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Energies, Volume 6, Issue 4 (April 2013), Pages 1802-2318

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Research

Open AccessArticle The Use of Energy Storage Systems for Supporting the Voltage Needs of Urban and Suburban Railway Contact Lines
Energies 2013, 6(4), 1802-1820; doi:10.3390/en6041802
Received: 23 November 2012 / Revised: 13 March 2013 / Accepted: 18 March 2013 / Published: 27 March 2013
Cited by 9 | PDF Full-text (386 KB) | HTML Full-text | XML Full-text
Abstract
The paper aims to contribute to the use of electric double layer capacitor (EDLC) sets for boosting voltages of contact lines in urban and suburban railway traction systems. Different electrical configurations of contact lines are considered and investigated. For each of them, [...] Read more.
The paper aims to contribute to the use of electric double layer capacitor (EDLC) sets for boosting voltages of contact lines in urban and suburban railway traction systems. Different electrical configurations of contact lines are considered and investigated. For each of them, proper mathematical models are suggested to evaluate the electrical performances of the contact lines. They give rise, also, to sample design procedures for the sizing of the most appropriate energy storage systems, to be distributed along the lines, for boosting line voltages and avoiding undesired voltage drops. A numerical example based on the “Cumana” suburban Naples railway network is presented to give an idea of the weights and sizes of electric double layer capacitors needed to boost the voltage of a sample contact line. In particular, three different EDLC systems, for a overall installed energy of 9.6 kWh, have been placed nearby the stations presenting the highest voltage drops during the most representative situation of trains’ service. The new voltage drop is equal to 32% of that obtained in absence of EDLCs. Full article
Open AccessArticle Analytical and Experimental Study of Recycling Baffled Double-Pass Solar Air Heaters with Attached Fins
Energies 2013, 6(4), 1821-1842; doi:10.3390/en6041821
Received: 25 January 2013 / Revised: 14 March 2013 / Accepted: 14 March 2013 / Published: 28 March 2013
Cited by 1 | PDF Full-text (376 KB) | HTML Full-text | XML Full-text
Abstract
The study of the heat transfer of solar air heaters with a new design using an absorbing plate with fins and baffles, which facilitate the recycling of flowing air, is reported. The mathematical formulation and analytical analysis for such a recyclic baffled [...] Read more.
The study of the heat transfer of solar air heaters with a new design using an absorbing plate with fins and baffles, which facilitate the recycling of flowing air, is reported. The mathematical formulation and analytical analysis for such a recyclic baffled double-pass solar air heater were developed theoretically. The performance of the device was studied experimentally as well. The theoretical predicted and experimental results were compared with another design, i.e., a downward-type single-pass solar air heater without recycle and double-pass operations reported in our previous work. Significant improvement in heat-transfer efficiency is achieved with the baffle and fin design due to the recycling heating and the extended heat transfer area. The effects of mass flow rate and recycle ratio on the heat-transfer efficiency enhancement as well as on the power consumption increment are also discussed. Full article
Open AccessArticle System Design and Analysis of a Directly Air-Assisted Turbocharged SI Engine with Camshaft Driven Valves
Energies 2013, 6(4), 1843-1862; doi:10.3390/en6041843
Received: 5 February 2013 / Revised: 20 March 2013 / Accepted: 21 March 2013 / Published: 28 March 2013
PDF Full-text (270 KB) | HTML Full-text | XML Full-text
Abstract
The availability of compressed air in combination with downsizing and turbocharging is a promising approach to improve the fuel economy and the driveability of internal combustion engines. The compressed air is used to boost and start the engine. It is generated during [...] Read more.
The availability of compressed air in combination with downsizing and turbocharging is a promising approach to improve the fuel economy and the driveability of internal combustion engines. The compressed air is used to boost and start the engine. It is generated during deceleration phases by running the engine as a piston compressor. In this paper, a camshaft-driven valve is considered for the control of the air exchange between the tank and the combustion chamber. Such a valve system is cost-effective and robust. Each pneumatic engine mode is realized by a separate cam. The air mass transfer in each mode is analyzed. Special attention is paid to the tank pressure dependence. The air demand in the boost mode is found to increase with the tank pressure. However, the dependence on the tank pressure is small in the most relevant operating region. The air demand of the pneumatic start shows a piecewise continuous dependence on the tank pressure. Finally, a tank sizing method is proposed which uses a quasi-static simulation. It is applied to a compact class vehicle, for which a tank volume of less than 10 L is sufficient. A further reduction of the tank volume is limited by the specifications imposed on the pneumatic start. Full article
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Open AccessArticle Experimental Study Related to the Mooring Design for the 1.5 MW Wave Dragon WEC Demonstrator at DanWEC
Energies 2013, 6(4), 1863-1886; doi:10.3390/en6041863
Received: 28 January 2013 / Revised: 22 March 2013 / Accepted: 25 March 2013 / Published: 2 April 2013
Cited by 3 | PDF Full-text (627 KB) | HTML Full-text | XML Full-text
Abstract
The paper presents the results of an experimental study identifying the response of a 1.5 MW Wave Dragon to extreme conditions typical of the DanWEC test center. The best strategies allowing for a reduction in the extreme mooring tension have also been [...] Read more.
The paper presents the results of an experimental study identifying the response of a 1.5 MW Wave Dragon to extreme conditions typical of the DanWEC test center. The best strategies allowing for a reduction in the extreme mooring tension have also been investigated, showing that this is possible by increasing the surge natural period of the system. The most efficient strategy in doing this is to provide the mooring system with a large horizontal compliance (typically in the order of 100 s), which shall be therefore assumed as design configuration. If this is not possible, it can also be partly achieved by lowering the floating level to a minimum (survivability mode) and by adopting a negative trim position. The adoption of the design configuration would determine in a 100-year storm extreme mooring tensions in the order of 0.9 MN, 65% lower than the worst case experienced in the worst case configuration. At the same time it would lead to a reduction in the extreme motion response, resulting in heave and pitch oscillation heights of 7 m and 19° and surge excursion of 12 m. Future work will numerically identify mooring configurations that could provide the desired compliance. Full article
(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)
Open AccessArticle Support Vector Regression Model Based on Empirical Mode Decomposition and Auto Regression for Electric Load Forecasting
Energies 2013, 6(4), 1887-1901; doi:10.3390/en6041887
Received: 28 November 2012 / Revised: 2 February 2013 / Accepted: 25 March 2013 / Published: 2 April 2013
Cited by 10 | PDF Full-text (542 KB) | HTML Full-text | XML Full-text
Abstract
Electric load forecasting is an important issue for a power utility, associated with the management of daily operations such as energy transfer scheduling, unit commitment, and load dispatch. Inspired by strong non-linear learning capability of support vector regression (SVR), this paper presents [...] Read more.
Electric load forecasting is an important issue for a power utility, associated with the management of daily operations such as energy transfer scheduling, unit commitment, and load dispatch. Inspired by strong non-linear learning capability of support vector regression (SVR), this paper presents a SVR model hybridized with the empirical mode decomposition (EMD) method and auto regression (AR) for electric load forecasting. The electric load data of the New South Wales (Australia) market are employed for comparing the forecasting performances of different forecasting models. The results confirm the validity of the idea that the proposed model can simultaneously provide forecasting with good accuracy and interpretability. Full article
(This article belongs to the Special Issue Hybrid Advanced Techniques for Forecasting in Energy Sector)
Open AccessArticle Application of Coordinated SOFC and SMES Robust Control for Stabilizing Tie-Line Power
Energies 2013, 6(4), 1902-1917; doi:10.3390/en6041902
Received: 10 January 2013 / Revised: 22 February 2013 / Accepted: 27 February 2013 / Published: 3 April 2013
Cited by 8 | PDF Full-text (542 KB) | HTML Full-text | XML Full-text
Abstract
Wind power causes fluctuations in power systems and introduces issues concerning system stability and power quality because of the lack of controllability of its discontinuous and intermittent resources. This paper presents a coordinated control strategy for solid oxide fuel cells (SOFCs) and [...] Read more.
Wind power causes fluctuations in power systems and introduces issues concerning system stability and power quality because of the lack of controllability of its discontinuous and intermittent resources. This paper presents a coordinated control strategy for solid oxide fuel cells (SOFCs) and superconducting magnetic energy storage (SMES) to match the intermittent wind power generation and compensate for the rapid load changes. An optimal H∞ control method, where the weighting function selection is expressed as an optimization problem, is proposed to mitigate tie-line power fluctuations and the mixed-sensitivity approach is used to deal with the interference suppression. Simulation results show that the proposed method significantly improves the smoothing effect of wind power fluctuations. Compared with the conventional control method, the proposed method has better anti-interference performance in various operating situations. Full article
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Open AccessArticle Hybrid Predictive Models for Accurate Forecasting in PV Systems
Energies 2013, 6(4), 1918-1929; doi:10.3390/en6041918
Received: 9 January 2013 / Revised: 8 February 2013 / Accepted: 26 February 2013 / Published: 3 April 2013
Cited by 25 | PDF Full-text (1459 KB) | HTML Full-text | XML Full-text
Abstract
The accurate forecasting of energy production from renewable sources represents an important topic also looking at different national authorities that are starting to stimulate a greater responsibility towards plants using non-programmable renewables. In this paper the authors use advanced hybrid evolutionary techniques [...] Read more.
The accurate forecasting of energy production from renewable sources represents an important topic also looking at different national authorities that are starting to stimulate a greater responsibility towards plants using non-programmable renewables. In this paper the authors use advanced hybrid evolutionary techniques of computational intelligence applied to photovoltaic systems forecasting, analyzing the predictions obtained by comparing different definitions of the forecasting error. Full article
(This article belongs to the Special Issue Hybrid Advanced Techniques for Forecasting in Energy Sector)
Open AccessArticle High Pressure Oxydesulphurisation of Coal—A Parametric Study
Energies 2013, 6(4), 1930-1943; doi:10.3390/en6041930
Received: 11 December 2012 / Revised: 5 March 2013 / Accepted: 6 March 2013 / Published: 3 April 2013
Cited by 2 | PDF Full-text (511 KB) | HTML Full-text | XML Full-text
Abstract
The current study is focused on controlling sulphur emissions by pre-treating coal to remove sulphur prior to combustion using the oxydesulphurisation technique. Three British coals were chosen for the study. Working with these coals gave a better insight to the oxydesulphurisation reactions [...] Read more.
The current study is focused on controlling sulphur emissions by pre-treating coal to remove sulphur prior to combustion using the oxydesulphurisation technique. Three British coals were chosen for the study. Working with these coals gave a better insight to the oxydesulphurisation reactions for pyritic and organic sulphur. Effect of air and oxygen pressure in a fixed time interval on sulphur removal was studied by series of experimental runs at various temperatures. Heating value recoveries were significant. Increase in oxygen content is reported as a measure of carbon loss. The coal samples were analyzed according to British standard methods. Experimental results demonstrate that the sulphur removal was enhanced with the increase in air pressure, particularly up to 100 bars, with only a small decrease in calorific value at a particular temperature. Increasing temperature was witnessed to be more important in sulphur removal than increasing pressure. Full article
Open AccessArticle Evaluation and Optimization of a Traditional North-Light Roof on Industrial Plant Energy Consumption
Energies 2013, 6(4), 1944-1960; doi:10.3390/en6041944
Received: 28 December 2012 / Revised: 2 March 2013 / Accepted: 6 March 2013 / Published: 3 April 2013
PDF Full-text (854 KB) | HTML Full-text | XML Full-text
Abstract
Increasingly strict energy policies, rising energy prices, and a desire for a positive corporate image currently serve as incentives for multinational corporations to reduce their plants’ energy consumption. This paper quantitatively investigates and discusses the value of a traditional north-light roof using [...] Read more.
Increasingly strict energy policies, rising energy prices, and a desire for a positive corporate image currently serve as incentives for multinational corporations to reduce their plants’ energy consumption. This paper quantitatively investigates and discusses the value of a traditional north-light roof using a complete building energy simulation and optimization framework. The findings indicate that the north-light system yields positive building energy performance for several climate zones, including: (i) Humid Subtropical; (ii) Semiarid Continental; (iii) Mediterranean; and (iv) Subtropical Highland. In the Subtropical Highland climate zone, for example, the building energy consumption of a north-light roof is up to 54% less than that of a conventional flat roof. Based on these positive findings, this paper further presents an optimization framework that alters the north-light roof shape to further improve its energy performance. To quantitatively guarantee a high probability of finding satisfactory designs while reducing the computational processing time, ordinal optimization is introduced into the scheme. The Subtropical Highland case study shows further energy building consumption reduction of 26% for an optimized north-light roof shape. The presented evaluation and optimization framework could be used in designing a plant with integrated north-lights roof that aim at energy efficiency while maintaining environmental occupant comfort levels. Full article
(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)
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Open AccessArticle Experimental Update of the Overtopping Model Used for the Wave Dragon Wave Energy Converter
Energies 2013, 6(4), 1961-1992; doi:10.3390/en6041961
Received: 5 February 2013 / Revised: 15 March 2013 / Accepted: 26 March 2013 / Published: 3 April 2013
Cited by 3 | PDF Full-text (2255 KB) | HTML Full-text | XML Full-text
Abstract
An overtopping model specifically suited for Wave Dragon is needed in order to improve the reliability of its performance estimates. The model shall be comprehensive of all relevant physical processes that affect overtopping and flexible to adapt to any local conditions and [...] Read more.
An overtopping model specifically suited for Wave Dragon is needed in order to improve the reliability of its performance estimates. The model shall be comprehensive of all relevant physical processes that affect overtopping and flexible to adapt to any local conditions and device configuration. An experimental investigation is carried out to update an existing formulation suited for 2D draft-limited, low-crested structures, in order to include the effects on the overtopping flow of the wave steepness, the 3D geometry of Wave Dragon, the wing reflectors, the device motions and the non-rigid connection between platform and reflectors. The study is carried out in four phases, each of them specifically targeted at quantifying one of these effects through a sensitivity analysis and at modeling it through custom-made parameters. These are depending on features of the wave or the device configuration, all of which can be measured in real-time. Instead of using new fitting coefficients, this approach allows a broader applicability of the model beyond the Wave Dragon case, to any overtopping WEC or structure within the range of tested conditions. Predictions reliability of overtopping over Wave Dragon increased, as the updated model allows improved accuracy and precision respect to the former version. Full article
(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)
Open AccessArticle Optimal Constant DC Link Voltage Operation of a Wave Energy Converter
Energies 2013, 6(4), 1993-2006; doi:10.3390/en6041993
Received: 6 February 2013 / Revised: 21 March 2013 / Accepted: 22 March 2013 / Published: 8 April 2013
Cited by 8 | PDF Full-text (3537 KB) | HTML Full-text | XML Full-text
Abstract
This article proposes a simple and reliable damping strategy for wave powerfarm operation of small-scale point-absorber converters. The strategy is based on passiverectification onto a constant DC-link, making it very suitable for grid integration of the farm.A complete model of the system [...] Read more.
This article proposes a simple and reliable damping strategy for wave powerfarm operation of small-scale point-absorber converters. The strategy is based on passiverectification onto a constant DC-link, making it very suitable for grid integration of the farm.A complete model of the system has been developed in Matlab Simulink, and uses real sitedata as input. The optimal constant DC-voltage is evaluated as a function of the significantwave height and energy period of the waves. The total energy output of the WEC is derivedfor one year of experimental site data. The energy output is compared for two cases, onewhere the optimal DC-voltage is determined and held constant at half-hour basis throughoutthe year, and one where a selected value of the DC-voltage is kept constant throughout theyear regardless of sea state. Full article
(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)
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Open AccessArticle A New State of Charge Estimation Method for LiFePO4 Battery Packs Used in Robots
Energies 2013, 6(4), 2007-2030; doi:10.3390/en6042007
Received: 30 November 2012 / Revised: 11 March 2013 / Accepted: 13 March 2013 / Published: 8 April 2013
Cited by 13 | PDF Full-text (712 KB) | HTML Full-text | XML Full-text
Abstract
The accurate state of charge (SOC) estimation of the LiFePO4 battery packs used in robot applications is required for better battery life cycle, performance, reliability, and economic issues. In this paper, a new SOC estimation method, “Modified ECE + EKF”, is [...] Read more.
The accurate state of charge (SOC) estimation of the LiFePO4 battery packs used in robot applications is required for better battery life cycle, performance, reliability, and economic issues. In this paper, a new SOC estimation method, “Modified ECE + EKF”, is proposed. The method is the combination of the modified Equivalent Coulombic Efficiency (ECE) method and the Extended Kalman Filter (EKF) method. It is based on the zero-state hysteresis battery model, and adopts the EKF method to correct the initial value used in the Ah counting method. Experimental results show that the proposed technique is superior to the traditional techniques, such as ECE + EKF and ECE + Unscented Kalman Filter (UKF), and the accuracy of estimation is within 1%. Full article
(This article belongs to the Special Issue Li-ion Batteries and Energy Storage Devices)
Open AccessArticle Evaluation of a Model for Predicting the Tidal Velocity in Fjord Entrances
Energies 2013, 6(4), 2031-2051; doi:10.3390/en6042031
Received: 29 January 2013 / Revised: 29 March 2013 / Accepted: 30 March 2013 / Published: 9 April 2013
Cited by 2 | PDF Full-text (2691 KB) | HTML Full-text | XML Full-text
Abstract
Sufficiently accurate and low-cost estimation of tidal velocities is of importance when evaluating a potential site for a tidal energy farm. Here we suggest and evaluate a model to calculate the tidal velocity in fjord entrances. The model is compared with tidal [...] Read more.
Sufficiently accurate and low-cost estimation of tidal velocities is of importance when evaluating a potential site for a tidal energy farm. Here we suggest and evaluate a model to calculate the tidal velocity in fjord entrances. The model is compared with tidal velocities from Acoustic Doppler Current Profiler (ADCP) measurements in the tidal channel Skarpsundet in Norway. The calculated velocity value from the model corresponded well with the measured cross-sectional average velocity, but was shown to underestimate the velocity in the centre of the channel. The effect of this was quantified by calculating the kinetic energy of the flow for a 14-day period. A numerical simulation using TELEMAC-2D was performed and validated with ADCP measurements. Velocity data from the simulation was used as input for calculating the kinetic energy at various locations in the channel. It was concluded that the model presented here is not accurate enough for assessing the tidal energy resource. However, the simplicity of the model was considered promising in the use of finding sites where further analyses can be made. Full article
(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)
Open AccessArticle Optimizing the Production of Biodiesel Using Lipase Entrapped in Biomimetic Silica
Energies 2013, 6(4), 2052-2064; doi:10.3390/en6042052
Received: 21 March 2013 / Accepted: 29 March 2013 / Published: 10 April 2013
Cited by 6 | PDF Full-text (9278 KB) | HTML Full-text | XML Full-text
Abstract
We entrapped lipase from Pseudomonas cepacia in polyallylamine-mediated biomimetic silica, and then applied entrapped lipase to the synthesis of biodiesel with soybean oil or waste cooking oil as a feedstock. The effects of reaction temperature, substrate molar ratio (methanol/oil) and n-hexane [...] Read more.
We entrapped lipase from Pseudomonas cepacia in polyallylamine-mediated biomimetic silica, and then applied entrapped lipase to the synthesis of biodiesel with soybean oil or waste cooking oil as a feedstock. The effects of reaction temperature, substrate molar ratio (methanol/oil) and n-hexane content (w/w of oil) were evaluated using response surface methodology (RSM) combined with Box-Behnken design. The optimal reaction conditions for soybean oil were 43.6 °C, substrate molar ratio of 4.3%, and 75% n-hexane. The predicted and experimental values of biodiesel conversion were 79% and 76%, respectively. The optimal reaction conditions for waste cooking oil were 43.3 °C, substrate molar ratio of 5%, and 38% n-hexane. The predicted and experimental values of conversion were 68% and 67%, respectively. The conversion efficiency remained the same even after 1-month storage of entrapped lipase at 4 °C or room temperature. Full article
Open AccessArticle Estimating Energy- and Eco-Balances for Continuous Bio-Ethanol Production Using a Blenke Cascade System
Energies 2013, 6(4), 2065-2083; doi:10.3390/en6042065
Received: 29 January 2013 / Revised: 29 March 2013 / Accepted: 29 March 2013 / Published: 11 April 2013
PDF Full-text (468 KB) | HTML Full-text | XML Full-text
Abstract
Energy and environmental effects of wheat-based fuel, produced continuously by a Blenke cascade system, were assessed. Two scenarios: (1) no-co-products utilization scenario; and (2) co-products utilization scenario, were compared. A Life Cycle Assessment (LCA) model was used for analysis. The scope covered [...] Read more.
Energy and environmental effects of wheat-based fuel, produced continuously by a Blenke cascade system, were assessed. Two scenarios: (1) no-co-products utilization scenario; and (2) co-products utilization scenario, were compared. A Life Cycle Assessment (LCA) model was used for analysis. The scope covered a cradle-to-gate inventory. The results from energy analysis showed, that wheat-based ethanol has a positive average net energy value (NEV), NEV = 3.35 MJ/kg ethanol with an average net energy ratio (NER), NER = 1.14 MJ/MJ fossils for scenario 1, while for scenario 2, NEV = 20 MJ/kg ethanol with NER = 3.94 MJ/MJ fossils. The environmental performance analysis indicated that in scenario 1, the strongest contribution to environmental impacts was from the ethanol conversion stage; whereas in scenario 2, it was from wheat production stage. The use of a continuous fermentation system based on Blenke cascade is a promising technology that increases wheat based bio-ethanol’s energy benefits. In addition, the calculated parameters show the potential to significantly reduce emissions level. Full article
Open AccessArticle Design and Implement a Digital H∞ Robust Controller for a MW-Class PMSG-Based Grid-Interactive Wind Energy Conversion System
Energies 2013, 6(4), 2084-2109; doi:10.3390/en6042084
Received: 21 January 2013 / Revised: 19 March 2013 / Accepted: 2 April 2013 / Published: 16 April 2013
Cited by 13 | PDF Full-text (2288 KB) | HTML Full-text | XML Full-text
Abstract
A digital H∞ controller for a permanent magnet synchronous generator (PMSG) based wind energy conversion system (WECS) is presented. Wind energy is an uncertain fluctuating resource which requires a tight control management. So, it is still an exigent task for the control [...] Read more.
A digital H∞ controller for a permanent magnet synchronous generator (PMSG) based wind energy conversion system (WECS) is presented. Wind energy is an uncertain fluctuating resource which requires a tight control management. So, it is still an exigent task for the control design engineers. The conventional proportional-integral (PI) control is not ideal during high turbulence wind velocities, and the nonlinear behavior of the power converters. These are raising interest towards the robust control concepts. The robust design is to find a controller, for a given system, such that the closed-loop system becomes robust that assurance high-integrity and fault tolerant control system, robust H∞ control theory has befallen a standard design method of choice over the past two decades in industrial control applications. The robust H∞ control theory is also gaining eminence in the WECS. Due to the implementation complexity for the continuous H∞ controller, and availability of the high speedy micro-controllers, the design of a sample-data or a digital H∞ controller is very important for the realistic implementation. But there isn’t a single research to evaluate the performance of the digital H∞ controller for the WECS. In this paper, the proposed digital H∞ controller schemes comprise for the both generator and grid interactive power converters, and the control performances are compared with the conventional PI controller and the fuzzy controller. Simulation results confirm the efficacy of the proposed method Energies 2013, 6 2085 which are ensured the WECS stabilities, mitigate shaft stress, and improving the DC-link voltage and output power qualities. Full article
Open AccessArticle Assessing Tolerance-Based Robust Short-Term Load Forecasting in Buildings
Energies 2013, 6(4), 2110-2129; doi:10.3390/en6042110
Received: 18 January 2013 / Revised: 12 March 2013 / Accepted: 18 March 2013 / Published: 17 April 2013
Cited by 4 | PDF Full-text (357 KB) | HTML Full-text | XML Full-text
Abstract
Short-term load forecasting (STLF) in buildings differs from its broader counterpart in that the load to be predicted does not seem to be stationary, seasonal and regular but, on the contrary, it may be subject to sudden changes and variations on its [...] Read more.
Short-term load forecasting (STLF) in buildings differs from its broader counterpart in that the load to be predicted does not seem to be stationary, seasonal and regular but, on the contrary, it may be subject to sudden changes and variations on its consumption behaviour. Classical STLF methods do not react fast enough to these perturbations (i.e., they are not robust) and the literature on building STLF has not yet explored this area. Hereby, we evaluate a well-known post-processing method (Learning Window Reinitialization) applied to two broadly-used STLF algorithms (Autoregressive Model and Support Vector Machines) in buildings to check their adaptability and robustness. We have tested the proposed method with real-world data and our results state that this methodology is especially suited for buildings with non-regular consumption profiles, as classical STLF methods are enough to model regular-profiled ones. Full article
(This article belongs to the Special Issue Hybrid Advanced Techniques for Forecasting in Energy Sector)
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Open AccessArticle A New Two-Stage Approach to Short Term Electrical Load Forecasting
Energies 2013, 6(4), 2130-2148; doi:10.3390/en6042130
Received: 28 December 2012 / Revised: 11 March 2013 / Accepted: 1 April 2013 / Published: 18 April 2013
Cited by 2 | PDF Full-text (16348 KB) | HTML Full-text | XML Full-text
Abstract
In the deregulated energy market, the accuracy of load forecasting has a significant effect on the planning and operational decision making of utility companies. Electric load is a random non-stationary process influenced by a number of factors which make it difficult to [...] Read more.
In the deregulated energy market, the accuracy of load forecasting has a significant effect on the planning and operational decision making of utility companies. Electric load is a random non-stationary process influenced by a number of factors which make it difficult to model. To achieve better forecasting accuracy, a wide variety of models have been proposed. These models are based on different mathematical methods and offer different features. This paper presents a new two-stage approach for short-term electrical load forecasting based on least-squares support vector machines. With the aim of improving forecasting accuracy, one more feature was added to the model feature set, the next day average load demand. As this feature is unknown for one day ahead, in the first stage, forecasting of the next day average load demand is done and then used in the model in the second stage for next day hourly load forecasting. The effectiveness of the presented model is shown on the real data of the ISO New England electricity market. The obtained results confirm the validity advantage of the proposed approach. Full article
(This article belongs to the Special Issue Hybrid Advanced Techniques for Forecasting in Energy Sector)
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Open AccessArticle Single Switched Capacitor Battery Balancing System Enhancements
Energies 2013, 6(4), 2149-2174; doi:10.3390/en6042149
Received: 31 December 2012 / Revised: 31 January 2013 / Accepted: 11 March 2013 / Published: 18 April 2013
Cited by 11 | PDF Full-text (3199 KB) | HTML Full-text | XML Full-text
Abstract
Battery management systems (BMS) are a key element in electric vehicle energy storage systems. The BMS performs several functions concerning to the battery system, its key task being balancing the battery cells. Battery cell unbalancing hampers electric vehicles’ performance, with differing individual [...] Read more.
Battery management systems (BMS) are a key element in electric vehicle energy storage systems. The BMS performs several functions concerning to the battery system, its key task being balancing the battery cells. Battery cell unbalancing hampers electric vehicles’ performance, with differing individual cell voltages decreasing the battery pack capacity and cell lifetime, leading to the eventual failure of the total battery system. Quite a lot of cell balancing topologies have been proposed, such as shunt resistor, shuttling capacitor, inductor/transformer based and DC energy converters. The shuttling capacitor balancing systems in particular have not been subject to much research efforts however, due to their perceived low balancing speed and high cost. This paper tries to fill this gap by briefly discussing the shuttling capacitor cell balancing topologies, focusing on the single switched capacitor (SSC) cell balancing and proposing a novel procedure to improve the SSC balancing system performance. This leads to a new control strategy for the SSC system that can decrease the balancing system size, cost, balancing time and that can improve the SSC balancing system efficiency. Full article
Open AccessArticle Bio-Hydrogen Production from Pineapple Waste Extract by Anaerobic Mixed Cultures
Energies 2013, 6(4), 2175-2190; doi:10.3390/en6042175
Received: 27 December 2012 / Revised: 7 March 2013 / Accepted: 2 April 2013 / Published: 18 April 2013
Cited by 5 | PDF Full-text (449 KB) | HTML Full-text | XML Full-text
Abstract
A statistical experimental design was employed to optimize factors that affect the production of hydrogen from the glucose contained in pineapple waste extract by anaerobic mixed cultures. Results from Plackett-Burman design indicated that substrate concentration, initial pH and FeSO4 concentration had [...] Read more.
A statistical experimental design was employed to optimize factors that affect the production of hydrogen from the glucose contained in pineapple waste extract by anaerobic mixed cultures. Results from Plackett-Burman design indicated that substrate concentration, initial pH and FeSO4 concentration had a statistically significant (p ≤ 0.05) influence on the hydrogen production potential (Ps) and the specific hydrogen production rate (SHPR). The path of steepest ascent was undertaken to approach the optimal region of these three significant factors which was then optimized using response surface methodology (RSM) with central composite design (CCD). The presence of a substrate concentration of 25.76 g-total sugar/L, initial pH of 5.56, and FeSO4 concentration of 0.81 g/L gave a maximum predicted Ps of 5489 mL H2/L, hydrogen yield of 1.83 mol H2/mol glucose, and SHPR of 77.31 mL H2/g-volatile suspended solid (VSS) h. A verification experiment indicated highly reproducible results with the observed Ps and SHPR being only 1.13% and 1.14% different from the predicted values. Full article
Open AccessArticle Modeling Evaluation of Tidal Stream Energy and the Impacts of Energy Extraction on Hydrodynamics in the Taiwan Strait
Energies 2013, 6(4), 2191-2203; doi:10.3390/en6042191
Received: 7 February 2013 / Revised: 13 April 2013 / Accepted: 14 April 2013 / Published: 18 April 2013
Cited by 4 | PDF Full-text (1535 KB) | HTML Full-text | XML Full-text
Abstract
Tidal stream speeds in straits are accelerated because of geographic and bathymetric features. For instance, narrow channels and shallows can cause high tidal stream energy. In this study, water level and tidal current were simulated using a three-dimensional semi-implicit Eulerian-Lagrangian finite-element model [...] Read more.
Tidal stream speeds in straits are accelerated because of geographic and bathymetric features. For instance, narrow channels and shallows can cause high tidal stream energy. In this study, water level and tidal current were simulated using a three-dimensional semi-implicit Eulerian-Lagrangian finite-element model to investigate the complex tidal characteristics in the Taiwan Strait and to determine potential locations for harnessing tidal stream energy. The model was driven by nine tidal components (M2, S2, N2, K2, K1, O1, P1, Q1, and M4) at open boundaries. The modeling results were validated with the measured data, including water level and tidal current. Through the model simulations, we found that the highest tidal currents occurred at the Penghu Channel in the Taiwan Strait. The Penghu Channel is an appropriate location for the deployment of a tidal turbine array because of its deep and flat bathymetry. The impacts of energy extraction on hydrodynamics were assessed by considering the momentum sink approach. The simulated results indicate that only minimal impacts would occur on water level and tidal current in the Taiwan Strait if a turbine array (55 turbines) was installed in the Penghu Channel. Full article
(This article belongs to the Special Issue Energy from the Ocean - Wave and Tidal Energy)
Open AccessArticle On the Feasibility of Using Poles Computed from Frequency Domain Spectroscopy to Assess Oil Impregnated Paper Insulation Conditions
Energies 2013, 6(4), 2204-2220; doi:10.3390/en6042204
Received: 28 January 2013 / Revised: 18 March 2013 / Accepted: 21 March 2013 / Published: 18 April 2013
Cited by 12 | PDF Full-text (357 KB) | HTML Full-text | XML Full-text
Abstract
Frequency Domain Spectroscopy (FDS) is an effective tool allowing assessing the condition of oil-paper insulation system in power equipment. However, results from these measurements are known to be greatly influenced by various parameters, including insulation aging, moisture content, and insulation geometry/volume, together [...] Read more.
Frequency Domain Spectroscopy (FDS) is an effective tool allowing assessing the condition of oil-paper insulation system in power equipment. However, results from these measurements are known to be greatly influenced by various parameters, including insulation aging, moisture content, and insulation geometry/volume, together with environmental condition such as temperature. In this contribution, a series of experiments have been performed under controlled laboratory conditions. The dielectric response of the oil impregnated paper, along with the degree of polymerization and moisture content, were monitored. Since dielectric parameters are geometry dependent, poles (independent of the geometry) which depends on resistivity and permittivity, were considered to assess the condition of the insulation. From the investigations performed on new and aged samples, it is shown that poles (P) can be regarded as insulation aging indicator. It is also shown that a per unit value based on the Dielectric Dissipation Factor (DDF), measured in the frequency range from 1 to 1000 Hz can be correlated to moisture content in the insulation paper. Full article
Open AccessArticle Economic Modeling of Compressed Air Energy Storage
Energies 2013, 6(4), 2221-2241; doi:10.3390/en6042221
Received: 24 January 2013 / Revised: 26 February 2013 / Accepted: 21 March 2013 / Published: 18 April 2013
Cited by 6 | PDF Full-text (472 KB) | HTML Full-text | XML Full-text
Abstract
Due to the variable nature of wind resources, the increasing penetration level of wind power will have a significant impact on the operation and planning of the electric power system. Energy storage systems are considered an effective way to compensate for the [...] Read more.
Due to the variable nature of wind resources, the increasing penetration level of wind power will have a significant impact on the operation and planning of the electric power system. Energy storage systems are considered an effective way to compensate for the variability of wind generation. This paper presents a detailed production cost simulation model to evaluate the economic value of compressed air energy storage (CAES) in systems with large-scale wind power generation. The co-optimization of energy and ancillary services markets is implemented in order to analyze the impacts of CAES, not only on energy supply, but also on system operating reserves. Both hourly and 5-minute simulations are considered to capture the economic performance of CAES in the day-ahead (DA) and real-time (RT) markets. The generalized network flow formulation is used to model the characteristics of CAES in detail. The proposed model is applied on a modified IEEE 24-bus reliability test system. The numerical example shows that besides the economic benefits gained through energy arbitrage in the DA market, CAES can also generate significant profits by providing reserves, compensating for wind forecast errors and intra-hour fluctuation, and participating in the RT market. Full article
Open AccessArticle Torsional Stiffness Effects on the Dynamic Stability of a Horizontal Axis Wind Turbine Blade
Energies 2013, 6(4), 2242-2261; doi:10.3390/en6042242
Received: 23 January 2013 / Revised: 14 March 2013 / Accepted: 3 April 2013 / Published: 19 April 2013
Cited by 6 | PDF Full-text (943 KB) | HTML Full-text | XML Full-text
Abstract
Aeroelastic instability problems have become an increasingly important issue due to the increased use of larger horizontal axis wind turbines. To maintain these large structures in a stable manner, the blade design process should include studies on the dynamic stability of the [...] Read more.
Aeroelastic instability problems have become an increasingly important issue due to the increased use of larger horizontal axis wind turbines. To maintain these large structures in a stable manner, the blade design process should include studies on the dynamic stability of the wind turbine blade. Therefore, fluid-structure interaction analyses of the large-scaled wind turbine blade were performed with a focus on dynamic stability in this study. A finite element method based on the large deflection beam theory is used for structural analysis considering the geometric nonlinearities. For the stability analysis, a proposed aerodynamic approach based on Greenberg’s extension of Theodorsen’s strip theory and blade element momentum method were employed in conjunction with a structural model. The present methods proved to be valid for estimations of the aerodynamic responses and blade behavior compared with numerical results obtained in the previous studies. Additionally, torsional stiffness effects on the dynamic stability of the wind turbine blade were investigated. It is demonstrated that the damping is considerably influenced by variations of the torsional stiffness. Also, in normal operating conditions, the destabilizing phenomena were observed to occur with low torsional stiffness. Full article
Open AccessArticle Energy Management and Smart Grids
Energies 2013, 6(4), 2262-2290; doi:10.3390/en6042262
Received: 14 January 2013 / Revised: 18 March 2013 / Accepted: 19 March 2013 / Published: 22 April 2013
Cited by 24 | PDF Full-text (1724 KB) | HTML Full-text | XML Full-text
Abstract
The paper outlines energy management concepts and the smart grid evolution. The necessity of considering energy management as a crucial innovation in load supplying to permit a more powerful penetration of renewable energy usage at the building and city level and to [...] Read more.
The paper outlines energy management concepts and the smart grid evolution. The necessity of considering energy management as a crucial innovation in load supplying to permit a more powerful penetration of renewable energy usage at the building and city level and to perform energy savings and CO2 emissions reduction is pointed out. The driving factors to enhance the current power distribution are presented, and the benefits concerning smart grids are underlined. In the paper, a specific energy management analysis is reported by considering all the electric value chain, and the demand-side management and distributed on site control actions are described. To verify the benefit of energy management control actions, a house simulator and a grid simulator are here presented and the results discussed in three different scenarios. Moreover, in the paper, the evaluation of ecological benefits are reported, and a cost benefit analysis of the energy management system is performed. Results pointed out that with the standard control actions, the system is not economic for the end user, and only by using energy management systems with renewable energy, in site production remunerative energy savings can be reached. Finally the evolution of smart grids is presented, focusing on potential benefits and technical problems. The active grids, microgrids and virtual utility are described, and final consideration on hypothetical scenarios is presented in the conclusion. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
Open AccessArticle Effect of Burnable Absorbers on Inert Matrix Fuel Performance and Transuranic Burnup in a Low Power Density Light-Water Reactor
Energies 2013, 6(4), 2291-2304; doi:10.3390/en6042291
Received: 21 January 2013 / Revised: 20 March 2013 / Accepted: 4 April 2013 / Published: 22 April 2013
PDF Full-text (1821 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Zirconium dioxide has received particular attention as a fuel matrix because of its ability to form a solid solution with transuranic elements, natural radiation stability and desirable mechanical properties. However, zirconium dioxide has a lower coefficient of thermal conductivity than uranium dioxide [...] Read more.
Zirconium dioxide has received particular attention as a fuel matrix because of its ability to form a solid solution with transuranic elements, natural radiation stability and desirable mechanical properties. However, zirconium dioxide has a lower coefficient of thermal conductivity than uranium dioxide and this presents an obstacle to the deployment of these fuels in commercial reactors. Here we show that axial doping of a zirconium dioxide based fuel with erbium reduces power peaking and fuel temperature. Full core simulations of a modified AP1000 core were done using MCNPX 2.7.0. The inert matrix fuel contained 15 w/o transuranics at its beginning of life and constituted 28% of the assemblies in the core. Axial doping reduced power peaking at startup by more than ~23% in the axial direction and reduced the peak to average power within the core from 1.80 to 1.44. The core was able to remain critical between refueling while running at a simulated 2000 MWth on an 18 month refueling cycle. The results show that the reactor would maintain negative core average reactivity and void coefficients during operation. This type of fuel cycle would reduce the overall production of transuranics in a pressurized water reactor by 86%. Full article
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Open AccessArticle Comparative Study of Dynamic Programming and Pontryagin’s Minimum Principle on Energy Management for a Parallel Hybrid Electric Vehicle
Energies 2013, 6(4), 2305-2318; doi:10.3390/en6042305
Received: 23 January 2013 / Revised: 1 April 2013 / Accepted: 11 April 2013 / Published: 22 April 2013
Cited by 30 | PDF Full-text (448 KB) | HTML Full-text | XML Full-text
Abstract
This paper compares two optimal energy management methods for parallel hybrid electric vehicles using an Automatic Manual Transmission (AMT). A control-oriented model of the powertrain and vehicle dynamics is built first. The energy management is formulated as a typical optimal control problem [...] Read more.
This paper compares two optimal energy management methods for parallel hybrid electric vehicles using an Automatic Manual Transmission (AMT). A control-oriented model of the powertrain and vehicle dynamics is built first. The energy management is formulated as a typical optimal control problem to trade off the fuel consumption and gear shifting frequency under admissible constraints. The Dynamic Programming (DP) and Pontryagin’s Minimum Principle (PMP) are applied to obtain the optimal solutions. Tuning with the appropriate co-states, the PMP solution is found to be very close to that from DP. The solution for the gear shifting in PMP has an algebraic expression associated with the vehicular velocity and can be implemented more efficiently in the control algorithm. The computation time of PMP is significantly less than DP. Full article

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