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Energies, Volume 2, Issue 4 (December 2009), Pages 805-1213

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Editorial

Jump to: Research, Review

Open AccessEditorial Energies—A Trans-Disciplinary Journal
Energies 2009, 2(4), 1007-1008; doi:10.3390/en20401007
Received: 26 October 2009 / Published: 5 November 2009
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Abstract
It is customary for a new Editor to address the audience of the Journal he is called to contribute to, to define or redefine its aims and scope and to state or restate its scientific and strategic priorities. In my case, this task
[...] Read more.
It is customary for a new Editor to address the audience of the Journal he is called to contribute to, to define or redefine its aims and scope and to state or restate its scientific and strategic priorities. In my case, this task is made much easier by the excellent relationship that has been established, in the two months since my nomination, with the Editorial Staff and with the Editorial Board of Energies. [...] Full article

Research

Jump to: Editorial, Review

Open AccessArticle Changing Energy Requirements in the Mediterranean Under Changing Climatic Conditions
Energies 2009, 2(4), 805-815; doi:10.3390/en20400805
Received: 10 September 2009 / Accepted: 25 September 2009 / Published: 30 September 2009
Cited by 14 | PDF Full-text (2095 KB)
Abstract
This study investigates the impacts of climate change on energy requirements in the Mediterranean. Energy requirements, especially for space heating and cooling, are closely linked to several weather variables, mainly air temperature. The analysis is based on daily temperature outputs from several regional
[...] Read more.
This study investigates the impacts of climate change on energy requirements in the Mediterranean. Energy requirements, especially for space heating and cooling, are closely linked to several weather variables, mainly air temperature. The analysis is based on daily temperature outputs from several regional climate models run at a resolution of 25 km × 25 km in the framework of EU project ENSEMBLES using the A1B emissions scenario. The impacts of changes in temperature on energy requirements are investigated using the concept of degree days, defined as the difference of mean air temperature from a base temperature. Base temperature should be chosen to coincide with the minimum energy consumption. In this way, changes in heating and cooling requirements between the reference and the future period are calculated and areas about to undergo large changes identified. These changes are calculated between a 30-year reference period 1961–1990 and a near future period 2021–2050 taking the ensemble mean of all regional climate models. The near-term future has been chosen instead of the frequently used end-of-the-century period to assist policy makers in their planning. In general, a decrease in energy requirements is projected under future milder winters and an increase under hotter summers. Full article
(This article belongs to the Special Issue Energy Solutions in the Era of Climate Change)
Open AccessArticle Investigating the Effect of Large Wind Farms on Energy in the Atmosphere
Energies 2009, 2(4), 816-838; doi:10.3390/en20400816
Received: 21 August 2009 / Accepted: 27 September 2009 / Published: 30 September 2009
Cited by 15 | PDF Full-text (665 KB) | HTML Full-text | XML Full-text
Abstract
This study presents a parameterization of the interaction between wind turbines and the atmosphere and estimates the global and regional atmospheric energy losses due to such interactions. The parameterization is based on the Blade Element Momentum theory, which calculates forces on turbine blades.
[...] Read more.
This study presents a parameterization of the interaction between wind turbines and the atmosphere and estimates the global and regional atmospheric energy losses due to such interactions. The parameterization is based on the Blade Element Momentum theory, which calculates forces on turbine blades. Should wind supply the world’s energy needs, this parameterization estimates energy loss in the lowest 1 km of the atmosphere to be ~0.007%. This is an order of magnitude smaller than atmospheric energy loss from aerosol pollution and urbanization, and orders of magnitude less than the energy added to the atmosphere from doubling CO2. Also, the net heat added to the environment due to wind dissipation is much less than that added by thermal plants that the turbines displace. Full article
(This article belongs to the Special Issue Wind Energy)
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Open AccessArticle Contrasting Electricity Demand with Wind Power Supply: Case Study in Hungary
Energies 2009, 2(4), 839-850; doi:10.3390/en20400839
Received: 25 August 2009 / Accepted: 27 September 2009 / Published: 30 September 2009
Cited by 1 | PDF Full-text (863 KB) | HTML Full-text | XML Full-text
Abstract
We compare the demand of a large electricity consumer with supply given by wind farms installed at two distant geographic locations. Obviously such situation is rather unrealistic, however our main goal is a quantitative characterization of the intermittency of wind electricity. The consumption
[...] Read more.
We compare the demand of a large electricity consumer with supply given by wind farms installed at two distant geographic locations. Obviously such situation is rather unrealistic, however our main goal is a quantitative characterization of the intermittency of wind electricity. The consumption pattern consists of marked daily and weekly cycles interrupted by periods of holidays. In contrast, wind electricity production has neither short-time nor seasonal periodicities. We show that wind power integration over a restricted area cannot provide a stable baseload supply, independently of the excess capacity. Further essential result is that the statistics are almost identical for a weekly periodic pattern of consumption and a constant load of the same average value. The length of both adequate supply and shortfall intervals exhibits a scale-free (power-law) frequency distribution, possible consequences are shortly discussed. Full article
(This article belongs to the Special Issue Wind Energy)
Open AccessArticle A Novel Technique to Determine Concentration-Dependent Solvent Dispersion in Vapex
Energies 2009, 2(4), 851-872; doi:10.3390/en20400851
Received: 1 September 2009 / Accepted: 20 September 2009 / Published: 12 October 2009
Cited by 8 | PDF Full-text (426 KB) | HTML Full-text | XML Full-text
Abstract
Vapex (vapor extraction of heavy oil and bitumen) is a promising recovery technology because it consumes low energy, and is very environmentally-friendly. The dispersion of solvents into heavy oil and bitumen is a crucial transport property governing Vapex. The accurate determination of solvent
[...] Read more.
Vapex (vapor extraction of heavy oil and bitumen) is a promising recovery technology because it consumes low energy, and is very environmentally-friendly. The dispersion of solvents into heavy oil and bitumen is a crucial transport property governing Vapex. The accurate determination of solvent dispersion in Vapex is essential to effectively predict the amount and time scale of oil recovery as well to optimize the field operations. In this work, a novel technique is developed to experimentally determine the concentration-dependent dispersion coefficient of a solvent in Vapex process. The principles of variational calculus are utilized in conjunction with a mass transfer model of the experimental Vapex process. A computational algorithm is developed to optimally compute solvent dispersion as a function of its concentration in heavy oil. The developed technique is applied to Vapex utilizing propane as a solvent. The results show that dispersion of propane is a unimodal function of its concentration in bitumen. Full article
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Open AccessArticle Physical Basis for Creating Energy and Resource-Saving Rheo-Technology in Oil Production
Energies 2009, 2(4), 900-914; doi:10.3390/en20400900
Received: 11 September 2009 / Accepted: 9 October 2009 / Published: 14 October 2009
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Abstract
In a previous paper we presented the results of our investigations on the application of externally imposed temperature fields for the improvement of the non-Newtonian properties of raw oil in the well and also on the possible use of electric and magnetic fields
[...] Read more.
In a previous paper we presented the results of our investigations on the application of externally imposed temperature fields for the improvement of the non-Newtonian properties of raw oil in the well and also on the possible use of electric and magnetic fields in the water flooding process of the oil layer. In this article, some additional results are presented with regards to the application of external pressure fields to the same purpose, with the goal of increasing the well output and improve the efficiency of gaslift wells and oil pipelines. The possibility of regulating the gas-liquid system saturation pressure is discussed as well, to expand the opportunity of varying the well operating regime. Full article
Open AccessArticle Map-Based Repowering and Reorganization of a Wind Resource Area to Minimize Burrowing Owl and Other Bird Fatalities
Energies 2009, 2(4), 915-943; doi:10.3390/en20400915
Received: 26 August 2009 / Accepted: 19 October 2009 / Published: 23 October 2009
Cited by 5 | PDF Full-text (949 KB) | HTML Full-text | XML Full-text
Abstract
Wind turbines in the Altamont Pass Wind Resource Area (Alameda/Contra Costa Counties, California, USA) generate about 730 GWh of electricity annually, but have been killing thousands of birds each year, including 2 grid cell among 187,908 grid cells sampled from 2,281,169 grid cells
[...] Read more.
Wind turbines in the Altamont Pass Wind Resource Area (Alameda/Contra Costa Counties, California, USA) generate about 730 GWh of electricity annually, but have been killing thousands of birds each year, including <2,000 raptors and hundreds of burrowing owls. We have developed collision hazard maps and hazard ratings of wind turbines to guide relocation of existing wind turbines and careful repowering to modern turbines to reduce burrowing owl fatalities principally, and other birds secondarily. Burrowing owls selected burrow sites lower on slopes and on smaller, shallower slopes than represented by the average 10 × 10 m2 grid cell among 187,908 grid cells sampled from 2,281,169 grid cells comprising a digital elevation model (DEM) of the study area. Fuzzy logic and discriminant function analysis produced likelihood surfaces encompassing most burrowing owl burrows within a fraction of the study area, and the former corresponded with burrowing owl fatalities and the latter with other raptor fatalities. Our ratings of wind turbine hazard were more predictive of burrowing owl fatalities, but would be more difficult to implement. Careful repowering to modern wind turbines would most reduce fatalities of burrowing owls and other birds while adding about 1,000 GWh annually toward California’s 33% Renewable Portfolio Standard. Full article
(This article belongs to the Special Issue Wind Energy)
Open AccessArticle Synthesis and Evaluation of Highly Tolerant Pd Electrocatalysts as Cathodes in Direct Ethylene Glycol Fuel Cells (DEGFC)
Energies 2009, 2(4), 944-956; doi:10.3390/en20400944
Received: 29 July 2009 / Accepted: 11 September 2009 / Published: 27 October 2009
Cited by 7 | PDF Full-text (678 KB) | HTML Full-text | XML Full-text
Abstract
Highly selective Pd electrocatalysts were synthesized by the formic acid (FA) method and evaluated as cathodes for DEGFC applications. In rotating disc measurements in acid medium, the Pd/C cathode showed important catalytic activity for the Oxygen Reduction Reaction (ORR). In the presence of
[...] Read more.
Highly selective Pd electrocatalysts were synthesized by the formic acid (FA) method and evaluated as cathodes for DEGFC applications. In rotating disc measurements in acid medium, the Pd/C cathode showed important catalytic activity for the Oxygen Reduction Reaction (ORR). In the presence of ethylene glycol (EG, C2H6O2), Pd/C exhibited a noteworthy electrochemical behavior and full tolerance to the organic molecule. No current density peaks associated to the EG oxidation reaction emerged and the shift in onset potential for the ORR (Eonset) toward more negative potentials was negligible on this cathode. As a comparison, commercial Pt/C was tested under the same conditions showing a poor selectivity for the ORR when EG was present. The detrimental effect of EG on the Pt electrocatalysts resulted in high intensity current density peaks due to the oxidation of EG and a significant shift in Eonset. The evaluation of Pd/C in a DEGFC operating at 80 °C demonstrated its good performance as cathode material. Given these results, it is expected that highly efficient Pd-based cathodes can find application in DEGFCs. Full article
(This article belongs to the Special Issue Fuel Cells)
Open AccessArticle Development of an Inclined Plate Extractor-Separator for Immiscible Liquids
Energies 2009, 2(4), 957-975; doi:10.3390/en20400957
Received: 21 September 2009 / Accepted: 20 October 2009 / Published: 27 October 2009
PDF Full-text (920 KB) | HTML Full-text | XML Full-text
Abstract
A new inclined plates extractor-separator is developed for operation with immiscible liquids in which extraction and separation is achieved in one unit contrary to mixer settlers. The inclined plates extractor-separator combines turbulent jets for contacting, and an inclined plate for separation of the
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A new inclined plates extractor-separator is developed for operation with immiscible liquids in which extraction and separation is achieved in one unit contrary to mixer settlers. The inclined plates extractor-separator combines turbulent jets for contacting, and an inclined plate for separation of the two phases. The inclined plates extractor-separator does not have any moving part inside the vessel. This feature makes it free from the mechanical problems associated with conventional apparatus. The proposed inclined plates extractor-separator was operated in batch mode under various operating conditions to evaluate its performance on the basis of extraction efficiency. Water (light phase) was used as solvent to extract ethyl acetate from a heavy phase pool of tetrachloroethylene and ethyl acetate. The ethyl acetate content was analysed using chromatography. A hydrodynamic study was carried out using high speed photography to understand the mechanisms occurring during mass transfer across the two phases. Furthermore, it was found that the proposed inclined plate extractor-separator reduces the overall operating time by 67% and consumes only 13% of the power in comparison to a mixer-settler. A hydraulic power consumption comparison with a mixer settler and a gullwing extractor-separator is also presented. Full article
Open AccessArticle Reaction Engineering of Direct Coal Liquefaction
Energies 2009, 2(4), 976-1006; doi:10.3390/en20400976
Received: 14 October 2009 / Accepted: 23 October 2009 / Published: 29 October 2009
Cited by 13 | PDF Full-text (1577 KB) | HTML Full-text | XML Full-text
Abstract
Direct coal liquefaction has been studied and practiced since the 1930s. It was used in Germany during World War II to produce synthetic fuels when there was no oil allowed into the country. Since then, it has been studied in the United States
[...] Read more.
Direct coal liquefaction has been studied and practiced since the 1930s. It was used in Germany during World War II to produce synthetic fuels when there was no oil allowed into the country. Since then, it has been studied in the United States and many different technologies have been investigated. Since the US is rich in coal resources, this is one way to be energy independent. Most of the development activity occurred in the 1980s and numerous technologies were studied, the most notable of these being H-Coal, Exxon Donor Solvent, Solvent Refined Coal, and Two Stage Liquefaction. The key elements of these technologies, particularly the reaction/reactor scheme, are discussed in this review. Full article
(This article belongs to the Special Issue Coal Gasification and Liquefaction)
Open AccessArticle A Proposal of Ecologic Taxes Based on Thermo-Economic Performance of Heat Engine Models
Energies 2009, 2(4), 1042-1056; doi:10.3390/en20401042
Received: 24 August 2009 / Accepted: 27 September 2009 / Published: 10 November 2009
PDF Full-text (320 KB) | HTML Full-text | XML Full-text
Abstract
Within the context of Finite-Time Thermodynamics (FTT) a simplified thermal power plant model (the so-called Novikov engine) is analyzed under economical criteria by means of the concepts of profit function and the costs involved in the performance of the power plant. In this
[...] Read more.
Within the context of Finite-Time Thermodynamics (FTT) a simplified thermal power plant model (the so-called Novikov engine) is analyzed under economical criteria by means of the concepts of profit function and the costs involved in the performance of the power plant. In this study, two different heat transfer laws are used, the so called Newton’s law of cooling and the Dulong-Petit’s law of cooling. Two FTT optimization criteria for the performance analysis are used: the maximum power regime (MP) and the so-called ecological criterion. This last criterion leads the engine model towards a mode of performance that appreciably diminishes the engine’s wasted energy. In this work, it is shown that the energy-unit price produced under maximum power conditions is cheaper than that produced under maximum ecological (ME) conditions. This was accomplished by using a typical definition of profits function stemming from economics. The MP-regime produces considerably more wasted energy toward the environment, thus the MP energy-unit price is subsidized by nature. Due to this fact, an ecological tax is proposed, which could be a certain function of the price difference between the MP and ME modes of power production. Full article
(This article belongs to the Special Issue Energy Economics)
Open AccessArticle Esterification of Fatty Acids with Short-Chain Alcohols over Commercial Acid Clays in a Semi-Continuous Reactor
Energies 2009, 2(4), 1107-1117; doi:10.3390/en20401107
Received: 18 September 2009 / Accepted: 6 November 2009 / Published: 19 November 2009
Cited by 15 | PDF Full-text (114 KB) | HTML Full-text | XML Full-text
Abstract
Production of fatty acid esters from stearic, oleic, and palmitic acids and short-chain alcohols (methanol, ethanol, propanol, and butanol) for the production of biodiesel was investigated in this work. A series of montmorillonite-based clays catalysts (KSF, KSF/0, KP10, and K10) were used as
[...] Read more.
Production of fatty acid esters from stearic, oleic, and palmitic acids and short-chain alcohols (methanol, ethanol, propanol, and butanol) for the production of biodiesel was investigated in this work. A series of montmorillonite-based clays catalysts (KSF, KSF/0, KP10, and K10) were used as acidic catalysts. The influence of the specific surface area and the acidity of the catalysts on the esterification rate were investigated. The best catalytic activities were obtained with KSF/0 catalyst. The esterification reaction has been carried out efficiently in a semi-continuous reactor at 150°C temperature higher than the boiling points of water and alcohol. The reactor used enabled the continuous removal of water and esterification with hydrated alcohol (ethanol 95%) without affecting the original activity of the clay. Full article
Open AccessArticle Electromagnetic Interference on Large Wind Turbines
Energies 2009, 2(4), 1118-1129; doi:10.3390/en20401118
Received: 27 September 2009 / Accepted: 18 November 2009 / Published: 20 November 2009
Cited by 10 | PDF Full-text (420 KB) | HTML Full-text | XML Full-text
Abstract
Electromagnetic interference (EMI) can both affect and be transmitted by mega-watt wind turbines. This paper provides a general overview on EMI with respect to mega-watt wind turbines. Possibilities of measuring all types of electromagnetic interference are shown. Electromagnetic fields resulting from a GSM
[...] Read more.
Electromagnetic interference (EMI) can both affect and be transmitted by mega-watt wind turbines. This paper provides a general overview on EMI with respect to mega-watt wind turbines. Possibilities of measuring all types of electromagnetic interference are shown. Electromagnetic fields resulting from a GSM transmitter mounted on a mega-watt wind turbine will be analyzed in detail. This cellular system operates as a real-time communication link. The method-of-moments is used to analytically describe the electro-magnetic fields. The electromagnetic interference will be analyzed under the given boundary condition with a commercial simulation tool. Different transmitter positions are judged on the basis of their radiation patterns. The principal EMI mechanisms are described and taken into consideration. Full article
(This article belongs to the Special Issue Wind Energy)
Open AccessArticle Creating Synergies from Renewable Energy Investments, a Community Success Story from Lolland, Denmark
Energies 2009, 2(4), 1151-1169; doi:10.3390/en20401151
Received: 9 October 2009 / Accepted: 23 November 2009 / Published: 27 November 2009
Cited by 8 | PDF Full-text (893 KB) | HTML Full-text | XML Full-text
Abstract
The island of Lolland is a showcase example of a remote local community being able to stand up to the challenges of facing environmental and social consequences of climate change while creating economic opportunities. This island has had many years of experience in
[...] Read more.
The island of Lolland is a showcase example of a remote local community being able to stand up to the challenges of facing environmental and social consequences of climate change while creating economic opportunities. This island has had many years of experience in implementing renewable energy (RE) projects as a way to combating peripheral poverty and promoting economic growth in a relatively remote area. The development strategy lies within the unique concept of Lolland Community Testing Facilities (CTF), which creates a forum between the private sector, research institutions and local political authorities by exploiting synergies among green investments and providing an international testing and demonstration platform for renewable energy technology and products. The present paper aims at giving an overview of integrated longer term energy planning based on Lolland CTF, its components and main features, while highlighting those critical characteristics that could make the CTF model successful and relevant for RE-based local development worldwide. Full article
(This article belongs to the Special Issue Energy Economics)
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Open AccessArticle High Performance Cascading Adsorption Refrigeration Cycle with Internal Heat Recovery Driven by a Low Grade Heat Source Temperature
Energies 2009, 2(4), 1170-1191; doi:10.3390/en20401170
Received: 26 October 2009 / Accepted: 26 November 2009 / Published: 30 November 2009
Cited by 9 | PDF Full-text (317 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the performance of an advanced cascading adsorption cycle that utilizes a driven heat source temperature between 90–130 ºC. The cycle consists of four beds that contain silica gel as an adsorber fill. Two of the beds work in a single
[...] Read more.
This paper presents the performance of an advanced cascading adsorption cycle that utilizes a driven heat source temperature between 90–130 ºC. The cycle consists of four beds that contain silica gel as an adsorber fill. Two of the beds work in a single stage cycle that is driven by an external heat source, while the other two beds work in a mass recovery cycle that is driven by waste heat of sensible and adsorption heat of the high temperature cycle. The performances, in terms of the coefficient of performance (COP) and the specific cooling power (SCP), are compared with conventional cascading-without-mass-recovery and single-stage cycles. The paper also presents the effect of the adsorbent mass on performance. The results show that the proposed cycle with mass recovery produces as high of a COP as the COP that is produced by the conventional cascading cycle. However, it produces a lower SCP than that of the single-stage cycle. Full article
Open AccessArticle The Technology of Waste, Biofuels and Global Warming in Viable Closed Loop, Sustainable Operations
Energies 2009, 2(4), 1192-1200; doi:10.3390/en20401192
Received: 18 November 2009 / Accepted: 30 November 2009 / Published: 3 December 2009
Cited by 2 | PDF Full-text (174 KB) | HTML Full-text | XML Full-text
Abstract
This research set out to explore and develop a route relating the recycling of urban and industrial wastes to land to produce agricultural crops with energy crops in the rotation, using the green leaf to “harvest” sunlight and to examine the sequestration of
[...] Read more.
This research set out to explore and develop a route relating the recycling of urban and industrial wastes to land to produce agricultural crops with energy crops in the rotation, using the green leaf to “harvest” sunlight and to examine the sequestration of carbon dioxide and release of oxygen in a sustainable closed loop. Further, to establish if the pollution, particularly of nitrogen and phosphates (often associated with cultivations and use of mineral fertilisers) could be reduced or eliminated, so as to be able to develop systems which could contribute to the reversal of global warming. Finally, to probe whether practical operators on the ground could understand the technology, use it, and express what they were doing in a way acceptable to a wider society. Full article
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Open AccessArticle Electricity Consumption and GHG Emissions in GCC Countries
Energies 2009, 2(4), 1201-1213; doi:10.3390/en20401201
Received: 23 October 2009 / Accepted: 21 November 2009 / Published: 16 December 2009
Cited by 19 | PDF Full-text (568 KB) | HTML Full-text | XML Full-text
Abstract
CO2, N2O, and CH4 are the three most widespread Greenhouse Gases (GHGs). Electricity consumption and the related CO2-equivalent gas emissions resulting from oil and gas combustion for the six countries that comprise the Cooperation Council for
[...] Read more.
CO2, N2O, and CH4 are the three most widespread Greenhouse Gases (GHGs). Electricity consumption and the related CO2-equivalent gas emissions resulting from oil and gas combustion for the six countries that comprise the Cooperation Council for the Arab States of the Gulf [Kingdom of Saudi Arabia (KSA), Kuwait, Bahrain, Oman, United Arab Emirates (UAE) and Qatar; also referred to as the Gulf Cooperation Council, GCC)] have been compared. The analysis of the relevant data shows that GCC countries contribute significantly to the global CO2 emissions, and that the majority of their emissions are concentrated in the energy extraction and conversion sectors, mainly from oil drilling and electricity production. Some analysis is offered as to the reasons behind the excessive increase in the electrical demand that is obviously linked to a non-rational pattern of electricity consumption. Full article

Review

Jump to: Editorial, Research

Open AccessReview Transition Metal Carbides and Nitrides as Electrode Materials for Low Temperature Fuel Cells
Energies 2009, 2(4), 873-899; doi:10.3390/en20400873
Received: 28 August 2009 / Accepted: 25 September 2009 / Published: 13 October 2009
Cited by 120 | PDF Full-text (2042 KB) | HTML Full-text | XML Full-text
Abstract
Transition metal carbides (TMCs) and transition metal nitrides (TMNs) have attracted attention as promising electrocatalysts that could replace noble metals of high price and limited supply. Relative to parent metals, TMC and TMN behave like noble metals for electrochemical reactions such as oxidation
[...] Read more.
Transition metal carbides (TMCs) and transition metal nitrides (TMNs) have attracted attention as promising electrocatalysts that could replace noble metals of high price and limited supply. Relative to parent metals, TMC and TMN behave like noble metals for electrochemical reactions such as oxidation of hydrogen, CO and alcohols, and reduction of oxygen. When TMC and TMN are combined with other metals, the electrocatalytic synergy is often observed in electrochemical reactions. Thus, combinations with a minute amount of Pt or even non-Pt metals give performance comparable to heavily loaded Pt-based electrocatalysts for low temperature fuel cells. It appears that TMC based electrocatalysts are more active as anode catalysts for oxidation of fuels, whereas TMN based catalysts are more active for cathode catalysts for oxygen reduction and more stable. Full article
(This article belongs to the Special Issue Fuel Cells)
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Open AccessReview Energy Storage in Bifunctional TiO2 Composite Materials under UV and Visible Light
Energies 2009, 2(4), 1009-1030; doi:10.3390/en20401009
Received: 30 September 2009 / Accepted: 28 October 2009 / Published: 6 November 2009
Cited by 8 | PDF Full-text (781 KB) | HTML Full-text | XML Full-text
Abstract
This paper provides an overview of recent studies on energy storage in bifunctional TiO2 composite materials under UV and visible light. The working mechanism, property improvements and applications of these bifunctional TiO2 composite systems are introduced, respectively. The latest results obtained
[...] Read more.
This paper provides an overview of recent studies on energy storage in bifunctional TiO2 composite materials under UV and visible light. The working mechanism, property improvements and applications of these bifunctional TiO2 composite systems are introduced, respectively. The latest results obtained in our laboratory, especially a new process for photoelectric conversion and energy storage in TiO2/Cu2O bilayer films under visible light, are also presented. Hopefully this review will stimulate more fundamental and applied research on this subject in the future. Full article
(This article belongs to the Special Issue Solar Cells)
Open AccessReview Impacts of Large Scale Wind Penetration on Energy Supply Industry
Energies 2009, 2(4), 1031-1041; doi:10.3390/en20401031
Received: 11 August 2009 / Accepted: 5 November 2009 / Published: 9 November 2009
Cited by 10 | PDF Full-text (181 KB) | HTML Full-text | XML Full-text
Abstract
Large penetration of Renewable Energy Sources (RES) impacts Energy Supply Industry (ESI) in many aspects leading to a fundamental change in electric power systems. It raises a number of technical challenges to the Transmission System Operators (TSOs), Distribution System Operators (DSOs) and Wind
[...] Read more.
Large penetration of Renewable Energy Sources (RES) impacts Energy Supply Industry (ESI) in many aspects leading to a fundamental change in electric power systems. It raises a number of technical challenges to the Transmission System Operators (TSOs), Distribution System Operators (DSOs) and Wind Turbine Generators (WTG) constructors. This paper aims to present in a thorough and coherent way the redrawn picture for Energy Systems under these conditions. Topics related to emergent technical challenges, technical solutions required and finally the impact on ESI due to large wind power penetration, are analyzed. Finally, general conclusions are extracted about the ESI current and future state and general directions are recommended. Full article
(This article belongs to the Special Issue Wind Energy)
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Open AccessReview A Review of Water Management in Polymer Electrolyte Membrane Fuel Cells
Energies 2009, 2(4), 1057-1106; doi:10.3390/en20401057
Received: 4 September 2009 / Accepted: 11 November 2009 / Published: 17 November 2009
Cited by 84 | PDF Full-text (1362 KB) | HTML Full-text | XML Full-text
Abstract
At present, despite the great advances in polymer electrolyte membrane fuel cell (PEMFC) technology over the past two decades through intensive research and development activities, their large-scale commercialization is still hampered by their higher materials cost and lower reliability and durability. In this
[...] Read more.
At present, despite the great advances in polymer electrolyte membrane fuel cell (PEMFC) technology over the past two decades through intensive research and development activities, their large-scale commercialization is still hampered by their higher materials cost and lower reliability and durability. In this review, water management is given special consideration. Water management is of vital importance to achieve maximum performance and durability from PEMFCs. On the one hand, to maintain good proton conductivity, the relative humidity of inlet gases is typically held at a large value to ensure that the membrane remains fully hydrated. On the other hand, the pores of the catalyst layer (CL) and the gas diffusion layer (GDL) are frequently flooded by excessive liquid water, resulting in a higher mass transport resistance. Thus, a subtle equilibrium has to be maintained between membrane drying and liquid water flooding to prevent fuel cell degradation and guarantee a high performance level, which is the essential problem of water management. This paper presents a comprehensive review of the state-of-the-art studies of water management, including the experimental methods and modeling and simulation for the characterization of water management and the water management strategies. As one important aspect of water management, water flooding has been extensively studied during the last two decades. Herein, the causes, detection, effects on cell performance and mitigation strategies of water flooding are overviewed in detail. In the end of the paper the emphasis is given to: (i) the delicate equilibrium of membrane drying vs. water flooding in water management; (ii) determining which phenomenon is principally responsible for the deterioration of the PEMFC performance, the flooding of the porous electrode or the gas channels in the bipolar plate, and (iii) what measures should be taken to prevent water flooding from happening in PEMFCs. Full article
(This article belongs to the Special Issue Fuel Cells)
Open AccessReview Strategies for Lowering Solid Oxide Fuel Cells Operating Temperature
Energies 2009, 2(4), 1130-1150; doi:10.3390/en20401130
Received: 27 October 2009 / Accepted: 13 November 2009 / Published: 25 November 2009
Cited by 35 | PDF Full-text (794 KB) | HTML Full-text | XML Full-text
Abstract
Lowering the operating temperature of solid oxide fuel cells (SOFCs) to the intermediate range (500–700 ºC) has become one of the main SOFC research goals. High operating temperatures put numerous requirements on materials selection and on secondary units, limiting the commercial development of
[...] Read more.
Lowering the operating temperature of solid oxide fuel cells (SOFCs) to the intermediate range (500–700 ºC) has become one of the main SOFC research goals. High operating temperatures put numerous requirements on materials selection and on secondary units, limiting the commercial development of SOFCs. The present review first focuses on the main effects of reducing the operating temperature in terms of materials stability, thermo-mechanical mismatch, thermal management and efficiency. After a brief survey of the state-of-the-art materials for SOFCs, attention is focused on emerging oxide-ionic conductors with high conductivity in the intermediate range of temperatures with an introductory section on materials technology for reducing the electrolyte thickness. Finally, recent advances in cathode materials based on layered mixed ionic-electronic conductors are highlighted because the decreasing temperature converts the cathode into the major source of electrical losses for the whole SOFC system. It is concluded that the introduction of alternative materials that would enable solid oxide fuel cells to operate in the intermediate range of temperatures would have a major impact on the commercialization of fuel cell technology. Full article
(This article belongs to the Special Issue Fuel Cells)
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energies@mdpi.com
Tel. +41 61 683 77 34
Fax: +41 61 302 89 18
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