Energies

Article

12 pages, 499 KiB

Open AccessEditor’s ChoiceArticle

Estimating Air Density Using Observations and Re-Analysis Outputs for Wind Energy Purposes

by Rogier Floors and Morten Nielsen

Energies 2019, 12(11), 2038; https://doi.org/10.3390/en12112038 - 28 May 2019

Cited by 22 | Viewed by 5146

A method to estimate air density as a function of elevation for wind energy resource assessments is presented. The current practice of using nearby measurements of pressure and temperature is compared with a method that uses re-analysis data. It is found that using [...] Read more.

A method to estimate air density as a function of elevation for wind energy resource assessments is presented. The current practice of using nearby measurements of pressure and temperature is compared with a method that uses re-analysis data. It is found that using re-analysis data to estimate air density gives similar or smaller mean absolute errors compared to using measurements that were on average located 40 km away. A method to interpolate power curves that are valid for different air densities is presented. The new model is implemented in the industry-standard model for wind resource assessment and compared with the current version of that model and shown to lead to more accurate assessment of the air density at different elevations. Full article

(This article belongs to the Section A: Sustainable Energy)

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34 pages, 3085 KiB

Open AccessEditor’s ChoiceArticle

Measured Performance of a Mixed-Use Commercial-Building Ground Source Heat Pump System in Sweden

by Jeffrey D. Spitler and Signhild Gehlin

Energies 2019, 12(10), 2020; https://doi.org/10.3390/en12102020 - 27 May 2019

Cited by 39 | Viewed by 7253

Abstract

When the new student center at Stockholm University in Sweden was completed in the fall of 2013 it was thoroughly instrumented. The 6300 m² four-story building with offices, a restaurant, study lounges, and meeting rooms was designed to be energy efficient with [...] Read more.

When the new student center at Stockholm University in Sweden was completed in the fall of 2013 it was thoroughly instrumented. The 6300 m² four-story building with offices, a restaurant, study lounges, and meeting rooms was designed to be energy efficient with a planned total energy use of 25 kWh/m²/year. Space heating and hot water are provided by a ground source heat pump (GSHP) system consisting of five 40 kW off-the-shelf water-to-water heat pumps connected to 20 boreholes in hard rock, drilled to a depth of 200 m. Space cooling is provided by direct cooling from the boreholes. This paper uses measured performance data from Studenthuset to calculate the actual thermal performance of the GSHP system during one of its early years of operation. Monthly system coefficients-of-performance and coefficients-of-performance for both heating and cooling operation are presented. In the first months of operation, several problems were corrected, leading to improved performance. This paper provides long-term measured system performance data from a recently installed GSHP system, shows how the various system components affect the performance, presents an uncertainty analysis, and describes how some unanticipated consequences of the design may be ameliorated. Seasonal performance factors (SPF) are evaluated based on the SEPEMO (“SEasonal PErformance factor and MOnitoring for heat pump systems”) boundary schema. For heating (“H”), SPFs of 3.7 ± 0.2 and 2.7 ± 0.13 were obtained for boundaries H2 and H3, respectively. For cooling (“C”), a C2 SPF of 27 ± 5 was obtained. Results are compared to measured performance data from 55 GSHP systems serving commercial buildings that are reported in the literature. Full article

(This article belongs to the Special Issue Modelling and Monitoring of Geothermal Heating and Cooling Systems)

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25 pages, 11094 KiB

Open AccessEditor’s ChoiceArticle

Roof Cutting Parameters Design for Gob-Side Entry in Deep Coal Mine: A Case Study

by Deyuan Fan, Xuesheng Liu, Yunliang Tan, Shilin Song, Qingheng Gu, Lei Yan and Qiang Xu

Energies 2019, 12(10), 2032; https://doi.org/10.3390/en12102032 - 27 May 2019

Cited by 44 | Viewed by 3777

Abstract

Roof cutting is an effective technique for controlling the deformation and failure of the surrounding rock in deep gob-side entry. The determination of the roof cutting parameters has become a popular research subject. Initially, two mechanical models are established for the non-roof-cutting and [...] Read more.

Roof cutting is an effective technique for controlling the deformation and failure of the surrounding rock in deep gob-side entry. The determination of the roof cutting parameters has become a popular research subject. Initially, two mechanical models are established for the non-roof-cutting and roof-cutting of gob-side entry in deep mining conditions. On this basis, the necessity and significance of roof cutting is revealed by analysing the stress and displacement of roadside prop. The Universal Distinct Element Code numerical simulation model is established to determine the key roof-cutting parameters (cutting angle and cutting height) according to the on-site situation of No. 2415 headentry of the Suncun coal mine, China. The numerical simulation results show that with the cutting angle and height increase, the vertical stress and horizontal displacement of the coal wall first increase and then decrease, as in the case of the vertical stress and displacement of roadside prop. Therefore, the optimum roof cutting parameters are determined as a cutting angle of 70° and cutting height of 8 m. Finally, a field application was performed at the No. 2415 headentry of the Suncun coal mine. In situ investigations show that after 10 m lagged the working face, the stress and displacement of roadside prop are obviously reduced with the hanging roof smoothly cut down, and they are stable at 19 MPa and 145 mm at 32 m behind the working face, respectively. This indicates that the stability of the surrounding rock was effectively controlled. This research demonstrates that the key parameters determined through a numerical simulation satisfactorily meet the production requirements and provide a reference for ensuring safe production in deep mining conditions. Full article

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17 pages, 1699 KiB

Open AccessEditor’s ChoiceArticle

Experimental and Numerical Characterization of the Sliding Rotary Vane Expander Intake Pressure in Order to Develop a Novel Control-Diagnostic Procedure

by Fabio Fatigati, Marco Di Bartolomeo, Davide Di Battista and Roberto Cipollone

Energies 2019, 12(10), 1970; https://doi.org/10.3390/en12101970 - 23 May 2019

Cited by 21 | Viewed by 2794

Abstract

Waste heat recovery via Organic Rankine Cycle (ORC)-based power units represents one of the most promising solutions to counteract the effects of CO₂ emissions on climate change. Nevertheless, several aspects are still limiting its development on the on-the-road transportation sector. Among these [...] Read more.

Waste heat recovery via Organic Rankine Cycle (ORC)-based power units represents one of the most promising solutions to counteract the effects of CO₂ emissions on climate change. Nevertheless, several aspects are still limiting its development on the on-the-road transportation sector. Among these aspects, the significant variations of the conditions of the hot source (exhaust gases) are a crucial point. Therefore, the components of the ORC-based unit operate far from the design point if the main operating parameters of the plant are not suitably controlled. The maximum pressure of the cycle is one of the most important variables to be controlled for the importance it has on the effectiveness of the recovery and on safety of operation. In this paper, a wide experimental and theoretical activity was performed in order to define the operating parameters that mostly affect the maximum pressure of the recovery unit. The results showed that the mass flow rate provided by the pump and the expander volumetric efficiency were the main drivers that affect the plant maximum pressure. Subsequently, through a validated model of the expander, a diagnostic map was outlined to evaluate if the expander and, consequently, the whole plant were properly working. Full article

(This article belongs to the Section J: Thermal Management)

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15 pages, 2509 KiB

Open AccessEditor’s ChoiceArticle

Post-Closure Performance Assessment for Deep Borehole Disposal of Cs/Sr Capsules

by Geoff A. Freeze, Emily Stein and Patrick V. Brady

Energies 2019, 12(10), 1980; https://doi.org/10.3390/en12101980 - 23 May 2019

Cited by 6 | Viewed by 4311

Abstract

Post-closure performance assessment (PA) calculations suggest that deep borehole disposal of cesium (Cs)/strontium (Sr) capsules, a U.S. Department of Energy (DOE) waste form (WF), is safe, resulting in no releases to the biosphere over 10,000,000 years when the waste is placed in a [...] Read more.

Post-closure performance assessment (PA) calculations suggest that deep borehole disposal of cesium (Cs)/strontium (Sr) capsules, a U.S. Department of Energy (DOE) waste form (WF), is safe, resulting in no releases to the biosphere over 10,000,000 years when the waste is placed in a 3–5 km deep waste disposal zone. The same is true when a hypothetical breach of a stuck waste package (WP) is assumed to occur at much shallower depths penetrated by through-going fractures. Cs and Sr retardation in the host rock is a key control over movement. Calculated borehole performance would be even stronger if credit was taken for the presence of the WP. Full article

(This article belongs to the Special Issue Deep Borehole Disposal of Nuclear Waste)

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17 pages, 3501 KiB

Open AccessEditor’s ChoiceArticle

Thermal Assessment of Nano-Particulate Graphene-Water/Ethylene Glycol (WEG 60:40) Nano-Suspension in a Compact Heat Exchanger

by M. M. Sarafraz, Mohammad Reza Safaei, Zhe Tian, Marjan Goodarzi, Enio Pedone Bandarra Filho and M. Arjomandi

Energies 2019, 12(10), 1929; https://doi.org/10.3390/en12101929 - 20 May 2019

Cited by 111 | Viewed by 4624

Abstract

In the present study, we report the results of the experiments conducted on the convective heat transfer of graphene nano-platelets dispersed in water-ethylene glycol. The graphene nano-suspension was employed as a coolant inside a micro-channel and heat-transfer coefficient (HTC) and pressure drop (PD) [...] Read more.

In the present study, we report the results of the experiments conducted on the convective heat transfer of graphene nano-platelets dispersed in water-ethylene glycol. The graphene nano-suspension was employed as a coolant inside a micro-channel and heat-transfer coefficient (HTC) and pressure drop (PD) values of the system were reported at different operating conditions. The results demonstrated that the use of graphene nano-platelets can potentially augment the thermal conductivity of the working fluid by 32.1% (at wt. % = 0.3 at 60 °C). Likewise, GNP nano-suspension promoted the Brownian motion and thermophoresis effect, such that for the tests conducted within the mass fractions of 0.1%–0.3%, the HTC of the system was improved. However, a trade-off was identified between the PD value and the HTC. By assessing the thermal performance evaluation criteria (TPEC) of the system, it was identified that the thermal performance of the system increased by 21% despite a 12.1% augmentation in the PD value. Furthermore, with an increment in the fluid flow and heat-flux applied to the micro-channel, the HTC was augmented, showing the potential of the nano-suspension to be utilized in high heat-flux thermal applications. Full article

(This article belongs to the Special Issue Experimental Heat Transfer in Energy Systems)

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15 pages, 4193 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Supercapacitor Storage Sizing Analysis for a Series Hybrid Vehicle

by Massimiliano Passalacqua, Mauro Carpita, Serge Gavin, Mario Marchesoni, Matteo Repetto, Luis Vaccaro and Sébastien Wasterlain

Energies 2019, 12(9), 1759; https://doi.org/10.3390/en12091759 - 9 May 2019

Cited by 14 | Viewed by 3645

Abstract

The increasing interest in Hybrid Electric Vehicles led to the study of new powertrain structures. In particular, it was demonstrated in the technical literature how series architecture can be more efficient, compared to parallel one, if supercapacitors are used as storage system. Since [...] Read more.

The increasing interest in Hybrid Electric Vehicles led to the study of new powertrain structures. In particular, it was demonstrated in the technical literature how series architecture can be more efficient, compared to parallel one, if supercapacitors are used as storage system. Since supercapacitors are characterized by high efficiency and high power density, but have low specific energy, storage sizing is a critical point with this technology. In this study, a detailed analysis on the effect of supercapacitor storage sizing on series architecture was carried out. In particular, in series architecture, supercapacitor storage sizing influences both engine number of starts and the energy that can be stored during regenerative braking. The first aspect affects the comfort, whereas the second aspect directly influences powertrain efficiency. Vehicle model and Energy Management System were studied and simulations were carried out for different storage energy, in order to define the optimal sizing. Full article

(This article belongs to the Special Issue Energy Efficiency in Electric Motors, Drives, Power Converters and Related Systems)

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26 pages, 829 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

City Branding, Sustainable Urban Development and the Rentier State. How Do Qatar, Abu Dhabi and Dubai Present Themselves in the Age of Post Oil and Global Warming?

by Martin De Jong, Thomas Hoppe and Negar Noori

Energies 2019, 12(9), 1657; https://doi.org/10.3390/en12091657 - 30 Apr 2019

Cited by 42 | Viewed by 11401

Abstract

In the past three decades Qatar, Abu Dhabi and Dubai have realised a meteoric economic rise. Whereas the former two can be considered ‘rentier states’ heavily depending on oil (and gas) revenues, the latter only leans on oil for a mere 6% of [...] Read more.

In the past three decades Qatar, Abu Dhabi and Dubai have realised a meteoric economic rise. Whereas the former two can be considered ‘rentier states’ heavily depending on oil (and gas) revenues, the latter only leans on oil for a mere 6% of its gross domestic product (GDP). Although the economic rise has brought considerable welfare, it has also led these emirates to attain the world’s highest per capita carbon footprint. To address this problem Qatar, Abu Dhabi and Dubai seem to have formulated policies with regard to sustainable urbanisation and adopted strong branding strategies to promote them internally and externally. In this paper we examine which steps have been taken to substantiate their claims to sustainable urbanisation, in branding as well as in actions taken towards implementation. We find that all three have been very active in branding their sustainable urbanisation policies, through visions and policy frameworks as well as prestigious development projects, but that the former is substantially more impressive than the latter. Results also show there is a difference between Abu Dhabi and Qatar on the one hand, and Dubai on the other. Dubai has large number of small ‘free economic zones’, academic institutions for developing a knowledge economy, and smart and/or sustainable urban neighbourhoods, while Qatar and Abu Dhabi have a small number of very large ones. From the three, it is currently Dubai which has taken the lead in this development, largely completing its industrial transition with vast economic diversification and urban expansion. However, across the board this has had little effect on its ecological footprint. Full article

(This article belongs to the Special Issue Approaches, Advances and Applications in Sustainable Development of Smart Cities )

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17 pages, 1268 KiB

Open AccessEditor’s ChoiceArticle

Concatenate Convolutional Neural Networks for Non-Intrusive Load Monitoring across Complex Background

by Qian Wu and Fei Wang

Energies 2019, 12(8), 1572; https://doi.org/10.3390/en12081572 - 25 Apr 2019

Cited by 58 | Viewed by 6372

Abstract

Non-Intrusive Load Monitoring (NILM) provides a way to acquire detailed energy consumption and appliance operation status through a single sensor, which has been proven to save energy. Further, besides load disaggregation, advanced applications (e.g., demand response) need to recognize on/off events of appliances [...] Read more.

Non-Intrusive Load Monitoring (NILM) provides a way to acquire detailed energy consumption and appliance operation status through a single sensor, which has been proven to save energy. Further, besides load disaggregation, advanced applications (e.g., demand response) need to recognize on/off events of appliances instantly. In order to shorten the time delay for users to acquire the event information, it is necessary to analyze extremely short period electrical signals. However, the features of those signals are easily submerged in complex background loads, especially in cross-user scenarios. Through experiments and observations, it can be found that the feature of background loads is almost stationary in a short time. On the basis of this result, this paper provides a novel model called the concatenate convolutional neural network to separate the feature of the target load from the load mixed with the background. For the cross-user test on the UK Domestic Appliance-Level Electricity dataset (UK-DALE), it turns out that the proposed model remarkably improves accuracy, robustness, and generalization of load recognition. In addition, it also provides significant improvements in energy disaggregation compared with the state-of-the-art. Full article

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13 pages, 202 KiB

Open AccessEditor’s ChoiceArticle

Who Might Be Interested in a Deep Borehole Disposal Facility for Their Radioactive Waste?

by Neil A. Chapman

Energies 2019, 12(8), 1542; https://doi.org/10.3390/en12081542 - 24 Apr 2019

Cited by 20 | Viewed by 4509

Abstract

The deep borehole disposal (DBD) concept for certain types of radioactive wastes has been discussed for many decades, but has enjoyed limited R&D interest compared to ‘conventional’ geological disposal in an excavated repository at a few hundreds of metres depth. This article explores [...] Read more.

The deep borehole disposal (DBD) concept for certain types of radioactive wastes has been discussed for many decades, but has enjoyed limited R&D interest compared to ‘conventional’ geological disposal in an excavated repository at a few hundreds of metres depth. This article explores the circumstances under which a national waste management programme might wish to consider DBD. Starting with an assumption that further R&D will answer technical issues of DBD feasibility, it examines the types of waste that might be routed to borehole disposal and the strategic drivers that might make DBD attractive. The article concludes by identifying the types of national programme that might wish to pursue DBD further and the pre-requisites for them to give it serious consideration. Full article

(This article belongs to the Special Issue Deep Borehole Disposal of Nuclear Waste)

14 pages, 1540 KiB

Open AccessEditor’s ChoiceArticle

Environmental Decision Support System for Biogas Upgrading to Feasible Fuel

by Eric Santos-Clotas, Alba Cabrera-Codony, Alba Castillo, Maria J. Martín, Manel Poch and Hèctor Monclús

Energies 2019, 12(8), 1546; https://doi.org/10.3390/en12081546 - 24 Apr 2019

Cited by 20 | Viewed by 3723

Abstract

Biogas production is a growing market and the existing conversion technologies require different biogas quality and characteristics. In pursuance of assisting decision-makers in biogas upgrading an environmental decision support system (EDSS) was developed. Since the field is rapidly progressing, this tool is easily [...] Read more.

Biogas production is a growing market and the existing conversion technologies require different biogas quality and characteristics. In pursuance of assisting decision-makers in biogas upgrading an environmental decision support system (EDSS) was developed. Since the field is rapidly progressing, this tool is easily updatable with new data from technical and scientific literature through the knowledge acquisition level. By a thorough technology review, the diagnosis level evaluates a wide spectrum of technologies for eliminating siloxanes, H₂S, and CO₂ from biogas, which are scored in a supervision level based upon environmental, economic, social and technical criteria. The sensitivity of the user towards those criteria is regarded by the EDSS giving a response based on its preferences. The EDSS was validated with data from a case-study for removing siloxanes from biogas in a sewage plant. The tool described the flow diagram of treatment alternatives and estimated the performance and effluent quality, which matched the treatment currently given in the facility. Adsorption onto activated carbon was the best-ranked technology due to its great efficiency and maturity as a commercial technology. On the other hand, biological technologies obtained high scores when economic and environmental criteria were preferred. The sensitivity analysis proved to be effective allowing the identification of the challenges and opportunities for the technologies considered. Full article

(This article belongs to the Special Issue Artificial Intelligence in Data Science For Energy Management in Sustainability)

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33 pages, 23846 KiB

Open AccessEditor’s ChoiceArticle

A Holistic Methodology for Optimizing Industrial Resource Efficiency

by Maziar Kermani, Ivan D. Kantor, Anna S. Wallerand, Julia Granacher, Adriano V. Ensinas and François Maréchal

Energies 2019, 12(7), 1315; https://doi.org/10.3390/en12071315 - 5 Apr 2019

Cited by 14 | Viewed by 5043

Abstract

Efficient consumption of energy and material resources, including water, is the primary focus for process industries to reduce their environmental impact. The Conference of Parties in Paris (COP21) highlighted the prominent role of industrial energy efficiency in combating climate change by reducing greenhouse [...] Read more.

Efficient consumption of energy and material resources, including water, is the primary focus for process industries to reduce their environmental impact. The Conference of Parties in Paris (COP21) highlighted the prominent role of industrial energy efficiency in combating climate change by reducing greenhouse gas emissions. Consumption of energy and material resources, especially water, are strongly interconnected and, therefore, must be treated simultaneously using a holistic approach to identify optimal solutions for efficient processing. Such approaches must consider energy and water recovery within a comprehensive process integration framework which includes options such as organic Rankine cycles for electricity generation from low–medium-temperature heat. This work addresses the importance of holistic approaches by proposing a methodology for simultaneous consideration of heat, mass, and power in industrial processes. The methodology is applied to a kraft pulp mill. In doing so, freshwater consumption is reduced by more than 60%, while net power output is increased by a factor of up to six (from 3.2 MW to between 10–26 MW). The results show that interactions among these elements are complex and therefore underline the necessity of such comprehensive methods to explore their optimal integration with industrial processes. The potential applications of this work are vast, extending from total site resource integration to addressing synergies in the context of industrial symbiosis. Full article

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

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32 pages, 2364 KiB

Open AccessEditor’s ChoiceArticle

Impact of Grid-Scale Electricity Storage and Electric Vehicles on Renewable Energy Penetration: A Case Study for Italy

by Sara Bellocchi, Michele Manno, Michel Noussan and Michela Vellini

Energies 2019, 12(7), 1303; https://doi.org/10.3390/en12071303 - 4 Apr 2019

Cited by 25 | Viewed by 4728

Abstract

Storage technologies are progressively emerging as a key measure to accommodate high shares of intermittent renewables with a view to guarantee their effective integration towards a profound decarbonisation of existing energy systems. This study aims to evaluate to what extent electricity storage can [...] Read more.

Storage technologies are progressively emerging as a key measure to accommodate high shares of intermittent renewables with a view to guarantee their effective integration towards a profound decarbonisation of existing energy systems. This study aims to evaluate to what extent electricity storage can contribute to a significant renewable penetration by absorbing otherwise-curtailed renewable surplus and quantitatively defines the associated costs. Under a Smart Energy System perspective, a variety of future scenarios are defined for the Italian case based on a progressively increasing renewable and storage capacity feeding an ever-larger electrified demand mostly made up of electric vehicles and, to some extent, heat pumps and power-to-gas/liquid technologies. Results are compared in terms of crucial environmental and techno-economic indicators and discussed with respect to storage operating parameters. The outcome of this analysis reveals the remarkable role of electricity storage in increasing system flexibility and reducing, in the range 24–44%, the renewable capacity required to meet a given sustainability target. Nonetheless, such achievements become feasible only under relatively low investment and operating costs, condition that excludes electrochemical storage solutions and privileges low-cost alternatives that at present, however, exist only at a pilot or demonstration scale. Full article

(This article belongs to the Special Issue Grid-Scale Energy Storage Management)

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26 pages, 6802 KiB

Open AccessEditor’s ChoiceArticle

Pelleting of Pine and Switchgrass Blends: Effect of Process Variables and Blend Ratio on the Pellet Quality and Energy Consumption

by Jaya Shankar Tumuluru

Energies 2019, 12(7), 1198; https://doi.org/10.3390/en12071198 - 28 Mar 2019

Cited by 51 | Viewed by 5452

Abstract

The blending of woody and herbaceous biomass can influence pellet quality and the energy consumption of the process. This work aims to understand the pelleting characteristics of 2-inch top-pine residue blended with switchgrass at high moisture content. The process variables tested are blend [...] Read more.

The blending of woody and herbaceous biomass can influence pellet quality and the energy consumption of the process. This work aims to understand the pelleting characteristics of 2-inch top-pine residue blended with switchgrass at high moisture content. The process variables tested are blend moisture content, length-to-diameter (L/D) ratio in the pellet die, and the blend ratio. A flat die pellet mill was also used in this study. The pine and switchgrass blend ratios that were tested include: (1) 25% 2-inch top pine residue with 75% switchgrass; (2) 50% 2-inch top pine residue with 50% switchgrass; and (3) 75% 2-inch top pine residue with 25% switchgrass. The pelleting process conditions tested included the L/D ratio in the pellet die (i.e., 1.5 to 2.6) and the blend moisture content (20 to 30%, w.b.). Analysis of experimental data indicated that blending 25% switchgrass with 75% 2-inch top pine residue and 50% switchgrass with 50% 2-inch top pine residue resulted in pellets with a bulk density of > 550 kg/m³ and durability of > 95%. Optimization of the response surface models developed for process conditions in terms of product properties indicated that a higher L/D ratio of 2.6 and a lower blend-moisture content of 20% (w.b.) maximized bulk density and durability. Higher pine in the blends improved the pellet durability and reduced energy consumption. Full article

(This article belongs to the Special Issue Woody Biomass for Bioenergy Production)

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14 pages, 2601 KiB

Open AccessEditor’s ChoiceArticle

Comparative Evaluation of Coated and Non-Coated Carbon Electrodes in a Microbial Fuel Cell for Treatment of Municipal Sludge

by Arpita Nandy, Mohita Sharma, Senthil Velan Venkatesan, Nicole Taylor, Lisa Gieg and Venkataraman Thangadurai

Energies 2019, 12(6), 1034; https://doi.org/10.3390/en12061034 - 16 Mar 2019

Cited by 31 | Viewed by 4307

Abstract

This study aims to provide insight into the cost-effective catalyst on power generation in a microbial fuel cell (MFC) for treatment of municipal sludge. Power production from MFCs with carbon, Fe₂O₃, and Pt electrodes were compared. The MFC with [...] Read more.

This study aims to provide insight into the cost-effective catalyst on power generation in a microbial fuel cell (MFC) for treatment of municipal sludge. Power production from MFCs with carbon, Fe₂O₃, and Pt electrodes were compared. The MFC with no coating on carbon generated the least power density (6.72 mW·m⁻²) while the MFC with Fe₂O₃-coating on carbon anodes and carbon cathodes generated a 78% higher power output (30.18 mW·m⁻²). The third MFC with Fe₂O₃-coated carbon anodes and Pt on carbon as the cathode catalyst generated the highest power density (73.16 mW·m⁻²) at room temperature. Although the power generated with a conventional Pt catalyst was more than two-fold higher than Fe₂O₃, this study suggests that Fe₂O₃ can be investigated further as an efficient, low-cost, and alternative catalyst of Pt, which can be optimized for improving performance of MFCs. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results demonstrated reduced resistance of MFCs and better charge transfer between biofilm and electrodes containing coated anodes compared to non-coated anodes. Scanning electron microscopy (SEM) was used to analyze biofilm morphology and microbial community analysis was performed using 16S rRNA gene sequencing, which revealed the presence of known anaerobic fermenters and methanogens that may play a key role in energy generation in the MFCs. Full article

(This article belongs to the Special Issue Biological Fuel Cells and Their Applications)

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19 pages, 1348 KiB

Open AccessEditor’s ChoiceArticle

Analysis of the Energy Consumption Behavior of European RES Cooperative Members

by Nikolaos Sifakis, Nikolaos Savvakis, Tryfon Daras and Theocharis Tsoutsos

Energies 2019, 12(6), 970; https://doi.org/10.3390/en12060970 - 13 Mar 2019

Cited by 23 | Viewed by 4592

Abstract

REScoops are cooperatives of renewable energy producers and/or consumers that are being formed in the developing European Smart Grid. Today, there are more than 2397 REScoops with more than 650,000 members. Their development indicates the necessity of producing and consuming green energy, assists [...] Read more.

REScoops are cooperatives of renewable energy producers and/or consumers that are being formed in the developing European Smart Grid. Today, there are more than 2397 REScoops with more than 650,000 members. Their development indicates the necessity of producing and consuming green energy, assists the fight against energy poverty, and reduces greenhouse gas emissions by utilizing smart management systems and self-consumption techniques. An essential objective of the H2020 REScoop Plus project is to stimulate better understanding and promote the cooperatives’ commitment to behavioral change. To achieve such a goal, this paper presents the methodology adopted to assess the energy-saving activities and behavior of the REScoops. In order to obtain relevant conclusions, a detailed statistical analysis was undertaken. Moreover, the analysis led to an effective classification of the various members, providing insights regarding their contribution to consumption reduction according to various specific characteristics. The statistical analysis showed that REScoop members contribute significantly to energy conservation and the reduction of harmful gas emissions, and subsequently, the majority of the energy efficiency (EE) interventions led to achieving more than 20% reductions. Specific practices, already adopted by the REScoops, lead to increased energy efficiency and environmental benefits. Full article

(This article belongs to the Special Issue Development and Implementation of Models of Electricity Market 2019)

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17 pages, 1521 KiB

Open AccessEditor’s ChoiceArticle

A Techno-Economic Analysis of Vehicle-to-Building: Battery Degradation and Efficiency Analysis in the Context of Coordinated Electric Vehicle Charging

by Stefan Englberger, Holger Hesse, Daniel Kucevic and Andreas Jossen

Energies 2019, 12(5), 955; https://doi.org/10.3390/en12050955 - 12 Mar 2019

Cited by 26 | Viewed by 10584

Abstract

In the context of the increased acceptance and usage of electric vehicles (EVs), vehicle-to-building (V2B) has proven to be a new and promising use case. Although this topic is already being discussed in literature, there is still a lack of experience on how [...] Read more.

In the context of the increased acceptance and usage of electric vehicles (EVs), vehicle-to-building (V2B) has proven to be a new and promising use case. Although this topic is already being discussed in literature, there is still a lack of experience on how such a system, of allowing bidirectional power flows between an EV and building, will work in a residential environment. The challenge is to optimize the interplay of electrical load, photovoltaic (PV) generation, EV, and optionally a home energy storage system (HES). In total, fourteen different scenarios are explored for a German household. A two-step approach is used, which combines a computationally efficient linear optimizer with a detailed modelling of the non-linear effects on the battery. The change in battery degradation, storage system efficiency, and operating expenses (OPEX) as a result of different, unidirectional and bidirectional, EV charging schemes is examined for both an EV battery and a HES. The simulations show that optimizing unidirectional charging can improve the OPEX by 15%. The addition of V2B leads to a further 11% cost reduction, however, this corresponds with a 12% decrease in EV battery lifetime. Techno-economic analysis reveals that the V2B charging solution with no HES leads to strong self-consumption improvements (EUR 1381 savings over ten years), whereas, this charging scheme would not be justified for a residential prosumer with a HES (only EUR 160 savings). Full article

(This article belongs to the Special Issue Energy Storage and Management for Electric Vehicles)

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19 pages, 4243 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Economic Analysis and Environmental Impact Assessment of Heat Pump-Assisted Distillation in a Gas Fractionation Unit

by Jisook Lee, Yongho Son, Kwang Soon Lee and Wangyun Won

Energies 2019, 12(5), 852; https://doi.org/10.3390/en12050852 - 5 Mar 2019

Cited by 19 | Viewed by 5641

Abstract

The depletion of fossil fuels and environmental pollution (e.g., greenhouse gas emissions) through the combustion of fossil fuels have stimulated studies on new technologies able to curtail the energy consumption of existing fractionation units. In this regard, heat pumps have garnered substantial attention [...] Read more.

The depletion of fossil fuels and environmental pollution (e.g., greenhouse gas emissions) through the combustion of fossil fuels have stimulated studies on new technologies able to curtail the energy consumption of existing fractionation units. In this regard, heat pumps have garnered substantial attention due to their potential to improve the process energy efficiency. This study aims to provide extensive economic analysis and environmental impact assessment of the application of heat pumps under different conditions and scenarios. For this purpose, we first selected three important conditions: feed composition, plant capacity, and fuel price. Then, we performed a range of analyses to identify the major costs and environmental drivers. The economics and environmental impact of heat pump-assisted distillation was investigated and compared with those of conventional distillation. Full article

(This article belongs to the Section C: Energy Economics and Policy)

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28 pages, 7289 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Characterization of Wave Energy Potential for the Baltic Sea with Focus on the Swedish Exclusive Economic Zone

by Erik Nilsson, Anna Rutgersson, Adam Dingwell, Jan-Victor Björkqvist, Heidi Pettersson, Lars Axell, Johan Nyberg and Erland Strömstedt

Energies 2019, 12(5), 793; https://doi.org/10.3390/en12050793 - 27 Feb 2019

Cited by 22 | Viewed by 6254

Abstract

In this study, a third-generation wave model is used to examine the wave power resource for the Baltic Sea region at an unprecedented one-kilometer-scale resolution for the years 1998 to 2013. Special focus is given to the evaluation and description of wave field [...] Read more.

In this study, a third-generation wave model is used to examine the wave power resource for the Baltic Sea region at an unprecedented one-kilometer-scale resolution for the years 1998 to 2013. Special focus is given to the evaluation and description of wave field characteristics for the Swedish Exclusive Economic Zone (SEEZ). It is carried out to provide a more detailed assessment of the potential of waves as a renewable energy resource for the region. The wave energy potential is largely controlled by the distance from the coast and the fetch associated with the prevailing dominant wave direction. The ice cover is also shown to significantly influence the wave power resource, especially in the most northern basins of the SEEZ. For the areas in focus here, the potential annual average wave energy flux reaches 45 MWh/m/year in the two sub-basins with the highest wave energies, but local variations are up to 65 MWh/m/year. The assessment provides the basis for a further detailed identification of potential sites for wave energy converters. An outlook is given for additional aspects studied within a broad multi-disciplinary project to assess the conditions for offshore wave energy conversion within the SEEZ. Full article

(This article belongs to the Special Issue Wave Energy Conversion)

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29 pages, 1796 KiB

Open AccessEditor’s ChoiceArticle

Inter-Criteria Dependencies-Based Decision Support in the Sustainable wind Energy Management

by Paweł Ziemba

Energies 2019, 12(4), 749; https://doi.org/10.3390/en12040749 - 24 Feb 2019

Cited by 43 | Viewed by 4517

Abstract

Decision problems related to the wind energy require considering many, often interrelated and dependent on each other, criteria. To solve such problems, decision systems based on Multi-Criteria Decision Analysis (MCDA) methods are usually used. Unfortunately, most methods assume independence between the criteria, therefore, [...] Read more.

Decision problems related to the wind energy require considering many, often interrelated and dependent on each other, criteria. To solve such problems, decision systems based on Multi-Criteria Decision Analysis (MCDA) methods are usually used. Unfortunately, most methods assume independence between the criteria, therefore, their application in decision problems related to the wind energy is debatable. This paper presents the use of the Analytic Network Process (ANP) method to solve a decision problem consisting in selecting the location and design of a wind farm. The use of the ANP method allows capturing the complexity of the decision problem by taking into consideration dependencies between criteria. As part of the verification of the solution, the results of the ANP method were compared with those of the Analytic Hierarchy Process (AHP) method, which uses only hierarchical dependencies between criteria. The conducted verification showed that the inter-criteria dependencies may have a significant influence on the obtained solution. On the basis of the conducted sensitivity analysis and the research into robustness of the rankings to the rank reversal phenomenon, it has been found out that the ranking obtained with the use of the ANP is characterized by a higher quality than by means of the AHP. Full article

(This article belongs to the Special Issue Assessment of Energy–Environment–Economy Interrelations)

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30 pages, 1968 KiB

Open AccessEditor’s ChoiceArticle

Minute-Scale Forecasting of Wind Power—Results from the Collaborative Workshop of IEA Wind Task 32 and 36

by Ines Würth, Laura Valldecabres, Elliot Simon, Corinna Möhrlen, Bahri Uzunoğlu, Ciaran Gilbert, Gregor Giebel, David Schlipf and Anton Kaifel

Energies 2019, 12(4), 712; https://doi.org/10.3390/en12040712 - 21 Feb 2019

Cited by 52 | Viewed by 7848

Abstract

The demand for minute-scale forecasts of wind power is continuously increasing with the growing penetration of renewable energy into the power grid, as grid operators need to ensure grid stability in the presence of variable power generation. For this reason, IEA Wind Tasks [...] Read more.

The demand for minute-scale forecasts of wind power is continuously increasing with the growing penetration of renewable energy into the power grid, as grid operators need to ensure grid stability in the presence of variable power generation. For this reason, IEA Wind Tasks 32 and 36 together organized a workshop on “Very Short-Term Forecasting of Wind Power” in 2018 to discuss different approaches for the implementation of minute-scale forecasts into the power industry. IEA Wind is an international platform for the research community and industry. Task 32 tries to identify and mitigate barriers to the use of lidars in wind energy applications, while IEA Wind Task 36 focuses on improving the value of wind energy forecasts to the wind energy industry. The workshop identified three applications that need minute-scale forecasts: (1) wind turbine and wind farm control, (2) power grid balancing, (3) energy trading and ancillary services. The forecasting horizons for these applications range from around 1 s for turbine control to 60 min for energy market and grid control applications. The methods that can be applied to generate minute-scale forecasts rely on upstream data from remote sensing devices such as scanning lidars or radars, or are based on point measurements from met masts, turbines or profiling remote sensing devices. Upstream data needs to be propagated with advection models and point measurements can either be used in statistical time series models or assimilated into physical models. All methods have advantages but also shortcomings. The workshop’s main conclusions were that there is a need for further investigations into the minute-scale forecasting methods for different use cases, and a cross-disciplinary exchange of different method experts should be established. Additionally, more efforts should be directed towards enhancing quality and reliability of the input measurement data. Full article

(This article belongs to the Special Issue Solar and Wind Energy Forecasting)

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16 pages, 8609 KiB

Open AccessEditor’s ChoiceArticle

Analysis on Thermal Performance of Ground Heat Exchanger According to Design Type Based on Thermal Response Test

by Sang Mu Bae, Yujin Nam, Jong Min Choi, Kwang Ho Lee and Jae Sang Choi

Energies 2019, 12(4), 651; https://doi.org/10.3390/en12040651 - 18 Feb 2019

Cited by 27 | Viewed by 4111

Abstract

A ground source heat pump (GSHP) system has higher performance than air source heat pump system due to the use of more efficient ground heat source. However, the GSHP system performance depends on ground thermal properties and groundwater conditions. There are many studies [...] Read more.

A ground source heat pump (GSHP) system has higher performance than air source heat pump system due to the use of more efficient ground heat source. However, the GSHP system performance depends on ground thermal properties and groundwater conditions. There are many studies on the improvement of GSHP system by developing ground heat exchanger (GHX) and heat exchange method. Several studies have suggested methods to improve heat exchange rate for the development of GHX. However, few real-scale experimental studies have quantitatively analyzed their performance using the same ground conditions. Therefore, the objective of this study was to evaluate the thermal performance of various pipe types of GHX by the thermal response test (TRT) under the same field and test conditions. Four kinds of GHX (HDPE type, HDPE-nano type, spiral fin type, and coaxial type) were constructed in the same site. Inlet and outlet temperatures of GHXs and effective thermal conductivity were measured through the TRT. In addition, the borehole thermal resistance was calculated to comparatively analyze the correlation of the heat exchange performance with each GHX. Result of the TRT revealed that averages effective thermal conductivities of HDPE type, HDPE-nano, spiral fin type, and coaxial type GHX were 2.25 W/m·K, 2.34 W/m·K, 2.55 W/m·K, and 2.16 W/m·K, respectively. In the result, it was found that the average borehole thermal resistance can be an important factor in TRT, but the effect of increased thermal conductivity of pipe material itself was not significant. Full article

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33 pages, 12801 KiB

Open AccessEditor’s ChoiceArticle

Comparison of Technologies for CO₂ Capture from Cement Production—Part 1: Technical Evaluation

by Mari Voldsund, Stefania Osk Gardarsdottir, Edoardo De Lena, José-Francisco Pérez-Calvo, Armin Jamali, David Berstad, Chao Fu, Matteo Romano, Simon Roussanaly, Rahul Anantharaman, Helmut Hoppe, Daniel Sutter, Marco Mazzotti, Matteo Gazzani, Giovanni Cinti and Kristin Jordal

Energies 2019, 12(3), 559; https://doi.org/10.3390/en12030559 - 12 Feb 2019

Cited by 157 | Viewed by 23207

Abstract

A technical evaluation of CO₂ capture technologies when retrofitted to a cement plant is performed. The investigated technologies are the oxyfuel process, the chilled ammonia process, membrane-assisted CO₂ liquefaction, and the calcium looping process with tail-end and integrated configurations. For comparison, [...] Read more.

A technical evaluation of CO₂ capture technologies when retrofitted to a cement plant is performed. The investigated technologies are the oxyfuel process, the chilled ammonia process, membrane-assisted CO₂ liquefaction, and the calcium looping process with tail-end and integrated configurations. For comparison, absorption with monoethanolamine (MEA) is used as reference technology. The focus of the evaluation is on emission abatement, energy performance, and retrofitability. All the investigated technologies perform better than the reference both in terms of emission abatement and energy consumption. The equivalent CO₂ avoided are 73–90%, while it is 64% for MEA, considering the average EU-28 electricity mix. The specific primary energy consumption for CO₂ avoided is 1.63–4.07 MJ/kg CO₂, compared to 7.08 MJ/kg CO₂ for MEA. The calcium looping technologies have the highest emission abatement potential, while the oxyfuel process has the best energy performance. When it comes to retrofitability, the post-combustion technologies show significant advantages compared to the oxyfuel and to the integrated calcium looping technologies. Furthermore, the performance of the individual technologies shows strong dependencies on site-specific and plant-specific factors. Therefore, rather than identifying one single best technology, it is emphasized that CO₂ capture in the cement industry should be performed with a portfolio of capture technologies, where the preferred choice for each specific plant depends on local factors. Full article

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18 pages, 3519 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Bottom-Up Approach to Lithium-Ion Battery Cost Modeling with a Focus on Cathode Active Materials

by Marc Wentker, Matthew Greenwood and Jens Leker

Energies 2019, 12(3), 504; https://doi.org/10.3390/en12030504 - 5 Feb 2019

Cited by 170 | Viewed by 28764

Abstract

In this study, we develop a method for calculating electric vehicle lithium-ion battery pack performance and cost. To begin, we construct a model allowing for calculation of cell performance and material cost using a bottom-up approach starting with real-world material costs. It thus [...] Read more.

In this study, we develop a method for calculating electric vehicle lithium-ion battery pack performance and cost. To begin, we construct a model allowing for calculation of cell performance and material cost using a bottom-up approach starting with real-world material costs. It thus provides a supplement to existing models, which often begin with fixed cathode active material (CAM) prices that do not reflect raw metal price fluctuations. We collect and display data from the London Metal Exchange to show that such metal prices, in this case specifically cobalt and nickel, do indeed fluctuate and cannot be assumed to remain static or decrease consistently. We input this data into our model, which allows for a visualization of the effects of these metal price fluctuations on the prices of the CAMs. CAMs analyzed include various lithium transition metal oxide-type layered oxide (NMC and NCA) technologies, as well as cubic spinel oxide (LMO), high voltage spinel oxide (LNMO), and lithium metal phosphate (LFP). The calculated CAM costs are combined with additional cell component costs in order to calculate full cell costs, which are in turn scaled up to full battery pack costs. Economies of scale are accounted for separately for each cost fraction. Full article

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19 pages, 5488 KiB

Open AccessEditor’s ChoiceArticle

Exergy-Based and Economic Evaluation of Liquefaction Processes for Cryogenics Energy Storage

by Sarah Hamdy, Francisco Moser, Tatiana Morosuk and George Tsatsaronis

Energies 2019, 12(3), 493; https://doi.org/10.3390/en12030493 - 4 Feb 2019

Cited by 51 | Viewed by 5669

Abstract

Cryogenics-based energy storage (CES) is a thermo-electric bulk-energy storage technology, which stores electricity in the form of a liquefied gas at cryogenic temperatures. The charging process is an energy-intensive gas liquefaction process and the limiting factor to CES round trip efficiency (RTE). During [...] Read more.

Cryogenics-based energy storage (CES) is a thermo-electric bulk-energy storage technology, which stores electricity in the form of a liquefied gas at cryogenic temperatures. The charging process is an energy-intensive gas liquefaction process and the limiting factor to CES round trip efficiency (RTE). During discharge, the liquefied gas is pressurized, evaporated and then super-heated to drive a gas turbine. The cold released during evaporation can be stored and supplied to the subsequent charging process. In this research, exergy-based methods are applied to quantify the effect of cold storage on the thermodynamic performance of six liquefaction processes and to identify the most cost-efficient process. For all liquefaction processes assessed, the integration of cold storage was shown to multiply the liquid yield, reduce the specific power requirement by 50–70% and increase the exergetic efficiency by 30–100%. The Claude-based liquefaction processes reached the highest exergetic efficiencies (76–82%). The processes reached their maximum efficiency at different liquefaction pressures. The Heylandt process reaches the highest RTE (50%) and the lowest specific power requirement (1021 kJ/kg). The lowest production cost of liquid air (18.4 €/ton) and the lowest specific investment cost (<700 €/kW_char) were achieved by the Kapitza process. Full article

(This article belongs to the Special Issue Selected Papers from PRES 2018: The 21st Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction)

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17 pages, 5222 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Techno-Economic Assessment of Solar Hydrogen Production by Means of Thermo-Chemical Cycles

by Massimo Moser, Matteo Pecchi and Thomas Fend

Energies 2019, 12(3), 352; https://doi.org/10.3390/en12030352 - 23 Jan 2019

Cited by 43 | Viewed by 5760

Abstract

This paper presents the system analysis and the techno-economic assessment of selected solar hydrogen production paths based on thermochemical cycles. The analyzed solar technology is Concentrated Solar Power (CSP). Solar energy is used in order to run a two-step thermochemical cycle based on [...] Read more.

This paper presents the system analysis and the techno-economic assessment of selected solar hydrogen production paths based on thermochemical cycles. The analyzed solar technology is Concentrated Solar Power (CSP). Solar energy is used in order to run a two-step thermochemical cycle based on two different red-ox materials, namely nickel-ferrite and cerium dioxide (ceria). Firstly, a flexible mathematical model has been implemented to design and to operate the system. The tool is able to perform annual yield calculations based on hourly meteorological data. Secondly, a sensitivity analysis over key-design and operational techno-economic parameters has been carried out. The main outcomes are presented and critically discussed. The technical comparison of nickel-ferrite and ceria cycles showed that the integration of a large number of reactors can be optimized by considering a suitable time displacement among the activation of the single reactors working in parallel. In addition the comparison demonstrated that ceria achieves higher efficiency than nickel-ferrite (13.4% instead 6.4%), mainly because of the different kinetics. This difference leads to a lower LCOH for ceria (13.06 €/kg and 6.68 €/kg in the base case and in the best case scenario, respectively). Full article

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14 pages, 5109 KiB

Open AccessEditor’s ChoiceArticle

Parametric Study of a Gurney Flap Implementation in a DU91W(2)250 Airfoil

by Iñigo Aramendia, Unai Fernandez-Gamiz, Ekaitz Zulueta, Aitor Saenz-Aguirre and Daniel Teso-Fz-Betoño

Energies 2019, 12(2), 294; https://doi.org/10.3390/en12020294 - 18 Jan 2019

Cited by 33 | Viewed by 5553

Abstract

The growth in size and weight of wind turbines over the last years has led to the development of flow control devices, such as Gurney flaps (GFs). In the current work, a parametric study is presented to find the optimal GF length to [...] Read more.

The growth in size and weight of wind turbines over the last years has led to the development of flow control devices, such as Gurney flaps (GFs). In the current work, a parametric study is presented to find the optimal GF length to improve the airfoil aerodynamic performance. Therefore, the influence of GF lengths from 0.25% to 3% of the airfoil chord c on a widely used DU91W(2)250 airfoil has been investigated by means of RANS based numerical simulations at Re = 2 × 10⁶. The numerical results showed that, for positive angles of attack, highest values of the lift-to-drag ratio C_L/C_D are obtained with GF lengths between 0.25% c and 0.75% c. Particularly, an increase of 21.57 in C_L/C_D ratio has been obtained with a GF length of 0.5% c at 2° of angle of attack AoA. The influence of GFs decreased at AoAs larger than 5°, where only a GF length of 0.25% c provides a slight improvement in terms of C_L/C_D ratio enhancement. Additionally, an ANN has been developed to predict the aerodynamic efficiency of the airfoil in terms of C_L/C_D ratio. This tool allows to obtain an accurate prediction model of the aerodynamic behavior of the airfoil with GFs. Full article

(This article belongs to the Special Issue Wind Turbine Power Optimization Technology)

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18 pages, 6616 KiB

Open AccessEditor’s ChoiceArticle

Simulation of the Filling Capability in Vane Pumps

by Massimo Rundo, Giorgio Altare and Paolo Casoli

Energies 2019, 12(2), 283; https://doi.org/10.3390/en12020283 - 17 Jan 2019

Cited by 26 | Viewed by 5140

Abstract

In positive displacement pumps, the main volumetric loss at high speed is due to the incomplete filling of the variable volume chambers. The prediction of the limit speed and of the maximum flow rate delivered by a pump can be obtained only through [...] Read more.

In positive displacement pumps, the main volumetric loss at high speed is due to the incomplete filling of the variable volume chambers. The prediction of the limit speed and of the maximum flow rate delivered by a pump can be obtained only through Computational Fluid Dynamics (CFD) simulations, since the shape, the orientation, and the movement of the chambers with respect to the inlet volume must be considered, along with the non-uniform distribution of the gaseous phase, due to the dissolved air release. In this paper, the influence of different geometric parameters on the filling of a vane pump has been investigated through the commercial software PumpLinx^®. At first, a model of a reference pump has been created and validated with different configurations of the suction flow area, then a simplified model has been used for assessing the influence of the geometry of the rotating assembly. It was found that a pump with a low ratio between the axial thickness and the diameter has a higher volumetric efficiency if the chambers are fed from one side only. Opposite behaviors were found in the case of pumps with small diameters and high thicknesses. Moreover, the filling could be improved by increasing the number of chambers, and by reducing the diameter of the rotor, even only locally. Full article

(This article belongs to the Special Issue Energy Efficiency and Controllability of Fluid Power Systems 2018)

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17 pages, 3573 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

EV Idle Time Estimation on Charging Infrastructure, Comparing Supervised Machine Learning Regressions

by Alexandre Lucas, Ricardo Barranco and Nazir Refa

Energies 2019, 12(2), 269; https://doi.org/10.3390/en12020269 - 16 Jan 2019

Cited by 49 | Viewed by 6318

Abstract

The adoption of electric vehicles (EV) has to be complemented with the right charging infrastructure roll-out. This infrastructure is already in place in many cities throughout the main markets of China, EU and USA. Public policies are both taken at regional and/or at [...] Read more.

The adoption of electric vehicles (EV) has to be complemented with the right charging infrastructure roll-out. This infrastructure is already in place in many cities throughout the main markets of China, EU and USA. Public policies are both taken at regional and/or at a city level targeting both EV adoption, but also charging infrastructure management. A growing trend is the increasing idle time over the years (time an EV is connected without charging), which directly impacts on the sizing of the infrastructure, hence its cost or availability. Such a phenomenon can be regarded as an opportunity but may very well undermine the same initiatives being taken to promote adoption; in any case it must be measured, studied, and managed. The time an EV takes to charge depends on its initial/final state of charge (SOC) and the power being supplied to it. The problem however is to estimate the time the EV remains parked after charging (idle time), as it depends on many factors which simple statistical analysis cannot tackle. In this study we apply supervised machine learning to a dataset from the Netherlands and analyze three regression algorithms, Random Forest, Gradient Boosting and XGBoost, identifying the most accurate one and main influencing parameters. The model can provide useful information for EV users, policy maker and network owners to better manage the network, targeting specific variables. The best performing model is XGBoost with an R² score of 60.32% and mean absolute error of 1.11. The parameters influencing the model the most are: The time of day in which the charging sessions start and the total energy supplied with 22.35%, 15.57% contribution respectively. Partial dependencies of variables and model performances are presented and implications on public policies discussed. Full article

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20 pages, 3251 KiB

Open AccessEditor’s ChoiceArticle

Generation Expansion Planning Model for Integrated Energy System Considering Feasible Operation Region and Generation Efficiency of Combined Heat and Power

by Woong Ko and Jinho Kim

Energies 2019, 12(2), 226; https://doi.org/10.3390/en12020226 - 11 Jan 2019

Cited by 31 | Viewed by 4304

Abstract

Integrated energy systems can provide a more efficient supply than individual systems by using resources such as cogeneration. To foster efficient management of these systems, the flexible operation of cogeneration resources should be considered for the generation expansion planning model to satisfy the [...] Read more.

Integrated energy systems can provide a more efficient supply than individual systems by using resources such as cogeneration. To foster efficient management of these systems, the flexible operation of cogeneration resources should be considered for the generation expansion planning model to satisfy the varying demand of energy including heat and electricity, which are interdependent and present different seasonal characteristics. We propose an optimization model of the generation expansion planning for an integrated energy system considering the feasible operation region and efficiency of a combined heat and power (CHP) resource. The proposed model is formulated as a mixed integer linear programming problem to minimize the sum of the annualized cost of the integrated energy system. Then, we set linear constraints of energy resources and describe linearized constraints of a feasible operation region and a generation efficiency of the CHP resource for application to the problem. The effectiveness of the proposed optimization problem is verified through a case study comparing with results of a conventional optimization model that uses constant heat-to-power ratio and generation efficiency of the CHP resource. Furthermore, we evaluate planning schedules and total generation efficiency profiles of the CHP resource for the compared optimization models. Full article

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19 pages, 5822 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Igniting Soaring Droplets of Promising Fuel Slurries

by Alexander Bogomolov, Timur Valiullin, Ksenia Vershinina, Sergey Shevyrev and Nikita Shlegel

Energies 2019, 12(2), 208; https://doi.org/10.3390/en12020208 - 10 Jan 2019

Cited by 12 | Viewed by 3899

Abstract

High rates of environmental pollution by boilers and thermal power plants burning coal of different grades are the main reason for active research in the world aimed at the development of alternative fuels. The solution to the formulated problem acceptable in terms of [...] Read more.

High rates of environmental pollution by boilers and thermal power plants burning coal of different grades are the main reason for active research in the world aimed at the development of alternative fuels. The solution to the formulated problem acceptable in terms of environmental, technical and economic criteria is the creation of composite slurry fuels with the use of fine coal or coal processing and enrichment waste, water of different quality, and oil sludge additive. This study considers modern technologies of burning slurry fuels as well as perspective research methods of the corresponding processes. A model combustion chamber is developed for the adequate study of ignition processes. The calculation of the basic geometric dimensions is presented. The necessity of manufacturing the combustion chamber in the form of an object of complex geometry is substantiated. With its use, several typical modes of slurry fuel ignition are determined. Principal differences of ignition conditions of a single droplet and group of fuel droplets are shown. Typical vortex structures at the fuel spray injection are shown. A comparison with the trajectories of fuel aerosol droplets in real combustion chambers used for the combustion of slurry fuels is undertaken. Full article

(This article belongs to the Special Issue Sustainability of Fossil Fuels)

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19 pages, 7397 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Analysis of the Performance of Various PV Module Technologies in Peru

by Irene Romero-Fiances, Emilio Muñoz-Cerón, Rafael Espinoza-Paredes, Gustavo Nofuentes and Juan De la Casa

Energies 2019, 12(1), 186; https://doi.org/10.3390/en12010186 - 8 Jan 2019

Cited by 45 | Viewed by 6171

Abstract

A knowledge gap exists about the actual behavior of PV grid-connected systems (PVGCS) using various PV technologies in Peru. This paper presents the results of an over three-year-long performance evaluation of a 3.3-kWp monocrystalline silicon (sc-Si) PVGCS located in Arequipa, a 3.3-kWp sc-Si [...] Read more.

A knowledge gap exists about the actual behavior of PV grid-connected systems (PVGCS) using various PV technologies in Peru. This paper presents the results of an over three-year-long performance evaluation of a 3.3-kWp monocrystalline silicon (sc-Si) PVGCS located in Arequipa, a 3.3-kWp sc-Si PVGCS located in Tacna, and a 3-kWp policrystalline (mc-Si) PVGCS located in Lima. An assessment of the performance of a 3.5-kWp amorphous silicon/crystalline silicon hetero-junction (a-Si/µc-Si) PVGCS during over one and a half years of being in Lima is also presented. The annual final yields obtained lie within 1770–1992 kWh/kW, 1505–1540 kWh/kW, and 736–833 kWh/kW for Arequipa, Tacna, and Lima, respectively, while the annual PV array energy yield achieved by a-Si/µc-Si is 1338 kWh/kW. The annual performance ratio stays in the vicinity of 0.83 for sc-Si in Arequipa and Tacna while this parameter ranges from 0.70 to 0.77 for mc-Si in Lima. An outstanding DC annual performance ratio of 0.97 is found for a-Si/µc-Si in the latter site. The use of sc-Si and presumably, mc-Si PV modules in desert climates, such as that of Arequipa and Tacna, is encouraged. However, sc-Si and presumably, mc-Si-technologies experience remarkable temperature and low irradiance losses in Lima. By contrast, a-Si/µc-Si PV modules perform much better in the latter site thanks to being less influenced by both temperature and low light levels. Full article

(This article belongs to the Special Issue Photovoltaics Lifetime Output Improvement: Advanced Monitoring, Failure Detection and Classification and Energy Forecasting)

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24 pages, 2028 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Determination of Optimal Location and Sizing of Solar Photovoltaic Distribution Generation Units in Radial Distribution Systems

by Minh Quan Duong, Thai Dinh Pham, Thang Trung Nguyen, Anh Tuan Doan and Hai Van Tran

Energies 2019, 12(1), 174; https://doi.org/10.3390/en12010174 - 6 Jan 2019

Cited by 120 | Viewed by 8177

Abstract

This paper presents an effective biogeography-based optimization (BBO) for optimal location and sizing of solar photovoltaic distributed generation (PVDG) units to reduce power losses while maintaining voltage profile and voltage harmonic distortion at the limits. This applied algorithm was motivated by biogeography, that [...] Read more.

This paper presents an effective biogeography-based optimization (BBO) for optimal location and sizing of solar photovoltaic distributed generation (PVDG) units to reduce power losses while maintaining voltage profile and voltage harmonic distortion at the limits. This applied algorithm was motivated by biogeography, that the study of the distribution of biological species through time and space. This technique is able to expand the searching space and retain good solution group at each generation. Therefore, the applied method can significantly improve performance. The effectiveness of the applied algorithm is validated by testing it on IEEE 33-bus and IEEE 69-bus radial distribution systems. The obtained results are compared with the genetic algorithm (GA), the particle swarm optimization algorithm (PSO) and the artificial bee colony algorithm (ABC). As a result, the applied algorithm offers better solution quality and accuracy with faster convergence. Full article

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

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17 pages, 713 KiB

Open AccessEditor’s ChoiceArticle

Fault Characterization of a Proton Exchange Membrane Fuel Cell Stack

by Samuel Simon Araya, Fan Zhou, Simon Lennart Sahlin, Sobi Thomas, Christian Jeppesen and Søren Knudsen Kær

Energies 2019, 12(1), 152; https://doi.org/10.3390/en12010152 - 2 Jan 2019

Cited by 38 | Viewed by 5860

Abstract

In this paper, the main faults in a commercial proton exchange membrane fuel cell (PEMFC) stack for micro-combined heat and power (

μ

-CHP) application are investigated, with the scope of experimentally identifying fault indicators for diagnosis purposes. The tested faults were reactant [...] Read more.

In this paper, the main faults in a commercial proton exchange membrane fuel cell (PEMFC) stack for micro-combined heat and power (

μ

-CHP) application are investigated, with the scope of experimentally identifying fault indicators for diagnosis purposes. The tested faults were reactant starvation (both fuel and oxidant), flooding, drying, CO poisoning, and H₂S poisoning. Galvanostatic electrochemical impedance spectroscopy (EIS) measurements were recorded between 2 kHz and 0.1 Hz on a commercial stack of 46 cells of a 100-

{cm}^{2}

active area each. The results, obtained through distribution of relaxation time (DRT) analysis of the EIS data, show that characteristic peaks of the DRT and their changes with the different fault intensity levels can be used to extract the features of the tested faults. It was shown that flooding and drying present features on the opposite ends of the frequency spectrum due the effect of drying on the membrane conductivity and the blocking effect of flooding that constricts the reactants’ flow. Moreover, it was seen that while the effect of CO poisoning is limited to high frequency processes, above 100 Hz, the effects of H₂S extend to below 10 Hz. Finally, the performance degradation due to all the tested faults, including H₂S poisoning, is recoverable to a great extent, implying that condition correction after fault detection can contribute to prolonged lifetime of the fuel cell. Full article

(This article belongs to the Special Issue Fuel Cell Systems Design and Control)

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14 pages, 1664 KiB

Open AccessEditor’s ChoiceArticle

Thermodynamic Efficiency Gains and their Role as a Key ‘Engine of Economic Growth’

by Marco Sakai, Paul E. Brockway, John R. Barrett and Peter G. Taylor

Energies 2019, 12(1), 110; https://doi.org/10.3390/en12010110 - 29 Dec 2018

Cited by 29 | Viewed by 7850

Abstract

Increasing energy efficiency is commonly viewed as providing a key stimulus to economic growth, through investment in efficient technologies, reducing energy use and costs, enabling productivity gains, and generating jobs. However, this view is received wisdom, as empirical validation has remained elusive. A [...] Read more.

Increasing energy efficiency is commonly viewed as providing a key stimulus to economic growth, through investment in efficient technologies, reducing energy use and costs, enabling productivity gains, and generating jobs. However, this view is received wisdom, as empirical validation has remained elusive. A central problem is that current energy-economy models are not thermodynamically consistent, since they do not include the transformation of energy in physical terms from primary to end-use stages. In response, we develop the UK MAcroeconometric Resource COnsumption (MARCO-UK) model, the first econometric economy-wide model to explicitly include thermodynamic efficiency and end energy use (energy services). We find gains in thermodynamic efficiency are a key ‘engine of economic growth’, contributing 25% of the increases to gross domestic product (GDP) in the UK over the period of 1971–2013. This confirms an underrecognised role for energy in enabling economic growth. We attribute most of the thermodynamic efficiency gains to endogenised technical change. We also provide new insights into how the ‘efficiency-led growth engine’ mechanism works in the whole economy. Our results imply a slowdown in thermodynamic efficiency gains will constrain economic growth, whilst future energy-GDP decoupling will be harder to achieve than we suppose. This confirms the imperative for economic models to become thermodynamically consistent. Full article

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22 pages, 2270 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Crane Overload Protection Controller for Blade Lifting Operation Based on Model Predictive Control

by Zhengru Ren, Roger Skjetne and Zhen Gao

Energies 2019, 12(1), 50; https://doi.org/10.3390/en12010050 - 24 Dec 2018

Cited by 29 | Viewed by 5285

Abstract

Lifting is a frequently used offshore operation. In this paper, a nonlinear model predictive control (NMPC) scheme is proposed to overcome the sudden peak tension and snap loads in the lifting wires caused by lifting speed changes in a wind turbine blade lifting [...] Read more.

Lifting is a frequently used offshore operation. In this paper, a nonlinear model predictive control (NMPC) scheme is proposed to overcome the sudden peak tension and snap loads in the lifting wires caused by lifting speed changes in a wind turbine blade lifting operation. The objectives are to improve installation efficiency and ensure operational safety. A simplified three-dimensional crane-wire-blade model is adopted to design the optimal control algorithm. A crane winch servo motor is controlled by the NMPC controller. The direct multiple shooting approach is applied to solve the nonlinear programming problem. High-fidelity simulations of the lifting operations are implemented based on a turbulent wind field with the MarIn and CaSADi toolkit in MATLAB. By well-tuned weighting matrices, the NMPC controller is capable of preventing snap loads and axial peak tension, while ensuring efficient lifting operation. The performance is verified through a sensitivity study, compared with a typical PD controller. Full article

(This article belongs to the Special Issue Recent Advances in Offshore Wind Technology)

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18 pages, 2685 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

City Scale Demand Side Management in Three Different-Sized District Heating Systems

by Kaisa Kontu, Jussi Vimpari, Petri Penttinen and Seppo Junnila

Energies 2018, 11(12), 3370; https://doi.org/10.3390/en11123370 - 1 Dec 2018

Cited by 25 | Viewed by 5226

Abstract

Demand side management can add flexibility to a district heating (DH) system by balancing the customer’s hourly fluctuating heat demand. The aim of this study is to analyze how different demand side management control strategies, implemented into different customer segments, impact DH production. [...] Read more.

Demand side management can add flexibility to a district heating (DH) system by balancing the customer’s hourly fluctuating heat demand. The aim of this study is to analyze how different demand side management control strategies, implemented into different customer segments, impact DH production. A city scale heat demand model is constructed from the hourly heat consumption data of different customer segments. This model is used to build several demand side management scenarios to examine the effect of them on both, the heat producer, and the customers. The simulations are run for three different-sized DH systems, representing typical DH systems in Finland, in order to understand how the demand side management implementations affect the production. The findings imply that the demand side management strategy must be built individually for each specific DH system; the changing consumption profiles of different customer segments should be taken into consideration. The results show that the value of demand side management for a DH companies remains low (less than 2% in cost savings), having an effect mostly upon the medium loads without any significant decrease in annual peak heat loads. Also, the findings reflect that the DH pricing models should be developed to make demand side management more attractive to DH customers. Full article

(This article belongs to the Special Issue District Heating)

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14 pages, 4192 KiB

Open AccessEditor’s ChoiceArticle

Comparative Thermodynamic Analysis of Kalina and Kalina Flash Cycles for Utilizing Low-Grade Heat Sources

by Kyoung Hoon Kim, Chul Ho Han and Hyung Jong Ko

Energies 2018, 11(12), 3311; https://doi.org/10.3390/en11123311 - 27 Nov 2018

Cited by 7 | Viewed by 3085

Abstract

The Kalina flash cycle (KFC) is a novel, recently proposed modification of the Kalina cycle (KC) equipped with a flash vessel. This study performs a comparative analysis of the thermodynamic performance of KC and KFC utilizing low-grade heat sources. How separator pressure, flash [...] Read more.

The Kalina flash cycle (KFC) is a novel, recently proposed modification of the Kalina cycle (KC) equipped with a flash vessel. This study performs a comparative analysis of the thermodynamic performance of KC and KFC utilizing low-grade heat sources. How separator pressure, flash pressure, and ammonia mass fraction affect the system performance is systematically and parametrically investigated. Dependences of net power and cycle efficiencies on these parameters as well as the mass flow rate, heat transfer rate and power production at the cycle components are analyzed. For a given set of separator pressure and ammonia mass fraction, there exists an optimum flash pressure making exergy efficiency locally maximal. For these pressures, which are higher for higher separator pressure and lower ammonia mass fraction, KFC shows better performance than KC both in net power and cycle efficiencies. At higher ammonia mass fraction, however, the difference is smaller. While the maximum power production increases with separator pressure, the dependence is quite weak for the maximum values of both efficiencies. Full article

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

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13 pages, 2474 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Approaches to Methods of Risk Analysis and Assessment Regarding the Gas Supply to a City

by Barbara Tchórzewska-Cieślak and Katarzyna Pietrucha-Urbanik

Energies 2018, 11(12), 3304; https://doi.org/10.3390/en11123304 - 26 Nov 2018

Cited by 9 | Viewed by 3266

Abstract

Analysis and assessment of the reliability and safety of a gas-supply system is a key issue, given its status as critical infrastructure. A gas-supply system is characterised by continuous operation and a consequent need to achieve a high level of operating reliability and [...] Read more.

Analysis and assessment of the reliability and safety of a gas-supply system is a key issue, given its status as critical infrastructure. A gas-supply system is characterised by continuous operation and a consequent need to achieve a high level of operating reliability and safety. Such a system has its unique aspects, with particular elements having their different functions while also simultaneously interacting in the context of the integral whole. In such circumstances, risk analysis can prove useful in planning activity to prevent damage, and also in the devising of rescue scenarios. Thus, the purpose of the analysis presented here has been to supply the information that is necessary in decision-making relating to risk reduction. One of the most comprehensive assessment methods is based on the expected value of gas shortage. Basic formulae with which to determine a generalised indicator of system reliability are also presented, with risk viewed as synonymous with the unreliability of gas supply. This paper then proposes a method by which an indicator of the expected efficiency of operation may also be determined as the quotient of chance and absolute risk. The thinking in this article has been developed on the basis of data from a real gas-supply system, while the computational methods deployed allowed applications to draw conclusions regarding possible modification of the expected gas shortages method. Full article

(This article belongs to the Special Issue Energy and Environment)

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26 pages, 4905 KiB

Open AccessEditor’s ChoiceArticle

Realistic Wind Farm Layout Optimization through Genetic Algorithms Using a Gaussian Wake Model

by Nicolas Kirchner-Bossi and Fernando Porté-Agel

Energies 2018, 11(12), 3268; https://doi.org/10.3390/en11123268 - 23 Nov 2018

Cited by 59 | Viewed by 7146

Abstract

Wind Farm Layout Optimization (WFLO) can be useful to minimize power losses associated with turbine wakes in wind farms. This work presents a new evolutionary WFLO methodology integrated with a recently developed and successfully validated Gaussian wake model (Bastankhah and Porté-Agel model). Two [...] Read more.

Wind Farm Layout Optimization (WFLO) can be useful to minimize power losses associated with turbine wakes in wind farms. This work presents a new evolutionary WFLO methodology integrated with a recently developed and successfully validated Gaussian wake model (Bastankhah and Porté-Agel model). Two different parametrizations of the evolutionary methodology are implemented, depending on if a baseline layout is considered or not. The proposed scheme is applied to two real wind farms, Horns Rev I (Denmark) and Princess Amalia (the Netherlands), and two different turbine models, V80-2MW and NREL-5MW. For comparison purposes, these four study cases are also optimized under the traditionally used top-hat wake model (Jensen model). A systematic overestimation of the wake losses by the Jensen model is confirmed herein. This allows it to attain bigger power output increases with respect to the baseline layouts (between 0.72% and 1.91%) compared to the solutions attained through the more realistic Gaussian model (0.24–0.95%). The proposed methodology is shown to outperform other recently developed layout optimization methods. Moreover, the electricity cable length needed to interconnect the turbines decreases up to 28.6% compared to the baseline layouts. Full article

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21 pages, 5498 KiB

Open AccessEditor’s ChoiceArticle

Multi-Agent System with Plug and Play Feature for Distributed Secondary Control in Microgrid—Controller and Power Hardware-in-the-Loop Implementation

by Tung-Lam Nguyen, Efren Guillo-Sansano, Mazheruddin H. Syed, Van-Hoa Nguyen, Steven M. Blair, Luis Reguera, Quoc-Tuan Tran, Raphael Caire, Graeme M. Burt, Catalin Gavriluta and Ngoc-An Luu

Energies 2018, 11(12), 3253; https://doi.org/10.3390/en11123253 - 22 Nov 2018

Cited by 32 | Viewed by 5302

Abstract

Distributed control and optimization strategies are a promising alternative approach to centralized control within microgrids. In this paper, a multi-agent system is developed to deal with the distributed secondary control of islanded microgrids. Two main challenges are identified in the coordination of a [...] Read more.

Distributed control and optimization strategies are a promising alternative approach to centralized control within microgrids. In this paper, a multi-agent system is developed to deal with the distributed secondary control of islanded microgrids. Two main challenges are identified in the coordination of a microgrid: (i) interoperability among equipment from different vendors; and (ii) online re-configuration of the network in the case of alteration of topology. To cope with these challenges, the agents are designed to communicate with physical devices via the industrial standard IEC 61850 and incorporate a plug and play feature. This allows interoperability within a microgrid at agent layer as well as allows for online re-configuration upon topology alteration. A test case of distributed frequency control of islanded microgrid with various scenarios was conducted to validate the operation of proposed approach under controller and power hardware-in-the-loop environment, comprising prototypical hardware agent systems and realistic communications network. Full article

(This article belongs to the Special Issue Methods and Concepts for Designing and Validating Smart Grid Systems)

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19 pages, 3092 KiB

Open AccessEditor’s ChoiceArticle

Estimating the Economic Impacts of Net Metering Schemes for Residential PV Systems with Profiling of Power Demand, Generation, and Market Prices

by Antans Sauhats, Laila Zemite, Lubov Petrichenko, Igor Moshkin and Aivo Jasevics

Energies 2018, 11(11), 3222; https://doi.org/10.3390/en11113222 - 20 Nov 2018

Cited by 32 | Viewed by 5313

Abstract

This article analyses the influence of supporting scheme variants on the profitability of a projected investment of residential photovoltaic systems. The focus of the paper lies in evaluating the feasibility for the power system of solar power generation technologies to achieve a balance [...] Read more.

This article analyses the influence of supporting scheme variants on the profitability of a projected investment of residential photovoltaic systems. The focus of the paper lies in evaluating the feasibility for the power system of solar power generation technologies to achieve a balance between energy generation and support costs in a more efficient way. The case study is based on a year-long time series of examples with an hourly resolution of electricity prices from the Nord Pool power market, in addition to the power demand and solar generation of Latvian prosumers. Electric energy generation and the consumption of big data from more than 100 clients were collected. Based on these data, we predict the processes for the next 25 years, and we estimate economic indicators using a detailed description of the net metering billing system and the Monte-Carlo method. A recommendation to change the current net system to a superior one, taking into account the market cost of energy, concludes the paper. Full article

(This article belongs to the Special Issue Solar and Wind Energy Forecasting)

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18 pages, 1501 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optimal Portfolio for LNG Importation in Korea Using a Two-Step Portfolio Model and a Fuzzy Analytic Hierarchy Process

by Juhan Kim and Jinsoo Kim

Energies 2018, 11(11), 3049; https://doi.org/10.3390/en11113049 - 6 Nov 2018

Cited by 14 | Viewed by 4274

Abstract

A new energy transition policy in Korea has increased the importance of liquefied natural gas (LNG) in the energy mix. The Asia-Pacific LNG market is inflexible because long-term contracts are dominant. This market characteristic means that the development of policies that ensure a [...] Read more.

A new energy transition policy in Korea has increased the importance of liquefied natural gas (LNG) in the energy mix. The Asia-Pacific LNG market is inflexible because long-term contracts are dominant. This market characteristic means that the development of policies that ensure a stable supply of LNG is essential. We developed a new model for the optimal LNG import portfolio. The model consists of a two-step portfolio model combining the mean-variance (MV) portfolio and the linear programming (LP) model. In the first step, the MV model was applied to derive the optimal ratio between the long-term and spot contracts. Next, the LP model was used to determine the optimal LNG portfolio. We also applied a fuzzy analytic hierarchy process (AHP) to determine the weights of the cost factors. The application of the fuzzy AHP enabled this research to reflect the tangible and intangible costs more effectively. The optimal LNG portfolio showed that the optimal ratios for the long-term and spot contracts are 89.72% and 10.28% respectively, and the supply ratios in the Middle East and Southeast Asia decreased, while those in the Far East and Oceania significantly increased. The proposed model is able to build an effective LNG import strategy because it reflects the characteristics of LNG markets better than previous models. Full article

(This article belongs to the Special Issue Energy Policy in South Korea)

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16 pages, 3478 KiB

Open AccessEditor’s ChoiceArticle

One-Hour Prediction of the Global Solar Irradiance from All-Sky Images Using Artificial Neural Networks

by Cristian Crisosto, Martin Hofmann, Riyad Mubarak and Gunther Seckmeyer

Energies 2018, 11(11), 2906; https://doi.org/10.3390/en11112906 - 25 Oct 2018

Cited by 45 | Viewed by 4577

Abstract

We present a method to predict the global horizontal irradiance (GHI) one hour ahead in one-minute resolution using Artificial Neural Networks (ANNs). A feed-forward neural network with Levenberg–Marquardt Backpropagation (LM-BP) was used and was trained with four years of data from all-sky images [...] Read more.

We present a method to predict the global horizontal irradiance (GHI) one hour ahead in one-minute resolution using Artificial Neural Networks (ANNs). A feed-forward neural network with Levenberg–Marquardt Backpropagation (LM-BP) was used and was trained with four years of data from all-sky images and measured global irradiance as input. The pictures were recorded by a hemispheric sky imager at the Institute of Meteorology and Climatology (IMuK) of the Leibniz Universität Hannover, Hannover, Germany (52.23° N, 09.42° E, and 50 m above sea level). The time series of the global horizontal irradiance was measured using a thermopile pyranometer at the same site. The new method was validated with a test dataset from the same source. The irradiance is predicted for the first 10–30 min very well; after this time, the length of which is dependent on the weather conditions, the agreement between predicted and observed irradiance is reasonable. Considering the limited range that the camera and the ANN can “see”, this is not surprising. When comparing the results to the persistence model, we observed that the forecast accuracy of the new model reduced both the Root Mean Square Error (RMSE) and the Mean Absolute Error (MAE) of the one-hour prediction by approximately 40% compared to the reference persistence model under various weather conditions, which demonstrates the high capability of the algorithm, especially within the first minutes. Full article

(This article belongs to the Special Issue Solar and Wind Energy Forecasting)

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23 pages, 29858 KiB

Open AccessEditor’s ChoiceArticle

Assessment of the Power Output of a Two-Array Clustered WEC Farm Using a BEM Solver Coupling and a Wave-Propagation Model

by Philip Balitsky, Gael Verao Fernandez, Vasiliki Stratigaki and Peter Troch

Energies 2018, 11(11), 2907; https://doi.org/10.3390/en11112907 - 25 Oct 2018

Cited by 21 | Viewed by 3254

Abstract

One of the key challenges in designing a Wave Energy Converter (WEC) farm is geometrical layout, as WECs hydrodynamically interact with one another. WEC positioning impacts both the power output of a given wave-energy project and any potential effects on the surrounding areas. [...] Read more.

One of the key challenges in designing a Wave Energy Converter (WEC) farm is geometrical layout, as WECs hydrodynamically interact with one another. WEC positioning impacts both the power output of a given wave-energy project and any potential effects on the surrounding areas. The WEC farm developer must seek to optimize WEC positioning to maximize power output while minimizing capital cost and any potential deleterious effects on the surrounding area. A number of recent studies have shown that a potential solution is placing WECs in dense arrays of several WECs with space between individual arrays for navigation. This innovative arrangement can also be used to reduce mooring and cabling costs. In this paper, we apply a novel one-way coupling method between the NEMOH BEM model and the MILDwave wave-propagation model to investigate the influence of WEC array separation distance on the power output and the surrounding wave field between two densely packed WEC arrays in a farm. An iterative method of applying the presented one-way coupling to interacting WEC arrays is used to compute the wave field in a complete WEC farm and to calculate its power output. The notion of WEC array ‘independence’ in a farm from a hydrodynamic point of view is discussed. The farm is modeled for regular and irregular waves for a number of wave periods, wave incidence angles, and various WEC array separation distances. We found strong dependency of the power output on the wave period and the wave incidence angle for regular waves at short WEC array–array separation distances. For irregular wave operational conditions, a large majority of WEC array configurations within a WEC farm were found to be hydrodynamically ‘independent’. Full article

(This article belongs to the Section A: Sustainable Energy)

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24 pages, 16173 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Coupling Methodology for Studying the Far Field Effects of Wave Energy Converter Arrays over a Varying Bathymetry

by Gael Verao Fernandez, Philip Balitsky, Vasiliki Stratigaki and Peter Troch

Energies 2018, 11(11), 2899; https://doi.org/10.3390/en11112899 - 25 Oct 2018

Cited by 27 | Viewed by 4156

Abstract

For renewable wave energy to operate at grid scale, large arrays of Wave Energy Converters (WECs) need to be deployed in the ocean. Due to the hydrodynamic interactions between the individual WECs of an array, the overall power absorption and surrounding wave field [...] Read more.

For renewable wave energy to operate at grid scale, large arrays of Wave Energy Converters (WECs) need to be deployed in the ocean. Due to the hydrodynamic interactions between the individual WECs of an array, the overall power absorption and surrounding wave field will be affected, both close to the WECs (near field effects) and at large distances from their location (far field effects). Therefore, it is essential to model both the near field and far field effects of WEC arrays. It is difficult, however, to model both effects using a single numerical model that offers the desired accuracy at a reasonable computational time. The objective of this paper is to present a generic coupling methodology that will allow to model both effects accurately. The presented coupling methodology is exemplified using the mild slope wave propagation model MILDwave and the Boundary Elements Methods (BEM) solver NEMOH. NEMOH is used to model the near field effects while MILDwave is used to model the WEC array far field effects. The information between the two models is transferred using a one-way coupling. The results of the NEMOH-MILDwave coupled model are compared to the results from using only NEMOH for various test cases in uniform water depth. Additionally, the NEMOH-MILDwave coupled model is validated against available experimental wave data for a 9-WEC array. The coupling methodology proves to be a reliable numerical tool as the results demonstrate a difference between the numerical simulations results smaller than 5% and between the numerical simulations results and the experimental data ranging from 3% to 11%. The simulations are subsequently extended for a varying bathymetry, which will affect the far field effects. As a result, our coupled model proves to be a suitable numerical tool for simulating far field effects of WEC arrays for regular and irregular waves over a varying bathymetry. Full article

(This article belongs to the Special Issue Offshore Renewable Energy: Ocean Waves, Tides and Offshore Wind)

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15 pages, 803 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Islanding Detection of Synchronous Distributed Generator Based on the Active and Reactive Power Control Loops

by Reza Zamani, Mohamad-Esmail Hamedani-Golshan, Hassan Haes Alhelou, Pierluigi Siano and Hemanshu R. Pota

Energies 2018, 11(10), 2819; https://doi.org/10.3390/en11102819 - 19 Oct 2018

Cited by 43 | Viewed by 6961

Abstract

There has been a considerable importance for the islanding detection due to the growing integration of distributed generations (DGs) in the modern power grids. This paper proposes a novel active islanding detection scheme for synchronous DGs, considering two additional compensators and a positive [...] Read more.

There has been a considerable importance for the islanding detection due to the growing integration of distributed generations (DGs) in the modern power grids. This paper proposes a novel active islanding detection scheme for synchronous DGs, considering two additional compensators and a positive feedback for each of active and reactive power control loops. The added blocks are designed using the small gain theorem and stability margins definition considering characteristics of open loop transfer functions of synchronous DG control loops. Islanding can be detected using the proposed method even where there is an exact match between generation and local load without sacrificing power quality. In addition, the performance of the proposed method can be retained even with high penetration of motor loads. The proposed scheme improves the stability and power quality of the grid, when the synchronous DG is subjected to the grid-connected disturbances. Furthermore, this method augments the stability margins of the system in the grid-connected conditions to enhance the disturbances ride-through capability of the system and reduce the negative impact of the active methods on the power quality. Simultaneous advantages of the proposed scheme are demonstrated by modeling a test system in MATLAB software and time-domain simulation achieved by PSCAD. Full article

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

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20 pages, 12508 KiB

Open AccessEditor’s ChoiceArticle

A Short-Term Wind Speed Forecasting Model by Using Artificial Neural Networks with Stochastic Optimization for Renewable Energy Systems

by Chiou-Jye Huang and Ping-Huan Kuo

Energies 2018, 11(10), 2777; https://doi.org/10.3390/en11102777 - 16 Oct 2018

Cited by 77 | Viewed by 6576

Abstract

To efficiently manage unstable wind power generation, precise short-term wind speed forecasting is critical. To overcome the challenges in wind speed forecasting, this paper proposes a new convolutional neural network algorithm for short-term forecasting. In this paper, the forecasting performance of the proposed [...] Read more.

To efficiently manage unstable wind power generation, precise short-term wind speed forecasting is critical. To overcome the challenges in wind speed forecasting, this paper proposes a new convolutional neural network algorithm for short-term forecasting. In this paper, the forecasting performance of the proposed algorithm was compared to that of four other artificial intelligence algorithms commonly used in wind speed forecasting. Numerical testing results based on data from a designated wind site in Taiwan were used to demonstrate the efficiency of above-mentioned proposed learning method. Mean absolute error (MAE) and root-mean-square error (RMSE) were adopted as accuracy evaluation indexes in this paper. Experimental results indicate that the MAE and RMSE values of the proposed algorithm are 0.800227 and 0.999978, respectively, demonstrating very high forecasting accuracy. Full article

(This article belongs to the Special Issue Energy Economy, Sustainable Energy and Energy Saving)

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18 pages, 23472 KiB

Open AccessEditor’s ChoiceArticle

A Novel Phase Current Reconstruction Method for a Three-Level Neutral Point Clamped Inverter (NPCI) with a Neutral Shunt Resistor

by Yungdeug Son and Jangmok Kim

Energies 2018, 11(10), 2616; https://doi.org/10.3390/en11102616 - 1 Oct 2018

Cited by 14 | Viewed by 4775

Abstract

This paper presents three phase current reconstruction methods for a three-level neutral point clamped inverter (NPCI) by measuring the voltage of a shunt resistor placed in the neutral point of the inverter. In order to accurately acquire the phase currents from the shunt [...] Read more.

This paper presents three phase current reconstruction methods for a three-level neutral point clamped inverter (NPCI) by measuring the voltage of a shunt resistor placed in the neutral point of the inverter. In order to accurately acquire the phase currents from the shunt resister, the dwell time of the active voltage vectors need to exceed the minimum time. On the other hand, if the time of active voltage is shorter than the minimum time, the current measurement becomes impossible. In this paper, unmeasurable regions for current are classified into three areas. Area 1 is a region in which both phase currents can be measure. Therefore, it is not necessary to restore the current. In Area 2, only one phase current can be measured. Thus, an estimation or restoration method is needed to measure another phase current. In this paper, the current estimation method using an electrical model of the motor is proposed. Area 3 is the region in which both phase currents can not be measured. In this case, it is necessary to move the voltage vector to the current measurable area by injecting the voltage. In this paper, Area 3 is divided into 36 sectors to inject optimal voltage. The proposed methods have the advantages of high current measurement accuracy and low THD (total harmonic distortion). The effectiveness of the proposed methods are verified through experimental results. Full article

(This article belongs to the Special Issue Multilevel Converters: Analysis, Modulation, Topologies, and Applications)

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16 pages, 2313 KiB

Open AccessEditor’s ChoiceArticle

Real-World Measurement of Hybrid Buses’ Fuel Consumption and Pollutant Emissions in a Metropolitan Urban Road Network

by Christos Keramydas, Georgios Papadopoulos, Leonidas Ntziachristos, Ting-Shek Lo, Kwok-Lam Ng, Hok-Lai Anson Wong and Carol Ka-Lok Wong

Energies 2018, 11(10), 2569; https://doi.org/10.3390/en11102569 - 26 Sep 2018

Cited by 27 | Viewed by 6121

Abstract

This study investigates pollutant emissions and fuel consumption of six Euro VI hybrid-diesel public transport buses operating on different scheduled routes in a metropolitan urban road network. Portable emission measurement systems (PEMS) are used in measurements and results are compared to those obtained [...] Read more.

This study investigates pollutant emissions and fuel consumption of six Euro VI hybrid-diesel public transport buses operating on different scheduled routes in a metropolitan urban road network. Portable emission measurement systems (PEMS) are used in measurements and results are compared to those obtained from a paired number of Euro V conventional buses of the same body type used as control over the same routes. The selected routes vary from urban to highway driving and the experimentation was conducted over the first half of 2015. The available emissions data correspond to a wide range of driving, operating, and ambient conditions. Fuel consumption, distance- and energy-based emission levels are derived and presented in a comparative manner. The effect of different factors, including speed, ambient temperature, and road grade on fuel consumption and emissions performance is investigated. Mean fuel consumption of hybrid buses was found 6.1% lower than conventional ones, from 20% lower up to 16% higher, over six routes tested in total. The mean route difference between the two technologies was not statistically significant. Air conditioning decreased consumption benefits of the hybrid buses. Decrease of the mean route speed from 15 km h⁻¹ tο 8 km h⁻¹ increased the hybrid buses consumption by 63%. Nitrogen oxides (NO_x) emissions of the Euro VI hybrid buses were 93 ± 5% lower than conventional Euro V ones. Nitrous oxide (N₂O) emissions from hybrid Euro VI buses made up 5.9% of total greenhouse gas emissions and largely offset carbon dioxide (CO₂) benefits. The results suggest that hybrid urban buses need to be assessed under realistic operation and environmental conditions to assess their true environmental and fuel consumption benefits. Full article

(This article belongs to the Section A: Sustainable Energy)

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