http://www.mdpi.com/journal/energies Latest open access articles published in Energies at http://www.mdpi.com/journal/energies/ http://www.mdpi.com/1996-1073/5/2/270/ An experimental investigation was carried out to study the NOx formation and reduction by primary measures for five types of biomass (straw, peat, sewage sludge, forest residues/Grot, and wood pellets) and their mixtures. To minimize the NOx level in biomass-fired boilers, combustion experiments were performed in a laboratory scale multifuel fixed grate reactor using staged air combustion. Flue gas was extracted to measure final levels of CO, CO2, CxHy, O2, NO, NO2, N2O, and other species. The fuel gas compositions between the first and second stage were also monitored. The experiments showed good combustion quality with very low concentrations of unburnt species in the flue gas. Under optimum conditions, a NOx reduction of 50–80% was achieved, where the highest reduction represents the case with the highest fuel-N content. The NOx emission levels were very sensitive to the primary excess air ratio and an optimum value for primary excess air ratio was seen at about 0.9. Conversion of fuel nitrogen to NOx showed great dependency on the initial fuel-N content, where the blend with the highest nitrogen content had lowest conversion rate. Between 1–25% of the fuel-N content is converted to NOx depending on the fuel blend and excess air ratio. Sewage sludge is suggested as a favorable fuel to be blended with straw. It resulted in a higher NOx reduction and low fuel-N conversion to NOx. Tops and branches did not show desirable NOx reduction and made the combustion also more unstable. N2O emissions were very low, typically below 5 ppm at 11% O2 in the dry flue gas, except for mixtures with high nitrogen content, where values up to 20 ppm were observed. The presented results are part of a larger study on problematic fuels, also considering ash content and corrosive compounds which have been discussed elsewhere. http://www.mdpi.com/1996-1073/5/2/270/ Wed, 08 Feb 2012 00:00:00 CET Energies 2012-02-08 5 2 Article 270 290 1996-1073 Experimental Investigation on NOx Reduction by Primary Measures in Biomass Combustion: Straw, Peat, Sewage Sludge, Forest Residues and Wood Pellets 2012-02-08 doi: 10.3390/en5020270 Ehsan Houshfar Terese Løvås Øyvind Skreiberg http://www.mdpi.com/1996-1073/5/2/258/ To develop indigenous alternative and renewable energy resources, long-term subsidy programs (1986–1991 and 2000–present) for solar water heaters have been enforced in Taiwan. By the end of 2010, the total installed area of solar collectors had exceeded 2 million square meters. However, over 98% of solar water heaters were used in residential systems for hot water production, with the areas of installed solar collector being less than 10 square meters. There were only 98 systems with area of solar collectors installed exceeding 100 square meters put into operation from 2001 to 2010. These systems were mainly installed for water heating in dormitories, swimming pools, restaurants, and manufacturing plants. In the present study, a comprehensive survey of these large-scale solar water heaters was conducted. The objectives of the survey were to assess the system performance and to collect feedback from individual users. It is found that lack of experience in system design and maintenance are the key factors affecting reliable operation of a system. Hourly, daily and long-term field measurements of a dormitory system were also examined to evaluate its thermal efficiencies. Results indicated that thermal efficiency of the system is associated with the daily solar radiation. Hot water use pattern and operation of auxiliary heater should be taken into account in system design. http://www.mdpi.com/1996-1073/5/2/258/ Tue, 07 Feb 2012 00:00:00 CET Energies 2012-02-07 5 2 Article 258 269 1996-1073 Field Surveys of Non-Residential Solar Water Heating Systems in Taiwan 2012-02-07 doi: 10.3390/en5020258 Wei-Min Lin Keh-Chin Chang Yi-Mei Liu Kung-Ming Chung http://www.mdpi.com/1996-1073/5/2/243/ The purpose of this work is to investigate the influence of n-hexane addition on in situ transesterification of a solid raw material for biodiesel production. Extraction and reaction of macroalgae oil has been performed simultaneously in a batch reactor adding n-hexane with the reactants. In order to analyze the influence of n-hexane on the transesterification, the reaction was also carried out with sunflower oil. The results show that the presence of n-hexane does not have an important effect on the transesterification. It was also observed that this method requires large quantities of methanol to carry out the reaction. The best reaction conditions for in situ transesterification of marine macroalgae were 300:1 methanol-to-oil molar ratio, 1% catalyst concentration, 60 °C reaction temperature and 11 h reaction time, resulting in a methyl esters yield of 17.1%. Thus, biodiesel production from macroalgae by transesterification in situ could be feasible, using hexane for the extraction and eliminating the previous extraction. This integrated method is thus effective and technically attractive. http://www.mdpi.com/1996-1073/5/2/243/ Mon, 06 Feb 2012 00:00:00 CET Energies 2012-02-06 5 2 Article 243 257 1996-1073 Influence of n-Hexane on in Situ Transesterification of Marine Macroalgae 2012-02-06 doi: 10.3390/en5020243 Angel Sánchez Rocio Maceiras Angeles Cancela Mónica Rodríguez http://www.mdpi.com/1996-1073/5/2/227/ The search for energy efficient construction solutions is still pending in the agro-food industry, in which a large amount of energy is often consumed unnecessarily when storing products. The main objective of this research is to promote high energy efficiency built environments, which aim to reduce energy consumption in this sector. We analyze the suitability of using the thermal inertia of the ground to provide an adequate environment for the storage and conservation of agro-food products. This research compares different construction solutions based on the use of ground thermal properties, analyzing their effectiveness to decrease annual outdoor variations and provide adequate indoor conditions. The analysis undertaken is based on over five million pieces of data, obtained from an uninterrupted four year monitoring process of various constructions with different levels of thermal mass, ranging from high volume constructions to others lacking this resource. It has been proven that constructive solutions based on the use of ground thermal inertia are more effective than other solutions when reducing the effects of outdoor conditions, even when these have air conditioning systems. It is possible to reach optimal conditions to preserve agro-food products such as wine, with a good design and an adequate amount of terrain, without having to use air conditioning systems. The results of this investigation could be of great use to the agro-food industry, becoming a reference when it comes to the design of energy efficient constructions. http://www.mdpi.com/1996-1073/5/2/227/ Thu, 02 Feb 2012 00:00:00 CET Energies 2012-02-02 5 2 Article 227 242 1996-1073 Ground Thermal Inertia for Energy Efficient Building Design: A Case Study on Food Industry 2012-02-02 doi: 10.3390/en5020227 Fernando R. Mazarrón Jaime Cid-Falceto Ignacio Cañas http://www.mdpi.com/1996-1073/5/2/193/ The Sea-wave Slot-cone Generator (SSG) is a Wave Energy Converter based on the wave overtopping principle; it employs several reservoirs placed on top of each other, in which the energy of incoming waves is stored as potential energy. Then, the captured water runs through turbines for electricity production. The system works under a wide spectrum of different wave conditions, giving a high overall efficiency. It can be suitable for shoreline and breakwater applications and presents particular advantages, such as sharing structure costs, availability of grid connection and recirculation of water inside the harbor, as the outlet of the turbines is on the rear part of the system. Recently, plans for the SSG pilot installations are in progress at the Svaaheia site (Norway), the port of Hanstholm (Denmark) and the port of Garibaldi (Oregon, USA). In the last-mentioned two projects, the Sea-wave Slot-cone Generator technology is integrated into the outer harbor breakwater and jetty reconstruction projects. In the last years extensive studies have been performed on the hydraulic and the structural response of this converter, with the aim of optimizing the design process. The investigations have been conducted by physical model tests and numerical simulations and many results have been published on both conference proceedings and journals. The main scope of this paper is reviewing the most significant findings, to provide the reader with an organic overview on the present status of knowledge. http://www.mdpi.com/1996-1073/5/2/193/ Tue, 31 Jan 2012 00:00:00 CET Energies 2012-01-31 5 2 Review 193 226 1996-1073 The SSG Wave Energy Converter: Performance, Status and Recent Developments 2012-01-31 doi: 10.3390/en5020193 Diego Vicinanza Lucia Margheritini Jens Peter Kofoed Mariano Buccino http://www.mdpi.com/1996-1073/5/2/181/ The mechanical properties of methane hydrate are important to the stability of borehole and methane extraction from a methane hydrate reservoir. In this study, a series of triaxial compression tests were carried out on laboratory-formed methane hydrate-ice mixtures with various methane hydrate contents. Axial loading was conducted at an axial strain rate of 1.33%/min and a constant temperature of −10 °C. The results indicate that: (1) the deformation behavior is strongly affected by confining pressure and methane hydrate content; (2) the failure strength significantly increases with confining pressure when confining pressure is less than 10 MPa, and decreases with methane hydrate content; (3) the cohesion decreases with methane hydrate content, while the internal friction angle increases with methane hydrate content; (4) the strength of ice specimens are higher than that of methane hydrate-ice mixture specimens; Based on the experimental data, the relationship among failure strength, confining pressure and methane hydrate content was obtained, and a modified Mohr-Coulomb criterion considering the influence of methane hydrate content on shear strength was proposed. http://www.mdpi.com/1996-1073/5/2/181/ Mon, 30 Jan 2012 00:00:00 CET Energies 2012-01-30 5 2 Article 181 192 1996-1073 Experimental Research on the Mechanical Properties of Methane Hydrate-Ice Mixtures 2012-01-30 doi: 10.3390/en5020181 Yanghui Li Yongchen Song Weiguo Liu Feng Yu http://www.mdpi.com/1996-1073/5/1/168/ The author has already presented some papers which allow studying cable systems by means of the multiconductor cell analysis (MCA). This method considers the cable system in its real asymmetry without simplified and approximated hypotheses. The multiconductor matrix procedure based on the use of admittance matrices, which account for the line cells (with earth return currents), different types of screen bonding, possible multiple circuits (single and double circuit or more), allows predicting the steady-state regime of any cable system. In the previous papers, these matrix algorithms have been presented with reference to a short extra-high voltage (EHV) double-circuit cross-bonded (CB) underground cable (UGC) system. Since the cable link was short, the shunt reactive compensation was not necessary and consequently not considered. In this paper the procedure is generalized in order to take into account three single-phase (or also one three-phase) reactors installed at the cable ends or also at intermediate locations. http://www.mdpi.com/1996-1073/5/1/168/ Mon, 23 Jan 2012 00:00:00 CET Energies 2012-01-23 5 1 Article 168 180 1996-1073 Steady State Assessment of Shunt Compensated EHV Insulated Cables by Means of Multiconductor Cell Analysis (MCA) 2012-01-23 doi: 10.3390/en5010168 Roberto Benato http://www.mdpi.com/1996-1073/5/1/157/ Converter transformers are the key and the most important components in high voltage direct current (HVDC) power transmission systems. Statistics show that the failure rate of HVDC converter transformers is approximately twice of that of transformers in AC power systems. This paper presents an approach integrated with a two-dimensional cloud model and an entropy-based weight model to evaluate the condition of HVDC converter transformers. The integrated approach can describe the complexity of HVDC converter transformers and achieve an effective assessment of their condition. Data from electrical testing, DGA, oil testing, and visual inspection were chosen to form the double-level assessment index system. Analysis results show that the integrated approach is capable of providing a relevant and effective assessment which in turn, provides valuable information for the maintenance of HVDC converter transformers. http://www.mdpi.com/1996-1073/5/1/157/ Mon, 23 Jan 2012 00:00:00 CET Energies 2012-01-23 5 1 Article 157 167 1996-1073 A Two-Dimensional Cloud Model for Condition Assessment of HVDC Converter Transformers 2012-01-23 doi: 10.3390/en5010157 Jian Li Zhiman He Youyuan Wang Jinzhuang Lv Linjie Zhao http://www.mdpi.com/1996-1073/5/1/138/ The increased activity in the field of Battery Electric Vehicles (BEVs) and Hybrid Electric Vehicles (HEVs) have led to an increase in standardization work, performed by both world-wide organizations like the IEC or the ISO, as by regional and national bodies such as CEN, CENELEC, SAE or JEVA. The issues of these standards cover several topics: safety, performance and operational/dimension issues. This paper reports a brief overview of current standardization activities of lithium batteries based on IEC 62660-1/2 and ISO 12405-1/2. Furthermore, in this paper, a series of innovative test procedures for lithium-ion batteries are presented. Thanks to these tests, the general characteristics of a battery such as charge and discharge capabilities, power performances and life cycle can be determined. Then, a new approach for extracting the life cycle of a battery in function of depth of discharge has been developed. http://www.mdpi.com/1996-1073/5/1/138/ Thu, 19 Jan 2012 00:00:00 CET Energies 2012-01-19 5 1 Article 138 156 1996-1073 Standardization Work for BEV and HEV Applications: Critical Appraisal of Recent Traction Battery Documents 2012-01-19 doi: 10.3390/en5010138 Noshin Omar Mohamed Daowd Omar Hegazy Grietus Mulder Jean-Marc Timmermans Thierry Coosemans Peter Van den Bossche Joeri Van Mierlo http://www.mdpi.com/1996-1073/5/1/119/ A new type of brushless double rotor machine (BDRM) is proposed in this paper. The BDRM is an important component in compound-structure permanent-magnet synchronous machine (CS-PMSM) systems, which are promising for power-split hybrid electric vehicle (HEV) applications. The BDRM can realize the speed adjustment between claw-pole rotor and permanent-magnet rotor without brushes and slip rings. The structural characteristics of the BDRM are described and its magnetic circuit model is built. Reactance parameters of the BDRM are deduced by an analytical method. It is found that the size characteristics of the BDRM are different from those of conventional machines. The new sizing and torque equations are analyzed and the theoretical results are used in the optimization process. Studies of the analytical magnetic circuit and finite element method (FEM) model show that the BDRM tends to have high leakage flux and low power factor, and then the method to obtain high power factor is discussed. Furthermore, a practical methodology of the BDRM design is developed, which includes an analytical tool, 2D field calculation and performance evaluation by 3D field calculation. Finally, different topologies of the BDRM are compared and an optimum prototype is designed. http://www.mdpi.com/1996-1073/5/1/119/ Thu, 19 Jan 2012 00:00:00 CET Energies 2012-01-19 5 1 Article 119 137 1996-1073 Performance Analysis and Simulation of a Novel Brushless Double Rotor Machine for Power-Split HEV Applications 2012-01-19 doi: 10.3390/en5010119 Ping Zheng Qian Wu Jing Zhao Chengde Tong Jingang Bai Quanbin Zhao http://www.mdpi.com/1996-1073/5/1/101/ Due to the very complex sets of component systems, interrelated thermodynamic processes and seasonal change in operating conditions, it is relatively difficult to find an accurate model for turbine cycle of nuclear power plants (NPPs). This paper deals with the modeling of turbine cycles to predict turbine-generator output using an adaptive neuro-fuzzy inference system (ANFIS) for Unit 1 of the Kuosheng NPP in Taiwan. Plant operation data obtained from Kuosheng NPP between 2006 and 2011 were verified using a linear regression model with a 95% confidence interval. The key parameters of turbine cycle, including turbine throttle pressure, condenser backpressure, feedwater flow rate and final feedwater temperature are selected as inputs for the ANFIS based turbine cycle model. In addition, a thermodynamic turbine cycle model was developed using the commercial software PEPSE® to compare the performance of the ANFIS based turbine cycle model. The results show that the proposed ANFIS based turbine cycle model is capable of accurately estimating turbine-generator output and providing more reliable results than the PEPSE® based turbine cycle models. Moreover, test results show that the ANFIS performed better than the artificial neural network (ANN), which has also being tried to model the turbine cycle. The effectiveness of the proposed neuro-fuzzy based turbine cycle model was demonstrated using the actual operating data of Kuosheng NPP. Furthermore, the results also provide an alternative approach to evaluate the thermal performance of nuclear power plants. http://www.mdpi.com/1996-1073/5/1/101/ Thu, 19 Jan 2012 00:00:00 CET Energies 2012-01-19 5 1 Article 101 118 1996-1073 Modeling of Turbine Cycles Using a Neuro-Fuzzy Based Approach to Predict Turbine-Generator Output for Nuclear Power Plants 2012-01-19 doi: 10.3390/en5010101 Yea-Kuang Chan Jyh-Cherng Gu http://www.mdpi.com/1996-1073/5/1/92/ Growth rate of a hydrate layer at the guest/liquid-water interface is analyzed considering the conjugate process of the mass-transfer and hydrate crystal growth. Hydrate-layer growth rate data in the literature are often compiled according to the system subcooling (∆T ≡ Teq − Tex, where Teq is the equilibrium dissociation temperature of the hydrate and Tex is the system temperature), suggesting predominant heat transfer limitations. In this paper, we investigate how the existing data on hydrate-layer growth is better correlated to mass transfer of the guest species in liquid water in three-phase equilibrium with bulk guest fluid and hydrate. We have analyzed the conjugate processes of mass-transfer/hydrate-layer-growth following our previous study on the hydrate crystal growth into liquid water saturated with a guest substance. A dimensionless parameter representing the hydrate-layer growth rate is derived from the analysis. This analysis is based on the idea that the growth rate is controlled by the mass transfer of the hydrate-guest substance, dissolved in the bulk of liquid water, to the front of the growing hydrate-layer along the guest/water interface. The variations in the hydrate-layer growth rate observed in the previous studies are related to the dimensionless parameter. http://www.mdpi.com/1996-1073/5/1/92/ Wed, 18 Jan 2012 00:00:00 CET Energies 2012-01-18 5 1 Article 92 100 1996-1073 Correlation of the Growth Rate of the Hydrate Layer at a Guest/Liquid-Water Interface to Mass Transfer Resistance 2012-01-18 doi: 10.3390/en5010092 Masatoshi Kishimoto Ryo Ohmura http://www.mdpi.com/1996-1073/5/1/71/ As a new technology, electric mobility has the potential to achieve a reduction in CO2 emissions and contribute to the transition from the current transportation system to a better one, environmentally speaking. The objective of the paper is to aid the necessary decision-making for the adoption and development of electric vehicles in Spain, taking the time horizon of 2020. This will be achieved by building a System Dynamics model for various scenarios that will be used for the analysis and comparison of various dynamic variables, as well as to determine how, and to what extent, they will influence the number of electric vehicles that will run on Spanish roads in the coming years, focusing on the cost variable. http://www.mdpi.com/1996-1073/5/1/71/ Thu, 12 Jan 2012 00:00:00 CET Energies 2012-01-12 5 1 Article 71 91 1996-1073 Is the Electric Vehicle an Attractive Option for Customers? 2012-01-12 doi: 10.3390/en5010071 Israel García Luis Javier Miguel http://www.mdpi.com/1996-1073/5/1/58/ An integrated full-field reservoir simulation study has been performed to determine the reservoir management and production strategies in a mature sandstone reservoir. The reservoir is a candidate for an enhanced oil recovery process or otherwise subject to abandonment. Based on its charateristics, the reservoir was found to be most suited for a surfactant/polymer (SP) flood. The study started with a large data gathering and the building of a full-field three-dimensional geological model. Subsequently, a full field simulation model was built and used to history match the water flood. The history match of the water flood emphasizes the areas with remaining high oil saturations, establishes the initial condition of the reservoir for an SP flood, and generates a forecast of reserves for continued water flood operations. A sector model was constructed from the full field model and then used to study different design parameters to maximize the project profitability from the SP flood. An economic model, based on the estimated recovery, residual oil in-place, oil price, and operating costs, has been implemented in order to optimize the project profitability. The study resulted in the selection of surfactant and polymer concentrations and slug size that yielded the best economic returns when applied in this reservoir. The study shows that, in today’s oil prices, surfactant/polymer flood when applied in this reservoir has increased the ultimate oil recovery and provide a significant financial returns. http://www.mdpi.com/1996-1073/5/1/58/ Wed, 11 Jan 2012 00:00:00 CET Energies 2012-01-11 5 1 Article 58 70 1996-1073 The Potential of a Surfactant/Polymer Flood in a Middle Eastern Reservoir 2012-01-11 doi: 10.3390/en5010058 Ridha Gharbi Abdullah Alajmi Meshal Algharaib http://www.mdpi.com/1996-1073/5/1/45/ The compound-structure permanent-magnet synchronous machine (CS-PMSM), comprising a double rotor machine (DRM) and a permanent-magnet (PM) motor, is a promising electronic-continuously variable transmission (e-CVT) concept for hybrid electric vehicles (HEVs). By CS-PMSM, independent speed and torque control of the vehicle engine is realized without a planetary gear unit. However, the slip rings and brushes of the conventional CS-PMSM are considered a major drawback for vehicle application. In this paper, a brushless flux-modulated CS-PMSM is investigated. The operating principle and basic working modes of the CS-PMSM are discussed. Mathematical models of the CS-PMSM system are given, and joint control of the two integrated machines is proposed. As one rotor of the DRM is mechanically connected with the rotor of the PM motor, special rotor position detection and torque allocation methods are required. Simulation is carried out by Matlab/Simulink, and the feasibility of the control system is proven. Considering the complexity of the controller, a single digital signal processor (DSP) is used to perform the interconnected control of dual machines instead of two separate ones, and a typical hardware implementation is proposed. http://www.mdpi.com/1996-1073/5/1/45/ Thu, 05 Jan 2012 00:00:00 CET Energies 2012-01-05 5 1 Article 45 57 1996-1073 Modeling and Control of a Flux-Modulated Compound-Structure Permanent-Magnet Synchronous Machine for Hybrid Electric Vehicles 2012-01-05 doi: 10.3390/en5010045 Ping Zheng Chengde Tong Jingang Bai Jing Zhao Yi Sui Zhiyi Song http://www.mdpi.com/1996-1073/5/1/32/ Nowadays, subjects such as eco-design requirements, product rating or code compliance with regard to energy efficiency are expanding towards a pan-European level. This leads to the necessity of defining zones within the European region, which share common climatic characteristics and will further facilitate the quick estimation of building energy performance. Towards this direction stands the current paper; it presents an approach for defining climatic zones in Europe on the basis of the amount of heating and cooling degree days. It is applied for the climate classification of selected European cities and is compared with the conventional scheme based solely on heating degree days. Since the approach is orientated mainly towards the assessment of building energy performance, its outcomes are evaluated with regard to the actual heating and cooling energy needs of a reference building unit with office use located in representative cities of the proposed climatic zones and facing the four cardinal orientations. The classification of climatic zones on the basis of both heating and cooling degree days leads to more realistic results, since nowadays cooling needs form a substantial part of the energy balance of the building, especially in the Mediterranean regions. http://www.mdpi.com/1996-1073/5/1/32/ Thu, 29 Dec 2011 00:00:00 CET Energies 2011-12-29 5 1 Article 32 44 1996-1073 On the Establishment of Climatic Zones in Europe with Regard to the Energy Performance of Buildings 2011-12-29 doi: 10.3390/en5010032 Katerina Tsikaloudaki Kostas Laskos Dimitrios Bikas http://www.mdpi.com/1996-1073/5/1/22/ China has achieved notable success in developing its economy with approximate 10 percent average annual GDP growth over the last two decades. At the same time, energy consumption and CO2 emissions almost doubled every five years, which led China to be the world top emitter in 2007. In response, China’s government has put forward a carbon mitigation target of 40%–45% reduction of CO2 emission intensity by 2020. To better understand the potential for success or failure of such a policy, it is essential to assess different driving forces such as population, lifestyle and technology and their associated CO2 emissions. This study confirms that increase of affluence has been the main driving force for China’s CO2 emissions since the late 1970s, which outweighs reductions achieved through technical progress. Meanwhile, the contribution of population growth to CO2 emissions was relatively small. We also found a huge disparity between urban and rural households in terms of changes of lifestyle and consumption patterns. Lifestyles in urban China are beginning to resemble Western lifestyles, and approaching their level of CO2 emissions. Therefore, in addition to the apparent inefficiencies in terms of production technologies there is also a lot of room for improvement on the consumption side especially in interaction of current infrastructure investments and future consumption. http://www.mdpi.com/1996-1073/5/1/22/ Tue, 27 Dec 2011 00:00:00 CET Energies 2011-12-27 5 1 Article 22 31 1996-1073 Changing Lifestyles Towards a Low Carbon Economy: An IPAT Analysis for China 2011-12-27 doi: 10.3390/en5010022 Klaus Hubacek Kuishuang Feng Bin Chen http://www.mdpi.com/1996-1073/5/1/1/ This paper proposes a structure for long-term energy demand forecasting. The proposed hybrid approach, called HPLLNF, uses the local linear neuro-fuzzy (LLNF) model as the forecaster and utilizes the Hodrick–Prescott (HP) filter for extraction of the trend and cyclic components of the energy demand series. Besides, the sophisticated technique of mutual information (MI) is employed to select the most relevant input features with least possible redundancies for the forecast model. Each generated component by the HP filter is then modeled through an LLNF model. Starting from an optimal least square estimation, the local linear model tree (LOLIMOT) learning algorithm increases the complexity of the LLNF model as long as its performance is improved. The proposed HPLLNF model with MI-based input selection is applied to the problem of long-term energy forecasting in three different case studies, including forecasting of the gasoline, crude oil and natural gas demand over the next 12 months. The obtained forecasting results reveal the noteworthy performance of the proposed approach for long-term energy demand forecasting applications. http://www.mdpi.com/1996-1073/5/1/1/ Thu, 22 Dec 2011 00:00:00 CET Energies 2011-12-22 5 1 Article 1 21 1996-1073 Mid-Term Energy Demand Forecasting by Hybrid Neuro-Fuzzy Models 2011-12-22 doi: 10.3390/en5010001 Hossein Iranmanesh Majid Abdollahzade Arash Miranian http://www.mdpi.com/1996-1073/4/12/2295/ The establishment of low-carbon cities has been suggested all over the World, since cities are key drivers of energy usage and the associated carbon emissions. This paper presents a scenario analysis of future energy consumption and carbon emissions for the city of Beijing. The Long-range Energy Alternatives Planning (LEAP) model is used to simulate a range of pathways and to analyze how these would change energy consumption and carbon emissions from 2007 to 2030. Three scenarios have been designed to describe future energy strategies in relation to the development of Beijing city, namely a reference scenario (RS), control scenario (CS), and integrated scenario (IS). The results show that under the IS the total energy demand in Beijing is expected to reach 88.61 million tonnes coal equivalent (Mtce) by 2030 (59.32 Mtce in 2007), 55.82% and 32.72% lower than the values under the RS and the CS, respectively. The total carbon emissions in 2030 under the IS, although higher than the 2007 level, will be 62.22% and 40.27% lower than under the RS and the CS, respectively, with emissions peaking in 2026 and declining afterwards. In terms of the potential for reduction of energy consumption and carbon emissions, the industrial sector will continue to act as the largest contributor under the IS and CS compared with the RS, while the building and transport sectors are identified as promising fields for achieving effective control of energy consumption and carbon emissions over the next two decades. The calculation results show that an integrated package of measures is the most effective in terms of energy savings and carbon emissions mitigation, although it also faces the largest challenge to achieve the related targets. http://www.mdpi.com/1996-1073/4/12/2295/ Tue, 20 Dec 2011 00:00:00 CET Energies 2011-12-20 4 12 Article 2295 2310 1996-1073 Alternative Scenarios for the Development of a Low-Carbon City: A Case Study of Beijing, China 2011-12-20 doi: 10.3390/en4122295 Lixiao Zhang Yueyi Feng Bin Chen http://www.mdpi.com/1996-1073/4/12/2273/ This paper presents an analysis of the energy exchange resulting from a 2D steady magnetohydrodynamics (MHD) flow past a permeable surface with partial slip in the presence of the viscous dissipation effect under convective heating boundary conditions. A magnetic field can effectively control the motion of an electrically conducting fluid in micro scale systems, which can be applied for fluid transportation. Local similarity solutions for the transformed governing equations are obtained, and the reduced ordinary differential equations solved numerically via an explicit Runge-Kutta (4, 5) formula, the Dormand-Prince pair and shooting method, which is valid for fixed positions along the surface. The effects of various physical parameters, such as the magnetic parameter, the slip coefficient, the suction/injection parameter, the Biot number, the Prandtl number and the Eckert number, on the flow and heat transfer characteristics are presented graphically and discussed. The results indicate that the heat transfer rate increases with the increase in Biot number, slip coefficient, suction and magnetic parameter, whereas it decreases with the increase in Eckert number and injection. http://www.mdpi.com/1996-1073/4/12/2273/ Tue, 20 Dec 2011 00:00:00 CET Energies 2011-12-20 4 12 Article 2273 2294 1996-1073 Effects of Viscous Dissipation on the Slip MHD Flow and Heat Transfer past a Permeable Surface with Convective Boundary Conditions 2011-12-20 doi: 10.3390/en4122273 Mohammad H. Yazdi Shahrir Abdullah Ishak Hashim Kamaruzzaman Sopian http://www.mdpi.com/1996-1073/4/12/2249/ Guangdong is China’s largest province in terms of energy consumption. The energy-related carbon emissions in Guangdong province are calculated, and two extended and improved decomposition models for energy-related carbon emissions are established with the Logarithmic Mean Divisia Index method based on the basic principle of Kaya identity. Main results are as follows: (1) the energy-related carbon emissions from the three strata of industry, except the primary industry, and household energy consumption in Guangdong province show increasing trend from 1995 to 2009; (2) the main driving and inhibiting factors which influence energy-related carbon emissions are economic output and energy intensity, respectively, while the contributions of energy mix, industrial structures, population size and living standards are not significant during the period of interest. It is concluded that optimizing the energy mix by exploiting new energy sources and cutting down energy intensity by developing low-carbon technologies are the two most effective approaches to reduce carbon emissions for Guangdong province in the future. The results and proposals in this paper provided reference for relevant administrative departments in the Government of Guangdong province to develop policies for energy conservation and emission reduction as well as to promote development of low-carbon economy. http://www.mdpi.com/1996-1073/4/12/2249/ Mon, 19 Dec 2011 00:00:00 CET Energies 2011-12-19 4 12 Article 2249 2272 1996-1073 Study on the Decomposition of Factors Affecting Energy-Related Carbon Emissions in Guangdong Province, China 2011-12-19 doi: 10.3390/en4122249 Wenxiu Wang Yaoqiu Kuang Ningsheng Huang http://www.mdpi.com/1996-1073/4/12/2236/ Wind turbine reliability is an important issue for wind energy cost minimization, especially by reduction of operation and maintenance costs for critical components and by increasing wind turbine availability. To develop an optimal operation and maintenance plan for critical components, it is necessary to understand the physics of their failure and be able to develop reliability prediction models. Such a model is proposed in this paper for an IGBT power electronic module. IGBTs are critical components in wind turbine converter systems. These are multilayered devices where layers are soldered to each other and they operate at a thermal-power cycling environment. Temperature loadings affect the reliability of soldered joints by developing cracks and fatigue processes that eventually result in failure. Based on Miner’s rule a linear damage model that incorporates a crack development and propagation processes is discussed. A statistical analysis is performed for appropriate model parameter selection. Based on the proposed model, a layout for component life prediction with crack movement is described in details. http://www.mdpi.com/1996-1073/4/12/2236/ Thu, 15 Dec 2011 00:00:00 CET Energies 2011-12-15 4 12 Article 2236 2248 1996-1073 Reliability Assessment of Solder Joints in Power Electronic Modules by Crack Damage Model for Wind Turbine Applications 2011-12-15 doi: 10.3390/en4122236 Erik E. Kostandyan John D. Sørensen http://www.mdpi.com/1996-1073/4/12/2224/ Vehicle to Grid technology allows the batteries of electric vehicles to operate as energy storage elements for renewable energy power systems. The Z-Source inverter is a new and attractive topology for the power electronics interface. In this paper, the equivalent DC-link voltage ripple of a single-phase Z-Source inverter for Vehicle to Grid applications is analyzed in this paper before deriving a general design approach for the Z-Source network. These theoretical findings, and design rule for a Z-Source network have been confirmed by computer simulations and a laboratory-implemented prototype. http://www.mdpi.com/1996-1073/4/12/2224/ Thu, 15 Dec 2011 00:00:00 CET Energies 2011-12-15 4 12 Article 2224 2235 1996-1073 Analysis of a Single-Phase Z-Source Inverter for Battery Discharging in Vehicle to Grid Applications 2011-12-15 doi: 10.3390/en4122224 Yifan Yu Qianfan Zhang Bin Liang Xiaofei Liu Shumei Cui http://www.mdpi.com/1996-1073/4/12/2212/ In biodiesel production, the vegetable oil used as raw material for transesterification should be free of water and free fatty acids (FFAs), which may consume catalyst and reduce catalyst efficiency. In this work biodiesel was prepared from acidified oils (AO) through a supercritical methanol route, in which the esterification of FFAs and transesterification of glyceride with methanol occurred simultaneously. The effects of the mass ratio of methanol to AO, the operation temperature as well as the water content on the FFAs conversion and glycerol yield were investigated. The results indicated that the FFAs conversion for esterification under the condition of 1:1 methanol/oil ratio, 310 °C and 15 min reaction time reached 98.7%, and the glycerol yield for transesterification under 0.25:1 methanol/oil ratio, 290 °C and 20 min reaction time reached 63.5% respectively. http://www.mdpi.com/1996-1073/4/12/2212/ Wed, 14 Dec 2011 00:00:00 CET Energies 2011-12-14 4 12 Article 2212 2223 1996-1073 Biodiesel Production from Acidified Oils via Supercritical Methanol 2011-12-14 doi: 10.3390/en4122212 Jincheng Ding Benqiao He Jianxin Li http://www.mdpi.com/1996-1073/4/12/2196/ This paper presents a numerical computation method for determining the magnetic field of high-current busducts of circular cross-section geometry, based on the subdivision of the busduct phase conductors and screens into the conductor filaments and the subsequent application of the mesh-current method, with the aid of the geometric mean distance method. The mathematical model takes into account the skin effect and the proximity effects, as well as the complete electromagnetic coupling between phase conductors and metal enclosures (i.e., screens) of the single-phase isolated busduct system (of circular cross-section geometry). This model could be readily applied to the computation of the magnetic field of the Gas Insulated Transmission Lines (GIL) as well. http://www.mdpi.com/1996-1073/4/12/2196/ Tue, 13 Dec 2011 00:00:00 CET Energies 2011-12-13 4 12 Article 2196 2211 1996-1073 Numerical Analysis of the Magnetic Field of High-Current Busducts and GIL Systems 2011-12-13 doi: 10.3390/en4122196 Petar Sarajcev http://www.mdpi.com/1996-1073/4/12/2180/ Due to Japan’s recent nuclear crisis and petroleum price hikes, the search for renewable energy sources has become an issue of immediate concern. A promising candidate attracting much global attention is solar energy, as it is green and also inexhaustible. A maximum power point tracking (MPPT) controller is employed in such a way that the output power provided by a photovoltaic (PV) system is boosted to its maximum level. However, in the context of abrupt changes in irradiance, conventional MPPT controller approaches suffer from insufficient robustness against ambient variation, inferior transient response and a loss of output power as a consequence of the long duration required of tracking procedures. Accordingly, in this work the maximum power point tracking is carried out successfully using a sliding mode extremum-seeking control (SMESC) method, and the tracking performances of three controllers are compared by simulations, that is, an extremum-seeking controller, a sinusoidal extremum-seeking controller and a sliding mode extremum-seeking controller. Being able to track the maximum power point promptly in the case of an abrupt change in irradiance, the SMESC approach is proven by simulations to be superior in terms of system dynamic and steady state responses, and an excellent robustness along with system stability is demonstrated as well. http://www.mdpi.com/1996-1073/4/12/2180/ Thu, 08 Dec 2011 00:00:00 CET Energies 2011-12-08 4 12 Article 2180 2195 1996-1073 Comparison of Extremum-Seeking Control Techniques for Maximum Power Point Tracking in Photovoltaic Systems 2011-12-08 doi: 10.3390/en4122180 Her-Terng Yau Chen-Han Wu http://www.mdpi.com/1996-1073/4/12/2166/ Cogging torque exists between rotor mounted permanent magnets and stator teeth due to magnetic attraction and this is an undesired phenomenon which produces output ripple, vibration and noise in machines. The purpose of this paper is to study the existence and effects of cogging torque, and to present a novel, rapid, half magnet pole pair technique for forecasting and evaluating cogging torque. The technique uses the finite element method as well as Matlab research and development oriented software tools to reduce numerous computing jobs and simulation time. An example of a rotor-skewed structure used to reduce cogging torque of permanent magnet synchronous machines is evaluated and compared with a conventional analysis method for the same motor to verify the effectiveness of the proposed approach. The novel method is proved valuable and suitable for large-capacity machine design. http://www.mdpi.com/1996-1073/4/12/2166/ Tue, 06 Dec 2011 00:00:00 CET Energies 2011-12-06 4 12 Article 2166 2179 1996-1073 A Novel Cogging Torque Simulation Method for Permanent-Magnet Synchronous Machines 2011-12-06 doi: 10.3390/en4122166 Chun-Yu Hsiao Sheng-Nian Yeh Jonq-Chin Hwang http://www.mdpi.com/1996-1073/4/12/2151/ Combined heat and power (CHP) systems in both power stations and large plants are becoming one of the most important tools for reducing energy requirements and consequently the overall carbon footprint of fundamental industrial activities. While power stations employ topping cycles where the heat rejected from the cycle is supplied to domestic and industrial consumers, the plants that produce surplus heat can utilise bottoming cycles to generate electrical power. Traditionally the waste heat available at high temperatures was used to generate electrical power, whereas energy at lower temperatures was either released to the environment or used for commercial or domestic heating. However the introduction of new engines, such as the ones using the organic Rankine cycle, capable of employing condensing temperatures very close to the ambient temperature, has made the generation of electrical power at low temperatures also convenient. On the other hand, district heating is becoming more and more significant since it has been extended to include cooling in the warm months and underground storage of thermal energy to cope with variable demand. These developments imply that electric power generation and district heating/cooling may become alternative and not complementary solutions for waste energy of industrial plants. Therefore the overall energy management requires the introduction of an optimisation algorithm to select the best strategy. In this paper we propose an algorithm for the minimisation of a suitable cost function, for any given variable heat demand from commercial and domestic users, with respect to all independent variables, i.e., temperatures and flowrates of warm fluid streams leaving the plants and volume and nature of underground storage. The results of the preliminary process integration analysis based on pinch technology are used in this algorithm to provide bounds on the values of temperatures. http://www.mdpi.com/1996-1073/4/12/2151/ Tue, 06 Dec 2011 00:00:00 CET Energies 2011-12-06 4 12 Article 2151 2165 1996-1073 Optimal Design of Cogeneration Systems in Industrial Plants Combined with District Heating/Cooling and Underground Thermal Energy Storage 2011-12-06 doi: 10.3390/en4122151 Andrea Reverberi Adriana Del Borghi Vincenzo Dovì http://www.mdpi.com/1996-1073/4/12/2133/ A dielectric barrier discharge (DBD) produces a homogenous discharge with low energy consumption, offering broad developmental prospects, and this discharge process is also the mechanism through which charges are transported. Higher reaction efficiency is achieved when more charges are transported. Focusing on the electrode configuration of the multineedle-to-cylinder (MC) system, i.e., the structure of needles arrayed on the inner coaxial rod, the effect of needle arrangement, including needle length (NL), inter axial needle distance (ID), and inter axial needle rotation angle (INRA), on the transported charge per cycle and discharge power in DBDs is investigated. The finite-element method (FEM) and quasi-static field simulation are adopted to study the active region (AR) where the electric field strength exceeds the breakdown electric field strength between MC electrodes because this region plays a dominant role in DBD. The improvement of its volume ratio in the reactor allows an increase in discharge power. The simulation results are in accordance with the experimental results, which illustrate that quasi-static field simulation is effective and reliable. Simulation results show that mutual effects of nearby needles and between needles and the inner rod exist. As a result, shorter ID (1.5 mm), needles with similar lengths (3.5 mm) are arranged, and an INRA of 0° is proven to be the optimal structure because it produces the highest AR volume ratio. The result is experimentally validated by transported charges per cycle and discharge power obtained through Lissajous figures. http://www.mdpi.com/1996-1073/4/12/2133/ Fri, 02 Dec 2011 00:00:00 CET Energies 2011-12-02 4 12 Article 2133 2150 1996-1073 Dielectric Barrier Discharge Characteristics of Multineedle-to-Cylinder Configuration 2011-12-02 doi: 10.3390/en4122133 Xiaojing Wang Qing Yang Chenguo Yao Xiaoxing Zhang Caixin Sun http://www.mdpi.com/1996-1073/4/12/2132/ The authors would like to make the following corrections to their published paper in Energies [1]. [...] http://www.mdpi.com/1996-1073/4/12/2132/ Wed, 30 Nov 2011 00:00:00 CET Energies 2011-11-30 4 12 Correction 2132 2132 1996-1073 Correction: Hu, X.; Sun, F. and Zou, Y. Estimation of State of Charge of a Lithium-Ion Battery Pack for Electric Vehicles Using an Adaptive Luenberger Observer. Energies 2010, 3, 1586–1603 2011-11-30 doi: 10.3390/en4122132 Xiaosong Hu Fengchun Sun Yuan Zou http://www.mdpi.com/1996-1073/4/11/2115/ The primary energy consumption in residential buildings is determined by the envelope thermal characteristics, air change, outside climatic data, users’ behaviour and the adopted heating system and its control. The new Italian regulations strongly suggest the installation of centralized boilers in renovated buildings with more than four apartments. This work aims to investigate the differences in primary energy consumption and efficiency among several independent and centralized heating systems installed in Northern Italy. The analysis is carried out through the following approach: firstly building heating loads are evaluated using the software TRNSYS® and, then, heating system performances are estimated through a simplified model based on the European Standard EN 15316. Several heating systems have been analyzed, evaluating: independent and centralized configurations, condensing and traditional boilers, radiator and radiant floor emitters and solar plant integration. The heating systems are applied to four buildings dating back to 2010, 2006, 1960s and 1930s. All the combinations of heating systems and buildings are analyzed in detail, evaluating efficiency and primary energy consumption. In most of the cases the choice between centralized and independent heating systems has minor effects on primary energy consumption, less than 3%: the introduction of condensing technology and the integration with solar heating plant can reduce energy consumption by 11% and 29%, respectively. http://www.mdpi.com/1996-1073/4/11/2115/ Thu, 24 Nov 2011 00:00:00 CET Energies 2011-11-24 4 11 Article 2115 2131 1996-1073 Efficiency Analysis of Independent and Centralized Heating Systems for Residential Buildings in Northern Italy 2011-11-24 doi: 10.3390/en4112115 Matteo Zago Andrea Casalegno Renzo Marchesi Fabio Rinaldi http://www.mdpi.com/1996-1073/4/11/2094/ By July 2011, North American carsharing had grown to an industry of nearly 640,000 members since its inception on the continent more than 15 years ago. Carsharing engenders changes in member travel patterns both towards and away from public transit and non-motorized modes. This study, which builds on the work of two previous studies, evaluates this shift in travel based on a 6281 respondent survey completed in late-2008 by members of major North American carsharing organizations. Across the entire sample, the results showed an overall decline in public transit use that was statistically significant, as 589 carsharing members reduced rail use and 828 reduced bus use, while 494 increased rail use and 732 increased bus use. Thus for every five members that use rail less, four members use rail more, and for every 10 members that ride a bus less, almost nine members ride the bus more. The people increasing and decreasing their transit use are fundamentally different in terms of how carsharing impacts their travel environment. This reduction, however, is also not uniform across all organizations; it is primarily driven by a minority (three of eleven) of participating organizations. At the same time, members exhibited a statistically significant increase in travel by walking, bicycling, and carpooling. Across the sample, 756 members increased walking versus a 568 decrease, 628 increased bicycling versus a 235 decrease, and 289 increased carpooling versus a decrease of 99  study participants. The authors found that 970 members reduced their auto commuting to work, while 234 increased it. Interestingly, when these shifts are combined across modes, more people increased their overall public transit and non-motorized modal use after joining carsharing than decreased it. Data collected on the commute distance of respondents found that carsharing members tend to have shorter commutes than most people living in the same zip code. The analysis also evaluates the distribution of residential population density of members and its association with average changes in driving. The analysis finds that average driving reductions are consistent across population densities up to 10,000 persons/square kilometer but become more varied at higher densities. http://www.mdpi.com/1996-1073/4/11/2094/ Thu, 24 Nov 2011 00:00:00 CET Energies 2011-11-24 4 11 Article 2094 2114 1996-1073 The Impact of Carsharing on Public Transit and Non-Motorized Travel: An Exploration of North American Carsharing Survey Data 2011-11-24 doi: 10.3390/en4112094 Elliot Martin Susan Shaheen http://www.mdpi.com/1996-1073/4/11/2077/ Condition Monitoring (CM) of wind turbines can greatly reduce the maintenance costs for wind farms, especially for offshore wind farms. A new condition monitoring method for a wind turbine gearbox using temperature trend analysis is proposed. Autoassociative Kernel Regression (AAKR) is used to construct the normal behavior model of the gearbox temperature. With a proper construction of the memory matrix, the AAKR model can cover the normal working space for the gearbox. When the gearbox has an incipient failure, the residuals between AAKR model estimates and the measurement temperature will become significant. A moving window statistical method is used to detect the changes of the residual mean value and standard deviation in a timely manner. When one of these parameters exceeds predefined thresholds, an incipient failure is flagged. In order to simulate the gearbox fault, manual temperature drift is added to the initial Supervisory Control and Data Acquisitions (SCADA) data. Analysis of simulated gearbox failures shows that the new condition monitoring method is effective. http://www.mdpi.com/1996-1073/4/11/2077/ Wed, 23 Nov 2011 00:00:00 CET Energies 2011-11-23 4 11 Article 2077 2093 1996-1073 Wind Turbine Gearbox Condition Monitoring with AAKR and Moving Window Statistic Methods 2011-11-23 doi: 10.3390/en4112077 Peng Guo Nan Bai http://www.mdpi.com/1996-1073/4/11/2061/ The key factors in the energy-saving design of a building’s exterior in Taiwan are the thermal performance of the roof and window glazing. This study used the eQUEST software to investigate how different types of roof construction, window glasses and sunshield types affect the energy consumption in residential buildings under common scenarios. The simulation results showed that the use of an appropriate window glass significantly reduced the annual energy consumption, followed by the shading device, whereas the roof construction produced less of an energy-efficiency benefit. By using a low-E glass and a 1.5 × 1.5 m box shading (e.g., balcony), this could save approximately 15.1 and 13.6% of the annual electricity consumption of air conditioners, respectively. Therefore, having control over the dominant factors in the building envelope is indeed an important step in the path to achieving energy savings and carbon reduction in residential houses. http://www.mdpi.com/1996-1073/4/11/2061/ Wed, 23 Nov 2011 00:00:00 CET Energies 2011-11-23 4 11 Article 2061 2076 1996-1073 Energy-Saving Potential of Building Envelope Designs in Residential Houses in Taiwan 2011-11-23 doi: 10.3390/en4112061 Chi-Ming Lai Yao-Hong Wang http://www.mdpi.com/1996-1073/4/11/2049/ The aim of this study was to confirm the effects of two-stage combustion on the combustion and NOx reduction characteristics of a four cylinder direct injection diesel engine. In order to analyze the combustion and emission characteristics, various injection parameters, such as injection quantity, injection timing and injection pressure were used under constant engine speed and engine load. In addition, the experimental results of two-stage combustion are compared to the single injection when injection timing is 5° BTDC. The experimental results showed that NOx emissions were significantly reduced when applying two-stage combustion. In particular, an injection strategy when the first and second injections have a same quantity, the results showed the maximum reduction of NOx emissions in this experiment. The NOx emissions were also reduced when the timing of the first injection was advanced. However, NOx emissions indicated almost similar concentration regardless of first injection timings when the first injection timing was earlier than 50° BTDC. In the case of soot emissions were slightly increased compare to the single injection cases at tested conditions. http://www.mdpi.com/1996-1073/4/11/2049/ Tue, 22 Nov 2011 00:00:00 CET Energies 2011-11-22 4 11 Article 2049 2060 1996-1073 Effect of Two-Stage Fuel Injection Parameters on NOx Reduction Characteristics in a DI Diesel Engine 2011-11-22 doi: 10.3390/en4112049 Kyusoo Jeong Donggon Lee Sungwook Park Chang Sik Lee http://www.mdpi.com/1996-1073/4/11/2038/ Fish screens at hydroelectric dams help to protect rearing and migrating fish by preventing them from passing through the turbines and directing them towards the bypass channels by means of a sweeping flow parallel to the screen. However, fish screens may actually be harmful to fish if the fish become impinged on the surface of the screen or become disoriented due to poor flow conditions near the screen. Recent modifications to the vertical barrier screens (VBS) in the gate wells at the Bonneville Dam second powerhouse (B2) were intended to increase the guidance of juvenile salmonids into the juvenile bypass system but have resulted in higher mortality and descaling rates of hatchery subyearling Chinook salmon during the 2008 juvenile salmonid passage season. To investigate the potential cause of the high mortality and descaling rates, an in situ water velocity measurement study was conducted using acoustic Doppler velocimeters in the gate well slots at turbine units 12A and 14A of B2. From the measurements collected, the average approach velocity, sweep velocity, and the root mean square value of the velocity fluctuations were calculated. The approach velocities measured across the face of the VBS were variable and typically less than 0.3 m/s, but fewer than 50% were less than or equal to 0.12 m/s. There was also large variance in sweep velocities across the face of the VBS with most measurements recorded at less than 1.5 m/s. Results of this study revealed that the approach velocities in the gate wells exceeded criteria intended to improve fish passage conditions that were recommended by National Marine Fisheries Service and the Washington State Department of Fish and Wildlife. The turbulence measured in the gate well may also result in suboptimal fish passage conditions but no established guidelines to contrast those results have been published. http://www.mdpi.com/1996-1073/4/11/2038/ Tue, 22 Nov 2011 00:00:00 CET Energies 2011-11-22 4 11 Article 2038 2048 1996-1073 Water Velocity Measurements on a Vertical Barrier Screen at the Bonneville Dam Second Powerhouse 2011-11-22 doi: 10.3390/en4112038 James S. Hughes Z. Daniel Deng Mark A. Weiland Jayson J. Martinez Yong Yuan http://www.mdpi.com/1996-1073/4/11/2027/ In this paper, the promoting effects of ash and biomass gas reburning on N2O decomposition were investigated based on a fluidized bed reactor, with the assessment of the influence of O2 on N2O decomposition with circulating ashes. Experimental results show that different metal oxides contained in ash play distinct roles in the process of N2O decomposition with biomass gas reburning. Compared with other components in ash, CaO is proven to be very active and has the greatest promoting impact on N2O decomposition. It is also found that O2, even in small amounts, can weaken the promoting effect of ash on N2O decomposition by using biomass gas reburning. http://www.mdpi.com/1996-1073/4/11/2027/ Mon, 21 Nov 2011 00:00:00 CET Energies 2011-11-21 4 11 Article 2027 2037 1996-1073 Experimental Research on Heterogeneous N2O Decomposition with Ash and Biomass Gasification Gas 2011-11-21 doi: 10.3390/en4112027 Junjiao Zhang Yongping Yang Xiaoying Hu Changqing Dong Qiang Lu Wu Qin http://www.mdpi.com/1996-1073/4/11/2002/ The demands for alternative energy resources have been increasing exponentially in the 21st century due to continuous industrial development, depletion of fossil fuels and emerging environmental consciousness. Renewable energy sources, including wind energy, hydropower energy, geothermal energy, solar energy, biomass energy and ocean power, have received increasing attention as alternative means of meeting global energy demands. After Japan's Fukushima nuclear plant disaster in March 2011, more and more countries are having doubt about the safety of nuclear plants. As a result, safe and renewable energy sources are attracting even more attention these days. Wind energy production, with its relatively safer and positive environmental characteristics, has evolved in the past few decades from a marginal activity into a multi-billion dollar industry. In this research, a comprehensive evaluation model is constructed to select a suitable location for developing a wind farm. The model incorporates interpretive structural modeling (ISM), benefits, opportunities, costs and risks (BOCR) and fuzzy analytic network process (FANP). Experts in the field are invited to contribute their expertise in evaluating the importance of the factors and various aspects of the wind farm evaluation problem, and the most suitable wind farm can finally be generated from the model. A case study is carried out in Taiwan in evaluating the expected performance of several potential wind farms, and a recommendation is provided for selecting the most appropriate wind farm for construction. http://www.mdpi.com/1996-1073/4/11/2002/ Mon, 21 Nov 2011 00:00:00 CET Energies 2011-11-21 4 11 Article 2002 2026 1996-1073 An Integrated Multi-Criteria Decision Making Model for Evaluating Wind Farm Performance 2011-11-21 doi: 10.3390/en4112002 He-Yau Kang Meng-Chan Hung W. L. Pearn Amy H. I. Lee Mei-Sung Kang http://www.mdpi.com/1996-1073/4/11/1973/ This paper presents a tool for the analysis of conversion of organic waste into energy. The tool is a program that uses waste characterization parameters and mass flow rates at each stage of the waste treatment process to predict the given products. The specific waste treatment process analysed in this paper is anaerobic digestion. The different waste treatment stages of the anaerobic digestion process are: conditioning of input waste, secondary treatment, drying of sludge, conditioning of digestate, treatment of digestate, storage of liquid and solid effluent, disposal of liquid and solid effluents, purification, utilization and storage of combustible gas. The program uses mass balance equations to compute the amount of CH4, NH3, CO2 and H2S produced from anaerobic digestion of organic waste, and hence the energy available. Case studies are also presented. http://www.mdpi.com/1996-1073/4/11/1973/ Fri, 18 Nov 2011 00:00:00 CET Energies 2011-11-18 4 11 Article 1973 2001 1996-1073 A Computer Program for Modeling the Conversion of Organic Waste to Energy 2011-11-18 doi: 10.3390/en4111973 Rachel Namuli Claude B. Laflamme Pragasen Pillay http://www.mdpi.com/1996-1073/4/11/1950/ Numerous studies have concluded that connectivity is one of the most important factors controlling the success of improved oil recovery processes. Interwell connectivity evaluation can help identify flow barriers and conduits and provide tools for reservoir management and production optimization. The multiwell productivity index (MPI)-based method provides the connectivity indices between well pairs based on injection/production data. By decoupling the effects of well locations, skin factors, injection rates, and the producers’ bottomhole pressures from the calculated connectivity, the heterogeneity matrix obtained by this method solely represents the heterogeneity and possible anisotropy of the formation. Previously, the MPI method was developed for bounded reservoirs with limited numbers of wells. In this paper, we extend the MPI method to deal with cases of large numbers of wells and open reservoirs. To handle open reservoirs, we applied some modifications to the MPI method by adding a virtual well to the system. In cases with large numbers of wells, we applied a model reduction strategy based on the location of the wells, called windowing. Integration of these approaches with the MPI method can quickly and efficiently model field data to optimize well patterns and flood parameters. http://www.mdpi.com/1996-1073/4/11/1950/ Mon, 14 Nov 2011 00:00:00 CET Energies 2011-11-14 4 11 Article 1950 1972 1996-1073 Analysis of Injection and Production Data for Open and Large Reservoirs 2011-11-14 doi: 10.3390/en4111950 Danial Kaviani Peter Valkó Jerry Jensen http://www.mdpi.com/1996-1073/4/11/1937/ The performance of an electrical generator using bio-fuel and gasoline blends of different composition as fuel in a single cylinder engine is presented. The effect of an optimized blend ratio of bio-fuel with gasoline on engine performance improvement and thereby on the electrical generator output is studied. Bio-fuels such as ethanol, butanol and methanol are blended with gasoline in different proportions and evaluated for performance. The effects of different bio-fuel/gasoline blending ratios are compared experimentally with that of the gasoline alone using the output power developed by the electric generator as the evaluation parameter. With a composition of 10% ethanol–gasoline, the engine performance is increased up to 6% and with a blending ratio of 20% butanol–gasoline the performance is increased up to 8% compared to the use of 100% gasoline. The investigations are performed on a portable generator used in palm tree harvesting applications. http://www.mdpi.com/1996-1073/4/11/1937/ Thu, 10 Nov 2011 00:00:00 CET Energies 2011-11-10 4 11 Article 1937 1949 1996-1073 Performance Improvement of a Portable Electric Generator Using an Optimized Bio-Fuel Ratio in a Single Cylinder Two-Stroke Engine 2011-11-10 doi: 10.3390/en4111937 Norhisam Misron Suhairi Rizuan Aravind Vaithilingam Nashiren Farzilah Mailah Hanamoto Tsuyoshi Yamada Hiroaki Shirai Yoshihito http://www.mdpi.com/1996-1073/4/11/1916/ Wind-tunnel experiments were carried out to better understand boundary layer effects on the flow pattern inside and above a model wind farm under thermally neutral conditions. Cross-wire anemometry was used to characterize the turbulent flow structure at different locations around a 10 by 3 array of model wind turbines aligned with the mean flow and arranged in two different layouts (inter-turbine separation of 5 and 7 rotor diameters in the direction of the mean flow by 4 rotor diameters in its span). Results suggest that the turbulent flow can be characterized in two broad regions. The first, located below the turbine top tip height, has a direct effect on the performance of the turbines. In that region, the turbulent flow statistics appear to reach equilibrium as close as the third to fourth row of wind turbines for both layouts. In the second region, located right above the first one, the flow adjusts slowly. There, two layers can be identified: an internal boundary layer where the flow is affected by both the incoming wind and the wind turbines, and an equilibrium layer, where the flow is fully adjusted to the wind farm. An adjusted logarithmic velocity distribution is observed in the equilibrium layer starting from the sixth row of wind turbines. The effective surface roughness length induced by the wind farm is found to be higher than that predicted by some existing models. Momentum recovery and turbulence intensity are shown to be affected by the wind farm layout. Power spectra show that the signature of the tip vortices, in both streamwise and vertical velocity components, is highly affected by both the relative location in the wind farm and the wind farm layout. http://www.mdpi.com/1996-1073/4/11/1916/ Tue, 08 Nov 2011 00:00:00 CET Energies 2011-11-08 4 11 Article 1916 1936 1996-1073 Turbulent Flow Inside and Above a Wind Farm: A Wind-Tunnel Study 2011-11-08 doi: 10.3390/en4111916 Leonardo P. Chamorro Fernando Porté-Agel http://www.mdpi.com/1996-1073/4/11/1897/ This paper considers the Global Thermodynamic Potential (GTP) indicator to perform a unified assessment of greenhouse gas (GHG) emissions, and to systematically reveal the emission embodiment in the production, consumption, and international trade of the Chinese economy in 2007 as the most recent year available with input-output table and updated inventory data. The results show that the estimated total direct GHG emissions by the Chinese economy in 2007 amount to 10,657.5 Mt CO2-eq by the GTPs with 40.6% from CH4 emissions in magnitude of the same importance as CO2 emissions. The five sectors of Electric Power/Steam and Hot Water Production and Supply, Smelting and Pressing of Ferrous and Nonferrous Metals, Nonmetal Mineral Products, Agriculture, and Coal Mining and Dressing, are responsible for 83.3% of the total GHG emissions with different emission structures. The demands of coal and coal-electricity determine the structure of emission embodiment to an essential extent. The Construction sector holds the top GHG emissions embodied in both domestic production and domestic consumption. The GHG emission embodied in gross capital formation is more than those in other components of final demand characterized by extensive investment and limited household consumption. China is a net exporter of embodied GHG emissions, with a remarkable share of direct emission induced by international trade, such as textile products, industrial raw materials, and primary machinery and equipment products exports. The fractions of CH4 in the component of embodied GHG emissions in the final demand are much greater than those fractions calculated by the Global Warming Potentials, which highlight the importance of CH4 emissions for the case of China and indicate the essential effect of CH4 emissions on global climate change. To understand the full context to achieve GHG emission mitigation, this study provides a new insight to address China’s GHG emissions status and hidden emission information induced by the final demand to the related policy-makers. http://www.mdpi.com/1996-1073/4/11/1897/ Fri, 04 Nov 2011 00:00:00 CET Energies 2011-11-04 4 11 Article 1897 1915 1996-1073 Embodiment Analysis for Greenhouse Gas Emissions by Chinese Economy Based on Global Thermodynamic Potentials 2011-11-04 doi: 10.3390/en4111897 Bo Zhang Suping Peng Xiangyang Xu Lijie Wang http://www.mdpi.com/1996-1073/4/11/1880/ Waste tire pyrolysis oil has high potential to replace conventional fossil liquid fuels due to its high calorific heating value. However, the large amounts of sulfurous compounds in this oil hinders its application. Thus, the aim of this research was to investigate the possibility to apply the photo-assisted oxidation catalyzed by titanium dioxide (TiO2, Degussa P-25) to partially remove sulfurous compounds in the waste tire pyrolysis oil under milder reaction conditions without hydrogen consumption. A waste tire pyrolysis oil with 0.84% (w/w) of sulfurous content containing suspended TiO2 was irradiated by using a high-pressure mercury lamp for 7 h. The oxidized sulfur compounds were then migrated into the solvent-extraction phase. A maximum % sulfur removal of 43.6% was achieved when 7 g/L of TiO2 was loaded into a 1/4 (v/v) mixture of pyrolysis waste tire oil/acetonitrile at 50 °C in the presence of air. Chromatographic analysis confirmed that the photo-oxidized sulfurous compounds presented in the waste tire pyrolysis oil had higher polarity, which were readily dissolved and separated in distilled water. The properties of the photoxidized product were also reported and compared to those of crude oil. http://www.mdpi.com/1996-1073/4/11/1880/ Thu, 03 Nov 2011 00:00:00 CET Energies 2011-11-03 4 11 Article 1880 1896 1996-1073 Photocatalytic Desulfurization of Waste Tire Pyrolysis Oil 2011-11-03 doi: 10.3390/en4111880 Phakakrong Trongkaew Thanes Utistham Prasert Reubroycharoen Napida Hinchiranan http://www.mdpi.com/1996-1073/4/11/1858/ Because of its strong inherent safety features and the high outlet temperature, the modular high temperature gas-cooled nuclear reactor (MHTGR) is the chosen technology for a new generation of nuclear power plants. Such power plants are being considered for industrial applications with a wide range of power levels, thus power-level regulation is very important for their efficient and stable operation. Exploiting the large scale asymptotic closed-loop stability provided by nonlinear controllers, a nonlinear power-level regulator is presented in this paper that is based upon both the techniques of feedback dissipation and well-established backstepping. The virtue of this control strategy, i.e., the ability of globally asymptotic stabilization, is that it takes advantage of the inherent zero-state detectability property of the MHTGR dynamics. Moreover, this newly built power-level regulator is also robust towards modeling uncertainty in the control rod dynamics. If modeling uncertainty of the control rod dynamics is small enough to be omitted, then this control law can be simplified to a classical proportional feedback controller. The comparison of the control performance between the newly-built power controller and the simplified controller is also given through numerical study and theoretical analysis. http://www.mdpi.com/1996-1073/4/11/1858/ Tue, 01 Nov 2011 00:00:00 CET Energies 2011-11-01 4 11 Article 1858 1879 1996-1073 Output Feedback Dissipation Control for the Power-Level of Modular High-Temperature Gas-Cooled Reactors 2011-11-01 doi: 10.3390/en4111858 Zhe Dong http://www.mdpi.com/1996-1073/4/11/1840/ The battery management system (BMS) is a critical component of electric and hybrid electric vehicles. The purpose of the BMS is to guarantee safe and reliable battery operation. To maintain the safety and reliability of the battery, state monitoring and evaluation, charge control, and cell balancing are functionalities that have been implemented in BMS. As an electrochemical product, a battery acts differently under different operational and environmental conditions. The uncertainty of a battery’s performance poses a challenge to the implementation of these functions. This paper addresses concerns for current BMSs. State evaluation of a battery, including state of charge, state of health, and state of life, is a critical task for a BMS. Through reviewing the latest methodologies for the state evaluation of batteries, the future challenges for BMSs are presented and possible solutions are proposed as well. http://www.mdpi.com/1996-1073/4/11/1840/ Mon, 31 Oct 2011 00:00:00 CET Energies 2011-10-31 4 11 Review 1840 1857 1996-1073 Battery Management Systems in Electric and Hybrid Vehicles 2011-10-31 doi: 10.3390/en4111840 Yinjiao Xing Eden W. M. Ma Kwok L. Tsui Michael Pecht http://www.mdpi.com/1996-1073/4/10/1779/ Hybrid Propulsion is an attractive alternative to conventional liquid and solid rocket motors. This is an active area of research and technological developments. Potential wide application of Hybrid Engines opens the possibility for safer and more flexible space vehicle launching and manoeuvring. The present paper discusses fundamental combustion issues related to further development of Hybrid Rockets. The emphasis is made on the two aspects: (1) properties of potential polymeric fuels, and their modification, and (2) implementation of comprehensive CFD models for combustion in Hybrid Engines. Fundamentals of polymeric fuel combustion are discussed. Further, steps necessary to accurately describe their burning behaviour by means of CFD models are investigated. Final part of the paper presents results of preliminary CFD simulations of fuel burning process in Hybrid Engine using a simplified set-up. http://www.mdpi.com/1996-1073/4/10/1779/ Mon, 24 Oct 2011 00:00:00 CEST Energies 2011-10-24 4 10 Article 1779 1839 1996-1073 Polymer Combustion as a Basis for Hybrid Propulsion: A Comprehensive Review and New Numerical Approaches 2011-10-24 doi: 10.3390/en4101779 Vasily Novozhilov Paul Joseph Keiichi Ishiko Toru Shimada Hui Wang Jun Liu http://www.mdpi.com/1996-1073/4/10/1763/ This research aims at providing evidence of particle suspension contributions to emulsion stability, which has been cited as a contributing factor in crude oil recovery by low-salinity waterflooding. Kaolinite and silica particle dispersions were characterized as functions of brine salinity. A reference aqueous phase, representing reservoir brine, was used and then diluted with distilled water to obtain brines at 10 and 100 times lower Total Dissolved Solid (TDS). Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) were used to examine at the morphology and composition of clays. The zeta potential and particle size distribution were also measured. Emulsions were prepared by mixing a crude oil with brine, with and without dispersed particles to investigate emulsion stability. The clay zeta potential as a function of pH was used to investigate the effect of particle charge on emulsion stability. The stability was determined through bottle tests and optical microscopy. Results show that both kaolinite and silica promote emulsion stability. Also, kaolinite, roughly 1 mm in size, stabilizes emulsions better than larger clay particles. Silica particles of larger size (5 µm) yielded more stable emulsions than smaller silica particles do. Test results show that clay particles with zero point of charge (ZPC) at low pH become less effective at stabilizing emulsions, while silica stabilizes emulsions better at ZPC. These result shed light on emulsion stabilization in low-salinity waterflooding. http://www.mdpi.com/1996-1073/4/10/1763/ Mon, 24 Oct 2011 00:00:00 CEST Energies 2011-10-24 4 10 Article 1763 1778 1996-1073 Kaolinite and Silica Dispersions in Low-Salinity Environments: Impact on a Water-in-Crude Oil Emulsion Stability 2011-10-24 doi: 10.3390/en4101763 Xiuyu Wang Vladimir Alvarado http://www.mdpi.com/1996-1073/4/10/1748/ With the mass introduction of wind power in Northern China, wind power variability has appeared. In this article, both existing electric heat pumps (EHPs) and coal-fired combined heat and power (CHP) facilities, which are generally equipped with extraction-condensing steam turbines coupled with district heating for space heating purposes, are proposed to incorporate the variability of wind power equivalently. The authors’ proposal arises from the facts that: (1) EHPs can provide space heating in the domestic sector with little thermal comfort change (e.g., energy carriers for space heating purposes can be switched from heating water to electricity); (2) coal-fired CHP units in Northern China can usually generate more electrical power corresponding to a shaved thermal power production. Thus, it is suggested that heating water from CHP units be shaved when the wind generation is low due to the variability of wind power, so as to enable more electrical power production and compensate for the corresponding insufficient wind generation. Following this, in the future and for some space heating loads at appropriate distances, electricity used as energy carrier should be converted by electric heat pumps for space heating. Thus, more electricity consumption will be achieved so as to avoid wasting wind power when the wind generation it is high. A numerical simulation is performed in order to illustrate the authors’ proposal. It is shown that the impact of variability of wind generation can be equivalently reduced to a great extent, which enable more wind power integration instead of curtailment and potential energy conservation. Moreover, in contrast to before, both the thermal and electrical power of coal-fired CHP units are no longer constants. In addition, the ratio of electrical to thermal power of CHP units is no longer constant either, and results in less energy consumption compared with fixed ratio. Finally, electricity consumed by end users’ EHPs, which are devoted to space heating for various spatial distances and time points, is figured out. http://www.mdpi.com/1996-1073/4/10/1748/ Mon, 24 Oct 2011 00:00:00 CEST Energies 2011-10-24 4 10 Article 1748 1762 1996-1073 Incorporating the Variability of Wind Power with Electric Heat Pumps 2011-10-24 doi: 10.3390/en4101748 Hongyu Long Ruilin Xu Jianjun He http://www.mdpi.com/1996-1073/4/10/1728/ This paper describes an experimental investigation of formation damage in a fractured carbonate core sample under underbalanced drilling (UBD) conditions. A major portion of this study has concentrated on problems which are often associated with UBD and the development of a detailed protocol for proper design and execution of an UBD program. Formation damage effects, which may occur even if the underbalanced pressure condition is maintained 100% of the time during drilling operation, have been studied. One major concern for formation damage during UBD operations is the loss of the under-balanced pressure condition. Hence, it becomes vital to evaluate the sensitivity of the formation to the effect of an overbalanced pulse situation. The paper investigates the effect of short pulse overbalance pressure during underbalanced conditions in a fractured chalk core sample. Special core tests using a specially designed core holder are conducted on the subject reservoir core. Both overbalance and underbalanced tests were conducted with four UBD drilling fluids. Core testing includes measurements of the initial permeability and return permeability under two different pressure conditions (underbalanced and overbalanced). Then the procedure is followed by applying a differential pressure on the core samples to mimic the drawdown effect to determine the return permeability capacity. In both UBD and short pulse OBP four mud formulations are used which are: lab oil, brine (3% KCL), water-based mud (bentonite with XC polymer) and fresh water. The return permeability measurements show that a lab oil system performed fairly well during UBD and short OB conditions. The results indicate that a short overbalance pressure provides a significant reduction in permeability of the fractured formations. In most tests, even application of a high drawdown pressure during production cannot restore the initial permeability by more than 40%. http://www.mdpi.com/1996-1073/4/10/1728/ Mon, 24 Oct 2011 00:00:00 CEST Energies 2011-10-24 4 10 Review 1728 1747 1996-1073 Experimental Study of Formation Damage during Underbalanced-Drilling in Naturally Fractured Formations 2011-10-24 doi: 10.3390/en4101728 Siroos Salimi Ali Ghalambor http://www.mdpi.com/1996-1073/4/10/1696/ Transmission investments are currently needed to meet an increasing electricity demand, to address security of supply concerns, and to reach carbon-emissions targets. A key issue when assessing the benefits from an expanded grid concerns the valuation of the uncertain cash flows that result from the expansion. We propose a valuation model that accommodates both physical and economic uncertainties following the Real Options approach. It combines optimization techniques with Monte Carlo simulation. We illustrate the use of our model in a simplified, two-node grid and assess the decision whether to invest or not in a particular upgrade. The generation mix includes coal- and natural gas-fired stations that operate under carbon constraints. The underlying parameters are estimated from observed market data. http://www.mdpi.com/1996-1073/4/10/1696/ Fri, 21 Oct 2011 00:00:00 CEST Energies 2011-10-21 4 10 Article 1696 1727 1996-1073 Valuing Expansions of the Electricity Transmission Network under Uncertainty: The Binodal Case 2011-10-21 doi: 10.3390/en4101696 Luis M. Abadie José M. Chamorro http://www.mdpi.com/1996-1073/4/10/1687/ Year-round operation of biorefineries can be possible only if the continuous flow of cellulosic biomass is guaranteed. If corn (Zea mays) stover is the primary cellulosic biomass, it is essential to recognize that this feedstock has a short annual harvest window (≤1–2 months) and therefore cost effective storage techniques that preserve feedstock quality must be identified. This study evaluated two outdoor and one indoor storage strategies for corn stover bales in Iowa. High- and low-moisture stover bales were prepared in the fall of 2009, and stored either outdoors with two different types of cover (tarp and breathable film) or within a building for 3 or 9 months. Dry matter loss (DML), changes in moisture and biomass compositions (fiber and ultimate analyses) were determined. DML for bales stored outdoor with tarp and breathable film covers were in the ranges of 5–11 and 14–17%, respectively. More than half of the total DML occurred early during the storage. There were measurable differences in carbon, hydrogen, nitrogen, sulfur, oxygen, cellulose, hemi-cellulose and acid detergent lignin for the different storage treatments, but the changes were small and within a narrow range. For the bale storage treatments investigated, cellulose content increased by as much as 4%s from an initial level of ~41%, hemicellulose content changed by −2 to 1% from ~34%, and acid detergent lignin contents increased by as much as 3% from an initial value of ~5%. Tarp covered bales stored the best in this study, but other methods, such as tube-wrapping, and economics need further investigation. http://www.mdpi.com/1996-1073/4/10/1687/ Fri, 21 Oct 2011 00:00:00 CEST Energies 2011-10-21 4 10 Article 1687 1695 1996-1073 Outdoor Storage Characteristics of Single-Pass Large Square Corn Stover Bales in Iowa 2011-10-21 doi: 10.3390/en4101687 Ajay Shah Matthew J. Darr Keith Webster Christopher Hoffman http://www.mdpi.com/1996-1073/4/10/1657/ In view of the great contribution of coal-fired units to CO2 emissions, the coupled coal and power system with consideration of CO2 mitigation is a typical sub-system of the highly emitting Chinese energy system for low-carbon studies. In this study, an inexact mix-integer two-stage programming (IMITSP) model for the management of low-carbon energy systems was developed based on the integration of multiple inexact programming techniques. Uncertainties and complexities related to the carbon mitigation issues in the coupled coal and power system can be effectively reflected and dealt with in this model. An optimal CO2 mitigation strategy associated with stochastic power-generation demand under specific CO2 mitigation targets could be obtained. Dynamic analysis of capacity expansion, facility improvement, coal selection, as well as coal blending within a multi-period and multi-option context could be facilitated. The developed IMITSP model was applied to a semi-hypothetical case of long-term coupled management of coal and power within a low-carbon energy system in north China. The generated decision alternatives could help decision makers identify desired strategies related to coal production and allocation, CO2 emission mitigation, as well as facility capacity upgrade and expansion under various social-economic, ecological, environmental and system-reliability constraints. It could also provide interval solutions with a minimized system cost, a maximized system reliability and a maximized power-generation demand security. Moreover, the developed model could provide an in-depth insight into various CO2 mitigation technologies and the associated environmental and economic implications under a given reduction target. Tradeoffs among system costs, energy security and CO2 emission reduction could be analyzed. http://www.mdpi.com/1996-1073/4/10/1657/ Fri, 21 Oct 2011 00:00:00 CEST Energies 2011-10-21 4 10 Article 1657 1686 1996-1073 An Inexact Mix-Integer Two-Stage Linear Programming Model for Supporting the Management of a Low-Carbon Energy System in China 2011-10-21 doi: 10.3390/en4101657 Ye Liu Guohe Huang Yanpeng Cai Cong Dong http://www.mdpi.com/1996-1073/4/10/1624/ Energy is crucial in supporting people’s daily lives and the continual quest for human development. Due to the associated complexities and uncertainties, decision makers and planners are facing increased pressure to respond more effectively to a number of energy-related issues and conflicts, as well as GHG emission mitigation within the multiple scales of energy management systems (EMSs). This quandary requires a focused effort to resolve a wide range of issues related to EMSs, as well as the associated economic and environmental implications. Effective systems analysis approaches under uncertainty to successfully address interactions, complexities, uncertainties, and changing conditions associated with EMSs is desired, which require a systematic investigation of the current studies on energy systems. Systems analysis and optimization modeling for low-carbon energy systems planning with the consideration of GHG emission reduction under uncertainty is thus comprehensively reviewed in this paper. A number of related methodologies and applications related to: (a) optimization modeling of GHG emission mitigation; (b) optimization modeling of energy systems planning under uncertainty; and (c) model-based decision support tools are examined. Perspectives of effective management schemes are investigated, demonstrating many demanding areas for enhanced research efforts, which include issues of data availability and reliability, concerns in uncertainty, necessity of post-modeling analysis, and usefulness of development of simulation techniques. http://www.mdpi.com/1996-1073/4/10/1624/ Fri, 21 Oct 2011 00:00:00 CEST Energies 2011-10-21 4 10 Review 1624 1656 1996-1073 A Review on Optimization Modeling of Energy Systems Planning and GHG Emission Mitigation under Uncertainty 2011-10-21 doi: 10.3390/en4101624 Yong Zeng Yanpeng Cai Guohe Huang Jing Dai http://www.mdpi.com/1996-1073/4/10/1601/ The production of fermentable sugar solutions for bioethanol production is optimized. The process of acid hydrolysis using dilute H2SO4 was selected. Suitable lignocellulosics which are abundant in the Mediterranean (corn stover, hardwood and wheat straw) were investigated, and therefore their exploitation could be economically feasible. The process was studied in the two most common hydrolyzators (batch and continuous stirred) by developing a specific simulator for different raw materials. The simulation was applied in a wide range of temperatures (100–240 °C) and acid concentrations (0.5–3.0% w/w), in order to optimize the productivity of fermentable pentosans and hexosans. It was confirmed that the production of sugar-rich solutions required a two-stage process; in the first stage the degradation of sugars takes place, since pentoses are formulated under milder conditions than hexoses; in the second stage of simulation, a variety of samples with high sugar concentration and low degradation products are tested. The xylose productivity ranges between 85–95% under the most optimal conditions compared to the theoretical values, while large variations in glucose were frequent (10–55%) in comparison with the theoretical values. The best theoretical results were achieved for wheat straw hydrolysis in a batch reactor. http://www.mdpi.com/1996-1073/4/10/1601/ Thu, 20 Oct 2011 00:00:00 CEST Energies 2011-10-20 4 10 Article 1601 1623 1996-1073 Optimization of the Dilute Acid Hydrolyzator for Cellulose-to-Bioethanol Saccharification 2011-10-20 doi: 10.3390/en4101601 Theocharis Tsoutsos Dimitris Bethanis http://www.mdpi.com/1996-1073/4/10/1574/ Overtopping wave energy converters (OWECs) are designed to extract energy from ocean waves based on wave overtopping into a reservoir, which is emptied into the ocean through a set of low-head turbines, and typically feature a low crest freeboard and a smooth impermeable steep slope. In the process of optimizing the performance of OWECs, the question arises whether adapting the slope geometry to the variable wave characteristics at the deployment site (i.e., geometry control) can increase the overall hydraulic efficiency and overall hydraulic power compared to a fixed slope geometry. The effect of five different geometry control scenarios on the overall hydraulic efficiency and overall hydraulic power of OWECs has been simulated for three possible deployment sites using empirical prediction formulae. The results show that the effect of an adaptive slope angle is relatively small. On the other hand, adapting the crest freeboard of the OWECs to the wave characteristics increases the overall hydraulic efficiency and power. Based on the simulations, gains in overall hydraulic power of at least 30% are achievable when applying an adaptive crest freeboard compared to a fixed crest freeboard. http://www.mdpi.com/1996-1073/4/10/1574/ Wed, 19 Oct 2011 00:00:00 CEST Energies 2011-10-19 4 10 Article 1574 1600 1996-1073 On the Effects of Geometry Control on the Performance of Overtopping Wave Energy Converters 2011-10-19 doi: 10.3390/en4101574 Lander Victor Peter Troch Jens Peter Kofoed http://www.mdpi.com/1996-1073/4/10/1563/ Oil-impregnated paper is widely used in power transmission equipment as a reliable insulation. However, copper sulphide deposition on oil-paper insulation can lead to insulation failures in power transformers. This paper presents the influences of copper sulfur corrosion and copper sulphide deposition on copper wires and oil-paper insulation in power transformers. Thermal aging tests of paper-wrapped copper wires and bare copper wires in insulating oil were carried out at 130 °C and 150 °C in laboratory. The corrosive characteristics of paper-wrapped copper wires and bare copper wires were analyzed. Dielectric properties of insulation paper and insulating oil were also analyzed at different stages of the thermal aging tests using a broadband dielectric spectrometer. Experiments and analysis results show that copper sulfide deposition on surfaces of copper wires and insulation paper changes the surface structures of copper wires and insulation paper. Copper sulfur corrosion changes the dielectric properties of oil-paper insulation, and the copper sulfide deposition greatly reduces the electrical breakdown strength of oil-paper insulation. Metal passivator is capable of preventing copper wires from sulfur corrosion. The experimental results are helpful for investigations for fault diagnosis of internal insulation in power transformers. http://www.mdpi.com/1996-1073/4/10/1563/ Wed, 12 Oct 2011 00:00:00 CEST Energies 2011-10-12 4 10 Article 1563 1573 1996-1073 Influences of Corrosive Sulfur on Copper Wires and Oil-Paper Insulation in Transformers 2011-10-12 doi: 10.3390/en4101563 Jian Li Zhiman He Lianwei Bao Lijun Yang http://www.mdpi.com/1996-1073/4/10/1542/ The global energy shortage has revived the interest in hydroelectric power, but extreme geological condition always pose challenges to the construction of hydroelectric power stations with large underground caverns. To solve the problem of safe design of large underground caverns, a Chinese-style intelligent stability design, representing recent developments in Chinese techniques for the construction of underground hydropower systems is presented. The basic aim of this method is to help designers improve the stability and design efficiency of large underground hydropower cavern groups. Its flowchart consists of two parts, one is initial design with an ordinal structure, and the other is dynamic design with a closed loop structure. In each part of the flowchart, analysis techniques, analysis content and design parameters for caverns’ stability are defined, respectively. Thus, the method provides designers with a bridge from the basic information of objective engineering to reasonable design parameters for managing the stability of hydraulic cavern groups. Application to two large underground caverns shows that it is a scientific and economical method for safely constructing underground hydraulic caverns. http://www.mdpi.com/1996-1073/4/10/1542/ Mon, 10 Oct 2011 00:00:00 CEST Energies 2011-10-10 4 10 Article 1542 1562 1996-1073 Intelligent Stability Design of Large Underground Hydraulic Caverns: Chinese Method and Practice 2011-10-10 doi: 10.3390/en4101542 Quan Jiang Xiating Feng http://www.mdpi.com/1996-1073/4/10/1508/ Climate change has a large impact on water resources and thus on hydropower. Hydroelectric power generation is closely linked to the regional hydrological situation of a watershed and reacts sensitively to changes in water quantity and seasonality. The development of hydroelectric power generation in the Upper Danube basin was modelled for two future decades, namely 2021–2030 and 2051–2060, using a special hydropower module coupled with the physically-based hydrological model PROMET. To cover a possible range of uncertainties, 16 climate scenarios were taken as meteorological drivers which were defined from different ensemble outputs of a stochastic climate generator, based on the IPCC-SRES-A1B emission scenario and four regional climate trends. Depending on the trends, the results show a slight to severe decline in hydroelectric power generation. Whilst the mean summer values indicate a decrease, the mean winter values display an increase. To show past and future regional differences within the Upper Danube basin, three hydropower plants at individual locations were selected. Inter-annual differences originate predominately from unequal contributions of the runoff compartments rain, snow- and ice-melt. http://www.mdpi.com/1996-1073/4/10/1508/ Fri, 30 Sep 2011 00:00:00 CEST Energies 2011-09-30 4 10 Article 1508 1541 1996-1073 How Will Hydroelectric Power Generation Develop under Climate Change Scenarios? A Case Study in the Upper Danube Basin 2011-09-30 doi: 10.3390/en4101508 Franziska Koch Monika Prasch Heike Bach Wolfram Mauser Florian Appel Markus Weber http://www.mdpi.com/1996-1073/4/10/1495/ Monthly forecasting of electric energy consumption is important for planning the generation and distribution of power utilities. However, the features of this time series are so complex that directly modeling is difficult. Three kinds of relatively simple series can be derived when a discrete wavelet transform is used to extract the raw features, namely, the rising trend, periodic waves, and stochastic series. After the elimination of the stochastic series, the rising trend and periodic waves were modeled separately by a grey model and radio basis function neural networks. Adding the forecasting values of each model can yield the forecasting results for monthly electricity consumption. The grey model has a good capability for simulating any smoothing convex trend. In addition, this model can mitigate minor stochastic effects on the rising trend. The extracted periodic wave series, which contain relatively less information and comprise simple regular waves, can improve the generalization capability of neural networks. The case study on electric energy consumption in China shows that the proposed method is better than those traditionally used in terms of both forecasting precision and expected risk. http://www.mdpi.com/1996-1073/4/10/1495/ Wed, 28 Sep 2011 00:00:00 CEST Energies 2011-09-28 4 10 Article 1495 1507 1996-1073 Forecasting Monthly Electric Energy Consumption Using Feature Extraction 2011-09-28 doi: 10.3390/en4101495 Ming Meng Dongxiao Niu Wei Sun http://www.mdpi.com/1996-1073/4/10/1478/ Automotive manufacturing is energy-intensive. The consumed energy contributes to the generation of significant amounts of greenhouse gas (GHG) emissions by the automotive manufacturing industry. In this paper, a study is conducted on assessing the application potential of such clean energy power systems as solar PV, wind and fuel cells in reducing the GHG emissions of the global auto manufacturing industry. The study is conducted on the representative solar PV, wind and fuel cell clean energy systems available on the commercial market in six representative locations of GM’s global facilities, including the United States, Mexico, Brazil, China, Egypt and Germany. The results demonstrate that wind power is superior to other two clean energy technologies in the economic performance of the GHG mitigation effect. Among these six selected countries, the highest GHG emission mitigation potential is in China, through wind power supply. The maximum GHG reduction could be up to 60 tons per $1,000 economic investment on wind energy supply in China. The application of wind power systems in the United States and Germany could also obtain relatively high GHG reductions of between 40–50 tons per $1,000 economic input. When compared with wind energy, the use of solar and fuel cell power systems have much less potential for GHG mitigation in the six countries selected. The range of median GHG mitigation values resulting from solar and wind power supply are almost at the same level. http://www.mdpi.com/1996-1073/4/10/1478/ Wed, 28 Sep 2011 00:00:00 CEST Energies 2011-09-28 4 10 Article 1478 1494 1996-1073 Cost Benefit Analysis of Using Clean Energy Supplies to Reduce Greenhouse Gas Emissions of Global Automotive Manufacturing 2011-09-28 doi: 10.3390/en4101478 Qiang Zhai Huajun Cao Xiang Zhao Chris Yuan http://www.mdpi.com/1996-1073/4/9/1461/ Regenerative braking is an effective approach for electric vehicles (EVs) to extend their driving range. A fuzzy-logic-based regenerative braking strategy (RBS) integrated with series regenerative braking is developed in this paper to advance the level of energy-savings. From the viewpoint of securing car stability in braking operations, the braking force distribution between the front and rear wheels so as to accord with the ideal distribution curve are considered to prevent vehicles from experiencing wheel lock and slip phenomena during braking. Then, a fuzzy RBS using the driver’s braking force command, vehicle speed, battery SOC, battery temperature are designed to determine the distribution between friction braking force and regenerative braking force to improve the energy recuperation efficiency. The experimental results on an “LF620” prototype EV validated the feasibility and effectiveness of regenerative braking and showed that the proposed fuzzy RBS was endowed with good control performance. The maximum driving range of LF620 EV was improved by 25.7% compared with non-RBS conditions. http://www.mdpi.com/1996-1073/4/9/1461/ Thu, 22 Sep 2011 00:00:00 CEST Energies 2011-09-22 4 9 Article 1461 1477 1996-1073 An Intelligent Regenerative Braking Strategy for Electric Vehicles 2011-09-22 doi: 10.3390/en4091461 Guoqing Xu Weimin Li Kun Xu Zhibin Song http://www.mdpi.com/1996-1073/4/9/1443/ Recently, interest in microgrids, which are composed of distributed generation (DG), distributed storage (DS), and loads, has been growing as a potentially effective clean energy system to mitigate against climate change. The microgrid is operated in the grid-connected mode and the islanded mode according to the conditions of the upstream power grid. The role of the energy storage system (ESS) is especially important to maintain constant the frequency and voltage of an islanded microgrid. For this reason, various approaches for ESS control have been put forth. In this paper, a fuzzy PID controller is proposed to improve the frequency control performance of the ESS. This fuzzy PID controller consists of a fuzzy logic controller and a conventional PI controller, connected in series. The fuzzy logic controller has two input signals, and then the output signal of the fuzzy logic controller is the input signal of the conventional PI controller. For comparison of control performance, gains of each PI controller and fuzzy PID controller are tuned by the particle swam optimization (PSO) algorithm. In the simulation study, the control performance of the fuzzy PID was also tested under various operating conditions using the PSCAD/EMTDC simulation platform. http://www.mdpi.com/1996-1073/4/9/1443/ Thu, 22 Sep 2011 00:00:00 CEST Energies 2011-09-22 4 9 Article 1443 1460 1996-1073 Designing an Energy Storage System Fuzzy PID Controller for Microgrid Islanded Operation 2011-09-22 doi: 10.3390/en4091443 Jong-Yul Kim Hak-Man Kim Seul-Ki Kim Jin-Hong Jeon Heung-Kwan Choi http://www.mdpi.com/1996-1073/4/9/1428/ The emergy concept, integrated with a multi-objective linear programming method, was used to model the agricultural structure of Xinjiang Uygur Autonomous Region under the consideration of the need to develop a low-carbon economy. The emergy indices before and after the structural optimization were evaluated. In the reconstructed model, the proportions of agriculture, forestry and artificial grassland should be adjusted from 19:2:1 to 5.2:1:2.5; the Emergy Yield Ratio (1.48) was higher than the average local (0.49) and national levels (0.27); and the Emergy Investment Ratio (11.1) was higher than the current structure (4.93) and that obtained from the 2003 data (0.055) in Xinjiang Uygur Autonomous Region, the Water Emergy Cost (0.055) should be reduced compared to that before the adjustment (0.088). The measurement of all the parameters validated the positive impact of the modeled agricultural structure. The self-sufficiency ratio of the system increased from the original level of 0.106 to 0.432, which indicated a better coupling effect among the subsystems within the whole system. The comparative advantage index between the two systems before and after optimization was approximately 2:1. When the mountain ecosystem service value was considered, excessive animal husbandry led to a 1.41 × 1010 RMB·a−1 indirect economic loss, which was 4.15 times the GDP during the same time period. The functional improvement of the modeled structure supports the plan to “construct a central oasis and protect the surrounding mountains and deserts” to develop a sustainable agricultural system. Conserved natural grassland can make a large contribution to the carbon storage; and therefore, it is wise alternative that promote a low-carbon economic development strategy. http://www.mdpi.com/1996-1073/4/9/1428/ Wed, 21 Sep 2011 00:00:00 CEST Energies 2011-09-21 4 9 Article 1428 1442 1996-1073 Emergy-Based Adjustment of the Agricultural Structure in a Low-Carbon Economy in Manas County of China 2011-09-21 doi: 10.3390/en4091428 Xiaobin Dong Yufang Zhang Weijia Cui Bin Xun Baohua Yu Sergio Ulgiati Xinshi Zhang http://www.mdpi.com/1996-1073/4/9/1410/ The main purpose of this paper is to establish a signal decomposition system aiming at mixed over-voltages in power systems. In an electric power system, over-voltage presents a great threat for the system safety. Analysis and identification of over-voltages is helpful to improve the stability and safety of power systems. Through statistical analysis of a collection of field over-voltage records, it was found that a kind of complicated signals created by mixing of multiple different over-voltages is difficult to identify correctly with current classification algorithms. In order to improve the classification and identification accuracy of over-voltages, a mixed over-voltage decomposition system based on the atomic decomposition and a damped sinusoid atom dictionary has been established. This decomposition system is optimized by using particle swarm optimization and the fast Fourier transform. Aiming at possible fault decomposition results during decomposition of the over-voltage signal, a double-atom decomposition algorithm is proposed in this paper. By taking three typical mixed over-voltages as examples, the validity of the algorithm is demonstrated. http://www.mdpi.com/1996-1073/4/9/1410/ Tue, 20 Sep 2011 00:00:00 CEST Energies 2011-09-20 4 9 Article 1410 1427 1996-1073 Mixed Over-Voltage Decomposition Using Atomic Decompositions Based on a Damped Sinusoids Atom Dictionary 2011-09-20 doi: 10.3390/en4091410 Qing Yang Jing Wang Wenxia Sima Lin Chen Tao Yuan http://www.mdpi.com/1996-1073/4/9/1391/ How to design a production process with low carbon emissions and low environmental impact as well as high manufacturing performance is a key factor in the success of low-carbon production. It is important to address concerns about climate change for the large carbon emission source manufacturing industries because of their high energy consumption and environmental impact during the manufacturing stage of the production life cycle. In this paper, methodology for determining a production process is developed. This methodology integrates process determination from three different levels: new production processing, selected production processing and batch production processing. This approach is taken within a manufacturing enterprise based on prior research. The methodology is aimed at providing decision support for implementing Environmentally Benign Manufacturing (EBM) and low-carbon production to improve the environmental performance of the manufacturing industry. At the first level, a decision-making model for new production processes based on the Genetic Simulated Annealing Algorithm (GSAA) is presented. The decision-making model considers not only the traditional factors, such as time, quality and cost, but also energy and resource consumption and environmental impact, which are different from the traditional methods. At the second level, a methodology is developed based on an IPO (Input-Process-Output) model that integrates assessments of resource consumption and environmental impact in terms of a materials balance principle for batch production processes. At the third level, based on the above two levels, a method for determining production processes that focus on low-carbon production is developed based on case-based reasoning, expert systems and feature technology for designing the process flow of a new component. Through the above three levels, a method for determining the production process to identify, quantify, assess, and optimize the production process with the goal of reducing and ultimately minimizing the environmental impact while maximizing the resource efficiency is effectively presented. The feasibility of the method is verified by a case study of a whole production process design at the above three levels. http://www.mdpi.com/1996-1073/4/9/1391/ Wed, 14 Sep 2011 00:00:00 CEST Energies 2011-09-14 4 9 Article 1391 1409 1996-1073 Improved Methods for Production Manufacturing Processes in Environmentally Benign Manufacturing 2011-09-14 doi: 10.3390/en4091391 Xian-Chun Tan Yan-Yan Wang Bai-He Gu Ze-Kun Mu Can Yang http://www.mdpi.com/1996-1073/4/9/1376/ China is experiencing a high speed economic development which may exert great pressure on the environment and energy systems. To measure the environmental and energy performance during the economic development process, this paper selected 30 provinces, cities or autonomous regions as the decision making unit (DMU), and proposed a Green GDP index (GGI) in view of energy intensity and pollution intensity using the generalized Data Envelopment Analysis (DEA) method, and the developing trends of integrated energy and environment efficiency of DMUs from 2006 to 2010 are also demonstrated by the Malmquist index. Results show that the integrated energy and environment efficiency varies for each DMU. GGI were both 1 in Beijing and Shanghai. GGI values for the developed cities in Eastern China, such as Guangdong, Fujian, Zhejiang, Tianjin, Jiangsu, and Hainan, ranked high, while those in the Northeast and Middle China remained relatively low. Moreover, there is a positive relationship between the GGI and per capita GDP with a correlation coefficient of 0.75. Increases in GGI are also observed in the results, representing great achievements are acquired in energy conservation and emission reduction. However, the GGIs do not converge to the green frontier across the provinces. http://www.mdpi.com/1996-1073/4/9/1376/ Fri, 09 Sep 2011 00:00:00 CEST Energies 2011-09-09 4 9 Article 1376 1390 1996-1073 Temporal and Spatial Analysis of Integrated Energy and Environment Efficiency in China Based on a Green GDP Index 2011-09-09 doi: 10.3390/en4091376 Weibin Lin Jin Yang Bin Chen http://www.mdpi.com/1996-1073/4/9/1362/ The overall life of oil-immersed power transformers depends on the long-term life of the oil–paper insulation system throughout continuous operation. Studying the reliability assessment methods for oil–paper insulation can help determine the reliability level of power transformers accurately, and ensure their safe and stable operation. In the present paper, the life of oil–paper insulation is proven to obey the Weibull distribution under eight different temperatures set by the Weibull reliability probability paper; the failure mechanisms of the different temperatures are highly consistent. The Weibull distribution reliability curve cluster of oil–paper insulation is plotted under different temperatures by which an oil–paper insulation reliability assessment method is proposed. Lastly, the statistical validation experiment of the proposed method is conducted, which proves its theoretical validity. Thus, the present study puts forward a simple and effective method for the oil–paper insulation reliability assessment of power transformers under different temperatures at different life stages. http://www.mdpi.com/1996-1073/4/9/1362/ Fri, 09 Sep 2011 00:00:00 CEST Energies 2011-09-09 4 9 Article 1362 1375 1996-1073 Reliability Evaluation Method for Oil–Paper Insulation in Power Transformers 2011-09-09 doi: 10.3390/en4091362 Youyuan Wang Senlian Gong Stanislaw Grzybowski http://www.mdpi.com/1996-1073/4/9/1337/ Physical fundamentals of traveling wave reactor are considered. We show that the condition of existence of nuclear burning soliton-like wave in a neutron-multiplying medium is determined in general by two conditions. The first condition (necessary) is determined by relationship between the equilibrium concentration and critical concentration of active (fissionable) isotope that is a consequence of the Bohr–Sommerfeld quantization condition. The second condition (sufficient) is set by the so-called Wigner quantum statistics, or more accurately, by a statistics of the Gaussian simplectic ensembles with respect to the parameter that describes the squared width of burning wave front of nuclear fuel active component. http://www.mdpi.com/1996-1073/4/9/1337/ Fri, 09 Sep 2011 00:00:00 CEST Energies 2011-09-09 4 9 Article 1337 1361 1996-1073 Traveling Wave Reactor and Condition of Existence of Nuclear Burning Soliton-Like Wave in Neutron-Multiplying Media 2011-09-09 doi: 10.3390/en4091337 Vitaliy D. Rusov Elena P. Linnik Victor A. Tarasov Tatiana N. Zelentsova Igor V. Sharph Vladimir N. Vaschenko Sergey I. Kosenko Margarita E. Beglaryan Sergey A. Chernezhenko Pavel A. Molchinikolov Sergey I. Saulenko Olga A. Byegunova http://www.mdpi.com/1996-1073/4/9/1336/ It has been brought to our attention by an official faculty committee at Colorado State University that portions of the data of this article [1] are not derived from experimental activities. In particular, the ICP-AES data in Table 1 for Compound 6, and the cycle data plotted at cycle 15 and greater in Figure 9b represent projected rather than actual data. After confirming this case with the authors, we have determined that indeed this manuscript clearly violates our editorial policy as well as the generally accepted ethics of scientific publication. Consequently, the Editorial Team and Publisher have determined that it should be retracted. We apologize for any inconvenience this may cause. http://www.mdpi.com/1996-1073/4/9/1336/ Wed, 31 Aug 2011 00:00:00 CEST Energies 2011-08-31 4 9 Retraction 1336 1336 1996-1073 Retraction: Manivannan, V.; Chennabasappa, M.; Garrett, J. Optimization and Characterization of Lithium Ion Cathode Materials in the System (1 – x – y)LiNi0.8Co0.2O2 • xLi2MnO3 • yLiCoO2. Energies 2010, 3, 847-865. 2011-08-31 doi: 10.3390/en4091336 Brietta L. Pike http://www.mdpi.com/1996-1073/4/9/1321/ Microalgal biofuel research in China has made noticeable progress, and algae cultivation for biofuel production is considered to be an important contribution to Greenhouse Gas (GHG) mitigation and energy security. In this paper, the algal biofuel potentiality in China was reviewed from the points of view of algal biodiversity, algal culture collection, GHGs (especially CO2) mitigation, and the availability of the required sunlight, wastewater and land resources. The cultivation of microalgae utilizing power plants gas with large amounts of CO2 and wastewaters from urban households, industry and animal husbandry are suitable for large scale production in China. Land is hardly a limitation for algae cultivation. http://www.mdpi.com/1996-1073/4/9/1321/ Wed, 31 Aug 2011 00:00:00 CEST Energies 2011-08-31 4 9 Review 1321 1335 1996-1073 Available Resources for Algal Biofuel Development in China 2011-08-31 doi: 10.3390/en4091321 Shuhao Huo Renjie Dong Zhongming Wang Changle Pang Zhenhong Yuan Shunni Zhu Li Chen http://www.mdpi.com/1996-1073/4/9/1301/ This paper proposes a simple and effective method for classification of fundamental ferroresonance, single phase-to-ground and wire breakage over-voltages. In isolated neutral networks, power frequency over-voltages due to ferroresonance, single phase-to-ground and wire breakage may exist for a long time, and have very highly similar voltage features. If the improper suppression operation is applied due to incorrect identification, the accident is likely to worsen further. In this paper, the voltage and current features of these faults are analyzed, and a new effective classification criterion for fundamental ferroresonance and single phase-to-ground based on zero sequence current is proposed. A comprehensive identification method based on voltage, current and zero sequence current features is proposed, which is feasible and promising for real applications. http://www.mdpi.com/1996-1073/4/9/1301/ Mon, 29 Aug 2011 00:00:00 CEST Energies 2011-08-29 4 9 Article 1301 1320 1996-1073 Classification of Fundamental Ferroresonance, Single Phase-to-Ground and Wire Breakage Over-Voltages in Isolated Neutral Networks 2011-08-29 doi: 10.3390/en4091301 Lin Chen Qing Yang Jing Wang Wenxia Sima Tao Yuan http://www.mdpi.com/1996-1073/4/9/1278/ During their long-term outdoor field service, overhead transmission lines will be exposed to strikes by lightning, corrosion by chemical contaminants, ice-shedding, wind vibration of conductors, line galloping, external destructive forces and so on, which will generally cause a series of latent faults such as aluminum strand fracture. This may lead to broken transmission lines which will have a very strong impact on the safe operation of power grids that if the latent faults cannot be recognized and fixed as soon as possible. The detection of broken strands in transmission lines using inspection robots equipped with suitable detectors is a method with good prospects. In this paper, a method for detecting broken strands in transmission lines using an eddy current transducer (ECT) carried by a robot is developed, and an approach for identifying broken strands in transmission lines based on an S-transform is proposed. The proposed approach utilizes the S-transform to extract the module and phase information at each frequency point from detection signals. Through module phase and comparison, the characteristic frequency points are ascertained, and the fault information of the detection signal is constructed. The degree of confidence of broken strand identification is defined by the Shannon fuzzy entropy (SFE-BSICD). The proposed approach combines module information while utilizing phase information, SFE-BSICD, and the energy, so the reliability is greatly improved. These characteristic qualities of broken strands in transmission lines are used as the input of a multi-classification SVM, allowing the number of broken strands to be determined. Through experimental field verification, it can be shown that the proposed approach displays high accuracy and the SFE-BSICD is defined reasonably. http://www.mdpi.com/1996-1073/4/9/1278/ Mon, 29 Aug 2011 00:00:00 CEST Energies 2011-08-29 4 9 Article 1278 1300 1996-1073 An S-Transform and Support Vector Machine (SVM)-Based Online Method for Diagnosing Broken Strands in Transmission Lines 2011-08-29 doi: 10.3390/en4091278 Xingliang Jiang Yunfeng Xia Jianlin Hu Zhijin Zhang Lichun Shu Caxin Sun http://www.mdpi.com/1996-1073/4/9/1258/ This paper reviews and compares software tools for the planning and design of small hydropower (SHP) plants. The main emphasis is on small scale hydropower resource assessment computer tools and methodologies for the development of SHP plants corresponding to a preliminary or prefeasibility study level. The paper presents a brief evaluation of the historic software tools and the current tools used in the small hydro industry. The reviewed tools vary from simple initial estimates to quite sophisticated software. The integration of assessment tools into Geographic Information System (GIS) environments has led to a leap forward in the strengthening of the evaluation of the power potential of water streams in the case of the spatial variability of different factors affecting stream power. A number of countries (e.g., Canada, Italy, Norway, Scotland and the US) have re-assessed their hydropower capacities based on spatial information of their water stream catchments, developing tools for automated hydro-site identification and deploying GIS-based tools, so-called Atlases, of small-scale hydropower resources on the Internet. However, a reliable assessment of real SHP site feasibility implies some “on the ground” surveying, but this traditional assessment can be greatly facilitated using GIS techniques that involve the spatial variability of catchment characteristics. http://www.mdpi.com/1996-1073/4/9/1258/ Fri, 26 Aug 2011 00:00:00 CEST Energies 2011-08-26 4 9 Review 1258 1277 1996-1073 Tools for Small Hydropower Plant Resource Planning and Development: A Review of Technology and Applications 2011-08-26 doi: 10.3390/en4091258 Petras Punys Antanas Dumbrauskas Algis Kvaraciejus Gitana Vyciene http://www.mdpi.com/1996-1073/4/8/1246/ Demand planning for electricity consumption is a key success factor for the development of any countries. However, this can only be achieved if the demand is forecasted accurately. In this research, different forecasting methods—autoregressive integrated moving average (ARIMA), artificial neural network (ANN) and multiple linear regression (MLR)—were utilized to formulate prediction models of the electricity demand in Thailand. The objective was to compare the performance of these three approaches and the empirical data used in this study was the historical data regarding the electricity demand (population, gross domestic product: GDP, stock index, revenue from exporting industrial products and electricity consumption) in Thailand from 1986 to 2010. The results showed that the ANN model reduced the mean absolute percentage error (MAPE) to 0.996%, while those of ARIMA and MLR were 2.80981 and 3.2604527%, respectively. Based on these error measures, the results indicated that the ANN approach outperformed the ARIMA and MLR methods in this scenario. However, the paired test indicated that there was no significant difference among these methods at α = 0.05. According to the principle of parsimony, the ARIMA and MLR models might be preferable to the ANN one because of their simple structure and competitive performance http://www.mdpi.com/1996-1073/4/8/1246/ Mon, 22 Aug 2011 00:00:00 CEST Energies 2011-08-22 4 8 Article 1246 1257 1996-1073 Forecasting Electricity Demand in Thailand with an Artificial Neural Network Approach 2011-08-22 doi: 10.3390/en4081246 Karin Kandananond http://www.mdpi.com/1996-1073/4/8/1211/ The efficiencies of energy extraction and conversion systems are typically expressed using energy return ratios (ERRs) such as the net energy ratio (NER) or energy return on investment (EROI). A lack of a general mathematical framework prevents inter-comparison of NER/EROI estimates between authors: methods used are not standardized, nor is there a framework for succinctly reporting results in a consistent fashion. In this paper we derive normalized mathematical forms of four ERRs for energy extraction and conversion pathways. A bottom-up (process model) formulation is developed for an n-stage energy harvesting and conversion pathway with various system boundaries. Formations with the broadest system boundaries use insights from life cycle analysis to suggest a hybrid process model/economic input output based framework. These models include indirect energy consumption due to external energy inputs and embodied energy in materials. Illustrative example results are given for simple energy extraction and conversion pathways. Lastly, we discuss the limitations of this approach and the intersection of this methodology with “top-down” economic approaches. http://www.mdpi.com/1996-1073/4/8/1211/ Fri, 19 Aug 2011 00:00:00 CEST Energies 2011-08-19 4 8 Article 1211 1245 1996-1073 A General Mathematical Framework for Calculating Systems-Scale Efficiency of Energy Extraction and Conversion: Energy Return on Investment (EROI) and Other Energy Return Ratios 2011-08-19 doi: 10.3390/en4081211 Adam R. Brandt Michael Dale http://www.mdpi.com/1996-1073/4/8/1197/ Current office buildings are becoming more and more energy efficient. In particular the importance of heating is decreasing, but the share of electricity use is increasing. When the CO2 equivalent emissions are considered, the CO2 emissions from embodied energy make up an important share of the total, indicating that the building materials have a high importance which is often ignored when only the energy efficiency of running the building is considered. This paper studies a new office building in design phase and offers different alternatives to influence building energy consumption, CO2 equivalent emissions from embodied energy from building materials and CO2 equivalent emissions from energy use and how their relationships should be treated. In addition this paper studies how we should weight the primary energy use and the CO2 equivalent emissions of different design options. The results showed that the reduction of energy use reduces both the primary energy use and CO2 equivalent emissions. Especially the reduction of electricity use has a high importance for both primary energy use and CO2 emissions when fossil fuels are used. The lowest CO2 equivalent emissions were achieved when bio-based, renewable energies or nuclear power was used to supply energy for the office building. Evidently then the share of CO2 equivalent emissions from the embodied energy of building materials and products became the dominant source of CO2 equivalent emissions. The lowest primary energy was achieved when bio-based local heating or renewable energies, in addition to district cooling, were used. The highest primary energy was for the nuclear power option. http://www.mdpi.com/1996-1073/4/8/1197/ Fri, 19 Aug 2011 00:00:00 CEST Energies 2011-08-19 4 8 Article 1197 1210 1996-1073 A Carbon Footprint of an Office Building 2011-08-19 doi: 10.3390/en4081197 Miimu Airaksinen Pellervo Matilainen http://www.mdpi.com/1996-1073/4/8/1178/ Battery fast charging is one of the most significant and difficult techniques affecting the commercialization of electric vehicles (EVs). In this paper, we propose a fast charge framework based on model predictive control, with the aim of simultaneously reducing the charge duration, which represents the out-of-service time of vehicles, and the increase in temperature, which represents safety and energy efficiency during the charge process. The RC model is employed to predict the future State of Charge (SOC). A single mode lumped-parameter thermal model and a neural network trained by real experimental data are also applied to predict the future temperature in simulations and experiments respectively. A genetic algorithm is then applied to find the best charge sequence under a specified fitness function, which consists of two objectives: minimizing the charging duration and minimizing the increase in temperature. Both simulation and experiment demonstrate that the Pareto front of the proposed method dominates that of the most popular constant current constant voltage (CCCV) charge method. http://www.mdpi.com/1996-1073/4/8/1178/ Wed, 17 Aug 2011 00:00:00 CEST Energies 2011-08-17 4 8 Article 1178 1196 1996-1073 Model Predictive Control-Based Fast Charging for Vehicular Batteries 2011-08-17 doi: 10.3390/en4081178 Jingyu Yan Guoqing Xu Huihuan Qian Yangsheng Xu Zhibin Song http://www.mdpi.com/1996-1073/4/8/1163/ Biomass gasification has yet to obtain industrial acceptance. The high residual tar concentrations in syngas prevent any ambitious utilization. In this paper a novel gas purification technology based on catalytic hydrocracking is introduced, whereby most of the tarry components can be converted and removed. Pilot scale experiments were carried out with an updraft gasifier. The hydrocracking catalyst was palladium (Pd). The results show the dominant role of temperature and flow rate. At a constant flow rate of 20 Nm3/h and temperatures of 500 °C, 600 °C and 700 °C the tar conversion rates reached 44.9%, 78.1% and 92.3%, respectively. These results could be increased up to 98.6% and 99.3% by using an operating temperature of 700 °C and lower flow rates of 15 Nm3/h and 10 Nm3/h. The syngas quality after the purification process at 700 °C/10 Nm3/h is acceptable for inner combustion (IC) gas engine utilization. http://www.mdpi.com/1996-1073/4/8/1163/ Fri, 12 Aug 2011 00:00:00 CEST Energies 2011-08-12 4 8 Article 1163 1177 1996-1073 Removal and Conversion of Tar in Syngas from Woody Biomass Gasification for Power Utilization Using Catalytic Hydrocracking 2011-08-12 doi: 10.3390/en4081163 Jiu Huang Klaus Gerhard Schmidt Zhengfu Bian http://www.mdpi.com/1996-1073/4/8/1148/ Operation of doubly fed induction generators subjected to transient unbalanced voltage dips is analyzed in this article to verify the fulfillment of the Spanish grid code. Akagi’s p-q theory is not used for this study, because control of the electronic converter is not the main goal of the paper, but rather to know the physical phenomena involved in the wind turbine when voltage dips occur. Hence, the magnetizing reactive power of the induction generators and their components, which are related with the magnetic fields and determine operation of these machines, are expressed through the reactive power formulations established in the technical literature by three well-known approaches: the delayed voltage (DV) method, Czarnecki’s Current’s Physical Components (CPC) theory and Emanuel’s approach. Non-fundamental and negative-sequence components of the magnetizing reactive power are respectively established to define the effects of the distortion and voltage imbalances on the magnetic fields and electromagnetic torques. Also, fundamental-frequency positive-sequence and negative-sequence reactive powers are decomposed into two components: due to the reactive loads and caused by the imbalances. This decomposition provides additional information about the effects of the imbalances on the main magnetic field and electromagnetic torque of the induction generator. All the above mentioned reactive powers are finally applied to one actual wind turbine subjected to a two-phase voltage dip in order to explain its operation under such transient conditions. http://www.mdpi.com/1996-1073/4/8/1148/ Mon, 08 Aug 2011 00:00:00 CEST Energies 2011-08-08 4 8 Article 1148 1162 1996-1073 Analysis of Wind Generator Operations under Unbalanced Voltage Dips in the Light of the Spanish Grid Code 2011-08-08 doi: 10.3390/en4081148 Vicente León-Martínez Joaquín Montañana-Romeu http://www.mdpi.com/1996-1073/4/8/1138/ The development of the smart grid has resulted in new requirements for fault prediction of power transformers. This paper presents an entropy-based Bagging (E-Bagging) method for prediction of characteristic parameters related to power transformers faults. A parameter of comprehensive information entropy of sample data is brought forward to improve the resampling process of the E-Bagging method. The generalization ability of the E-Bagging is enhanced significantly by the comprehensive information entropy. A total of sets of 1200 oil-dissolved gas data of transformers are used as examples of fault prediction. The comparisons between the E-Bagging and the traditional Bagging and individual prediction approaches are presented. The results show that the E-Bagging possesses higher accuracy and greater stability of prediction than the traditional Bagging and individual prediction approaches. http://www.mdpi.com/1996-1073/4/8/1138/ Thu, 04 Aug 2011 00:00:00 CEST Energies 2011-08-04 4 8 Article 1138 1147 1996-1073 Entropy-Based Bagging for Fault Prediction of Transformers Using Oil-Dissolved Gas Data 2011-08-04 doi: 10.3390/en4081138 Yuanbing Zheng Caixin Sun Jian Li Qing Yang Weigen Chen http://www.mdpi.com/1996-1073/4/8/1129/ Gas hydrate formation processes in porous media are always accompanied by water transfer. To study the transfer characteristics comprehensively, two kinds of layered media consisting of coarse sand and loess were used to form methane hydrate in them. An apparatus with three PF-meter sensors detecting water content and temperature changes in media during the formation processes was applied to study the water transfer characteristics. It was experimentally observed that the hydrate formation configurations in different layered media were similar; however, the water transfer characteristics and water conversion ratios were different. http://www.mdpi.com/1996-1073/4/8/1129/ Tue, 02 Aug 2011 00:00:00 CEST Energies 2011-08-02 4 8 Article 1129 1137 1996-1073 Water Transfer Characteristics during Methane Hydrate Formation Processes in Layered Media 2011-08-02 doi: 10.3390/en4081129 Peng Zhang Qingbai Wu Yibin Pu Yousheng Deng http://www.mdpi.com/1996-1073/4/8/1112/ Assessment of the potential of a polymer flood for mobility control requires an accurate model on the viscosities of displacement fluids involved in the process. Because most polymers used in EOR exhibit shear-thinning behavior, the effective viscosity of a polymer solution is a highly nonlinear function of shear rate. A reservoir simulator including the model for the shear-rate dependence of viscosity was used to investigate shear-thinning effects of polymer solution on the performance of the layered reservoir in a five-spot pattern operating under polymer flood followed by waterflood. The model can be used as a quantitative tool to evaluate the comparative studies of different polymer flooding scenarios with respect to shear-rate dependence of fluids’ viscosities. Results of cumulative oil recovery and water-oil ratio are presented for parameters of shear-rate dependencies, permeability heterogeneity, and crossflow. The results of this work have proven the importance of taking non-Newtonian behavior of polymer solution into account for the successful evaluation of polymer flood processes. Horizontal and vertical permeabilities of each layer are shown to impact the predicted performance substantially. In reservoirs with a severe permeability contrast between horizontal layers, decrease in oil recovery and sudden increase in WOR are obtained by the low sweep efficiency and early water breakthrough through highly permeable layer, especially for shear-thinning fluids. An increase in the degree of crossflow resulting from sufficient vertical permeability is responsible for the enhanced sweep of the low permeability layers, which results in increased oil recovery. It was observed that a thinning fluid coefficient would increase injectivity significantly from simulations with various injection rates. A thorough understanding of polymer rheology in the reservoir and accurate numerical modeling are of fundamental importance for the exact estimation on the performance of polymer flood. http://www.mdpi.com/1996-1073/4/8/1112/ Tue, 02 Aug 2011 00:00:00 CEST Energies 2011-08-02 4 8 Article 1112 1128 1996-1073 Performance of a Polymer Flood with Shear-Thinning Fluid in Heterogeneous Layered Systems with Crossflow 2011-08-02 doi: 10.3390/en4081112 Kun Sang Lee http://www.mdpi.com/1996-1073/4/7/1102/ Spring harvested corn stover was used for direct combustion in a 146 kW dual chamber boiler designed for wood logs. Stover had a very low moisture content (6.83 ± 0.17%), a gross calorific value (GCV) of 18.57 MJ/kg of dry matter (±0.32 MJ/kg DM) and an ash content of 5.88% (±1.15%). Small stover bales (8.83 ± 0.90 kg) were placed manually in the upper combustion chamber at a rate of 10.5 to 12.8 kg/h over a 24-h period, with three replications, and compared to a control wood combustion trial (12.1 kg/h during 24 h). The overall heat transfer efficiency for stover was lower than for wood (57% vs. 77%). Stover bales produced on average 7.5% ash which included about 2% of unburned residues while wood produced 1.7% ash. CO gas emissions averaged 1324 mg/m³ for stover (118 mg/m³ for wood). The corn stover showed a good calorific potential, but it would have to be densified and the boiler should be modified to improve airflow, completeness of combustion and handling of the large amount of ash formed. http://www.mdpi.com/1996-1073/4/7/1102/ Fri, 22 Jul 2011 00:00:00 CEST Energies 2011-07-22 4 7 Article 1102 1111 1996-1073 Combustion of Corn Stover Bales in a Small 146-kW Boiler 2011-07-22 doi: 10.3390/en4071102 René Morissette Philippe Savoie Joey Villeneuve http://www.mdpi.com/1996-1073/4/7/1087/ This paper presents an Improved Bagging Algorithm (IBA) to recognize ultra-high-frequency (UHF) signals of partial discharges (PDs). This approach establishes the sample information entropy for each sample and the re-sampling process of the traditional Bagging algorithm is optimized. Four typical discharge models were designed in the laboratory to simulate the internal insulation faults of power transformers. The optimized third order Peano fractal antenna was applied to capture the PD UHF signals. Multi-scale fractal dimensions as well as energy parameters extracted from the decomposed signals by wavelet packet transform were used as the characteristic parameters for pattern recognition. In order to verify the effectiveness of the proposed algorithm, the back propagation neural network (BPNN) and the support vector machine (SVM) based on the IBA were adopted in this paper to carry out the pattern recognition for PD UHF signals. Experimental results show that the proposed approach of IBA can effectively enhance the generalization capability and also improve the accuracy of the recognition for PD UHF signals. http://www.mdpi.com/1996-1073/4/7/1087/ Thu, 21 Jul 2011 00:00:00 CEST Energies 2011-07-21 4 7 Article 1087 1101 1996-1073 Improved Bagging Algorithm for Pattern Recognition in UHF Signals of Partial Discharges 2011-07-21 doi: 10.3390/en4071087 Tianyan Jiang Jian Li Yuanbing Zheng Caixin Sun http://www.mdpi.com/1996-1073/4/7/1058/ Several researchers have proposed that mobility control mechanisms can positively contribute to oil recovery in the case of emulsions generated in Enhanced-Oil Recovery (EOR) operations. Chemical EOR techniques that use alkaline components or/and surfactants are known to produce undesirable emulsions that create operational problems and are difficult to break. Other water-based methods have been less studied in this sense. EOR processes such as polymer flooding and LoSalTM injection require adjustments of water chemistry, mainly by lowering the ionic strength of the solution or by decreasing hardness. The decreased ionic strength of EOR solutions can give rise to more stable water-in-oil emulsions, which are speculated to improve mobility ratio between the injectant and the displaced oil. The first step toward understanding the connection between the emulsions and EOR mechanisms is to show that EOR conditions, such as salinity and hardness requirements, among others, are conducive to stabilizing emulsions. In order to do this, adequate stability proxies are required. This paper reviews commonly used emulsion stability proxies and explains the advantages and disadvantage of methods reviewed. This paper also reviews aqueous-based EOR processes with focus on heavy oil to contextualize in-situ emulsion stabilization conditions. This context sets the basis for comparison of emulsion stability proxies. http://www.mdpi.com/1996-1073/4/7/1058/ Mon, 18 Jul 2011 00:00:00 CEST Energies 2011-07-18 4 7 Review 1058 1086 1996-1073 Stability Proxies for Water-in-Oil Emulsions and Implications in Aqueous-based Enhanced Oil Recovery 2011-07-18 doi: 10.3390/en4071058 Vladimir Alvarado Xiuyu Wang Mehrnoosh Moradi http://www.mdpi.com/1996-1073/4/7/1051/ Damage to the Fukushima Nuclear Power Plant by the recent earthquake and tsunami that hit northern Japan should stimulate consideration of alternative sources of energy. In particular, if managed appropriately, the 25.1 million ha of Japanese forests could be an important source of wood biomass for bioenergy production. Here, we discuss policy incentives for substituting wood bioenergy for nuclear power, thereby creating a safer society while better managing the forest resources in Japan. http://www.mdpi.com/1996-1073/4/7/1051/ Wed, 06 Jul 2011 00:00:00 CEST Energies 2011-07-06 4 7 Communication 1051 1057 1996-1073 Time to Substitute Wood Bioenergy for Nuclear Power in Japan 2011-07-06 doi: 10.3390/en4071051 Nophea Sasaki Toshiaki Owari Francis E. Putz http://www.mdpi.com/1996-1073/4/7/1036/ Optimal utilization of available water resources has become more urgent due to the rapid growth of the economy and population. The joint operation of the Three Gorges cascade and Qingjiang cascade reservoirs in China was studied in this paper. Choosing maximization of hydropower generation and hydropower revenue as objective functions respectively, optimal models were established for individual and joint operation of the cascade reservoirs. The models were solved by the progressive optimality algorithm. The storage and electric compensation benefits among cascade reservoirs were analyzed. The daily inflow data of consecutive hydrological years of 1982–1987 were selected for a case study. Compared with the design operation rule, the joint operation of the multi-reservoir system can generate 5.992 billion kWh of extra power or an increase of 5.70% by the objective function of maximum hydropower generation. Through reservoir storage compensation, the spilled water of the Three Gorges and Qingjiang cascade reservoirs was decreased by 78.741 and 5.384 billion m3, respectively. http://www.mdpi.com/1996-1073/4/7/1036/ Mon, 04 Jul 2011 00:00:00 CEST Energies 2011-07-04 4 7 Article 1036 1050 1996-1073 Joint Operation of the Multi-Reservoir System of the Three Gorges and the Qingjiang Cascade Reservoirs 2011-07-04 doi: 10.3390/en4071036 Shenglian Guo Jionghong Chen Yu Li Pan Liu Tianyuan Li http://www.mdpi.com/1996-1073/4/7/1025/ The new energy revolution, of which the primary energy will be based on renewable energy sources and the terminal energy will be based on electric power, will have a revolutionary impact on the future power grids. In order to develop the corresponding power grid for the future energy system, first of all, the architecture and mode of operation of the future power grid must be investigated. In this paper, we suggest that the DC—dominant operation mode for transmission system, distribution network and distributed power system should be developed, and a MP-MC dominated transmission architecture (multiple powers to multiple consumers) and the two-way power exchange control (TPEC) should be employed to build “wide-area super virtual power plants” (WASVPPs) which cover all the major power plants in a wide range, allowing the consumers to obtain a stable and reliable supply of electricity from the “cloud powering” created by WASVPP and the distributed power system which is connected to the grid. http://www.mdpi.com/1996-1073/4/7/1025/ Mon, 04 Jul 2011 00:00:00 CEST Energies 2011-07-04 4 7 Article 1025 1035 1996-1073 Discussions on the Architecture and Operation Mode of Future Power Grids 2011-07-04 doi: 10.3390/en4071025 Liye Xiao Liangzhen Lin Yi Liu http://www.mdpi.com/1996-1073/4/7/1010/ The aim of this article was to assess some of the main lighting software programs habitually used in architecture, subjecting them to a series of trials and analyzing the light distribution obtained in situations with different orientations, dates and geometry. The analysis examines Lightscape 3.2, Desktop Radiance 2.0, Lumen Micro 7.5, Ecotect 5.5 and Dialux 4.4. http://www.mdpi.com/1996-1073/4/7/1010/ Wed, 29 Jun 2011 00:00:00 CEST Energies 2011-06-29 4 7 Article 1010 1024 1996-1073 Towards an Analysis of Daylighting Simulation Software 2011-06-29 doi: 10.3390/en4071010 Ignacio Acosta Jaime Navarro Juan J. Sendra http://www.mdpi.com/1996-1073/4/6/998/ Typically the aim in the construction process is to calculate the energy, space and cost efficiency in the design phase. These factors’ influence on decision making extends to the whole building process. How these decisions affect the use of the building and user satisfaction as well as maintenance is still not that well understood. This study analyses different schools and day care centers and their energy as well as primary energy use. The buildings are located in southern Finland. Each building has had different objectives with respect to energy efficiency in the design phase. Our objective was to find out how those decisions made in the design and construction phase have influenced the overall energy performance of the building compared to existing building stock of similar building type. The results show that the studied buildings had lower thermal energy consumption compared to existing building stock. Thus the special attention in the design phase allowed achieving the desired goal. However, for the electricity consumption such a correlation could not be found. One of the reasons could be also different service level of buildings (more equipment). Also other quality values could not be compared since such data were not available from the existing building stock. As many earlier studies have indicated users have a high influence on the energy consumption. In the future, when feed-back from the users are obtained it will be interesting to analyze the results and compare what kind of influence that user behavior will have on the overall energy consumption of the studied buildings. http://www.mdpi.com/1996-1073/4/6/998/ Mon, 27 Jun 2011 00:00:00 CEST Energies 2011-06-27 4 6 Article 998 1009 1996-1073 Energy Use in Day Care Centers and Schools 2011-06-27 doi: 10.3390/en4070998 Miimu Airaksinen http://www.mdpi.com/1996-1073/4/6/978/ Based on an analysis of the working principles of the hydraulic variable pitch system of a wind turbine, a novel Petri net model and reliability evaluation method are proposed. First, Petri net theory is adopted to build a model for each discrete state of the operation of the hydraulic pitch system of the wind turbine and at the same time a fault Petri net model is established. Then through qualitative analysis and quantitative calculations based on the fault Petri net, the system reliability indexes are obtained. During the qualitative analysis process, in order to more conveniently find the minimal cut sets of the fault Petri net, a Visual C++ 6.0-based algorithm is compiled and the minimal cut sets are tested correctly with another method. During the quantitative calculation process, the fault probability has been obtained from the equations according to the fault probability of libraries and transitions between different states. Not only does the proposed Petri net describe the structure, function and operation of the hydraulic pitch system with a graphic language, but the fault Petri net model can also clearly express the logical relations among faults. The novel Petri net model offers simple calculations and the prospect of broad applicability and the new reliability evaluation method provides an important reference for the performance evaluation of these systems. http://www.mdpi.com/1996-1073/4/6/978/ Thu, 23 Jun 2011 00:00:00 CEST Energies 2011-06-23 4 6 Article 978 997 1996-1073 Petri Net Model and Reliability Evaluation for Wind Turbine Hydraulic Variable Pitch Systems 2011-06-23 doi: 10.3390/en4060978 Xiyun Yang Jinxia Li Wei Liu Peng Guo http://www.mdpi.com/1996-1073/4/6/960/ Accurate electric load forecasting has become the most important issue in energy management; however, electric load demonstrates a seasonal/cyclic tendency from economic activities or the cyclic nature of climate. The applications of the support vector regression (SVR) model to deal with seasonal/cyclic electric load forecasting have not been widely explored. The purpose of this paper is to present a SVR model which combines the seasonal adjustment mechanism and a chaotic immune algorithm (namely SSVRCIA) to forecast monthly electric loads. Based on the operation procedure of the immune algorithm (IA), if the population diversity of an initial population cannot be maintained under selective pressure, then IA could only seek for the solutions in the narrow space and the solution is far from the global optimum (premature convergence). The proposed chaotic immune algorithm (CIA) based on the chaos optimization algorithm and IA, which diversifies the initial definition domain in stochastic optimization procedures, is used to overcome the premature local optimum issue in determining three parameters of a SVR model. A numerical example from an existing reference is used to elucidate the forecasting performance of the proposed SSVRCIA model. The forecasting results indicate that the proposed model yields more accurate forecasting results than the ARIMA and TF-ε-SVR-SA models, and therefore the SSVRCIA model is a promising alternative for electric load forecasting. http://www.mdpi.com/1996-1073/4/6/960/ Fri, 17 Jun 2011 00:00:00 CEST Energies 2011-06-17 4 6 Article 960 977 1996-1073 SVR with Hybrid Chaotic Immune Algorithm for Seasonal Load Demand Forecasting 2011-06-17 doi: 10.3390/en4060960 Wei-Chiang Hong Yucheng Dong Chien-Yuan Lai Li-Yueh Chen Shih-Yung Wei http://www.mdpi.com/1996-1073/4/6/948/ This study integrates photovoltaic (PV) system, building structure, and heat flow mechanism to propose the notion of ventilated Building-Integrated Photovoltaic (BIPV) walls. The energy-saving potential of the ventilated BIPV walls was investigated via engineering considerations and computational fluid dynamics (CFD) simulations. The results show that the heat removal rate and indoor heat gain of the proposed ventilated BIPV walls were dominantly affected by outdoor wind velocity and airflow channel width. Correlations for predicting the heat removal rate and indoor heat gain, the reduction ratio of the indoor heat gain, CO2 reduction, and induced indoor air exchange are introduced. http://www.mdpi.com/1996-1073/4/6/948/ Tue, 14 Jun 2011 00:00:00 CEST Energies 2011-06-14 4 6 Article 948 959 1996-1073 Energy Saving Evaluation of the Ventilated BIPV Walls 2011-06-14 doi: 10.3390/en4060948 Chi-Ming Lai Yi-Pin Lin http://www.mdpi.com/1996-1073/4/6/928/ An adsorption microcalorimeter was designed and built in our laboratory and used for the determination of differential adsorption heats in different samples of porous solids: activated carbon granules, activated carbon pellets, an activated carbon monolith and a zeolite sample. This work shows the relationship between adsorption heat and the pore size of different porous solids using adsorption of NH3, CO and N2O. The result shows that the thermal effect can be related with textural properties and superficial chemical groups of the studied porous solids. The values of differential heats of N2O adsorption in the investigated systems have shown that this interaction is weaker than that with CO. Small amounts of N2O are chemisorbed in the investigated systems. For the room temperature adsorption of N2O, the strongest active sites for the interaction with Brönsted acid groups in the ACM structure were identified. The values determined are between −60 kJ/mol and −110 kJ/mol for ZMOR and ACM, respectively, for the adsorption of N2O and −95 kJ/mol and −130 kJ/mol for the adsorption of CO. http://www.mdpi.com/1996-1073/4/6/928/ Fri, 10 Jun 2011 00:00:00 CEST Energies 2011-06-10 4 6 Article 928 947 1996-1073 Textural Characterization and Energetics of Porous Solids by Adsorption Calorimetry 2011-06-10 doi: 10.3390/en4060928 Vanessa Silenia Garcia-Cuello Liliana Giraldo Juan C. Moreno-Pirajan http://www.mdpi.com/1996-1073/4/6/913/ Numerous studies have estimated the optimum thickness of thermal insulation materials used in building walls for different climate conditions. The economic parameters (inflation rate, discount rate, lifetime and energy costs), the heating/cooling loads of the building, the wall structure and the properties of the insulation material all affect the optimum insulation thickness. This study focused on the investigation of these parameters that affect the optimum thermal insulation thickness for building walls. To determine the optimum thickness and payback period, an economic model based on life-cycle cost analysis was used. As a result, the optimum thermal insulation thickness increased with increasing the heating and cooling energy requirements, the lifetime of the building, the inflation rate, energy costs and thermal conductivity of insulation. However, the thickness decreased with increasing the discount rate, the insulation material cost, the total wall resistance, the coefficient of performance (COP) of the cooling system and the solar radiation incident on a wall. In addition, the effects of these parameters on the total life-cycle cost, payback periods and energy savings were also investigated. http://www.mdpi.com/1996-1073/4/6/913/ Tue, 07 Jun 2011 00:00:00 CEST Energies 2011-06-07 4 6 Article 913 927 1996-1073 Parametric Investigation of Optimum Thermal Insulation Thickness for External Walls 2011-06-07 doi: 10.3390/en4060913 Omer Kaynakli http://www.mdpi.com/1996-1073/4/6/894/ A new phenomenological model, the TP (Temperature Phase) model, is presented to carry out optimization calculations for turbulent diffusion combustion in a high-pressure common rail diesel engine. Temperature is the most important parameter in the TP model, which includes two parts: an auto-ignition and a soot model. In the auto-ignition phase, different reaction mechanisms are built for different zones. For the soot model, different methods are used for different temperatures. The TP model is then implemented in KIVA code instead of original model to carry out optimization. The results of cylinder pressures, the corresponding heat release rates, and soot with variation of injection time, variation of rail pressure and variation of speed among TP model, KIVA standard model and experimental data are analyzed. The results indicate that the TP model can carry out optimization and CFD (computational fluid dynamics) and can be a useful tool to study turbulent diffusion combustion. http://www.mdpi.com/1996-1073/4/6/894/ Fri, 03 Jun 2011 00:00:00 CEST Energies 2011-06-03 4 6 Article 894 912 1996-1073 A Phenomenological Model for Prediction Auto-Ignition and Soot Formation of Turbulent Diffusion Combustion in a High Pressure Common Rail Diesel Engine 2011-06-03 doi: 10.3390/en4060894 Yongfeng Liu Jianwei Yang Jianmin Sun Aihua Zhu Qinghui Zhou http://www.mdpi.com/1996-1073/4/6/878/ Direct Numerical Simulations (DNS) have been conducted to study the response of initially laminar spherical premixed methane–air flame kernels to successively higher turbulence intensities at five different equivalence ratios. The numerical experiments include a 16-species/25-step skeletal mechanism for methane oxidation and a multicomponent molecular transport model. Highly turbulent conditions (with integral Reynolds numbers up to 4513) have been accessed. The effect of turbulence on the physical properties of the flame, in particular its consumption speed Sc, which is an interesting measure of the turbulent flame speed ST has been investigated. Local quenching events are increasingly observed for highly turbulent conditions, particularly for lean mixtures. The obtained results qualitatively confirm the expected trend regarding correlations between u′/SL and the consumption speed: Sc first increases, roughly linearly, with u′/SL (low turbulence zone), then levels off (bending zone) before decreasing again (quenching limit) for too intense turbulence. For a fixed value of u′/SL, Sc/SL varies with the mixture equivalence ratio, showing that additional parameters should probably enter phenomenological expressions relating these two quantities. http://www.mdpi.com/1996-1073/4/6/878/ Fri, 27 May 2011 00:00:00 CEST Energies 2011-05-27 4 6 Article 878 893 1996-1073 Impact of Turbulence Intensity and Equivalence Ratio on the Burning Rate of Premixed Methane–Air Flames 2011-05-27 doi: 10.3390/en4060878 Gordon Fru Dominique Thévenin Gábor Janiga http://www.mdpi.com/1996-1073/4/6/845/ This article reviews and compares assessments of three biodiesel fuels: (1) transesterified lipids, (2) hydrotreated vegetable oils (HVO), and (3) woody biomass-to-liquid (BTL) Fischer-Tropsch diesel and selected feedstock options. The article attempts to rank the environmental performance and costs of fuel and feedstock combinations. Due to inter-study differences in goal and study assumptions, the ranking was mostly qualitative and intra-study results are emphasized. Results indicate that HVO made from wastes or by-products such as tall oil, tallow or used cooking oil outperform transesterified lipids and BTL from woody material, both with respect to environmental life cycle impacts and costs. These feedstock options are, however, of limited availability, and to produce larger volumes of biofuels other raw materials must also be used. BTL from woody biomass seems promising with good environmental performance and the ability not to compete with food production. Production of biofuels from agricultural feedstock sources requires much energy and leads to considerable emissions due to agrochemical inputs. Thus, such biodiesel fuels are ranked lowest in this comparison. Production of feedstock is the most important life cycle stage. Avoiding detrimental land use changes and maintaining good agricultural or forestry management practices are the main challenges to ensure that biofuels can be a sustainable option for the future transport sector. http://www.mdpi.com/1996-1073/4/6/845/ Wed, 25 May 2011 00:00:00 CEST Energies 2011-05-25 4 6 Review 845 877 1996-1073 Environmental Impacts and Costs of Hydrotreated Vegetable Oils, Transesterified Lipids and Woody BTL—A Review 2011-05-25 doi: 10.3390/en4060845 Kathrin Sunde Andreas Brekke Birger Solberg http://www.mdpi.com/1996-1073/4/5/826/ The destabilized complex hydride system composed of LiNH2:MgH2 (1:1 molar ratio) is one of the leading candidates of hydrogen storage with a reversible hydrogen storage capacity of 8.1 wt%. A low sorption enthalpy of ~32 kJ/mole H2 was first predicted by Alapati et al. utilizing first principle density function theory (DFT) calculations and has been subsequently confirmed empirically by Lu et al. through differential thermal analysis (DTA). This enthalpy suggests that favorable sorption kinetics should be obtainable at temperatures in the range of 160 °C to 200 °C. Preliminary experiments reported in the literature indicate that sorption kinetics are substantially lower than expected in this temperature range despite favorable thermodynamics. Systematic isothermal and isobaric sorption experiments were performed using a Sievert’s apparatus to form a baseline data set by which to compare kinetic results over the pressure and temperature range anticipated for use of this material as a hydrogen storage media. Various material preparation methods and compositional modifications were performed in attempts to increase the kinetics while lowering the sorption temperatures. This paper outlines the results of these systematic tests and describes a number of beneficial additions which influence kinetics as well as NH3 formation. http://www.mdpi.com/1996-1073/4/5/826/ Fri, 20 May 2011 00:00:00 CEST Energies 2011-05-20 4 5 Article 826 844 1996-1073 Affects of Mechanical Milling and Metal Oxide Additives on Sorption Kinetics of 1:1 LiNH2/MgH2 Mixture 2011-05-20 doi: 10.3390/en4050826 Donald L. Anton Christine J. Price Joshua Gray