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Energies, Volume 7, Issue 9 (September 2014), Pages 5502-6224

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Open AccessArticle Modeling and Analysis of Transport Processes and Efficiency of Combined SOFC and PEMFC Systems
Energies 2014, 7(9), 5502-5522; doi:10.3390/en7095502
Received: 20 May 2014 / Revised: 12 August 2014 / Accepted: 19 August 2014 / Published: 25 August 2014
Cited by 3 | PDF Full-text (6114 KB) | HTML Full-text | XML Full-text
Abstract
A hybrid fuel cell system (~10 kWe) for an average family house including heating is proposed. The investigated system comprises a Solid Oxide Fuel Cell (SOFC) on top of a Polymer Electrolyte Fuel Cell (PEFC). Hydrogen produced from the off-gases of the [...] Read more.
A hybrid fuel cell system (~10 kWe) for an average family house including heating is proposed. The investigated system comprises a Solid Oxide Fuel Cell (SOFC) on top of a Polymer Electrolyte Fuel Cell (PEFC). Hydrogen produced from the off-gases of the SOFC can be fed directly to the PEFC. Simulations for the proposed system were conducted using different fuels. Here, results for natural gas (NG), dimethyl ether (DME) and ethanol as a fuel are presented and analysed. Behaviour of the proposed system is further investigated by comparing the effects of key factors such as utilisation factor, operating conditions, oxygen-to-carbon (O/C) ratios and fuel preheating effects on these fuels. The combined system improves the overall electrical conversion efficiency compared with standalone PEFC or SOFC systems. For the combined SOFC and PEFC system, the overall power production was increased by 8%–16% and the system efficiency with one of the fuels is found to be 12% higher than that of the standalone SOFC system. Full article
(This article belongs to the Special Issue Reacting Transport Phenomena in Solid Oxide Fuel Cells)
Open AccessArticle Predictive Densities for Day-Ahead Electricity Prices Using Time-Adaptive Quantile Regression
Energies 2014, 7(9), 5523-5547; doi:10.3390/en7095523
Received: 1 May 2014 / Revised: 30 July 2014 / Accepted: 15 August 2014 / Published: 25 August 2014
Cited by 8 | PDF Full-text (1271 KB) | HTML Full-text | XML Full-text
Abstract
A large part of the decision-making problems actors of the power system are facing on a daily basis requires scenarios for day-ahead electricity market prices. These scenarios are most likely to be generated based on marginal predictive densities for such prices, then [...] Read more.
A large part of the decision-making problems actors of the power system are facing on a daily basis requires scenarios for day-ahead electricity market prices. These scenarios are most likely to be generated based on marginal predictive densities for such prices, then enhanced with a temporal dependence structure. A semi-parametric methodology for generating such densities is presented: it includes: (i) a time-adaptive quantile regression model for the 5%–95% quantiles; and (ii) a description of the distribution tails with exponential distributions. The forecasting skill of the proposed model is compared to that of four benchmark approaches and the well-known the generalist autoregressive conditional heteroskedasticity (GARCH) model over a three-year evaluation period. While all benchmarks are outperformed in terms of forecasting skill overall, the superiority of the semi-parametric model over the GARCH model lies in the former’s ability to generate reliable quantile estimates. Full article
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Open AccessArticle Performance of Siloxane Mixtures in a High-Temperature Organic Rankine Cycle Considering the Heat Transfer Characteristics during Evaporation
Energies 2014, 7(9), 5548-5565; doi:10.3390/en7095548
Received: 30 June 2014 / Revised: 5 August 2014 / Accepted: 18 August 2014 / Published: 26 August 2014
Cited by 9 | PDF Full-text (2243 KB) | HTML Full-text | XML Full-text
Abstract
The application of the Organic Rankine Cycle to high temperature heat sources is investigated on the case study of waste heat recovery from a selected biogas plant. Two different modes of operation are distinguished: pure electric power and combined heat and power [...] Read more.
The application of the Organic Rankine Cycle to high temperature heat sources is investigated on the case study of waste heat recovery from a selected biogas plant. Two different modes of operation are distinguished: pure electric power and combined heat and power generation. The siloxanes hexamethyldisiloxane (MM) and octamethyltrisiloxane (MDM) are chosen as working fluids. Moreover, the effect of using mixtures of these components is analysed. Regarding pure electricity generation, process simulations using the simulation tool Aspen Plus show an increase in second law efficiency of 1.3% in case of 97/03 wt % MM/MDM-mixture, whereas for the combined heat and power mode a 60/40 wt % MM/MDM-mixture yields the highest efficiency with an increase of nearly 3% compared to most efficient pure fluid. Next to thermodynamic analysis, measurements of heat transfer coefficients of these siloxanes as well as their mixtures are conducted and Kandlikar’s correlation is chosen to describe the results. Based on that, heat exchanger areas for preheater and evaporator are calculated in order to check whether the poorer heat transfer characteristics of mixtures devalue their efficiency benefit due to increased heat transfer areas. Results show higher heat transfer areas of 0.9% and 14%, respectively, compared to MM. Full article
(This article belongs to the Special Issue Waste Heat Recovery—Strategy and Practice)
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Open AccessArticle Differential Protection for an Outgoing Transformer of Large-Scale Doubly Fed Induction Generator-Based Wind Farms
Energies 2014, 7(9), 5566-5585; doi:10.3390/en7095566
Received: 20 June 2014 / Revised: 20 August 2014 / Accepted: 21 August 2014 / Published: 26 August 2014
Cited by 3 | PDF Full-text (1113 KB) | HTML Full-text | XML Full-text
Abstract
With the rapid development of wind energy, relay protection for large-scale wind farms has been attracting some researchers, due to the absence of standards. Based on the large-scale doubly fed induction generator (DFIG)-based wind farms located in Gansu Province, China, this paper [...] Read more.
With the rapid development of wind energy, relay protection for large-scale wind farms has been attracting some researchers, due to the absence of standards. Based on the large-scale doubly fed induction generator (DFIG)-based wind farms located in Gansu Province, China, this paper studies the differential protection for the outgoing power transformer of large-scale DFIG-based wind farms. According to the equivalent circuit of the power grid integrated with wind farms, the main frequency components of current and voltage during faults are identified mathematically and then verified by simulations. The results show that the frequencies of current and voltage at the terminals of outgoing transmission lines are inconsistent. Following the feature of frequency inconsistency, the adaptability of differential protection is analyzed, and it is found that differential protection for an outgoing transformer in large-scale wind farms may fail once ignoring the frequency inconsistency. Simulation studies demonstrate that inconsistent frequency characteristics will deteriorate the sensitivity and reliability of differential protection. Finally, several suggestions are provided for improving the performance of relay protections for large-scale DFIG-based wind farms. Full article
Open AccessArticle Effect of Torrefaction on the Properties of Corn Stalk to Enhance Solid Fuel Qualities
Energies 2014, 7(9), 5586-5600; doi:10.3390/en7095586
Received: 19 June 2014 / Revised: 11 August 2014 / Accepted: 21 August 2014 / Published: 27 August 2014
Cited by 4 | PDF Full-text (294 KB) | HTML Full-text | XML Full-text
Abstract
This study presents the effects of torrefaction on the basic characteristics of corn stalks. Corn stalks were torrefied in a horizontal tubular reactor at temperatures ranging from 150 °C to 400 °C, for torrefaction periods varying from 0 min to 50 min. [...] Read more.
This study presents the effects of torrefaction on the basic characteristics of corn stalks. Corn stalks were torrefied in a horizontal tubular reactor at temperatures ranging from 150 °C to 400 °C, for torrefaction periods varying from 0 min to 50 min. The torrefied corn stalk products were characterized in terms of their elemental composition, energy yield, ash content, and volatile fraction. The gaseous products were also analyzed. Thermogravimetric analysis (TGA) of the samples was carried out in order to obtain the apparent activation energy for the torrefaction of corn stalks. The weight loss data according to the degradation temperature were analyzed using three different methods. The energy and mass yield were found to decrease with an increase in the temperature, whereas the higher heating value (HHV) increased. From this work, it was found that the compounds with oxygen were emitted at a temperature lower than that for hydrocarbon gases and the temperatures of 290–330 °C were the optimum torrefaction temperatures for corn stalks. Full article
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Open AccessArticle The Global Surge in Energy Innovation
Energies 2014, 7(9), 5601-5623; doi:10.3390/en7095601
Received: 26 June 2014 / Revised: 8 August 2014 / Accepted: 20 August 2014 / Published: 27 August 2014
Cited by 1 | PDF Full-text (753 KB) | HTML Full-text | XML Full-text
Abstract
Policymakers are seeking a transformation of the energy system driven by concerns about climate change, energy security and affordability. At the same time, emerging developments in underpinning science and engineering are opening up new possibilities across the whole technology spectrum covering renewables [...] Read more.
Policymakers are seeking a transformation of the energy system driven by concerns about climate change, energy security and affordability. At the same time, emerging developments in underpinning science and engineering are opening up new possibilities across the whole technology spectrum covering renewables and other supply side technologies, energy demand and energy infrastructure. This paper reviews both the “policy pull” for energy innovation activities and the “science and technology push”. It explores the expectations of a variety of organisations in both the public and private sector regarding these pressures and possibilities by assessing various scenarios and outlook exercises that have been published since 2013. It reveals a wide range of beliefs about the future development of the energy system. The paper then moves on to analyse private sector expenditure on energy research and development (R&D) and public sector budgets for energy R&D and demonstration (RD&D). This analysis demonstrates significant divergences in patterns of innovation between the private and public sectors and leads to the hypothesis that the private sector is, broadly, taking measures to reinforce the existing energy paradigm while the public sector is focusing on new energy technologies that support wider policy objectives. This pattern is consistent with past technological transitions, with innovation efforts that would transform the energy system being counteracted by countervailing efforts that reinforce the existing fossil fuel-based paradigm. Full article
(This article belongs to the Special Issue Sustainable Energy Innovation: Strategies to Accelerate Progress)
Open AccessArticle A Model-Free Approach for Maximizing Power Production of Wind Farm Using Multi-Resolution Simultaneous Perturbation Stochastic Approximation
Energies 2014, 7(9), 5624-5646; doi:10.3390/en7095624
Received: 16 May 2014 / Revised: 15 August 2014 / Accepted: 19 August 2014 / Published: 27 August 2014
Cited by 4 | PDF Full-text (3002 KB) | HTML Full-text | XML Full-text
Abstract
This paper provides a model-free approach based on the Multi-Resolution Simultaneous Perturbation Stochastic Approximation (MR-SPSA) for maximizing power production of wind farms. The main advantage is that the method based on MR-SPSA can achieve fast controller tuning without any plant model by [...] Read more.
This paper provides a model-free approach based on the Multi-Resolution Simultaneous Perturbation Stochastic Approximation (MR-SPSA) for maximizing power production of wind farms. The main advantage is that the method based on MR-SPSA can achieve fast controller tuning without any plant model by exploiting the information of the wind farm configuration such as turbines location and wind direction. In order to simulate the performance of the model-free scheme, a wind farm model with dynamic characterization of wake interaction between turbines is used and then the proposed method is applied to the Horns Rev wind farm. Simulation results illustrate that the method based on MR-SPSA achieves the maximum total power production with faster convergence compared with other existing model-free methods. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
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Open AccessArticle Modeling Analysis of Bi-Layer Ni-(ZrO2)x(Y2O3)1−x Anodes for Anode-Supported Intermediate Temperature-Solid Oxide Fuel Cells
Energies 2014, 7(9), 5647-5674; doi:10.3390/en7095647
Received: 26 June 2014 / Revised: 1 August 2014 / Accepted: 1 August 2014 / Published: 28 August 2014
Cited by 3 | PDF Full-text (1160 KB) | HTML Full-text | XML Full-text
Abstract
Intermediate temperature-solid oxide fuel cell (IT-SOFC) Ni-(ZrO2)x(Y2O3)1−x (Ni-YSZ) anodes formed by two layers, with different thicknesses and morphologies, offer the possibility of obtaining adequate electrochemical performance coupled to satisfactory mechanical properties. We [...] Read more.
Intermediate temperature-solid oxide fuel cell (IT-SOFC) Ni-(ZrO2)x(Y2O3)1−x (Ni-YSZ) anodes formed by two layers, with different thicknesses and morphologies, offer the possibility of obtaining adequate electrochemical performance coupled to satisfactory mechanical properties. We investigate bi-layered Ni-YSZ anodes from a modeling point of view. The model includes reaction kinetics (Butler-Volmer equation), mass transport (Dusty-Gas model), and charge transport (Ohm’s law), and allows to gain an insight into the distribution of the electrochemical reaction within the electrode. Additionally, the model allows to evaluate a reciprocal overall electrode resistance 1/Rp ≈ 6 S·cm−2 for a bi-layer electrode formed by a 10 µm thick active layer (AL) composed of 0.25 µm radius Ni and YSZ particles (34% vol. Ni), coupled to a 700 µm thick support layer (SL) formed by 0.5 µm radius Ni and YSZ particles (50% vol. Ni), and operated at a temperature of 1023 K. Simulation results compare satisfactorily to literature experimental data. The model allows to investigate, in detail, the effect of morphological and geometric parameters on the various sources of losses, which is the first step for an optimized electrode design. Full article
(This article belongs to the Special Issue Reacting Transport Phenomena in Solid Oxide Fuel Cells)
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Open AccessArticle An Acausal Li-Ion Battery Pack Model for Automotive Applications
Energies 2014, 7(9), 5675-5700; doi:10.3390/en7095675
Received: 24 July 2014 / Revised: 13 August 2014 / Accepted: 19 August 2014 / Published: 28 August 2014
Cited by 8 | PDF Full-text (3031 KB) | HTML Full-text | XML Full-text
Abstract
In this work, a novel acausal and reconfigurable battery pack model is presented. The model structure adopted for the battery cell is based on an equivalent circuit representation. The circuit elements are modified to take account of both hysteresis and diffusion limitation. [...] Read more.
In this work, a novel acausal and reconfigurable battery pack model is presented. The model structure adopted for the battery cell is based on an equivalent circuit representation. The circuit elements are modified to take account of both hysteresis and diffusion limitation. The latter is known to be a nonlinear function of large operating currents or long operating times. It is shown that the integration of a current dependent time constant within the cell model better emulates the solid diffusional dynamics of lithium intercalation into the active material under large electrical loads. The advantages of an acausal modeling approach, when scaling-up individual cell models into a complete battery system are also presented. Particular consideration is given to emulating the impact of cell to cell variations on pack performance. Using statistical analysis of battery tests, cell model parameter variations are characterized and quantified. The cell and scaled-up pack model are parameterized for a number of commercially available cell formats, energy capacities and chemistries. The new models are validated using transient, real-world, electrical data measured from an electric vehicle (EV) operating within an urban environment. Full article
(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)
Open AccessArticle Performance of a Small-Scale, Variable Temperature Fixed Dome Digester in a Temperate Climate
Energies 2014, 7(9), 5701-5716; doi:10.3390/en7095701
Received: 4 June 2014 / Revised: 17 July 2014 / Accepted: 6 August 2014 / Published: 1 September 2014
PDF Full-text (860 KB) | HTML Full-text | XML Full-text
Abstract
Small-scale digesters, similar to popular Chinese designs, have the potential to address the energy needs of smaller dairy farmers in temperate U.S. climates. To assess this potential, a 1.14 m3 (300 gallon) modified fixed-dome digester was installed and operated, at variable [...] Read more.
Small-scale digesters, similar to popular Chinese designs, have the potential to address the energy needs of smaller dairy farmers in temperate U.S. climates. To assess this potential, a 1.14 m3 (300 gallon) modified fixed-dome digester was installed and operated, at variable temperatures (5.3 to 27.9 °C) typical of the Midwestern United States, from March 2010 to March 2011 (363 days). Temperature, gas production, and other variables were recorded. The system was fed with dilute dairy manure with 6% volatile solids (VS) and an organic loading rate (OLR) ranging from 0.83 to 2.43 kg volatile solids (VS)/m3/day. The system was loaded with no interruption and exhibited no signs of inhibition from July 2010 to mid-November 2010 (129 days). During this period the digester temperature was over 20 °C with an average daily biogas production of 842 ± 69 L/day, a methane yield of 0.168 m3/kg VS added, and a Volatile Solids reduction of 36%. After the temperature dropped below 20 °C, the digester showed signs of inhibition and soured. These findings suggest that an ambient temperature, modified fixed dome digester could operate without temperature inhibition for approximately six months (169 days) a year in a temperate climate when digester temperatures exceed 20 °C. However, during colder months the digester temperature must maintained above 20 °C for viable gas production year round. Full article
Open AccessArticle Implications of Stably Stratified Atmospheric Boundary Layer Turbulence on the Near-Wake Structure of Wind Turbines
Energies 2014, 7(9), 5740-5763; doi:10.3390/en7095740
Received: 22 July 2014 / Revised: 21 August 2014 / Accepted: 26 August 2014 / Published: 2 September 2014
Cited by 3 | PDF Full-text (9229 KB) | HTML Full-text | XML Full-text
Abstract
Turbulence structure in the wake behind a full-scale horizontal-axis wind turbine under the influence of real-time atmospheric inflow conditions has been investigated using actuator-line-model based large-eddy-simulations. Precursor atmospheric boundary layer (ABL) simulations have been performed to obtain mean and turbulence states of [...] Read more.
Turbulence structure in the wake behind a full-scale horizontal-axis wind turbine under the influence of real-time atmospheric inflow conditions has been investigated using actuator-line-model based large-eddy-simulations. Precursor atmospheric boundary layer (ABL) simulations have been performed to obtain mean and turbulence states of the atmosphere under stable stratification subjected to two different cooling rates. Wind turbine simulations have revealed that, in addition to wind shear and ABL turbulence, height-varying wind angle and low-level jets are ABL metrics that influence the structure of the turbine wake. Increasing stability results in shallower boundary layers with stronger wind shear, steeper vertical wind angle gradients, lower turbulence, and suppressed vertical motions. A turbulent mixing layer forms downstream of the wind turbines, the strength and size of which decreases with increasing stability. Height dependent wind angle and turbulence are the ABL metrics influencing the lateral wake expansion. Further, ABL metrics strongly impact the evolution of tip and root vortices formed behind the rotor. Two factors play an important role in wake meandering: tip vortex merging due to the mutual inductance form of instability and the corresponding instability of the turbulent mixing layer. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
Open AccessArticle Evaluation of Mechanically and Adhesively Fixed External Insulation Systems Using Vacuum Insulation Panels for High-Rise Apartment Buildings
Energies 2014, 7(9), 5764-5786; doi:10.3390/en7095764
Received: 12 June 2014 / Revised: 19 August 2014 / Accepted: 26 August 2014 / Published: 3 September 2014
Cited by 3 | PDF Full-text (2160 KB) | HTML Full-text | XML Full-text
Abstract
Buildings account for a significant portion of a nation’s total energy consumption. To meet the global demand for greater energy efficiency, many countries are drastically strengthening insulation regulations for buildings. Thus, dramatically thicker wall insulation may be required, which can adversely affect [...] Read more.
Buildings account for a significant portion of a nation’s total energy consumption. To meet the global demand for greater energy efficiency, many countries are drastically strengthening insulation regulations for buildings. Thus, dramatically thicker wall insulation may be required, which can adversely affect the value of a building by reducing its effective floor area. Hence, high-performance insulation materials, such as vacuum insulation panels (VIPs), are of interest in building design. In this study, external insulation systems using VIPs were examined to determine their effectiveness in high-performance insulation systems for high-rise apartment buildings. A variety of mechanically and adhesively fixed external insulation systems with various insulation layer compositions have been proposed as alternatives to conventional internal insulation systems. The performance of conventional insulation systems and the proposed alternatives were compared through three-dimensional heat transfer simulations. The construction costs and the ease of installation of the various systems were also compared. The overall performance of each alternative in terms of the insulation performance, construction costs, and ease of installation was thus evaluated to determine the most effective alternative. Full article
(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)
Open AccessArticle Optimization Models and Methods for Demand-Side Management of Residential Users: A Survey
Energies 2014, 7(9), 5787-5824; doi:10.3390/en7095787
Received: 31 May 2014 / Revised: 5 August 2014 / Accepted: 25 August 2014 / Published: 4 September 2014
Cited by 17 | PDF Full-text (1343 KB) | HTML Full-text | XML Full-text
Abstract
The residential sector is currently one of the major contributors to the global energy balance. However, the energy demand of residential users has been so far largely uncontrollable and inelastic with respect to the power grid conditions. With the massive introduction of [...] Read more.
The residential sector is currently one of the major contributors to the global energy balance. However, the energy demand of residential users has been so far largely uncontrollable and inelastic with respect to the power grid conditions. With the massive introduction of renewable energy sources and the large variations in energy flows, also the residential sector is required to provide some flexibility in energy use so as to contribute to the stability and efficiency of the electric system. To address this issue, demand management mechanisms can be used to optimally manage the energy resources of customers and their energy demand profiles. A very promising technique is represented by demand-side management (DSM), which consists in a proactive method aimed at making users energy-efficient in the long term. In this paper, we survey the most relevant studies on optimization methods for DSM of residential consumers. Specifically, we review the related literature according to three axes defining contrasting characteristics of the schemes proposed: DSM for individual users versus DSM for cooperative consumers, deterministic DSM versus stochastic DSM and day-ahead DSM versus real-time DSM. Based on this classification, we provide a big picture of the key features of different approaches and techniques and discuss future research directions. Full article
(This article belongs to the Special Issue Microgrids)
Open AccessArticle Comparative Study of Two Daylighting Analysis Methods with Regard to Window Orientation and Interior Wall Reflectance
Energies 2014, 7(9), 5825-5846; doi:10.3390/en7095825
Received: 8 May 2014 / Revised: 8 August 2014 / Accepted: 2 September 2014 / Published: 5 September 2014
Cited by 4 | PDF Full-text (2709 KB) | HTML Full-text | XML Full-text
Abstract
The accuracy and speed of the daylighting analysis developed for use in EnergyPlus is better than its predecessors. In EnergyPlus, the detailed method uses the Split-flux algorithm whereas the DElight method uses the Radiosity algorithm. Many existing studies have addressed the two [...] Read more.
The accuracy and speed of the daylighting analysis developed for use in EnergyPlus is better than its predecessors. In EnergyPlus, the detailed method uses the Split-flux algorithm whereas the DElight method uses the Radiosity algorithm. Many existing studies have addressed the two methods, either individually or compared with other daylight analysis methods like Ray tracing but still there is lack of detailed comparative study of these two methods. Our previous studies show that the Split-flux method overestimates the illuminance, especially for the areas away from the window. The Radiosity method has the advantage of accurately predicting this illuminance because of how it deals with the diffuse light. For this study, the EnergyPlus model, which has been calibrated using data measured in a real building in previous studies, has also been used. The calibrated model has a south oriented window only. This model is then used to analyze the interior illuminance inside the room for north, west and east orientation of the window by rotating the model and by changing the wall reflectance of the model with south oriented window. Direct and diffuse component of the illuminance as well as the algorithms have been compared for a detailed analysis. Full article
(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)
Open AccessArticle Improving Wind Farm Dispatchability Using Model Predictive Control for Optimal Operation of Grid-Scale Energy Storage
Energies 2014, 7(9), 5847-5862; doi:10.3390/en7095847
Received: 19 June 2014 / Revised: 21 August 2014 / Accepted: 21 August 2014 / Published: 5 September 2014
Cited by 1 | PDF Full-text (2958 KB) | HTML Full-text | XML Full-text
Abstract
This paper demonstrates the use of model-based predictive control for energy storage systems to improve the dispatchability of wind power plants. Large-scale wind penetration increases the variability of power flow on the grid, thus increasing reserve requirements. Large energy storage systems collocated [...] Read more.
This paper demonstrates the use of model-based predictive control for energy storage systems to improve the dispatchability of wind power plants. Large-scale wind penetration increases the variability of power flow on the grid, thus increasing reserve requirements. Large energy storage systems collocated with wind farms can improve dispatchability of the wind plant by storing energy during generation over-the-schedule and sourcing energy during generation under-the-schedule, essentially providing on-site reserves. Model predictive control (MPC) provides a natural framework for this application. By utilizing an accurate energy storage system model, control actions can be planned in the context of system power and state-of-charge limitations. MPC also enables the inclusion of predicted wind farm performance over a near-term horizon that allows control actions to be planned in anticipation of fast changes, such as wind ramps. This paper demonstrates that model-based predictive control can improve system performance compared with a standard non-predictive, non-model-based control approach. It is also demonstrated that secondary objectives, such as reducing the rate of change of the wind plant output (i.e., ramps), can be considered and successfully implemented within the MPC framework. Specifically, it is shown that scheduling error can be reduced by 81%, reserve requirements can be improved by up to 37%, and the number of ramp events can be reduced by 74%. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
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Open AccessArticle Determining the Limiting Current Density of Vanadium Redox Flow Batteries
Energies 2014, 7(9), 5863-5873; doi:10.3390/en7095863
Received: 2 July 2014 / Revised: 18 August 2014 / Accepted: 27 August 2014 / Published: 5 September 2014
Cited by 2 | PDF Full-text (489 KB) | HTML Full-text | XML Full-text
Abstract
All-vanadium redox flow batteries (VRFBs) are used as energy storage systems for intermittent renewable power sources. The performance of VRFBs depends on materials of key components and operating conditions, such as current density, electrolyte flow rate and electrolyte composition. Mass transfer overpotential [...] Read more.
All-vanadium redox flow batteries (VRFBs) are used as energy storage systems for intermittent renewable power sources. The performance of VRFBs depends on materials of key components and operating conditions, such as current density, electrolyte flow rate and electrolyte composition. Mass transfer overpotential is affected by the electrolyte flow rate and electrolyte composition, which is related to the limiting current density. In order to investigate the effect of operating conditions on mass transport overpotential, this study established a relationship between the limiting current density and operating conditions. First, electrolyte solutions with different states of charge were prepared and used for a single cell to obtain discharging polarization curves under various operating conditions. The experimental results were then analyzed and are discussed in this paper. Finally, this paper proposes a limiting current density as a function of operating conditions. The result helps predict the effect of operating condition on the cell performance in a mathematical model. Full article
(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)
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Open AccessArticle Challenges in Bioenergy Production from Sugarcane Mills in Developing Countries: A Case Study
Energies 2014, 7(9), 5874-5898; doi:10.3390/en7095874
Received: 15 May 2014 / Revised: 6 August 2014 / Accepted: 27 August 2014 / Published: 10 September 2014
Cited by 1 | PDF Full-text (1991 KB) | HTML Full-text | XML Full-text
Abstract
Worldwide energy policies are moving towards a reduction of fossil fuels’ share in the energy mix and to invest in renewable and green energy sources. Biomass is one of these, and it represents, in the form of sugarcane, a strategic source in [...] Read more.
Worldwide energy policies are moving towards a reduction of fossil fuels’ share in the energy mix and to invest in renewable and green energy sources. Biomass is one of these, and it represents, in the form of sugarcane, a strategic source in Colombia, especially in the Valle del Cauca. In this region, the sugarcane industry is able to convert the energy content of the cane into different energy products, such as ethanol, electricity, and high-pressure steam, which are cogenerated via bagasse combustion. In this work, the case of a sucrose and ethanol production plant, which mills ten thousand tons of sugarcane per day, is considered. A tailor-made computational model was developed to assess the energy and material process balances in order to estimate the effect of different operating conditions on cogeneration boilers and turbines, and to optimize the overall process efficiency. The current situation was modeled with good precision from the developed model. Likewise, the concept of “Renewable Efficiency” was introduced to explain the degree of green power, which a process plant is able to produce. Consequently, new innovative solutions and process layouts were proposed in order to increase their renewable efficiency. With the new configurations, a convenient energy surplus of up to 33 MW can be reached, which could be sold in the national electricity grid, representing long-term interesting economic benefits for the company. Full article
(This article belongs to the Special Issue Biomass Resource Efficiency for the Biobased Industries)
Open AccessArticle The Forest Energy Chain in Tuscany: Economic Feasibility and Environmental Effects of Two Types of Biomass District Heating Plant
Energies 2014, 7(9), 5899-5921; doi:10.3390/en7095899
Received: 26 January 2014 / Revised: 19 August 2014 / Accepted: 27 August 2014 / Published: 10 September 2014
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Abstract
The purpose of this study was to examine two biomass district heating plants operating in Tuscany, with a specific focus on the ex-post evaluation of their economic and financial feasibility and of their environmental benefits. The former biomass district heating plant supplies [...] Read more.
The purpose of this study was to examine two biomass district heating plants operating in Tuscany, with a specific focus on the ex-post evaluation of their economic and financial feasibility and of their environmental benefits. The former biomass district heating plant supplies only public users (Comunità Montana della Lunigiana, CML: administrative body that coordinates the municipalities located in mountain areas), the latter supplies both public and private users (Municipality of San Romano in Garfagnana). Ex-post investment analysis was performed to check both the consistency of results with the forecasts made in the stage of the project design and on the factors, which may have reduced or jeopardized the estimated economic performance of the investment (ex-ante assessment). The results of the study point out appreciable results only in the case of biomass district heating plants involving private users and fuelled by biomasses sourced from third parties. In this case, the factors that most influence ex-post results include the conditions of the woody biomass local market (market prices), the policies of energy selling prices to private users and the temporal dynamics of private users’ connection. To ensure the consistency of ex-post economic outcome with the expected results it is thus important to: (i) have good knowledge of the woody local market; (ii) define energy selling prices that should be cheap for private users but consistent with energy production costs and (iii) constrain private users beforehand to prevent errors in the plant design and in the preliminary estimate of return on investment. Moreover, the results obtained during the monitoring activities could help in providing information on the effectiveness of the supporting measures adopted and also to orient future choices of policy makers and particularly designers, to identify the most efficient configuration of district heating organization for improving energy and environmental performances of communities, and to develop a chain model for the optimization of energy use in the municipality. Full article
(This article belongs to the Special Issue Biomass Resource Efficiency for the Biobased Industries)
Open AccessArticle A STATCOM with Supercapacitors for Low-Voltage Ride-Through in Fixed-Speed Wind Turbines
Energies 2014, 7(9), 5922-5952; doi:10.3390/en7095922
Received: 26 June 2014 / Revised: 20 August 2014 / Accepted: 3 September 2014 / Published: 10 September 2014
Cited by 3 | PDF Full-text (737 KB) | HTML Full-text | XML Full-text
Abstract
Fixed-speed wind generator (FSWG) technology has an important presence in countries where wind energy started to be developed more than a decade ago. This type of technology cannot be directly adapted to the grid codes, for example those requirements related to the [...] Read more.
Fixed-speed wind generator (FSWG) technology has an important presence in countries where wind energy started to be developed more than a decade ago. This type of technology cannot be directly adapted to the grid codes, for example those requirements related to the immunity level under voltage dips. That behavior is typically referred as low-voltage ride through (LVRT), and it usually implies certain reactive and active power injection requirements, both during a voltage dip and during the voltage recovery. In this context, a review is presented of the LVRT exigencies present in some of the countries with the most advanced grid codes (Denmark, Germany, Spain and the United Kingdom). In this paper, the capabilities of STATCOM-based devices for fulfilling the LVRT requirements in FSWGs are analyzed. For this purpose, two technologies are considered: a STATCOM with a supercapacitor, which improves its energy storage features; and a STATCOM with a supercapacitor and a DC-DC converter, to achieve higher discharge levels. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
Open AccessArticle A Semantic Middleware Architecture Focused on Data and Heterogeneity Management within the Smart Grid
Energies 2014, 7(9), 5953-5994; doi:10.3390/en7095953
Received: 3 June 2014 / Revised: 23 August 2014 / Accepted: 2 September 2014 / Published: 10 September 2014
Cited by 5 | PDF Full-text (2615 KB) | HTML Full-text | XML Full-text
Abstract
There is an increasing tendency of turning the current power grid, essentially unaware of variations in electricity demand and scattered energy sources, into something capable of bringing a degree of intelligence by using tools strongly related to information and communication technologies, thus [...] Read more.
There is an increasing tendency of turning the current power grid, essentially unaware of variations in electricity demand and scattered energy sources, into something capable of bringing a degree of intelligence by using tools strongly related to information and communication technologies, thus turning into the so-called Smart Grid. In fact, it could be considered that the Smart Grid is an extensive smart system that spreads throughout any area where power is required, providing a significant optimization in energy generation, storage and consumption. However, the information that must be treated to accomplish these tasks is challenging both in terms of complexity (semantic features, distributed systems, suitable hardware) and quantity (consumption data, generation data, forecasting functionalities, service reporting), since the different energy beneficiaries are prone to be heterogeneous, as the nature of their own activities is. This paper presents a proposal on how to deal with these issues by using a semantic middleware architecture that integrates different components focused on specific tasks, and how it is used to handle information at every level and satisfy end user requests. Full article
(This article belongs to the Special Issue Green IT and IT for Smart Energy Savings)
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Open AccessArticle An Adaptive Gain Nonlinear Observer for State of Charge Estimation of Lithium-Ion Batteries in Electric Vehicles
Energies 2014, 7(9), 5995-6012; doi:10.3390/en7095995
Received: 24 July 2014 / Revised: 25 August 2014 / Accepted: 1 September 2014 / Published: 10 September 2014
Cited by 7 | PDF Full-text (500 KB) | HTML Full-text | XML Full-text
Abstract
The state of charge (SOC) is important for the safety and reliability of battery operation since it indicates the remaining capacity of a battery. However, it is difficult to get an accurate value of SOC, because the SOC cannot [...] Read more.
The state of charge (SOC) is important for the safety and reliability of battery operation since it indicates the remaining capacity of a battery. However, it is difficult to get an accurate value of SOC, because the SOC cannot be directly measured by a sensor. In this paper, an adaptive gain nonlinear observer (AGNO) for SOC estimation of lithium-ion batteries (LIBs) in electric vehicles (EVs) is proposed. The second-order resistor–capacitor (2RC) equivalent circuit model is used to simulate the dynamic behaviors of a LIB, based on which the state equations are derived to design the AGNO for SOC estimation. The model parameters are identified using the exponential-function fitting method. The sixth-order polynomial function is used to describe the highly nonlinear relationship between the open circuit voltage (OCV) and the SOC. The convergence of the proposed AGNO is proved using the Lyapunov stability theory. Two typical driving cycles, including the New European Driving Cycle (NEDC) and Federal Urban Driving Schedule (FUDS) are adopted to evaluate the performance of the AGNO by comparing with the unscented Kalman filter (UKF) algorithm. The experimental results show that the AGNO has better performance than the UKF algorithm in terms of reducing the computation cost, improving the estimation accuracy and enhancing the convergence ability. Full article
Open AccessArticle Induced Voltages Ratio-Based Algorithm for Fault Detection, and Faulted Phase and Winding Identification of a Three-Winding Power Transformer
Energies 2014, 7(9), 6031-6049; doi:10.3390/en7096031
Received: 6 August 2014 / Revised: 5 September 2014 / Accepted: 9 September 2014 / Published: 12 September 2014
Cited by 3 | PDF Full-text (396 KB) | HTML Full-text | XML Full-text
Abstract
This paper proposes an algorithm for fault detection, faulted phase and winding identification of a three-winding power transformer based on the induced voltages in the electrical power system. The ratio of the induced voltages of the primary-secondary, primary-tertiary and secondary-tertiary windings is [...] Read more.
This paper proposes an algorithm for fault detection, faulted phase and winding identification of a three-winding power transformer based on the induced voltages in the electrical power system. The ratio of the induced voltages of the primary-secondary, primary-tertiary and secondary-tertiary windings is the same as the corresponding turns ratio during normal operating conditions, magnetic inrush, and over-excitation. It differs from the turns ratio during an internal fault. For a single phase and a three-phase power transformer with wye-connected windings, the induced voltages of each pair of windings are estimated. For a three-phase power transformer with delta-connected windings, the induced voltage differences are estimated to use the line currents, because the delta winding currents are practically unavailable. Six detectors are suggested for fault detection. An additional three detectors and a rule for faulted phase and winding identification are presented as well. The proposed algorithm can not only detect an internal fault, but also identify the faulted phase and winding of a three-winding power transformer. The various test results with Electromagnetic Transients Program (EMTP)-generated data show that the proposed algorithm successfully discriminates internal faults from normal operating conditions including magnetic inrush and over-excitation. This paper concludes by implementing the algorithm into a prototype relay based on a digital signal processor. Full article
Open AccessArticle Multiagent-Based Distributed Load Shedding for Islanded Microgrids
Energies 2014, 7(9), 6050-6062; doi:10.3390/en7096050
Received: 22 July 2014 / Revised: 5 September 2014 / Accepted: 9 September 2014 / Published: 15 September 2014
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Abstract
This paper addresses a multiagent-based distributed load shedding scheme to restore frequency for the microgrids during islanded operation. The objective of the proposed scheme is to realize a distributed load shedding considering its associated cost and the capacity of the flexible loads. [...] Read more.
This paper addresses a multiagent-based distributed load shedding scheme to restore frequency for the microgrids during islanded operation. The objective of the proposed scheme is to realize a distributed load shedding considering its associated cost and the capacity of the flexible loads. There are two advantages of the proposed scheme: (1) it is a distributed scheme using average-consensus theorem, which can discover the global information when only communications between immediate neighboring agents are used, moreover it can meet the requirements of plug-and-play operations more easily than a centralized scheme; (2) it is a new adaptive load shedding through the comprehensive weights which take into accounts the cost of load shedding and the capacity of flexible loads, these comprehensive weights are evaluated locally by making use of the adaptability and intelligence characteristics of agents. Simulation results in power systems computer aided design (PSCAD) illustrate the validity and adaptability of the proposed load shedding scheme. Full article
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Open AccessArticle False Shades of Green: The Case of Brazilian Amazonian Hydropower
Energies 2014, 7(9), 6063-6082; doi:10.3390/en7096063
Received: 30 June 2014 / Revised: 15 August 2014 / Accepted: 1 September 2014 / Published: 16 September 2014
Cited by 10 | PDF Full-text (563 KB) | HTML Full-text | XML Full-text
Abstract
The Federal Government of Brazil has ambitious plans to build a system of 58 additional hydroelectric dams in the Brazilian Amazon, with Hundreds of additional dams planned for other countries in the watershed. Although hydropower is often billed as clean energy, we [...] Read more.
The Federal Government of Brazil has ambitious plans to build a system of 58 additional hydroelectric dams in the Brazilian Amazon, with Hundreds of additional dams planned for other countries in the watershed. Although hydropower is often billed as clean energy, we argue that the environmental impacts of this project are likely to be large, and will result in substantial loss of biodiversity, as well as changes in the flows of ecological services. Moreover, the projects will generate significant greenhouse gas emissions from deforestation and decay of organic matter in the reservoirs. These emissions are equivalent to the five years of emissions that would be generated by gas powered plants of equivalent capacity. In addition, we examine the economic benefits of the hydropower in comparison to new alternatives, such as photovoltaic energy and wind power. We find that current costs of hydropower exceed alternatives, and the costs of costs of these alternatives are likely to fall substantially below those of hydropower, while the environmental damages from the dams will be extensive and irreversible. Full article
(This article belongs to the Special Issue Energy Transitions and Economic Change)
Open AccessArticle Performance Characterization and Auto-Ignition Performance of a Rapid Compression Machine
Energies 2014, 7(9), 6083-6104; doi:10.3390/en7096083
Received: 15 August 2014 / Revised: 7 September 2014 / Accepted: 15 September 2014 / Published: 22 September 2014
Cited by 2 | PDF Full-text (3107 KB) | HTML Full-text | XML Full-text
Abstract
A rapid compression machine (RCM) test bench is developed in this study. The performance characterization and auto-ignition performance tests are conducted at an initial temperature of 293 K, a compression ratio of 9.5 to 16.5, a compressed temperature of 650 K to [...] Read more.
A rapid compression machine (RCM) test bench is developed in this study. The performance characterization and auto-ignition performance tests are conducted at an initial temperature of 293 K, a compression ratio of 9.5 to 16.5, a compressed temperature of 650 K to 850 K, a driving gas pressure range of 0.25 MPa to 0.7 MPa, an initial pressure of 0.04 MPa to 0.09 MPa, and a nitrogen dilution ratio of 35% to 65%. A new type of hydraulic piston is used to address the problem in which the hydraulic buffer adversely affects the rapid compression process. Auto-ignition performance tests of the RCM are then performed using a DME–O2–N2 mixture. The two-stage ignition delay and negative temperature coefficient (NTC) behavior of the mixture are observed. The effects of driving gas pressure, compression ratio, initial pressure, and nitrogen dilution ratio on the two-stage ignition delay are investigated. Results show that both the first-stage and overall ignition delays tend to increase with increasing driving gas pressure. The driving gas pressure within a certain range does not significantly influence the compressed pressure. With increasing compression ratio, the first-stage ignition delay is shortened, whereas the second-stage ignition delay is extended. With increasing initial pressure, both the first-stage and second-stage ignition delays are shortened. The second-stage ignition delay is shortened to a greater extent than that of the first-stage. With increasing nitrogen dilution ratio, the first-stage ignition delay is shortened, whereas the second-stage is extended. Thus, overall ignition delay presents different trends under various compression ratios and compressed pressure conditions. Full article
Open AccessArticle Optimization of Design Pressure Ratio of Positive Displacement Expander for Vehicle Engine Waste Heat Recovery
Energies 2014, 7(9), 6105-6117; doi:10.3390/en7096105
Received: 31 July 2014 / Revised: 15 September 2014 / Accepted: 16 September 2014 / Published: 22 September 2014
Cited by 4 | PDF Full-text (1012 KB) | HTML Full-text | XML Full-text
Abstract
This study investigated the effect of the built-in volume ratio of an expander on the performance of a dual-loop Rankine cycle system for the engine waste heat recovery of a vehicle. Varying vehicle operating conditions can cause a positive displacement expander to [...] Read more.
This study investigated the effect of the built-in volume ratio of an expander on the performance of a dual-loop Rankine cycle system for the engine waste heat recovery of a vehicle. Varying vehicle operating conditions can cause a positive displacement expander to operate in both under- and over-expansion states. Therefore, analysis of the off-design performance of the expander is very important. Furthermore, the volume and weight of the expander must be considered in its optimization along with the efficiency. A simple modeling of the off-design operation of the expander showed that a built-in volume ratio that causes under-expansion rather than over-expansion at the target condition is more desirable. Full article
(This article belongs to the Special Issue Organic Rankine Cycle (ORC))
Open AccessArticle Methane Flux and Authigenic Carbonate in Shallow Sediments Overlying Methane Hydrate Bearing Strata in Alaminos Canyon, Gulf of Mexico
Energies 2014, 7(9), 6118-6141; doi:10.3390/en7096118
Received: 11 August 2014 / Revised: 4 September 2014 / Accepted: 9 September 2014 / Published: 23 September 2014
Cited by 1 | PDF Full-text (4789 KB) | HTML Full-text | XML Full-text
Abstract
In June 2007 sediment cores were collected in Alaminos Canyon, Gulf of Mexico across a series of seismic data profiles indicating rapid transitions between the presence of methane hydrates and vertical gas flux. Vertical profiles of dissolved sulfate, chloride, calcium, magnesium, and [...] Read more.
In June 2007 sediment cores were collected in Alaminos Canyon, Gulf of Mexico across a series of seismic data profiles indicating rapid transitions between the presence of methane hydrates and vertical gas flux. Vertical profiles of dissolved sulfate, chloride, calcium, magnesium, and dissolved inorganic carbon (DIC) concentrations in porewaters, headspace methane, and solid phase carbonate concentrations were measured at each core location to investigate the cycling of methane-derived carbon in shallow sediments overlying the hydrate bearing strata. When integrated with stable carbon isotope ratios of DIC, geochemical results suggest a significant fraction of the methane flux at this site is cycled into the inorganic carbon pool. The incorporation of methane-derived carbon into dissolved and solid inorganic carbon phases represents a significant sink in local carbon cycling and plays a role in regulating the flux of methane to the overlying water column at Alaminos Canyon. Targeted, high-resolution geochemical characterization of the biogeochemical cycling of methane-derived carbon in shallow sediments overlying hydrate bearing strata like those in Alaminos Canyon is critical to quantifying methane flux and estimating methane hydrate distributions in gas hydrate bearing marine sediments. Full article
(This article belongs to the Special Issue Coastal Ocean Natural Gas Hydrate 2014)
Open AccessArticle Business Models in the Smart Grid: Challenges, Opportunities and Proposals for Prosumer Profitability
Energies 2014, 7(9), 6142-6171; doi:10.3390/en7096142
Received: 5 July 2014 / Revised: 7 September 2014 / Accepted: 9 September 2014 / Published: 23 September 2014
Cited by 9 | PDF Full-text (980 KB) | HTML Full-text | XML Full-text
Abstract
Considering that non-renewable energy resources are dwindling, the smart grid turns out to be one of the most promising and compelling systems for the future of energy. Not only does it combine efficient energy consumption with avant-garde technologies related to renewable energies, [...] Read more.
Considering that non-renewable energy resources are dwindling, the smart grid turns out to be one of the most promising and compelling systems for the future of energy. Not only does it combine efficient energy consumption with avant-garde technologies related to renewable energies, but it is also capable of providing several beneficial utilities, such as power monitoring and data provision. When smart grid end users turn into prosumers, they become arguably the most important value creators within the smart grid and a decisive agent of change in terms of electricity usage. There is a plethora of research and development areas related to the smart grid that can be exploited for new business opportunities, thus spawning another branch of the so-called “green economy” focused on turning smart energy usage into a profitable business. This paper deals with emerging business models for smart grid prosumers, their strengths and weaknesses and puts forward new prosumer-oriented business models, along with their value propositions. Full article
(This article belongs to the Special Issue Energy Transitions and Economic Change)
Open AccessArticle Experimental Investigation of the Performance of a Hermetic Screw-Expander Organic Rankine Cycle
Energies 2014, 7(9), 6172-6185; doi:10.3390/en7096172
Received: 6 June 2014 / Revised: 15 August 2014 / Accepted: 22 September 2014 / Published: 23 September 2014
Cited by 5 | PDF Full-text (1514 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the authors experimentally investigate the performance of the organic Rankine cycle (ORC) and screw expander under the influence of supply pressure and pressure ratio over the expander. Three tests were performed with expander pressure ratios of 2.4–3.5, 3.0–4.6, and [...] Read more.
In this study, the authors experimentally investigate the performance of the organic Rankine cycle (ORC) and screw expander under the influence of supply pressure and pressure ratio over the expander. Three tests were performed with expander pressure ratios of 2.4–3.5, 3.0–4.6, and 3.3–6.1, which cover the over-expansion and under-expansion operating modes. The test results show a maximum expander isentropic efficiency of 72.4% and a relative cycle efficiency of 10.5% at an evaporation temperature of 101 °C and condensation temperature of 45 °C. At a given pressure ratio over the expander, a higher supply pressure to the expander causes a higher expander isentropic efficiency and higher cycle efficiency in the over-expansion mode. However, in the under-expansion mode, the higher supply pressure results in a lower expander isentropic efficiency and adversely affects the cycle efficiency. The results also show that under the condition of operation at a given pressure ratio, a higher supply pressure yields a larger power output owing to the increased mass flow rate at the higher supply pressure. The study results demonstrate that a screw-expander ORC can be operated with a wide range of heat sources and heat sinks with satisfactory cycle efficiency. Full article
(This article belongs to the Special Issue Waste Heat Recovery—Strategy and Practice)
Open AccessCommunication Optimization of Alkaline Flocculation for Harvesting of Scenedesmus quadricauda #507 and Chaetoceros muelleri #862
Energies 2014, 7(9), 6186-6195; doi:10.3390/en7096186
Received: 11 June 2014 / Revised: 13 August 2014 / Accepted: 17 September 2014 / Published: 24 September 2014
Cited by 1 | PDF Full-text (467 KB) | HTML Full-text | XML Full-text
Abstract
A response surface methodology (RSM) was used to evaluate the effects of pH and microalgal biomass concentration (BC) on alkaline flocculating activity for harvesting one freshwater green algae Scenedesmus quadricauda #507 and one marine diatom Chaetoceros muelleri #862. The pH value and [...] Read more.
A response surface methodology (RSM) was used to evaluate the effects of pH and microalgal biomass concentration (BC) on alkaline flocculating activity for harvesting one freshwater green algae Scenedesmus quadricauda #507 and one marine diatom Chaetoceros muelleri #862. The pH value and BC were in range of 9.0–12.0 and 0.20–2.30 g/L, respectively. Very high regression coefficient between the variables and the response indicates excellent evaluation of experimental data by second-order regressions. Optimum conditions for flocculating activity were estimated as follows: (i) pH 11.6, BC 0.54 g/L for strain #507 and (ii) pH 11.5, BC 0.42 g/L for strain #862. The maximum flocculating activity was around 94.7% and 100%, respectively. Furthermore, the addition of synthetic ocean water (SOW) to the freshwater #507 culture can increase the flocculating activity from 82.13%–88.79% in low algae concentration (0.52 g/L) and 82.92%–95.60% in high concentration (2.66 g/L). Full article
(This article belongs to the Special Issue Algae Based Technologies)
Open AccessArticle Estimating the Technical Improvement of Energy Efficiency in the Automotive Industry—Stochastic and Deterministic Frontier Benchmarking Approaches
Energies 2014, 7(9), 6196-6222; doi:10.3390/en7096196
Received: 10 July 2014 / Accepted: 15 September 2014 / Published: 25 September 2014
Cited by 2 | PDF Full-text (1462 KB) | HTML Full-text | XML Full-text
Abstract
The car manufacturing industry, one of the largest energy consuming industries, has been making a considerable effort to improve its energy intensity by implementing energy efficiency programs, in many cases supported by government research or financial programs. While many car manufacturers claim [...] Read more.
The car manufacturing industry, one of the largest energy consuming industries, has been making a considerable effort to improve its energy intensity by implementing energy efficiency programs, in many cases supported by government research or financial programs. While many car manufacturers claim that they have made substantial progress in energy efficiency improvement over the past years through their energy efficiency programs, the objective measurement of energy efficiency improvement has not been studied due to the lack of suitable quantitative methods. This paper proposes stochastic and deterministic frontier benchmarking models such as the stochastic frontier analysis (SFA) model and the data envelopment analysis (DEA) model to measure the effectiveness of energy saving initiatives in terms of the technical improvement of energy efficiency for the automotive industry, particularly vehicle assembly plants. Illustrative examples of the application of the proposed models are presented and demonstrate the overall benchmarking process to determine best practice frontier lines and to measure technical improvement based on the magnitude of frontier line shifts over time. Log likelihood ratio and Spearman rank-order correlation coefficient tests are conducted to determine the significance of the SFA model and its consistency with the DEA model. ENERGY STAR® EPI (Energy Performance Index) are also calculated. Full article

Review

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Open AccessReview The Gouy-Stodola Theorem in Bioenergetic Analysis of Living Systems (Irreversibility in Bioenergetics of Living Systems)
Energies 2014, 7(9), 5717-5739; doi:10.3390/en7095717
Received: 23 July 2014 / Revised: 9 August 2014 / Accepted: 22 August 2014 / Published: 1 September 2014
Cited by 16 | PDF Full-text (584 KB) | HTML Full-text | XML Full-text
Abstract
Thermodynamics studies the transformations of energy occurring in open systems. Living systems, with particular reference to cells, are complex systems in which energy transformations occur. Thermo-electro-chemical processes and transports occur across their border, the cells membranes. These processes take place with important [...] Read more.
Thermodynamics studies the transformations of energy occurring in open systems. Living systems, with particular reference to cells, are complex systems in which energy transformations occur. Thermo-electro-chemical processes and transports occur across their border, the cells membranes. These processes take place with important differences between healthy and diseased states. In particular, different thermal and biochemical behaviours can be highlighted between these two states and they can be related to the energy transformations inside the living systems, in particular the metabolic behaviour. Moreover, living systems waste heat. This heat is the consequence of the internal irreversibility. Irreversibility is effectively studied by using the Gouy-Stodola theorem. Consequently, this approach can be introduced in the analysis of the states of living systems, in order to obtain a unifying approach to study them. Indeed, this approach allows us to consider living systems as black boxes and analyze only the inflows and outflows and their changes in relation to the modification of the environment, so information on the systems can be obtained by analyzing their behaviour in relation to the modification of external perturbations. This paper presents a review of the recent results obtained in the thermodynamics analysis of cell systems. Full article
Open AccessReview Towards a Friendly Energy Management Strategy for Hybrid Electric Vehicles with Respect to Pollution, Battery and Drivability
Energies 2014, 7(9), 6013-6030; doi:10.3390/en7096013
Received: 16 April 2014 / Revised: 11 July 2014 / Accepted: 31 July 2014 / Published: 12 September 2014
Cited by 2 | PDF Full-text (427 KB) | HTML Full-text | XML Full-text
Abstract
The paper proposes a generic methodology to incorporate constraints (pollutant emission, battery health, drivability) into on-line energy management strategies (EMSs) for hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs). The integration of each constraint into the EMS, made with the [...] Read more.
The paper proposes a generic methodology to incorporate constraints (pollutant emission, battery health, drivability) into on-line energy management strategies (EMSs) for hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs). The integration of each constraint into the EMS, made with the Pontryagin maximum principle, shows a tradeoff between the fuel consumption and the constraint introduced. As state dynamics come into play (catalyst temperature, battery cell temperature, etc.), the optimization problem becomes more complex. Simulation results are presented to highlight the contribution of this generic strategy, including constraints compared to the standard approach. These results show that it is possible to find an energy management strategy that takes into account an increasing number of constraints (drivability, pollution, aging, environment, etc.). However, taking these constraints into account increases fuel consumption (the existence of a trade-off curve). This trade-off can be sometimes difficult to find, and the tools developed in this paper should help to find an acceptable solution quickly Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)

Other

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Open AccessCorrection Correction: Budea, S. Solar Air Collectors for Space Heating and Ventilation Applications—Performance and Case Studies under Romanian Climatic Conditions. Energies 2014, 7, 3781–3792
Energies 2014, 7(9), 6223; doi:10.3390/en7096223
Received: 27 August 2014 / Accepted: 15 September 2014 / Published: 25 September 2014
PDF Full-text (194 KB) | HTML Full-text | XML Full-text
Abstract An inadvertent error was found in the pdf version of paper [1]. On page 3785, Equation (2) was not displayed well and should be read...[...] Full article
Open AccessCorrection Correction: Rees, S. and Curtis, R. National Deployment of Domestic Geothermal Heat Pump Technology: Observations on the UK Experience 1995–2013. Energies 2014, 7, 5460–5499
Energies 2014, 7(9), 6224; doi:10.3390/en7096224
Received: 27 August 2014 / Accepted: 1 September 2014 / Published: 25 September 2014
PDF Full-text (241 KB) | HTML Full-text | XML Full-text
Abstract We have found the following error in the publishing history of this article which was recently published in Energies [1].[...] Full article

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