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Energies, Volume 6, Issue 6 (June 2013), Pages 2726-3096

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Open AccessArticle SOC Based Battery Cell Balancing with a Novel Topology and Reduced Component Count
Energies 2013, 6(6), 2726-2740; doi:10.3390/en6062726
Received: 7 April 2013 / Revised: 26 April 2013 / Accepted: 16 May 2013 / Published: 24 May 2013
Cited by 15 | PDF Full-text (638 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes a novel battery cell balancing topology with reduced component count and simplified control. The balancing algorithm is based on the state of charge (SOC) of each individual cell instead of cell voltage. The principle of the proposed topology is analyzed
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This paper proposes a novel battery cell balancing topology with reduced component count and simplified control. The balancing algorithm is based on the state of charge (SOC) of each individual cell instead of cell voltage. The principle of the proposed topology is analyzed and verified through simulation and experiments. Then an experimental battery test workbench is established to validate the proposed balancing algorithm. The experimental results show that the proposed balancing topology and associated algorithm can perform well in real applications. Full article
Open AccessArticle Turbulent Flow Characteristics and Dynamics Response of a Vertical-Axis Spiral Rotor
Energies 2013, 6(6), 2741-2758; doi:10.3390/en6062741
Received: 28 March 2013 / Revised: 15 May 2013 / Accepted: 17 May 2013 / Published: 29 May 2013
Cited by 2 | PDF Full-text (1148 KB) | HTML Full-text | XML Full-text
Abstract
The concept of a vertical-axis spiral wind rotor is proposed and implemented in the interest of adapting it to air flows from all directions and improving the rotor’s performance. A comparative study is performed between the proposed rotor and conventional Savonius rotor. Turbulent
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The concept of a vertical-axis spiral wind rotor is proposed and implemented in the interest of adapting it to air flows from all directions and improving the rotor’s performance. A comparative study is performed between the proposed rotor and conventional Savonius rotor. Turbulent flow features near the rotor blades are simulated with Spalart-Allmaras turbulence model. The torque coefficient of the proposed rotor is satisfactory in terms of its magnitude and variation through the rotational cycle. Along the height of the rotor, distinct spatial turbulent flow patterns vary with the upstream air velocity. Subsequent experiments involving a disk generator gives an in-depth understanding of the dynamic response of the proposed rotor under different operation conditions. The optimal tip-speed ratio of the spiral rotor is 0.4–0.5, as is shown in both simulation and experiment. Under normal and relative-motion flow conditions, and within the range of upstream air velocity from 1 to 12 m/s, the output voltage of the generator was monitored and statistically analyzed. It was found that normal air velocity fluctuations lead to a non-synchronous correspondence between upstream air velocity and output voltage. In contrast, the spiral rotor’s performance when operating from the back of a moving truck was significantly different to its performance under the natural conditions. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Isolation and Characterization of a Marine Microalga for Biofuel Production with Astaxanthin as a Co-Product
Energies 2013, 6(6), 2759-2772; doi:10.3390/en6062759
Received: 6 February 2013 / Revised: 17 May 2013 / Accepted: 18 May 2013 / Published: 29 May 2013
Cited by 7 | PDF Full-text (2947 KB) | HTML Full-text | XML Full-text
Abstract
Microalgae have been considered as a promising biomass for biofuel production, but freshwater resource consumption during the scaled-up cultivation are still a challenge. Obtaining robust marine strains capable of producing triacylglycerols and high value-added metabolites are critical for overcoming the limitations of water
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Microalgae have been considered as a promising biomass for biofuel production, but freshwater resource consumption during the scaled-up cultivation are still a challenge. Obtaining robust marine strains capable of producing triacylglycerols and high value-added metabolites are critical for overcoming the limitations of water resources and economical feasibility. In this study, a marine microalga with lipid and astaxanthin accumulation capability was isolated from Bohai Bay, China. The alga was named as Coelastrum sp. HA-1 based on its morphological and molecular identification. The major characteristics of HA-1 and the effects of nitrogen on its lipid and astaxanthin accumulations were investigated. Results indicated that the highest biomass, lipid and astaxanthin yields achieved were 50.9 g m−2 day−1, 18.0 g m−2 day−1 and 168.9 mg m−2 day−1, respectively, after cultivation for 24 days. The fatty acids of HA-1, identified in their majority as oleic acid (56.6%) and palmitic acid (25.9%), are desirable biofuel feedstocks. In addition, this alga can be harvested with simple sedimentation, achieving 98.2% removal efficiency after settling for 24 h. These results suggest that Coelastrum sp. HA-1 has several desirable key features that make it a potential candidate for biofuel production. Full article
(This article belongs to the Special Issue Algae Fuel 2013)
Open AccessCommunication Isolation and Fatty Acid Profile of Selected Microalgae Strains from the Red Sea for Biofuel Production
Energies 2013, 6(6), 2773-2783; doi:10.3390/en6062773
Received: 2 April 2013 / Revised: 18 May 2013 / Accepted: 20 May 2013 / Published: 30 May 2013
Cited by 18 | PDF Full-text (624 KB) | HTML Full-text | XML Full-text
Abstract
The isolation of lipid-rich autochthonous strains of microalgae is a crucial stage for the development of a microalgae-based biofuel production plant, as these microalgae already have the necessary adaptations to withstand competition, predation and the temperatures observed at each production site. This is
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The isolation of lipid-rich autochthonous strains of microalgae is a crucial stage for the development of a microalgae-based biofuel production plant, as these microalgae already have the necessary adaptations to withstand competition, predation and the temperatures observed at each production site. This is particularly important in extreme climates such as in Saudi Arabia. Resorting to fluorescence activated cell sorting (FACS) we screened for and isolated several microalgal strains from samples collected from the Red Sea. Relying on the fluorescence of BODIPY 505/515 (4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diazasindacene) and growth performance, four promising candidates were identified and the total lipid content and fatty acid profile was assessed for biofuels production. Selected isolates were classified as chlorophytes, belonging to three different genera: Picochlorum, Nannochloris and Desmochloris. The lipid contents were assessed microscopically by means of BODIPY 505/515-associated fluorescence to detect intracellular lipid bodies, which revealed several lipid drops in all selected strains. This result was confirmed by lipid gravimetric determination, which demonstrated that all strains under study presented inner cell lipid contents ranging from 20% to 25% of the biomass dry weight. Furthermore, the fatty acid methyl esters profile of all strains seems ideal for biodiesel production due to a low degree of polyunsaturated fatty acid methyl esters and high amount of palmitic and oleic acids. Full article
(This article belongs to the Special Issue Algae Fuel 2013)
Open AccessArticle The Performance Test of Three Different Horizontal Axis Wind Turbine (HAWT) Blade Shapes Using Experimental and Numerical Methods
Energies 2013, 6(6), 2784-2803; doi:10.3390/en6062784
Received: 7 March 2013 / Revised: 20 May 2013 / Accepted: 22 May 2013 / Published: 5 June 2013
Cited by 12 | PDF Full-text (1744 KB) | HTML Full-text | XML Full-text
Abstract
Three different horizontal axis wind turbine (HAWT) blade geometries with the same diameter of 0.72 m using the same NACA4418 airfoil profile have been investigated both experimentally and numerically. The first is an optimum (OPT) blade shape, obtained using improved blade element momentum
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Three different horizontal axis wind turbine (HAWT) blade geometries with the same diameter of 0.72 m using the same NACA4418 airfoil profile have been investigated both experimentally and numerically. The first is an optimum (OPT) blade shape, obtained using improved blade element momentum (BEM) theory. A detailed description of the blade geometry is also given. The second is an untapered and optimum twist (UOT) blade with the same twist distributions as the OPT blade. The third blade is untapered and untwisted (UUT). Wind tunnel experiments were used to measure the power coefficients of these blades, and the results indicate that both the OPT and UOT blades perform with the same maximum power coefficient, Cp = 0.428, but it is located at different tip speed ratio, λ = 4.92 for the OPT blade and λ = 4.32 for the UOT blade. The UUT blade has a maximum power coefficient of Cp = 0.210 at λ = 3.86. After the tests, numerical simulations were performed using a full three-dimensional computational fluid dynamics (CFD) method using the k-ω SST turbulence model. It has been found that CFD predictions reproduce the most accurate model power coefficients. The good agreement between the measured and computed power coefficients of the three models strongly suggest that accurate predictions of HAWT blade performance at full-scale conditions are also possible using the CFD method. Full article
(This article belongs to the Special Issue Wind Turbines 2013)
Open AccessArticle A Kalman Filter-Based Method for Reconstructing GMS-5 Global Solar Radiation by Introduction of In Situ Data
Energies 2013, 6(6), 2804-2818; doi:10.3390/en6062804
Received: 27 March 2013 / Revised: 3 June 2013 / Accepted: 3 June 2013 / Published: 7 June 2013
Cited by 4 | PDF Full-text (1670 KB) | HTML Full-text | XML Full-text
Abstract
Solar radiation is an important input for various land-surface energy balance models. Global solar radiation data retrieved from the Japanese Geostationary Meteorological Satellite 5 (GMS-5)/Visible and Infrared Spin Scan Radiometer (VISSR) has been widely used in recent years. However, due to the impact
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Solar radiation is an important input for various land-surface energy balance models. Global solar radiation data retrieved from the Japanese Geostationary Meteorological Satellite 5 (GMS-5)/Visible and Infrared Spin Scan Radiometer (VISSR) has been widely used in recent years. However, due to the impact of clouds, aerosols, solar elevation angle and bidirectional reflection, spatial or temporal deficiencies often exist in solar radiation datasets that are derived from satellite remote sensing, which can seriously affect the accuracy of application models of land-surface energy balance. The goal of reconstructing radiation data is to simulate the seasonal variation patterns of solar radiation, using various statistical and numerical analysis methods to interpolate the missing observations and optimize the whole time-series dataset. In the current study, a reconstruction method based on data assimilation is proposed. Using a Kalman filter as the assimilation algorithm, the retrieved radiation values are corrected through the continuous introduction of local in-situ global solar radiation (GSR) provided by the China Meteorological Data Sharing Service System (Daily radiation dataset_Version 3) which were collected from 122 radiation data collection stations over China. A complete and optimal set of time-series data is ultimately obtained. This method is applied and verified in China’s northern agricultural areas (humid regions, semi-humid regions and semi-arid regions in a warm temperate zone). The results show that the mean value and standard deviation of the reconstructed solar radiation data series are significantly improved, with greater consistency with ground-based observations than the series before reconstruction. The method implemented in this study provides a new solution for the time-series reconstruction of surface energy parameters, which can provide more reliable data for scientific research and regional renewable-energy planning. Full article
(This article belongs to the Special Issue Large Scale LUCC, Surface Energy Fluxes and Energy Use)
Open AccessArticle Influence of Maintenance Intervals on Performance and Emissions of a 192 kWel Biogas Gas Otto CHP Unit and Results of Lubricating Oil Quality Tests—Outcome from a Continuous Two-Year Measuring Campaign
Energies 2013, 6(6), 2819-2839; doi:10.3390/en6062819
Received: 16 February 2013 / Revised: 6 May 2013 / Accepted: 24 May 2013 / Published: 7 June 2013
Cited by 3 | PDF Full-text (4805 KB) | HTML Full-text | XML Full-text
Abstract
In the present work, we focus on long-term and permanent measurements of approximately two years on a 192 kWel Gas Otto CHP (combined heat and power) unit at a full-scale research biogas plant. In detail the influence of 600 h and 1800
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In the present work, we focus on long-term and permanent measurements of approximately two years on a 192 kWel Gas Otto CHP (combined heat and power) unit at a full-scale research biogas plant. In detail the influence of 600 h and 1800 h maintenance intervals on electrical efficiency consumption and exhaust gas emissions such as NOx and CO have been studied under real life conditions. Lubricating oil quality analyses throughout the CHP operation time are presented to show the destructive changes in property and its influence on condition based maintenance. The results confirm the well-known fact that after readjustment of the air-fuel ratio after 1800 h maintenance the emission values for NOx decline while CO increases. The emission-optimized operation mode leads to lower engine efficiency. The maintenance tasks carried out at 600 h intervals lead to lower NOx emissions in nine cases while in 14 cases the emissions remained unchanged. The permanent measurements proved their legitimacy showing various emission deviations from the limiting values prior and post maintenance. The results show that by monitoring the lubricating oil quality, the oil change intervals can be maximized while ensuring that engine performance is not endangered, and a longer engine lifespan can be expected. The oil analyses allow the operator to reduce maintenance expenditures while minimizing wear. Full article
Open AccessArticle Can Tidal Current Energy Provide Base Load?
Energies 2013, 6(6), 2840-2858; doi:10.3390/en6062840
Received: 11 March 2013 / Revised: 31 May 2013 / Accepted: 3 June 2013 / Published: 14 June 2013
Cited by 2 | PDF Full-text (7195 KB) | HTML Full-text | XML Full-text
Abstract
Tidal energy belongs to the class of intermittent but predictable renewable energy sources. In this paper, we consider a compact set of geographically diverse locations, which have been assessed to have significant tidal stream energy, and attempt to find the degree to which
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Tidal energy belongs to the class of intermittent but predictable renewable energy sources. In this paper, we consider a compact set of geographically diverse locations, which have been assessed to have significant tidal stream energy, and attempt to find the degree to which the resource in each location should be exploited so that the aggregate power from all locations has a low variance. An important characteristic of the locations chosen is that there is a good spread in the peak tidal flow times, though the geographical spread is relatively small. We assume that the locations, all on the island of Ireland, can be connected together and also assume a modular set of tidal turbines. We employ multi-objective optimisation to simultaneously minimise variance, maximise mean power and maximise minimum power. A Pareto front of optimal solutions in the form of a set of coefficients determining the degree of tidal energy penetration in each location is generated using a genetic algorithm. While for the example chosen the total mean power generated is not great (circa 100 MW), the case study demonstrated a methodology that can be applied to other location sets that exhibit similar delays between peak tidal flow times. Full article
(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)
Open AccessArticle Idle Operation with Low Intake Valve Lift in a Port Fuel Injected Engine
Energies 2013, 6(6), 2874-2891; doi:10.3390/en6062874
Received: 21 September 2012 / Revised: 28 November 2012 / Accepted: 25 December 2012 / Published: 14 June 2013
Cited by 5 | PDF Full-text (2073 KB) | HTML Full-text | XML Full-text
Abstract
Reducing fuel consumption is a prime objective in the automotive industry in order to meet regulatory and customer demands. Variable valve actuation offers many opportunities for improving the spark ignition engine’s performance in areas such as fuel economy and pollutant emissions. Our studies
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Reducing fuel consumption is a prime objective in the automotive industry in order to meet regulatory and customer demands. Variable valve actuation offers many opportunities for improving the spark ignition engine’s performance in areas such as fuel economy and pollutant emissions. Our studies revealed that the ability to control maximum intake valve lift does indeed offer the ability to control intake air mass, but also has the added benefit that it improves the fuel-air mixing process thanks to an increased turbulence, caused by the increased intake flow velocity. This is particularly important at idle and low part loads when low maximum lifts are to be used for improving the fuel economy or for achieving the required power. The paper focuses on the experimental results obtained when approaching idle operation with different intake valve laws. Results indicating the potential of using low intake valve lift for fuel economy and cyclic dispersion improvement are presented in this paper. Full article
(This article belongs to the Special Issue Combined Heat and Power – Strategy and Practice)
Open AccessArticle Transient Momentum Balance—A Method for Improving the Performance of Mean-Value Engine Plant Models
Energies 2013, 6(6), 2892-2926; doi:10.3390/en6062892
Received: 20 March 2013 / Revised: 5 June 2013 / Accepted: 6 June 2013 / Published: 14 June 2013
Cited by 4 | PDF Full-text (2204 KB) | HTML Full-text | XML Full-text
Abstract
Mean-value engine models (MVEMs) are frequently applied in system-level simulations of vehicle powertrains. In particular, MVEMs are a common choice in engine simulators, where real-time execution is mandatory. In the case of real-time applications with prescribed, fixed sampling times, the use of explicit
[...] Read more.
Mean-value engine models (MVEMs) are frequently applied in system-level simulations of vehicle powertrains. In particular, MVEMs are a common choice in engine simulators, where real-time execution is mandatory. In the case of real-time applications with prescribed, fixed sampling times, the use of explicit integration schemes is almost mandatory. Thus the stability of MVEMs is one of the main limitations when it comes to optimizing their performance. It is limited either by the minimum size of the gas volume elements or by the maximum integration time step. An innovative approach that addresses both constraints arises from the fact that the mass flow through the transfer elements of the MVEM is not modelled considering the quasi-steady assumption, but instead the mass-flow is calculated using a single transient momentum balance (TMB) equation. The proposed approach closely resembles phenomena in the physical model, since it considers both the flow-field history and the inertial effects arising from the time variation of the mass flow. It is shown in this paper that a consideration of the TMB equation improves the stability and/or the computational speed of the MVEMs, whereas it also makes it possible to capture physical phenomena in a more physically plausible manner. Full article
Open AccessArticle Experimental Analysis of the Input Variables’ Relevance to Forecast Next Day’s Aggregated Electric Demand Using Neural Networks
Energies 2013, 6(6), 2927-2948; doi:10.3390/en6062927
Received: 29 March 2013 / Revised: 6 June 2013 / Accepted: 6 June 2013 / Published: 17 June 2013
Cited by 4 | PDF Full-text (3656 KB) | HTML Full-text | XML Full-text
Abstract
Thanks to the built in intelligence (deployment of new intelligent devices and sensors in places where historically they were not present), the Smart Grid and Microgrid paradigms are able to take advantage from aggregated load forecasting, which opens the door for the implementation
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Thanks to the built in intelligence (deployment of new intelligent devices and sensors in places where historically they were not present), the Smart Grid and Microgrid paradigms are able to take advantage from aggregated load forecasting, which opens the door for the implementation of new algorithms to seize this information for optimization and advanced planning. Therefore, accuracy in load forecasts will potentially have a big impact on key operation factors for the future Smart Grid/Microgrid-based energy network like user satisfaction and resource saving, and new methods to achieve an efficient prediction in future energy landscapes (very different from the centralized, big area networks studied so far). This paper proposes different improved models to forecast next day’s aggregated load using artificial neural networks, taking into account the variables that are most relevant for the aggregated. In particular, seven models based on the multilayer perceptron will be proposed, progressively adding input variables after analyzing the influence of climate factors on aggregated load. The results section presents the forecast from the proposed models, obtained from real data. Full article
Open AccessArticle Research on a Hierarchical Dynamic Automatic Voltage Control System Based on the Discrete Event-Driven Method
Energies 2013, 6(6), 2949-2965; doi:10.3390/en6062949
Received: 19 April 2013 / Revised: 23 May 2013 / Accepted: 30 May 2013 / Published: 17 June 2013
Cited by 1 | PDF Full-text (1419 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, concepts and methods of hybrid control systems are adopted to establish a hierarchical dynamic automatic voltage control (HD-AVC) system, realizing the dynamic voltage stability of power grids. An HD-AVC system model consisting of three layers is built based on the
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In this paper, concepts and methods of hybrid control systems are adopted to establish a hierarchical dynamic automatic voltage control (HD-AVC) system, realizing the dynamic voltage stability of power grids. An HD-AVC system model consisting of three layers is built based on the hybrid control method and discrete event-driven mechanism. In the Top Layer, discrete events are designed to drive the corresponding control block so as to avoid solving complex multiple objective functions, the power system’s characteristic matrix is formed and the minimum amplitude eigenvalue (MAE) is calculated through linearized differential-algebraic equations. MAE is applied to judge the system’s voltage stability and security and construct discrete events. The Middle Layer is responsible for management and operation, which is also driven by discrete events. Control values of the control buses are calculated based on the characteristics of power systems and the sensitivity method. Then control values generate control strategies through the interface block. In the Bottom Layer, various control devices receive and implement the control commands from the Middle Layer. In this way, a closed-loop power system voltage control is achieved. Computer simulations verify the validity and accuracy of the HD-AVC system, and verify that the proposed HD-AVC system is more effective than normal voltage control methods. Full article
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Open AccessArticle The Effect of Effluent Recirculation in a Semi-Continuous Two-Stage Anaerobic Digestion System
Energies 2013, 6(6), 2966-2981; doi:10.3390/en6062966
Received: 5 May 2013 / Revised: 5 June 2013 / Accepted: 9 June 2013 / Published: 17 June 2013
Cited by 6 | PDF Full-text (362 KB) | HTML Full-text | XML Full-text
Abstract
The effect of recirculation in increasing organic loading rate (OLR) and decreasing hydraulic retention time (HRT) in a semi-continuous two-stage anaerobic digestion system using stirred tank reactor (CSTR) and an upflow anaerobic sludge bed (UASB) was evaluated. Two-parallel processes were in operation for
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The effect of recirculation in increasing organic loading rate (OLR) and decreasing hydraulic retention time (HRT) in a semi-continuous two-stage anaerobic digestion system using stirred tank reactor (CSTR) and an upflow anaerobic sludge bed (UASB) was evaluated. Two-parallel processes were in operation for 100 days, one with recirculation (closed system) and the other without recirculation (open system). For this purpose, two structurally different carbohydrate-based substrates were used; starch and cotton. The digestion of starch and cotton in the closed system resulted in production of 91% and 80% of the theoretical methane yield during the first 60 days. In contrast, in the open system the methane yield was decreased to 82% and 56% of the theoretical value, for starch and cotton, respectively. The OLR could successfully be increased to 4 gVS/L/day for cotton and 10 gVS/L/day for starch. It is concluded that the recirculation supports the microorganisms for effective hydrolysis of polyhydrocarbons in CSTR and to preserve the nutrients in the system at higher OLRs, thereby improving the overall performance and stability of the process. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2013)
Open AccessArticle Integration of Photovoltaics in Buildings—Support Policies Addressing Technical and Formal Aspects
Energies 2013, 6(6), 2982-3001; doi:10.3390/en6062982
Received: 5 March 2013 / Revised: 9 June 2013 / Accepted: 11 June 2013 / Published: 18 June 2013
Cited by 9 | PDF Full-text (783 KB) | HTML Full-text | XML Full-text
Abstract
The integration of photovoltaic (PV) generators in the envelope of a building by means of building-integrated photovoltaics (BIPV) offers an immense potential, both in market development and the production of renewable electric energy that is close to the point of electricity consumption. In
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The integration of photovoltaic (PV) generators in the envelope of a building by means of building-integrated photovoltaics (BIPV) offers an immense potential, both in market development and the production of renewable electric energy that is close to the point of electricity consumption. In Germany, for example, by integrating photovoltaics in buildings up to 50% of the electricity demand can be covered. The political support of BIPV would contribute to the development and installation of BIPV components and therefore also promote the development of new business areas for industries dealing with components used in building envelopes and photovoltaic generators. BIPV can be separated into three different integration types: “technical”, “formal” and “technical & formal”. Political instruments for the support of PV-installations, particularly BIPV are discussed in this paper using Germany and France as examples. Due to successful financial support policies, PV became the most powerful electricity production technology in Germany. In France, the unique financial support of BIPV is resulting in an exemplary development and growth of certified BIPV components available on the market and, from a technical, aesthetic architectural and legal certainty point of view, facilitating the easy and widespread integration of photovoltaic generators in buildings. Full article
Open AccessArticle A Counter-Current Heat-Exchange Reactor for the Thermal Stimulation of Hydrate-Bearing Sediments
Energies 2013, 6(6), 3002-3016; doi:10.3390/en6063002
Received: 25 March 2013 / Revised: 16 May 2013 / Accepted: 7 June 2013 / Published: 18 June 2013
Cited by 17 | PDF Full-text (2042 KB) | HTML Full-text | XML Full-text
Abstract
Since huge amounts of CH4 are bound in natural gas hydrates occurring at active and passive continental margins and in permafrost regions, the production of natural gas from hydrate-bearing sediments has become of more and more interest. Three different methods to destabilize
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Since huge amounts of CH4 are bound in natural gas hydrates occurring at active and passive continental margins and in permafrost regions, the production of natural gas from hydrate-bearing sediments has become of more and more interest. Three different methods to destabilize hydrates and release the CH4 gas are discussed in principle: thermal stimulation, depressurization and chemical stimulation. This study focusses on the thermal stimulation using a counter-current heat-exchange reactor for the in situ combustion of CH4. The principle of in situ combustion as a method for thermal stimulation of hydrate bearing sediments has been introduced and discussed earlier [1,2]. In this study we present the first results of several tests performed in a pilot plant scale using a counter-current heat-exchange reactor. The heat of the flameless, catalytic oxidation of CH4 was used for the decomposition of hydrates in sand within a LArge Reservoir Simulator (LARS). Different catalysts were tested, varying from diverse elements of the platinum group to a universal metal catalyst. The results show differences regarding the conversion rate of CH4 to CO2. The promising results of the latest reactor test, for which LARS was filled with sand and ca. 80% of the pore space was saturated with CH4 hydrate, are also presented in this study. The data analysis showed that about 15% of the CH4 gas released from hydrates would have to be used for the successful dissociation of all hydrates in the sediment using thermal stimulation via in situ combustion. Full article
(This article belongs to the Special Issue Natural Gas Hydrate)
Open AccessArticle A Combined Fuzzy-AHP and Fuzzy-GRA Methodology for Hydrogen Energy Storage Method Selection in Turkey
Energies 2013, 6(6), 3017-3032; doi:10.3390/en6063017
Received: 24 April 2013 / Revised: 30 May 2013 / Accepted: 13 June 2013 / Published: 20 June 2013
Cited by 14 | PDF Full-text (308 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we aim to select the most appropriate Hydrogen Energy Storage (HES) method for Turkey from among the alternatives of tank, metal hydride and chemical storage, which are determined based on expert opinions and literature review. Thus, we propose a Buckley
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In this paper, we aim to select the most appropriate Hydrogen Energy Storage (HES) method for Turkey from among the alternatives of tank, metal hydride and chemical storage, which are determined based on expert opinions and literature review. Thus, we propose a Buckley extension based fuzzy Analytical Hierarchical Process (Fuzzy-AHP) and linear normalization based fuzzy Grey Relational Analysis (Fuzzy-GRA) combined Multi Criteria Decision Making (MCDM) methodology. This combined approach can be applied to a complex decision process, which often makes sense with subjective data or vague information; and used to solve to solve HES selection problem with different defuzzification methods. The proposed approach is unique both in the HES literature and the MCDM literature. Full article
Open AccessArticle Modeling of a Point Absorber for Energy Conversion in Italian Seas
Energies 2013, 6(6), 3033-3051; doi:10.3390/en6063033
Received: 27 March 2013 / Revised: 31 May 2013 / Accepted: 15 June 2013 / Published: 20 June 2013
Cited by 19 | PDF Full-text (689 KB) | HTML Full-text | XML Full-text
Abstract
In the present paper, we investigate the feasibility of wave electricity production in Italian seas by the deployment of the Seabased wave energy converter (WEC). A numerical model of the coupled buoy-generator system is presented, which simulates the behavior of the wave energy
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In the present paper, we investigate the feasibility of wave electricity production in Italian seas by the deployment of the Seabased wave energy converter (WEC). A numerical model of the coupled buoy-generator system is presented, which simulates the behavior of the wave energy converter under regular waves of different wave heights and periods. The hydrodynamic forces, including excitation force, radiation impedance and hydrostatic force, are calculated by linear potential wave theory, and an analytical model is used for the linear generator. Two buoys of different radii are considered to explore the effect of buoy dimension on energy conversion and device efficiency. The power output is maximized by adding a submerged object to the floating buoy, in order to bring the system into resonance with the typical wave frequencies of the sites. The simulation results show a very good agreement with the published data on the Seabased WEC. The model is used to estimate energy production at eight Italian offshore locations. The results indicate that the degree of utilization of the device is higher than 20% at the two most energetic Italian sites (Alghero and Mazara del Vallo) and that it can be considerably increased if the floating body is connected to a submerged object, thanks to the resonant behavior of the WEC. In this case, the degree of utilization of the device would be higher than 40% at most of the study sites, with the highest value at Mazara del Vallo. The work enlarges the perspective, to be confirmed by experimental tests and more accurate numerical modeling, on clean electric power production from ocean waves in the Italian seas. Full article
(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)
Open AccessArticle Using Atmospheric Pressure Tendency to Optimise Battery Charging in Off-Grid Hybrid Wind-Diesel Systems for Telecoms
Energies 2013, 6(6), 3052-3071; doi:10.3390/en6063052
Received: 25 March 2013 / Revised: 31 March 2013 / Accepted: 13 June 2013 / Published: 20 June 2013
Cited by 1 | PDF Full-text (1596 KB) | HTML Full-text | XML Full-text
Abstract
Off grid telecom base stations in developing nations are powered by diesel generators. They are typically oversized and run at a fraction of their rated load for most of their operating lifetime. Running generators at partial load is inefficient and, over time, physically
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Off grid telecom base stations in developing nations are powered by diesel generators. They are typically oversized and run at a fraction of their rated load for most of their operating lifetime. Running generators at partial load is inefficient and, over time, physically damages the engine. A hybrid configuration uses a battery bank, which powers the telecoms’ load for a portion of the time. The generator only operates when the battery bank needs to be charged. Adding a wind turbine further reduces the generator run hours and saves fuel. The generator is oblivious to the current wind conditions, which leads to simultaneous generator-wind power production. As the batteries become charged by the generator, the wind turbine controller is forced to dump surplus power as heat through a resistive load. This paper details how the relationship between barometric pressure and wind speed can be used to add intelligence to the battery charger. A Simulink model of the system is developed to test the different battery charging configurations. This paper demonstrates that if the battery charger is aware of upcoming wind conditions, it will provide modest fuel savings and reduce generator run hours in small-scale hybrid energy systems. Full article
(This article belongs to the Special Issue Wind Turbines 2013)
Open AccessArticle Massively-Parallel Molecular Dynamics Simulation of Clathrate Hydrates on Blue Gene Platforms
Energies 2013, 6(6), 3072-3081; doi:10.3390/en6063072
Received: 28 March 2013 / Revised: 31 May 2013 / Accepted: 14 June 2013 / Published: 20 June 2013
Cited by 7 | PDF Full-text (254 KB) | HTML Full-text | XML Full-text
Abstract
Massively-parallel classical equilibrium molecular dynamics (MD) simulations have been performed to investigate the computational performance of the Simple Point Charge (SPC) model and single-particle model of Molinero et al. applied to simulation of methane hydrates, using systems consisting of several million particles, on
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Massively-parallel classical equilibrium molecular dynamics (MD) simulations have been performed to investigate the computational performance of the Simple Point Charge (SPC) model and single-particle model of Molinero et al. applied to simulation of methane hydrates, using systems consisting of several million particles, on a variety of Blue Gene/L, P and Q platforms. It was found that the newer Blue Gene/Q platform offers attractive performance for massively-parallel simulation. Full article
(This article belongs to the Special Issue Natural Gas Hydrate)
Open AccessArticle Quantitative Analysis of Lithium-Ion Battery Capacity Prediction via Adaptive Bathtub-Shaped Function
Energies 2013, 6(6), 3082-3096; doi:10.3390/en6063082
Received: 23 April 2013 / Revised: 15 June 2013 / Accepted: 18 June 2013 / Published: 21 June 2013
Cited by 15 | PDF Full-text (38993 KB) | HTML Full-text | XML Full-text
Abstract
Batteries are one of the most important components in many mechatronics systems, as they supply power to the systems and their failures may lead to reduced performance or even catastrophic results. Therefore, the prediction analysis of remaining useful life (RUL) of batteries is
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Batteries are one of the most important components in many mechatronics systems, as they supply power to the systems and their failures may lead to reduced performance or even catastrophic results. Therefore, the prediction analysis of remaining useful life (RUL) of batteries is very important. This paper develops a quantitative approach for battery RUL prediction using an adaptive bathtub-shaped function (ABF). ABF has been utilised to model the normalised battery cycle capacity prognostic curves, which attempt to predict the remaining battery capacity with given historical test data. An artificial fish swarm algorithm method with a variable population size (AFSAVP) is employed as the optimiser for the parameter determination of the ABF curves, in which the fitness function is defined in the form of a coefficient of determination (R2). A 4 x 2 cross-validation (CV) has been devised, and the results show that the method can work valuably for battery health management and battery life prediction. Full article
(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)

Review

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Open AccessReview Mitigation Techniques to Reduce the Impact of Wind Turbines on Radar Services
Energies 2013, 6(6), 2859-2873; doi:10.3390/en6062859
Received: 27 April 2013 / Revised: 29 May 2013 / Accepted: 30 May 2013 / Published: 14 June 2013
Cited by 4 | PDF Full-text (864 KB) | HTML Full-text | XML Full-text
Abstract
Radar services are occasionally affected by wind farms. This paper presents a comprehensive description of the effects that a wind farm may cause on the different radar services, and it compiles a review of the recent research results regarding the mitigation techniques to
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Radar services are occasionally affected by wind farms. This paper presents a comprehensive description of the effects that a wind farm may cause on the different radar services, and it compiles a review of the recent research results regarding the mitigation techniques to minimize this impact. Mitigation techniques to be applied at the wind farm and on the radar systems are described. The development of thorough impact studies before the wind farm is installed is presented as the best way to analyze in advance the potential for interference, and subsequently identify the possible solutions to allow the coexistence of wind farms and radar services. Full article
(This article belongs to the Special Issue Wind Turbines 2013)
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