Energies

11 pages, 2887 KiB

Open AccessArticle

Carbon Nanofibers Production via the Electrospinning Process

by Radu Dorin Andrei, Adriana Marinoiu, Elena Marin, Stanica Enache and Elena Carcadea

Energies 2020, 13(11), 3029; https://doi.org/10.3390/en13113029 - 11 Jun 2020

Cited by 7 | Viewed by 3211

Electrospun fibers with different concentrations of polyacrylonitrile (PAN) were synthesized and the results are reported in this study. The aim was to obtain carbon nanofibers for manufacturing gas diffusion layers for proton exchange membrane (PEM) fuel cells. The electrospun fibers obtained were carbonized [...] Read more.

Electrospun fibers with different concentrations of polyacrylonitrile (PAN) were synthesized and the results are reported in this study. The aim was to obtain carbon nanofibers for manufacturing gas diffusion layers for proton exchange membrane (PEM) fuel cells. The electrospun fibers obtained were carbonized at 1200 °C, 1300 °C, and 1400 °C, in order to have nanofibers with more than 96% of carbon atoms. The scanning electron microscopy (SEM) results revealed an increase in the diameter from 400–700 nm at 1200 °C to 1000–1400 nm at 1300 °C and 1400 °C. The Raman measurements disclose a higher degree of crystallinity for the sample carbonized at elevated temperatures. The surface area was estimated from the Brunauer–Emmett–Teller (BET) method and the results revealed an increase from 40.69 m²g⁻¹ to 66.89 m²g⁻¹ and 89.92 m²g⁻¹ as the carbonization temperature increased. Simultaneously, the pore volume increased with increasing carbonization temperature. The Fourier-transform infrared spectroscopy (FTIR) spectra reveal that during carbonization treatment, C≡N triple bonds are destroyed with the appearance of C=N double bonds. Decreasing the I_D/I_G intensities’ ratio from ~1.07 to ~1.00 denotes the defects reduction in carbonaceous materials due to the graphitization process. Therefore, the carbon fibers developed in optimum conditions are appropriate to be further used to produce gas diffusion layers for Proton-exchange membrane fuel cells (PEMFC). Full article

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

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22 pages, 55756 KiB

Open AccessArticle

Impacts of Global Climate Change on the Future Ocean Wave Power Potential: A Case Study from the Indian Ocean

by Harshinie Karunarathna, Pravin Maduwantha, Bahareh Kamranzad, Harsha Rathnasooriya and Kasun De Silva

Energies 2020, 13(11), 3028; https://doi.org/10.3390/en13113028 - 11 Jun 2020

Cited by 13 | Viewed by 3933

Abstract

This study investigates the impacts of global climate change on the future wave power potential, taking Sri Lanka as a case study from the northern Indian Ocean. The geographical location of Sri Lanka, which receives long-distance swell waves generated in the Southern Indian [...] Read more.

This study investigates the impacts of global climate change on the future wave power potential, taking Sri Lanka as a case study from the northern Indian Ocean. The geographical location of Sri Lanka, which receives long-distance swell waves generated in the Southern Indian Ocean, favors wave energy-harvesting. Waves projected by a numerical wave model developed using Simulating Waves Nearshore Waves (SWAN) wave model, which is forced by atmospheric forcings generated by an Atmospheric Global Climate Model (AGCM) within two time slices that represent “present” and “future” (end of century) wave climates, are used to evaluate and compare present and future wave power potential around Sri Lanka. The results reveal that there will be a 12–20% reduction in average available wave power along the south-west and south-east coasts of Sri Lanka in future. This reduction is due mainly to changes to the tropical south-west monsoon system because of global climate change. The available wave power resource attributed to swell wave component remains largely unchanged. Although a detailed analysis of monthly and annual average wave power under both “present” and “future” climates reveals a strong seasonal and some degree of inter-annual variability of wave power, a notable decadal-scale trend of variability is not visible during the simulated 25-year periods. Finally, the results reveal that the wave power attributed to swell waves are very stable over the long term. Full article

(This article belongs to the Special Issue Advances and Challenges in Harvesting Ocean Energy)

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14 pages, 5769 KiB

Open AccessArticle

Density Functional Theory-Based Molecular Modeling: Verification of Decisive Roles of Van der Waals Aggregation of Triiodide Ions for Effective Electron Transfer in Wet-Type N3-Dye-Sensitized Solar Cells

by Susumu Yanagisawa and Shozo Yanagida

Energies 2020, 13(11), 3027; https://doi.org/10.3390/en13113027 - 11 Jun 2020

Cited by 6 | Viewed by 2874

Abstract

Density functional theory-based molecular modeling (DFT/MM) validates that KI and I₂ undergo exothermic van der Waals (vdW) aggregation in acetonitrile (AN) or in the presence of 4-tert-butylpyridine (TBP), forming potassium triiodide (KI₃) and, further mutual vdW aggregation leads to the [...] Read more.

Density functional theory-based molecular modeling (DFT/MM) validates that KI and I₂ undergo exothermic van der Waals (vdW) aggregation in acetonitrile (AN) or in the presence of 4-tert-butylpyridine (TBP), forming potassium triiodide (KI₃) and, further mutual vdW aggregation leads to the formation of (KI₃)₂ and AN, (KI₃)₂ and (AN)₂ and (KI₃)₂ and TBP in the AN-based Dye sensitized solar cells (DSSC) electrolytes. All KI₃ aggregates have a very low energy gap, 0.17 eV, 0.14 eV and 0.05 eV of lowest unoccupied molecular orbital (LUMO) + 1 and LUMO, respectively, verifying efficient electron diffusion in μm-thick DSSC electrolytes. Hydrogen-bonding aggregation of anatase TiO₂ model, Ti₉O₁₈H and OH, with N3 (proton) dye is also validated by DFT/MM, and the energy structure verifies unidirectional electron flow from highest occupied molecular orbital (HOMO) on thiocyanide (SCN) groups of N3 dye to LUMO on the TiO₂ model at the aggregates. Further, DFT/MM for the aggregation of K⁺I₃⁻ with N3 verifies the most exothermic formation of the aggregate of N3 (proton) and K⁺I₃⁻. The UV-Vis spectra of N3 (proton) and K⁺I₃⁻ is consistent with reported incident photocurrent efficiency (IPCE) action spectra (λ = 450–800 nm) of N3-sensitized DSSC, verifying that the N3 dye of N3 (proton) and K⁺I₃⁻ becomes an effective sensitizer in the anode / TiO₂ / N3 (proton) / KI/I₂ / acetonitrile (AN) / cathode structured DSSC. The energy structure of LUMO and LUMO + 1 of the aggregates, Ti₉O₁₈H and OH and N3 (proton), N3 and K⁺I₃⁻, (KI₃)₂ and AN and (KI₃)₂ and TBP verifies high IPCE photocurrent and effective electron diffusion via KI₃-aggregates in the DSSC of Ti₉O₁₈H and OH and N3 (proton) and K⁺I₃⁻. Full article

(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)

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18 pages, 1738 KiB

Open AccessArticle

Decentralized Frequency Control of Battery Energy Storage Systems Distributed in Isolated Microgrid

by Watcharakorn Pinthurat and Branislav Hredzak

Energies 2020, 13(11), 3026; https://doi.org/10.3390/en13113026 - 11 Jun 2020

Cited by 13 | Viewed by 2824

Abstract

The penetration and integration of renewable energy sources into modern power systems has been increasing over recent years. This can lead to frequency excursion and low inertia due to renewable energy sources’ intermittency and absence of rotational synchronous machines. Battery energy storage systems [...] Read more.

The penetration and integration of renewable energy sources into modern power systems has been increasing over recent years. This can lead to frequency excursion and low inertia due to renewable energy sources’ intermittency and absence of rotational synchronous machines. Battery energy storage systems can play a crucial role in providing the frequency compensation because of their high ramp rate and fast response. In this paper, a decentralized frequency control system composed of three parts is proposed. The first part provides adaptive frequency droop control with its droop coefficient a function of the real-time state of charge of battery. The second part provides a fully decentralized frequency restoration. In the third part, a virtual inertia emulation improves the microgrid resilience. The presented results demonstrate that the proposed control system improves the microgrid resilience and mitigates the frequency deviation when compared with conventional

ω

-P droop control and existing control systems. The proposed control system is verified on Real-Time Digital Simulator (RTDS), with accurate microgrid model, nonlinear battery models and detailed switching models of power electronic converters. Full article

(This article belongs to the Section A1: Smart Grids and Microgrids)

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22 pages, 2957 KiB

Open AccessArticle

Joint Storage: A Mixed-Method Analysis of Consumer Perspectives on Community Energy Storage in Germany

by Esther Hoffmann and Franziska Mohaupt

Energies 2020, 13(11), 3025; https://doi.org/10.3390/en13113025 - 11 Jun 2020

Cited by 11 | Viewed by 2925

Abstract

In this paper, we analyze consumer attitudes toward and interest in community energy storage (CES) in Germany, based on five focus group discussions and an online survey of private owners of photovoltaic (PV) systems, as well as written surveys and workshops with the [...] Read more.

In this paper, we analyze consumer attitudes toward and interest in community energy storage (CES) in Germany, based on five focus group discussions and an online survey of private owners of photovoltaic (PV) systems, as well as written surveys and workshops with the residents of two residential developments where CES has been installed. We find that owners of PV systems are generally receptive to the idea of CES but are unfamiliar with it. They assume that CES is more resource- and cost-efficient than residential storage and appreciate the idea of professionally managed operation and maintenance, but are skeptical of whether fair and transparent distribution and billing can be realized. Consumers express a need for ancillary services, such as monitoring, information or energy management, but the interest in such services, however, is strongly dependent on their perception of the costs versus potential savings. Full article

(This article belongs to the Special Issue New Pathways for Community Energy and Storage)

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31 pages, 6902 KiB

Open AccessArticle

An Energy Model Using Sleeping Algorithms for Wireless Sensor Networks under Proactive and Reactive Protocols: A Performance Evaluation

by Carolina Del-Valle-Soto, Ramiro Velázquez, Leonardo J. Valdivia, Nicola Ivan Giannoccaro and Paolo Visconti

Energies 2020, 13(11), 3024; https://doi.org/10.3390/en13113024 - 11 Jun 2020

Cited by 15 | Viewed by 3094

Abstract

The continuous evolution of the Internet of Things (IoT) makes it possible to connect everyday objects to networks in order to monitor physical and environmental conditions, which is made possible due to wireless sensor networks (WSN) that enable the transfer of data. However, [...] Read more.

The continuous evolution of the Internet of Things (IoT) makes it possible to connect everyday objects to networks in order to monitor physical and environmental conditions, which is made possible due to wireless sensor networks (WSN) that enable the transfer of data. However, it has also brought about many challenges that need to be addressed, such as excess energy consumption. Accordingly, this paper presents and analyzes wireless network energy models using five different communication protocols: Ad Hoc On-Demand Distance Vector (AODV), Multi-Parent Hierarchical (MPH), Dynamic Source Routing (DSR), Low Energy Adaptive Clustering Hierarchy (LEACH) and Zigbee Tree Routing (ZTR). First, a series of metrics are defined to establish a comparison and determine which protocol exhibits the best energy consumption performance. Then, simulations are performed and the results are compared with real scenarios. The energy analysis is conducted with three proposed sleeping algorithms: Modified Sleeping Crown (MSC), Timer Sleeping Algorithm (TSA), and Local Energy Information (LEI). Thereafter, the proposed algorithms are compared by virtue of two widely used wireless technologies, namely Zigbee and WiFi. Indeed, the results suggest that Zigbee has a better energy performance than WiFi, but less redundancy in the topology links, and this study favors the analysis with the simulation of protocols with different nature. The tested scenario is implemented into a university campus to show a real network running. Full article

(This article belongs to the Special Issue Electronic Systems and Energy Harvesting Methods for Automation, Mechatronics and Automotive)

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21 pages, 4178 KiB

Open AccessReview

Thermal Storage Using Metallic Phase Change Materials for Bus Heating—State of the Art of Electric Buses and Requirements for the Storage System

by Werner Kraft, Veronika Stahl and Peter Vetter

Energies 2020, 13(11), 3023; https://doi.org/10.3390/en13113023 - 11 Jun 2020

Cited by 13 | Viewed by 4459

Abstract

Battery-powered electric buses currently face the challenges of high cost and limited range, especially in winter conditions, where interior heating is required. To face both challenges, the use of thermal energy storage based on metallic phase change materials for interior heating, also called [...] Read more.

Battery-powered electric buses currently face the challenges of high cost and limited range, especially in winter conditions, where interior heating is required. To face both challenges, the use of thermal energy storage based on metallic phase change materials for interior heating, also called thermal high-performance storage, is considered. By replacing the battery capacity through such an energy storage system, which is potentially lighter, smaller, and cheaper than the batteries used in buses, an overall reduction in cost and an increase of range in winter conditions could be reached. Since the use of thermal high-performance storage as a heating system in a battery-powered electric bus is a new approach, the requirements for such a system first need to be known to be able to proceed with further steps. To find these requirements, a review of the relevant state of the art of battery-powered electric buses, with a focus on heating systems, was done. Other relevant aspects were vehicle types, electric architecture, battery systems, and charging strategies. With the help of this review, requirements for thermal high-performance storage as a heating system for a battery-powered electric bus were produced. Categories for these requirements were the thermal capacity and performance, long-term stability, mass and volume, cost, electric connection, thermal connection, efficiency, maintenance, safety, adjustment, and ecology. Full article

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

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15 pages, 7546 KiB

Open AccessArticle

Optimization of Vehicle Braking Distance Using a Fuzzy Controller

by Peter Girovský, Jaroslava Žilková and Ján Kaňuch

Energies 2020, 13(11), 3022; https://doi.org/10.3390/en13113022 - 11 Jun 2020

Cited by 11 | Viewed by 2970

Abstract

The paper presents the study of an anti-lock braking system (ABS) that has been complemented by a fuzzy controller. The fuzzy controller was used to improve the braking performance of the vehicle, particularly in critical situations, for example, when braking a vehicle on [...] Read more.

The paper presents the study of an anti-lock braking system (ABS) that has been complemented by a fuzzy controller. The fuzzy controller was used to improve the braking performance of the vehicle, particularly in critical situations, for example, when braking a vehicle on wet road. The controller for the ABS was designed in the MATLAB/Simulink program. The designed controller was simulated on a medium-size vehicle model. During testing, three braking systems were simulated on the vehicle model. We compared the performance of a braking system without an ABS, a system with a threshold-based conventional ABS, and a braking system with the proposed ABS with a fuzzy controller. These three braking systems were simulation tested during braking the vehicle on a dry straight road and on a road with combined road adhesion. A maneuverability test was conducted, where the vehicle had to avoid an obstacle while braking. The results of each test are provided at the end of the paper. Full article

(This article belongs to the Special Issue Electric Systems for Transportation)

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32 pages, 735 KiB

Open AccessArticle

What Motivates Behavior Change? Analyzing User Intentions to Adopt Clean Technologies in Low-Resource Settings Using the Theory of Planned Behavior

by Mohammad H. Pakravan and Nordica MacCarty

Energies 2020, 13(11), 3021; https://doi.org/10.3390/en13113021 - 11 Jun 2020

Cited by 11 | Viewed by 2679

Abstract

Understanding and integrating the user’s decision-making process into product design and distribution strategies is likely to lead to higher adoption rates and ultimately increased impacts, particularly for those products that require a change in habit or behavior such as clean energy technologies. This [...] Read more.

Understanding and integrating the user’s decision-making process into product design and distribution strategies is likely to lead to higher adoption rates and ultimately increased impacts, particularly for those products that require a change in habit or behavior such as clean energy technologies. This study applies the Theory of Planned Behavior (TPB) in design for global development, where understanding the tendency to adopt beneficial technologies based on parsimonious approaches is critical to programmatic impact. To investigate robustness and applicability of behavioral models in a data scarce setting, this study applies TPB to the adoption of biomass cookstoves in a sample size of two remote communities in Honduras and Uganda before and after a trial period. Using multiple ordinal logistic regressions, the intention to adopt the technology was modeled. Results quantify the influence of these factors on households’ intentions to cook their main meals with improved cookstoves. For example, the intention of participants with slightly stronger beliefs regarding the importance of reducing smoke emissions was 3.3 times higher than average to cook more main meals with clean cookstoves. The quantitative method of this study enables technology designers to design and develop clean technologies that better suit user behavior, needs, and priorities. In addition, the data driven approach of this study provides insights for policy makers to design policies such as subsidies, information campaigns, and supply chains that reflect behavioral attributes for culturally tailored clean technology adoption initiatives. Furthermore, this work discusses potential sources of bias and statistical challenges in data-scarce regions, and outlines methods to address them. Full article

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18 pages, 7239 KiB

Open AccessArticle

Energy Savings in an Office Building with High WWR Using Glazing Systems Combining Thermochromic and Electrochromic Layers

by Michaela Detsi, Aris Manolitsis, Ioannis Atsonios, Ioannis Mandilaras and Maria Founti

Energies 2020, 13(11), 3020; https://doi.org/10.3390/en13113020 - 11 Jun 2020

Cited by 18 | Viewed by 2946

Abstract

This paper assesses energy savings in terms of heating, cooling, and artificial lighting achieved in an office building with a high Window to Wall Ratio (WWR), located in Athens and Stockholm. Six different configurations of triple pane windows combining thermochromic, electrochromic, and low-e [...] Read more.

This paper assesses energy savings in terms of heating, cooling, and artificial lighting achieved in an office building with a high Window to Wall Ratio (WWR), located in Athens and Stockholm. Six different configurations of triple pane windows combining thermochromic, electrochromic, and low-e coatings in Insulated Glass Units (IGUs) are examined to quantify the potential of increasing energy savings in office buildings. The combination of electrochromic and thermochromic layers on the outer pane of the triple IGU, achieved an 18.5% and 8.1% reduction in annual primary energy use for Athens and Stockholm, respectively. The used switching strategy ensured the visual comfort of the employees and provided adequate daylight in both cases. It was found that in Stockholm the cooling system can be downsized considerably, achieving important cost reduction in the HVAC system. The analysis also takes into account the reduction of thermal storage in the building envelope due to the switchable windows. This reduction is beneficial in the case of Athens, but it can reduce energy savings in Stockholm. Therefore, for colder climates, it is important to increase window heat gains through the development of layers with higher g-value in the clear state and through the application of appropriate switching strategies. Full article

(This article belongs to the Special Issue Energy Efficiency, Savings and Storage in Buildings Combined with Advanced Energy Systems and Materials)

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17 pages, 4990 KiB

Open AccessArticle

Investigation of Fast, Secure and Reliable Network Restoration after Blackouts

by Elmira Torabi Makhsos, Yi Guo, Wolfgang Gawlik, Benjamin Cox, Philipp Hinkel, Marian Zugck, Wolfram Wellßow, Robert Schmaranz, Ewald Traxler and Leopold Fiedler

Energies 2020, 13(11), 3019; https://doi.org/10.3390/en13113019 - 11 Jun 2020

Viewed by 1863

Abstract

Integrating distributed generation into power grids creates various technical challenges for network operation. Volatility of renewable energy resources may increase the probability of blackouts. In order to restore networks fast, securely and reliably after blackouts, within the research project RestoreGrid4RES’s network restoration strategies, [...] Read more.

Integrating distributed generation into power grids creates various technical challenges for network operation. Volatility of renewable energy resources may increase the probability of blackouts. In order to restore networks fast, securely and reliably after blackouts, within the research project RestoreGrid4RES’s network restoration strategies, the related issues caused by distributed generation are investigated and novel methods to face those challenges are developed. This paper focuses on (i) algorithms to identify possible restoration paths, (ii) key performance indicators for the assessment of grid restoration options and (iii) an evaluation of the results for network restoration strategies. Full article

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19 pages, 5485 KiB

Open AccessArticle

Influence of Torrefaction and Pelletizing of Sawdust on the Design Parameters of a Fixed Bed Gasifier

by Hao Luo, Lukasz Niedzwiecki, Amit Arora, Krzysztof Mościcki, Halina Pawlak-Kruczek, Krystian Krochmalny, Marcin Baranowski, Mayank Tiwari, Anshul Sharma, Tanuj Sharma and Zhimin Lu

Energies 2020, 13(11), 3018; https://doi.org/10.3390/en13113018 - 11 Jun 2020

Cited by 11 | Viewed by 3513

Abstract

Gasification of biomass in fixed bed gasifiers is a well-known technology, with its origins dating back to the beginning of 20th century. It is a technology with good prospects, in terms of small scale, decentralized power co-generation. However, the understanding of the process [...] Read more.

Gasification of biomass in fixed bed gasifiers is a well-known technology, with its origins dating back to the beginning of 20th century. It is a technology with good prospects, in terms of small scale, decentralized power co-generation. However, the understanding of the process is still not fully developed. Therefore, assessment of the changes in the design of a gasifier is typically performed with extensive prototyping stage, thus introducing significant cost. This study presents experimental results of gasification of a single pellet and bed of particles of raw and torrefied wood. The procedure can be used for obtaining design parameters of a fixed bed gasifier. Results of two suits of experiments, namely pyrolysis and CO₂ gasification are presented. Moreover, results of pyrolysis of pellets are compared against a numerical model, developed for thermally thick particles. Pyrolysis time, predicted by model, was in good agreement with experimental results, despite some differences in the time when half of the initial mass was converted. Conversion times for CO₂ gasification were much longer, despite higher temperature of the process, indicating importance of the reduction reactions. Overall, the obtained results could be helpful in developing a complete model of gasification of thermally thick particles in a fixed bed. Full article

(This article belongs to the Special Issue Selected Papers from ISCP 2019—XXIV International Symposium on Combustion Processes)

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18 pages, 5728 KiB

Open AccessArticle

Stochastic Modeling of the Levelized Cost of Electricity for Solar PV

by Chul-Yong Lee and Jaekyun Ahn

Energies 2020, 13(11), 3017; https://doi.org/10.3390/en13113017 - 11 Jun 2020

Cited by 32 | Viewed by 3542

Abstract

With the development of renewable energy, a key measure for reducing greenhouse gas emissions, interest in the levelized cost of electricity (LCOE) is increasing. Although the input variables used in the LCOE calculation, such as capacity factor, capital expenditure, annual power plant operations [...] Read more.

With the development of renewable energy, a key measure for reducing greenhouse gas emissions, interest in the levelized cost of electricity (LCOE) is increasing. Although the input variables used in the LCOE calculation, such as capacity factor, capital expenditure, annual power plant operations and maintenance cost, discount and interest rate, and economic life, vary according to region and project, most existing studies estimate the LCOE by using a deterministic methodology. In this study, the stochastic approach was used to estimate the LCOE for solar photovoltaic (PV) in South Korea. In addition, this study contributed to deriving realistic analysis results by securing the actual data generated in the solar PV project compared to the existing studies. The results indicate that the LCOE for commercial solar power ranged from KRW 115 (10 cents)/kWh to KRW 197.4 (18 cents)/kWh at a confidence level of 95%. The median was estimated at KRW 160.03 (15 cents)/kWh. The LCOE for residential solar power ranged from KRW 109.7 (10 cents)/kWh to KRW 194.1 (18 cents)/kWh at a 95% confidence level and a median value of KRW 160.03 (15 cents)/kWh. A sensitivity analysis shows that capital expenditure has the most significant impact on the LCOE for solar power, followed by the discount rate and corporate tax. This study proposes that policymakers implement energy policies to reduce solar PV hardware and soft costs. Full article

(This article belongs to the Special Issue End-Users’ Perspectives on Energy Policy and Technology)

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23 pages, 1965 KiB

Open AccessArticle

A Chronological Literature Review of Electric Vehicle Interactions with Power Distribution Systems

by Andrés Arias-Londoño, Oscar Danilo Montoya and Luis Fernando Grisales-Noreña

Energies 2020, 13(11), 3016; https://doi.org/10.3390/en13113016 - 11 Jun 2020

Cited by 17 | Viewed by 5388

Abstract

In the last decade, the deployment of electric vehicles (EVs) has been largely promoted. This development has increased challenges in the power systems in the context of planning and operation due to the massive amount of recharge needed for EVs. Furthermore, EVs may [...] Read more.

In the last decade, the deployment of electric vehicles (EVs) has been largely promoted. This development has increased challenges in the power systems in the context of planning and operation due to the massive amount of recharge needed for EVs. Furthermore, EVs may also offer new opportunities and can be used to support the grid to provide auxiliary services. In this regard, and considering the research around EVs and power grids, this paper presents a chronological background review of EVs and their interactions with power systems, particularly electric distribution networks, considering publications from the IEEE Xplore database. The review is extended from 1973 to 2019 and is developed via systematic classification using key categories that describe the types of interactions between EVs and power grids. These interactions are in the framework of the power quality, study of scenarios, electricity markets, demand response, demand management, power system stability, Vehicle-to-Grid (V2G) concept, and optimal location of battery swap and charging stations. Full article

(This article belongs to the Special Issue Microgrids: Planning, Protection and Control)

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21 pages, 1621 KiB

Open AccessArticle

Optimal Sizing of a Hybrid Wind-Photovoltaic-Battery Plant to Mitigate Output Fluctuations in a Grid-Connected System

by Abdullah Al Shereiqi, Amer Al-Hinai, Mohammed Albadi and Rashid Al-Abri

Energies 2020, 13(11), 3015; https://doi.org/10.3390/en13113015 - 11 Jun 2020

Cited by 11 | Viewed by 2877

Abstract

A novel optimization strategy is proposed to achieve a reliable hybrid plant of wind, solar, and battery (HWSPS). This strategy’s purpose is to reduce the power losses in a wind farm and at the same time reduce the fluctuations in the output of [...] Read more.

A novel optimization strategy is proposed to achieve a reliable hybrid plant of wind, solar, and battery (HWSPS). This strategy’s purpose is to reduce the power losses in a wind farm and at the same time reduce the fluctuations in the output of HWSPS generation. In addition, the proposed strategy is different from previous studies in that it does not involve a load demand profile. The process of defining the HWSPS capacity is carried out in two main stages. In the first stage, an optimal wind farm is determined using the genetic algorithm subject to site dimensions and spacing between the turbines, taking Jensen’s wake effect model into consideration to eliminate the power losses due to the wind turbines’ layout. In the second stage, a numerical iterative algorithm is deployed to get the optimal combination of photovoltaic and energy storage system sizes in the search space based on the wind reference power generated by the moving average. The reliability indices and cost are the basis for obtaining the optimal combination of photovoltaic and energy storage system according to a contribution factor with 100 different configurations. A case study in Thumrait in the Sultanate of Oman is used to verify the usefulness of the proposed optimal sizing approach. Full article

(This article belongs to the Special Issue Energy Storage Integrated Process Systems)

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15 pages, 512 KiB

Open AccessArticle

Biological Waste Management in the Case of a Pandemic Emergency and Other Natural Disasters. Determination of Bioenergy Production from Floricultural Waste and Modeling of Methane Production Using Deep Neural Modeling Methods

by Jakub Frankowski, Maciej Zaborowicz, Jacek Dach, Wojciech Czekała and Jacek Przybył

Energies 2020, 13(11), 3014; https://doi.org/10.3390/en13113014 - 11 Jun 2020

Cited by 19 | Viewed by 2450

Abstract

In relation to the situation caused by the pandemic, which may also take place in the future, there is a need to find effective solutions to improve the economic situation of the floristry industry. The production and sale of flowers is time-consuming and [...] Read more.

In relation to the situation caused by the pandemic, which may also take place in the future, there is a need to find effective solutions to improve the economic situation of the floristry industry. The production and sale of flowers is time-consuming and long-term. Therefore, any information that causes the impossibility of selling the plants will result in a reduction of profitability or bankruptcy of such companies. Research on rationally utilizing biowaste from plant cultivation as well as unsold flowers for environmental protection and effective use of their potential as a raw material for bioenergy production were examined in this article. The aim of this study was to analyze the energetic potential of the biodegradable fraction of waste from floriculture. The trials included floricultural waste containing the stems, leaves and flowers of different species and hybrid tulips (Tulipa L.), roses (Rosa L.), sunflowers (Helianthus L.) and chrysanthemums (Dendranthema Des Moul.). Their biogas and methane production as well as heat of combustion were determined experimentally. The calorific value was calculated on the basis of results from selected floricultural waste and its chemical composition. The biogas production was tested on different levels of plant material fragmentation (chaff, macerate) in fermentation processes with two ranges of temperature (meso- and thermophilic fermentation). The presented results show that the highest calorific values were determined for dry stems of roses (18,520 kJ/kg) and sunflowers (18,030 kJ/kg). In turn, the lowest were obtained for dried chrysanthemums and tulips, for which the heating value reached 15,560 kJ/kg and 15,210 kJ/kg. In addition, based on one ton of the fresh mass of biowaste from floriculture, the largest biogas production including the control was obtained from the chrysanthemum chaff by mesophilic anaerobic digestion. Moreover, the largest volume of methane was received by thermophilic anaerobic digestion of roses. The highest content of biomethane (56.68%) was reached by thermophilic fermentation of roses. The energy production of the analyzed substrates was also calculated, based on the amount of biogas produced in the containers for anaerobic digestion. Additionally, a deep neural network model, which predicted the production of methane gas, was created. Owing to the properties of the network, the level of significance of variables used for modelling and prediction of biogas production was determined. The neural modelling process was carried out with the use of the H₂O program. Full article

(This article belongs to the Section A4: Bio-Energy)

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19 pages, 5360 KiB

Open AccessReview

A Review on Bio-Based Catalysts (Immobilized Enzymes) Used for Biodiesel Production

by Samuel Santos, Jaime Puna and João Gomes

Energies 2020, 13(11), 3013; https://doi.org/10.3390/en13113013 - 11 Jun 2020

Cited by 60 | Viewed by 4627

Abstract

The continuous increase of the world’s population results in an increased demand for energy drastically from the industrial and domestic sectors as well. Moreover, the current public awareness regarding issues such as pollution and overuse of petroleum fuel has resulted in the development [...] Read more.

The continuous increase of the world’s population results in an increased demand for energy drastically from the industrial and domestic sectors as well. Moreover, the current public awareness regarding issues such as pollution and overuse of petroleum fuel has resulted in the development of research approaches concerning alternative renewable energy sources. Amongst the various options for renewable energies used in transportation systems, biodiesel is considered the most suitable replacement for fossil-based diesel. In what concerns the industrial application for biodiesel production, homogeneous catalysts such as sodium hydroxide, potassium hydroxide, sulfuric acid, and hydrochloric acid are usually selected, but their removal after reaction could prove to be rather complex and sometimes polluting, resulting in increases on the production costs. Therefore, there is an open field for research on new catalysts regarding biodiesel production, which can comprise heterogeneous catalysts. Apart from that, there are other alternatives to these chemical catalysts. Enzymatic catalysts have also been used in biodiesel production by employing lipases as biocatalysts. For economic reasons, and reusability and recycling, the lipases urged to be immobilized on suitable supports, thus the concept of heterogeneous biocatalysis comes in existence. Just like other heterogeneous catalytic materials, this one also presents similar issues with inefficiency and mass-transfer limitations. A solution to overcome the said limitations can be to consider the use of nanostructures to support enzyme immobilization, thus obtaining new heterogeneous biocatalysts. This review mainly focuses on the application of enzymatic catalysts as well as nano(bio)catalysts in transesterification reaction and their multiple methods of synthesis. Full article

(This article belongs to the Collection Feature Papers in Bio-Energy)

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20 pages, 978 KiB

Open AccessArticle

Modeling the Price Stability and Predictability of Post Liberalized Gas Markets Using the Theory of Information

by Anis Hoayek, Hassan Hamie and Hans Auer

Energies 2020, 13(11), 3012; https://doi.org/10.3390/en13113012 - 11 Jun 2020

Cited by 1 | Viewed by 2497

Abstract

Energy markets in the United States and Europe are getting more liberalized. The question of whether the liberalization of the gas industry in both markets has led to stable prices and less concentrated markets has appealed great interest among the scientific community. This [...] Read more.

Energy markets in the United States and Europe are getting more liberalized. The question of whether the liberalization of the gas industry in both markets has led to stable prices and less concentrated markets has appealed great interest among the scientific community. This study aims to measure the power and efficiency of an information structure contained in the gas prices time series. This assessment is useful to the oversight duty of regulators in such markets in the post liberalized era. First, econometric and mathematical methods based on game theory, records theory, and Shannon entropy are used to measure the following indicators: level of competition, price stability, and price uncertainty respectively—for both markets. Second, the level of information generated by these indicators is quantified using the information theory. The results of this innovative two-step approach show that the functioning of the European market requires the regulator’s intervention. This intervention is done by applying additional rules to enhance the competitive aspect of the market. This is not that case for the U.S. market. Also, the value of the information contained in both markets’ wholesale gas prices, although in asymmetric terms, is significant, and therefore proves to be an important instrument for the regulators. Full article

(This article belongs to the Special Issue Operation, Regulation and Planning of Power and Natural Gas Systems)

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14 pages, 3577 KiB

Open AccessArticle

Efficient Unbalanced Three-Phase Network Modelling for Optimal PV Inverter Control

by Chi-Thang Phan-Tan and Martin Hill

Energies 2020, 13(11), 3011; https://doi.org/10.3390/en13113011 - 11 Jun 2020

Cited by 2 | Viewed by 2042

Abstract

High penetration levels of renewable energy generation in the distribution network require voltage regulation to avoid excessive voltage at generating nodes. To effectively control the network and optimize network hosting capacity, the distribution system operator must have an efficient model for power flow [...] Read more.

High penetration levels of renewable energy generation in the distribution network require voltage regulation to avoid excessive voltage at generating nodes. To effectively control the network and optimize network hosting capacity, the distribution system operator must have an efficient model for power flow analysis. This paper presents the formulas and steps to express the power flow analysis equations of an unbalanced 3-phase network in matrix form suited to programmed solutions. A benchmark MATLAB/Simulink network with unbalanced distribution lines, photovoltaic inverters, and loads is built to verify the matrix model. To demonstrate the application of the model, the control of reverse energy flow from the photovoltaic inverters to keep the voltage in the network below the regulated level is simulated. Two decentralized control algorithms are applied in the network, including an on/off and a multi-objective constrained optimization controller. The detailed construction of the optimization problem for the 3-phase network in matrix form, which is consistent with the power flow calculation, is described. Simulation with the control methods over a day shows that the total active power of the on/off and optimized controllers deliver 41.92% and 99.39% of the available solar power, respectively, while maintaining the network node voltages within limits. Full article

(This article belongs to the Special Issue Dynamic Scheduling, Optimisation and Control of Futures Smart Grids)

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21 pages, 5954 KiB

Open AccessArticle

A Novel Voltage Injection Based Offline Parameters Identification for Current Controller Auto Tuning in SPMSM Drives

by Jiang Long, Ming Yang, Yangyang Chen, Dianguo Xu and Frede Blaabjerg

Energies 2020, 13(11), 3010; https://doi.org/10.3390/en13113010 - 11 Jun 2020

Cited by 7 | Viewed by 2164

Abstract

This paper presents a comprehensive study on a novel voltage injection based offline parameter identification method for surface mounted permanent magnet synchronous motors (SPMSMs). It gives solutions to obtain stator resistance, d- and q-axes inductances, and permanent magnet (PM) flux linkage [...] Read more.

This paper presents a comprehensive study on a novel voltage injection based offline parameter identification method for surface mounted permanent magnet synchronous motors (SPMSMs). It gives solutions to obtain stator resistance, d- and q-axes inductances, and permanent magnet (PM) flux linkage that are totally independent of current and speed controllers, and it is able to track variations in q-axis inductance caused by magnetic saturation. With the proposed voltage amplitude selection strategies, a closed-loop-like current and speed control is achieved throughout the identification process. It provides a marked difference compared with the existing methods that are based on open-loop voltage injection and renders a more simplified and industry-friendly solution compared with methods that rely on controllers. Inverter nonlinearity effect compensation is not required because its voltage error is removed by enabling the motor to function at a designed routine. The proposed method is validated through two SPMSMs with different power rates. It shows that the required parameters can be accurately identified and the proportional-integral current controller auto-tuning is achieved only with very limited motor data such as rated current and number of pole pairs. Full article

(This article belongs to the Section E: Electric Vehicles)

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18 pages, 6143 KiB

Open AccessArticle

The Application of the Bispectrum Analysis to Detect the Rotor Unbalance of the Induction Motor Supplied by the Mains and Frequency Converter

by Pawel Ewert

Energies 2020, 13(11), 3009; https://doi.org/10.3390/en13113009 - 11 Jun 2020

Cited by 10 | Viewed by 2677

Abstract

This article presents the effectiveness of bispectrum analysis for the detection of the rotor unbalance of an induction motor supplied by the mains and a frequency converter. Two diagnostic signals were analyzed, as well as the stator current and mechanical vibrations of the [...] Read more.

This article presents the effectiveness of bispectrum analysis for the detection of the rotor unbalance of an induction motor supplied by the mains and a frequency converter. Two diagnostic signals were analyzed, as well as the stator current and mechanical vibrations of the tested motors. The experimental tests were realized for two low-power induction motors, with one and two pole pairs, respectively. The unbalance was modeled using a test mass mounted on a specially prepared disc and directly on the rotor and the influence of this unbalance location was tested and discussed. The results of the bispectrum analysis are compared with results of Fourier transform and the effectiveness of unbalance detection are discussed and compared. The influence of the registration time of the analyzed signal on the quality of fault symptom analyses using both transforms was also tested. It is shown that the bispectrum analysis provides an increased number of fault symptoms in comparison with the classical spectral analysis as well as it is not sensitive to a shorter registration time of the diagnostic signals. Full article

(This article belongs to the Special Issue Modern Electrical Drives: Trends, Problems, and Challenges)

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20 pages, 2944 KiB

Open AccessArticle

Enhanced Cooling of LED Filament Bulbs Using an Embedded Tri-Needle/Ring Ionic Wind Device

by Chunlin Xu, Huai Zheng, Jie Liu, Jingcao Chu, Xiaoliang Zeng, Rong Sun and Sheng Liu

Energies 2020, 13(11), 3008; https://doi.org/10.3390/en13113008 - 11 Jun 2020

Cited by 6 | Viewed by 2484

Abstract

Improving the heat dissipation ability for light-emitting diode (LED) filament bulb is very difficult. A tri-needle/ring ionic wind generator was developed to improve the heat dissipation condition of bulbs. The operation characteristics of the ionic wind generator, such as the electrode gap, inception [...] Read more.

Improving the heat dissipation ability for light-emitting diode (LED) filament bulb is very difficult. A tri-needle/ring ionic wind generator was developed to improve the heat dissipation condition of bulbs. The operation characteristics of the ionic wind generator, such as the electrode gap, inception voltage, and discharge current with regard to the operation voltage, were studied by experiments. The ionic wind velocity within the bulb was investigated under different electrode gaps and applied voltages. The temperature drop achieved by the ionic was were tested with the consideration of many operation parameters for analysis. The experiments showed that ionic wind can provide efficient and stable cooling effect for LED filament bulbs. The temperature drop of LED junction can reach 30 °C at best. Good stability and adjustability of the ionic wind generator were demonstrated by tracing the temperature history of LED filaments in long-term tests. Finally, the light efficiency of LED filament bulbs with ionic wind cooling was studied. The experimental results showed that light efficiency was improved by 7.3% under the best cooling case. The experimental results indicate that the embedded ionic wind generator can provide an effective solution for cooling LED filament bulbs. Full article

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

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11 pages, 1105 KiB

Open AccessArticle

Pipe Hydraulic Resistances Identification of District Heating Networks Based on Matrix Analysis

by Yongxin Liu, Peng Wang and Peng Luo

Energies 2020, 13(11), 3007; https://doi.org/10.3390/en13113007 - 11 Jun 2020

Cited by 4 | Viewed by 1712

Abstract

District heating networks (DHNs) are essential municipal infrastructure in the north of China. Obtaining accurate resistance characteristics is a critical step to improve the operating regulation level of DHNs. In this paper, pipe hydraulic resistances (PHRs) are introduced to express the resistance characteristics. [...] Read more.

District heating networks (DHNs) are essential municipal infrastructure in the north of China. Obtaining accurate resistance characteristics is a critical step to improve the operating regulation level of DHNs. In this paper, pipe hydraulic resistances (PHRs) are introduced to express the resistance characteristics. A hydraulic model of a DHN can be established by using observed data of pressures and discharges. The boundary nodes are taken as observed sites. After establishing a matrix equation and analyzing the rank of its coefficient matrix, the authors propose a method to determine all the PHRs uniquely, by using a small number of observed sites and operating conditions. Furthermore, when observed errors are introduced, the adverse impact can be weakened by increasing the number of operating conditions and the accuracy of observed devices. When the observed error ranges are 1% and 0.5%, the results show that the average relative errors of identified PHRs are 2.4% and 1.1% respectively, which can be acceptable in engineering. Then, a loop DHN can be transformed into several branch DHNs, which are identified individually. Full article

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20 pages, 3648 KiB

Open AccessArticle

Study of the Effect of Addition of Hydrogen to Natural Gas on Diaphragm Gas Meters

by Jacek Jaworski, Paweł Kułaga and Tomasz Blacharski

Energies 2020, 13(11), 3006; https://doi.org/10.3390/en13113006 - 11 Jun 2020

Cited by 47 | Viewed by 5303

Abstract

Power-to-gas technology plays a key role in the success of the energy transformation. This paper addresses issues related to the legal and technical regulations specifying the rules for adding hydrogen to the natural gas network. The main issue reviewed is the effects of [...] Read more.

Power-to-gas technology plays a key role in the success of the energy transformation. This paper addresses issues related to the legal and technical regulations specifying the rules for adding hydrogen to the natural gas network. The main issue reviewed is the effects of the addition of hydrogen to natural gas on the durability of diaphragm gas meters. The possibility of adding hydrogen to the gas network requires confirmation of whether, within the expected hydrogen concentrations, long-term operation of gas meters will be ensured without compromising their metrological properties and operational safety. Methods for testing the durability of gas meters applied at test benches and sample results of durability tests of gas meters are presented. Based on these results, a metrological and statistical analysis was carried out to establish whether the addition of hydrogen affects the durability of gas meters over time. The most important conclusion resulting from the conducted study indicates that, for the tested gas meter specimens, there was no significant metrological difference between the obtained changes of errors of indications after testing the durability of gas meters with varying hydrogen content (from 0% to 15%). Full article

(This article belongs to the Section A5: Hydrogen Energy)

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28 pages, 2056 KiB

Open AccessArticle

Multiple Site Intraday Solar Irradiance Forecasting by Machine Learning Algorithms: MGGP and MLP Neural Networks

by Gabriel Mendonça de Paiva, Sergio Pires Pimentel, Bernardo Pinheiro Alvarenga, Enes Gonçalves Marra, Marco Mussetta and Sonia Leva

Energies 2020, 13(11), 3005; https://doi.org/10.3390/en13113005 - 11 Jun 2020

Cited by 34 | Viewed by 3480

Abstract

The forecasting of solar irradiance in photovoltaic power generation is an important tool for the integration of intermittent renewable energy sources (RES) in electrical utility grids. This study evaluates two machine learning (ML) algorithms for intraday solar irradiance forecasting: multigene genetic programming (MGGP) [...] Read more.

The forecasting of solar irradiance in photovoltaic power generation is an important tool for the integration of intermittent renewable energy sources (RES) in electrical utility grids. This study evaluates two machine learning (ML) algorithms for intraday solar irradiance forecasting: multigene genetic programming (MGGP) and the multilayer perceptron (MLP) artificial neural network (ANN). MGGP is an evolutionary algorithm white-box method and is a novel approach in the field. Persistence, MGGP and MLP were compared to forecast irradiance at six locations, within horizons from 15 to 120 min, in order to compare these methods based on a wide range of reliable results. The assessment of exogenous inputs indicates that the use of additional weather variables improves irradiance forecastability, resulting in improvements of 5.68% for mean absolute error (MAE) and 3.41% for root mean square error (RMSE). It was also verified that iterative predictions improve MGGP accuracy. The obtained results show that location, forecast horizon and error metric definition affect model accuracy dominance. Both Haurwitz and Ineichen clear sky models have been implemented, and the results denoted a low influence of these models in the prediction accuracy of multivariate ML forecasting. In a broad perspective, MGGP presented more accurate and robust results in single prediction cases, providing faster solutions, while ANN presented more accurate results for ensemble forecasting, although it presented higher complexity and requires additional computational effort. Full article

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

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17 pages, 9906 KiB

Open AccessArticle

Wake Statistics of Different-Scale Wind Turbines under Turbulent Boundary Layer Inflow

by Xiaolei Yang, Daniel Foti, Christopher Kelley, David Maniaci and Fotis Sotiropoulos

Energies 2020, 13(11), 3004; https://doi.org/10.3390/en13113004 - 11 Jun 2020

Cited by 4 | Viewed by 2662

Abstract

Subscale wind turbines can be installed in the field for the development of wind technologies, for which the blade aerodynamics can be designed in a way similar to that of a full-scale wind turbine. However, it is not clear whether the wake of [...] Read more.

Subscale wind turbines can be installed in the field for the development of wind technologies, for which the blade aerodynamics can be designed in a way similar to that of a full-scale wind turbine. However, it is not clear whether the wake of a subscale turbine, which is located closer to the ground and faces different incoming turbulence, is also similar to that of a full-scale wind turbine. In this work we investigate the wakes from a full-scale wind turbine of rotor diameter 80 m and a subscale wind turbine of rotor diameter of 27 m using large-eddy simulation with the turbine blades and nacelle modeled using actuator surface models. The blade aerodynamics of the two turbines are the same. In the simulations, the two turbines also face the same turbulent boundary inflows. The computed results show differences between the two turbines for both velocity deficits and turbine-added turbulence kinetic energy. Such differences are further analyzed by examining the mean kinetic energy equation. Full article

(This article belongs to the Special Issue Numerical Simulation of Wind Turbines)

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10 pages, 1884 KiB

Open AccessFeature PaperArticle

A Novel Approach for the Determination of Sorption Equilibria and Sorption Enthalpy Used for MOF Aluminium Fumarate with Water

by Eric Laurenz, Gerrit Füldner, Lena Schnabel and Gerhard Schmitz

Energies 2020, 13(11), 3003; https://doi.org/10.3390/en13113003 - 11 Jun 2020

Cited by 5 | Viewed by 2176

Abstract

Adsorption chillers offer an environmentally friendly solution for the valorisation of waste or solar heat for cooling demands. A recent application is high efficiency data centre cooling, where heat from CPUs is used to drive the process, providing cooling for auxiliary loads. The [...] Read more.

Adsorption chillers offer an environmentally friendly solution for the valorisation of waste or solar heat for cooling demands. A recent application is high efficiency data centre cooling, where heat from CPUs is used to drive the process, providing cooling for auxiliary loads. The metal organic framework aluminium fumarate with water is potentially a suitable material pair for this low temperature driven application. A targeted heat exchanger design is a prerequisite for competitiveness, requiring, amongst other things, a sound understanding of adsorption equilibria and adsorption enthalpy. A novel method is employed for their determination based on small isothermal and isochoric state changes, applied with an apparatus developed initially for volume swing frequency response measurement, to samples with a binder-based adsorbent coating. The adsorption enthalpy is calculated through the Clausius–Clapeyron equation from the obtained slopes of the isotherm and isobar, while the absolute uptake is determined volumetrically. The isotherm confirms the step-like form known for aluminium fumarate, with a temperature dependent inflection point at

p_{rel} \approx

0.25, 0.28 and 0.33 for 30 °C, 40 °C and 60 °C. The calculated differential enthalpy of adsorption is 2.90 ± 0.05 MJ/kg (52.2 ± 1.0 kJ/mol) on average, which is about 10–15% higher than expected by a simple Dubinin approximation. Full article

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21 pages, 6655 KiB

Open AccessArticle

Techno-Economic Analysis of Biofuel, Solar and Wind Multi-Source Small-Scale CHP Systems

by Angelo Algieri, Pietropaolo Morrone and Sergio Bova

Energies 2020, 13(11), 3002; https://doi.org/10.3390/en13113002 - 11 Jun 2020

Cited by 17 | Viewed by 2863

Abstract

The aim of the paper is the techno-economic analysis of innovative integrated combined heat and power (CHP) systems for the exploitation of different renewable sources in the residential sector. To this purpose, a biofuel-driven organic Rankine cycle (ORC) is combined with a wind [...] Read more.

The aim of the paper is the techno-economic analysis of innovative integrated combined heat and power (CHP) systems for the exploitation of different renewable sources in the residential sector. To this purpose, a biofuel-driven organic Rankine cycle (ORC) is combined with a wind turbine, a photovoltaic system and an auxiliary boiler. The subsystems work in parallel to satisfy the electric and heat demand of final users: a block of 40 dwellings in a smart community. A 12.6 kW_el ORC is selected according to a thermal-driven strategy, while wind and solar subsystems are introduced to increase the global system efficiency and the electric self-consumption. The ORC can be switched-off or operated at partial load when solar and/or wind sources are significant. A multi-variable optimization has been carried out to find the proper size of the wind turbine and photovoltaic subsystems and to define the suitable operating strategy. To this purpose, several production wind turbines (1.0–60.0 kW_el) and photovoltaic units (0.3–63.0 kW_el) have been considered with the aim of finding the optimal trade-off between the maximum electric self-consumption and the minimum payback period and electric surplus. The multi-objective optimization suggests the integration of 12.6 kW_el ORC with 10 kW_el wind turbine and 6.3 kW_el photovoltaic subsystem. The investigation demonstrates that the proposed multi-source integrated system offers a viable solution for smart-communities and distributed energy production with a significant improvement in the global system efficiency (+7.5%) and self-consumption (+15.0%) compared to the sole ORC apparatus. Full article

(This article belongs to the Special Issue Multi-Source Energy Systems)

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43 pages, 14356 KiB

Open AccessArticle

Efficient History Matching of Thermally Induced Fractures Using Coupled Geomechanics and Reservoir Simulation

by Misfer Almarri

Energies 2020, 13(11), 3001; https://doi.org/10.3390/en13113001 - 11 Jun 2020

Cited by 3 | Viewed by 2174

Abstract

Waterflooding is a common recovery method used to maintain reservoir pressure and improve reservoir oil sweep efficiency. However, injecting cold water into a reservoir alters the state of in-situ formation stress and can result in the formation fracturing. In other words, it can [...] Read more.

Waterflooding is a common recovery method used to maintain reservoir pressure and improve reservoir oil sweep efficiency. However, injecting cold water into a reservoir alters the state of in-situ formation stress and can result in the formation fracturing. In other words, it can cause the initiation and growth of thermally induced fractures (TIFs), even when the original fracture propagation pressure is not exceeded. TIFs can cause non-uniform distribution of the fluid flow in wellbores, a reduction in sweep efficiency, and early water breakthrough in nearby production wells. Modelling and history matching workflows that consider the dynamic nature of the TIF problem are critical. These workflows improve and validate reservoir and geomechanical models, identify and confirm observed TIF onset and propagation periods, and provide a history-matched sector model with the rock mechanical and thermal properties and stress gradients that can be used with confidence for subsequent studies. Modelling and the underlining assumptions of fluid flow in the TIF and reservoir matrix, as well as geomechanical changes due to cooling of the reservoir during injection, are detailed below. A 3D reservoir simulator coupled with 2D finite element TIF and geomechanical models were used to manually history match an injector (NI6) in the N Field sector reservoir model in which a TIF was observed. In this study, history matching workflows were developed to consider the dynamic nature of TIF development during waterflooding. The reservoir and geomechanical models were improved and validated via the observed TIF onset and propagation periods. The history-matched models produced can be used with confidence in subsequent studies. The practical workflows and guidelines developed here can be used in waterflooding operations during the modelling, design, and planning stages. The novelty of this study is the coupling approach of different complex processes done in order to capture dynamic changes during waterflooding operations. A similar history matching study could not be found in the literature. Full article

(This article belongs to the Special Issue Mathematical Modeling of Fluid Flow and Heat Transfer in Petroleum Industries and Geothermal Applications 2020)

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16 pages, 6574 KiB

Open AccessArticle

The Effect of Biomass Pellet Length, Test Conditions and Torrefaction on Mechanical Durability Characteristics According to ISO Standard 17831-1

by Hamid Gilvari, Wiebren De Jong and Dingena L. Schott

Energies 2020, 13(11), 3000; https://doi.org/10.3390/en13113000 - 11 Jun 2020

Cited by 23 | Viewed by 2699

Abstract

With the recent increase in biomass pellet consumption, the mechanical degradation of pellets during transport and handling has become more important. ISO standard 17831-1 is an accepted global standard that is commonly used amongst researchers and industries to determine the mechanical durability of [...] Read more.

With the recent increase in biomass pellet consumption, the mechanical degradation of pellets during transport and handling has become more important. ISO standard 17831-1 is an accepted global standard that is commonly used amongst researchers and industries to determine the mechanical durability of pellets. However, the measured mechanical durability sometimes fails to match the certificate accompanying the shipment. In such cases, pellet length specifications are suspected to play a role. This paper studies the effect of pellet length on mechanical durability for various types of commercially produced biomass pellets. In addition, the effect of test conditions and torrefaction on the mechanical durability of biomass pellets has been investigated. To study the effect of pellet length, pellets were classified into three groups: shorter than 15 mm, 15 to 30 mm, and longer than 30 mm, and their length distributions were measured using an in-house image processing tool. Then, the mechanical durability of pellets was measured using ISO standard 17831-1. The mechanical durability results were compared to random-sized pellet samples. To study the effect of test conditions, the mechanical durability test was operated at different time intervals to elucidate the effect of tumbling at different conditions. The results show that the mechanical durability depends highly on the length distribution of the pellets, with a difference between categories of up to 13%. It was also observed that the mechanical durability remains relatively constant after a specific time interval. Based on the results, we highly recommend modifying the current ISO standard to account for the pellet length distribution (PLD). Full article

(This article belongs to the Special Issue Wood-Based Bioenergy)

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