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Energies, Volume 3, Issue 4 (April 2010), Pages 592-898

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Research

Jump to: Review

Open AccessArticle Assessment of the Effects of Flow Rate and Ionic Strength on the Performance of an Air-Cathode Microbial Fuel Cell Using Electrochemical Impedance Spectroscopy
Energies 2010, 3(4), 592-606; doi:10.3390/en3040592
Received: 5 January 2010 / Revised: 27 February 2010 / Accepted: 15 March 2010 / Published: 26 March 2010
Cited by 20 | PDF Full-text (245 KB) | HTML Full-text | XML Full-text
Abstract
Impedance changes of the anode, cathode and solution were examined for an air-cathode microbial fuel cell (MFC) under varying conditions. An MFC inoculated with a pre-enriched microbial culture resulted in a startup time of less than ten days. Over this period, the anode
[...] Read more.
Impedance changes of the anode, cathode and solution were examined for an air-cathode microbial fuel cell (MFC) under varying conditions. An MFC inoculated with a pre-enriched microbial culture resulted in a startup time of less than ten days. Over this period, the anode impedance decreased below the cathode impedance, suggesting a cathode-limited power output. Increasing the anode flow rate did not impact the anode impedance significantly, but it decreased the cathode impedance by 65%. Increasing the anode-medium ionic strength also decreased the cathode impedance. These impedance results provide insight into electron and proton transport mechanisms and can be used to improve MFC performance. Full article
(This article belongs to the Special Issue Fuel Cells)
Open AccessArticle Investigating “Egusi” (Citrullus Colocynthis L.) Seed Oil as Potential Biodiesel Feedstock
Energies 2010, 3(4), 607-618; doi:10.3390/en3040607
Received: 22 October 2009 / Revised: 31 December 2009 / Accepted: 15 January 2010 / Published: 30 March 2010
Cited by 20 | PDF Full-text (302 KB) | HTML Full-text | XML Full-text
Abstract
Biodiesel’s acceptance as a substitute for fossil-derived diesel has grown the world over. However, the food-fuel debate over conventional vegetable oils has rekindled research interest in exploring lesser known and minor oil crops. In this work, egusi melon seed oil was studied for
[...] Read more.
Biodiesel’s acceptance as a substitute for fossil-derived diesel has grown the world over. However, the food-fuel debate over conventional vegetable oils has rekindled research interest in exploring lesser known and minor oil crops. In this work, egusi melon seed oil was studied for the first time as a potential feedstock for biodiesel production. Crude egusi melon seed oil was transesterified using sodium methoxide as the catalyst at 60 °C and an oil/methanol ratio of 1:6 to produce its corresponding methyl esters. Egusi melon oil methyl ester (EMOME) yield was 82%. Gas chromatographic analysis of EMOME showed that it was composed mainly of palmitic, stearic, oleic, linoleic and linolenic esters, which is similar to the profile of sunflower, soybean and safflower oil. All the measured fuel properties of EMOME satisfied both the ASTM D6751 and the EN 14214 biodiesel standards. Fuel properties of EMOME were essentially identical with those of soybean, safflower and sunflower biodiesel. Remarkably, the kinematic viscosity of EMOME was measured to be 3.83 mm2/s, a value lower than most biodiesel fuels reported in the literature. The potential of egusi melon seed oil as a biodiesel feedstock is clearly presented in this study. Full article
Open AccessArticle A Wind Farm Electrical Systems Evaluation with EeFarm-II
Energies 2010, 3(4), 619-633; doi:10.3390/en3040619
Received: 27 January 2010 / Accepted: 20 February 2010 / Published: 31 March 2010
Cited by 7 | PDF Full-text (1125 KB) | HTML Full-text | XML Full-text
Abstract
EeFarm-II is used to evaluate 13 different electrical systems for a 200 MW wind farm with a 100 km connection to shore. The evaluation is based on component manufacturer data of 2009. AC systems are compared to systems with DC connections inside the
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EeFarm-II is used to evaluate 13 different electrical systems for a 200 MW wind farm with a 100 km connection to shore. The evaluation is based on component manufacturer data of 2009. AC systems are compared to systems with DC connections inside the wind farm and DC connection to shore. Two options have the best performance for this wind farm size and distance: the AC system and the system with a DC connection to shore. EeFarm-II is a user friendly computer program for wind farm electrical and economic evaluation. It has been built as a Simulink Library in the graphical interface of Matlab-Simulink. EeFarm-II contains models of wind turbines, generators, transformers, AC cables, inductors, nodes, splitters, PWM converters, thyristor converters, DC cables, choppers and statcoms. Full article
(This article belongs to the Special Issue Wind Energy)
Open AccessArticle A Shrouded Wind Turbine Generating High Output Power with Wind-lens Technology
Energies 2010, 3(4), 634-649; doi:10.3390/en3040634
Received: 20 January 2010 / Revised: 6 February 2010 / Accepted: 27 February 2010 / Published: 31 March 2010
Cited by 80 | PDF Full-text (1230 KB) | HTML Full-text | XML Full-text
Abstract
We have developed a new wind turbine system that consists of a diffuser shroud with a broad-ring brim at the exit periphery and a wind turbine inside it. The shrouded wind turbine with a brimmed diffuser has demonstrated power augmentation by a factor
[...] Read more.
We have developed a new wind turbine system that consists of a diffuser shroud with a broad-ring brim at the exit periphery and a wind turbine inside it. The shrouded wind turbine with a brimmed diffuser has demonstrated power augmentation by a factor of about 2–5 compared with a bare wind turbine, for a given turbine diameter and wind speed. This is because a low-pressure region, due to a strong vortex formation behind the broad brim, draws more mass flow to the wind turbine inside the diffuser shroud. Full article
(This article belongs to the Special Issue Wind Energy)
Open AccessArticle New Approaches for Very Short-term Steady-State Analysis of An Electrical Distribution System with Wind Farms
Energies 2010, 3(4), 650-670; doi:10.3390/en3040650
Received: 21 February 2010 / Revised: 23 March 2010 / Accepted: 29 March 2010 / Published: 1 April 2010
Cited by 8 | PDF Full-text (249 KB) | HTML Full-text | XML Full-text
Abstract
Distribution networks are undergoing radical changes due to the high level of penetration of dispersed generation. Dispersed generation systems require particular attention due to their incorporation of uncertain energy sources, such as wind farms, and due to the impacts that such sources have
[...] Read more.
Distribution networks are undergoing radical changes due to the high level of penetration of dispersed generation. Dispersed generation systems require particular attention due to their incorporation of uncertain energy sources, such as wind farms, and due to the impacts that such sources have on the planning and operation of distribution networks. In particular, the foreseeable, extensive use of wind turbine generator units in the future requires that distribution system engineers properly account for their impacts on the system. Many new technical considerations must be addressed, including protection coordination, steady-state analysis, and power quality issues. This paper deals with the very short-term, steady-state analysis of a distribution system with wind farms, for which the time horizon of interest ranges from one hour to a few hours ahead. Several wind-forecasting methods are presented in order to obtain reliable input data for the steady-state analysis. Both deterministic and probabilistic methods were considered and used in performing deterministic and probabilistic load-flow analyses. Numerical applications on a 17-bus, medium-voltage, electrical distribution system with various wind farms connected at different busbars are presented and discussed. Full article
(This article belongs to the Special Issue Wind Energy)
Open AccessArticle Fabrication and Characterization of Fullerene-Based Bulk Heterojunction Solar Cells with Porphyrin, CuInS2, Diamond and Exciton-Diffusion Blocking Layer
Energies 2010, 3(4), 671-685; doi:10.3390/en3040671
Received: 26 February 2010 / Accepted: 15 March 2010 / Published: 8 April 2010
Cited by 27 | PDF Full-text (667 KB) | HTML Full-text | XML Full-text
Abstract
Fullerene-based bulk heterojunction solar cells were fabricated, and the electronic and optical properties were investigated. C60 were used as n-type semiconductors, and porphyrin, CuInS2 and diamond were used as p-type semiconductors. An effect of exciton-diffusion blocking layer of perylene derivative on
[...] Read more.
Fullerene-based bulk heterojunction solar cells were fabricated, and the electronic and optical properties were investigated. C60 were used as n-type semiconductors, and porphyrin, CuInS2 and diamond were used as p-type semiconductors. An effect of exciton-diffusion blocking layer of perylene derivative on the solar cells between active layer and metal layer was also investigated. Optimized structures with the exciton-diffusion blocking layer improved conversion efficiencies. Electronic structures of the molecules were investigated by molecular orbital calculation, and energy levels of the solar cells were discussed. Nanostructures of the solar cells were investigated by transmission electron microscopy, electron diffraction and X-ray diffraction, which indicated formation of mixed nanocrystals. Full article
(This article belongs to the Special Issue Solar Cells)
Open AccessArticle Mass and Aerodynamic Imbalance Estimates of Wind Turbines
Energies 2010, 3(4), 696-710; doi:10.3390/en3040696
Received: 18 January 2010 / Revised: 1 March 2010 / Accepted: 15 March 2010 / Published: 8 April 2010
Cited by 15 | PDF Full-text (410 KB) | HTML Full-text | XML Full-text
Abstract
Due to its effect on the operation time of wind turbines, rotor imbalances of a wind turbine have to be detected early enough. We present a method that determines inhomogeneous mass distributions of the rotor as well as deviations in the pitch angles
[...] Read more.
Due to its effect on the operation time of wind turbines, rotor imbalances of a wind turbine have to be detected early enough. We present a method that determines inhomogeneous mass distributions of the rotor as well as deviations in the pitch angles of the rotor blades from vibrational data only. To this end, a mathematical model connecting the load caused by the imbalances to the resulting vibrations was developed. After discretization, the resulting vibration equation was solved analytically. The inverse problem, i.e., the calculation of the mass and aerodynamic imbalance from vibrational data, was solved by using nonlinear regularization theory. Numerical simulations were performed using artificial vibration data. Full article
(This article belongs to the Special Issue Wind Energy)
Open AccessArticle Crowbar System in Doubly Fed Induction Wind Generators
Energies 2010, 3(4), 738-753; doi:10.3390/en3040738
Received: 3 February 2010 / Revised: 26 February 2010 / Accepted: 27 February 2010 / Published: 12 April 2010
Cited by 26 | PDF Full-text (546 KB) | HTML Full-text | XML Full-text
Abstract
In the last 15 years, the use of doubly fed induction machines in modern variable-speed wind turbines has increased rapidly. This development has been driven by the cost reduction as well as the low-loss generation of Insulated Gate Bipolar Transistors (IGBT). According to
[...] Read more.
In the last 15 years, the use of doubly fed induction machines in modern variable-speed wind turbines has increased rapidly. This development has been driven by the cost reduction as well as the low-loss generation of Insulated Gate Bipolar Transistors (IGBT). According to new grid code requirements, wind turbines must remain connected to the grid during grid disturbances. Moreover, they must also contribute to voltage support during and after grid faults. The crowbar system is essential to avoid the disconnection of the doubly fed induction wind generators from the network during faults. The insertion of the crowbar in the rotor circuits for a short period of time enables a more efficient terminal voltage control. As a general rule, the activation and the deactivation of the crowbar system is based only on the DC-link voltage level of the back-to-back converters. In this context, the authors discuss the critical rotor speed to analyze the instability of doubly fed induction generators during grid faults. Full article
(This article belongs to the Special Issue Wind Energy)
Open AccessArticle Integration of A Solid Oxide Fuel Cell into A 10 MW Gas Turbine Power Plant
Energies 2010, 3(4), 754-769; doi:10.3390/en3040754
Received: 4 February 2010 / Accepted: 9 March 2010 / Published: 14 April 2010
Cited by 13 | PDF Full-text (381 KB) | HTML Full-text | XML Full-text
Abstract
Power generation using gas turbine power plants operating on the Brayton cycle suffers from low efficiencies. In this work, a solid oxide fuel cell (SOFC) is proposed for integration into a 10 MW gas turbine power plant, operating at 30% efficiency. The SOFC
[...] Read more.
Power generation using gas turbine power plants operating on the Brayton cycle suffers from low efficiencies. In this work, a solid oxide fuel cell (SOFC) is proposed for integration into a 10 MW gas turbine power plant, operating at 30% efficiency. The SOFC system utilizes four heat exchangers for heat recovery from both the turbine outlet and the fuel cell outlet to ensure a sufficiently high SOFC temperature. The power output of the hybrid plant is 37 MW at 66.2% efficiency. A thermo-economic model predicts a payback period of less than four years, based on future projected SOFC cost estimates. Full article
(This article belongs to the Special Issue Fuel Cells)
Open AccessArticle Current Density Distribution Mapping in PEM Fuel Cells as An Instrument for Operational Measurements
Energies 2010, 3(4), 770-783; doi:10.3390/en3040770
Received: 3 February 2010 / Accepted: 23 February 2010 / Published: 14 April 2010
Cited by 8 | PDF Full-text (670 KB) | HTML Full-text | XML Full-text
Abstract
A newly developed measurement system for current density distribution mapping has enabled a new approach for operational measurements in proton exchange membrane fuel cells (PEMFC). Taking into account previously constructed measurement systems, a method based on a multi layer printed circuit board was
[...] Read more.
A newly developed measurement system for current density distribution mapping has enabled a new approach for operational measurements in proton exchange membrane fuel cells (PEMFC). Taking into account previously constructed measurement systems, a method based on a multi layer printed circuit board was chosen for the development of the new system. This type of system consists of a sensor, a special electronic device and the control and visualization PC. For the acquisition of the current density distribution values, a sensor device was designed and installed within a multilayer printed circuit board with integrated shunt resistors. Varying shunt values can be taken into consideration with a newly developed and evaluated calibration method. The sensor device was integrated in a PEM fuel cell stack to prove the functionality of the whole measurement system. A software application was implemented to visualize and save the measurement values. Its functionality was verified by operational measurements within a PEMFC system. Measurement accuracy and possible negative reactions of the sensor device during PEMFC operation are discussed in detail in this paper. The developed system enables operational measurements for different operating phases of PEM fuel cells. Additionally, this can be seen as a basis for new opportunities of optimization for fuel cell design and operation modes. Full article
(This article belongs to the Special Issue Fuel Cells)
Open AccessArticle Optimization and Characterization of Lithium Ion Cathode Materials in the System (1 – x – y)LiNi0.8Co0.2O2 • xLi2MnO3 • yLiCoO2
Energies 2010, 3(4), 847-865; doi:10.3390/en3040847
Received: 17 February 2010 / Accepted: 1 April 2010 / Published: 21 April 2010
Cited by 6 | PDF Full-text (1006 KB) | Retraction
Abstract This paper has been retracted on 31 August 2011. A Retraction note is published in Energies, 2011, 4, 1336 Full article
(This article belongs to the Special Issue Lithium-ion Batteries)
Open AccessArticle Biomass Pyrolysis: Comments on Some Sources of Confusions in the Definitions of Temperatures and Heating Rates
Energies 2010, 3(4), 886-898; doi:10.3390/en3040886
Received: 16 March 2010 / Accepted: 27 March 2010 / Published: 22 April 2010
Cited by 19 | PDF Full-text (226 KB) | HTML Full-text | XML Full-text
Abstract
Biomass pyrolysis is usually characterized on the basis of temperature and heating rate. Unfortunately, these parameters are badly defined in processing reactors as well as in laboratory devices. From the results of simplified models, the present paper points out the significant mistakes that
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Biomass pyrolysis is usually characterized on the basis of temperature and heating rate. Unfortunately, these parameters are badly defined in processing reactors as well as in laboratory devices. From the results of simplified models, the present paper points out the significant mistakes that can be made when assuming that the actual temperature and heating rate of reacting biomass particles are the same as those of the external heating medium. The difficulties in defining these two parameters are underlined in both cases of a heat source temperature supposed to be constant or to increase with time. Full article

Review

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Open AccessReview Energy Resources in the Future
Energies 2010, 3(4), 686-695; doi:10.3390/en3040686
Received: 20 January 2010 / Revised: 9 February 2010 / Accepted: 4 March 2010 / Published: 8 April 2010
Cited by 18 | PDF Full-text (149 KB) | HTML Full-text | XML Full-text | Correction | Supplementary Files
Abstract
Recent statistics indicate that in 2005 the world consumed about 0.5 ZJ (ZJ = 1021 Joules) of energy. If one assumes that the future world population stabilizes at 10 billions, and the people consume a similar amount of energy per capita to
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Recent statistics indicate that in 2005 the world consumed about 0.5 ZJ (ZJ = 1021 Joules) of energy. If one assumes that the future world population stabilizes at 10 billions, and the people consume a similar amount of energy per capita to that of the people in the presently developed countries, the world will need about 2 ZJ a year. A recent survey of the available future energy resources indicates that the energies recoverable from coal, oil and gas are only 23 ZJ, 6.7 ZJ and 6.4 ZJ, respectively. Other energy resources such as solar and wind have problems of fluctuation due to the weather conditions. However, the energy expected from known Uranium resources by breeder reactors is 227 ZJ and that from Lithium by fusion reactors is more than 175 ZJ. Therefore, it is important to make efforts to develop and use breeder reactors and fusion reactors to supply a major part of the energy need in the future. Full article
(This article belongs to the Special Issue Nuclear Fusion)
Open AccessReview Numerical Experiments Providing New Insights into Plasma Focus Fusion Devices
Energies 2010, 3(4), 711-737; doi:10.3390/en3040711
Received: 14 February 2010 / Accepted: 3 March 2010 / Published: 12 April 2010
Cited by 11 | PDF Full-text (556 KB) | HTML Full-text | XML Full-text
Abstract
Recent extensive and systematic numerical experiments have uncovered new insights into plasma focus fusion devices including the following: (1) a plasma current limitation effect, as device static inductance is reduced towards very small values; (2) scaling laws of neutron yield and soft x-ray
[...] Read more.
Recent extensive and systematic numerical experiments have uncovered new insights into plasma focus fusion devices including the following: (1) a plasma current limitation effect, as device static inductance is reduced towards very small values; (2) scaling laws of neutron yield and soft x-ray yield as functions of storage energies and currents; (3) a global scaling law for neutron yield as a function of storage energy combining experimental and numerical data showing that scaling deterioration has probably been interpreted as neutron ‘saturation’; and (4) a fundamental cause of neutron ‘saturation’. The ground-breaking insights thus gained may completely change the directions of plasma focus fusion research. Full article
(This article belongs to the Special Issue Nuclear Fusion)
Figures

Open AccessReview Efficiently Harvesting Sun Light for Silicon Solar Cells through Advanced Optical Couplers and A Radial p-n Junction Structure
Energies 2010, 3(4), 784-802; doi:10.3390/en3040784
Received: 29 January 2010 / Revised: 8 March 2010 / Accepted: 12 March 2010 / Published: 20 April 2010
Cited by 13 | PDF Full-text (1386 KB) | HTML Full-text | XML Full-text
Abstract
Silicon-based solar cells (SCs) promise to be an alternative energy source mainly due to: (1) a high efficiency-to-cost ratio, (2) the absence of environmental-degradation issues, and (3) great reliability. Transition from wafer-based to thin-film SC significantly reduces the cost of SCs, including the
[...] Read more.
Silicon-based solar cells (SCs) promise to be an alternative energy source mainly due to: (1) a high efficiency-to-cost ratio, (2) the absence of environmental-degradation issues, and (3) great reliability. Transition from wafer-based to thin-film SC significantly reduces the cost of SCs, including the cost from the material itself and the fabrication process. However, as the thickness of the absorption (or the active) layer decreases, the energy-conversion efficiency drops dramatically. As a consequence, we discuss here three techniques to increase the efficiency of silicon-based SCs: (1) photonic crystal (PC) optical couplers and (2) plasmonic optical couplers to increase efficiency of light absorption in the SCs, and (3) a radial p-n junction structure, decomposing light absorption and diffusion path into two orthogonal directions. The detailed mechanisms and recent research progress regarding these techniques are discussed in this review article. Full article
(This article belongs to the Special Issue Solar Cells)
Open AccessReview Recent Advances in Enzymatic Fuel Cells: Experiments and Modeling
Energies 2010, 3(4), 803-846; doi:10.3390/en3040803
Received: 4 January 2010 / Revised: 23 February 2010 / Accepted: 3 March 2010 / Published: 21 April 2010
Cited by 93 | PDF Full-text (1572 KB) | HTML Full-text | XML Full-text
Abstract
Enzymatic fuel cells convert the chemical energy of biofuels into electrical energy. Unlike traditional fuel cell types, which are mainly based on metal catalysts, the enzymatic fuel cells employ enzymes as catalysts. This fuel cell type can be used as an implantable power
[...] Read more.
Enzymatic fuel cells convert the chemical energy of biofuels into electrical energy. Unlike traditional fuel cell types, which are mainly based on metal catalysts, the enzymatic fuel cells employ enzymes as catalysts. This fuel cell type can be used as an implantable power source for a variety of medical devices used in modern medicine to administer drugs, treat ailments and monitor bodily functions. Some advantages in comparison to conventional fuel cells include a simple fuel cell design and lower cost of the main fuel cell components, however they suffer from severe kinetic limitations mainly due to inefficiency in electron transfer between the enzyme and the electrode surface. In this review article, the major research activities concerned with the enzymatic fuel cells (anode and cathode development, system design, modeling) by highlighting the current problems (low cell voltage, low current density, stability) will be presented. Full article
(This article belongs to the Special Issue Fuel Cells)
Open AccessReview Surface-Modified Membrane as A Separator for Lithium-Ion Polymer Battery
Energies 2010, 3(4), 866-885; doi:10.3390/en3040866
Received: 26 January 2010 / Revised: 21 February 2010 / Accepted: 26 February 2010 / Published: 23 April 2010
Cited by 42 | PDF Full-text (1287 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes the fabrication of novel modified polyethylene (PE) membranes using plasma technology to create high-performance and cost-effective separator membranes for practical applications in lithium-ion polymer batteries. The modified PE membrane via plasma modification process plays a critical role in improving wettability
[...] Read more.
This paper describes the fabrication of novel modified polyethylene (PE) membranes using plasma technology to create high-performance and cost-effective separator membranes for practical applications in lithium-ion polymer batteries. The modified PE membrane via plasma modification process plays a critical role in improving wettability and electrolyte retention, interfacial adhesion between separators and electrodes, and cycle performance of lithium-ion polymer batteries. This paper suggests that the performance of lithium-ion polymer batteries can be greatly enhanced by the plasma modification of commercial separators with proper functional materials for targeted application. Full article
(This article belongs to the Special Issue Lithium-ion Batteries)

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