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Energies, Volume 3, Issue 12 (December 2010), Pages 1831-2026

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Research

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Open AccessArticle A New Hybrid Algorithm Using Thermodynamic and Backward Ray-Tracing Approaches for Modeling Luminescent Solar Concentrators
Energies 2010, 3(12), 1831-1860; doi:10.3390/en3121831
Received: 24 September 2010 / Revised: 12 November 2010 / Accepted: 23 November 2010 / Published: 26 November 2010
Cited by 3 | PDF Full-text (434 KB) | HTML Full-text | XML Full-text
Abstract
A Luminescent Solar Concentrator (LSC) is a transparent plate containing luminescent material with photovoltaic (PV) cells attached to its edges. Sunlight entering the plate is absorbed by the luminescent material, which in turn emits light. The emitted light propagates through the plate and
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A Luminescent Solar Concentrator (LSC) is a transparent plate containing luminescent material with photovoltaic (PV) cells attached to its edges. Sunlight entering the plate is absorbed by the luminescent material, which in turn emits light. The emitted light propagates through the plate and arrives at the PV cells through total internal reflection. The ratio of the area of the relatively cheap polymer plate to that of the expensive PV cells is increased, and the cost per unit of solar electricity can be reduced by 75%. To improve the emission performance of LSCs, simulation modeling of LSCs becomes essential. Ray-tracing modeling is a popular approach for simulating LSCs due to its great ability of modeling various LSC structures under direct and diffuse sunlight. However, this approach requires substantial amount of measurement input data. Also, the simulation time is enormous because it is a forward-ray tracing method that traces all the rays propagating from the light source to the concentrator. On the other hand, the thermodynamic approach requires substantially less input parameters and simulation time, but it can only be used to model simple LSC designs with direct sunlight. Therefore, a new hybrid model was developed to perform various simulation studies effectively without facing the issues arisen from the existing ray-tracing and thermodynamic models. The simulation results show that at least 60% of the total output irradiance of a LSC is contributed by the light trapped and channeled by the LSC. The novelty of this hybrid model is the concept of integrating the thermodynamic model with a well-developed Radiance ray-tracing model, hence making this model as a fast, powerful and cost-effective tool for the design of LSCs. Full article
(This article belongs to the Special Issue Advances in Solar Energy)
Open AccessArticle A Method to Use Solar Energy for the Production of Gas from Marine Hydrate-Bearing Sediments: A Case Study on the Shenhu Area
Energies 2010, 3(12), 1861-1879; doi:10.3390/en3121861
Received: 2 November 2010 / Revised: 16 November 2010 / Accepted: 24 November 2010 / Published: 2 December 2010
Cited by 10 | PDF Full-text (520 KB) | HTML Full-text | XML Full-text
Abstract
A method is proposed that uses renewable solar energy to supply energy for the exploitation of marine gas hydrates using thermal stimulation. The system includes solar cells, which are installed on the platform and a distributor with electric heaters. The solar module is
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A method is proposed that uses renewable solar energy to supply energy for the exploitation of marine gas hydrates using thermal stimulation. The system includes solar cells, which are installed on the platform and a distributor with electric heaters. The solar module is connected with electric heaters via an insulated cable, and provides power to the heaters. Simplified equations are given for the calculation of the power of the electric heaters and the solar battery array. Also, a case study for the Shenhu area is provided to illustrate the calculation of the capacity of electric power and the solar cell system under ideal conditions. It is shown that the exploitation of marine gas hydrates by solar energy is technically and economically feasible in typical marine areas and hydrate reservoirs such as the Shenhu area. This method may also be used as a good assistance for depressurization exploitation of marine gas hydrates in the future. Full article
(This article belongs to the Special Issue Natural Gas Hydrate)
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Open AccessArticle Risk Reserve Constrained Economic Dispatch Model with Wind Power Penetration
Energies 2010, 3(12), 1880-1894; doi:10.3390/en3121880
Received: 30 October 2010 / Revised: 26 November 2010 / Accepted: 1 December 2010 / Published: 7 December 2010
Cited by 14 | PDF Full-text (186 KB) | HTML Full-text | XML Full-text
Abstract
This paper develops a modified economic dispatch (ED) optimization model with wind power penetration. Due to the uncertain nature of wind speed, both overestimation and underestimation of the available wind power are compensated using the up and down spinning reserves. In order to
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This paper develops a modified economic dispatch (ED) optimization model with wind power penetration. Due to the uncertain nature of wind speed, both overestimation and underestimation of the available wind power are compensated using the up and down spinning reserves. In order to determine both of these two reserve demands, the risk-based up and down spinning reserve constraints are presented considering not only the uncertainty of available wind power, but also the load forecast error and generator outage rates. The predictor-corrector primal-dual interior point (IP) method is utilized to solve the proposed ED model. Simulation results of a system with ten conventional generators and one wind farm demonstrate the effectiveness of the proposed method. Full article
(This article belongs to the Special Issue Wind Energy)
Open AccessArticle Creating a Global Grid of Distributed Fossil Fuel CO2 Emissions from Nighttime Satellite Imagery
Energies 2010, 3(12), 1895-1913; doi:10.3390/en3121895
Received: 21 November 2010 / Revised: 6 December 2010 / Accepted: 7 December 2010 / Published: 8 December 2010
Cited by 25 | PDF Full-text (3308 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The potential use of satellite observed nighttime lights for estimating carbon-dioxide (CO2) emissions has been demonstrated in several previous studies. However, the procedures for a moderate resolution (1 km2 grid cells) global map of fossil fuel CO2 emissions based
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The potential use of satellite observed nighttime lights for estimating carbon-dioxide (CO2) emissions has been demonstrated in several previous studies. However, the procedures for a moderate resolution (1 km2 grid cells) global map of fossil fuel CO2 emissions based on nighttime lights are still in the developmental phase. We report on the development of a method for mapping distributed fossil fuel CO2 emissions (excluding electric power utilities) at 30 arc-seconds or approximately 1 km2 resolution using nighttime lights data collected by the Defense Meteorological Satellite Program’s Operational Linescan System (DMSP-OLS). A regression model, Model 1, was initially developed based on carbon emissions from five sectors of the Vulcan data produced by the Purdue University and a nighttime satellite image of the U.S. The coefficient derived through Model 1 was applied to the global nighttime image but it resulted in underestimation of CO2 emissions for most of the world’s countries, and the states of the U.S. Thus, a second model, Model 2 was developed by allocating the distributed CO2 emissions (excluding emissions from utilities) using a combination of DMSP-OLS nighttime image and population count data from the U.S. Department of Energy's (DOE) LandScan grid. The CO2 emissions were distributed in proportion to the brightness of the DMSP nighttime lights in areas where lighting was detected. In areas with no DMSP detected lighting, the CO2 emissions were distributed based on population count, with the assumption that people who live in these areas emit half as much CO2 as people who live in the areas with DMSP detected lighting. The results indicate that the relationship between satellite observed nighttime lights and CO2 emissions is complex, with differences between sectors and variations in lighting practices between countries. As a result it is not possible to make independent estimates of CO2 emissions with currently available coarse resolution panchromatic satellite observed nighttime lights. However, the nighttime lights image in conjunction with the population grid can help in more accurate disaggregation of national CO2 emissions to a moderate resolution spatial grid. Full article
Open AccessArticle Hybrid Dielectric-Metallic Back Reflector for Amorphous Silicon Solar Cells
Energies 2010, 3(12), 1914-1933; doi:10.3390/en3121914
Received: 19 November 2010 / Accepted: 8 December 2010 / Published: 10 December 2010
Cited by 9 | PDF Full-text (491 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we present the design and fabrication of hybrid dielectric-metallic back surface reflectors, for applications in thin film amorphous silicon solar cells. Standard multilayer distributed Bragg reflectors, require a large number of layers in order to achieve high reflectance characteristics. As
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In this paper, we present the design and fabrication of hybrid dielectric-metallic back surface reflectors, for applications in thin film amorphous silicon solar cells. Standard multilayer distributed Bragg reflectors, require a large number of layers in order to achieve high reflectance characteristics. As it turns out, the addition of a metallic layer, to the base of such a multilayer mirror, enables a reduction in the number of dielectric layers needed to attain high reflectance performance. This paper explores the design, experimental realization and opportunities, in thin film amorphous silicon solar cells, afforded by such hybrid dielectric-metallic back surface reflectors. Full article
(This article belongs to the Special Issue Solar Cells)
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Open AccessArticle LES of a Meso Combustion Chamber with a Detailed Chemistry Model: Comparison between the Flamelet and EDC Models
Energies 2010, 3(12), 1943-1959; doi:10.3390/en3121943
Received: 20 October 2010 / Revised: 17 November 2010 / Accepted: 8 December 2010 / Published: 10 December 2010
Cited by 6 | PDF Full-text (373 KB) | HTML Full-text | XML Full-text
Abstract
The goal of this paper is to contribute to the design of high-performance mesocombustors, a field currently under rapid development, in particular for propulsion, e.g., for UAVs, and micro/meso-electrical power generators. This study is focused on a cylindrical combustor of 29 cm3,
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The goal of this paper is to contribute to the design of high-performance mesocombustors, a field currently under rapid development, in particular for propulsion, e.g., for UAVs, and micro/meso-electrical power generators. This study is focused on a cylindrical combustor of 29 cm3, fuelled by methane and air, which provides 2 kW of thermal power. The device was entirely designed and built at the Sapienza University of Rome and coupled with an ultra-micro turbine. Two 3D LES simulations with detailed chemistry are presented. They differ only for the combustion models, so that a model comparison can be carried out. The calculated maximum temperature inside the chamber, the gas exhaust temperature and the combustion efficiency are compared and discussed. The results, reported at two different physical times, show the effects of the different combustion models, which predict different temperature and species concentration maps, but similar values for the combustion efficiency. Thermal, chemical and kinematic maps show that the Eddy Dissipation Concept allows for a more accurate estimatation of the performance parameters for application to first-order design procedures. Full article
(This article belongs to the Special Issue Micro-Combustors)
Open AccessArticle Observation of Sintering of Clathrate Hydrates
Energies 2010, 3(12), 1960-1971; doi:10.3390/en3121960
Received: 25 October 2010 / Revised: 2 December 2010 / Accepted: 10 December 2010 / Published: 13 December 2010
Cited by 13 | PDF Full-text (577 KB) | HTML Full-text | XML Full-text
Abstract
Clathrate hydrates have recently received attention as novel storage and transportation materials for natural gases or hydrogen. These hydrates are treated as powders or particles, and moderate storage temperatures (around 253 K) are set for economic reasons. Thus, it is necessary to consider
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Clathrate hydrates have recently received attention as novel storage and transportation materials for natural gases or hydrogen. These hydrates are treated as powders or particles, and moderate storage temperatures (around 253 K) are set for economic reasons. Thus, it is necessary to consider the sintering of hydrate particles for their easy handling because the hydrates have a framework similar to that of ice, even though their sintering would require guest molecules in addition to water molecules. We observed the sintering process of clathrate hydrates to estimate the rate of sintering. Spherical tetrahydrofuran (THF) hydrate particles were used in observations of sintering under a microscope equipped with a CCD camera and a time-lapse video recorder. We found that THF hydrate particles stored at temperatures below the equilibrium condition sintered like ice particles. The sintering part was confirmed to be not ice, but THF hydrate, by increasing the temperature above 273 K after each experiment. The sintering rate was lower than that of ice particles under the normal vapor condition at the same temperature. However, it became of the same order when the atmosphere of the sample was saturated with THF vapor. This indicates that the sintering rate of THF hydrate was controlled by the transportation of guest molecules through the vapor phase accompanied with water molecules. Full article
(This article belongs to the Special Issue Natural Gas Hydrate)
Open AccessArticle A Multiagent System for Autonomous Operation of Islanded Microgrids Based on a Power Market Environment
Energies 2010, 3(12), 1972-1990; doi:10.3390/en3121972
Received: 25 October 2010 / Revised: 8 December 2010 / Accepted: 16 December 2010 / Published: 20 December 2010
Cited by 41 | PDF Full-text (604 KB) | HTML Full-text | XML Full-text
Abstract
One of the most important requirements of microgrid operation is to maintain a constant frequency such as 50 Hz or 60 Hz, which is closely related to a power balance between supply and demand. In general, microgrids are connected to power grids and
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One of the most important requirements of microgrid operation is to maintain a constant frequency such as 50 Hz or 60 Hz, which is closely related to a power balance between supply and demand. In general, microgrids are connected to power grids and surplus/shortage power of microgrids is traded with power grids. Since islanded microgrids are isolated from any power grids, the decrease in generation or load-shedding can be used to maintain the frequency when a power imbalance between supply and demand occurs. The power imbalance restricts the electricity use of consumers in the case of supply shortage and the power supply of suppliers in the case of supply surplus. Therefore, the islanded microgrid should be operated to reduce power imbalance conditions. Meanwhile, the microgrid is a small-scale power system and the employment of skillful operators for effective operation of its components requires high costs. Therefore, automatic operation of the components is effective realistically. In addition, the components are distributed in the microgrid and their operation should consider their owners’ profits. For these reasons, a multiagent system application can be a good alternative for microgrid operation. In this paper, we present a multiagent system for autonomous operation of the islanded microgrid on a power market environment. The proposed multiagent system is designed based on a cooperative operation scheme. We show the functionality and the feasibility of the proposed multiagent system through several tests. Full article
(This article belongs to the Special Issue Future Grid)
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Open AccessArticle First-Order Estimation of In-Place Gas Resources at the Nyegga Gas Hydrate Prospect, Norwegian Sea
Energies 2010, 3(12), 2001-2026; doi:10.3390/en3122001
Received: 26 October 2010 / Revised: 7 December 2010 / Accepted: 20 December 2010 / Published: 22 December 2010
Cited by 6 | PDF Full-text (4014 KB) | HTML Full-text | XML Full-text
Abstract
Gas hydrates have lately received increased attention as a potential future energy source, which is not surprising given their global and widespread occurrence. This article presents an integrated study of the Nyegga site offshore mid-Norway, where a gas hydrate prospect is defined on
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Gas hydrates have lately received increased attention as a potential future energy source, which is not surprising given their global and widespread occurrence. This article presents an integrated study of the Nyegga site offshore mid-Norway, where a gas hydrate prospect is defined on the basis of a multitude of geophysical models and one shallow geotechnical borehole. This prospect appears to hold around 625GSm3 (GSm3 = 109 standard cubic metres) of gas. The uncertainty related to the input parameters is dealt with through a stochastic calculation, giving a spread of in-place volumes of 183GSm3 (P90) to 1431GSm3 (P10). The resource density for Nyegga is found to be comparable to published resource assessments of other global hydrate provinces. Full article
(This article belongs to the Special Issue Natural Gas Hydrate)

Review

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Open AccessReview Perspectives on Hydrate Thermal Conductivity
Energies 2010, 3(12), 1934-1942; doi:10.3390/en3121934
Received: 28 October 2010 / Revised: 3 December 2010 / Accepted: 6 December 2010 / Published: 10 December 2010
Cited by 10 | PDF Full-text (136 KB) | HTML Full-text | XML Full-text
Abstract
In this review, the intriguing, anomalous behaviour of hydrate thermal conductivity will be described, and progress in performing experimental measurements will be described briefly. However particular attention shall be devoted to recent advances in the development of detailed theoretical understandings of mechanisms of
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In this review, the intriguing, anomalous behaviour of hydrate thermal conductivity will be described, and progress in performing experimental measurements will be described briefly. However particular attention shall be devoted to recent advances in the development of detailed theoretical understandings of mechanisms of thermal conduction in clathrate hydrates, and on how information gleaned from molecular simulation has contributed to mechanistic theoretical models. Full article
(This article belongs to the Special Issue Natural Gas Hydrate)
Open AccessReview Gas Hydrate Stability and Sampling: The Future as Related to the Phase Diagram
Energies 2010, 3(12), 1991-2000; doi:10.3390/en3121991
Received: 1 November 2010 / Revised: 13 December 2010 / Accepted: 16 December 2010 / Published: 21 December 2010
Cited by 3 | PDF Full-text (529 KB) | HTML Full-text | XML Full-text
Abstract
The phase diagram for methane + water is explained, in relation to hydrate applications, such as in flow assurance and in nature. For natural applications, the phase diagram determines the regions for hydrate formation for two- and three-phase conditions. Impacts are presented for sample preparation
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The phase diagram for methane + water is explained, in relation to hydrate applications, such as in flow assurance and in nature. For natural applications, the phase diagram determines the regions for hydrate formation for two- and three-phase conditions. Impacts are presented for sample preparation and recovery. We discuss an international study for “Round Robin” hydrate sample preparation protocols and testing. Full article
(This article belongs to the Special Issue Natural Gas Hydrate)

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