Energies

5209 KiB

Open AccessArticle

Impact of Scheduling Flexibility on Demand Profile Flatness and User Inconvenience in Residential Smart Grid System

by Naveed Ul Hassan, Muhammad Adeel Pasha, Chau Yuen, Shisheng Huang and Xiumin Wang

Energies 2013, 6(12), 6608-6635; https://doi.org/10.3390/en6126608 - 18 Dec 2013

Cited by 47 | Viewed by 7481

The objective of this paper is to study the impact of scheduling flexibility on both demand profile flatness and user inconvenience in residential smart grid systems. Temporal variations in energy consumption by end users result in peaks and troughs in the aggregated demand [...] Read more.

The objective of this paper is to study the impact of scheduling flexibility on both demand profile flatness and user inconvenience in residential smart grid systems. Temporal variations in energy consumption by end users result in peaks and troughs in the aggregated demand profile. In a residential smart grid, some of these peaks and troughs can be eliminated through appropriate load balancing algorithms. However, load balancing requires user participation by allowing the grid to re-schedule some of their loads. In general, more scheduling flexibility can result in more demand profile flatness, however the resulting inconvenience to users would also increase. In this paper, our objective is to help the grid determine an appropriate amount of scheduling flexibility that it should demand from users, based on which, proper incentives can be designed. We consider three different types of scheduling flexibility (delay, advance scheduling and flexible re-scheduling) in flexible loads and develop both optimal and sub-optimal scheduling algorithms. We discuss their implementation in centralized and distributed manners. We also identify the existence of a saturation point. Beyond this saturation point, any increase in scheduling flexibility does not significantly affect the flatness of the demand profile while user inconvenience continues to increase. Moreover, full participation of all the households is not required since increasing user participation only marginally increases demand profile flatness. Full article

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

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586 KiB

Open AccessArticle

Three-Phase Primary Control for Unbalance Sharing between Distributed Generation Units in a Microgrid

by Tine L. Vandoorn, Jeroen D. M. De Kooning, Jan Van de Vyver and Lieven Vandevelde

Energies 2013, 6(12), 6586-6607; https://doi.org/10.3390/en6126586 - 18 Dec 2013

Cited by 4 | Viewed by 5328

Abstract

For islanded microgrids, droop-based control concepts have been developed both in single and three-phase variants. The three-phase controllers often assume a balanced network; hence, unbalance sharing and/or mitigation remains a challenging issue. Therefore, in this paper, unbalance is considered in a three-phase islanded [...] Read more.

For islanded microgrids, droop-based control concepts have been developed both in single and three-phase variants. The three-phase controllers often assume a balanced network; hence, unbalance sharing and/or mitigation remains a challenging issue. Therefore, in this paper, unbalance is considered in a three-phase islanded microgrid in which the distributed generation (DG) units are operated by the voltage-based droop (VBD) control. For this purpose, the VBD control, which has been developed for single-phase systems, is extended for a three-phase application and an additional control loop is added for unbalance mitigation and sharing. The method is based on an unbalance mitigation scheme by DG units in grid-connected systems, which is altered for usage in grid-forming DG units with droop control. The reaction of the DG units to unbalance is determined by the main parameter of the additional control loop, viz., the distortion damping resistance, R_d. The effect of R_d on the unbalance mitigation is studied in this paper, i.e., dependent on _Rd, the DG units can be resistive for unbalance (RU) or they can contribute in the weakest phase (CW). The paper shows that the RU method decreases the line losses in the system and achieves better power equalization between the DG unit’s phases. However, it leads to a larger voltage unbalance near the loads. The CW method leads to a more uneven power between the DG unit’s phases and larger line losses, but a better voltage quality near the load. However, it can negatively affect the stability of the system. In microgrids with multiple DG units, the distortion damping resistance is set such that the unbalanced load can be shared between multiple DG units in an actively controlled manner rather than being determined by the microgrid configuration solely. The unit with the lowest distortion damping resistance provides relatively more of the unbalanced currents. Full article

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

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1167 KiB

Open AccessArticle

Optimal Scheduling for the Complementary Energy Storage System Operation Based on Smart Metering Data in the DC Distribution System

by Bokyung Ko, Nugroho Prananto Utomo, Gilsoo Jang, Jaehan Kim and Jintae Cho

Energies 2013, 6(12), 6569-6585; https://doi.org/10.3390/en6126569 - 18 Dec 2013

Cited by 7 | Viewed by 6095

Abstract

The increasing penetration of distributed generation (DG) sources in low-voltage grid feeders causes problems concerning voltage regulation. The penetration of DG sources such as photovoltaics (PVs) in the distribution system can significantly impact the power flow and voltage conditions on the customer side. [...] Read more.

The increasing penetration of distributed generation (DG) sources in low-voltage grid feeders causes problems concerning voltage regulation. The penetration of DG sources such as photovoltaics (PVs) in the distribution system can significantly impact the power flow and voltage conditions on the customer side. As the DG sources are more commonly connected to low-voltage distribution systems, voltage fluctuations in the distribution system are experienced because of the DG fluctuation and uncertainty. Therefore, the penetration of DGs in distribution systems is often limited by the required operating voltage ranges. By using an energy storage system (ESS), voltage fluctuation can be compensated for, thus satisfying the voltage regulation requirements. This paper presents an ESS scheduling algorithm based on the power injection data obtained from a smart metering system. The proposed ESS scheduling algorithm is designed for use within a direct current (DC) distribution grid, which comprises customers, each with a PV and an ESS system. The purpose of this ESS scheduling algorithm is to optimize the ESS scheduling by considering the complementary operation among all the ESSs. Full article

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

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406 KiB

Open AccessArticle

Analysis and Design of a Transverse-Flux Dual Rotor Machine for Power-Split Hybrid Electric Vehicle Applications

by Ping Zheng, Quanbin Zhao, Jingang Bai, Bin Yu, Zhiyi Song and Jing Shang

Energies 2013, 6(12), 6548-6568; https://doi.org/10.3390/en6126548 - 17 Dec 2013

Cited by 19 | Viewed by 8490

Abstract

A novel compound-structure transverse-flux permanent-magnet synchronous machine (CS-TFPMSM) is proposed in this paper, which is used in hybrid electric vehicles (HEVs) to fulfill the power-split function. The key component of the CS-TFPMSM is a brushless transverse-flux dual rotor machine (TFDRM). The TFDRM originates [...] Read more.

A novel compound-structure transverse-flux permanent-magnet synchronous machine (CS-TFPMSM) is proposed in this paper, which is used in hybrid electric vehicles (HEVs) to fulfill the power-split function. The key component of the CS-TFPMSM is a brushless transverse-flux dual rotor machine (TFDRM). The TFDRM originates from the transverse-flux machines, and is capable of speed adjustment between the transverse-flux rotor and the permanent-magnet rotor without using any brushes. The structure and principle of the TFDRM are described. The torque equations of the TFDRM are deduced, which are different from those of traditional machines. Based on the investigation, the TFDRM tends to have high leakage and a poor power factor. The method to obtain high power factor is discussed. The back electromotive force (BEMF) and torque of the TFDRM are simulated with the variation of parameters, such as pole-pair number, width of the permanent magnets (PMs), and so on. A prototype of a 10kW TFDRM is designed. Full article

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

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1351 KiB

Open AccessArticle

Evaluation of Green Buildings’ Overall Performance through in Situ Monitoring and Simulations

by Francesco Asdrubali, Cinzia Buratti, Franco Cotana, Giorgio Baldinelli, Michele Goretti, Elisa Moretti, Catia Baldassarri, Elisa Belloni, Francesco Bianchi, Antonella Rotili, Marco Vergoni, Domenico Palladino and Daniele Bevilacqua

Energies 2013, 6(12), 6525-6547; https://doi.org/10.3390/en6126525 - 17 Dec 2013

Cited by 46 | Viewed by 7454

Abstract

The evaluation of the overall performance of a green building is complex, since many construction, energy and environmental aspects have to be considered. The Umbria Region in Italy, through various public tenders, recently funded several residential buildings, innovative in terms of construction quality, [...] Read more.

The evaluation of the overall performance of a green building is complex, since many construction, energy and environmental aspects have to be considered. The Umbria Region in Italy, through various public tenders, recently funded several residential buildings, innovative in terms of construction quality, green technologies and sustainable solutions, such as natural building materials, integrated sunspaces, PV (photovoltaic) modules and solar collectors, geothermal heat pumps, that had to be adopted to obtain the public contribution. The University of Perugia carried out an extended monitoring of these buildings, in order to verify the actual achievement of design objectives, to certify the real savings in terms of energy and environmental loads and to assess the indoor comfort conditions for occupants. In situ thermal, acoustical and lighting measurements were carried out for more than one year. Energy simulations were performed by means of codes which implement the algorithms required by the Italian Law. Moreover, a comparison between real consumptions and simulated energy requirements was carried out. Finally, the buildings were characterized from the environmental sustainability point of view, using the method adopted by the Umbria Region. This assessment was borrowed from ITACA (Institute for Innovation and Transparency in Government Procurement and Environmental Compatibility) procedure [an Italian procedure similar to Leadership in Energy and Environmental Design (LEED)] and consists of 20 worksheets, one for each different performance indicator, at the aim of carefully describing the environmental quality of the building. Full article

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487 KiB

Open AccessArticle

Performance Analysis of an Integrated Fixed Bed Gasifier Model for Different Biomass Feedstocks

by Sharmina Begum, Mohammad G. Rasul, Delwar Akbar and Naveed Ramzan

Energies 2013, 6(12), 6508-6524; https://doi.org/10.3390/en6126508 - 16 Dec 2013

Cited by 78 | Viewed by 10168

Abstract

Energy recovery from biomass by gasification technology has attracted significant interest because it satisfies a key requirement of environmental sustainability by producing near zero emissions. Though it is not a new technology, studies on its integrated process simulation and analysis are limited, in [...] Read more.

Energy recovery from biomass by gasification technology has attracted significant interest because it satisfies a key requirement of environmental sustainability by producing near zero emissions. Though it is not a new technology, studies on its integrated process simulation and analysis are limited, in particular for municipal solid waste (MSW) gasification. This paper develops an integrated fixed bed gasifier model of biomass gasification using the Advanced System for Process ENngineering (Aspen) Plus software for its performance analysis. A computational model was developed on the basis of Gibbs free energy minimization. The model is validated with experimental data of MSW and food waste gasification available in the literature. A reasonable agreement between measured and predicted syngas composition was found. Using the validated model, the effects of operating conditions, namely air-fuel ratio and gasifier temperature, on syngas production are studied. Performance analyses have been done for four different feedstocks, namely wood, coffee bean husks, green wastes and MSWs. The ultimate and proximate analysis data for each feedstock was used for model development. It was found that operating parameters have a significant influence on syngas composition. An air-fuel ratio of 0.3 and gasifier temperature of 700 °C provides optimum performance for a fixed bed gasifier for MSWs, wood wastes, green wastes and coffee bean husks. The developed model can be useful for gasification of other biomasses (e.g., food wastes, rice husks, poultry wastes and sugarcane bagasse) to predict the syngas composition. Therefore, the study provides an integrated gasification model which can be used for different biomass feedstocks. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2013)

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377 KiB

Open AccessArticle

Improvement of the Sustainability of Existing School Buildings According to the Leadership in Energy and Environmental Design (LEED)^® Protocol: A Case Study in Italy

by Giuliano Dall'O', Elisa Bruni and Angela Panza

Energies 2013, 6(12), 6487-6507; https://doi.org/10.3390/en6126487 - 16 Dec 2013

Cited by 25 | Viewed by 8026

Abstract

School-age students spend much of their time in school buildings. The sustainability of these buildings should be a priority as better comfort with a high indoor air quality contributes to an improvement in the conditions for learning. Although new school buildings are often [...] Read more.

School-age students spend much of their time in school buildings. The sustainability of these buildings should be a priority as better comfort with a high indoor air quality contributes to an improvement in the conditions for learning. Although new school buildings are often built with high standards of sustainability and energy efficiency, the existing school building stock is generally characterised by very poor quality. The energy retrofit of existing school buildings in recent years is part of the policies of the European Union and, consequently, of the Member States. However, rarely do these measures consider aspects other than energy. This paper proposes and discusses a feasibility study which provides a considerable improvement in the environmental quality of 14 school buildings located in northern Italy: the objective is to ensure the requirements for Leadership in Energy and Environmental Design (LEED)^® certification. The analysis considers both the technical and economic aspects. The study shows that there is a technical feasibility: the credits are between 42 and 54, moreover the major cost (the cost of building envelope and heating systems retrofit is 82.9% of the total cost) is due to the improvement of energy efficiency. The improvement of sustainability is therefore a reasonable strategy even if the application of the LEED Protocol in the Italian context involves some critical issues that are discussed in the paper. Full article

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1487 KiB

Open AccessArticle

Functionalization of Aligned Carbon Nanotubes to Enhance the Performance of Fuel Cell

by Jingbo Liu, Yuan Yuan and Sajid Bashir

Energies 2013, 6(12), 6476-6486; https://doi.org/10.3390/en6126476 - 16 Dec 2013

Cited by 17 | Viewed by 5839

Abstract

The focus of this research lies on fundamental research to provide guidelines for the design of new nanocatalyst toward improvement of the performance of proton exchange membrane fuel cells (PEMFCs). To achieve this overarching goal, several specific steps were taken with aims to: [...] Read more.

The focus of this research lies on fundamental research to provide guidelines for the design of new nanocatalyst toward improvement of the performance of proton exchange membrane fuel cells (PEMFCs). To achieve this overarching goal, several specific steps were taken with aims to: (1) provide guidelines for the design of new catalysts; (2) promote nanocatalyst applications towards alternative energy applications; and (3) integrate advanced instrumentation into nanocharacterization and fuel cell (FC) electrochemical behavior. In tandem with these goals, the cathode catalysts were extensively refined to improve the performance of PEMFCs and minimize noble metal usage. In this study, the major accomplishment was producing aligned carbon nanotubes (ACNTs), which were then modified by platinum (Pt) nanoparticles via a post-functionalization colloidal chemistry approach. The Pt-ACNTs demonstrated improved cathodic catalycity, by building better device endurance and decreased Pt loading. It was also determined that surface mechanical properties, such as elastic modulus and hardness were increased. Collectively, these enhancements provided an improved FC device. The electrochemical analyses indicated that the power density of the PEMFCs was increased to 900 mW/cm² and current density to 3000 mA/cm², respectively. The Pt loading was controlled at lower than 0.2 mg/cm² to decrease the manufacturing expenses. Full article

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

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542 KiB

Open AccessArticle

A Combined Cooperative Braking Model with a Predictive Control Strategy in an Electric Vehicle

by Hongqiang Guo, Hongwen He and Fengchun Sun

Energies 2013, 6(12), 6455-6475; https://doi.org/10.3390/en6126455 - 13 Dec 2013

Cited by 18 | Viewed by 8083

Abstract

Cooperative braking with regenerative braking and mechanical braking plays an important role in electric vehicles for energy-saving control. Based on the parallel and the series cooperative braking models, a combined model with a predictive control strategy to get a better cooperative braking performance [...] Read more.

Cooperative braking with regenerative braking and mechanical braking plays an important role in electric vehicles for energy-saving control. Based on the parallel and the series cooperative braking models, a combined model with a predictive control strategy to get a better cooperative braking performance is presented. The balance problem between the maximum regenerative energy recovery efficiency and the optimum braking stability is solved through an off-line process optimization stream with the collaborative optimization algorithm (CO). To carry out the process optimization stream, the optimal Latin hypercube design (Opt LHD) is presented to discrete the continuous design space. To solve the poor real-time problem of the optimization, a high-precision predictive model based on the off-line optimization data of the combined model is built, and a predictive control strategy is proposed and verified through simulation. The simulation results demonstrate that the predictive control strategy and the combined model are reasonable and effective. Full article

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

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645 KiB

Open AccessArticle

Decentralized and Real-Time Power Dispatch Control for an Islanded Microgrid Supported by Distributed Power Sources

by Changsun Ahn and Huei Peng

Energies 2013, 6(12), 6439-6454; https://doi.org/10.3390/en6126439 - 13 Dec 2013

Cited by 27 | Viewed by 6059

Abstract

Microgrids can deploy traditional and/or renewable power sources to support remote sites. Utilizing renewable power sources requires more complicated control strategies to achieve acceptable power quality and maintain grid stability. In this research, we assume that the grid stability problem is already solved. [...] Read more.

Microgrids can deploy traditional and/or renewable power sources to support remote sites. Utilizing renewable power sources requires more complicated control strategies to achieve acceptable power quality and maintain grid stability. In this research, we assume that the grid stability problem is already solved. As a next step, we focus on how the power can be dispatched from multiple power sources for improved grid efficiency. Isolated microgrids frequently require reconfigurations because of the grid expansion or component failures. Therefore, the control strategies ideally should be implemented in a plug-and-play fashion. Moreover, these strategies ideally require no pre-knowledge of the grid structure, and as little communication with neighboring power sources as possible. The control objective is to minimize a cost function that can be adjusted to reflect the desire to minimize energy cost and/or losses. An algorithm is designed to satisfy a derived necessary condition of function optimality. Such conditions are obtained by formulating Lagrange functions. An equivalent grid model approximates the grid structure which was later confirmed to represent the grid behavior adequately. For decentralized operations, we execute the distributed control sequentially using a simple token communication protocol. The performance of the combined system identification-Lagrange function minimization algorithm is demonstrated through simulations. Full article

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

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545 KiB

Open AccessArticle

Operation Optimization Based on the Power Supply and Storage Capacity of an Active Distribution Network

by Wenpeng Yu, Dong Liu and Yuhui Huang

Energies 2013, 6(12), 6423-6438; https://doi.org/10.3390/en6126423 - 11 Dec 2013

Cited by 29 | Viewed by 6732

Abstract

Due to the interconnection and active management of Distributed Generation (DG) and Energy Storage Systems (ESSs), the traditional electrical distribution network has become an Active Distribution Network (ADN), posing challenges to the operation optimization of the network. The power supply and storage capacity [...] Read more.

Due to the interconnection and active management of Distributed Generation (DG) and Energy Storage Systems (ESSs), the traditional electrical distribution network has become an Active Distribution Network (ADN), posing challenges to the operation optimization of the network. The power supply and storage capacity indexes of a Local Autonomy Control Region (LACR), which consists of DGs, ESSs and the network, are proposed in this paper to quantify the power regulating range of a LACR. DG/ESS and the network are considered as a whole in the model of the indexes, considering both network constraints and power constraints of the DG/ESS. The index quantifies the maximum LACR power supplied to or received from ADN lines. Similarly, power supply and storage capacity indexes of the ADN line are also proposed to quantify the maximum power exchanged between ADN lines. Then a practical algorithm to calculate the indexes is presented, and an operation optimization model is proposed based on the indexes to maximum the economic benefit of DG/ESS. In the optimization model, the power supply reliability of the ADN line is also considered. Finally, the indexes of power supply and storage capacity and the optimization are demonstrated in a case study. Full article

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

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278 KiB

Open AccessArticle

Experimental Study on a Passive Fuel Cell/Battery Hybrid Power System

by Yong-Song Chen, Sheng-Miao Lin and Boe-Shong Hong

Energies 2013, 6(12), 6413-6422; https://doi.org/10.3390/en6126413 - 10 Dec 2013

Cited by 29 | Viewed by 6964

Abstract

A laboratory-scale passive hybrid power system for transportation applications is constructed and tested in this study. The hybrid power system consists of a fuel cell stack connected with a diode, a lithium-ion battery pack connected with a DC/DC power converter and another diode. [...] Read more.

A laboratory-scale passive hybrid power system for transportation applications is constructed and tested in this study. The hybrid power system consists of a fuel cell stack connected with a diode, a lithium-ion battery pack connected with a DC/DC power converter and another diode. The power converter is employed to regulate the output voltage of the battery pack. The dynamic responses of current and voltage of the stack to the start-up and acceleration of the load are experimentally investigated at two different selected output voltages of the DC/DC converter in the battery line. The power sharing of each power source and efficiency are also analyzed and discussed. Experimental results show that the battery can compensate for the shortage of supplied power for the load demand during the start-up and acceleration. The lowest operating voltage of the fuel cell stack is limited by the regulated output voltage of the DC/DC converter. The major power loss in the hybrid power system is attributed to the diodes. The power train efficiency can be improved by lowering the ratio of forward voltage drop of the diode to the operating voltage of the fuel cell stack. Full article

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

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414 KiB

Open AccessReview

Biofuel Production in Ireland—An Approach to 2020 Targets with a Focus on Algal Biomass

by Fionnuala Murphy, Ger Devlin, Rory Deverell and Kevin McDonnell

Energies 2013, 6(12), 6391-6412; https://doi.org/10.3390/en6126391 - 4 Dec 2013

Cited by 82 | Viewed by 13697

Abstract

Under the Biofuels Obligation Scheme in Ireland, the biofuels penetration rate target for 2013 was set at 6% by volume from a previous 4% from 2010. In 2012 the fuel blend reached 3%, with approximately 70 million L of biodiesel and 56 million [...] Read more.

Under the Biofuels Obligation Scheme in Ireland, the biofuels penetration rate target for 2013 was set at 6% by volume from a previous 4% from 2010. In 2012 the fuel blend reached 3%, with approximately 70 million L of biodiesel and 56 million L of ethanol blended with diesel and gasoline, respectively. Up to and including April 2013, the current blend rate in Ireland for biodiesel was 2.3% and for bioethanol was 3.7% which equates to approximately 37.5 million L of biofuel for the first four months of 2013. The target of 10% by 2020 remains, which equates to approximately 420 million L yr⁻¹. Achieving the biofuels target would require 345 ktoe by 2020 (14,400 TJ). Utilizing the indigenous biofuels in Ireland such as tallow, used cooking oil and oil seed rape leaves a shortfall of approximately 12,000 TJ or 350 million L (achieving only 17% of the 10% target) that must be either be imported or met by other renewables. Other solutions seem to suggest that microalgae (for biodiesel) and macroalgae (for bioethanol) could meet this shortfall for indigenous Irish production. This paper aims to review the characteristics of algae for biofuel production based on oil yields, cultivation, harvesting, processing and finally in terms of the European Union (EU) biofuels sustainability criteria, where, up to 2017, a 35% greenhouse gas (GHG) emissions reduction is required compared to fossil fuels. From 2017 onwards, a 50% GHG reduction is required for existing installations and from 2018, a 60% reduction for new installations is required. Full article

(This article belongs to the Special Issue Algae Fuel 2013)

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469 KiB

Open AccessArticle

Energy Analysis of a Student-Designed Solar House

by Samantha Wermager and Stuart Baur

Energies 2013, 6(12), 6373-6390; https://doi.org/10.3390/en6126373 - 4 Dec 2013

Cited by 10 | Viewed by 6359

Abstract

This paper presents the findings from an undergraduate research project concerning the energy efficiency, consumption, and generation of a 1000 ft² (92.9 m²) solar house. The results were compared to a home of similar size and layout, built using traditional [...] Read more.

This paper presents the findings from an undergraduate research project concerning the energy efficiency, consumption, and generation of a 1000 ft² (92.9 m²) solar house. The results were compared to a home of similar size and layout, built using traditional construction methods. The solar house was modeled after the Chameleon House: Missouri University of Science and Technology’s 2013 entry in the U.S. Department of Energy Solar Decathlon. The efficiency of the design was analyzed using Energy-10 Version 1.8 software. For this comparison, a fictional American couple was created and a breakdown of their energy-use habits was recorded to accurately depict the magnitude of energy consumption. A 71% energy savings was forecasted using the Energy-10 software through the incorporation of various energy-conserving strategies in the home’s design. In addition, if a 9.1 kW photovoltaic array is also installed on a home of this size, it is possible to fully offset the energy consumption of the home. The forecasted energy usage and production detailed in this report shall be used for analyzing the integrity of the design of the Chameleon House as well as future solar houses constructed by the Missouri S&T Solar House Team. Full article

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1740 KiB

Open AccessArticle

Effect of Tower Shadow and Wind Shear in a Wind Farm on AC Tie-Line Power Oscillations of Interconnected Power Systems

by Jin Tan, Weihao Hu, Xiaoru Wang and Zhe Chen

Energies 2013, 6(12), 6352-6372; https://doi.org/10.3390/en6126352 - 4 Dec 2013

Cited by 21 | Viewed by 7189

Abstract

This paper describes a frequency domain approach for evaluating the impact of tower shadow and wind shear effects (TSWS) on tie-line power oscillations. A simplified frequency domain model of an interconnected power system with a wind farm is developed. The transfer function, which [...] Read more.

This paper describes a frequency domain approach for evaluating the impact of tower shadow and wind shear effects (TSWS) on tie-line power oscillations. A simplified frequency domain model of an interconnected power system with a wind farm is developed. The transfer function, which relates the tie-line power variation to the mechanical power variation of a wind turbine, and the expression of the maximum magnitude of tie-line power oscillations are derived to identify the resonant condition and evaluate the potential risk. The effects of the parameters on the resonant magnitude of the tie-line power are also discussed. The frequency domain analysis reveals that TSWS can excite large tie-line power oscillations if the frequency of TSWS approaches the tie-line resonant frequency, especially in the case that the wind farm is integrated into a relatively small grid and the tie-line of the interconnected system is weak. Furthermore, the results of the theoretical analysis are validated through time domain simulations conducted in the two-area four-generator system and the Western Electric Coordinating Council 127 bus system. Full article

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

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42876 KiB

Open AccessArticle

Slotted Blades Savonius Wind Turbine Analysis by CFD

by Andrea Alaimo, Antonio Esposito, Alberto Milazzo, Calogero Orlando and Flavio Trentacosti

Energies 2013, 6(12), 6335-6351; https://doi.org/10.3390/en6126335 - 4 Dec 2013

Cited by 36 | Viewed by 12430

Abstract

In this paper a new bucket configuration for a Savonius wind generator is proposed. Numerical analyses are performed to estimate the performances of the proposed configuration by means of the commercial code COMSOL Multiphysics^® with respect to Savonius wind turbine with overlap [...] Read more.

In this paper a new bucket configuration for a Savonius wind generator is proposed. Numerical analyses are performed to estimate the performances of the proposed configuration by means of the commercial code COMSOL Multiphysics^® with respect to Savonius wind turbine with overlap only. Parametric analyses are performed, for a fixed overlap ratio, by varying the slot position; the results show that for slot positioned near the blade root, the Savonius rotor improves performances at low tip speed ratio, evidencing a better starting torque. This circumstance is confirmed by static analyses performed on the slotted blades in order to investigate the starting characteristic of the proposed Savonius wind generator configuration. Full article

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

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353 KiB

Open AccessArticle

Evaluation of the Effects of Nationwide Conservation Voltage Reduction on Peak-Load Shaving Using SOMAS Data

by Soon-Ryul Nam, Sang-Hee Kang, Joo-Ho Lee, Seon-Ju Ahn and Joon-Ho Choi

Energies 2013, 6(12), 6322-6334; https://doi.org/10.3390/en6126322 - 3 Dec 2013

Cited by 10 | Viewed by 5887

Abstract

In this paper we propose a new method to evaluate the effects of nationwide conservation voltage reduction (CVR) on peak-load shaving, using substation operating results management system (SOMAS) data. Its evaluation is based on a national CVR factor, which is defined as the [...] Read more.

In this paper we propose a new method to evaluate the effects of nationwide conservation voltage reduction (CVR) on peak-load shaving, using substation operating results management system (SOMAS) data. Its evaluation is based on a national CVR factor, which is defined as the weighted average of CVR factors associated with all transformer banks and weighting coefficients are determined by the reconstructed loads corresponding to each transformer bank. To make use of the data resulting from nationwide CVR without installing additional measuring devices, we adopt a linearized static-load model with a linearizing parameter. SOMAS data are used to evaluate the effects of nationwide CVR on peak-load shaving in the Korean power system. Evaluation results show that the national CVR factor of the Korean power system has small values in the summer season and large values in the winter season. This means that the effect of nationwide CVR on peak-load shaving in the Korean power system presents stronger benefits during winter months. Full article

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

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1512 KiB

Open AccessArticle

Thermal CFD Analysis of Tubular Light Guides

by Ondřej Šikula, Jitka Mohelníková and Josef Plášek

Energies 2013, 6(12), 6304-6321; https://doi.org/10.3390/en6126304 - 3 Dec 2013

Cited by 15 | Viewed by 6711

Abstract

Tubular light guides are applicable for daylighting of windowless areas in buildings. Despite their many positive indoor climate aspects they can also present some problems with heat losses and condensation. A computer CFD model focused on the evaluation of temperature distribution and air [...] Read more.

Tubular light guides are applicable for daylighting of windowless areas in buildings. Despite their many positive indoor climate aspects they can also present some problems with heat losses and condensation. A computer CFD model focused on the evaluation of temperature distribution and air flow inside tubular light guides of different dimensions was studied. The physical model of the tested light guides of lengths more than 0.60 m proves shows that Rayleigh numbers are adequate for a turbulent air flow. The turbulent model was applied despite the small heat flux differences between the turbulent and laminar model. The CFD simulations resulted into conclusions that the growing ratio of length/diameter increases the heat transmission loss/linear transmittance as much as by 50 percent. Tubular light guides of smaller diameters have lower heat transmission losses compared to the wider ones of the same lengths with the same outdoor temperature being taken into account. The simulation results confirmed the thermal bridge effect of the tubular light guide tube inside the insulated flat roof details. The thermal transmittance of the studied light guides in the whole roof area was substituted with the point thermal bridges. This substitution gives possibility for simple thermal evaluation of the tubular light pipes in roof constructions. Full article

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4611 KiB

Open AccessArticle

AC Power Local Network with Multiple Power Routers

by Ryo Takahashi, Yutaro Kitamori and Takashi Hikihara

Energies 2013, 6(12), 6293-6303; https://doi.org/10.3390/en6126293 - 2 Dec 2013

Cited by 17 | Viewed by 7244

Abstract

Controlling power flow and achieving appropriate matching between power sources and loads according to the quality of energy is expected to be one of the approaches to reduce wasted energy consumption. A power router, proposed recently, has the capability of realizing circuit switching [...] Read more.

Controlling power flow and achieving appropriate matching between power sources and loads according to the quality of energy is expected to be one of the approaches to reduce wasted energy consumption. A power router, proposed recently, has the capability of realizing circuit switching in a power distribution network. This study focuses on the feasibility of an AC power routing network system composed of multiple power routers. To evaluate the feasibility, we experimentally confirm the circuit switching operation of the parallel and series configurations of the power routers, so that the network system can be designed by the combination of parallel and series configurations. Full article

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

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1514 KiB

Open AccessArticle

A Methodology for Defining Electricity Demand in Energy Simulations Referred to the Italian Context

by Paola Caputo, Costa Gaia and Valentina Zanotto

Energies 2013, 6(12), 6274-6292; https://doi.org/10.3390/en6126274 - 2 Dec 2013

Cited by 26 | Viewed by 5277

Abstract

Electricity consumption in Europe is constantly increasing, despite the fact that in recent years, huge efforts in terms of programs and regulations have been made towards energy demand reduction and energy systems improvement. Since the electricity demand affects both the operation of the [...] Read more.

Electricity consumption in Europe is constantly increasing, despite the fact that in recent years, huge efforts in terms of programs and regulations have been made towards energy demand reduction and energy systems improvement. Since the electricity demand affects both the operation of the supply and distribution plants and the thermal loads of buildings, the importance of providing a proper definition of demand profiles is evident. The main aim of the paper is to provide a set of standard electricity profiles that can reasonably be adopted as input in energy simulations related to the built environment, with particular regards to the Italian context. The work presented in this paper originated within a wider long lasting research aimed at developing a platform for buildings’ energy simulations at district level, with particular reference to the Italian conditions. In this context, it was necessary to define hourly profiles regarding both occupancy and electricity use for lighting and appliances related to different building uses and typologies. For this purpose, the main methods and references for defining electricity loads in buildings were evaluated and average hourly profiles were accordingly developed for residential and commercial buildings. Then the related internal gains were determined and compared to the current Italian standards. Full article

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748 KiB

Open AccessArticle

How Efficient are Agitators in Biogas Digesters? Determination of the Efficiency of Submersible Motor Mixers and Incline Agitators by Measuring Nutrient Distribution in Full-Scale Agricultural Biogas Digesters

by Andreas Lemmer, Hans-Joachim Naegele and Jana Sondermann

Energies 2013, 6(12), 6255-6273; https://doi.org/10.3390/en6126255 - 2 Dec 2013

Cited by 70 | Viewed by 12280

Abstract

The goal of this work was to evaluate the efficiency of two different agitation systems by measuring the nutrient distribution in a digester fed with renewable energy crops and animal manure. The study was carried out at the practical research biogas plant of [...] Read more.

The goal of this work was to evaluate the efficiency of two different agitation systems by measuring the nutrient distribution in a digester fed with renewable energy crops and animal manure. The study was carried out at the practical research biogas plant of Hohenheim University. A unique probe sampling system has been developed that allows probe sampling from the top of the concrete roof into different parts and heights of the digester. The samples were then analyzed in the laboratory for natural fatty acids concentrations. Three different agitation setups were chosen for evaluation at continuous stirring and feeding procedures. The results showed that the analysis approach for agitator optimization through direct measurement of the nutrients distribution in the digester is promising. The type of the agitators and the agitation regime showed significant differences on local concentrations of organic acids, which are not correlated to the dry matter content. Simultaneous measurements on electric energy consumption of the different agitator types verify that by using the slow-moving incline agitator with large propeller diameters in favor of the fast-moving submersible mixer with smaller propeller diameters, the savings potential rises up to 70% by maintaining the mixing quality. Full article

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

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357 KiB

Open AccessArticle

Evaluation of Different CH₄-CO₂ Replacement Processes in Hydrate-Bearing Sediments by Measuring P-Wave Velocity

by Bei Liu, Heng Pan, Xiaohui Wang, Fengguang Li, Changyu Sun and Guangjin Chen

Energies 2013, 6(12), 6242-6254; https://doi.org/10.3390/en6126242 - 28 Nov 2013

Cited by 42 | Viewed by 6442

Abstract

The replacement of methane with carbon dioxide in natural gas hydrate-bearing sediments is considered a promising technology for simultaneously recovering natural gas and entrapping CO₂. During the CH₄-CO₂ replacement process, the variations of geophysical property of the hydrate [...] Read more.

The replacement of methane with carbon dioxide in natural gas hydrate-bearing sediments is considered a promising technology for simultaneously recovering natural gas and entrapping CO₂. During the CH₄-CO₂ replacement process, the variations of geophysical property of the hydrate reservoir need to be adequately known. Since the acoustic wave velocity is an important geophysical property, in this work, the variations of P-wave velocity of hydrate-bearing sediments were measured during different CH₄-CO₂ replacement processes using pure gaseous CO₂ and CO₂/N₂ gas mixtures. Our experimental results show that P-wave velocity continually decreased during all replacement processes. Compared with injecting pure gaseous CO₂, injection of CO₂/N₂ mixture can promote the replacement process, however, it is found that the sediment experiences a loss of stiffness during the replacement process, especially when using CO₂/N₂ gas mixtures. Full article

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8238 KiB

Open AccessArticle

Formation and Dissociation of Methane Hydrates from Seawater in Consolidated Sand: Mimicking Methane Hydrate Dynamics beneath the Seafloor

by Prasad B. Kerkar, Kristine Horvat, Devinder Mahajan and Keith W. Jones

Energies 2013, 6(12), 6225-6241; https://doi.org/10.3390/en6126225 - 28 Nov 2013

Cited by 19 | Viewed by 5808

Abstract

Methane hydrate formation and dissociation kinetics were investigated in seawater-saturated consolidated Ottawa sand-pack under sub-seafloor conditions to study the influence of effective pressure on formation and dissociation kinetics. To simulate a sub-seafloor environment, the pore-pressure was varied relative to confining pressure in successive [...] Read more.

Methane hydrate formation and dissociation kinetics were investigated in seawater-saturated consolidated Ottawa sand-pack under sub-seafloor conditions to study the influence of effective pressure on formation and dissociation kinetics. To simulate a sub-seafloor environment, the pore-pressure was varied relative to confining pressure in successive experiments. Hydrate formation was achieved by methane charging followed by sediment cooling. The formation of hydrates was delayed with increasing degree of consolidation. Hydrate dissociation by step-wise depressurization was instantaneous, emanating preferentially from the interior of the sand-pack. Pressure drops during dissociation and in situ temperature controlled the degree of endothermic cooling within sediments. In a closed system, the post-depressurization dissociation was succeeded by thermally induced dissociation and pressure-temperature conditions followed theoretical methane-seawater equilibrium conditions and exhibited excess pore pressure governed by the pore diameter. These post-depressurization equilibrium values for the methane hydrates in seawater saturated consolidated sand-pack were used to estimate the enthalpy of dissociation of 55.83 ± 1.41 kJ/mol. These values were found to be lower than those reported in earlier literature for bulk hydrates from seawater (58.84 kJ/mol) and pure water (62.61 kJ/mol) due to excess pore pressure generated within confined sediment system under investigation. However, these observations could be significant in the case of hydrate dissociation in a subseafloor environment where dissociation due to depressurization could result in an instantaneous methane release followed by slow thermally induced dissociation. The excess pore pressure generated during hydrate dissociation could be higher within fine-grained sediments with faults and barriers present in subseafloor settings which could cause shifting in geological layers. Full article

(This article belongs to the Special Issue Natural Gas Hydrate 2013)

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771 KiB

Open AccessArticle

Rapid Biogas Production by Compact Multi-Layer Membrane Bioreactor: Efficiency of Synthetic Polymeric Membranes

by Supansa Youngsukkasem, Hamidreza Barghi, Sudip K. Rakshit and Mohammad J. Taherzadeh

Energies 2013, 6(12), 6211-6224; https://doi.org/10.3390/en6126211 - 28 Nov 2013

Cited by 18 | Viewed by 7346

Abstract

Entrapment of methane-producing microorganisms between semi-permeable synthetic membranes in a multi-layer membrane bioreactor (MMBR) was studied and compared to the digestion capacity of a free-cell digester, using a hydraulic retention time of one day and organic loading rates (OLR) of 3.08, 6.16, and [...] Read more.

Entrapment of methane-producing microorganisms between semi-permeable synthetic membranes in a multi-layer membrane bioreactor (MMBR) was studied and compared to the digestion capacity of a free-cell digester, using a hydraulic retention time of one day and organic loading rates (OLR) of 3.08, 6.16, and 8.16 g COD/L·day. The reactor was designed to retain bacterial cells with uprising plug flow through a narrow tunnel between membrane layers, in order to acquire maximal mass transfer in a compact bioreactor. Membranes of hydrophobic polyamide 46 (PA) and hydroxyethylated polyamide 46 (HPA) as well as a commercial membrane of polyvinylidene fluoride (PVDF) were examined. While the bacteria in the free-cell digester were washed out, the membrane bioreactor succeeded in retaining them. Cross-flow of the liquid through the membrane surface and diffusion of the substrate through the membranes, using no extra driving force, allowed the bacteria to receive nutrients and to produce biogas. However, the choice of membrane type was crucial. Synthesized hydrophobic PA membrane was not effective for this purpose, producing 50–121 mL biogas/day, while developed HPA membrane and the reference PVDF were able to transfer the nutrients and metabolites while retaining the cells, producing 1102–1633 and 1016–1960 mL biogas/day, respectively. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2013)

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1424 KiB

Open AccessArticle

On the Efficacy of PCM to Shave Peak Temperature of Crystalline Photovoltaic Panels: An FDM Model and Field Validation

by Valerio Lo Brano, Giuseppina Ciulla, Antonio Piacentino and Fabio Cardona

Energies 2013, 6(12), 6188-6210; https://doi.org/10.3390/en6126188 - 28 Nov 2013

Cited by 34 | Viewed by 6878

Abstract

The exploitation of renewable energy sources and specifically photovoltaic (PV) devices have been showing significant growth; however, for a more effective development of this technology it is essential to have higher energy conversion performances. PV producers often declare a higher efficiency respect to [...] Read more.

The exploitation of renewable energy sources and specifically photovoltaic (PV) devices have been showing significant growth; however, for a more effective development of this technology it is essential to have higher energy conversion performances. PV producers often declare a higher efficiency respect to real conditions and this deviation is mainly due to the difference between nominal and real temperature conditions of the PV. In order to improve the solar cell energy conversion efficiency many authors have proposed a methodology to keep the temperature of a PV system lower: a modified crystalline PV system built with a normal PV panel coupled with a Phase Change Material (PCM) heat storage device. In this paper a thermal model analysis of the crystalline PV-PCM system based on a theoretical study using finite difference approach is described. The authors developed an algorithm based on an explicit finite difference formulation of energy balance of the crystalline PV-PCM system. Two sets of recursive equations were developed for two types of spatial domains: a boundary domain and an internal domain. The reliability of the developed model is tested by a comparison with data coming from a test facility. The results of numerical simulations are in good agreement with experimental data. Full article

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1730 KiB

Open AccessArticle

Co-Combustion of Animal Waste in a Commercial Waste-to-Energy BFB Boiler

by Farzad Moradian, Anita Pettersson, Solvie Herstad Svärd and Tobias Richards

Energies 2013, 6(12), 6170-6187; https://doi.org/10.3390/en6126170 - 27 Nov 2013

Cited by 16 | Viewed by 7945

Abstract

Co-combustion of animal waste, in waste-to-energy boilers, is considered a method to produce both heat and power and to dispose of possibly infected animal wastes. This research conducted full-scale combustion tests to identify the impact of changed fuel composition on a fluidized-bed boiler. [...] Read more.

Co-combustion of animal waste, in waste-to-energy boilers, is considered a method to produce both heat and power and to dispose of possibly infected animal wastes. This research conducted full-scale combustion tests to identify the impact of changed fuel composition on a fluidized-bed boiler. The impact was characterized by analyzing the deposit formation rate, deposit composition, ash composition, and emissions. Two combustion tests, denoted the reference case and animal waste case, were performed based on different fuel mixes. In the reference case, a normal solid waste fuel mix was combusted in the boiler, containing sorted industry and household waste. In the animal waste case, 20 wt% animal waste was added to the reference fuel mix. The collected samples, comprising sampling probe deposits, fuel mixes, bed ash, return sand, boiler ash, cyclone ash and filter ash, were analyzed using chemical fractionation, SEM-EDX and XRD. The results indicate decreased deposit formation due to animal waste co-combustion. SEM-EDX and chemical fractionation identified higher concentrations of P, Ca, S, and Cl in the bed materials in the animal waste case. Moreover, the risk of bed agglomeration was lower in the animal waste case and also a decreased rate of NO_x and SO₂ emissions were observed. Full article

(This article belongs to the Special Issue Biomass and Biofuels 2013)

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584 KiB

Open AccessArticle

Spatiotemporal Changes in Crop Residues with Potential for Bioenergy Use in China from 1990 to 2010

by Xinliang Xu, Ying Fu and Shuang Li

Energies 2013, 6(12), 6153-6169; https://doi.org/10.3390/en6126153 - 27 Nov 2013

Cited by 5 | Viewed by 5370

Abstract

China has abundant crop residues (CR_E) that could be used for bioenergy. The spatiotemporal characteristics of bioenergy production are crucial for high-efficiency use and appropriate management of bioenergy enterprises. In this study, statistical and remote-sensing data on crop yield in [...] Read more.

China has abundant crop residues (CR_E) that could be used for bioenergy. The spatiotemporal characteristics of bioenergy production are crucial for high-efficiency use and appropriate management of bioenergy enterprises. In this study, statistical and remote-sensing data on crop yield in China were used to estimate CR_E and to analyze its spatiotemporal changes between 1990 and 2010. In 2010, China’s CR_E was estimated to be approximately 133.24 Mt, and it was abundant in North and Northeast China, the middle and lower reaches of the Yangtze River, and South China; CR_E was scarce on the Loess and Qinghai–Tibet Plateaus. The quantity of CR_E increased clearly over the 20-year analysis period, mainly from an increase in residues produced on dry land. Changes in cultivated land use clearly influenced the changes in CR_E. The expansion of cultivated land, which mainly occurred in Northeast and Northwest China, increased CR_E by 5.18 Mt. The loss of cultivated land, which occurred primarily in North China and the middle and lower reaches of the Yangtze River, reduced CR_E by 3.55 Mt. Additionally, the interconversion of paddy fields and dry land, which occurred mostly in Northeast China, increased CR_E by 0.78 Mt. The findings of this article provide important information for policy makers in formulating plans and policies for crop-residue-based bioenergy development in China, and also for commercial ventures in deciding on locations and production schedules for generation of bioenergy. Full article

(This article belongs to the Special Issue Large Scale LUCC, Surface Energy Fluxes and Energy Use)

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961 KiB

Open AccessArticle

Hour-Ahead Wind Speed and Power Forecasting Using Empirical Mode Decomposition

by Ying-Yi Hong, Ti-Hsuan Yu and Ching-Yun Liu

Energies 2013, 6(12), 6137-6152; https://doi.org/10.3390/en6126137 - 25 Nov 2013

Cited by 48 | Viewed by 6703

Abstract

Operation of wind power generation in a large farm is quite challenging in a smart grid owing to uncertain weather conditions. Consequently, operators must accurately forecast wind speed/power in the dispatch center to carry out unit commitment, real power scheduling and economic dispatch. [...] Read more.

Operation of wind power generation in a large farm is quite challenging in a smart grid owing to uncertain weather conditions. Consequently, operators must accurately forecast wind speed/power in the dispatch center to carry out unit commitment, real power scheduling and economic dispatch. This work presents a novel method based on the integration of empirical mode decomposition (EMD) with artificial neural networks (ANN) to forecast the short-term (1 h ahead) wind speed/power. First, significant parameters for training the ANN are identified using the correlation coefficients. These significant parameters serve as inputs of the ANN. Owing to the volatile and intermittent wind speed/power, the historical time series of wind speed/power is decomposed into several intrinsic mode functions (IMFs) and a residual function through EMD. Each IMF becomes less volatile and therefore increases the accuracy of the neural network. The final forecasting results are achieved by aggregating all individual forecasting results from all IMFs and their corresponding residual functions. Real data related to the wind speed and wind power measured at a wind-turbine generator in Taiwan are used for simulation. The wind speed forecasting and wind power forecasting for the four seasons are studied. Comparative studies between the proposed method and traditional methods (i.e., artificial neural network without EMD, autoregressive integrated moving average (ARIMA), and persistence method) are also introduced. Full article

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

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Energies, Volume 6, Issue 12 (December 2013) – 28 articles , Pages 6137-6635

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