Energies

2 pages, 127 KiB

Open AccessCorrection

Correction: Arsalis A.; Alexandrou, A.N.; Georghiou, G.E. Thermoeconomic Modeling and Parametric Study of a Photovoltaic-Assisted 1 MW_e Combined Cooling, Heating, and Power System. Energies 2016, 9, 663

by Alexandros Arsalis, Andreas N. Alexandrou and George E. Georghiou

Energies 2017, 10(6), 829; https://doi.org/10.3390/en10060829 - 21 Jun 2017

Viewed by 2853

Abstract

We have found two inadvertent errors in our paper [1], and thus would like to make the following corrections: [...]
Full article

8 pages, 710 KiB

Open AccessArticle

Natural Gas Hydrate as a Storage Mechanism for Safe, Sustainable and Economical Production from Offshore Petroleum Reserves

by Michael T. Kezirian and S. Leigh Phoenix

Energies 2017, 10(6), 828; https://doi.org/10.3390/en10060828 - 20 Jun 2017

Cited by 33 | Viewed by 7001

Abstract

Century Fathom presents an innovative process to utilize clathrate hydrates for the production, storage and transportation of natural gas from off-shore energy reserves in deep ocean environments. The production scheme was developed by considering the preferred state of natural gas in the deep [...] Read more.

Century Fathom presents an innovative process to utilize clathrate hydrates for the production, storage and transportation of natural gas from off-shore energy reserves in deep ocean environments. The production scheme was developed by considering the preferred state of natural gas in the deep ocean and addressing the hazards associated with conventional techniques to transport natural gas. It also is designed to mitigate the significant shipping cost inherent with all methods. The resulting proposed scheme restrains transport in the hydrate form to the ocean and does not attempt to supply energy to the residential consumer. Instead; the target recipients are industrial operations. The resulting operational concept is intrinsically safer by design; environmentally sustainable and significantly cost-effective compared with currently proposed schemes for the use of natural gas hydrates and has the potential to be the optimal solution for new production of reserves; depending on the distance to shore and capacity of the petroleum reserve. A potential additional benefit is the byproduct of desalinated water. Full article

(This article belongs to the Special Issue Methane Hydrate Research and Development)

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20 pages, 6319 KiB

Open AccessArticle

Separation of CO₂ in a Solid Waste Management Incineration Facility Using Activated Carbon Derived from Pine Sawdust

by Inés Durán, Fernando Rubiera and Covadonga Pevida

Energies 2017, 10(6), 827; https://doi.org/10.3390/en10060827 - 20 Jun 2017

Cited by 27 | Viewed by 7015

Abstract

The selective separation of CO₂ from gas mixtures representative of flue gas generated in waste incineration systems is studied on two activated carbons obtained from pine sawdust and compared to a commercial activated carbon. Dynamic adsorption experiments were conducted in a fixed-bed [...] Read more.

The selective separation of CO₂ from gas mixtures representative of flue gas generated in waste incineration systems is studied on two activated carbons obtained from pine sawdust and compared to a commercial activated carbon. Dynamic adsorption experiments were conducted in a fixed-bed adsorption column using a binary mixture (N₂/CO₂) with a composition representative of incineration streams at temperatures from 30 to 70 °C. The adsorption behavior of humid mixtures (N₂/CO₂/H₂O) was also evaluated in order to assess the influence of water vapor in CO₂ adsorption at different relative humidity in the feed gas: 22% and 60%. Moreover, CO₂ adsorption was studied in less favorable conditions, i.e., departing from a bed initially saturated with H₂O. In addition, the effect of CO₂ on H₂O adsorption was examined.Experimental results showed that the CO₂ adsorption capacity can be reduced significantly by the adsorption of H₂O (up to 60% at high relative humidity conditions). On the other hand, the breakthrough tests over the adsorbent initially saturated with water vapor indicated that H₂O is little affected by CO₂ adsorption. The experimental results pointed out the biomass based carbons as best candidates for CO₂ separation under incineration flue gas conditions. Full article

(This article belongs to the Special Issue CO₂ Capture)

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23 pages, 14166 KiB

Open AccessArticle

Performance Evaluation of Photovoltaic Solar System with Different Cooling Methods and a Bi-Reflector PV System (BRPVS): An Experimental Study and Comparative Analysis

by Muhammad Adil Khan, Byeonghun Ko, Esebi Alois Nyari, S. Eugene Park and Hee-Je Kim

Energies 2017, 10(6), 826; https://doi.org/10.3390/en10060826 - 19 Jun 2017

Cited by 45 | Viewed by 9647

Abstract

Reducing the price of solar photovoltaic (PV) systems has been a constant challenge. Despite recent advances, solar PV systems are still more costly than conventional energy resources. For the first time, this study examines the effectiveness of three different structures/materials: (i) silvered glass [...] Read more.

Reducing the price of solar photovoltaic (PV) systems has been a constant challenge. Despite recent advances, solar PV systems are still more costly than conventional energy resources. For the first time, this study examines the effectiveness of three different structures/materials: (i) silvered glass plane mirror; (ii) convex spherical mirrors; and (iii) aluminum (Al) foil as reflector. Comparative analysis of four different cooling techniques, i.e., water sprinkling system, passive heat sink method, active air fan method, and closed loop method, for enhancement of output power was performed. A novel Bi reflector solar PV system (BRPVS) was suggested to control the working of the reflectors. The Al foil enhanced the power output compared to the others. In addition, the effect of using a reflector on the temperature of a solar PV system was studied. High operating temperatures resulted in a decrease in the maximum output power under the same solar radiation conditions. The combined enhancement of the output power by both Al foil BRPVS system and cooling system was almost 22.75–38.55%. An optimal control algorithm to use cooling and BRPVS in an efficient manner is described. Full article

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12 pages, 1821 KiB

Open AccessArticle

Flexibility-Based Evaluation of Variable Generation Acceptability in Korean Power System

by Chang-Gi Min and Mun-Kyeom Kim

Energies 2017, 10(6), 825; https://doi.org/10.3390/en10060825 - 18 Jun 2017

Cited by 17 | Viewed by 5179

Abstract

This study proposes an evaluation method for variable generation (VG) acceptability with an adequate level of power system flexibility. In this method, a risk index referred to as the ramping capability shortage expectation (RSE) is used to quantify flexibility. The RSE [...] Read more.

This study proposes an evaluation method for variable generation (VG) acceptability with an adequate level of power system flexibility. In this method, a risk index referred to as the ramping capability shortage expectation (RSE) is used to quantify flexibility. The RSE value of the current power system is selected as the adequate level of flexibility (i.e., RSE criterion). VG acceptability is represented by the VG penetration level for the RSE criterion. The proposed evaluation method was applied to the generation expansion plan in Korea for 2029 in order to examine the validity of the existing plan for VG penetration. Sensitivity analysis was also performed to analyze the effects of changes in system uncertainty on VG acceptability. The results show that the planned VG penetration level for 2029 can improve by approximately 12% while securing flexibility. Full article

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

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4 pages, 129 KiB

Open AccessEditorial

Editorial Special Issue “Combustion and Propulsion”

by Maria Grazia De Giorgi and Antonio Ficarella

Energies 2017, 10(6), 824; https://doi.org/10.3390/en10060824 - 18 Jun 2017

Viewed by 3080

Abstract

The increasing demand for socially and environmentally sustainable development requires appropriate use of energy resources, particularly in the transportation of people and goods.[...] Full article

(This article belongs to the Special Issue Combustion and Propulsion)

22 pages, 8705 KiB

Open AccessArticle

CFD Analysis on the Air-Side Thermal-Hydraulic Performance of Multi-Louvered Fin Heat Exchangers at Low Reynolds Numbers

by Arslan Saleem and Man-Hoe Kim

Energies 2017, 10(6), 823; https://doi.org/10.3390/en10060823 - 18 Jun 2017

Cited by 31 | Viewed by 8019

Abstract

The air-side thermal-hydraulic performance of multi-louvered aluminium fin heat exchangers is investigated. A systematic numerical study has been performed to analyze the air-sde thermal hydraulic characteristics over a wide range of Reynolds number i.e., from 30 to 500. Air-side heat transfer coefficient and [...] Read more.

The air-side thermal-hydraulic performance of multi-louvered aluminium fin heat exchangers is investigated. A systematic numerical study has been performed to analyze the air-sde thermal hydraulic characteristics over a wide range of Reynolds number i.e., from 30 to 500. Air-side heat transfer coefficient and pressure drop were calculated and validated over the mentioned band of Reynolds numbers. The critical Reynolds number was determined numerically; and also the variation of flow pattern along with the air-side heat transfer coefficient and pressure drop in a multi-louvered heat exchanger associated with

R e_{c r i}

has been reported. Moreover, a parametric study of the multi-louvered aluminium fin heat exchangers was also performed for 36 heat exchanger configurations with the louver angles (19–31°); fin pitches (1.0, 1.2, 1.4 mm) and flow depths (16, 20, 24 mm); and the geometric configuration exhibiting the highest air-side heat transfer coefficient was reported. The air-side heat transfer coefficient and pressure drop results for different geometrical configurations were presented in terms of Colburn j factor and Fanning friction factor f; as a function of Reynolds number based on louver pitch. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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18 pages, 9868 KiB

Open AccessArticle

Multi-Frequency Control in a Stand-Alone Multi-Microgrid System Using a Back-To-Back Converter

by Hyeong-Jun Yoo, Thai-Thanh Nguyen and Hak-Man Kim

Energies 2017, 10(6), 822; https://doi.org/10.3390/en10060822 - 17 Jun 2017

Cited by 44 | Viewed by 6045

Abstract

A stand-alone multi-microgrid (MMG) system can be formed by connecting multiple stand-alone microgrids (MGs). In the stand-alone MMG system where the frequencies of each MG system are different, a back-to-back (BTB) converter can be used for interconnecting the adjacent MG system. The frequency [...] Read more.

A stand-alone multi-microgrid (MMG) system can be formed by connecting multiple stand-alone microgrids (MGs). In the stand-alone MMG system where the frequencies of each MG system are different, a back-to-back (BTB) converter can be used for interconnecting the adjacent MG system. The frequency control performance of the MMG system can be improved by designing the suitable controller of the BTB converter. This study proposes a multi-frequency control in the BTB converter to improve the performance of frequency regulation in the MMG system. Autonomous power sharing between each MG system is achieved by using the proposed multi-frequency control. The stand-alone MMG system where two stand-alone MG systems with different nominal frequencies are interconnected using the BTB converter is simulated in this study to show the feasibility of the proposed multi-frequency controller. Each stand-alone MG system consists of an inverter-based distributed generator (DG) that uses a grid-forming converter with a conventional frequency droop controller. The inverter-based DG is responsible for the primary frequency control in each MG system. To show the effectiveness of the proposed multi-frequency control, a comparison study of the multi-frequency control and the single frequency control is presented in this study. Simulation results show that the system stability can be improved by using the proposed multi-frequency controller. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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23 pages, 2096 KiB

Open AccessArticle

Large-Eddy Simulations of Two In-Line Turbines in a Wind Tunnel with Different Inflow Conditions

by Umberto Ciri, Giovandomenico Petrolo, Maria Vittoria Salvetti and Stefano Leonardi

Energies 2017, 10(6), 821; https://doi.org/10.3390/en10060821 - 17 Jun 2017

Cited by 32 | Viewed by 4565

Abstract

Numerical simulations reproducing a wind tunnel experiment on two in-line wind turbines have been performed. The flow features and the array performances have been evaluated in different inflow conditions. Following the experimental setup, different inlet conditions are obtained by simulating two grids upstream [...] Read more.

Numerical simulations reproducing a wind tunnel experiment on two in-line wind turbines have been performed. The flow features and the array performances have been evaluated in different inflow conditions. Following the experimental setup, different inlet conditions are obtained by simulating two grids upstream of the array. The increased turbulence intensity due to the grids improves the wake recovery and the efficiency of the second turbine. However, the inlet grid induces off-design operation on the first turbine, decreasing the efficiency and increasing fatigue loads. Typical grid flow patterns are observed past the rotor of the first turbine, up to the near wake. Further downstream, the signature of the grid on the flow is quite limited. An assessment of numerical modeling aspects (subgrid scale tensor and rotor parameterization) has been performed by comparison with the experimental measurements. Full article

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13 pages, 4095 KiB

Open AccessFeature PaperArticle

Recycling COR-TEN^® Sea Containers into Service Modules for Military Applications: Thermal Analysis

by Carlos Ulloa, María Elena Arce, Guillermo Rey, José Luis Míguez and José Hernández

Energies 2017, 10(6), 820; https://doi.org/10.3390/en10060820 - 17 Jun 2017

Cited by 8 | Viewed by 4089

Abstract

It is thought that there are 14 million standardised sea containers out of order, equal to 23.3 million twenty-foot equivalent unit (TEU), which could be devoted for other purposes. The COR-TEN^®steel containers are the best, due to the features of the [...] Read more.

It is thought that there are 14 million standardised sea containers out of order, equal to 23.3 million twenty-foot equivalent unit (TEU), which could be devoted for other purposes. The COR-TEN^®steel containers are the best, due to the features of the materials, to be used in applications intended for the accommodation of people. One of the uses is framed in the area of humanitarian help, as service modules in areas of social emergency. Moreover, the deployment of these kinds of modules is quite simple, as the Army is generally able to transport containers in its units. In this project we have selected three typologies of service modules and we have designed modules based on sea containers which can fit into these typologies. The container chosen to be recycled is the 1 TEU, to which the closings and divisions are defined, which must reflect the different typologies of the service modules chosen. Afterwards, a study of thermal charges is carried out on three different settings of service modules located in five locations spread in different climate areas. Throughout a thermal simulation in Trnsys^® (V17, Thermal Energy System Specialists, LLC, Madison, WI, USA), the consumption and maximum demand of heat and cold are analysed. Based on these results, the best equipment to cover the energy demand of the modules analysed in this study could be chosen. Moreover, the results can be used to estimate the operational costs of the deployment of the modules. Full article

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23 pages, 1733 KiB

Open AccessArticle

Performance Analysis of Conjugate Gradient Algorithms Applied to the Neuro-Fuzzy Feedback Linearization-Based Adaptive Control Paradigm for Multiple HVDC Links in AC/DC Power System

by Saghir Ahmad and Laiq Khan

Energies 2017, 10(6), 819; https://doi.org/10.3390/en10060819 - 16 Jun 2017

Cited by 6 | Viewed by 4295

Abstract

The existing literature predominantly concentrates on the utilization of the gradient descent algorithm for control systems’ design in power systems for stability enhancement. In this paper, various flavors of the Conjugate Gradient (CG) algorithm have been employed to design the online neuro-fuzzy linearization-based [...] Read more.

The existing literature predominantly concentrates on the utilization of the gradient descent algorithm for control systems’ design in power systems for stability enhancement. In this paper, various flavors of the Conjugate Gradient (CG) algorithm have been employed to design the online neuro-fuzzy linearization-based adaptive control strategy for Line Commutated Converters’ (LCC) High Voltage Direct Current (HVDC) links embedded in a multi-machine test power system. The conjugate gradient algorithms are evaluated based on the damping of electro-mechanical oscillatory modes using MATLAB/Simulink. The results validate that all of the conjugate gradient algorithms have outperformed the gradient descent optimization scheme and other conventional and non-conventional control schemes. Full article

(This article belongs to the Section F: Electrical Engineering)

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25 pages, 2596 KiB

Open AccessArticle

Prototyping a Software Defined Utility

by Ramon Martín de Pozuelo, Agustín Zaballos, Joan Navarro and Guiomar Corral

Energies 2017, 10(6), 818; https://doi.org/10.3390/en10060818 - 16 Jun 2017

Cited by 8 | Viewed by 5429

Abstract

The smart grid can be seen as a hybrid system composed by many systems. From a large scale point of view, it combines the electric power system itself and a heterogeneous information and communication technology (ICT) infrastructure. Additionally, these systems are composed by [...] Read more.

The smart grid can be seen as a hybrid system composed by many systems. From a large scale point of view, it combines the electric power system itself and a heterogeneous information and communication technology (ICT) infrastructure. Additionally, these systems are composed by many building blocks that are designed and managed as separated systems which are hard to fully integrate between each other. Relying on the experiences arisen and the knowledge gathered from the partners during the development of the FP7 European projects INTEGRIS (intelligent electrical grid sensor communications) and FINESCE (future internet smart utility services), this paper presents the software defined utility (SDU) concept for the management of the smart grid and its security, which advocates for the migration of the utility infrastructure to software systems instead of relying on complex and rigid hardware based systems. Following this approach, SDU proposes the evolution of power systems’ ICT and the usage of programmable commodity hardware, low-cost sensors, and reliable high-speed IP-based communications underneath. More concretely, this paper proposes some building blocks for the deployment of the SDU (flexible data management infrastructure, context-aware security and web of things interface) and evaluates their functionalities and benefits for the smart grids of the future. Full article

(This article belongs to the Special Issue ICT for Energy)

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24 pages, 916 KiB

Open AccessArticle

Overview of Real-Time Simulation as a Supporting Effort to Smart-Grid Attainment

by Luis Ibarra, Antonio Rosales, Pedro Ponce, Arturo Molina and Raja Ayyanar

Energies 2017, 10(6), 817; https://doi.org/10.3390/en10060817 - 16 Jun 2017

Cited by 39 | Viewed by 7314

Abstract

The smart-grid approach undergoes many difficulties regarding the strategy that will enable its actual implementation. In this paper, an overview of real-time simulation technologies and their applicability to the smart-grid approach are presented as enabling steps toward the smart-grid’s actual implementation. The objective [...] Read more.

The smart-grid approach undergoes many difficulties regarding the strategy that will enable its actual implementation. In this paper, an overview of real-time simulation technologies and their applicability to the smart-grid approach are presented as enabling steps toward the smart-grid’s actual implementation. The objective of this work is to contribute with an introductory text for interested readers of real-time systems in the context of modern electric needs and trends. In addition, a comprehensive review of current applications of real-time simulation in electric systems is provided, together with the basis to understand real-time simulation and the topologies and hardware used to implement it. Furthermore, an overview of the evolution of real-time simulators in the industrial and academic background and its current challenges are introduced. Full article

(This article belongs to the Special Issue Energy Production Systems)

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16 pages, 4057 KiB

Open AccessArticle

A Multiconductor Model of Power Line Communication in Medium-Voltage Lines

by Lesek Franek and Petr Fiedler

Energies 2017, 10(6), 816; https://doi.org/10.3390/en10060816 - 15 Jun 2017

Cited by 14 | Viewed by 5734

Abstract

Most power line communication (PLC) models are designed to date simulate power lines as two-wire lines. However, in alternating current (AC) electrical distribution, the two-wire option is seldom applied, and medium-voltage lines are most often based on the three-phase configuration. In this context, [...] Read more.

Most power line communication (PLC) models are designed to date simulate power lines as two-wire lines. However, in alternating current (AC) electrical distribution, the two-wire option is seldom applied, and medium-voltage lines are most often based on the three-phase configuration. In this context, the influence of the ground, which constitutes another conductor with specific parameters, cannot be neglected. Two-wire models are characterized by limited accuracy, not allowing us to simulate certain major phenomena affecting PLC. This, for example, could embody the answer to the question of whether it is more advantageous to transmit a signal independently through each phase, reference the signal with respect to another phase or to use the ground as a reference. This paper discusses a multi-conductor model that eliminates the disadvantages outlined above; the proposed model exploits the multi-conductor telegrapher’s equations. In order to be able to include medium-voltage (MV)/ low-voltage (LV) transformers in medium-voltage network models, we constituted a transformer model. The designed models were validated on a real medium-voltage network. To be able to evaluate the suitability of the PLC, the noise in the medium voltage network was measured in order to determine the signal-to-noise ratio (SNR). Full article

(This article belongs to the Collection Smart Grid)

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21 pages, 10670 KiB

Open AccessArticle

A Non-Ventilated Solar Façade Concept Based on Selective and Transparent Insulation Material Integration: An Experimental Study

by Miroslav Čekon and Richard Slávik

Energies 2017, 10(6), 815; https://doi.org/10.3390/en10060815 - 15 Jun 2017

Cited by 23 | Viewed by 5996

Abstract

A new solar façade concept based on transparent insulation and a selective absorber is proposed, tested and compared with conventional insulation and a non-selective type of absorber, respectively. The presented study focuses on an experimental non-ventilated solar type of façade exposed to solar [...] Read more.

A new solar façade concept based on transparent insulation and a selective absorber is proposed, tested and compared with conventional insulation and a non-selective type of absorber, respectively. The presented study focuses on an experimental non-ventilated solar type of façade exposed to solar radiation both in the laboratory and in outdoor tests. Due to the high solar absorbance level of the façade, high- and low-emissivity contributions were primarily analysed. All of the implemented materials were contrasted from the thermal and optical point of view. An analysis was made of both thermodynamic and steady state procedures affecting the proposed solar façade concept. Experimental full scale tests on real building components were additionally involved during summer monitoring. An indicator of the temperature response generated by solar radiation exposure demonstrates the outdoor performance of the façade is closely related to overheating phenomena. From the thermal point of view, the proposed transparent insulation and selective absorber concept corresponds to the performance of conventional thermal insulation of identical material thickness; however, the non-selective prototype only provides 50% thermal performance. The results of the solar-based experiments show that with a small-scale experimental prototype, approximately no significant difference is measured when compared with a non-selective absorber type. The only difference was achieved at the maximum of 2.5 K, when the lower temperature was obtained in the solar selective concept. At the full-scale outdoor mode, the results indicate a maximum of 3.0 K difference, however the lower temperature achieves a non-selective approach. This solar façade can actively contribute to the thermal performance of building components during periods of heating. Full article

(This article belongs to the Special Issue Solar Energy Application in Buildings)

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Graphical abstract

15 pages, 251 KiB

Open AccessArticle

Economic Analysis of a Photovoltaic System: A Resource for Residential Households

by Federica Cucchiella, Idiano D’Adamo and Massimo Gastaldi

Energies 2017, 10(6), 814; https://doi.org/10.3390/en10060814 - 15 Jun 2017

Cited by 68 | Viewed by 7022

Abstract

New installed annual solar photovoltaic (PV) capacity was equal to 76.1 GW in 2016 (+49%), reaching the total of 305 GW around the world. PV sources are able to achieve a greater energy independence, to tackle the climate change and to promote economic [...] Read more.

New installed annual solar photovoltaic (PV) capacity was equal to 76.1 GW in 2016 (+49%), reaching the total of 305 GW around the world. PV sources are able to achieve a greater energy independence, to tackle the climate change and to promote economic opportunities. This work proposes an economic analysis based on well-known indicators: Net Present Value (NPV), Discounted Payback Time (DPBT) and Levelized Cost of Electricity (LCOE). Several case studies are evaluated for residential households. They are based on three critical variables: plant size (1, 2, 3, 4, 5 and 6 kW), levels of insolation (1350, 1450 and 1550 kWh/(m²×y)) and share of self-consumption (30%, 40% and 50%). The profitability is verified in all case studies examined in this work. The role of self-consumption, that is the harmonization between demanded and produced energy, is strategic in a mature market to improve financial performance. A sensitivity analysis, based on both electricity purchase and sales prices (critical variables), confirms these positive results. The Reduction in the Emissions of Carbon Dioxide (ER_cd) signifies an environmental improvement when a PV system is used as an alternative to a mix of fossil fuels. Finally, a policy proposal is examined based on a fiscal deduction of 50% fixing the period of deduction equal to 5 years. Full article

(This article belongs to the Section L: Energy Sources)

18 pages, 3112 KiB

Open AccessArticle

Deriving Optimal End of Day Storage for Pumped-Storage Power Plants in the Joint Energy and Reserve Day-Ahead Scheduling

by Manuel Chazarra, Juan I. Pérez-Díaz and Javier García-González

Energies 2017, 10(6), 813; https://doi.org/10.3390/en10060813 - 15 Jun 2017

Cited by 12 | Viewed by 4642

Abstract

This paper presents a new methodology to maximise the income and derive the optimal end of day storage of closed-loop and daily-cycle pumped-storage hydropower plants. The plants participate in the day-ahead energy market as a price-taker and in the secondary regulation reserve market [...] Read more.

This paper presents a new methodology to maximise the income and derive the optimal end of day storage of closed-loop and daily-cycle pumped-storage hydropower plants. The plants participate in the day-ahead energy market as a price-taker and in the secondary regulation reserve market as a price-maker, in the context of the Iberian electricity system. The real-time use of the committed reserves is considered in the model formulation. The operation of the plants with the proposed methodology is compared to the ones that use an end of day storage of an empty reservoir or half of the storage capacity. Results show that the proposed methodology increases the maximum theoretical income in all the plants analysed both if they only participate in the day-ahead energy market and if they also participate in the secondary regulation service. It is also shown that the increase in the maximum theoretical income strongly depends on the size of the plant. In addition, it is proven that the end of day storages change notably in the new reserve-driven strategies of pumped-storage hydropower plants and that the proposed methodology is even more recommended if the secondary regulation service is considered. Full article

(This article belongs to the Special Issue Hydropower 2017)

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15 pages, 1728 KiB

Open AccessArticle

Accurate Short-Term Power Forecasting of Wind Turbines: The Case of Jeju Island’s Wind Farm

by BeomJun Park and Jin Hur

Energies 2017, 10(6), 812; https://doi.org/10.3390/en10060812 - 15 Jun 2017

Cited by 15 | Viewed by 5810

Abstract

Short-term wind power forecasting is a technique which tells system operators how much wind power can be expected at a specific time. Due to the increasing penetration of wind generating resources into the power grids, short-term wind power forecasting is becoming an important [...] Read more.

Short-term wind power forecasting is a technique which tells system operators how much wind power can be expected at a specific time. Due to the increasing penetration of wind generating resources into the power grids, short-term wind power forecasting is becoming an important issue for grid integration analysis. The high reliability of wind power forecasting can contribute to the successful integration of wind generating resources into the power grids. To guarantee the reliability of forecasting, power curves need to be analyzed and a forecasting method used that compensates for the variability of wind power outputs. In this paper, we analyzed the reliability of power curves at each wind speed using logistic regression. To reduce wind power forecasting errors, we proposed a short-term wind power forecasting method using support vector machine (SVM) based on linear regression. Support vector machine is a type of supervised leaning and is used to recognize patterns and analyze data. The proposed method was verified by empirical data collected from a wind turbine located on Jeju Island. Full article

(This article belongs to the Special Issue Wind Generators Modelling and Control)

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25 pages, 2569 KiB

Open AccessArticle

Optimal Placement and Sizing of Renewable Distributed Generations and Capacitor Banks into Radial Distribution Systems

by Mahesh Kumar, Perumal Nallagownden and Irraivan Elamvazuthi

Energies 2017, 10(6), 811; https://doi.org/10.3390/en10060811 - 14 Jun 2017

Cited by 49 | Viewed by 8281

Abstract

In recent years, renewable types of distributed generation in the distribution system have been much appreciated due to their enormous technical and environmental advantages. This paper proposes a methodology for optimal placement and sizing of renewable distributed generation(s) (i.e., wind, solar and biomass) [...] Read more.

In recent years, renewable types of distributed generation in the distribution system have been much appreciated due to their enormous technical and environmental advantages. This paper proposes a methodology for optimal placement and sizing of renewable distributed generation(s) (i.e., wind, solar and biomass) and capacitor banks into a radial distribution system. The intermittency of wind speed and solar irradiance are handled with multi-state modeling using suitable probability distribution functions. The three objective functions, i.e., power loss reduction, voltage stability improvement, and voltage deviation minimization are optimized using advanced Pareto-front non-dominated sorting multi-objective particle swarm optimization method. First a set of non-dominated Pareto-front data are called from the algorithm. Later, a fuzzy decision technique is applied to extract the trade-off solution set. The effectiveness of the proposed methodology is tested on the standard IEEE 33 test system. The overall results reveal that combination of renewable distributed generations and capacitor banks are dominant in power loss reduction, voltage stability and voltage profile improvement. Full article

(This article belongs to the Special Issue Electric Power Systems Research 2017)

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14 pages, 2572 KiB

Open AccessArticle

Experimental Study on the Performance of Water Source Trans-Critical CO₂ Heat Pump Water Heater

by Xiufang Liu, Changhai Liu, Ze Zhang, Liang Chen and Yu Hou

Energies 2017, 10(6), 810; https://doi.org/10.3390/en10060810 - 14 Jun 2017

Cited by 22 | Viewed by 4871

Abstract

The effect of the discharge pressure on the performance of the trans-critical CO₂ heat pump with a low gas-cooler outlet temperature is experimentally investigated on a test rig of water source heat-pump water heater. The optimal discharge pressure of the trans-critical CO [...] Read more.

The effect of the discharge pressure on the performance of the trans-critical CO₂ heat pump with a low gas-cooler outlet temperature is experimentally investigated on a test rig of water source heat-pump water heater. The optimal discharge pressure of the trans-critical CO₂ heat pump is investigated under different external operation conditions. When the tap-water temperature is low, the characteristic of the S-shape isotherm at the supercritical region has little effect on the occurrence of the optimal discharge pressure; while the mass flow rate of CO₂, the suction pressure and the gas-cooler outlet temperature play a significant role in determining the emergence of the optimal discharge pressure. At the optimal discharge pressure, the COP reaches the peak; however, the corresponding heating capacity is still lower than its maximum, which is reached as the discharge pressure is slightly above the optimal discharge pressure. Reducing the tap-water flowrate or increasing the water-source temperature can increase the optimal discharge pressure. The COP is positively dependent on both the tap-water flowrate and the water-source temperature. In addition, the tap-water flowrate has a negligible influence on the maximum heating capacity while increasing the water-source temperature can greatly enhance the heating capacity. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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3 pages, 131 KiB

Open AccessEditorial

Recent Advances in Energy Time Series Forecasting

by Francisco Martínez-Álvarez, Alicia Troncoso and José C. Riquelme

Energies 2017, 10(6), 809; https://doi.org/10.3390/en10060809 - 14 Jun 2017

Cited by 3 | Viewed by 4557

Abstract

This editorial summarizes the performance of the special issue entitled Energy Time Series Forecasting, which was published in MDPI’s Energies journal. The special issue took place in 2016 and accepted a total of 21 papers from twelve different countries. Electrical, solar, or wind [...] Read more.

This editorial summarizes the performance of the special issue entitled Energy Time Series Forecasting, which was published in MDPI’s Energies journal. The special issue took place in 2016 and accepted a total of 21 papers from twelve different countries. Electrical, solar, or wind energy forecasting were the most analyzed topics, introducing brand new methods with very sound results. Full article

(This article belongs to the Special Issue Energy Time Series Forecasting)

20 pages, 1588 KiB

Open AccessArticle

Comprehensive Reactive Power Support of DFIG Adapted to Different Depth of Voltage Sags

by Yangwu Shen, Mingjian Cui, Qin Wang, Feifan Shen, Bin Zhang and Liqing Liang

Energies 2017, 10(6), 808; https://doi.org/10.3390/en10060808 - 14 Jun 2017

Cited by 19 | Viewed by 5026

Abstract

The low voltage ride-through (LVRT) capability of the doubly-fed induction generator (DFIG) significantly impacts upon the integration of wind power into the power grid. This paper develops a novel comprehensive control strategy to enhance the LVRT and reactive power support capacities of the [...] Read more.

The low voltage ride-through (LVRT) capability of the doubly-fed induction generator (DFIG) significantly impacts upon the integration of wind power into the power grid. This paper develops a novel comprehensive control strategy to enhance the LVRT and reactive power support capacities of the DFIG by installing the energy storage system (ESS). The ESS is connected to the DC-link capacitor of the DFIG and used to regulate the DC-link voltage during normal or fault operations. The unbalanced power between the captured wind power and the power injected to the grid during the transient process is absorbed or compensated by the ESS. The rotor-side converter (RSC) is used to control the maximum power production and the grid-side converter (GSC) is used to control the reactive power before participating in the voltage support. When the supply voltage continues to drop, the rotor speed is increased by controlling the RSC to realize the LVRT capability and help the GSC further enhance the reactive power support capability. The capacity of the GSC is dedicated to injecting the reactive power to the grid. An auxiliary transient pitch angle controller is proposed to protect the generator’s over speed. Both RSC and GSC act as reactive power sources to further enhance the voltage support capability with serious voltage sags. Simulations based on a single-machine infinite-bus power system verify the effectiveness of the developed comprehensive control strategy. Full article

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17 pages, 10857 KiB

Open AccessArticle

Energy Modelling and Automated Calibrations of Ancient Building Simulations: A Case Study of a School in the Northwest of Spain

by Ana Ogando, Natalia Cid and Marta Fernández

Energies 2017, 10(6), 807; https://doi.org/10.3390/en10060807 - 14 Jun 2017

Cited by 22 | Viewed by 5572

Abstract

In the present paper, the energy performance of buildings forming a school centre in the northwest of Spain was analyzed using a transient simulation of the energy model of the school, which was developed with TRNSYS, a software of proven reliability in the [...] Read more.

In the present paper, the energy performance of buildings forming a school centre in the northwest of Spain was analyzed using a transient simulation of the energy model of the school, which was developed with TRNSYS, a software of proven reliability in the field of thermal simulations. A deterministic calibration approach was applied to the initial building model to adjust the predictions to the actual performance of the school, data acquired during the temperature measurement campaign. The buildings under study were in deteriorated conditions due to poor maintenance over the years, presenting a big challenge for modelling and simulating it in a reliable way. The results showed that the proposed methodology is successful for obtaining calibrated thermal models of these types of damaged buildings, as the metrics employed to verify the final error showed a reduced normalized mean bias error (NMBE) of 2.73%. It was verified that a decrease of approximately 60% in NMBE and 17% in the coefficient of variation of the root mean square error (CV(RMSE)) was achieved due to the calibration process. Subsequent steps were performed with the aid of new software, which was developed under a European project that enabled the automated calibration of the simulations. Full article

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14 pages, 4227 KiB

Open AccessArticle

Implementation of a Real-Time Microgrid Simulation Platform Based on Centralized and Distributed Management

by Omid Abrishambaf, Pedro Faria, Luis Gomes, João Spínola, Zita Vale and Juan M. Corchado

Energies 2017, 10(6), 806; https://doi.org/10.3390/en10060806 - 14 Jun 2017

Cited by 57 | Viewed by 8080

Abstract

Demand response and distributed generation are key components of power systems. Several challenges are raised at both technical and business model levels for integration of those resources in smart grids and microgrids. The implementation of a distribution network as a test bed can [...] Read more.

Demand response and distributed generation are key components of power systems. Several challenges are raised at both technical and business model levels for integration of those resources in smart grids and microgrids. The implementation of a distribution network as a test bed can be difficult and not cost-effective; using computational modeling is not sufficient for producing realistic results. Real-time simulation allows us to validate the business model’s impact at the technical level. This paper comprises a platform supporting the real-time simulation of a microgrid connected to a larger distribution network. The implemented platform allows us to use both centralized and distributed energy resource management. Using an optimization model for the energy resource operation, a virtual power player manages all the available resources. Then, the simulation platform allows us to technically validate the actual implementation of the requested demand reduction in the scope of demand response programs. The case study has 33 buses, 220 consumers, and 68 distributed generators. It demonstrates the impact of demand response events, also performing resource management in the presence of an energy shortage. Full article

(This article belongs to the Special Issue Distributed Energy Resources Management)

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20 pages, 2417 KiB

Open AccessArticle

An Investigation of the Composition of the Flow in and out of a Two-Stroke Diesel Engine and Air Consumption Ratio

by Mirko Grljušić, Ivan Tolj and Gojmir Radica

Energies 2017, 10(6), 805; https://doi.org/10.3390/en10060805 - 13 Jun 2017

Cited by 5 | Viewed by 5834

Abstract

The aim of this research was to investigate the mass, substance and energy flow through two-stroke low speed Diesel engines. For this reason, a zero-dimensional model of the combustion in the engine was developed with a calculated amount and composition of exhaust gases. [...] Read more.

The aim of this research was to investigate the mass, substance and energy flow through two-stroke low speed Diesel engines. For this reason, a zero-dimensional model of the combustion in the engine was developed with a calculated amount and composition of exhaust gases. Due to the large amount of oxygen in the exhaust gases, a ratio of real air consumption and stoichiometric amount of air required for combustion of injected fuel was set. The calculated ratio showed that the engine consumed four times more air than needed for combustion in AFR_stoich. In this work, this was called the Air Consumption Factor or Ratio, and has not previously been mentioned in scientific literature. The air consumption ratio is defined as a factor of dry or humid air. To be more comprehensive, a modified diagram of the composition of the flow in and out of a two-stroke fuel injection engine and the cylinder was made. Full article

(This article belongs to the Section L: Energy Sources)

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18 pages, 7925 KiB

Open AccessEditor’s ChoiceArticle

A Novel Decentralized Economic Operation in Islanded AC Microgrids

by Hua Han, Lang Li, Lina Wang, Mei Su, Yue Zhao and Josep M. Guerrero

Energies 2017, 10(6), 804; https://doi.org/10.3390/en10060804 - 13 Jun 2017

Cited by 30 | Viewed by 5193

Abstract

Droop schemes are usually applied to the control of distributed generators (DGs) in microgrids (MGs) to realize proportional power sharing. The objective might, however, not suit MGs well for economic reasons. Addressing that issue, this paper proposes an alternative droop scheme for reducing [...] Read more.

Droop schemes are usually applied to the control of distributed generators (DGs) in microgrids (MGs) to realize proportional power sharing. The objective might, however, not suit MGs well for economic reasons. Addressing that issue, this paper proposes an alternative droop scheme for reducing the total active generation costs (TAGC). Optimal economic operation, DGs’ capacity limitations and system stability are fully considered basing on DGs’ generation costs. The proposed scheme utilizes the frequency as a carrier to realize the decentralized economic operation of MGs without communication links. Moreover, a fitting method is applied to balance DGs’ synchronous operation and economy. The effectiveness and performance of the proposed scheme are verified through simulations and experiments. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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14 pages, 2474 KiB

Open AccessArticle

Autonomous Wireless Self-Charging for Multi-Rotor Unmanned Aerial Vehicles

by Ali Bin Junaid, Aleksay Konoiko, Yahya Zweiri, M. Necip Sahinkaya and Lakmal Seneviratne

Energies 2017, 10(6), 803; https://doi.org/10.3390/en10060803 - 13 Jun 2017

Cited by 122 | Viewed by 12983

Abstract

Rotary-wing unmanned aerial vehicles (UAVs) have the ability to operate in confined spaces and to hover over point of interest, but they have limited flight time and endurance. Conventional contact-based charging system for UAVs has been used, but it requires high landing accuracy [...] Read more.

Rotary-wing unmanned aerial vehicles (UAVs) have the ability to operate in confined spaces and to hover over point of interest, but they have limited flight time and endurance. Conventional contact-based charging system for UAVs has been used, but it requires high landing accuracy for proper docking. Instead of the conventional system, autonomous wireless battery charging system for UAVs in outdoor conditions is proposed in this paper. UAVs can be wirelessly charged using the proposed charging system, regardless of yaw angle between UAVs and wireless charging pad, which can further reduce their control complexity for autonomous landing. The increased overall mission time eventually relaxes the limitations on payload and flight time. In this paper, a cost effective automatic recharging solution for UAVs in outdoor environments is proposed using wireless power transfer (WPT). This research proposes a global positioning system (GPS) and vision-based closed-loop target detection and a tracking system for precise landing of quadcopters in outdoor environments. The system uses the onboard camera to detect the shape, color and position of the defined target in image frame. Based on the offset of the target from the center of the image frame, control commands are generated to track and maintain the center position. Commercially available AR.Drone. was used to demonstrate the proposed concept which is equppied with bottom camera and GPS. Experiments and analyses showed good performance, and about 75% average WPT efficiency was achieved in this research. Full article

(This article belongs to the Special Issue Wireless Power Transfer)

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18 pages, 2576 KiB

Open AccessArticle

Transmission Power and Antenna Allocation for Energy-Efficient RF Energy Harvesting Networks with Massive MIMO

by Yu Min Hwang, Ji Ho Park, Yoan Shin, Jin Young Kim and Dong In Kim

Energies 2017, 10(6), 802; https://doi.org/10.3390/en10060802 - 13 Jun 2017

Cited by 5 | Viewed by 5629

Abstract

The optimum transmission strategy for maximizing energy efficiency (EE) of a multi-user massive multiple-input multiple-output (MIMO) system in radio frequency energy harvesting networks is investigated. We focus on dynamic time-switching (TS) antennas, to avoid the practical problems of power-splitting antennas, such as complex [...] Read more.

The optimum transmission strategy for maximizing energy efficiency (EE) of a multi-user massive multiple-input multiple-output (MIMO) system in radio frequency energy harvesting networks is investigated. We focus on dynamic time-switching (TS) antennas, to avoid the practical problems of power-splitting antennas, such as complex architectures, power loss and signal distortion when splitting the power of the received signal into power for information decoding (ID) and energy harvesting (EH). However, since a single TS antenna cannot serve ID and EH simultaneously, the MIMO system is considered in this paper. We thus formulate an EE optimization problem and propose an iterative algorithm as a tractable solution, including an antenna selection strategy to optimally switch each TS antenna between ID mode and EH mode using nonlinear fractional programming and the Lagrange dual method. Further, the problem is solved under practical constraints of maximum transmission power and outage probabilities for a minimum amount of harvested power and rate capacity for each user. Simulation results show that the proposed algorithm is more energy-efficient than that of baseline schemes, and demonstrates the trade-off between the required amount of harvested power and energy efficiency. Full article

(This article belongs to the Section F: Electrical Engineering)

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18 pages, 6089 KiB

Open AccessFeature PaperArticle

Thermal Response Testing Results of Different Types of Borehole Heat Exchangers: An Analysis and Comparison of Interpretation Methods

by Angelo Zarrella, Giuseppe Emmi, Samantha Graci, Michele De Carli, Matteo Cultrera, Giorgia Dalla Santa, Antonio Galgaro, David Bertermann, Johannes Müller, Luc Pockelé, Giulia Mezzasalma, Davide Righini, Mario Psyk and Adriana Bernardi

Energies 2017, 10(6), 801; https://doi.org/10.3390/en10060801 - 13 Jun 2017

Cited by 40 | Viewed by 6460

Abstract

The design phase of ground source heat pump systems is an extremely important one as many of the decisions made at that time can affect the system’s energy performance as well as installation and operating costs. The current study examined the interpretation of [...] Read more.

The design phase of ground source heat pump systems is an extremely important one as many of the decisions made at that time can affect the system’s energy performance as well as installation and operating costs. The current study examined the interpretation of thermal response testing measurements used to evaluate the equivalent ground thermal conductivity and thus to design the system. All the measurements were taken at the same geological site located in Molinella, Bologna (Italy) where a variety of borehole heat exchangers (BHEs) had been installed and investigated within the project Cheap-GSHPs (Cheap and efficient application of reliable Ground Source Heat exchangers and Pumps) of the European Union’s Horizon 2020 research and innovation program. The measurements were initially analyzed in accordance with the common interpretation based on the first-order approximation of the solution for the infinite line source model and then by utilizing the complete solutions of both the infinite line and cylinder source models. An inverse numerical approach based on a detailed model that considers the current geometry of the BHE and the axial heat transfer as well as the effect of weather on the ground surface was also used. Study findings revealed that the best result was generally obtained using the inverse numerical interpretation. Full article

(This article belongs to the Special Issue Low Enthalpy Geothermal Energy)

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20 pages, 7075 KiB

Open AccessArticle

Study on the Effects of Evaporation and Condensation on the Underfloor Space of Japanese Detached Houses Using CFD Analysis

by Wonseok Oh and Shinsuke Kato

Energies 2017, 10(6), 798; https://doi.org/10.3390/en10060798 - 13 Jun 2017

Cited by 3 | Viewed by 5752

Abstract

The purpose of this study is to determine the effects of evaporation and condensation on the underfloor space of Japanese detached houses. In this underfloor space, natural ventilation is applied. A typical Japanese wooden detached house is raised 0.3–0.5 m over an underfloor [...] Read more.

The purpose of this study is to determine the effects of evaporation and condensation on the underfloor space of Japanese detached houses. In this underfloor space, natural ventilation is applied. A typical Japanese wooden detached house is raised 0.3–0.5 m over an underfloor space made of concrete. The bottom of the underfloor space is usually paved with concrete, and the ceiling which is directly underneath the indoor occupant zone is made of wood. Computational fluid dynamics (CFD) analysis is applied to calculate the rates of the evaporation and condensation generated inside the underfloor under two conditions, namely, a constant (fixed) outdoor environmental condition and a fluctuating environmental condition. In the constant condition, we verified the effects of the outdoor humidity, ventilation rate, and ratio of wetted surface (RWS, ω) on the evaporation and condensation inside the underfloor space. In this condition, the rate of evaporation and condensation was quantified considering the varying outdoor humidity between 0 to 100%, and the RWS (ω = 1 or 0). In addition, the influence of the different ventilation rates at 1.0 m/s for normal and 0.05 m/s for stagnant wind velocities were confirmed. Under fluctuating environmental conditions, the outdoor conditions change for 24 h, so the RWS varies. Therefore, the rate of evaporation and condensation, the amount of the condensed water, and the area of condensation were confirmed. The results were as follows: with a high airflow rate on the underfloor space, the evaporation and condensation phenomenon occurs continuously and is easily affected by outdoor humidity, while under low airflow rate conditions, only the condensation appeared steadily. If the wind velocity is strong, the convective mass transfer on a surface becomes large. In a condition of the outdoor humidity and the airflow rate on underfloor are high, condensation mainly occurs in a corner of the underfloor space due to high evaporation by convection in the mainstream of the airflow. By contrast, when the airflow rate is low, condensation occurs along the air stream. Accordingly, this information could be employed as design considerations for the underfloor space at the architectural design stage. Full article

(This article belongs to the Special Issue Engineering Fluid Dynamics)

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Energies, Volume 10, Issue 6 (June 2017) – 95 articles

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