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Energies, Volume 9, Issue 6 (June 2016) – 90 articles

Cover Story (view full-size image): Hydraulic presses are widely used in metal forming processes, such as blanking, forming, punching, and cutting. These presses are also large energy consumers. With the objective of reducing energy consumption along with other objectives in the design of a hydraulic press, the comprehensive goal of structure and component optimization would be achieved. Methods and technologies that consider these objectives are presented which ensure function requirements are satisfied and energy is saved. View the paper
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390 KiB  
Correction
Correction: Yang, W.; Yang, J.; Guo, W.; Zeng, W.; Wang, C.; Saarinen, L.; Norrlund, P. A Mathematical Model and Its Application for Hydro Power Units under Different Operating Conditions. Energies 2015, 8, 10260–10275
by Weijia Yang, Jiandong Yang, Wencheng Guo, Wei Zeng, Chao Wang, Linn Saarinen and Per Norrlund
Energies 2016, 9(6), 477; https://doi.org/10.3390/en9060477 - 22 Jun 2016
Viewed by 4098
Abstract
The authors wish to make the following corrections to the published paper [1].[...] Full article
(This article belongs to the Special Issue Hydropower)
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6166 KiB  
Article
A Novel Design of Radio Frequency Energy Relays on Power Transmission Lines
by Jin Tong, Yigang He, Bing Li, Fangming Deng and Tao Wang
Energies 2016, 9(6), 476; https://doi.org/10.3390/en9060476 - 21 Jun 2016
Cited by 4 | Viewed by 6961
Abstract
In this paper, we investigate the energy problem of monitoring sensors on high-voltage power transmission lines and propose a wireless charging scheme for a Radio Frequency IDentification (RFID) sensor tag to solve a commercial efficiency problem: the maintenance-caused power outage. Considering the environmental [...] Read more.
In this paper, we investigate the energy problem of monitoring sensors on high-voltage power transmission lines and propose a wireless charging scheme for a Radio Frequency IDentification (RFID) sensor tag to solve a commercial efficiency problem: the maintenance-caused power outage. Considering the environmental influences on power transmission lines, a self-powered wireless energy relay is designed to meet the energy requirement of the passive RFID sensor tag. The relay can obtain the electric field energy from the transmission lines and wirelessly power the RFID sensor tags around for longer operating distance. A prototype of the energy relay is built and tested on a 110 kv line. The measurement results show that the energy relay can provide stable energy even with the influences of wind, noise and power outage. To our knowledge, it is the first work to power the RFID sensor tags on power transmission lines. Full article
(This article belongs to the Special Issue Wireless Rechargeable Sensor Networks)
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2950 KiB  
Article
Coordinated Control of Wave Energy Converters Subject to Motion Constraints
by Liguo Wang, Jens Engström, Mats Leijon and Jan Isberg
Energies 2016, 9(6), 475; https://doi.org/10.3390/en9060475 - 21 Jun 2016
Cited by 12 | Viewed by 5316
Abstract
In this paper, a generic coordinated control method for wave energy converters is proposed, and the constraints on motion amplitudes and the hydrodynamic interaction between converters are considered. The objective of the control problem is to maximize the energy converted from ocean waves, [...] Read more.
In this paper, a generic coordinated control method for wave energy converters is proposed, and the constraints on motion amplitudes and the hydrodynamic interaction between converters are considered. The objective of the control problem is to maximize the energy converted from ocean waves, and this is achieved by coordinating the power take-off (PTO) damping of each wave energy converter in the frequency domain in each sea state. In a case study, a wave energy farm consisting of four converters based on the concept developed by Uppsala University is studied. In the solution, motion constraints, including constraints on the amplitudes of displacement and velocity, are included. Twelve months of sea states, based on measured wave data at the Lysekil test site on the Swedish west coast, are used in the simulation to evaluate the performance of the wave energy farm using the new method. Results from the new coordinated control method and traditional control method are compared, indicating that the coordinated control of wave energy converters is an effective way to improve the energy production of wave energy farm in harmonic waves. Full article
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2514 KiB  
Article
Optimal Electric and Heat Energy Management of Multi-Microgrids with Sequentially-Coordinated Operations
by Nah-Oak Song, Ji-Hye Lee and Hak-Man Kim
Energies 2016, 9(6), 473; https://doi.org/10.3390/en9060473 - 21 Jun 2016
Cited by 11 | Viewed by 4886
Abstract
We propose an optimal electric and heat energy management for a cooperative multi-microgrid community. The sequentially-coordinated operation for heat energy is proposed in order to distribute the computational burden as an extension of “Optimal Energy Management of Multi-Microgrids with Sequentially Coordinated Operations” and [...] Read more.
We propose an optimal electric and heat energy management for a cooperative multi-microgrid community. The sequentially-coordinated operation for heat energy is proposed in order to distribute the computational burden as an extension of “Optimal Energy Management of Multi-Microgrids with Sequentially Coordinated Operations” and is following the sequentially-coordinated operations for electric energy in it. This sequentially-coordinated operation for heat energy is mathematically modeled and how to obtain the global heat energy optimization solution in the cooperative multi-microgrid community is presented. The global heat energy optimization is achieved for the cooperative community by adjusting the combined electric and heat energy production amounts of combined heat and power (CHP) generators and the heat energy production amount of heat only boilers (HOBs) which satisfy all heat loads, as well as optimize the external electric energy trading in order to minimize the unnecessary cost from the external electric trading, and/or maximize the profit from the external electric trading. To validate the proposed mathematical energy management models, a simulation study is also conducted. Full article
(This article belongs to the Special Issue Microgrids 2016)
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4267 KiB  
Article
Online Identification with Reliability Criterion and State of Charge Estimation Based on a Fuzzy Adaptive Extended Kalman Filter for Lithium-Ion Batteries
by Zhongwei Deng, Lin Yang, Yishan Cai and Hao Deng
Energies 2016, 9(6), 472; https://doi.org/10.3390/en9060472 - 21 Jun 2016
Cited by 11 | Viewed by 7268
Abstract
In the field of state of charge (SOC) estimation, the Kalman filter has been widely used for many years, although its performance strongly depends on the accuracy of the battery model as well as the noise covariance. The Kalman gain determines the confidence [...] Read more.
In the field of state of charge (SOC) estimation, the Kalman filter has been widely used for many years, although its performance strongly depends on the accuracy of the battery model as well as the noise covariance. The Kalman gain determines the confidence coefficient of the battery model by adjusting the weight of open circuit voltage (OCV) correction, and has a strong correlation with the measurement noise covariance (R). In this paper, the online identification method is applied to acquire the real model parameters under different operation conditions. A criterion based on the OCV error is proposed to evaluate the reliability of online parameters. Besides, the equivalent circuit model produces an intrinsic model error which is dependent on the load current, and the property that a high battery current or a large current change induces a large model error can be observed. Based on the above prior knowledge, a fuzzy model is established to compensate the model error through updating R. Combining the positive strategy (i.e., online identification) and negative strategy (i.e., fuzzy model), a more reliable and robust SOC estimation algorithm is proposed. The experiment results verify the proposed reliability criterion and SOC estimation method under various conditions for LiFePO4 batteries. Full article
(This article belongs to the Collection Electric and Hybrid Vehicles Collection)
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Article
Integrated Combined Heat and Power System Dispatch Considering Electrical and Thermal Energy Storage
by Rongxiang Yuan, Jun Ye, Jiazhi Lei and Timing Li
Energies 2016, 9(6), 474; https://doi.org/10.3390/en9060474 - 20 Jun 2016
Cited by 49 | Viewed by 5655
Abstract
Wind power has achieved great development in Northern China, but abundant wind power is dissipated, rather than utilized, due to inflexible electricity production of combined heat and power (CHP) units. In this paper, an integrated CHP system consisting of CHP units, wind power [...] Read more.
Wind power has achieved great development in Northern China, but abundant wind power is dissipated, rather than utilized, due to inflexible electricity production of combined heat and power (CHP) units. In this paper, an integrated CHP system consisting of CHP units, wind power plants, and condensing power plants is investigated to decouple the power and heat production on both the power supply side and heat supply side, by incorporating electrical energy storage (EES) and thermal energy storage (TES). Then the integrated CHP system dispatch (ICHPSD) model is formulated to reach the target of reducing wind power curtailment and primary energy consumption. Finally, the feasibility and effectiveness of the proposed ICHPSD model are verified by the six-bus system, and the simulation results show that EES has a better effect on wind power integration than TES. The annual net benefits by incorporating EES and TES increase with increasing wind penetration, but they gradually approach saturation. Introducing both EES and TES can largely increase the amount of wind power integration and improve the operation efficiency of the system. Full article
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3032 KiB  
Review
Variability Characteristics of European Wind and Solar Power Resources—A Review
by Ingeborg Graabak and Magnus Korpås
Energies 2016, 9(6), 449; https://doi.org/10.3390/en9060449 - 20 Jun 2016
Cited by 68 | Viewed by 10255
Abstract
This paper reviews the most recent and relevant research into the variability characteristics of wind and solar power resources in Europe. The background for this study is that wind and solar resources will probably constitute major components of the future European power system. [...] Read more.
This paper reviews the most recent and relevant research into the variability characteristics of wind and solar power resources in Europe. The background for this study is that wind and solar resources will probably constitute major components of the future European power system. Such resources are variable, and EU plans to balance the variability with more grids and demand response. Thus, planning for the future power system requires an in-depth understanding of the variability. Resource variability is a multi-faceted concept best described using a range of distinct characteristics, and this review is structured on the basis of seven of these: Distribution Long-Term (hours to years), Distribution Short-Term (less than one hour), Step Changes, Autocorrelation, Spatial Correlation, Cross Correlation and Predictable Patterns. The review presents simulations and empirical results related to resource variability for each of these characteristics. Results to date reveal that the variability characteristics of the future power system is limited understood. This study recommends the development of a scheme for greater systematic assessment of variability. Such a scheme will contribute to the understanding of the impacts of variability and will make it possible to compare alternative power production portfolios and impacts of grid expansions, demand response and storage technologies. Full article
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Article
A Natural Analogy to the Diffusion of Energy-Efficient Technologies
by José Antonio Moya
Energies 2016, 9(6), 471; https://doi.org/10.3390/en9060471 - 18 Jun 2016
Cited by 3 | Viewed by 4769
Abstract
A new mathematical approach to the diffusion of energy-efficient technologies is presented using the diffusion of natural processes as an analogy. This approach is applied to the diffusion of the electric arc furnace in Japan. The main advantage offered by the new approach [...] Read more.
A new mathematical approach to the diffusion of energy-efficient technologies is presented using the diffusion of natural processes as an analogy. This approach is applied to the diffusion of the electric arc furnace in Japan. The main advantage offered by the new approach is the incorporation of an average effect of barriers to, and support measures for, innovation. This approach also incorporates some of the parameters influencing the cost-effectiveness of the investment in the new technology as the main driver for adopting the innovation. The straightforward equivalence between natural phenomena and the diffusion of innovation requires the conceptual abstraction of setting a dimension (and defining) the medium in which the diffusion takes place. This new approach opens new research paths to analysing under what circumstances innovations can take-off, the effect of barriers in the diffusion of energy efficient technologies, or how the diffusion process is incorporated in energy-system models. Full article
(This article belongs to the Special Issue Industrial Energy Efficiency)
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616 KiB  
Article
Lifetime-Aware Cloud Data Centers: Models and Performance Evaluation
by Luca Chiaraviglio, Antonio Cianfrani, Marco Listanti, William Liu and Marco Polverini
Energies 2016, 9(6), 470; https://doi.org/10.3390/en9060470 - 18 Jun 2016
Cited by 8 | Viewed by 4087
Abstract
We present a model to evaluate the server lifetime in cloud data centers (DCs). In particular, when the server power level is decreased, the failure rate tends to be reduced as a consequence of the limited number of components powered on. However, the [...] Read more.
We present a model to evaluate the server lifetime in cloud data centers (DCs). In particular, when the server power level is decreased, the failure rate tends to be reduced as a consequence of the limited number of components powered on. However, the variation between the different power states triggers a failure rate increase. We therefore consider these two effects in a server lifetime model, subject to an energy-aware management policy. We then evaluate our model in a realistic case study. Our results show that the impact on the server lifetime is far from negligible. As a consequence, we argue that a lifetime-aware approach should be pursued to decide how and when to apply a power state change to a server. Full article
(This article belongs to the Special Issue Energy-Efficient and Sustainable Networking)
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6526 KiB  
Article
Coordination Control Strategy for AC/DC Hybrid Microgrids in Stand-Alone Mode
by Dwi Riana Aryani and Hwachang Song
Energies 2016, 9(6), 469; https://doi.org/10.3390/en9060469 - 18 Jun 2016
Cited by 39 | Viewed by 7204
Abstract
Interest in DC microgrids is rapidly increasing along with the improvement of DC power technology because of its advantages. To support the integration process of DC microgrids with the existing AC utility grids, the form of hybrid AC/DC microgrids is considered for higher [...] Read more.
Interest in DC microgrids is rapidly increasing along with the improvement of DC power technology because of its advantages. To support the integration process of DC microgrids with the existing AC utility grids, the form of hybrid AC/DC microgrids is considered for higher power conversion efficiency, lower component cost and better power quality. In the system, AC and DC portions are connected through interlink bidirectional AC/DC converters (IC) with a proper control system and power management. In the stand-alone operation mode of AC/DC hybrid microgrids, the control of power injection through the IC is crucial in order to maintain the system security. This paper mainly deals with a coordination control strategy of IC and a battery energy storage system (BESS) converter under stand-alone operation. A coordinated control strategy for the IC, which considers the state of charge (SOC) level of BESS and the load shedding scheme as the last resort, is proposed to obtain better power sharing between AC and DC subgrids. The scheme will be tested with a hybrid AC/DC microgrid, using the tool of the PSCAD/EMTDC software. Full article
(This article belongs to the Special Issue Selected Papers from 5th Asia-Pacific Forum on Renewable Energy)
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9840 KiB  
Article
Climate Resilient Low-Income Tropical Housing
by Arman Hashemi
Energies 2016, 9(6), 468; https://doi.org/10.3390/en9060468 - 17 Jun 2016
Cited by 19 | Viewed by 6449
Abstract
Located in East Africa, Uganda is one of the most economically deprived countries that is likely to be dramatically affected by climate change. Over 50% of Ugandan families live in single-roomed overcrowded properties and over 60% of the country’s urban population live in [...] Read more.
Located in East Africa, Uganda is one of the most economically deprived countries that is likely to be dramatically affected by climate change. Over 50% of Ugandan families live in single-roomed overcrowded properties and over 60% of the country’s urban population live in slums. Moreover, the gradual shift towards relatively modern and low thermal resistance building materials, in addition to imminent thermal discomfort due to global warming, may considerably affect the health and wellbeing of low-income people, the majority of whom live in low quality homes with very little or no access to basic amenities. This paper evaluates the effects of various construction methods as well as refurbishment strategies on thermal comfort in low-income houses in Uganda. It is aimed at helping low-income populations adapt to climate changes by developing simple, effective and affordable refurbishment strategies that could easily be applied to existing buildings. Dynamic thermal simulations are conducted in EnergyPlus. The adaptive model defined in BS EN 15251 and CIBSE TM52 is used to evaluate the risk and extent of thermal discomfort. Roofing methods/materials are found to be the key factor in reducing/increasing the risk of overheating. According to the results, roof insulation, painting the roof with low solar absorptance materials and inclusion of false ceilings are, respectively, the most effective and practical refurbishment strategies in terms of improving thermal comfort in low-income houses in Uganda. All refurbishment strategies helped to pass Criterion 3 of CIBSE TM52, as an indicator of “future climate scenarios”, making low-income houses/populations more climate resilient. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change 2016)
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3143 KiB  
Article
Streamer Propagation and Breakdown in a Very Small Point-Insulating Plate Gap in Mineral Oil and Ester Liquids at Positive Lightning Impulse Voltage
by Pawel Rozga
Energies 2016, 9(6), 467; https://doi.org/10.3390/en9060467 - 17 Jun 2016
Cited by 21 | Viewed by 6082
Abstract
This article presents the results of comparative studies on streamer propagation and breakdown in a point-insulating plate electrode system in mineral oil and two ester liquids. The studies were performed for a 10-mm gap and a positive standard lightning impulse. The work was [...] Read more.
This article presents the results of comparative studies on streamer propagation and breakdown in a point-insulating plate electrode system in mineral oil and two ester liquids. The studies were performed for a 10-mm gap and a positive standard lightning impulse. The work was focused on the comparison of light waveforms registered using the photomultiplier technique. The results indicated that both esters demonstrate a lower resistance against the appearance of fast energetic streamers than mineral oil. The reason for such a conclusion is that the number of lightning impulses supplied to the electrode system for which the above-mentioned fast streamers appeared at a given voltage level was always higher in the case of ester liquids than mineral oil. In terms of breakdown, the esters tested were assessed as more susceptible to the appearance of breakdown in the investigated electrode system. The number of breakdowns recorded in the case of esters was always greater than the corresponding number of breakdowns in mineral oil. This may be supposed on the basis of the obtained results that imply that, in both synthetic and natural ester, the formed breakdown channel, which bridged the gap through the surface of pressboard plate, is characterized by higher energy than in the case of mineral oil. Full article
(This article belongs to the Special Issue Power Transformer Diagnostics, Monitoring and Design Features)
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5599 KiB  
Article
Assessment of Retrofitting Measures for a Large Historic Research Facility Using a Building Energy Simulation Model
by Young Tae Chae, Young M. Lee and David Longinott
Energies 2016, 9(6), 466; https://doi.org/10.3390/en9060466 - 17 Jun 2016
Cited by 5 | Viewed by 5526
Abstract
A calibrated building simulation model was developed to assess the energy performance of a large historic research building. The complexity of space functions and operational conditions with limited availability of energy meters makes it hard to understand the end-used energy consumption in detail [...] Read more.
A calibrated building simulation model was developed to assess the energy performance of a large historic research building. The complexity of space functions and operational conditions with limited availability of energy meters makes it hard to understand the end-used energy consumption in detail and to identify appropriate retrofitting options for reducing energy consumption and greenhouse gas (GHG) emissions. An energy simulation model was developed to study the energy usage patterns not only at a building level, but also of the internal thermal zones, and system operations. The model was validated using site measurements of energy usage and a detailed audit of the internal load conditions, system operation, and space programs to minimize the discrepancy between the documented status and actual operational conditions. Based on the results of the calibrated model and end-used energy consumption, the study proposed potential energy conservation measures (ECMs) for the building envelope, HVAC system operational methods, and system replacement. It also evaluated each ECM from the perspective of both energy and utility cost saving potentials to help retrofitting plan decision making. The study shows that the energy consumption of the building was highly dominated by the thermal requirements of laboratory spaces. Among other ECMs the demand management option of overriding the setpoint temperature is the most cost effective measure. Full article
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771 KiB  
Article
Scheduling of Electricity Storage for Peak Shaving with Minimal Device Wear
by Thijs Van der Klauw, Johann L. Hurink and Gerard J. M. Smit
Energies 2016, 9(6), 465; https://doi.org/10.3390/en9060465 - 17 Jun 2016
Cited by 6 | Viewed by 4084
Abstract
In this work, we investigate scheduling problems for electrical energy storage systems and formulate an algorithm that finds an optimal solution with minimal charging cycles in the case of a single device. For the considered problems, the storage system is used to reduce [...] Read more.
In this work, we investigate scheduling problems for electrical energy storage systems and formulate an algorithm that finds an optimal solution with minimal charging cycles in the case of a single device. For the considered problems, the storage system is used to reduce the peaks of the production and consumption within (part of) the electricity distribution grid, while minimizing device wear. The presented mathematical model of the storage systems captures the general characteristic of electrical energy storage devices while omitting the details of the specific technology used to store the energy. In this way, the model can be applied to a wide range of settings. Within the model, the wear of the storage devices is modeled by either: (1) the total energy throughput; or (2) the number of switches between charging and discharging, the so-called charging cycles. For the first case, where the energy throughput determines the device wear, a linear programming formulation is given. For the case where charging cycles are considered, an NP-hardness proof is given for instances with multiple storage devices. Furthermore, several observations about the structure of the problem are given when considering a single device. Using these observations, we develop a polynomial time algorithm of low complexity that determines an optimal solution. Furthermore, the solutions produced by this algorithm also minimize the throughput, next to the charging cycles, of the device. Due to the low complexity, the algorithm can be applied in various decentralized smart grid applications within future electricity distribution grids. Full article
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Article
Interdependencies between Biofuel, Fuel and Food Prices: The Case of the Brazilian Ethanol Market
by Deborah Bentivoglio, Adele Finco and Mirian Rumenos Piedade Bacchi
Energies 2016, 9(6), 464; https://doi.org/10.3390/en9060464 - 17 Jun 2016
Cited by 38 | Viewed by 5932
Abstract
Brazil is currently the world’s largest sugar producer and exporter, as well as the world’s largest producer and consumer of sugarcane ethanol as a transportation fuel. The growth of this market originates from a combination of government policies and technological change, in both [...] Read more.
Brazil is currently the world’s largest sugar producer and exporter, as well as the world’s largest producer and consumer of sugarcane ethanol as a transportation fuel. The growth of this market originates from a combination of government policies and technological change, in both the sugarcane ethanol processing sector and the manufacture of flex-fuel vehicles. In recent years however, ethanol production has been questioned due to its possible impact on food prices. The present paper aims to explore the impact of Brazilian ethanol prices on sugar and gasoline prices. The relationships between a times series of these prices are investigated using a Vector Error Correction Model (VECM), supported by Granger Causality tests. In addition, Impulse Response Functions (IRFs) and Forecast Error Variance Decompositions (FEVD) are computed in order to investigate the dynamic interrelationships within these series. Our results suggest that ethanol prices are affected by both food and fuel prices, but that there is no strong evidence that changes in ethanol prices have an impact on food prices. Full article
(This article belongs to the Special Issue Agriculture and Energy)
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Article
Market Equilibrium and Impact of Market Mechanism Parameters on the Electricity Price in Yunnan’s Electricity Market
by Chuntian Cheng, Fu Chen, Gang Li and Qiyu Tu
Energies 2016, 9(6), 463; https://doi.org/10.3390/en9060463 - 17 Jun 2016
Cited by 13 | Viewed by 5194
Abstract
In this paper, a two-dimensional Cournot model is proposed to study generation companies’ (GENCO’s) strategic quantity-setting behaviors in the newly established Yunnan’s electricity market. A hybrid pricing mechanism is introduced to Yunnan’s electricity market with the aim to stimulate electricity demand. Market equilibrium [...] Read more.
In this paper, a two-dimensional Cournot model is proposed to study generation companies’ (GENCO’s) strategic quantity-setting behaviors in the newly established Yunnan’s electricity market. A hybrid pricing mechanism is introduced to Yunnan’s electricity market with the aim to stimulate electricity demand. Market equilibrium is obtained by iteratively solving each GENCO’s profit maximization problem and finding their optimal bidding outputs. As the market mechanism is a key element of the electricity market, impacts of different market mechanism parameters on electricity price and power generation in market equilibrium state should be fully assessed. Therefore, based on the proposed model, we precisely explore the impacts on market equilibrium of varying parameters such as the number of GENCOs, the quantity of ex-ante obligatory-use electricity contracts (EOECs) and the elasticity of demand. Numerical analysis results of Yunnan’s electricity market show that these parameters have notable but different effects on electricity price. A larger number of GENCOs or less EOEC contracted with GENCOs will have positive effects on reducing the price. With the increase of demand elasticity, the price falls first and then rises. Comparison of different mechanisms and relationship between different parameters are also analyzed. These results should be of practical interest to market participants or market designers in Yunnan’s or other similar markets. Full article
(This article belongs to the Special Issue Forecasting Models of Electricity Prices)
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6526 KiB  
Article
Energy Converter with Inside Two, Three, and Five Connected H2/Air Swirling Combustor Chambers: Solar and Combustion Mode Investigations
by Angelo Minotti
Energies 2016, 9(6), 461; https://doi.org/10.3390/en9060461 - 17 Jun 2016
Cited by 5 | Viewed by 3377
Abstract
This work reports the performance of an energy converter characterized by an emitting parallelepiped element with inside two, three, or five swirling connected combustion chambers. In particular, the idea is to adopt the heat released by H2/air combustion, occurring in the [...] Read more.
This work reports the performance of an energy converter characterized by an emitting parallelepiped element with inside two, three, or five swirling connected combustion chambers. In particular, the idea is to adopt the heat released by H2/air combustion, occurring in the connected swirling chambers, to heat up the emitting surfaces of the thermally-conductive emitting parallelepiped brick. The final goal consists in obtaining the highest emitting surface temperature and the highest power delivered to the ambient environment, with the simultaneous fulfillment of four design constraints: dimension of the emitting surface fixed to 30 × 30 mm2, solar mode thermal efficiency greater than 20%, emitting surface peak temperature T > 1000 K, and its relative ∆T < 100 K in the combustion mode operation. The connected swirling meso-combustion chambers, inside the converter, differ only in their diameters. Combustion simulations are carried out adopting 500 W of injected chemical power, stoichiometric conditions, and detailed chemistry. All provide high chemical efficiency, η > 99.9%, and high peak temperature, but the emitting surface ∆T is strongly sensitive to the geometrical configuration. The present work is related to the “EU-FP7-HRC-Power” project, aiming at developing micro-meso hybrid sources of power, compatible with a thermal/electrical conversion by thermo-photovoltaic cells. Full article
(This article belongs to the Special Issue Micro Combustor)
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Article
Optimal Scheduling of Energy Storage System for Self-Sustainable Base Station Operation Considering Battery Wear-Out Cost
by Yohwan Choi and Hongseok Kim
Energies 2016, 9(6), 462; https://doi.org/10.3390/en9060462 - 16 Jun 2016
Cited by 54 | Viewed by 7627
Abstract
A self-sustainable base station (BS) where renewable resources and energy storage system (ESS) are interoperably utilized as power sources is a promising approach to save energy and operational cost in communication networks. However, high battery price and low utilization of ESS intended for [...] Read more.
A self-sustainable base station (BS) where renewable resources and energy storage system (ESS) are interoperably utilized as power sources is a promising approach to save energy and operational cost in communication networks. However, high battery price and low utilization of ESS intended for uninterruptible power supply (UPS) necessitates active utilization of ESS. This paper proposes a multi-functional framework of ESS using dynamic programming (DP) for realizing a sustainable BS. We develop an optimal charging and discharging scheduling algorithm considering a detailed battery wear-out model to minimize operational cost as well as to prolong battery lifetime. Our approach significantly reduces total cost compared to the conventional method that does not consider battery wear-out. Extensive experiments for several scenarios exhibit that total cost is reduced by up to 70.6% while battery wear-out is also reduced by 53.6%. The virtue of the proposed framework is its wide applicability beyond sustainable BS and thus can be also used for other types of load in principle. Full article
(This article belongs to the Special Issue Energy-Efficient and Sustainable Networking)
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8576 KiB  
Article
Combining Unsteady Blade Pressure Measurements and a Free-Wake Vortex Model to Investigate the Cycle-to-Cycle Variations in Wind Turbine Aerodynamic Blade Loads in Yaw
by Moutaz Elgammi and Tonio Sant
Energies 2016, 9(6), 460; https://doi.org/10.3390/en9060460 - 16 Jun 2016
Cited by 12 | Viewed by 5970
Abstract
Prediction of the unsteady aerodynamic flow phenomenon on wind turbines is challenging and still subject to considerable uncertainty. Under yawed rotor conditions, the wind turbine blades are subjected to unsteady flow conditions as a result of the blade advancing and retreating effect and [...] Read more.
Prediction of the unsteady aerodynamic flow phenomenon on wind turbines is challenging and still subject to considerable uncertainty. Under yawed rotor conditions, the wind turbine blades are subjected to unsteady flow conditions as a result of the blade advancing and retreating effect and the development of a skewed vortical wake created downstream of the rotor plane. Blade surface pressure measurements conducted on the NREL Phase VI rotor in yawed conditions have shown that dynamic stall causes the wind turbine blades to experience significant cycle-to-cycle variations in aerodynamic loading. These effects were observed even though the rotor was subjected to a fixed speed and a uniform and steady wind flow. This phenomenon is not normally predicted by existing dynamic stall models integrated in wind turbine design codes. This paper couples blade pressure measurements from the NREL Phase VI rotor to a free-wake vortex model to derive the angle of attack time series at the different blade sections over multiple rotor rotations and three different yaw angles. Through the adopted approach it was possible to investigate how the rotor self-induced aerodynamic load fluctuations influence the unsteady variations in the blade angles of attack and induced velocities. The hysteresis loops for the normal and tangential load coefficients plotted against the angle of attack were plotted over multiple rotor revolutions. Although cycle-to-cycle variations in the angles of attack at the different blade radial locations and azimuth positions are found to be relatively small, the corresponding variations in the normal and tangential load coefficients may be significant. Following a statistical analysis, it was concluded that the load coefficients follow a normal distribution at the majority of blade azimuth angles and radial locations. The results of this study provide further insight on how existing engineering models for dynamic stall may be improved through the integration of stochastic models to be able to account for the cycle-to-cycle variability in the unsteady wind turbine blade loads under yawed conditions. Full article
(This article belongs to the Special Issue Modeling and Simulation for Wind Turbine Loads Analysis)
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6965 KiB  
Article
A Novel Protection Method for Single Line-to-Ground Faults in Ungrounded Low-Inertia Microgrids
by Liuming Jing, Dae-Hee Son, Sang-Hee Kang and Soon-Ryul Nam
Energies 2016, 9(6), 459; https://doi.org/10.3390/en9060459 - 16 Jun 2016
Cited by 13 | Viewed by 8223
Abstract
This paper proposes a novel protection method for single line-to-ground (SLG) faults in ungrounded low-inertia microgrids. The proposed method includes microgrid interface protection and unit protection. The microgrid interface protection is based on the difference between the zero-sequence voltage angle and the zero-sequence [...] Read more.
This paper proposes a novel protection method for single line-to-ground (SLG) faults in ungrounded low-inertia microgrids. The proposed method includes microgrid interface protection and unit protection. The microgrid interface protection is based on the difference between the zero-sequence voltage angle and the zero-sequence current angle at the microgrid interconnection transformer for fast selection of the faulty feeder. The microgrid unit protection is based on a comparison of the three zero-sequence current phase directions at each junction point of load or distributed energy resources. Methods are also included to locate the minimum fault section. The fault section location technology operates according to the coordination of microgrid unit protection. The proposed method responds to SLG faults that may occur in both the grid and the microgrid. Simulations of an ungrounded low-inertia microgrid with a relay model were carried out using Power System Computer Aided Design (PSCAD)/Electromagnetic Transients including DC (EMTDC). Full article
(This article belongs to the Special Issue Smart Microgrids: Developing the Intelligent Power Grid of Tomorrow)
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3344 KiB  
Article
Analysis and Solution for Operations of Overcurrent Relay in Wind Power System
by Yeonho Ok, Jaewon Lee and Jaeho Choi
Energies 2016, 9(6), 458; https://doi.org/10.3390/en9060458 - 16 Jun 2016
Cited by 7 | Viewed by 6278
Abstract
Wind power systems are being integrated increasingly into the power grid because of their large capacity and easy access to the transmission grid. The reliability of wind power plants is very important and the elimination of protective relay’s malfunctions is essential to the [...] Read more.
Wind power systems are being integrated increasingly into the power grid because of their large capacity and easy access to the transmission grid. The reliability of wind power plants is very important and the elimination of protective relay’s malfunctions is essential to the mitigation of power quality problems due to the frequent starts and stops of high capacity wind generators. In this study, the problem of frequent false operations of the protective relays are analyzed using real data as line voltages, line currents, and wind speed. A new re-coordination of the overcurrent relay (OCR) based on the wind speed is proposed to avoid frequent operations of relays and tested for a grid-connected wind farm. This study verifies that the false actions by the OCRs that are not accompanied by actual electrical faults in the power grid or wind power system can be solved by the appropriate re-coordination of the OCR. Full article
(This article belongs to the Collection Wind Turbines)
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4178 KiB  
Article
New Scheme for Seamless Operation for Stand-Alone Power Systems
by Hyun-Jun Kim, Yoon-Seok Lee, Byung-Moon Han and Young-Doo Yoon
Energies 2016, 9(6), 457; https://doi.org/10.3390/en9060457 - 15 Jun 2016
Cited by 2 | Viewed by 5031
Abstract
On remote islands photovoltaic (PV) panels with battery energy storage systems (BESSs) supply electric power to customers in parallel operation with engine generators (EGs) to reduce fuel consumption and environmental burden. A BESS operates in voltage control mode when it supplies power to [...] Read more.
On remote islands photovoltaic (PV) panels with battery energy storage systems (BESSs) supply electric power to customers in parallel operation with engine generators (EGs) to reduce fuel consumption and environmental burden. A BESS operates in voltage control mode when it supplies power to loads alone, while it operates in current control mode when it supplies power to loads in parallel with the EG. This paper proposes a smooth mode change of the BESS from current control to voltage control by using initial value at the output of integral part in the voltage controller, and a smooth mode change from voltage control to current control by tracking the EG output voltage to the BESS output voltage using a phase-locked loop (PLL). The feasibility of the proposed scheme was verified through computer simulations and experiments with a scaled prototype. Full article
(This article belongs to the Collection Smart Grid)
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3853 KiB  
Article
Application of a Heat Flux Sensor in Wind Power Electronics
by Elvira Baygildina, Liudmila Smirnova, Kirill Murashko, Raimo Juntunen, Andrey Mityakov, Mikko Kuisma, Olli Pyrhönen, Pasi Peltoniemi, Katja Hynynen, Vladimir Mityakov and Sergey Sapozhnikov
Energies 2016, 9(6), 456; https://doi.org/10.3390/en9060456 - 14 Jun 2016
Cited by 5 | Viewed by 6422
Abstract
This paper proposes and investigates the application of the gradient heat flux sensor (GHFS) for measuring the local heat flux in power electronics. Thanks to its thinness, the sensor can be placed between the semiconductor module and the heat sink. The GHFS has [...] Read more.
This paper proposes and investigates the application of the gradient heat flux sensor (GHFS) for measuring the local heat flux in power electronics. Thanks to its thinness, the sensor can be placed between the semiconductor module and the heat sink. The GHFS has high sensitivity and yields direct measurements without an interruption to the normal power device operation, which makes it attractive for power electronics applications. The development of systems for monitoring thermal loading and methods for online detection of degradation and failure of power electronic devices is a topical and crucial task. However, online condition monitoring (CM) methods, which include heat flux sensors, have received little research attention so far. In the current research, an insulated-gate bipolar transistor (IGBT) module-based test setup with the GHFS implemented on the base plate of one of the IGBTs is introduced. The heat flux experiments and the IGBT power losses obtained by simulations show similar results. The findings give clear evidence that the GHFS can provide an attractive condition monitoring method for the thermal loading of power devices. Full article
(This article belongs to the Collection Wind Turbines)
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1729 KiB  
Article
A Stackelberg Game Theoretic Analysis of Incentive Effects under Perceived Risk for China’s Straw-Based Power Plant Supply Chain
by Lingling Wang and Tsunemi Watanabe
Energies 2016, 9(6), 455; https://doi.org/10.3390/en9060455 - 14 Jun 2016
Cited by 18 | Viewed by 5464
Abstract
The rapid expansion of the biomass power generation industry has resulted in the conversion of substantial agricultural waste (crop straw) into energy feedstock, thereby increasing the income of farmers and promoting the development of rural areas. However, the promising industry faces financial deficits [...] Read more.
The rapid expansion of the biomass power generation industry has resulted in the conversion of substantial agricultural waste (crop straw) into energy feedstock, thereby increasing the income of farmers and promoting the development of rural areas. However, the promising industry faces financial deficits because of difficulties in collecting straw from farmers. To determine strategies for overcoming the biomass supply problem, we apply Stackelberg game theory in modeling the Chinese biomass supply chain and design incentive scenarios under stakeholder risk perception. We illustrate the proposed methodology through an empirical case study on China and demonstrate the effects of incentives on farmers and middlemen. Results show that with incentives, straw quantity and stakeholder profit are expected to increase. Incentives exert a particularly remarkable effect on farmers, with such inducements producing the highest social welfare. Moreover, perceived risk dramatically affects stakeholder profit. Mitigating the risk perception of farmers is expected to significantly advance the development of the biomass power generation industry, increase stakeholder profit, and decrease the amount of incentives needed. Full article
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8095 KiB  
Article
Study of the Injection Control Strategies of a Compression Ignition Free Piston Engine Linear Generator in a One-Stroke Starting Process
by Huihua Feng, Yuyao Guo, Yu Song, Chendong Guo and Zhengxing Zuo
Energies 2016, 9(6), 453; https://doi.org/10.3390/en9060453 - 14 Jun 2016
Cited by 12 | Viewed by 6818
Abstract
For a compression ignition (CI) free piston engine linear generator (FPLG), injection timing is one of the most important parameters that affect its performance, especially for the one-stroke starting operation mode. In this paper, two injection control strategies are proposed using piston position [...] Read more.
For a compression ignition (CI) free piston engine linear generator (FPLG), injection timing is one of the most important parameters that affect its performance, especially for the one-stroke starting operation mode. In this paper, two injection control strategies are proposed using piston position and velocity signals. It was found experimentally that the injection timing’s influence on the compression ratio, the peak in-cylinder gas pressure and the indicated work (IW) is different from that of traditional reciprocating CI engines. The maximum IW of the ignition starting cylinder, say left cylinder (LC) and the right cylinder (RC) are 132.7 J and 138.1 J, respectively. The thermal-dynamic model for simulating the working processes of the FPLG are built and verified by experimental results. The numerical simulation results show that the running instability and imbalance between LC and RC are the obvious characters when adopting the injection strategy of the velocity feedback. These could be solved by setting different triggering velocity thresholds for the two cylinders. The IW output from the FPLG under this strategy is higher than that of adopting the position feedback strategy, and the maximum IW of the RC could reach 162.3 J. Under this strategy, the prototype is able to achieve better starting conditions and could operate continuously for dozens of cycles. Full article
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1195 KiB  
Article
Managing Climate Policy Information Facilitating Knowledge Transfer to Policy Makers
by Charikleia Karakosta and Alexandros Flamos
Energies 2016, 9(6), 454; https://doi.org/10.3390/en9060454 - 13 Jun 2016
Cited by 8 | Viewed by 4948
Abstract
In the challenging context of intense negotiations and radical developments in the field of climate policy, informing stakeholders about opportunities and pathways and about scientific insights and warnings is important to help create positive dynamics. Policy makers need digestible information to design good [...] Read more.
In the challenging context of intense negotiations and radical developments in the field of climate policy, informing stakeholders about opportunities and pathways and about scientific insights and warnings is important to help create positive dynamics. Policy makers need digestible information to design good policies, and understand their options and the possible impacts of these options. They need access to well-structured knowledge, as well as appropriate techniques to manage information and data. However, available information is often difficult to access, not in the right format and of limited use to stakeholders. The range of knowledge needs identified has to be effectively addressed by providing interested parties with suitable, to-the-point information, covering the identified gaps. This is the main aim of this article that proposes the design and development of a climate policy database, which contains all the resources that can cover the identified knowledge gaps. The resources are derived from a broad range of existing reports, research and climate policy decisions at different levels. The goal is to render climate policy associated stakeholders able to extract key policy conclusions. The added value of this database was verified by users and stakeholders that generally argued that the climate policy database facilitates solid understanding of climate policy implications and fosters collaborative knowledge exchange in the field. Full article
(This article belongs to the Special Issue Energy Policy and Climate Change 2016)
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2904 KiB  
Article
Sliding Mode Variable Structure Control of a Bearingless Induction Motor Based on a Novel Reaching Law
by Zebin Yang, Ling Wan, Xiaodong Sun, Fangli Li and Lin Chen
Energies 2016, 9(6), 452; https://doi.org/10.3390/en9060452 - 13 Jun 2016
Cited by 18 | Viewed by 5056
Abstract
In order to improve the performance of the Bearingless Induction Motor (BIM) under large disturbances (such as parameter variations and load disturbances), an adaptive variable-rated sliding mode controller (ASMC) is designed to obtain better performance of the speed regulation system. Firstly, the [...] Read more.
In order to improve the performance of the Bearingless Induction Motor (BIM) under large disturbances (such as parameter variations and load disturbances), an adaptive variable-rated sliding mode controller (ASMC) is designed to obtain better performance of the speed regulation system. Firstly, the L 1 norm of state variables is applied to the conventional exponential reaching law and an adaptive variable-rated exponential reaching law is proposed to reduce system chattering and improve bad convergence performance of the sliding mode variable structure. Secondly, an integral sliding-mode hyper plane is produced according to the speed error in speed regulation system of BIM. Current signal is extracted by the combination of the sliding-mode hyper plane, the electromagnetic torque and the equation of motion. Finally, the feedback speed can adjust operating state adaptively according to speed error and make system chattering-free moving. The simulation and experiment results show that the proposed ASMC can not only enhance the robustness of the system’s uncertainties, but also improve the dynamic performance and suppress system chattering. Full article
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6504 KiB  
Article
Metamaterial Absorber Comprised of Butt-Facing U-Shaped Nanoengineered Gold Metasurface
by Masih Ghasemi and Pankaj Kumar Choudhury
Energies 2016, 9(6), 451; https://doi.org/10.3390/en9060451 - 13 Jun 2016
Cited by 14 | Viewed by 4558
Abstract
The paper reports spectral features of the absorbed electromagnetic (EM) waves in a new kind of multilayered plasmonic metamaterial thin film comprised of homogenous layers of copper and silicon as the bottom and the middle sections (of the thin film), respectively, and the [...] Read more.
The paper reports spectral features of the absorbed electromagnetic (EM) waves in a new kind of multilayered plasmonic metamaterial thin film comprised of homogenous layers of copper and silicon as the bottom and the middle sections (of the thin film), respectively, and the inhomogeneous U-shaped nanoengineered gold layer as the top. Each unit cell of the top metasurface consists of one upside and one downside U-shaped (butt-facing) structure. The absorbance of EM waves is simulated in the wavelength range of 200−1500 nm under different incidence angles considering the wave as being transmitted from the metasurface side. The low-order TE and TM modes are taken into account for the estimation of wave absorbance under varying metasurfaces as well as silicon layer thicknesses. It has been found that the nanoengineered gold layer causes higher confinement of power in silicon, which can be further controlled by suitably adjusting its thickness. Further, the increased thickness of metasurface results in shifts in absorption peak along with the existence of dual-absorption maxima in the visible spectral range. The obtained spectral features reveal possible application of the proposed structure as a prudent metamaterial absorber, which can be exploited for EM heating purposes. Full article
(This article belongs to the Special Issue Dielectric Materials for Energy Storage)
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6136 KiB  
Article
NMOS-Based Integrated Modular Bypass for Use in Solar Systems (NIMBUS): Intelligent Bypass for Reducing Partial Shading Power Loss in Solar Panel Applications
by Pieter Bauwens and Jan Doutreloigne
Energies 2016, 9(6), 450; https://doi.org/10.3390/en9060450 - 11 Jun 2016
Cited by 9 | Viewed by 4924
Abstract
NMOS-based Integrated Modular Bypass for Use in Solar systems (NIMBUS) is designed as a replacement for the traditional bypass diode, used in common solar panels. Because of the series connection between the individual solar cells, the power output of a photovoltaic (PV) panel [...] Read more.
NMOS-based Integrated Modular Bypass for Use in Solar systems (NIMBUS) is designed as a replacement for the traditional bypass diode, used in common solar panels. Because of the series connection between the individual solar cells, the power output of a photovoltaic (PV) panel will drop disproportionally under partial shading. Currently, this is solved by dividing the PV panel into substrings, each with a diode bypass placed in parallel. This allows an alternative current path. However, the diodes still have a significant voltage drop (about 350 mV), and due to the fairly large currents in a panel, the diodes are dissipating power that we would rather see at the output of the panel. The NIMBUS chip, being a low-voltage-drop switch, aims to replace these diodes and, thus, reduce that power loss. NIMBUS is a smart bypass: a completely stand-alone system that detects the failing of one or more cells and activates when necessary. It is designed for a 100-mV voltage drop under a 5-A load current. When two or more NIMBUS chips are placed in parallel, an internal synchronization circuit ensures proper operation to provide for larger load currents. This paper will elaborate on the operation, design and implementation of the NIMBUS chip, as well as on the first measurements. Full article
(This article belongs to the Special Issue Nano-Structured Solar Cells)
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1714 KiB  
Article
Thermo-Economic and Heat Transfer Optimization of Working-Fluid Mixtures in a Low-Temperature Organic Rankine Cycle System
by Oyeniyi A. Oyewunmi and Christos N. Markides
Energies 2016, 9(6), 448; https://doi.org/10.3390/en9060448 - 9 Jun 2016
Cited by 89 | Viewed by 9282
Abstract
In the present paper, we consider the employment of working-fluid mixtures in organic Rankine cycle (ORC) systems with respect to thermodynamic and heat-transfer performance, component sizing and capital costs. The selected working-fluid mixtures promise reduced exergy losses due to their non-isothermal phase-change behaviour, [...] Read more.
In the present paper, we consider the employment of working-fluid mixtures in organic Rankine cycle (ORC) systems with respect to thermodynamic and heat-transfer performance, component sizing and capital costs. The selected working-fluid mixtures promise reduced exergy losses due to their non-isothermal phase-change behaviour, and thus improved cycle efficiencies and power outputs over their respective pure-fluid components. A multi-objective cost-power optimization of a specific low-temperature ORC system (operating with geothermal water at 98 °C) reveals that the use of working-fluid-mixtures does indeed show a thermodynamic improvement over the pure-fluids. At the same time, heat transfer and cost analyses, however, suggest that it also requires larger evaporators, condensers and expanders; thus, the resulting ORC systems are also associated with higher costs. In particular, 50% n-pentane + 50% n-hexane and 60% R-245fa + 40% R-227ea mixtures lead to the thermodynamically optimal cycles, whereas pure n-pentane and pure R-245fa have lower plant costs, both estimated as having ∼14% lower costs per unit power output compared to the thermodynamically optimal mixtures. These conclusions highlight the importance of using system cost minimization as a design objective for ORC plants. Full article
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