en7010043
Received: 24 September 2013 / Revised: 9 December 2013 / Accepted: 17 December 2013 / Published: 24 December 2013
Cited by 4 | PDF Full-text (691 KB) | HTML Full-text | XML Full-text
Abstract
Gasification is a thermo-chemical process to convert carbon-based products such as biomass and coal into a gas mixture known as synthetic gas or syngas. Various types of gasification methods exist, and fluidized bed gasification is one of them which is considered more efficient
[...] Read more.
Gasification is a thermo-chemical process to convert carbon-based products such as biomass and coal into a gas mixture known as synthetic gas or syngas. Various types of gasification methods exist, and fluidized bed gasification is one of them which is considered more efficient than others as fuel is fluidized in oxygen, steam or air. This paper presents an experimental and numerical investigation of fluidized bed gasification of solid waste (SW) (wood). The experimental measurement of syngas composition was done using a pilot scale gasifier. A numerical model was developed using Advanced System for Process ENgineering (Aspen) Plus software. Several Aspen Plus reactor blocks were used along with user defined FORTRAN and Excel code. The model was validated with experimental results. The study found very similar performance between simulation and experimental results, with a maximum variation of 3%. The validated model was used to study the effect of air-fuel and steam-fuel ratio on syngas composition. The model will be useful to predict the various operating parameters of a pilot scale SW gasification plant, such as temperature, pressure, air-fuel ratio and steam-fuel ratio. Therefore, the model can assist researchers, professionals and industries to identify optimized conditions for SW gasification. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
Open AccessArticle Analysis of Solid and Aqueous Phase Products from Hydrothermal Carbonization of Whole and Lipid-Extracted Algae
Energies 2014, 7(1), 62-79; doi:10.3390/en7010062
Received: 30 October 2013 / Revised: 11 December 2013 / Accepted: 18 December 2013 / Published: 30 December 2013
Cited by 8 | PDF Full-text (576 KB) | HTML Full-text | XML Full-text
Abstract
Microalgae have tremendous potential as a feedstock for production of liquid biofuels, particularly biodiesel fuel via transesterification of algal lipids. However, biodiesel production results in significant amounts of algal residues, or “lipid extracted algae” (LEA). Suitable utilization of the LEA residue will improve
[...] Read more.
Microalgae have tremendous potential as a feedstock for production of liquid biofuels, particularly biodiesel fuel via transesterification of algal lipids. However, biodiesel production results in significant amounts of algal residues, or “lipid extracted algae” (LEA). Suitable utilization of the LEA residue will improve the economics of algal biodiesel. In the present study, we evaluate the hydrothermal carbonization (HTC) of whole and lipid extracted algal (Spirulina maxima) feedstocks in order to produce a solid biofuel (hydrochar) and value-added co-products in the aqueous phase. HTC experiments were performed using a 2-L Parr reactor (batch type) at 175–215 °C with a 30-min holding time. Solid, aqueous and gaseous products were analyzed using various laboratory methods to evaluate the mass and carbon balances, and investigate the existence of high value chemicals in the aqueous phase. The HTC method is effective in creating an energy dense, solid hydrochar from both whole algae and LEA at lower temperatures as compared to lignocellulosic feedstocks, and is effective at reducing the ash content in the resulting hydrochar. However, under the treatment temperatures investigated, less than 1% of the starting dry algae mass was recovered as an identified high-value chemical in the aqueous phase. Full article
(This article belongs to the Special Issue Algae Fuel 2013)
Open AccessArticle Three-Dimensional CFD Modeling of Transport Phenomena in a Cross-Flow Anode-Supported Planar SOFC
Energies 2014, 7(1), 80-98; doi:10.3390/en7010080
Received: 22 November 2013 / Revised: 18 December 2013 / Accepted: 23 December 2013 / Published: 31 December 2013
Cited by 1 | PDF Full-text (1049 KB) | HTML Full-text | XML Full-text
Abstract
In this study, a three-dimensional computational fluid dynamics (CFD) model is developed for an anode-supported planar SOFC from the Chinese Academy of Science Ningbo Institute of Material Technology and Engineering (NIMTE). The simulation results of the developed model are in good agreement with
[...] Read more.
In this study, a three-dimensional computational fluid dynamics (CFD) model is developed for an anode-supported planar SOFC from the Chinese Academy of Science Ningbo Institute of Material Technology and Engineering (NIMTE). The simulation results of the developed model are in good agreement with the experimental data obtained under the same conditions. With the simulation results, the distribution of temperature, flow velocity and the gas concentrations through the cell components and gas channels is presented and discussed. Potential and current density distributions in the cell and overall fuel utilization are also presented. It is also found that the temperature gradients exist along the length of the cell, and the maximum value of the temperature for the cross-flow is at the outlet region of the cell. The distribution of the current density is uneven, and the maximum current density is located at the interfaces between the channels, ribs and the electrodes, the maximum current density result in a large over-potential and heat source in the electrodes, which is harmful to the overall performance and working lifespan of the fuel cells. A new type of flow structure should be developed to make the current flow be more evenly distributed and promote most of the TPB areas to take part in the electrochemical reactions. Full article
(This article belongs to the Special Issue Reacting Transport Phenomena in Solid Oxide Fuel Cells)
Open AccessArticle Energy-Regenerative Braking Control of Electric Vehicles Using Three-Phase Brushless Direct-Current Motors
Energies 2014, 7(1), 99-114; doi:10.3390/en7010099
Received: 26 November 2013 / Revised: 19 December 2013 / Accepted: 25 December 2013 / Published: 31 December 2013
Cited by 8 | PDF Full-text (741 KB) | HTML Full-text | XML Full-text
Abstract
Regenerative braking provides an effective way of extending the driving range of battery powered electric vehicles (EVs). This paper analyzes the equivalent power circuit and operation principles of an EV using regenerative braking control technology. During the braking period, the switching sequence of
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Regenerative braking provides an effective way of extending the driving range of battery powered electric vehicles (EVs). This paper analyzes the equivalent power circuit and operation principles of an EV using regenerative braking control technology. During the braking period, the switching sequence of the power converter is controlled to inverse the output torque of the three-phase brushless direct-current (DC) motor, so that the braking energy can be returned to the battery. Compared with the presented methods, this technology can achieve several goals: energy recovery, electric braking, ultra-quiet braking and extending the driving range. Merits and drawbacks of different braking control strategy are further elaborated. State-space model of the EVs under energy-regenerative braking operation is established, considering that parameter variations are unavoidable due to temperature change, measured error, un-modeled dynamics, external disturbance and time-varying system parameters, a sliding mode robust controller (SMRC) is designed and implemented. Phase current and DC-link voltage are selected as the state variables, respectively. The corresponding control law is also provided. The proposed control scheme is compared with a conventional proportional-integral (PI) controller. A laboratory EV for experiment is setup to verify the proposed scheme. Experimental results show that the drive range of EVs can be improved about 17% using the proposed controller with energy-regeneration control. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
Open AccessArticle A Load Fluctuation Characteristic Index and Its Application to Pilot Node Selection
Energies 2014, 7(1), 115-129; doi:10.3390/en7010115
Received: 22 October 2013 / Revised: 17 December 2013 / Accepted: 27 December 2013 / Published: 3 January 2014
Cited by 4 | PDF Full-text (957 KB) | HTML Full-text | XML Full-text
Abstract
The operation of power systems has been complicated by the rapid diversification of loads. Analyzing load characteristics becomes necessary to different utilities in energy management systems to ensure the reliability of power systems. Here, we describe a method of analyzing and quantifying the
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The operation of power systems has been complicated by the rapid diversification of loads. Analyzing load characteristics becomes necessary to different utilities in energy management systems to ensure the reliability of power systems. Here, we describe a method of analyzing and quantifying the load characteristics and introduce its application to pilot nodes selection for zone based voltage control. We propose a new index, the Q-fluctuation (QF), to quantify the load characteristic of reactive power based on an analysis of historical data. A second index, the V-fluctuation (VF), which is a combination of the QF and the Q–V sensitivity that reflects structural information for the grid describes the voltage deviation at each node. These indices are used to construct the voltage fluctuation space, which is then used to select the pilot node for each zone. Simulation studies using IEEE 14-bus and 118-bus systems are described, and used to demonstrate the advantages of the proposed method. The method was able to improve the secondary voltage control and enhance the grid reliability in response to structural changes. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
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Open AccessArticle Optimal Sizing of Battery Storage Systems for Industrial Applications when Uncertainties Exist
Energies 2014, 7(1), 130-149; doi:10.3390/en7010130
Received: 21 October 2013 / Revised: 11 December 2013 / Accepted: 27 December 2013 / Published: 3 January 2014
Cited by 7 | PDF Full-text (331 KB) | HTML Full-text | XML Full-text
Abstract
Demand response (DR) can be very useful for an industrial facility, since it allows noticeable reductions in the electricity bill due to the significant value of energy demand. Although most industrial processes have stringent constraints in terms of hourly active power, DR only
[...] Read more.
Demand response (DR) can be very useful for an industrial facility, since it allows noticeable reductions in the electricity bill due to the significant value of energy demand. Although most industrial processes have stringent constraints in terms of hourly active power, DR only becomes attractive when performed with the contemporaneous use of battery energy storage systems (BESSs). When this option is used, an optimal sizing of BESSs is desirable, because the investment costs can be significant. This paper deals with the optimal sizing of a BESS installed in an industrial facility to reduce electricity costs. A four-step procedure, based on Decision Theory, was used to obtain a good solution for the sizing problem, even when facing uncertainties; in fact, we think that the sizing procedure must properly take into account the unavoidable uncertainties introduced by the cost of electricity and the load demands of industrial facilities. Three approaches provided by Decision Theory were applied, and they were based on: (1) the minimization of expected cost; (2) the regret felt by the sizing engineer; and (3) a mix of (1) and (2). The numerical applications performed on an actual industrial facility provided evidence of the effectiveness of the proposed procedure. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle The Influence of Output Variability from Renewable Electricity Generation on Net Energy Calculations
Energies 2014, 7(1), 150-172; doi:10.3390/en7010150
Received: 28 October 2013 / Revised: 9 December 2013 / Accepted: 17 December 2013 / Published: 6 January 2014
PDF Full-text (821 KB) | HTML Full-text | XML Full-text
Abstract
One key approach to analyzing the feasibility of energy extraction and generation technologies is to understand the net energy they contribute to society. These analyses most commonly focus on a simple comparison of a source’s expected energy outputs to the required energy inputs,
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One key approach to analyzing the feasibility of energy extraction and generation technologies is to understand the net energy they contribute to society. These analyses most commonly focus on a simple comparison of a source’s expected energy outputs to the required energy inputs, measured in the form of energy return on investment (EROI). What is not typically factored into net energy analysis is the influence of output variability. This omission ignores a key attribute of biological organisms and societies alike: the preference for stable returns with low dispersion versus equivalent returns that are intermittent or variable. This biologic predilection for stability, observed and refined in academic financial literature, has a direct relationship to many new energy technologies whose outputs are much more variable than traditional energy sources. We investigate the impact of variability on net energy metrics and develop a theoretical framework to evaluate energy systems based on existing financial and biological risk models. We then illustrate the impact of variability on nominal energy return using representative technologies in electricity generation, with a more detailed analysis on wind power, where intermittence and stochastic availability of hard-to-store electricity will be factored into theoretical returns. Full article
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Open AccessArticle Mathematical Modeling Analysis and Optimization of Key Design Parameters of Proton-Conductive Solid Oxide Fuel Cells
Energies 2014, 7(1), 173-190; doi:10.3390/en7010173
Received: 19 November 2013 / Revised: 20 December 2013 / Accepted: 24 December 2013 / Published: 7 January 2014
Cited by 4 | PDF Full-text (856 KB) | HTML Full-text | XML Full-text
Abstract
A proton-conductive solid oxide fuel cell (H-SOFC) has the advantage of operating at higher temperatures than a PEM fuel cell, but at lower temperatures than a SOFC. This study proposes a mathematical model for an H-SOFC in order to simulate the performance and
[...] Read more.
A proton-conductive solid oxide fuel cell (H-SOFC) has the advantage of operating at higher temperatures than a PEM fuel cell, but at lower temperatures than a SOFC. This study proposes a mathematical model for an H-SOFC in order to simulate the performance and optimize the flow channel designs. The model analyzes the average mass transfer and species’ concentrations in flow channels, which allows the determination of an average concentration polarization in anode and cathode gas channels, the proton conductivity of electrolyte membranes, as well as the activation polarization. An electrical circuit for the current and proton conduction is applied to analyze the ohmic losses from an anode current collector to a cathode current collector. The model uses relatively less amount of computational time to find the V-I curve of the fuel cell, and thus it can be applied to compute a large amount of cases with different flow channel dimensions and operating parameters for optimization. The modeling simulation results agreed satisfactorily with the experimental results from literature. Simulation results showed that a relatively small total width of flow channel and rib, together with a small ratio of the rib’s width versus the total width, are preferable for obtaining high power densities and thus high efficiency. Full article
(This article belongs to the Special Issue Reacting Transport Phenomena in Solid Oxide Fuel Cells)
Open AccessArticle Optimal PID Controller Design Based on PSO-RBFNN for Wind Turbine Systems
Energies 2014, 7(1), 191-209; doi:10.3390/en7010191
Received: 17 September 2013 / Revised: 27 November 2013 / Accepted: 31 December 2013 / Published: 7 January 2014
Cited by 11 | PDF Full-text (474 KB) | HTML Full-text | XML Full-text
Abstract
A strategy was proposed to determine the optimal operating point for the proportional-integral-derivative (PID) controller of a wind turbine, and identify the stability regions in the parameter space. The proposed approach combined particle swarm optimization (PSO) and radial basis function neural network (RBFNN)
[...] Read more.
A strategy was proposed to determine the optimal operating point for the proportional-integral-derivative (PID) controller of a wind turbine, and identify the stability regions in the parameter space. The proposed approach combined particle swarm optimization (PSO) and radial basis function neural network (RBFNN) algorithms. These intelligent algorithms are artificial learning mechanisms that can determine the optimal operating points, and were used to generate the function representing the most favorable operating  parameters from each parameter of  for the stability region of the PID controller. A graphical method was used to determine the 2D or 3D vision boundaries of the PID-type controller space in closed-loop wind turbine systems. The proposed techniques were demonstrated using simulations of a drive train model without time delay and a pitch control model with time delay. Finally, the 3D stability boundaries were determined the proposed graphical approach with and without time delay systems. Full article
Open AccessArticle Implementation and Control of a Residential Electrothermal Microgrid Based on Renewable Energies, a Hybrid Storage System and Demand Side Management
Energies 2014, 7(1), 210-237; doi:10.3390/en7010210
Received: 17 October 2013 / Revised: 31 December 2013 / Accepted: 2 January 2014 / Published: 8 January 2014
Cited by 10 | PDF Full-text (509 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes an energy management strategy for a residential electrothermal microgrid, based on renewable energy sources. While grid connected, it makes use of a hybrid electrothermal storage system, formed by a battery and a hot water tank along with an electrical water
[...] Read more.
This paper proposes an energy management strategy for a residential electrothermal microgrid, based on renewable energy sources. While grid connected, it makes use of a hybrid electrothermal storage system, formed by a battery and a hot water tank along with an electrical water heater as a controllable load, which make possible the energy management within the microgrid. The microgrid emulates the operation of a single family home with domestic hot water (DHW) consumption, a heating, ventilation and air conditioning (HVAC) system as well as the typical electric loads. An energy management strategy has been designed which optimizes the power exchanged with the grid profile in terms of peaks and fluctuations, in applications with high penetration levels of renewables. The proposed energy management strategy has been evaluated and validated experimentally in a full scale residential microgrid built in our Renewable Energy Laboratory, by means of continuous operation under real conditions. The results show that the combination of electric and thermal storage systems with controllable loads is a promising technology that could maximize the penetration level of renewable energies in the electric system. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle An Integrated Modeling Approach to Evaluate and Optimize Data Center Sustainability, Dependability and Cost
Energies 2014, 7(1), 238-277; doi:10.3390/en7010238
Received: 10 October 2013 / Revised: 29 November 2013 / Accepted: 15 December 2013 / Published: 8 January 2014
PDF Full-text (2116 KB) | HTML Full-text | XML Full-text
Abstract
Data centers have evolved dramatically in recent years, due to the advent of social networking services, e-commerce and cloud computing. The conflicting requirements are the high availability levels demanded against the low sustainability impact and cost values. The approaches that evaluate and optimize
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Data centers have evolved dramatically in recent years, due to the advent of social networking services, e-commerce and cloud computing. The conflicting requirements are the high availability levels demanded against the low sustainability impact and cost values. The approaches that evaluate and optimize these requirements are essential to support designers of data center architectures. Our work aims to propose an integrated approach to estimate and optimize these issues with the support of the developed environment, Mercury. Mercury is a tool for dependability, performance and energy flow evaluation. The tool supports reliability block diagrams (RBD), stochastic Petri nets (SPNs), continuous-time Markov chains (CTMC) and energy flow (EFM) models. The EFM verifies the energy flow on data center architectures, taking into account the energy efficiency and power capacity that each device can provide (assuming power systems) or extract (considering cooling components). The EFM also estimates the sustainability impact and cost issues of data center architectures. Additionally, a methodology is also considered to support the modeling, evaluation and optimization processes. Two case studies are presented to illustrate the adopted methodology on data center power systems. Full article
Open AccessArticle Analysis of the Dynamic Performance of Self-Excited Induction Generators Employed in Renewable Energy Generation
Energies 2014, 7(1), 278-294; doi:10.3390/en7010278
Received: 5 November 2013 / Revised: 5 December 2013 / Accepted: 7 January 2014 / Published: 10 January 2014
PDF Full-text (430 KB) | HTML Full-text | XML Full-text
Abstract
Incentives, such as the Feed-in-tariff are expected to lead to continuous increase in the deployment of Small Scale Embedded Generation (SSEG) in the distribution network. Self-Excited Induction Generators (SEIG) represent a significant segment of potential SSEG. The quality of SEIG output voltage magnitude
[...] Read more.
Incentives, such as the Feed-in-tariff are expected to lead to continuous increase in the deployment of Small Scale Embedded Generation (SSEG) in the distribution network. Self-Excited Induction Generators (SEIG) represent a significant segment of potential SSEG. The quality of SEIG output voltage magnitude and frequency is investigated in this paper to support the SEIG operation for different network operating conditions. The dynamic behaviour of the SEIG resulting from disconnection, reconnection from/to the grid and potential operation in islanding mode is studied in detail. The local load and reactive power supply are the key factors that determine the SEIG performance, as they have significant influence on the voltage and frequency change after disconnection from the grid. Hence, the aim of this work is to identify the optimum combination of the reactive power supply (essential for self excitation of the SEIG) and the active load (essential for balancing power generation and demand). This is required in order to support the SEIG operation after disconnection from the grid, during islanding and reconnection to the grid. The results show that the generator voltage and speed (frequency) can be controlled and maintained within the statuary limits. This will enable safe disconnection and reconnection of the SEIG from/to the grid and makes it easier to operate in islanding mode. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle Optimization of the Interconnect Ribs for a Cathode-Supported Solid Oxide Fuel Cell
Energies 2014, 7(1), 295-313; doi:10.3390/en7010295
Received: 6 November 2013 / Revised: 30 December 2013 / Accepted: 2 January 2014 / Published: 10 January 2014
Cited by 7 | PDF Full-text (794 KB) | HTML Full-text | XML Full-text
Abstract
A comprehensive mathematical model of the performance of the cathode-supported solid oxide fuel cell (SOFC) with syngas fuel is presented. The model couples the intricate interdependency between the ionic conduction, electronic conduction, gas transport, the electrochemical reaction processes in the functional layers and
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A comprehensive mathematical model of the performance of the cathode-supported solid oxide fuel cell (SOFC) with syngas fuel is presented. The model couples the intricate interdependency between the ionic conduction, electronic conduction, gas transport, the electrochemical reaction processes in the functional layers and on the electrode/electrolyte interfaces, methane steam reforming (MSR) and the water gas shift reaction (WGSR). The validity of the mathematical model is demonstrated by the excellent agreement between the numerical and experimental I-V curves. The effect of anode rib width and cathode rib width on gas diffusion and cell performance is examined. The results show conclusively that the cell performance is strongly influenced by the rib width. Furthermore, the anode optimal rib width is smaller than that for cathode, which is contrary to anode-supported SOFC. Finally, the formulae for the anode and cathode optimal rib width are given, which provide an easy to use guidance for the broad SOFC engineering community. Full article
(This article belongs to the Special Issue Reacting Transport Phenomena in Solid Oxide Fuel Cells)
Open AccessArticle The Oil and Gas Discourse from the Perspective of the Canadian and Albertan Governments, Non-Governmental Organizations and the Oil and Gas Industry
Energies 2014, 7(1), 314-333; doi:10.3390/en7010314
Received: 20 November 2013 / Revised: 23 December 2013 / Accepted: 7 January 2014 / Published: 16 January 2014
PDF Full-text (241 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Three of the major players in the discussion of the production of oil and gas are: (1) government; (2) the oil and gas industry and (3) non-governmental organizations (NGOs). A comparison of contributions from these three sources using a list of positive and
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Three of the major players in the discussion of the production of oil and gas are: (1) government; (2) the oil and gas industry and (3) non-governmental organizations (NGOs). A comparison of contributions from these three sources using a list of positive and negative words from the General Inquirer Category Listings showed that industry provided a very positive message about the production and consumption of oil and gas that is generally reinforced by government whereas NGOs advocated for a reduction in the use of oil and gas. Messages delivered by each player are focused on the same topics in either a positive or negative way and are often contradictory. The authors submit to be properly informed the public must consider all the sources in order to avoid bias. A mind map is presented in a supplementary file which summarizes information from each source in a comprehensive way. This approach can be used by consumers when considering the choice of using oil and gas and can be extended to the discourse beyond Canada. Full article
Open AccessArticle Emission Characteristics of a CI Engine Running with a Range of Biodiesel Feedstocks
Energies 2014, 7(1), 334-350; doi:10.3390/en7010334
Received: 4 November 2013 / Revised: 7 January 2014 / Accepted: 8 January 2014 / Published: 16 January 2014
Cited by 10 | PDF Full-text (1647 KB) | HTML Full-text | XML Full-text
Abstract
Currently, alternative fuels are being investigated in detail for application in compression ignition (CI) engines resulting in exciting potential opportunities to increase energy security and reduce gas emissions. Biodiesel is one of the alternative fuels which is renewable and environmentally friendly and can
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Currently, alternative fuels are being investigated in detail for application in compression ignition (CI) engines resulting in exciting potential opportunities to increase energy security and reduce gas emissions. Biodiesel is one of the alternative fuels which is renewable and environmentally friendly and can be used in diesel engines with little or no modifications. The objective of this study is to investigate the effects of biodiesel types and biodiesel fraction on the emission characteristics of a CI engine. The experimental work was carried out on a four-cylinder, four-stroke, direct injection (DI) and turbocharged diesel engine by using biodiesel made from waste oil, rapeseed oil, corn oil and comparing them to normal diesel. The fuels used in the analyses are B10, B20, B50, B100 and neat diesel. The engine was operated over a range of engine speeds. Based on the measured parameters, detailed analyses were carried out on major regulated emissions such as NOx, CO, CO2, and THC. It has been seen that the biodiesel types (sources) do not result in any significant differences in emissions. The results also clearly indicate that the engine running with biodiesel and blends have higher NOx emission by up to 20%. However, the emissions of the CI engine running on neat biodiesel (B100) were reduced by up to 15%, 40% and 30% for CO, CO2 and THC emissions respectively, as compared to diesel fuel at various operating conditions. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
Open AccessArticle Polarization Curve of a Non-Uniformly Aged PEM Fuel Cell
Energies 2014, 7(1), 351-364; doi:10.3390/en7010351
Received: 11 November 2013 / Revised: 3 January 2014 / Accepted: 8 January 2014 / Published: 16 January 2014
Cited by 1 | PDF Full-text (362 KB) | HTML Full-text | XML Full-text
Abstract
We develop a semi-analytical model for polarization curve of a polymer electrolyte membrane (PEM) fuel cell with distributed (aged) along the oxygen channel MEA transport and kinetic parameters of the membrane–electrode assembly (MEA). We show that the curve corresponding to varying along the
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We develop a semi-analytical model for polarization curve of a polymer electrolyte membrane (PEM) fuel cell with distributed (aged) along the oxygen channel MEA transport and kinetic parameters of the membrane–electrode assembly (MEA). We show that the curve corresponding to varying along the channel parameter, in general, does not reduce to the curve for a certain constant value of this parameter. A possibility to determine the shape of the deteriorated MEA parameter along the oxygen channel by fitting the model equation to the cell polarization data is demonstrated. Full article
(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells)
Open AccessArticle Three-Phase Harmonic Analysis Method for Unbalanced Distribution Systems
Energies 2014, 7(1), 365-384; doi:10.3390/en7010365
Received: 8 November 2013 / Revised: 18 December 2013 / Accepted: 9 January 2014 / Published: 20 January 2014
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Abstract
Due to the unbalanced features of distribution systems, a three-phase harmonic analysis method is essential to accurately analyze the harmonic impact on distribution systems. Moreover, harmonic analysis is the basic tool for harmonic filter design and harmonic resonance mitigation; therefore, the computational performance
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Due to the unbalanced features of distribution systems, a three-phase harmonic analysis method is essential to accurately analyze the harmonic impact on distribution systems. Moreover, harmonic analysis is the basic tool for harmonic filter design and harmonic resonance mitigation; therefore, the computational performance should also be efficient. An accurate and efficient three-phase harmonic analysis method for unbalanced distribution systems is proposed in this paper. The variations of bus voltages, bus current injections and branch currents affected by harmonic current injections can be analyzed by two relationship matrices developed from the topological characteristics of distribution systems. Some useful formulas are then derived to solve the three-phase harmonic propagation problem. After the harmonic propagation for each harmonic order is calculated, the total harmonic distortion (THD) for bus voltages can be calculated accordingly. The proposed method has better computational performance, since the time-consuming full admittance matrix inverse employed by the commonly-used harmonic analysis methods is not necessary in the solution procedure. In addition, the proposed method can provide novel viewpoints in calculating the branch currents and bus voltages under harmonic pollution which are vital for harmonic filter design. Test results demonstrate the effectiveness and efficiency of the proposed method. Full article
Open AccessArticle Distributed Load-Shedding System for Agent-Based Autonomous Microgrid Operations
Energies 2014, 7(1), 385-401; doi:10.3390/en7010385
Received: 19 November 2013 / Revised: 18 December 2013 / Accepted: 9 January 2014 / Published: 20 January 2014
Cited by 9 | PDF Full-text (576 KB) | HTML Full-text | XML Full-text
Abstract
A microgrid is an eco-friendly power system because renewable sources are used as main power sources. In the islanded operation mode of a microgrid, maintaining the balance between power supply and power demand is a very important problem. In the case of surplus
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A microgrid is an eco-friendly power system because renewable sources are used as main power sources. In the islanded operation mode of a microgrid, maintaining the balance between power supply and power demand is a very important problem. In the case of surplus supply, decreased generation output and/or charge of distributed storages can be applied to solve the imbalance between power supply and demand. In the case of supply shortages, increased generation output and/or discharge of distributed storages can be applied. Especially in the case of critical supply shortages, load shedding should be applied. In a distributed load-shedding approach, microgrid components need to make decisions autonomously. For autonomous microgrid operation, a multi-agent system has been investigated. In this paper, a distributed load-shedding system for agent-based autonomous operation of a microgrid is designed. The designed system is implemented and tested to show the functionality and feasibility of the proposed system. Full article
(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)
Open AccessArticle Modeling and Design Optimization of Variable-Speed Wind Turbine Systems
Energies 2014, 7(1), 402-419; doi:10.3390/en7010402
Received: 25 November 2013 / Revised: 13 January 2014 / Accepted: 15 January 2014 / Published: 21 January 2014
Cited by 8 | PDF Full-text (385 KB) | HTML Full-text | XML Full-text
Abstract
As a result of the increase in energy demand and government subsidies, the usage of wind turbine system (WTS) has increased dramatically. Due to the higher energy production of a variable-speed WTS as compared to a fixed-speed WTS, the demand for this type
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As a result of the increase in energy demand and government subsidies, the usage of wind turbine system (WTS) has increased dramatically. Due to the higher energy production of a variable-speed WTS as compared to a fixed-speed WTS, the demand for this type of WTS has increased. In this study, a new method for the calculation of the power output of variable-speed WTSs is proposed. The proposed model is developed from the S-type curve used for population growth, and is only a function of the rated power and rated (nominal) wind speed. It has the advantage of enabling the user to calculate power output without using the rotor power coefficient. Additionally, by using the developed model, a mathematical method to calculate the value of rated wind speed in terms of turbine capacity factor and the scale parameter of the Weibull distribution for a given wind site is also proposed. Design optimization studies are performed by using the particle swarm optimization (PSO) and artificial bee colony (ABC) algorithms, which are applied into this type of problem for the first time. Different sites such as Northern and Mediterranean sites of Europe have been studied. Analyses for various parameters are also presented in order to evaluate the effect of rated wind speed on the design parameters and produced energy cost. Results show that proposed models are reliable and very useful for modeling and optimization of WTSs design by taking into account the wind potential of the region. Results also show that the PSO algorithm has better performance than the ABC algorithm for this type of problem. Full article
Open AccessArticle A Static Voltage Security Region for Centralized Wind Power Integration—Part I: Concept and Method
Energies 2014, 7(1), 420-443; doi:10.3390/en7010420
Received: 26 November 2013 / Revised: 4 January 2014 / Accepted: 17 January 2014 / Published: 22 January 2014
Cited by 5 | PDF Full-text (813 KB) | HTML Full-text | XML Full-text
Abstract
When large wind farms are centrally integrated in a power grid, cascading tripping faults induced by voltage issues are becoming a great challenge. This paper therefore proposes a concept of static voltage security region to guarantee that the voltage will remain within operation
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When large wind farms are centrally integrated in a power grid, cascading tripping faults induced by voltage issues are becoming a great challenge. This paper therefore proposes a concept of static voltage security region to guarantee that the voltage will remain within operation limits under both base conditions and N-1 contingencies. For large wind farms, significant computational effort is required to calculate the exact boundary of the proposed security region. To reduce this computational burden and facilitate the overall analysis, the characteristics of the security region are first analyzed, and its boundary components are shown to be strictly convex. Approximate security regions are then proposed, which are formed by a set of linear cutting planes based on special operating points known as near points and inner points. The security region encompassed by cutting planes is a good approximation to the actual security region. The proposed procedures are demonstrated on a modified nine-bus system with two wind farms. The simulation confirmed that the cutting plane technique can provide a very good approximation to the actual security region. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
Open AccessArticle A Static Voltage Security Region for Centralized Wind Power Integration—Part II: Applications
Energies 2014, 7(1), 444-461; doi:10.3390/en7010444
Received: 26 November 2013 / Revised: 12 January 2014 / Accepted: 13 January 2014 / Published: 22 January 2014
Cited by 6 | PDF Full-text (511 KB) | HTML Full-text | XML Full-text
Abstract
In Part I of this work, a static voltage security region was introduced to guarantee the safety of wind farm reactive power outputs under both base conditions and N-1 contingency. In this paper, a mathematical representation of the approximate N-1 security region has
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In Part I of this work, a static voltage security region was introduced to guarantee the safety of wind farm reactive power outputs under both base conditions and N-1 contingency. In this paper, a mathematical representation of the approximate N-1 security region has further studied to provide better coordination among wind farms and help prevent cascading tripping following a single wind farm trip. Besides, the influence of active power on the security region is studied. The proposed methods are demonstrated for N-1 contingency cases in a nine-bus system. The simulations verify that the N-1 security region is a small subset of the security region under base conditions. They also illustrate the fact that if the system is simply operated below the reactive power limits, without coordination among the wind farms, the static voltage is likely to exceed its limit. A two-step optimal adjustment strategy is introduced to shift insecure operating points into the security region under N-1 contingency. Through extensive numerical studies, the effectiveness of the proposed technique is confirmed. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
Open AccessArticle Analysis of Organic and Inorganic Contaminants in Dried Sewage Sludge and By-Products of Dried Sewage Sludge Gasification
Energies 2014, 7(1), 462-476; doi:10.3390/en7010462
Received: 26 November 2013 / Revised: 17 January 2014 / Accepted: 17 January 2014 / Published: 22 January 2014
Cited by 13 | PDF Full-text (459 KB) | HTML Full-text | XML Full-text
Abstract
Organic and inorganic contaminants in sewage sludge may cause their presence also in the by-products formed during gasification processes. Thus, this paper presents multidirectional chemical instrumental activation analyses of dried sewage sludge as well as both solid (ash, char coal) and liquid (tar)
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Organic and inorganic contaminants in sewage sludge may cause their presence also in the by-products formed during gasification processes. Thus, this paper presents multidirectional chemical instrumental activation analyses of dried sewage sludge as well as both solid (ash, char coal) and liquid (tar) by-products formed during sewage gasification in a fixed bed reactor which was carried out to assess the extent of that phenomenon. Significant differences were observed in the type of contaminants present in the solid and liquid by-products from the dried sewage sludge gasification. Except for heavy metals, the characteristics of the contaminants in the by-products, irrespective of their form (solid and liquid), were different from those initially determined in the sewage sludge. It has been found that gasification promotes the migration of certain valuable inorganic compounds from sewage sludge into solid by-products which might be recovered. On the other hand, the liquid by-products resulting from sewage sludge gasification require a separate process for their treatment or disposal due to their considerable loading with toxic and hazardous organic compounds (phenols and their derivatives). Full article
Open AccessArticle Application and Comparison of Different Combustion Models of High Pressure LOX/CH4 Jet Flames
Energies 2014, 7(1), 477-497; doi:10.3390/en7010477
Received: 18 December 2013 / Revised: 14 January 2014 / Accepted: 15 January 2014 / Published: 22 January 2014
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Abstract
The present work focuses on the numerical modeling of combustion in liquid-propellant rocket engines. Pressure and temperature are well above thermodynamic critical points of both the propellants and then the reactants show liquid-like characteristics of density and gas-like characteristics for diffusivity. The aim
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The present work focuses on the numerical modeling of combustion in liquid-propellant rocket engines. Pressure and temperature are well above thermodynamic critical points of both the propellants and then the reactants show liquid-like characteristics of density and gas-like characteristics for diffusivity. The aim of the work is an efficient numerical description of the phenomena and RANS simulations were performed for this purpose. Hence, in the present work different kinetics, combustion models and thermodynamic approaches were used for combustion modeling first in a trans-critical environment, then in the sub-critical state. For phases treatment the pure Eulerian single phase approach was compared with the Lagrangian/Eulerian description. For modeling combustion, the Probability Density Function (PDF) equilibrium and flamelet approaches and the Eddy Dissipation approach, with two different chemical kinetic mechanisms (the Jones-Lindstedt and the Skeletal model), were used. Real Gas (Soave-Redlich-Kwong and Peng-Robinson) equations were applied. To estimate the suitability of different strategies in phenomenon description, a comparison with experimental data from the literature was performed, using the results for different operative conditions of the Mascotte test bench: trans-critical and subcritical condition for oxygen injection. The main result of this study is the individuation of the DPM approach of the most versatile methods to reproduce cryogenic combustion adapted for different operating conditions and producing good results. Full article

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