Energies

516 KiB

Open AccessArticle

Energy and Exergy Analysis and Optimization of Combined Heat and Power Systems. Comparison of Various Systems

by Michel Feidt and Monica Costea

Energies 2012, 5(9), 3701-3722; https://doi.org/10.3390/en5093701 - 24 Sep 2012

Cited by 30 | Viewed by 7138

The paper presents a comparison of various CHP system configurations, such as Vapour Turbine, Gas Turbine, Internal Combustion Engine, External Combustion Engine (Stirling, Ericsson), when different thermodynamic criteria are considered, namely the first law efficiency and exergy efficiency. Thermodynamic optimization of these systems [...] Read more.

The paper presents a comparison of various CHP system configurations, such as Vapour Turbine, Gas Turbine, Internal Combustion Engine, External Combustion Engine (Stirling, Ericsson), when different thermodynamic criteria are considered, namely the first law efficiency and exergy efficiency. Thermodynamic optimization of these systems is performed intending to maximize the exergy, when various practical related constraints (imposed mechanical useful energy, imposed heat demand, imposed heat to power ratio) or main physical limitations (limited heat availability, maximum system temperature allowed, thermo-mechanical constraints) are taken into account. A sensitivity analysis to model parameters is given. The results have shown that the various added constraints were useful for the design allowing to precise the influence of the model main parameters on the system design. Future perspective of the work and recommendations are stated. Full article

(This article belongs to the Special Issue Exergy Analysis of Energy Systems)

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296 KiB

Open AccessArticle

A Revisit to the Hydrogen Desorption/Absorption Behaviors of LiAlH₄/LiBH₄: Effects of Catalysts

by Pattaraporn Sridechprasat, Labhatrada Phuirot, Pramoch Rangsunvigit, Boonyarach Kitiyanan and Santi Kulprathipanja

Energies 2012, 5(9), 3691-3700; https://doi.org/10.3390/en5093691 - 21 Sep 2012

Cited by 6 | Viewed by 5693

Abstract

The hydrogen desorption/absorption behaviors of LiAlH₄/LiBH₄ with a focus on the effects of catalysts, namely TiCl₃, TiO₂, VCl₃, and ZrCl₄, were investigated using a thermal-volumetric apparatus. The hydrogen desorption was performed from [...] Read more.

The hydrogen desorption/absorption behaviors of LiAlH₄/LiBH₄ with a focus on the effects of catalysts, namely TiCl₃, TiO₂, VCl₃, and ZrCl₄, were investigated using a thermal-volumetric apparatus. The hydrogen desorption was performed from room temperature to 300 °C with a heating rate of 2 °C min⁻¹. The LiAlH₄–LiBH₄ mixture with a molar ratio of 2:1 decomposed between 100 and 220 °C, and the hydrogen desorption capacity reached up to 6.6 wt %. Doping 1 mol % of a catalyst to the mixture resulted in the two-step decomposition and a decrease in the hydrogen desorption temperature. All the doped samples provided lower amountz of desorbed hydrogen than that obtained from the undoped one. No hydrogen absorption was observed under 8.5 MPa of hydrogen pressure and 300 °C for 6 h. Despite the fact each of the catalysts may affect the hydrogen storage behaviors of the mixture differently, none resulted in a change in the sample reversibility. Full article

(This article belongs to the Special Issue Hydrogen Energy and Fuel Cells)

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449 KiB

Open AccessArticle

Dispatch Method for Independently Owned Hydropower Plants in the Same River Flow

by Ivan Rajšl, Perica Ilak, Marko Delimar and Slavko Krajcar

Energies 2012, 5(9), 3674-3690; https://doi.org/10.3390/en5093674 - 19 Sep 2012

Cited by 11 | Viewed by 5698

Abstract

This paper proposes a coexistence model for two independent companies both operating hydropower plants in the same river flow, based on a case study of the Cetina river basin in Croatia. Companies are participants of the day-ahead electricity market. The incumbent company owns [...] Read more.

This paper proposes a coexistence model for two independent companies both operating hydropower plants in the same river flow, based on a case study of the Cetina river basin in Croatia. Companies are participants of the day-ahead electricity market. The incumbent company owns the existing hydropower plants and holds concessions for the water. The new company decides to build a pump storage hydropower plant that uses one of the existing reservoirs as its lower reservoir. Meeting reservoir water balance is affected by decisions by both companies which are independently seeking maximal profit. Methods for water use settlement and preventing of spillage are proposed. A mixed-integer linear programming approach is used. Head effects on output power levels are also considered. Existences of dispatches that satisfy both companies are shown. Full article

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Graphical abstract

628 KiB

Open AccessArticle

An Improved Quantum-Behaved Particle Swarm Optimization Method for Economic Dispatch Problems with Multiple Fuel Options and Valve-Points Effects

by Qun Niu, Zhuo Zhou, Hong-Yun Zhang and Jing Deng

Energies 2012, 5(9), 3655-3673; https://doi.org/10.3390/en5093655 - 19 Sep 2012

Cited by 31 | Viewed by 6235

Abstract

Quantum-behaved particle swarm optimization (QPSO) is an efficient and powerful population-based optimization technique, which is inspired by the conventional particle swarm optimization (PSO) and quantum mechanics theories. In this paper, an improved QPSO named SQPSO is proposed, which combines QPSO with a selective [...] Read more.

Quantum-behaved particle swarm optimization (QPSO) is an efficient and powerful population-based optimization technique, which is inspired by the conventional particle swarm optimization (PSO) and quantum mechanics theories. In this paper, an improved QPSO named SQPSO is proposed, which combines QPSO with a selective probability operator to solve the economic dispatch (ED) problems with valve-point effects and multiple fuel options. To show the performance of the proposed SQPSO, it is tested on five standard benchmark functions and two ED benchmark problems, including a 40-unit ED problem with valve-point effects and a 10-unit ED problem with multiple fuel options. The results are compared with differential evolution (DE), particle swarm optimization (PSO) and basic QPSO, as well as a number of other methods reported in the literature in terms of solution quality, convergence speed and robustness. The simulation results confirm that the proposed SQPSO is effective and reliable for both function optimization and ED problems. Full article

(This article belongs to the Special Issue Hybrid Advanced Techniques for Forecasting in Energy Sector)

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574 KiB

Open AccessArticle

An Innovative Reconfigurable Integrated Converter Topology Suitable for Distributed Generation

by Renato Rizzo, Pietro Tricoli and Ivan Spina

Energies 2012, 5(9), 3640-3654; https://doi.org/10.3390/en5093640 - 18 Sep 2012

Cited by 26 | Viewed by 6269

Abstract

The electricity market and environmental concerns, with wide utilization of renewable sources, have improved the diffusion of distributed generation units changing the operations of distribution grids from passive networks to microgrids. A microgrid includes a cluster of electrical loads, energy storage devices and [...] Read more.

The electricity market and environmental concerns, with wide utilization of renewable sources, have improved the diffusion of distributed generation units changing the operations of distribution grids from passive networks to microgrids. A microgrid includes a cluster of electrical loads, energy storage devices and microsources, which provide both power and heat to their local area. A microgrid has usually one connection point to the utility grid through power electronic converters placed at customers’ sites. This paper analyses a Reconfigurable Integrated Converter (RIC) used for a domestic microgrid with inputs from the AC mains and photovoltaic arrays, and two DC outputs at different voltage levels. A RIC as a dual-boost DC-DC converter is proposed, modelled and analysed in the paper. The advantages of such a topology in comparison with traditional boost converters are outlined. Reported simulations results give evidence on the controllability of this converter and the capability of achieving the desired voltage outputs with reduced ripple. Full article

(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)

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1322 KiB

Open AccessArticle

Preliminary Ray Tracing and Experimental Study on the Effect of Mirror Coating on the Optical Efficiency of a Solid Dielectric Compound Parabolic Concentrator

by Gang Pei, Guiqiang Li, Yuehong Su, Jie Ji, Saffa Riffat and Hongfei Zheng

Energies 2012, 5(9), 3627-3639; https://doi.org/10.3390/en5093627 - 18 Sep 2012

Cited by 32 | Viewed by 6753

Abstract

This study aims to determine the necessity of applying a mirror coating on the side of a truncated solid dielectric CPC (compound parabolic concentrator) since ray tracing analysis has revealed that part of the incoming rays do not undergo total internal reflection, even [...] Read more.

This study aims to determine the necessity of applying a mirror coating on the side of a truncated solid dielectric CPC (compound parabolic concentrator) since ray tracing analysis has revealed that part of the incoming rays do not undergo total internal reflection, even within the half acceptance angle of the CPC. An experiment was designed and conducted indoors and outdoors to study the effect of mirror coating on the optical performance of a solid dielectric CPC. Ray tracing was also employed for the detailed analysis and its results are compared with the measurements. Based on these, a concept of partial coating is proposed and verified through simulation. The results show that a partly coated solid dielectric CPC may have a better optical efficiency than a solid CPC without coating for a certain range of incidence angles. Full article

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1157 KiB

Open AccessArticle

Effect of Smart Rotor Control Using a Deformable Trailing Edge Flap on Load Reduction under Normal and Extreme Turbulence

by Wei Yu, Ming Ming Zhang and Jian Zhong Xu

Energies 2012, 5(9), 3608-3626; https://doi.org/10.3390/en5093608 - 18 Sep 2012

Cited by 26 | Viewed by 6493

Abstract

This paper presents a newly developed aero-servo-elastic platform for implementing smart rotor control and shows its effectiveness with aerodynamic loads on large-scale offshore wind turbines. The platform was built by improving the FAST/Aerodyn codes with the integration of an external deformable trailing edge [...] Read more.

This paper presents a newly developed aero-servo-elastic platform for implementing smart rotor control and shows its effectiveness with aerodynamic loads on large-scale offshore wind turbines. The platform was built by improving the FAST/Aerodyn codes with the integration of an external deformable trailing edge flap controller in the Matlab/Simulink software. Smart rotor control was applied to an Upwind/NREL 5 MW reference wind turbine under various operating wind conditions in accordance with the IEC Normal Turbulence Model (NTM) and Extreme Turbulence Model (ETM). Results showed that, irrespective of whether the NTM or ETM case was considered, aerodynamic load in terms of blade flapwise root moment and tip deflection were effectively reduced. Furthermore, the smart rotor control also positively affected generator power, pitch system and tower load. These results laying a foundation for a future migration of the “smart rotor control” concept into the design of large-scale offshore wind turbines. Full article

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1546 KiB

Open AccessArticle

Harmonic Analysis and Fault-Tolerant Capability of a Semi-12-Phase Permanent-Magnet Synchronous Machine Used for EVs

by Ping Zheng, Fan Wu, Yi Sui, Pengfei Wang, Yu Lei and Haipeng Wang

Energies 2012, 5(9), 3586-3607; https://doi.org/10.3390/en5093586 - 17 Sep 2012

Cited by 16 | Viewed by 7342

Abstract

This paper deals with a fault-tolerant semi-12-phase permanent-magnet synchronous machine (PMSM) used for electric vehicles. High fault-tolerant and low toque ripple features are achieved by employing fractional slot concentrated windings (FSCWs) and open windings. Excessive magnetomotive force (MMF) harmonic components can lead to [...] Read more.

This paper deals with a fault-tolerant semi-12-phase permanent-magnet synchronous machine (PMSM) used for electric vehicles. High fault-tolerant and low toque ripple features are achieved by employing fractional slot concentrated windings (FSCWs) and open windings. Excessive magnetomotive force (MMF) harmonic components can lead to thermal demagnetization of rotor magnets as well as high core loss. An improved all-teeth-wound winding disposition that changes the winding factor of each harmonic is applied to suppress harmonics. A relatively large slot leakage inductance that limits the short-circuit current (SCC) induced in the short-circuited winding is proposed to deal with short-circuit fault. Fault-tolerant controls up to two phases open circuited are investigated in this paper based on keeping the same torque-producing MMF. The fault-tolerant control strategies corresponding to each faulty mode are studied and compared to ensure high performance operation. Full article

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417 KiB

Open AccessArticle

Performance Analysis and Optimization of a Solar Powered Stirling Engine with Heat Transfer Considerations

by Chieh-Li Chen, Chia-En Ho and Her-Terng Yau

Energies 2012, 5(9), 3573-3585; https://doi.org/10.3390/en5093573 - 17 Sep 2012

Cited by 46 | Viewed by 6607

Abstract

This paper investigates the optimization of the performance of a solar powered Stirling engine based on finite-time thermodynamics. Heat transference in the heat exchangers between a concentrating solar collector and the Stirling engine is studied. The irreversibility of a Stirling engine is considered [...] Read more.

This paper investigates the optimization of the performance of a solar powered Stirling engine based on finite-time thermodynamics. Heat transference in the heat exchangers between a concentrating solar collector and the Stirling engine is studied. The irreversibility of a Stirling engine is considered with the heat transfer following Newton's law. The power generated by a Stirling engine is used as an objective function for maximum power output design with the concentrating solar collector temperature and the engine thermal efficiency as the optimization parameters. The maximum output power of engine and its corresponding system parameters are determined using a genetic algorithm. Full article

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281 KiB

Open AccessArticle

Energy Efficiency in the Brazilian Pulp and Paper Industry

by Guilherme Fracaro, Esa Vakkilainen, Marcelo Hamaguchi and Samuel Nelson Melegari de Souza

Energies 2012, 5(9), 3550-3572; https://doi.org/10.3390/en5093550 - 17 Sep 2012

Cited by 35 | Viewed by 6658

Abstract

Industrial energy efficiency has received increasing attention in many countries because of its importance in the pursuit of energy supply security, increased economic competitiveness and in the mitigation of greenhouse gases emissions. This paper aimed to evaluate the energy consumption development of the [...] Read more.

Industrial energy efficiency has received increasing attention in many countries because of its importance in the pursuit of energy supply security, increased economic competitiveness and in the mitigation of greenhouse gases emissions. This paper aimed to evaluate the energy consumption development of the Brazilian pulp and paper industry through an energy decomposition analysis and an energy efficiency index approach over a 30 years period. An international comparison with other important paper-producing countries (i.e., Canada, United States of America, Finland and Sweden) was carried out. It was concluded that despite a significant increase in the energy efficiency levels, responsible for 5.6 PJ savings in electricity consumption and for 38.6 PJ savings in fuels consumption between 1979 and 2009, a saving potential of 7.8 PJ and 146.2 PJ related to the annual consumption of electricity and fuels, respectively, could be identified in the Brazilian pulp and paper industry. Among the countries evolved in the international comparison, both the Swedish and Finnish industries were the most efficient, followed by the Brazilian, American and Canadian, the latter being the only one where there was a reduction in the energy efficiency levels from 1979 to 2009. Full article

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455 KiB

Open AccessArticle

A Method for Balancing a Single-Phase Loaded Three-Phase Induction Generator

by Yaw-Juen Wang and Ming-Hsueh Lee

Energies 2012, 5(9), 3534-3549; https://doi.org/10.3390/en5093534 - 13 Sep 2012

Cited by 7 | Viewed by 7231

Abstract

When a three-phase induction generator (IG) supplies unbalanced loads, its terminal voltages and line currents are also unbalanced, which may cause the IG to overheat and need to be derated. A single-phase loaded self-excited induction generator (SEIG) works under most unfavorable load unbalance [...] Read more.

When a three-phase induction generator (IG) supplies unbalanced loads, its terminal voltages and line currents are also unbalanced, which may cause the IG to overheat and need to be derated. A single-phase loaded self-excited induction generator (SEIG) works under most unfavorable load unbalance conditions. This paper proposes a three-capacitor circuit scheme and a method to find the values of the self-excitation capacitors that allow the SEIG to be balanced. The SEIG is modeled by a two-port network equivalent circuit that resolves the SEIG into its positive- and negative-sequence circuits associated with the self-excitation capacitors and the load. The network can then be analyzed by common AC circuit analysis techniques. Successful results for balancing the SEIG supplying a single-phase load have been achieved by properly choosing the values of the excitation capacitors. The proposed method has also been validated by experiments on a 0.37 kW SEIG. Full article

(This article belongs to the Special Issue Electrical Power and Energy Systems)

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191 KiB

Open AccessArticle

Molecular Dynamics Simulations of Clathrate Hydrates on Specialised Hardware Platforms

by Nicola Varini, Niall J. English and Christian R. Trott

Energies 2012, 5(9), 3526-3533; https://doi.org/10.3390/en5093526 - 12 Sep 2012

Cited by 16 | Viewed by 5553

Abstract

Classical equilibrium molecular dynamics (MD) simulations have been performed to investigate the computational performance of the Simple Point Charge (SPC) and TIP4P water models applied to simulation of methane hydrates, and also of liquid water, on a variety of specialised hardware platforms, in [...] Read more.

Classical equilibrium molecular dynamics (MD) simulations have been performed to investigate the computational performance of the Simple Point Charge (SPC) and TIP4P water models applied to simulation of methane hydrates, and also of liquid water, on a variety of specialised hardware platforms, in addition to estimation of various equilibrium properties of clathrate hydrates. The FPGA-based accelerator MD-GRAPE 3 was used to accelerate substantially the computation of non-bonded forces, while GPU-based platforms were also used in conjunction with CUDA-enabled versions of the LAMMPS MD software packages to reduce computational time dramatically. The dependence of molecular system size and scaling with number of processors was also investigated. Considering performance relative to power consumption, it is seen that GPU-based computing is quite attractive. Full article

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537 KiB

Open AccessReview

Biotechnological Utilization with a Focus on Anaerobic Treatment of Cheese Whey: Current Status and Prospects

by Aspasia A. Chatzipaschali and Anastassios G. Stamatis

Energies 2012, 5(9), 3492-3525; https://doi.org/10.3390/en5093492 - 10 Sep 2012

Cited by 98 | Viewed by 12735

Abstract

Cheese whey utilization is of major concern nowadays. Its high organic matter content, in combination with the high volumes produced and limited treatment options make cheese whey a serious environmental problem. However, the potential production of biogas (methane), hydrogen or other marketable products [...] Read more.

Cheese whey utilization is of major concern nowadays. Its high organic matter content, in combination with the high volumes produced and limited treatment options make cheese whey a serious environmental problem. However, the potential production of biogas (methane), hydrogen or other marketable products with a simultaneous high COD reduction through appropriate treatment proves that cheese whey must be considered as an energy resource rather than a pollutant. The presence of biodegradable components in the cheese whey coupled with the advantages of anaerobic digestion processes over other treatment methods makes anaerobic digestion an attractive and suitable treatment option. This paper intends to review the most representative applications of anaerobic treatment of cheese whey currently being exploited and under research. Moreover, an effort has been made to categorize the common characteristics of the various research efforts and find a comparative basis, as far as their results are concerned. In addition, a number of dairy industries already using such anaerobic digestion systems are presented. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2012)

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515 KiB

Open AccessArticle

Experimental Study on Frost Height of Round Plate Fin-Tube Heat Exchangers for Mobile Heat Pumps

by Moo-Yeon Lee, Yongchan Kim and Dong-Yeon Lee

Energies 2012, 5(9), 3479-3491; https://doi.org/10.3390/en5093479 - 10 Sep 2012

Cited by 14 | Viewed by 6609

Abstract

The objective of this study was to provide experimental data that could be used to predict frost growth and frost performance of a round plate fin-tube heat exchanger for low temperature heat pumps used in zero emission vehicles under cold weather conditions. In [...] Read more.

The objective of this study was to provide experimental data that could be used to predict frost growth and frost performance of a round plate fin-tube heat exchanger for low temperature heat pumps used in zero emission vehicles under cold weather conditions. In this study, round plate fin-tube heat exchangers were tested with variation of the fin space, air flow rate, relative humidity, and inlet air temperature. Frost height was measured and considered with the boundary layer interruption between fins. Frost height for 8.0 mm of fin space was increased by approximately 91.9% with an increase of relative humidity from 50.0% to 80.0%. The growth rate of frost height at 1.2 m³/min was observed to be 13.0% greater than that at 0.8 m³/min. Finally, the variation of the blockage ratio with fin space would be an important reference for designing advanced heat exchangers that operate under cold weather conditions. Full article

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245 KiB

Open AccessArticle

The Economic Cost of Unsupplied Diesel Product in Korea Using Input-Output Analysis

by Myunghwan Kim and Seung-Hoon Yoo

Energies 2012, 5(9), 3465-3478; https://doi.org/10.3390/en5093465 - 06 Sep 2012

Cited by 3 | Viewed by 4949

Abstract

Diesel is an essential factor in industrial production and development, and thus its stable supply is a crucial element for economic growth. The supply shortage of diesel has massive economic costs, namely supply shortage costs. This paper attempts to apply input-output (I-O) analysis [...] Read more.

Diesel is an essential factor in industrial production and development, and thus its stable supply is a crucial element for economic growth. The supply shortage of diesel has massive economic costs, namely supply shortage costs. This paper attempts to apply input-output (I-O) analysis to measuring the supply shortage cost of industrial diesel in Korea by finding an optimal way of allocating the limited diesel resources to different sectors according to the objective of maximizing overall value-added. To this end, a static I-O framework is presented using a recently published I-O table. The results indicate that the marginal cost of unsupplied diesel ranges from KRW 716 (USD 0.65) to KRW 113,376 (USD 103.07) per liter and these costs depend not only on the shortage rate of each non-diesel sector but also on the level of its own final demand. The quantitative results are useful for policy-makers to set economic reliability standards, develop optimum curtailment levels and priorities, and plan curtailment strategies for diesel supply and demand. Full article

1531 KiB

Open AccessArticle

Feasibility Study of Micro-Wind Turbines for Powering Wireless Sensors on a Cable-Stayed Bridge

by Jong-Woong Park, Hyung-Jo Jung, Hongki Jo and Billie F. Spencer, Jr.

Energies 2012, 5(9), 3450-3464; https://doi.org/10.3390/en5093450 - 06 Sep 2012

Cited by 37 | Viewed by 9144

Abstract

In this study, the feasibility of using micro-wind turbines to power wireless sensors on a cable-stayed bridge is comprehensively investigated. To this end, the wind environment around a bridge onto which a turbine is installed is examined, as is the power consumption of [...] Read more.

In this study, the feasibility of using micro-wind turbines to power wireless sensors on a cable-stayed bridge is comprehensively investigated. To this end, the wind environment around a bridge onto which a turbine is installed is examined, as is the power consumption of a wireless sensor. Feasible alternators and rotors are then carefully selected to make an effective small wind generator (known as a micro-wind turbine). Using the three specially selected micro-wind turbines, a series of experiments was conducted to find the turbine best able to generate the largest amount of power. Finally, a horizontal-axis micro-wind turbine with a six-blade rotor was combined with a wireless sensor to validate experimentally its actual power-charging capability. It is demonstrated that the micro-wind turbine can generate sufficient electricity to power a wireless sensor under moderate wind conditions. Full article

(This article belongs to the Special Issue Wind Turbines)

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1359 KiB

Open AccessReview

Wind Turbine Blade Design

by Peter J. Schubel and Richard J. Crossley

Energies 2012, 5(9), 3425-3449; https://doi.org/10.3390/en5093425 - 06 Sep 2012

Cited by 330 | Viewed by 92575

Abstract

A detailed review of the current state-of-art for wind turbine blade design is presented, including theoretical maximum efficiency, propulsion, practical efficiency, HAWT blade design, and blade loads. The review provides a complete picture of wind turbine blade design and shows the dominance of [...] Read more.

A detailed review of the current state-of-art for wind turbine blade design is presented, including theoretical maximum efficiency, propulsion, practical efficiency, HAWT blade design, and blade loads. The review provides a complete picture of wind turbine blade design and shows the dominance of modern turbines almost exclusive use of horizontal axis rotors. The aerodynamic design principles for a modern wind turbine blade are detailed, including blade plan shape/quantity, aerofoil selection and optimal attack angles. A detailed review of design loads on wind turbine blades is offered, describing aerodynamic, gravitational, centrifugal, gyroscopic and operational conditions. Full article

(This article belongs to the Special Issue Wind Turbines)

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4597 KiB

Open AccessArticle

Reducing the Energy Demand of Multi-Dwelling Units in a Mediterranean Climate Using Solar Protection Elements

by Ángel L. León, Samuel Domínguez, Miguel A. Campano and Cristina Ramírez-Balas

Energies 2012, 5(9), 3398-3424; https://doi.org/10.3390/en5093398 - 06 Sep 2012

Cited by 21 | Viewed by 6974

Abstract

It is known that glazed openings are very important elements in the energetic behavior of buildings, especially in Mediterranean climates where there are many hours of solar radiation. The objective of this study was to determine the influence of solar protection on the [...] Read more.

It is known that glazed openings are very important elements in the energetic behavior of buildings, especially in Mediterranean climates where there are many hours of solar radiation. The objective of this study was to determine the influence of solar protection on the energy demand of public housing structures in these climates. To this end, the reduction in energy demand achieved by fixed solar protectors in combination with mobile protectors (blinds) was quantified, including an evaluation of the influence of their geometry, dimensions, degree of openness, and the orientation of the opening. To analyze and quantify energetic demand, a block of public housing units in a neighborhood of Seville (latitude 37°23' N) was used as a model. This block is typical of public housing in the Mediterranean region. Simulated energetic models were created using DesignBuilder, achieving reductions in the annual energy demand from 10% to 27% according to the orientation chosen. The results and conclusions of the study are applicable to new construction, energetic rehabilitation projects, and/or the improvement of existing buildings. Full article

(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)

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381 KiB

Open AccessArticle

Exergoeconomic Evaluation of a Modern Ultra-Supercritical Power Plant

by Ligang Wang, Yongping Yang, Changqing Dong, Zhiping Yang, Gang Xu and Lingnan Wu

Energies 2012, 5(9), 3381-3397; https://doi.org/10.3390/en5093381 - 06 Sep 2012

Cited by 47 | Viewed by 7713

Abstract

In this paper, the exergoeconomic analysis was conducted to an existing ultra-supercritical coal-fired power plant in China to understand the cost-formation process, to evaluate the economic performance of each component and to find possible solutions for more cost-effective designs. The total revenue requirement [...] Read more.

In this paper, the exergoeconomic analysis was conducted to an existing ultra-supercritical coal-fired power plant in China to understand the cost-formation process, to evaluate the economic performance of each component and to find possible solutions for more cost-effective designs. The total revenue requirement (TRR) and the specific exergy costing (SPECO) methods were applied for economic analysis and exergy costing, respectively. Quantitative balances of exergy and exergetic costs as well as necessary auxiliary equations for both individual component and the overall system were established. The results show that the exergoeconomic factors of the furnace and heat exchangers at low temperature levels, including air preheater and low-pressure feedwater preheaters, are rather small; while those of other components are relatively large. Moving more heat absorption into furnace to use the effective radiation heat transfer, increasing the air preheating temperature and adding more low pressure feedwater preheaters can be promising solutions for future design. Full article

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1890 KiB

Open AccessArticle

A Method for Identification of Driving Patterns in Hybrid Electric Vehicles Based on a LVQ Neural Network

by Hongwen He, Chao Sun and Xiaowei Zhang

Energies 2012, 5(9), 3363-3380; https://doi.org/10.3390/en5093363 - 05 Sep 2012

Cited by 50 | Viewed by 8077

Abstract

Driving patterns exert an important influence on the fuel economy of vehicles, especially hybrid electric vehicles. This paper aims to build a method to identify driving patterns with enough accuracy and less sampling time compared than other driving pattern recognition algorithms. Firstly a [...] Read more.

Driving patterns exert an important influence on the fuel economy of vehicles, especially hybrid electric vehicles. This paper aims to build a method to identify driving patterns with enough accuracy and less sampling time compared than other driving pattern recognition algorithms. Firstly a driving pattern identifier based on a Learning Vector Quantization neural network is established to analyze six selected representative standard driving cycles. Micro-trip extraction and Principal Component Analysis methods are applied to ensure the magnitude and diversity of the training samples. Then via Matlab/Simulink, sample training simulation is conducted to determine the minimum neuron number of the Learning Vector Quantization neural network and, as a result, to help simplify the identifier model structure and reduce the data convergence time. Simulation results have proved the feasibility of this method, which decreases the sampling window length from about 250–300 s to 120 s with an acceptable accuracy. The driving pattern identifier is further used in an optimized co-simulation together with a parallel hybrid vehicle model and improves the fuel economy by about 8%. Full article

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655 KiB

Open AccessArticle

An Intelligent Multiagent System for Autonomous Microgrid Operation

by Hak-Man Kim, Yujin Lim and Tetsuo Kinoshita

Energies 2012, 5(9), 3347-3362; https://doi.org/10.3390/en5093347 - 05 Sep 2012

Cited by 56 | Viewed by 8042

Abstract

A microgrid is an eco-friendly power system because renewable sources such as solar and wind power are used as the main power sources. For this reason, much research, development, and demonstration projects have recently taken place in many countries. Operation is one of [...] Read more.

A microgrid is an eco-friendly power system because renewable sources such as solar and wind power are used as the main power sources. For this reason, much research, development, and demonstration projects have recently taken place in many countries. Operation is one of the important research topics for microgrids. For efficient and economical microgrid operation, a human operator is required as in other power systems, but it is difficult because there are some restrictions related to operation costs and privacy issues. To overcome the restriction, autonomous operation for microgrids is required. Recently, an intelligent agent system for autonomous microgrid operation has been studied as a potential solution. This paper proposes a multiagent system for autonomous microgrid operation. To build the multiagent system, the functionalities of agents, interactions among agents, and an effective agent protocol have been designed. The proposed system has been implemented by using an ADIPS/DASH framework as an agent platform. The intelligent multiagent system for microgrid operation based on the proposed scheme is tested to show the functionality and feasibility on a distributed environment through the Internet. Full article

(This article belongs to the Special Issue Electrical Power and Energy Systems)

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334 KiB

Open AccessArticle

A Fuzzy Group Forecasting Model Based on Least Squares Support Vector Machine (LS-SVM) for Short-Term Wind Power

by Qian Zhang, Kin Keung Lai, Dongxiao Niu, Qiang Wang and Xuebin Zhang

Energies 2012, 5(9), 3329-3346; https://doi.org/10.3390/en5093329 - 05 Sep 2012

Cited by 43 | Viewed by 6579

Abstract

Many models have been developed to forecast wind farm power output. It is generally difficult to determine whether the performance of one model is consistently better than that of another model under all circumstances. Motivated by this finding, we aimed to integrate groups [...] Read more.

Many models have been developed to forecast wind farm power output. It is generally difficult to determine whether the performance of one model is consistently better than that of another model under all circumstances. Motivated by this finding, we aimed to integrate groups of models into an aggregated model using fuzzy theory to obtain further performance improvements. First, three groups of least squares support vector machine (LS-SVM) forecasting models were developed: univariate LS-SVM models, hybrid models using auto-regressive moving average (ARIMA) and LS-SVM and multivariate LS-SVM models. Each group of models is selected by a decorrelation maximisation method, and the remaining models can be regarded as experts in forecasting. Next, fuzzy aggregation and a defuzzification procedure are used to combine all of these forecasting results into the final forecast. For sample randomization, we statistically compare models. Results show that this group-forecasting model performs well in terms of accuracy and consistency. Full article

(This article belongs to the Special Issue Hybrid Advanced Techniques for Forecasting in Energy Sector)

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699 KiB

Open AccessArticle

Response Surface Methodology: An Emphatic Tool for Optimized Biodiesel Production Using Rice Bran and Sunflower Oils

by Muhammad Waseem Mumtaz, Ahmad Adnan, Farooq Anwar, Hamid Mukhtar, Muhammad Asam Raza, Farooq Ahmad and Umer Rashid

Energies 2012, 5(9), 3307-3328; https://doi.org/10.3390/en5093307 - 04 Sep 2012

Cited by 67 | Viewed by 7506

Abstract

The current study describes the emphatic use of response surface methodology for the optimized biodiesel production using chemical and enzymatic transesterification of rice bran and sunflower oils. Optimal biodiesel yields were determined to be 65.3 ± 2.0%, 73.4 ± 3.5%, 96.5 ± 1.6%, [...] Read more.

The current study describes the emphatic use of response surface methodology for the optimized biodiesel production using chemical and enzymatic transesterification of rice bran and sunflower oils. Optimal biodiesel yields were determined to be 65.3 ± 2.0%, 73.4 ± 3.5%, 96.5 ± 1.6%, 89.3 ± 2.0% and 41.7 ± 3.9% for rice bran oil and 65.6 ± 1.2%, 82.1 ± 1.7%, 92.5 ± 2.8%, 72.6 ± 1.6% and 50.4 ± 2.5% for sunflower oil via the transesterification catalyzed by NaOH, KOH and NaOCH₃,NOVOZYME-435 and A.n. Lipase, respectively. Based upon analysis of variance (ANOVA) and Response Surface plots significant impact of reaction parameters under study was ascertained. FTIR spectroscopic and HPLC methods were employed for monitoring the transesterification reaction progress while GC-MS analysis was performed to evaluate the compositional analysis of biodiesel. The fuel properties of both the rice bran and sunflower oil based biodiesel were shown to be technically compatible with the ASTM D6751 and EN 14214 standards. The monitoring of exhaust emission of synthesized biodiesels and their blends revealed a marked reduction in carbon monoxide (CO) and particulate matter (PM) levels, whereas an irregular trend was observed for NO_x emissions. Full article

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433 KiB

Open AccessArticle

Kinetic Study of the Pyrolysis of Waste Printed Circuit Boards Subject to Conventional and Microwave Heating

by Jing Sun, Wenlong Wang, Zhen Liu, Qingluan Ma, Chao Zhao and Chunyuan Ma

Energies 2012, 5(9), 3295-3306; https://doi.org/10.3390/en5093295 - 31 Aug 2012

Cited by 79 | Viewed by 8204

Abstract

This paper describes a kinetic study of the decomposition of waste printed circuit boards (WPCB) under conventional and microwave-induced pyrolysis conditions. We discuss the heating rates and the influence of the pyrolysis on the thermal decomposition kinetics of WPCB. We find that the [...] Read more.

This paper describes a kinetic study of the decomposition of waste printed circuit boards (WPCB) under conventional and microwave-induced pyrolysis conditions. We discuss the heating rates and the influence of the pyrolysis on the thermal decomposition kinetics of WPCB. We find that the thermal degradation of WPCB in a controlled conventional thermogravimetric analyzer (TGA) occurred in the temperature range of 300 °C–600 °C, where the main pyrolysis of organic matter takes place along with an expulsion of volumetric volatiles. The corresponding activation energy is decreased from 267 kJ/mol to 168 kJ/mol with increased heating rates from 20 °C/min to 50 °C/min. Similarly, the process of microwave-induced pyrolysis of WPCB material manifests in only one stage, judging by experiments with a microwave power of 700 W. Here, the activation energy is determined to be only 49 kJ/mol, much lower than that found in a conventional TGA subject to a similar heating rate. The low activation energy found in microwave-induced pyrolysis suggests that the adoption of microwave technology for the disposal of WPCB material and even for waste electronic and electrical equipment (WEEE) could be an attractive option. Full article

(This article belongs to the Special Issue Waste to Energy Technologies)

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748 KiB

Open AccessArticle

More Wind Power Integration with Adjusted Energy Carriers for Space Heating in Northern China

by Hongyu Long, Kunyao Xu, Ruilin Xu and Jianjun He

Energies 2012, 5(9), 3279-3294; https://doi.org/10.3390/en5093279 - 31 Aug 2012

Cited by 10 | Viewed by 6463 | Correction

Abstract

In Northern China, due to the high penetration of coal-fired cogeneration facilities, which are generally equipped with extraction-condensing steam turbines, lots of wind power resources may be wasted during the heating season. In contrast, considerable coal is consumed in the power generation sector. [...] Read more.

In Northern China, due to the high penetration of coal-fired cogeneration facilities, which are generally equipped with extraction-condensing steam turbines, lots of wind power resources may be wasted during the heating season. In contrast, considerable coal is consumed in the power generation sector. In this article, firstly it is revealed that there exists a serious divergence in the ratio of electrical to thermal energy between end users’ demand and the cogenerations’ production during off-peak load at night, which may negate active power-balancing of the electric power grid. Secondly, with respect to this divergence only occurring during off-peak load at night, a temporary proposal is given so as to enable the integration of more wind power. The authors suggest that if the energy carrier for part of the end users’ space heating is switched from heating water to electricity (e.g., electric heat pumps (EHPs) can provide space heating in the domestic sector), the ratio of electricity to heating water load should be adjusted to optimize the power dispatch between cogeneration units and wind turbines, resulting in fuel conservation. With this proposal, existing infrastructures are made full use of, and no additional ones are required. Finally a numerical simulation is performed in order to illustrate both the technical and economic feasibility of the aforementioned proposal, under ongoing infrastructures as well as electricity and space heating tariff conditions without changing participants’ benefits. The authors aim to persuade Chinese policy makers to enable EHPs to provide space heating to enable the integration of more wind power. Full article

(This article belongs to the Special Issue Wind Turbines)

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493 KiB

Open AccessArticle

Performance of Thermosyphon Solar Water Heaters in Series

by Yi-Mei Liu, Kung-Ming Chung, Keh-Chin Chang and Tsong-Sheng Lee

Energies 2012, 5(9), 3266-3278; https://doi.org/10.3390/en5093266 - 30 Aug 2012

Cited by 31 | Viewed by 6842

Abstract

More than a single thermosyphon solar water heater may be employed in applications when considerable hot water consumption is required. In this experimental investigation, eight typical Taiwanese solar water heaters were connected in series. Degree of temperature stratification and thermosyphon flow rate in [...] Read more.

More than a single thermosyphon solar water heater may be employed in applications when considerable hot water consumption is required. In this experimental investigation, eight typical Taiwanese solar water heaters were connected in series. Degree of temperature stratification and thermosyphon flow rate in a horizontal tank were evaluated. The system was tested under no-load, intermittent and continuous load conditions. Results showed that there was stratification in tanks under the no-load condition. Temperature stratification also redeveloped after the draw-off. Analysis of thermal performance of the system was conducted for each condition. Full article

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3051 KiB

Open AccessArticle

A Practical Protection Coordination Strategy Applied to Secondary and Facility Microgrids

by Dae-Geun Jin, Jong-Chan Choi, Dong-Jun Won, Hak-Ju Lee, Woo-Kyu Chae and Jung-Sung Park

Energies 2012, 5(9), 3248-3265; https://doi.org/10.3390/en5093248 - 30 Aug 2012

Cited by 11 | Viewed by 5563

Abstract

In a conventional distribution system, protection algorithms are designed to operate on a unidirectional high fault-current level. In a microgrid, a fault current from distributed generation (DG) may bring about a relay malfunction because of the bidirectional and relatively small fault current. Therefore, [...] Read more.

In a conventional distribution system, protection algorithms are designed to operate on a unidirectional high fault-current level. In a microgrid, a fault current from distributed generation (DG) may bring about a relay malfunction because of the bidirectional and relatively small fault current. Therefore, the conventional protection scheme is not applicable to microgrids and a new protection method must be developed. In this paper, two protection coordination algorithms which can be applied for facility and secondary microgrids are proposed, respectively. The proposed protection algorithms eliminate faults not by the EMS signal but by directional relays. Moreover, this makes the algorithms flexible regardless of the types and numbers of DG. The proposed protection algorithms were simulated at the KEPCO RI Microgrid Demonstration Site. Full article

(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)

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437 KiB

Open AccessArticle

Performance Analysis and Working Fluid Selection of a Supercritical Organic Rankine Cycle for Low Grade Waste Heat Recovery

by Hong Gao, Chao Liu, Chao He, Xiaoxiao Xu, Shuangying Wu and Yourong Li

Energies 2012, 5(9), 3233-3247; https://doi.org/10.3390/en5093233 - 30 Aug 2012

Cited by 102 | Viewed by 9167

Abstract

The performance analysis of a supercritical organic Rankine cycle system driven by exhaust heat using 18 organic working fluids is presented. Several parameters, such as the net power output, exergy efficiency, expander size parameter (SP), and heat exchanger requirement of evaporator [...] Read more.

The performance analysis of a supercritical organic Rankine cycle system driven by exhaust heat using 18 organic working fluids is presented. Several parameters, such as the net power output, exergy efficiency, expander size parameter (SP), and heat exchanger requirement of evaporator and the condenser, were used to evaluate the performance of this recovery cycle and screen the working fluids. The results reveal that in most cases, raising the expander inlet temperature is helpful to improve the net power output and the exergy efficiency. However, the effect of the expander inlet pressure on those parameters is related to the expander inlet temperature and working fluid used. Either lower expander inlet temperature and pressure, or higher expander inlet temperature and pressure, generally makes the net power output more. Lower expander inlet temperature results in larger total heat transfer requirement and expander size. According to the screening criteria of both the higher output and the lower investment, the following working fluids for the supercritical ORC system are recommended: R152a and R143a. Full article

(This article belongs to the Special Issue Waste to Energy Technologies)

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2258 KiB

Open AccessArticle

Impacts of Ventilation Ratio and Vent Balance on Cooling Load and Air Flow of Naturally Ventilated Attics

by Shimin Wang and Zhigang Shen

Energies 2012, 5(9), 3218-3232; https://doi.org/10.3390/en5093218 - 29 Aug 2012

Cited by 14 | Viewed by 6873

Abstract

The impacts of ventilation ratio and vent balance on cooling load and air flow of naturally ventilated attics are studied in this paper using an unsteady computational fluid dynamics (CFD) model. Buoyancy-driven turbulent ventilations in attics of gable-roof residential buildings are simulated for [...] Read more.

The impacts of ventilation ratio and vent balance on cooling load and air flow of naturally ventilated attics are studied in this paper using an unsteady computational fluid dynamics (CFD) model. Buoyancy-driven turbulent ventilations in attics of gable-roof residential buildings are simulated for typical summer conditions. Ventilation ratios from 1/400 to 1/25 combined with both balanced and unbalanced vent configurations are investigated. The modeling results show that the air flows in the attics are steady and exhibit a general streamline pattern that is qualitatively insensitive to the variations in ventilation ratio and vent configuration. The predicted temperature fields are characterized by thermal stratification, except for the soffit regions. It is demonstrated that an increase in ventilation ratio will reduce attic cooling load. Compared with unbalanced vent configurations, balanced attic ventilation is shown to be the optimal solution in both maximizing ventilating flow rate and minimizing cooling load for attics with ventilation ratio lower than 1/100. For attics with ventilation ratios greater than 1/67, a configuration of large ridge vent with small soffit vent favors ventilating air flow enhancement, while a configuration of small ridge vent with large soffit vent results in the lowest cooling energy consumption. Full article

(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)

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3014 KiB

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Energy from Agricultural and Animal Farming Residues: Potential at a Local Scale

by Giulia Fiorese and Giorgio Guariso

Energies 2012, 5(9), 3198-3217; https://doi.org/10.3390/en5093198 - 28 Aug 2012

Cited by 9 | Viewed by 6700

Abstract

Animal wastes from high-density farming have severe impacts on the nitrogen cycle. According to current regulations, the disposal of manure on cropland is constrained by nitrogen content in the agricultural soils. On the contrary, anaerobic digestion (AD) of these wastes can produce energy [...] Read more.

Animal wastes from high-density farming have severe impacts on the nitrogen cycle. According to current regulations, the disposal of manure on cropland is constrained by nitrogen content in the agricultural soils. On the contrary, anaerobic digestion (AD) of these wastes can produce energy and a digestate, which is easier to handle than manure and can be applied for agronomic uses. When herbaceous crops are co-digested with manure to increase the efficiency of biogas production, the nitrogen content in the digestate further increases, unless these larger plants are equipped with nitrogen stripping technologies. We propose a model to compare larger (cooperative) and smaller (single parcel) AD conversion plants. The whole process is modeled: from the collection of manures, to the cultivation of energy crops, to the disposal of the digestate. The model maximizes the energy produced on the basis of available biomass, road network, local heat demand and local availability of land for digestate disposal. Results are the optimal size and location of the plants, their technology and collection basins. The environmental performances of such plants are also evaluated. The study has been applied to the province of Forlì-Cesena, an Italian district where animal farming is particularly relevant. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2012)

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Energies, Volume 5, Issue 9 (September 2012) – 32 articles , Pages 3167-3722

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