Energies

1391 KiB

Open AccessArticle

Determining the Maximum Depth of Hydrothermal Circulation Using Geothermal Mapping and Seismicity to Delineate the Depth to Brittle-Plastic Transition in Northern Honshu, Japan

by Yota Suzuki, Seiichiro Ioka and Hirofumi Muraoka

Energies 2014, 7(5), 3503-3511; https://doi.org/10.3390/en7053503 - 23 May 2014

Cited by 17 | Viewed by 7631

Abstract

This paper defines the maximum possible vertical extent of hydrothermal circulation in granitic crust, and thus the maximum depth within which geothermal reservoirs can be encountered. To evaluate prospective geothermal fields we constructed a geothermal database in northern Honshu, Japan that includes 571 [...] Read more.

This paper defines the maximum possible vertical extent of hydrothermal circulation in granitic crust, and thus the maximum depth within which geothermal reservoirs can be encountered. To evaluate prospective geothermal fields we constructed a geothermal database in northern Honshu, Japan that includes 571 points of thermal data of existing wells and hot springs. Depth-temperature curves were normalized by the Activity Index for three-dimensional extrapolation and a depth contour map of the 380 °C isotherm was plotted as an assumed brittle-plastic transition for granitic crust. Shallower-depth anomalies of the brittle-plastic transition on this map are closely coincident with the Quaternary volcanoes and their prospective geothermal fields. It should be noted that the bottom of the spatial distribution of seismicity in the volcanic fields shows strong correlation to the 380 °C isotherm. This result indicates reliability of the subsurface three-dimensional thermal map and suggests that the 380 °C isotherm strongly constrains the bottom surface of seismicity, fracturing and hydrothermal convection in granitic crust. Full article

(This article belongs to the Special Issue Geothermal Energy: Delivering on the Global Potential)

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1145 KiB

Open AccessArticle

An Improved CO₂ Separation and Purification System Based on Cryogenic Separation and Distillation Theory

by Gang Xu, Feifei Liang, Yongping Yang, Yue Hu, Kai Zhang and Wenyi Liu

Energies 2014, 7(5), 3484-3502; https://doi.org/10.3390/en7053484 - 23 May 2014

Cited by 173 | Viewed by 17148

Abstract

In this study, an improved CO₂ separation and purification system is proposed based on in-depth analyses of cryogenic separation and distillation theory as well as the phase transition characteristics of gas mixtures containing CO₂. Multi-stage compression, refrigeration, and separation are [...] Read more.

In this study, an improved CO₂ separation and purification system is proposed based on in-depth analyses of cryogenic separation and distillation theory as well as the phase transition characteristics of gas mixtures containing CO₂. Multi-stage compression, refrigeration, and separation are adopted to separate the majority of the CO₂ from the gas mixture with relatively low energy penalty and high purity. Subsequently, the separated crude liquid CO₂ is distilled under high pressure and near ambient temperature conditions so that low energy penalty purification is achieved. Simulation results indicate that the specific energy consumption for CO₂ capture is only 0.425 MJ/kgCO₂ with 99.9% CO₂ purity for the product. Techno-economic analysis shows that the total plant investment is relatively low. Given its technical maturity and great potential in large-scale production, compared to conventional MEA and Selexol^TM absorption methods, the cost of CO₂ capture of the proposed system is reduced by 57.2% and 45.9%, respectively. The result of this study can serve as a novel approach to recovering CO₂ from high CO₂ concentration gas mixtures. Full article

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1794 KiB

Open AccessArticle

Multi-Faceted Assessment of a Wireless Communications Infrastructure for the Green Neighborhoods of the Smart Grid

by Gregorio López, Pedro Moura, José Ignacio Moreno and José Manuel Camacho

Energies 2014, 7(5), 3453-3483; https://doi.org/10.3390/en7053453 - 22 May 2014

Cited by 24 | Viewed by 10236

Abstract

Reducing electricity consumption and integrating renewable power generation sources represent two of the main drivers of the so-called Smart Grid. Machine-to-Machine (M2M) communications will play a key role on making such a Smart Grid a reality, since they will enable the required bidirectional [...] Read more.

Reducing electricity consumption and integrating renewable power generation sources represent two of the main drivers of the so-called Smart Grid. Machine-to-Machine (M2M) communications will play a key role on making such a Smart Grid a reality, since they will enable the required bidirectional real-time bulk information exchange. However, communications for the Smart Grid present specific requirements from both technical and economic perspectives, so it is crucial to evaluate how existing communication architectures and technologies meet them before undertaking the important investments needed to deploy this kind of infrastructure on a large scale. The main goal of this paper is to evaluate, from different perspectives, the core M2M communications infrastructure of a platform designed to reduce electricity consumption and integrate renewable generation at residential level. Such a communications infrastructure is fully based on widely deployed wireless communications technologies such as IEEE 802.11 and General Packet Radio Service (GPRS). Notably, the paper assesses the operational costs of using different security solutions in the GPRS segment and the performance of the selected communications technologies based on different metrics (goodput, in the case of IEEE 802.11, and transmission time, in the case of GPRS). Full article

(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)

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827 KiB

Open AccessArticle

Fast Estimation of State of Charge for Lithium-Ion Batteries

by Shing-Lih Wu, Hung-Cheng Chen and Shuo-Rong Chou

Energies 2014, 7(5), 3438-3452; https://doi.org/10.3390/en7053438 - 22 May 2014

Cited by 25 | Viewed by 7577

Abstract

This paper presents a novel impedance-based approach to efficiently estimate the state of charge (SOC) of a Li-ion battery. By using an AC impedance analyzer, a database is constructed, containing records of AC impedance versus SOC. In practical applications, the SOC values can [...] Read more.

This paper presents a novel impedance-based approach to efficiently estimate the state of charge (SOC) of a Li-ion battery. By using an AC impedance analyzer, a database is constructed, containing records of AC impedance versus SOC. In practical applications, the SOC values can be found instantly once the contents of the database are referenced. For validation purposes, AC impedance comparisons are conducted using AC impedance analyzer as a benchmark at SOC of 0%, 50% and 100%, which indicate errors of 8.636%, 2.604% and 0.600%, respectively. Full article

(This article belongs to the Special Issue Selected Papers from the 2014 International Symposium on Computer, Consumer and Control (IS3C2014))

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1186 KiB

Open AccessArticle

Hierarchical Communication Network Architectures for Offshore Wind Power Farms

by Mohamed A. Ahmed and Young-Chon Kim

Energies 2014, 7(5), 3420-3437; https://doi.org/10.3390/en7053420 - 22 May 2014

Cited by 22 | Viewed by 9306

Abstract

Nowadays, large-scale wind power farms (WPFs) bring new challenges for both electric systems and communication networks. Communication networks are an essential part of WPFs because they provide real-time control and monitoring of wind turbines from a remote location (local control center). However, different [...] Read more.

Nowadays, large-scale wind power farms (WPFs) bring new challenges for both electric systems and communication networks. Communication networks are an essential part of WPFs because they provide real-time control and monitoring of wind turbines from a remote location (local control center). However, different wind turbine applications have different requirements in terms of data volume, latency, bandwidth, QoS, etc. This paper proposes a hierarchical communication network architecture that consist of a turbine area network (TAN), farm area network (FAN), and control area network (CAN) for offshore WPFs. The two types of offshore WPFs studied are small-scale WPFs close to the grid and medium-scale WPFs far from the grid. The wind turbines are modelled based on the logical nodes (LN) concepts of the IEC 61400-25 standard. To keep pace with current developments in wind turbine technology, the network design takes into account the extension of the LNs for both the wind turbine foundation and meteorological measurements. The proposed hierarchical communication network is based on Switched Ethernet. Servers at the control center are used to store and process the data received from the WPF. The network architecture is modelled and evaluated via OPNET. We investigated the end-to-end (ETE) delay for different WPF applications. The results are validated by comparing the amount of generated sensing data with that of received traffic at servers. The network performance is evaluated, analyzed and discussed in view of end-to-end (ETE) delay for different link bandwidths. Full article

(This article belongs to the Special Issue Selected Papers from the 2014 International Symposium on Computer, Consumer and Control (IS3C2014))

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Graphical abstract

2366 KiB

Open AccessArticle

Performance Analysis of the Vehicle Diesel Engine-ORC Combined System Based on a Screw Expander

by Kai Yang, Hongguang Zhang, Songsong Song, Jian Zhang, Yuting Wu, Yeqiang Zhang, Hongjin Wang, Ying Chang and Chen Bei

Energies 2014, 7(5), 3400-3419; https://doi.org/10.3390/en7053400 - 22 May 2014

Cited by 28 | Viewed by 12475

Abstract

To achieve energy saving and emission reduction for vehicle diesel engines, the organic Rankine cycle (ORC) was employed to recover waste heat from vehicle diesel engines, R245fa was used as ORC working fluid, and the resulting vehicle diesel engine-ORC combined system was presented. [...] Read more.

To achieve energy saving and emission reduction for vehicle diesel engines, the organic Rankine cycle (ORC) was employed to recover waste heat from vehicle diesel engines, R245fa was used as ORC working fluid, and the resulting vehicle diesel engine-ORC combined system was presented. The variation law of engine exhaust energy rate under various operating conditions was obtained, and the running performances of the screw expander were introduced. Based on thermodynamic models and theoretical calculations, the running performance of the vehicle diesel engine-ORC combined system was analyzed under various engine operating condition scenarios. Four evaluation indexes were defined: engine thermal efficiency increasing ratio (ETEIR), waste heat recovery efficiency (WHRE), brake specific fuel consumption (BSFC) of the combined system, and improvement ratio of BSFC (IRBSFC). Results showed that when the diesel engine speed is 2200 r/min and diesel engine torque is 1200 N·m, the power output of the combined system reaches its maximum of approximately 308.6 kW, which is 28.6 kW higher than that of the diesel engine. ETEIR, WHRE, and IRBSFC all reach their maxima at 10.25%, 9.90%, and 9.30%, respectively. Compared with that of the diesel engine, the BSFC of the combined system is obviously improved under various engine operating conditions. Full article

(This article belongs to the Special Issue Waste Heat Recovery—Strategy and Practice)

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Graphical abstract

719 KiB

Open AccessArticle

by Carlos Luna, Cristobal Verdugo, Enrique D. Sancho, Diego Luna, Juan Calero, Alejandro Posadillo, Felipa M. Bautista and Antonio A. Romero

Energies 2014, 7(5), 3383-3399; https://doi.org/10.3390/en7053383 - 22 May 2014

Cited by 15 | Viewed by 7362

Abstract

A new biodiesel-like biofuel is obtained by the enzymatic ethanolysis reaction of sunflower oil with ethanol, in free solvent media, by using BIOLIPASE-R, a multipurpose alimentary additive from Biocon^®-Spain that is a low cost lipase from a strain of Rhizopus oryzae [...] Read more.

A new biodiesel-like biofuel is obtained by the enzymatic ethanolysis reaction of sunflower oil with ethanol, in free solvent media, by using BIOLIPASE-R, a multipurpose alimentary additive from Biocon^®-Spain that is a low cost lipase from a strain of Rhizopus oryzae. This biofuel is composed by two parts of fatty acid ethyl esters (FAEE) and one of monoglyceride (MG), which in this form integrates glycerol, through the application of the 1,3-selective lipases. Thus, this process minimizes waste generation and maximizes the efficiency of the process because no residual glycerol is produced. Response surface methodology (RSM) is employed to evaluate the main reaction parameters (reaction temperature, oil/ethanol ratio and pH) on the sunflower oil conversion. Water content and amount of lipase were also previously investigated. Regarding the results, we found that it operates optimally with a water content of the reaction medium of 0.15%, 0.05%–0.1% lipase by weight relative to the weight of oil used, 20 °C, volume ratio (mL/mL) oil/ethanol 12/3.5 and pH 12 (by addition of 50 µL of 10 N NaOH solution). These results have proven a very good efficiency of the biocatalyst in the studied selective process. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International e-Conference on Energies — Whither Energy Conversion? Present Trends, Current Problems and Realistic Future Solutions)

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Graphical abstract

1524 KiB

Open AccessReview

Reviewing Microgrids from a Multi-Agent Systems Perspective

by Jorge J. Gomez-Sanz, Sandra Garcia-Rodriguez, Nuria Cuartero-Soler and Luis Hernandez-Callejo

Energies 2014, 7(5), 3355-3382; https://doi.org/10.3390/en7053355 - 22 May 2014

Cited by 51 | Viewed by 8335

Abstract

The construction of Smart Grids leads to the main question of what kind of intelligence such grids require and how to build it. Some authors choose an agent based solution to realize this intelligence. However, there may be some misunderstandings in the way [...] Read more.

The construction of Smart Grids leads to the main question of what kind of intelligence such grids require and how to build it. Some authors choose an agent based solution to realize this intelligence. However, there may be some misunderstandings in the way this technology is being applied. This paper exposes some considerations of this subject, focusing on the Microgrid level, and shows a practical example through INGENIAS methodology, which is a methodology for the development of Agent Oriented systems that applies Model Driven Development techniques to produce fully functional Multi-Agent Systems. Full article

(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)

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2900 KiB

Open AccessArticle

Applicability of Synthetic Aperture Radar Wind Retrievals on Offshore Wind Resources Assessment in Hangzhou Bay, China

by Rui Chang, Rong Zhu, Merete Badger, Charlotte Bay Hasager, Rongwei Zhou, Dong Ye and Xiaowei Zhang

Energies 2014, 7(5), 3339-3354; https://doi.org/10.3390/en7053339 - 20 May 2014

Cited by 25 | Viewed by 7416

Abstract

In view of the high cost and sparse spatial resolution of offshore meteorological observations, ocean winds retrieved from satellites are valuable in offshore wind resource assessment as a supplement to in situ measurements. This study examines satellite synthetic aperture radar (SAR) images from [...] Read more.

In view of the high cost and sparse spatial resolution of offshore meteorological observations, ocean winds retrieved from satellites are valuable in offshore wind resource assessment as a supplement to in situ measurements. This study examines satellite synthetic aperture radar (SAR) images from ENVISAT advanced SAR (ASAR) for mapping wind resources with high spatial resolution. Around 181 collected pairs of wind data from SAR wind maps and from 13 meteorological stations in Hangzhou Bay are compared. The statistical results comparing in situ wind speed and SAR-based wind speed show a standard deviation (SD) of 1.99 m/s and correlation coefficient of R = 0.67. The model wind directions, which are used as input for the SAR wind speed retrieval, show a high correlation coefficient (R = 0.89) but a large standard deviation (SD = 42.3°) compared to in situ observations. The Weibull probability density functions are compared at one meteorological station. The SAR-based results appear not to estimate the mean wind speed, Weibull scale and shape parameters and wind power density from the full in situ data set so well due to the lower number of satellite samples. Distributions calculated from the concurrent 81 SAR and in situ samples agree well. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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Graphical abstract

1087 KiB

Open AccessArticle

Design and Evaluation of a Photovoltaic/Thermal-Assisted Heat Pump Water Heating System

by Huan-Liang Tsai

Energies 2014, 7(5), 3319-3338; https://doi.org/10.3390/en7053319 - 20 May 2014

Cited by 39 | Viewed by 7458

Abstract

This paper presents the design, modelling and performance evaluation of a photovoltaic/thermal-assisted heat pump water heating (PVTA-HPWH) system. The cooling effect of a refrigerant simultaneously enhances the PVT efficiency and effectively improves the coefficient of performance (COP) of the HPWH system. The proposed [...] Read more.

This paper presents the design, modelling and performance evaluation of a photovoltaic/thermal-assisted heat pump water heating (PVTA-HPWH) system. The cooling effect of a refrigerant simultaneously enhances the PVT efficiency and effectively improves the coefficient of performance (COP) of the HPWH system. The proposed model was built in the MATLAB/Simulink environment by considering the reciprocal energy exchange between a PVT evaporator and a HPWH system. In addition, the power consumption needs of the HPWH are provided by the PV electricity using a model-based control methodology. System performance is evaluated through a real field test. The results have demonstrated the power autarchy of the proposed PVTA-HPWH system with better PVT efficiency and COP. In addition, the good agreement between the model simulation and the experimental measurements demonstrate the proposed model with sufficient confidence. Full article

(This article belongs to the Special Issue Selected Papers from the 2014 International Symposium on Computer, Consumer and Control (IS3C2014))

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1198 KiB

Open AccessArticle

Dynamic Hybrid Model for Short-Term Electricity Price Forecasting

by Marin Cerjan, Marin Matijaš and Marko Delimar

Energies 2014, 7(5), 3304-3318; https://doi.org/10.3390/en7053304 - 20 May 2014

Cited by 35 | Viewed by 7366

Abstract

Accurate forecasting tools are essential in the operation of electric power systems, especially in deregulated electricity markets. Electricity price forecasting is necessary for all market participants to optimize their portfolios. In this paper we propose a hybrid method approach for short-term hourly electricity [...] Read more.

Accurate forecasting tools are essential in the operation of electric power systems, especially in deregulated electricity markets. Electricity price forecasting is necessary for all market participants to optimize their portfolios. In this paper we propose a hybrid method approach for short-term hourly electricity price forecasting. The paper combines statistical techniques for pre-processing of data and a multi-layer (MLP) neural network for forecasting electricity price and price spike detection. Based on statistical analysis, days are arranged into several categories. Similar days are examined by correlation significance of the historical data. Factors impacting the electricity price forecasting, including historical price factors, load factors and wind production factors are discussed. A price spike index (CWI) is defined for spike detection and forecasting. Using proposed approach we created several forecasting models of diverse model complexity. The method is validated using the European Energy Exchange (EEX) electricity price data records. Finally, results are discussed with respect to price volatility, with emphasis on the price forecasting accuracy. Full article

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1217 KiB

Open AccessArticle

A Boiler Room in a 600-Bed Hospital Complex: Study, Analysis, and Implementation of Energy Efficiency Improvements

by Juan-Carlos Fraile, Julio San-José and Ana González-Alonso

Energies 2014, 7(5), 3282-3303; https://doi.org/10.3390/en7053282 - 19 May 2014

Cited by 7 | Viewed by 10591

Abstract

The aim of energy efficiency is to use less energy to provide the same service. In hospitals, energy efficiency offers a powerful and cost-effective tool to reduce greenhouse gas emissions, fuel consumption, and also running costs. Over a six-month period, the six gas-fired [...] Read more.

The aim of energy efficiency is to use less energy to provide the same service. In hospitals, energy efficiency offers a powerful and cost-effective tool to reduce greenhouse gas emissions, fuel consumption, and also running costs. Over a six-month period, the six gas-fired boilers that provide both a hospital’s heat and hot water were monitored. Analysis of the data obtained led to several actions being implemented in the hospital boiler room control system to improve the efficiency of the heat production system. Comparative studies were conducted, during similar weather periods, of the performance of the hospital’s hot water production system before and after the controls were implemented. Results indicate that the control actions applied proved to be effective. Finally; the paper offers a financial; primary energy saving and CO₂ reduction analysis that points to a 3,434.00 €/week savings in natural gas consumption; and a cut in CO₂ emissions of 20.3 tons/week; as compared to the reference facility. Full article

(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)

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Graphical abstract

1825 KiB

Open AccessArticle

A Multi-Element Diffuser Augmented Wind Turbine

by Søren Hjort and Helgi Larsen

Energies 2014, 7(5), 3256-3281; https://doi.org/10.3390/en7053256 - 19 May 2014

Cited by 41 | Viewed by 10671

Abstract

A new class of diffuser augmented wind turbines (DAWTs) is presented. The new diffuser concept exploits aero-dynamic principles for the creation of high-lift airfoil configurations known from the aircraft industry. Combining this with our objective of obtaining a compact power-efficient design has enabled [...] Read more.

A new class of diffuser augmented wind turbines (DAWTs) is presented. The new diffuser concept exploits aero-dynamic principles for the creation of high-lift airfoil configurations known from the aircraft industry. Combining this with our objective of obtaining a compact power-efficient design has enabled creation of a family of DAWT designs with energy capture potentials which exceed the power efficiency based on the diffuser exit area by 50%. The paper presents the 1D momentum theory governing the DAWTs, and discusses upper limits for power extraction, similar to the Betz limit applicable for bare Horizontal-Axis Wind Turbines (HAWTs). Inviscid axisymmetric panel code calculations are then used to drive the diffuser design towards higher power coefficients. Axisymmetric actuator disk Navier-Stokes calculations reveal the types of stall that inhibit the functionality of the ideal inviscid optimum, leading the design towards the new class of DAWTs. DAWT performance has been differently measured over time, creating confusion. Proper comparison with performance of existing DAWT designs is therefore emphasized. This involves reference to established literature results, and recalculation of earlier DAWT designs in an attempt to project all results onto a common metric. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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Graphical abstract

590 KiB

Open AccessArticle

Valuation of Wind Energy Projects: A Real Options Approach

by Luis M. Abadie and José M. Chamorro

Energies 2014, 7(5), 3218-3255; https://doi.org/10.3390/en7053218 - 19 May 2014

Cited by 43 | Viewed by 9021

Abstract

We address the valuation of an operating wind farm and the finite-lived option to invest in it under different reward/support schemes: a constant feed-in tariff, a premium on top of the electricity market price (either a fixed premium or a variable subsidy such [...] Read more.

We address the valuation of an operating wind farm and the finite-lived option to invest in it under different reward/support schemes: a constant feed-in tariff, a premium on top of the electricity market price (either a fixed premium or a variable subsidy such as a renewable obligation certificate or ROC), and a transitory subsidy, among others. Futures contracts on electricity with ever longer maturities enable market-based valuations to be undertaken. The model considers up to three sources of uncertainty: the electricity price, the level of wind generation, and the certificate (ROC) price where appropriate. When analytical solutions are lacking, we resort to a trinomial lattice combined with Monte Carlo simulation; we also use a two-dimensional binomial lattice when uncertainty in the ROC price is considered. Our data set refers to the UK. The numerical results show the impact of several factors involved in the decision to invest: the subsidy per MWh generated, the initial lump-sum subsidy, the maturity of the investment option, and electricity price volatility. Different combinations of variables can help bring forward investments in wind generation. One-off policies, e.g., a transitory initial subsidy, seem to have a stronger effect than a fixed premium per MWh produced. Full article

(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)

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350 KiB

Open AccessArticle

Online Parameter Identification of Ultracapacitor Models Using the Extended Kalman Filter

by Lei Zhang, Zhenpo Wang, Fengchun Sun and David G. Dorrell

Energies 2014, 7(5), 3204-3217; https://doi.org/10.3390/en7053204 - 15 May 2014

Cited by 91 | Viewed by 8072

Abstract

Ultracapacitors (UCs) are the focus of increasing attention in electric vehicle and renewable energy system applications due to their excellent performance in terms of power density, efficiency, and lifespan. Modeling and parameterization of UCs play an important role in model-based regulation and management [...] Read more.

Ultracapacitors (UCs) are the focus of increasing attention in electric vehicle and renewable energy system applications due to their excellent performance in terms of power density, efficiency, and lifespan. Modeling and parameterization of UCs play an important role in model-based regulation and management for a reliable and safe operation. In this paper, an equivalent circuit model template composed of a bulk capacitor, a second-order capacitance-resistance network, and a series resistance, is employed to represent the dynamics of UCs. The extended Kalman Filter is then used to recursively estimate the model parameters in the Dynamic Stress Test (DST) on a specially established test rig. The DST loading profile is able to emulate the practical power sinking and sourcing of UCs in electric vehicles. In order to examine the accuracy of the identified model, a Hybrid Pulse Power Characterization test is carried out. The validation result demonstrates that the recursively calibrated model can precisely delineate the dynamic voltage behavior of UCs under the discrepant loading condition, and the online identification approach is thus capable of extracting the model parameters in a credible and robust manner. Full article

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1830 KiB

Open AccessReview

A Review on Cold Start of Proton Exchange Membrane Fuel Cells

by Zhongmin Wan, Huawei Chang, Shuiming Shu, Yongxiang Wang and Haolin Tang

Energies 2014, 7(5), 3179-3203; https://doi.org/10.3390/en7053179 - 13 May 2014

Cited by 110 | Viewed by 12528

Abstract

Successful and rapid startup of proton exchange membrane fuel cells (PEMFCs) at subfreezing temperatures (also called cold start) is of great importance for their commercialization in automotive and portable devices. In order to maintain good proton conductivity, the water content in the membrane [...] Read more.

Successful and rapid startup of proton exchange membrane fuel cells (PEMFCs) at subfreezing temperatures (also called cold start) is of great importance for their commercialization in automotive and portable devices. In order to maintain good proton conductivity, the water content in the membrane must be kept at a certain level to ensure that the membrane remains fully hydrated. However, the water in the pores of the catalyst layer (CL), gas diffusion layer (GDL) and the membrane may freeze once the cell temperature decreases below the freezing point (T_f). Thus, methods which could enable the fuel cell startup without or with slight performance degradation at subfreezing temperature need to be studied. This paper presents an extensive review on cold start of PEMFCs, including the state and phase changes of water in PEMFCs, impacts of water freezing on PEMFCs, numerical and experimental studies on PEMFCs, and cold start strategies. The impacts on each component of the fuel cell are discussed in detail. Related numerical and experimental work is also discussed. It should be mentioned that the cold start strategies, especially the enumerated patents, are of great reference value on the practical cold start process. Full article

(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells)

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734 KiB

Open AccessArticle

Equivalent Consumption Minimization Strategy for the Control of Real Driving NOx Emissions of a Diesel Hybrid Electric Vehicle

by Tobias Nüesch, Alberto Cerofolini, Giorgio Mancini, Nicolò Cavina, Christopher Onder and Lino Guzzella

Energies 2014, 7(5), 3148-3178; https://doi.org/10.3390/en7053148 - 12 May 2014

Cited by 102 | Viewed by 13306

Abstract

Motivated by the fact that the real driving NOx emissions (RDE) of conventional diesel vehicles can exceed the legislation norms by far, a concept for the control of RDE with a diesel parallel hybrid electric vehicle (HEV) is proposed. By extending the well-known [...] Read more.

Motivated by the fact that the real driving NOx emissions (RDE) of conventional diesel vehicles can exceed the legislation norms by far, a concept for the control of RDE with a diesel parallel hybrid electric vehicle (HEV) is proposed. By extending the well-known equivalent consumption minimization strategy (ECMS), the power split degree of freedom is used to control the NOx emissions and the battery state of charge (SOC) simultaneously. Through an appropriate formulation of the problem, the feedback control is shown to be separable into two dependent PI controllers. By hardware-in-the-loop (HIL) experiments, as well as by simulations, the proposed method is shown to minimize the fuel consumption while tracking a given reference trajectory for both the NOx emissions and the battery SOC. Full article

(This article belongs to the Special Issue Advances in Hybrid Vehicles)

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1092 KiB

Open AccessArticle

Development of a Direct Methanol Fuel Cell with Lightweight Disc Type Current Collectors

by Yean-Der Kuan, Shin-Min Lee and Ming-Feng Sung

Energies 2014, 7(5), 3136-3147; https://doi.org/10.3390/en7053136 - 12 May 2014

Cited by 15 | Viewed by 7279

Abstract

The direct methanol fuel cell (DMFC) adopts methanol solution as a fuel suitable for low power portable applications. A miniature, lightweight, passive air-breathing design is therefore desired. This paper presents a novel planar disc-type DMFC with multiple cells containing a novel developed lightweight [...] Read more.

The direct methanol fuel cell (DMFC) adopts methanol solution as a fuel suitable for low power portable applications. A miniature, lightweight, passive air-breathing design is therefore desired. This paper presents a novel planar disc-type DMFC with multiple cells containing a novel developed lightweight current collector at both the anode and cathode sides. The present lightweight current collector adopts FR4 Glass/Epoxy as the substrate with the current collecting areas located at the corresponding membrane electrolyte assembly (MEA) areas. The current collecting areas are fabricated by sequentially coating a corrosion resistant layer and electrical conduction layer via the thermal evaporation technique. The anode current collector has carved flow channels for fuel transport and production. The cathode current collector has drilled holes for passive air breathing. In order to ensure feasibility in the present concept a 3-cell prototype DMFC module with lightweight disc type current collectors is designed and constructed. Experiments were conducted to measure the cell performance. The results show that the highest cell power output is 54.88 mW·cm⁻² and successfully demonstrate the feasibility of this novel design. Full article

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698 KiB

Open AccessArticle

Preparation of Slag Wool by Integrated Waste-Heat Recovery and Resource Recycling of Molten Blast Furnace Slags: From Fundamental to Industrial Application

by Dawei Zhao, Zuotai Zhang, Xulong Tang, Lili Liu and Xidong Wang

Energies 2014, 7(5), 3121-3135; https://doi.org/10.3390/en7053121 - 9 May 2014

Cited by 47 | Viewed by 9856

Abstract

The present paper investigated the process of the slag wool fabrication using high temperature blast furnace (BF) slag modified by coal ash (CA). The liquidus temperature and viscosity of the slag system with different mass ratios of BF slag and CA were measured [...] Read more.

The present paper investigated the process of the slag wool fabrication using high temperature blast furnace (BF) slag modified by coal ash (CA). The liquidus temperature and viscosity of the slag system with different mass ratios of BF slag and CA were measured through an inner cylinder rotation method. The approximate mass ratio used to fabricate the slag wool was therefore determined and slag wool was then successfully prepared with a high-speed air injection method in the laboratory. The effect of mBF/m ratio, slag temperature for injection and air pressure on the preparation of slag wool was systematically investigated. The mechanical and thermal properties were also studied to confirm the long-term working conditions of the slag wool. An industry-scale slag wool production application was established. The energy consumption and the pollutant generation, were analyzed and compared with the traditional production method, which indicated a 70% reduction in energy consumption and a 90% pollution emission decrease. Full article

(This article belongs to the Special Issue Waste Heat Recovery—Strategy and Practice)

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Graphical abstract

680 KiB

Open AccessArticle

Condition Parameter Modeling for Anomaly Detection in Wind Turbines

by Yonglong Yan, Jian Li and David Wenzhong Gao

Energies 2014, 7(5), 3104-3120; https://doi.org/10.3390/en7053104 - 6 May 2014

Cited by 34 | Viewed by 7564

Abstract

Data collected from the supervisory control and data acquisition (SCADA) system, used widely in wind farms to obtain operational and condition information about wind turbines (WTs), is of important significance for anomaly detection in wind turbines. The paper presents a novel model for [...] Read more.

Data collected from the supervisory control and data acquisition (SCADA) system, used widely in wind farms to obtain operational and condition information about wind turbines (WTs), is of important significance for anomaly detection in wind turbines. The paper presents a novel model for wind turbine anomaly detection mainly based on SCADA data and a back-propagation neural network (BPNN) for automatic selection of the condition parameters. The SCADA data sets are determined through analysis of the cumulative probability distribution of wind speed and the relationship between output power and wind speed. The automatic BPNN-based parameter selection is for reduction of redundant parameters for anomaly detection in wind turbines. Through investigation of cases of WT faults, the validity of the automatic parameter selection-based model for WT anomaly detection is verified. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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629 KiB

Open AccessArticle

An Optimal Reactive Power Control Strategy for a DFIG-Based Wind Farm to Damp the Sub-Synchronous Oscillation of a Power System

by Bin Zhao, Hui Li, Mingyu Wang, Yaojun Chen, Shengquan Liu, Dong Yang, Chao Yang, Yaogang Hu and Zhe Chen

Energies 2014, 7(5), 3086-3103; https://doi.org/10.3390/en7053086 - 5 May 2014

Cited by 11 | Viewed by 8584

Abstract

This study presents the auxiliary damping control with the reactive power loop on the rotor-side converter of doubly-fed induction generator (DFIG)-based wind farms to depress the sub-synchronous resonance oscillations in nearby turbogenerators. These generators are connected to a series capacitive compensation transmission system. [...] Read more.

This study presents the auxiliary damping control with the reactive power loop on the rotor-side converter of doubly-fed induction generator (DFIG)-based wind farms to depress the sub-synchronous resonance oscillations in nearby turbogenerators. These generators are connected to a series capacitive compensation transmission system. First, the damping effect of the reactive power control of the DFIG-based wind farms was theoretically analyzed, and a transfer function between turbogenerator speed and the output reactive power of the wind farms was introduced to derive the analytical expression of the damping coefficient. The phase range to obtain positive damping was determined. Second, the PID phase compensation parameters of the auxiliary damping controller were optimized by a genetic algorithm to obtain the optimum damping in the entire subsynchronous frequency band. Finally, the validity and effectiveness of the proposed auxiliary damping control were demonstrated on a modified version of the IEEE first benchmark model by time domain simulation analysis with the use of DigSILENT/PowerFactory. Theoretical analysis and simulation results show that this derived damping factor expression and the condition of the positive damping can effectively analyze their impact on the system sub-synchronous oscillations, the proposed wind farms reactive power additional damping control strategy can provide the optimal damping effect over the whole sub-synchronous frequency band, and the control effect is better than the active power additional damping control strategy based on the power system stabilizator. Full article

(This article belongs to the Special Issue Wind Turbines 2014)

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588 KiB

Open AccessArticle

Statistical Diagnosis of the Best Weibull Methods for Wind Power Assessment for Agricultural Applications

by Abul Kalam Azad, Mohammad Golam Rasul and Talal Yusaf

Energies 2014, 7(5), 3056-3085; https://doi.org/10.3390/en7053056 - 2 May 2014

Cited by 146 | Viewed by 10077

Abstract

The best Weibull distribution methods for the assessment of wind energy potential at different altitudes in desired locations are statistically diagnosed in this study. Seven different methods, namely graphical method (GM), method of moments (MOM), standard deviation method (STDM), maximum likelihood method (MLM), [...] Read more.

The best Weibull distribution methods for the assessment of wind energy potential at different altitudes in desired locations are statistically diagnosed in this study. Seven different methods, namely graphical method (GM), method of moments (MOM), standard deviation method (STDM), maximum likelihood method (MLM), power density method (PDM), modified maximum likelihood method (MMLM) and equivalent energy method (EEM) were used to estimate the Weibull parameters and six statistical tools, namely relative percentage of error, root mean square error (RMSE), mean percentage of error, mean absolute percentage of error, chi-square error and analysis of variance were used to precisely rank the methods. The statistical fittings of the measured and calculated wind speed data are assessed for justifying the performance of the methods. The capacity factor and total energy generated by a small model wind turbine is calculated by numerical integration using Trapezoidal sums and Simpson’s rules. The results show that MOM and MLM are the most efficient methods for determining the value of k and c to fit Weibull distribution curves. Full article

(This article belongs to the Special Issue Renewable Energy for Agriculture)

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1458 KiB

Open AccessArticle

A Simulation Framework for Optimal Energy Storage Sizing

by Carlos Suazo-Martínez, Eduardo Pereira-Bonvallet and Rodrigo Palma-Behnke

Energies 2014, 7(5), 3033-3055; https://doi.org/10.3390/en7053033 - 2 May 2014

Cited by 26 | Viewed by 7508

Abstract

Despite the increasing interest in Energy Storage Systems (ESS), quantification of their technical and economical benefits remains a challenge. To assess the use of ESS, a simulation approach for ESS optimal sizing is presented. The algorithm is based on an adapted Unit Commitment, [...] Read more.

Despite the increasing interest in Energy Storage Systems (ESS), quantification of their technical and economical benefits remains a challenge. To assess the use of ESS, a simulation approach for ESS optimal sizing is presented. The algorithm is based on an adapted Unit Commitment, including ESS operational constraints, and the use of high performance computing (HPC). Multiple short-term simulations are carried out within a multiple year horizon. Evaluation is performed for Chile's Northern Interconnected Power System (SING). The authors show that a single year evaluation could lead to sub-optimal results when evaluating optimal ESS size. Hence, it is advisable to perform long-term evaluations of ESS. Additionally, the importance of detailed simulation for adequate assessment of ESS contributions and to fully capture storage value is also discussed. Furthermore, the robustness of the optimal sizing approach is evaluated by means of a sensitivity analyses. The results suggest that regulatory frameworks should recognize multiple value streams from storage in order to encourage greater ESS integration. Full article

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3155 KiB

Open AccessArticle

A Combined State of Charge Estimation Method for Lithium-Ion Batteries Used in a Wide Ambient Temperature Range

by Fei Feng, Rengui Lu and Chunbo Zhu

Energies 2014, 7(5), 3004-3032; https://doi.org/10.3390/en7053004 - 2 May 2014

Cited by 79 | Viewed by 11731

Abstract

Ambient temperature is a significant factor that influences the characteristics of lithium-ion batteries, which can produce adverse effects on state of charge (SOC) estimation. In this paper, an integrated SOC algorithm that combines an advanced ampere-hour counting (Adv Ah) method and multistate open-circuit [...] Read more.

Ambient temperature is a significant factor that influences the characteristics of lithium-ion batteries, which can produce adverse effects on state of charge (SOC) estimation. In this paper, an integrated SOC algorithm that combines an advanced ampere-hour counting (Adv Ah) method and multistate open-circuit voltage (multi OCV) method, denoted as “Adv Ah + multi OCV”, is proposed. Ah counting is a simple and general method for estimating SOC. However, the available capacity and coulombic efficiency in this method are influenced by the operating states of batteries, such as temperature and current, thereby causing SOC estimation errors. To address this problem, an enhanced Ah counting method that can alter the available capacity and coulombic efficiency according to temperature is proposed during the SOC calculation. Moreover, the battery SOCs between different temperatures can be mutually converted in accordance with the capacity loss. To compensate for the accumulating errors in Ah counting caused by the low precision of current sensors and lack of accurate initial SOC, the OCV method is used for calibration and as a complement. Given the variation of available capacities at different temperatures, rated/non-rated OCV–SOCs are established to estimate the initial SOCs in accordance with the Ah counting SOCs. Two dynamic tests, namely, constant- and alternated-temperature tests, are employed to verify the combined method at different temperatures. The results indicate that our method can provide effective and accurate SOC estimation at different ambient temperatures. Full article

(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)

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2073 KiB

Open AccessArticle

Development of an Indoor Airflow Energy Harvesting System for Building Environment Monitoring

by Fei Fei, Shengli Zhou, John D. Mai and Wen Jung Li

Energies 2014, 7(5), 2985-3003; https://doi.org/10.3390/en7052985 - 2 May 2014

Cited by 22 | Viewed by 9238

Abstract

Wireless sensor networks (WSNs) have been widely used for intelligent building management applications. Typically, indoor environment parameters such as illumination, temperature, humidity and air quality are monitored and adjusted by an intelligent building management system. However, owing to the short life-span of the [...] Read more.

Wireless sensor networks (WSNs) have been widely used for intelligent building management applications. Typically, indoor environment parameters such as illumination, temperature, humidity and air quality are monitored and adjusted by an intelligent building management system. However, owing to the short life-span of the batteries used at the sensor nodes, the maintenance of such systems has been labor-intensive and time-consuming. This paper discusses a battery-less self-powering system that converts the mechanical energy from the airflow in ventilation ducts into electrical energy. The system uses a flutter energy conversion device (FECD) capable of working at low airflow speeds while installed on the ventilation ducts inside of buildings. A power management strategy implemented with a circuit system ensures sufficient power for driving commercial electronic devices. For instance, the power management circuit is capable of charging a 1 F super capacitor to 2 V under ventilation duct airflow speeds of less than 3 m/s. Full article

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374 KiB

Open AccessArticle

The Optimal Price Ratio of Typical Energy Sources in Beijing Based on the Computable General Equilibrium Model

by Yongxiu He, Yangyang Liu, Tian Xia, Min Du and Hongzhen Guo

Energies 2014, 7(5), 2961-2984; https://doi.org/10.3390/en7052961 - 30 Apr 2014

Cited by 11 | Viewed by 7475

Abstract

In Beijing, China, the rational consumption of energy is affected by the insufficient linkage mechanism of the energy pricing system, the unreasonable price ratio and other issues. This paper combines the characteristics of Beijing’s energy market, putting forward the society-economy equilibrium indicator R [...] Read more.

In Beijing, China, the rational consumption of energy is affected by the insufficient linkage mechanism of the energy pricing system, the unreasonable price ratio and other issues. This paper combines the characteristics of Beijing’s energy market, putting forward the society-economy equilibrium indicator R maximization taking into consideration the mitigation cost to determine a reasonable price ratio range. Based on the computable general equilibrium (CGE) model, and dividing four kinds of energy sources into three groups, the impact of price fluctuations of electricity and natural gas on the Gross Domestic Product (GDP), Consumer Price Index (CPI), energy consumption and CO₂ and SO₂ emissions can be simulated for various scenarios. On this basis, the integrated effects of electricity and natural gas price shocks on the Beijing economy and environment can be calculated. The results show that relative to the coal prices, the electricity and natural gas prices in Beijing are currently below reasonable levels; the solution to these unreasonable energy price ratios should begin by improving the energy pricing mechanism, through means such as the establishment of a sound dynamic adjustment mechanism between regulated prices and market prices. This provides a new idea for exploring the rationality of energy price ratios in imperfect competitive energy markets. Full article

(This article belongs to the Special Issue Energy Transitions and Economic Change)

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2077 KiB

Open AccessArticle

Autoregressive with Exogenous Variables and Neural Network Short-Term Load Forecast Models for Residential Low Voltage Distribution Networks

by Christopher Bennett, Rodney A. Stewart and Junwei Lu

Energies 2014, 7(5), 2938-2960; https://doi.org/10.3390/en7052938 - 30 Apr 2014

Cited by 67 | Viewed by 9448

Abstract

This paper set out to identify the significant variables which affect residential low voltage (LV) network demand and develop next day total energy use (NDTEU) and next day peak demand (NDPD) forecast models for each phase. The models were developed using both autoregressive [...] Read more.

This paper set out to identify the significant variables which affect residential low voltage (LV) network demand and develop next day total energy use (NDTEU) and next day peak demand (NDPD) forecast models for each phase. The models were developed using both autoregressive integrated moving average with exogenous variables (ARIMAX) and neural network (NN) techniques. The data used for this research was collected from a LV transformer serving 128 residential customers. It was observed that temperature accounted for half of the residential LV network demand. The inclusion of the double exponential smoothing algorithm, autoregressive terms, relative humidity and day of the week dummy variables increased model accuracy. In terms of R² and for each modelling technique and phase, NDTEU hindcast accuracy ranged from 0.77 to 0.87 and forecast accuracy ranged from 0.74 to 0.84. NDPD hindcast accuracy ranged from 0.68 to 0.74 and forecast accuracy ranged from 0.56 to 0.67. The NDTEU models were more accurate than the NDPD models due to the peak demand time series being more variable in nature. The NN models had slight accuracy gains over the ARIMAX models. A hybrid model was developed which combined the best traits of the ARIMAX and NN techniques, resulting in improved hindcast and forecast fits across the all three phases. Full article

(This article belongs to the Special Issue Smart Grids: The Electrical Power Network and Communication System)

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2141 KiB

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Battery Management System—Balancing Modularization Based on a Single Switched Capacitor and Bi-Directional DC/DC Converter with the Auxiliary Battery

by Mohamed Daowd, Mailier Antoine, Noshin Omar, Philippe Lataire, Peter Van Den Bossche and Joeri Van Mierlo

Energies 2014, 7(5), 2897-2937; https://doi.org/10.3390/en7052897 - 29 Apr 2014

Cited by 55 | Viewed by 23368

Abstract

Lithium-based batteries are considered as the most advanced batteries technology, which can be designed for high energy or high power storage systems. However, the battery cells are never fully identical due to the fabrication process, surrounding environment factors and differences between the cells [...] Read more.

Lithium-based batteries are considered as the most advanced batteries technology, which can be designed for high energy or high power storage systems. However, the battery cells are never fully identical due to the fabrication process, surrounding environment factors and differences between the cells tend to grow if no measures are taken. In order to have a high performance battery system, the battery cells should be continuously balanced for maintain the variation between the cells as small as possible. Without an appropriate balancing system, the individual cell voltages will differ over time and battery system capacity will decrease quickly. These issues will limit the electric range of the electric vehicle (EV) and some cells will undergo higher stress, whereby the cycle life of these cells will be shorter. Quite a lot of cell balancing/equalization topologies have been previously proposed. These balancing topologies can be categorized into passive and active balancing. Active topologies are categorized according to the active element used for storing the energy such as capacitor and/or inductive component as well as controlling switches or converters. This paper proposes an intelligent battery management system (BMS) including a battery pack charging and discharging control with a battery pack thermal management system. The BMS user input/output interfacing. The battery balancing system is based on battery pack modularization architecture. The proposed modularized balancing system has different equalization systems that operate inside and outside the modules. Innovative single switched capacitor (SSC) control strategy is proposed to balance between the battery cells in the module (inside module balancing, IMB). Novel utilization of isolated bidirectional DC/DC converter (IBC) is proposed to balance between the modules with the aid of the EV auxiliary battery (AB). Finally an experimental step-up has been implemented for the validation of the proposed balancing system. Full article

(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)

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479 KiB

Open AccessArticle

A New Topology and Control Strategy for a Hybrid Battery-Ultracapacitor Energy Storage System

by Changle Xiang, Yanzi Wang, Sideng Hu and Weida Wang

Energies 2014, 7(5), 2874-2896; https://doi.org/10.3390/en7052874 - 29 Apr 2014

Cited by 95 | Viewed by 10656

Abstract

This study investigates a new hybrid energy storage system (HESS), which consists of a battery bank and an ultra-capacitor (UC) bank, and a control strategy for this system. The proposed topology uses a bi-directional DC-DC converter with a lower power rating than those [...] Read more.

This study investigates a new hybrid energy storage system (HESS), which consists of a battery bank and an ultra-capacitor (UC) bank, and a control strategy for this system. The proposed topology uses a bi-directional DC-DC converter with a lower power rating than those used in the traditional HESS topology. The proposed HESS has four operating modes, and the proposed control strategy chooses the appropriate operating mode and regulates the distribution of power between the battery bank and the UC bank. Additionally, the control system prevents surges during mode switching and ensures that both the battery bank and the bi-directional DC-DC converter operate within their power limits. The proposed HESS is used to improve the performance of an existing power-split hybrid electric vehicle (HEV). A method for calculating the parameters of the proposed HESS is presented. A simulation model of the proposed HESS and control strategy was developed, and a scaled-down experimental platform was constructed. The results of the simulations and the experiments provide strong evidence for the feasibility of the proposed topology and the control strategy. The performance of the HESS is not influenced by the power limits of the bi-directional DC-DC converter. Full article

(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)

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311 KiB

Open AccessArticle

Energy Substitution, Technical Change and Rebound Effects

by Steve Sorrell

Energies 2014, 7(5), 2850-2873; https://doi.org/10.3390/en7052850 - 29 Apr 2014

Cited by 62 | Viewed by 12939

Abstract

This paper investigates the relationships between energy efficiency improvements by producers, the ease of substitution between energy and other inputs and the size of the resulting “rebound effects”. Fundamentally, easier substitution leads to larger rebounds. Focusing upon conceptual and methodological issues, the paper [...] Read more.

This paper investigates the relationships between energy efficiency improvements by producers, the ease of substitution between energy and other inputs and the size of the resulting “rebound effects”. Fundamentally, easier substitution leads to larger rebounds. Focusing upon conceptual and methodological issues, the paper highlights the challenges of estimating and modeling rebound effects with the help of production and cost functions and questions the robustness of the evidence base in this area. It argues that the multiple definitions of “elasticities of substitution” are a source of confusion, the most commonly estimated elasticity is of little practical value, the empirical literature is contradictory, prone to bias and difficult to use and there are only tenuous links between this literature and the assumptions used within energy-economic models. While “energy-augmenting technical change” provides the natural choice of independent variable for an estimate of rebound effects, most empirical studies do not estimate this form of technical change, many modeling studies do not simulate it and others simulate it in such a way as to underestimate rebound effects. As a result, the paper argues that current econometric and modeling studies do not provide reliable guidance on the magnitude of rebound effects in different industrial sectors. Full article

(This article belongs to the Special Issue Energy Transitions and Economic Change)

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Energies, Volume 7, Issue 5 (May 2014) – 35 articles , Pages 2740-3511

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