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Volume 14, April-1

Energies, Volume 14, Issue 8 (April-2 2021) – 183 articles

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Open AccessArticle
Study on the Implementation of a Solar Photovoltaic System with Self-Consumption in an Educational Building
Energies 2021, 14(8), 2214; https://doi.org/10.3390/en14082214 (registering DOI) - 15 Apr 2021
Abstract
In this work, the study of different remuneration schemes for the implementation of a solar energy system on a building was performed. The photovoltaic system was implemented on a public educational building, and four different schemes are compared to understand the economic feasibility [...] Read more.
In this work, the study of different remuneration schemes for the implementation of a solar energy system on a building was performed. The photovoltaic system was implemented on a public educational building, and four different schemes are compared to understand the economic feasibility of self-consuming solar energy with and without a battery system, versus selling to the electricity grid. The system performance is compared to the building’s needs, and the different consumption and grid-injection shares are analyzed. Three of the schemes are applied according to the conditions and requirements of the Portuguese Law, while the remaining one is not yet allowed, and so the legislation from another chosen country is considered. Lastly, a financial analysis was performed to evaluate and compare the feasibility of each project implementation. The results of this analysis show that both the non-legislated and legislated self-consumption schemes make for an attractive investment, and that savings resulting from the consumption of solar energy are much higher than the revenues from selling to the grid, which presents as the least attractive scheme. Finally, the battery implementation also does not show feasibility because the cost of technology is still too high, despite the reduction witnessed in recent years. Full article
(This article belongs to the Section Solar Energy and Photovoltaic Systems)
Open AccessArticle
Impact of Advanced Load-Frequency Control on Optimal Size of Battery Energy Storage in Islanded Microgrid System
Energies 2021, 14(8), 2213; https://doi.org/10.3390/en14082213 (registering DOI) - 15 Apr 2021
Abstract
The application of battery energy storage (BES) in microgrid systems has attracted much attention in recent years. It is because the BES is able to store excess power and discharge its power when needed. In islanded microgrid systems, BES is starting to be [...] Read more.
The application of battery energy storage (BES) in microgrid systems has attracted much attention in recent years. It is because the BES is able to store excess power and discharge its power when needed. In islanded microgrid systems, BES is starting to be considered as a unit that can regulate the system frequency. The control used in the BES to display frequency regulation performance is called load-frequency control (LFC). However, this participation resulted in the large size of the battery and high expansion planning cost. In this paper, an advanced LFC control that has frequency limitation compared to traditional LFC is proposed. The proposed control implies droop control as the base and has frequency limitations. Compared to the traditional LFC, the proposed control can reduce the system expansion planning costs. A performance simulation was done to validate battery performance. The results of the numerical simulation showed that the proposed control participated in reducing the operation cost. It directly led to a reduction in the expansion planning cost. A study of battery selection was conducted to draw the practicality of the BES sizing solutions. Full article
Open AccessArticle
The Energy Transition in the Visegrad Group Countries
Energies 2021, 14(8), 2212; https://doi.org/10.3390/en14082212 (registering DOI) - 15 Apr 2021
Abstract
The aim of the research is to analyse the energy transition in the Visegrad Group countries, because they depend on the production of energy from the burning of fossil fuels, and transition is a huge challenge for them. The diversity of the energy [...] Read more.
The aim of the research is to analyse the energy transition in the Visegrad Group countries, because they depend on the production of energy from the burning of fossil fuels, and transition is a huge challenge for them. The diversity of the energy transformation in the V4 countries was examined by using two qualitative methods, including literature analysis and comparative analysis. The timeframe of the study was set for the period from 2020 to 2030, as these years are crucial for the implementation of the European Green Deal Programme. Four diagnostic features were taken into account in the analysis: the share of RES in final energy consumption, reduction of CO2 emissions in the non-Emissions Trading System (ETS) sector, date of withdrawal of coal from the economy, and energy efficiency. The analysis shows that the V4 countries have different approaches and levels of energy transformation in their economies. Poland is in the most difficult situation, being the most dependent on the production of electricity from coal, as well as having the largest number of employees in the coal and around coal sector. The other countries of the group can base their transformation on nuclear energy, as each of them has at least four such power units. The increased use of biomass for energy and heat production is the most important stimulus for Renewable Energy Sources (RES) growth in the analysed countries. The ambivalent attitude of the political elite to unconventional sources in the four analysed countries significantly hinders the development of certain forms of green energy. However, it has been observed that an increasing proportion of the population, especially those living in regions of the country where there is no fossil fuel mining industry, has a positive attitude towards energy transformation. The study is the first that shows the state of involvement in the process of systemic change of the Visegrad Group countries. The results can serve as a starting point for understanding the reticence of this group of European countries towards the transformation phenomenon, as well as contributing to further research on the implementation of closed-circuit economies in the Visegrad Group countries. Full article
Open AccessArticle
Directional Hydraulic Characteristics of Reservoir Rocks for CO2 Geological Storage in the Pohang Basin, Southeast Korea
Energies 2021, 14(8), 2211; https://doi.org/10.3390/en14082211 (registering DOI) - 15 Apr 2021
Abstract
This study conducted core sampling of an offshore borehole for geological reservoir characterization of a potential CO2 storage site in southeast Korea. From this, two promising geological formations at ~739 and ~779 m were identified as prospective CO2 storage reservoirs. Injection [...] Read more.
This study conducted core sampling of an offshore borehole for geological reservoir characterization of a potential CO2 storage site in southeast Korea. From this, two promising geological formations at ~739 and ~779 m were identified as prospective CO2 storage reservoirs. Injection efficiency and CO2 migration were evaluated based on directional measurements of permeabilities from core plugs. The directional transport properties were determined using both a portable probe permeameter and a pressure cell capable of applying different in situ confining pressures. Both steady state and unsteady state measurements were used to determine permeability—the method selected according to the expected permeability range of the specific sample. This expected range was based on rapid screening measurements acquired using a portable probe permeameter (PPP). Anticipated performance of the prototypical CO2 injection site was evaluated based on flow modeling of the CO2 plume migration pathway including CO2 transport through the overlying formations based on the measured directional hydraulic properties. These analyses revealed that the injection efficiency at a depth of 739 m was double that at 779 m. These correlations among and distributions of the directional permeabilities of the potential CO2 geological storage site can be utilized for the assessment of CO2 storage capacity, injectivity, and leakage risk. Full article
(This article belongs to the Special Issue Challenges and Development on Carbon Capture and Storage)
Open AccessArticle
Fault Analysis and Non-Redundant Fault Tolerance in 3-Level Double Conversion UPS Systems Using Finite-Control-Set Model Predictive Control
Energies 2021, 14(8), 2210; https://doi.org/10.3390/en14082210 (registering DOI) - 15 Apr 2021
Abstract
Fault-tolerance is critical in power electronics, especially in Uninterruptible Power Supplies, given their role in protecting critical loads. Hence, it is crucial to develop fault-tolerant techniques to improve the resilience of these systems. This paper proposes a non-redundant fault-tolerant double conversion uninterruptible power [...] Read more.
Fault-tolerance is critical in power electronics, especially in Uninterruptible Power Supplies, given their role in protecting critical loads. Hence, it is crucial to develop fault-tolerant techniques to improve the resilience of these systems. This paper proposes a non-redundant fault-tolerant double conversion uninterruptible power supply based on 3-level converters. The proposed solution can correct open-circuit faults in all semiconductors (IGBTs and diodes) of all converters of the system (including the DC-DC converter), ensuring full-rated post-fault operation. This technique leverages the versatility of Finite-Control-Set Model Predictive Control to implement highly specific fault correction. This type of control enables a conditional exclusion of the switching states affected by each fault, allowing the converter to avoid these states when the fault compromises their output but still use them in all other conditions. Three main types of corrective actions are used: predictive controller adaptations, hardware reconfiguration, and DC bus voltage adjustment. However, highly differentiated corrective actions are taken depending on the fault type and location, maximizing post-fault performance in each case. Faults can be corrected simultaneously in all converters, as well as some combinations of multiple faults in the same converter. Experimental results are presented demonstrating the performance of the proposed solution. Full article
(This article belongs to the Special Issue Advances in Electric Drives and Power Electronics Fields)
Open AccessArticle
A Two-Dimensional Partitioning of Fracture–Matrix Flow in Fractured Reservoir Rock Using a Dual-Porosity Percolation Model
Energies 2021, 14(8), 2209; https://doi.org/10.3390/en14082209 (registering DOI) - 15 Apr 2021
Abstract
Fractures and micropores have varying contributions to the gas permeability of fractured reservoirs. The quantification of the contribution of fractures and micropores that form a dual-porosity system for gas permeability is critical when attempting to accurately evaluate gas production. However, due to insufficient [...] Read more.
Fractures and micropores have varying contributions to the gas permeability of fractured reservoirs. The quantification of the contribution of fractures and micropores that form a dual-porosity system for gas permeability is critical when attempting to accurately evaluate gas production. However, due to insufficient knowledge of fracture–matrix flow partitioning in such dual-porosity systems, it is challenging for previous models to quantitatively characterize the fracture heterogeneity and accurately evaluate the gas flow and permeability in fractured rocks. In this study, we propose a dual-porosity percolation model to quantitatively investigate the contributions of fractures and matrix micropores towards the gas permeability of fractured rocks. Using percolation theory, we establish fracture networks with complex heterogeneity, which are characterized by various fracture densities and percolation probabilities within a porous matrix with various fracture/matrix permeability ratios. The compressible Navier–Stokes and Brinkman equations were adopted to describe the gas flow in the fractures and porous matrix, respectively. The simulation results indicate that the gas permeability of the dual-porosity system has an exponential relationship with the fracture density and matrix permeability. The contribution of fractures and matrix micropores toward gas permeability can be classified by establishing a two-dimensional partitioning of the fracture–matrix flow related to the fracture heterogeneity and fracture/matrix permeability ratio. The contribution of matrix micropores cannot be neglected if the fracture density is lower than a critical value. Full article
Open AccessArticle
Stability Analysis of Shunt Active Power Filter with Predictive Closed-Loop Control of Supply Current
Energies 2021, 14(8), 2208; https://doi.org/10.3390/en14082208 (registering DOI) - 15 Apr 2021
Abstract
This paper presents a shunt active power filter connected to the grid via an LCL coupling circuit with implemented closed-loop control. The proposed control system allows selective harmonic currents compensation up to the 50th harmonic with the utilization of a model-based predictive current [...] Read more.
This paper presents a shunt active power filter connected to the grid via an LCL coupling circuit with implemented closed-loop control. The proposed control system allows selective harmonic currents compensation up to the 50th harmonic with the utilization of a model-based predictive current controller. As the system is fully predictive, it provides high effectiveness of the harmonic reduction, which is proved by waveforms achieved in performed tests. On the other hand, the control system is prone to loss of stability. Therefore, the paper is focused on the stability analysis of the discussed control system with the additional outer control loop of the supply current with predictive control of this current. The conducted stability analysis encompasses the assessment of system stability as a function of the coupling circuit parameter identification accuracy, whose values are implemented in the current controller, as well as parameters such as the sampling frequency and proportional–integral (PI) controller coefficients. The obtained results show that the ranges of the LCL circuit parameter identification accuracy for which the system remains stable are relatively wide. However, the most effective compensation of the supply current distortion is achieved for the parameters identified correctly, and the greatest impact on the compensation quality has the value of L1 inductance. Full article
(This article belongs to the Special Issue Active Power Filters and Power Quality)
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Open AccessArticle
Contribution of Wind Farms to the Stability of Power Systems with High Penetration of Renewables
Energies 2021, 14(8), 2207; https://doi.org/10.3390/en14082207 (registering DOI) - 15 Apr 2021
Abstract
Power system inertia is being reduced because of the increasing penetration of renewable energies, most of which use power electronic interfaces with the grid. This paper analyses the contribution of inertia emulation and droop control to the power system stability. Although inertia emulation [...] Read more.
Power system inertia is being reduced because of the increasing penetration of renewable energies, most of which use power electronic interfaces with the grid. This paper analyses the contribution of inertia emulation and droop control to the power system stability. Although inertia emulation may appear the best option to mitigate frequency disturbances, a thorough analysis of the shortcomings that face real-time implementations shows the opposite. Measurement noise and response delay for inertia emulation hinder controller performance, while the inherently fast droop response of electronic converters provides better frequency support. System stability, expressed in terms of rate of change of frequency (ROCOF) and frequency nadir, is therefore improved with droop control, compared to inertia emulation. Full article
(This article belongs to the Special Issue Modeling and Control of Wind Energy Conversion Systems)
Open AccessArticle
Model-Predictive-Control-Based Reference Governor for Fuel Cells in Automotive Application Compared with Performance from a Real Vehicle
Energies 2021, 14(8), 2206; https://doi.org/10.3390/en14082206 (registering DOI) - 15 Apr 2021
Abstract
In this paper, a real-time capable reference governor superordinate model predictive controller (RG-MPC) is developed for fuel cell (FC) control suitable for automotive application. The RG-MPC provides reference trajectories for the subordinate proportional-integral (PI) controllers, which act directly on the FC system. Antiwindup [...] Read more.
In this paper, a real-time capable reference governor superordinate model predictive controller (RG-MPC) is developed for fuel cell (FC) control suitable for automotive application. The RG-MPC provides reference trajectories for the subordinate proportional-integral (PI) controllers, which act directly on the FC system. Antiwindup and decoupling schemes, which are common problems in multivariable PI control, are unnecessary, given that the RG-MPC can inherently consider constraints and multivariable systems. The PI dynamics are incorporated into the prediction model used for control, ensuring the feasibility of the provided references for the PI controllers. The successive linearization technique is used in the RG-MPC to cope with the model’s nonlinear nature in real-time. The concept has been illustrated in a simulation scenario featuring efficient and safe power control of an FC stack in automotive application using real driving data obtained from an in-house-built FC vehicle. This work is the first step towards upgrading an existing, PI-based control scheme without the necessity of completely rebuilding the interface. Full article
Open AccessArticle
Improved Self-Sensing Speed Control of IPMSM Drive Based on Cascaded Nonlinear Control
Energies 2021, 14(8), 2205; https://doi.org/10.3390/en14082205 (registering DOI) - 15 Apr 2021
Abstract
This paper presents a nonlinear cascaded control design that has been developed to (1) improve the self-sensing speed control performance of an interior permanent magnet synchronous motor (IPMSM) drive by reducing its speed and torque ripples and its phase current harmonic distortion and [...] Read more.
This paper presents a nonlinear cascaded control design that has been developed to (1) improve the self-sensing speed control performance of an interior permanent magnet synchronous motor (IPMSM) drive by reducing its speed and torque ripples and its phase current harmonic distortion and (2) attain the maximum torque while utilizing the minimum drive current. The nonlinear cascaded control system consists of two nonlinear controls for the speed and current control loop. A fuzzy logic controller (FLC) is employed for the outer speed control loop to regulate the rotor shaft speed. Model predictive current control (MPCC) is utilized for the inner current control loop to regulate the drive phase currents. The nonlinear equation for the dq reference current is derived to implement the maximum torque per armature (MTPA) control to achieve the maximum torque while using the minimum current values. The model reference adaptive system (MRAS) was employed for the speed self-sensing mechanism. The self-sensing speed control performance of the IPMSM motor drive was compared with that of the traditional cascaded control schemes. The stability of the sensorless mechanism was studied using the pole placement method. The proposed nonlinear cascaded control was verified based on the simulation results. The robustness of the control design was ensured under various loads and in a wide speed range. The dynamic performance of the motor drive is improved while circumventing the need to tune the proportional-integral (PI) controller. The self-sensing speed control performance of the IPMSM drive was enhanced significantly by the designed cascaded control model. Full article
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Open AccessArticle
A General Framework for Multi-Criteria Based Feasibility Studies for Solar Energy Projects: Application to A Real-World Solar Farm
Energies 2021, 14(8), 2204; https://doi.org/10.3390/en14082204 (registering DOI) - 15 Apr 2021
Abstract
The growth of solar energy is projected to slow down during 2023–25 despite the fall in costs due to economic deceleration, reduced incentives, and market barriers including the lack of relevant and flexible energy project planning and decision-making tools. This study proposes a [...] Read more.
The growth of solar energy is projected to slow down during 2023–25 despite the fall in costs due to economic deceleration, reduced incentives, and market barriers including the lack of relevant and flexible energy project planning and decision-making tools. This study proposes a flexible and computationally simple multi-criteria decision analysis (MCDA)-based model that takes technical, financial, environmental, social and legal aspects of all project options as input and outputs a feasibility score for each option, which enables ranking the options and identifying the best alternative. The proposed model is applied to a real-world photovoltaic solar farm planned at a site in England and comprising nine different configurations formed by varying system capacity, energy storage option, mode of stakeholder, and network connections. The results of our study show that in this case the options without battery storage and a greater number of off-taker connections are more favorable than the options with battery storage. The analysis also shows that for the solar farm of the presented case study, ‘self-consumption fraction’ and ‘energy yield’, ‘net present value’, ‘life-cycle carbon emission reduction’, ‘ease of permit acquisition’ and ‘public approval’ are key sub-criteria for ‘technical’, ‘financial’, ‘environmental’, and ‘social and legal’ criteria, respectively. A sensitivity analysis was conducted to assess the confidence on the obtained solution, and a change in the first preference was noticed when ‘environmental’ and ‘social and legal’ aspects are given higher weight over ‘technical’ and ‘financial’ aspects. The results obtained are in line with the recommendations by experts, who carried out an independent feasibility analysis considering the same options. Full article
(This article belongs to the Special Issue Accelerating the Adoption of Solar Energy towards a Low-Carbon Future)
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Open AccessArticle
Sampling Primary Power Standard from DC up to 9 kHz Using Commercial Off-The-Shelf Components
Energies 2021, 14(8), 2203; https://doi.org/10.3390/en14082203 (registering DOI) - 15 Apr 2021
Abstract
In the framework of the empir projects myrails and windefcy, metas developed a primary standard for electrical power using commercial off-the-shelf components. The only custom part is the software that controls the sampling system and determines [...] Read more.
In the framework of the empir projects myrails and windefcy, metas developed a primary standard for electrical power using commercial off-the-shelf components. The only custom part is the software that controls the sampling system and determines the amplitude and phase of the different frequency components of voltage and current. The system operates from dc up to 9 kHz, even with distorted signals. The basic system is limited to 700 V and 21 A. Its power uncertainty is 15 μW/VA at power frequencies and increases to 1.8 mW/VA at 9 kHz. With the extension up to 1000 V and 360 A, the system reaches power uncertainties of 20 μW/VA at power frequencies, increasing to 510 μW/VA at 9 kHz. For higher voltages or higher currents, the same principle is used. However, the uncertainties are dominated by the stability of the sources. The voltage and current channels can also be used independently to calibrate and test power quality instruments. Thanks to a time-stamping system, the system can also be used to calibrate phasor measurement units, which are synchronised to utc. Full article
(This article belongs to the Special Issue 3rd International Colloquium on Smart Grid Metrology (SmaGriMet 2020))
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Open AccessArticle
Simulation Research on Regenerative Braking Control Strategy of Hybrid Electric Vehicle
Energies 2021, 14(8), 2202; https://doi.org/10.3390/en14082202 (registering DOI) - 15 Apr 2021
Abstract
This paper proposes a double layered multi parameters braking energy recovery control strategy for Hybrid Electric Vehicle, which can combine the mechanical brake system with the motor brake system in the braking process to achieve higher energy utilization efficiency and at the same [...] Read more.
This paper proposes a double layered multi parameters braking energy recovery control strategy for Hybrid Electric Vehicle, which can combine the mechanical brake system with the motor brake system in the braking process to achieve higher energy utilization efficiency and at the same time ensure that the vehicle has sufficient braking performance and safety performance. The first layer of the control strategy proposed in this paper aims to improve the braking force distribution coefficient of the front axle. On the basis of following the principle of braking force distribution, the braking force of the front axle and the rear axle is reasonably distributed according to the braking strength. The second layer is to obtain the proportional coefficient of regenerative braking, considering the influence of vehicle speed, braking strength, and power battery state of charge (SOC) on the front axle mechanical braking force and motor braking force distribution, and a three-input single-output fuzzy controller is designed to realize the coordinated control of mechanical braking force and motor braking force of the front axle. Finally, the AMESim and Matlab/Simulink co-simulation model was built; the braking energy recovery control strategy proposed in this paper was simulated and analyzed based on standard cycle conditions (the NEDC and WLTC), and the simulation results were compared with regenerative braking control strategies A and B. The research results show that the braking energy recovery rate of the proposed control strategy is respectively 2.42%, 18.08% and 2.56%, 16.91% higher than that of the control strategies A and B, which significantly improves the energy recovery efficiency of the vehicle. Full article
(This article belongs to the Special Issue Advanced Power Electronics in Hybrid Vehicles)
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Open AccessArticle
An Optimization Based Power Usage Scheduling Strategy Using Photovoltaic-Battery System for Demand-Side Management in Smart Grid
Energies 2021, 14(8), 2201; https://doi.org/10.3390/en14082201 (registering DOI) - 15 Apr 2021
Abstract
Due to rapid population growth, technology, and economic development, electricity demand is rising, causing a gap between energy production and demand. With the emergence of the smart grid, residents can schedule their energy usage in response to the Demand Response (DR) program offered [...] Read more.
Due to rapid population growth, technology, and economic development, electricity demand is rising, causing a gap between energy production and demand. With the emergence of the smart grid, residents can schedule their energy usage in response to the Demand Response (DR) program offered by a utility company to cope with the gap between demand and supply. This work first proposes a novel optimization-based energy management framework that adapts consumer power usage patterns using real-time pricing signals and generation from utility and photovoltaic-battery systems to minimize electricity cost, to reduce carbon emission, and to mitigate peak power consumption subjected to alleviating rebound peak generation. Secondly, a Hybrid Genetic Ant Colony Optimization (HGACO) algorithm is proposed to solve the complete scheduling model for three scenarios: without photovoltaic-battery systems, with photovoltaic systems, and with photovoltaic-battery systems. Thirdly, rebound peak generation is restricted by using Multiple Knapsack Problem (MKP) in the proposed algorithm. The presented model reduces the cost of using electricity, alleviates the peak load and peak-valley, mitigates carbon emission, and avoids rebound peaks without posing high discomfort to the consumers. To evaluate the applicability of the proposed framework comparatively with existing frameworks, simulations are conducted. The results show that the proposed HGACO algorithm reduced electricity cost, carbon emission, and peak load by 49.51%, 48.01%, and 25.72% in scenario I; by 55.85%, 54.22%, and 21.69% in scenario II, and by 59.06%, 57.42%, and 17.40% in scenario III, respectively, compared to without scheduling. Thus, the proposed HGACO algorithm-based energy management framework outperforms existing frameworks based on Ant Colony Optimization (ACO) algorithm, Particle Swarm Optimization (PSO) algorithm, Genetic Algorithm (GA), Hybrid Genetic Particle swarm Optimization (HGPO) algorithm. Full article
(This article belongs to the Special Issue Data-Intensive Computing in Smart Microgrids)
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Open AccessArticle
The Trend and Status of Energy Resources and Greenhouse Gas Emissions in the Malaysia Power Generation Mix
Energies 2021, 14(8), 2200; https://doi.org/10.3390/en14082200 (registering DOI) - 15 Apr 2021
Abstract
Environmental issues in energy policy, especially global warming, have received more attention lately than ever before. Excessive dependence on fossil fuels, deforestation, and land degradation are the three main factors that lead to increased carbon dioxide (CO2) emissions. Consequently, the global [...] Read more.
Environmental issues in energy policy, especially global warming, have received more attention lately than ever before. Excessive dependence on fossil fuels, deforestation, and land degradation are the three main factors that lead to increased carbon dioxide (CO2) emissions. Consequently, the global average temperature has doubled compared to anticipation. Various international protocols and agendas have been established, pledged to restore the global average temperature to the 1990 level. As a result, energy policies worldwide have also undergone various transformations to align with these protocols since then. As a developing nation, Malaysian’s electricity demand has continuously grown in the past two decades. To date, the electricity sector is still dominated by fossil fuels. Government incentives have been the most influential factor in the nation’s energy mix trend. Several energy policies implemented throughout the past 22 years have seen the shift from natural gas to coal power in power plants, and in more recent years, renewable energy resources. Numerous studies in the past have independently outlined the status of various energy source in Malaysia. However, they all fell short in providing the greenhouse gas (GHG) emissions in the Malaysian energy sector. Notably, the question that remains to be answered is how GHG emissions have changed in response to the amendment in the energy mix; hence, the effectiveness of policy change in this aspect remains unknown. This paper analysed the past and present trend of Malaysia electricity generation mix and the resultant GHG emissions. In particular, this paper focused on investigating the variation of combined specific GHG emissions in the Malaysian electricity sector, in response to the policy change within the past 22 years. This provides the insight for Malaysian policymakers to evaluate the effectiveness of past policies in GHG emissions and the measures to be taken in future. The finding of this paper shows the attention on the nation’s GHG emissions has evolved over the years, following the diversification in energy mix driven by the policy change. It was also found that, on average, it took a decade for a significant reduction in specific GHG emission to be visible since the government’s energy policy implementation. Full article
(This article belongs to the Special Issue Life Cycle Assessment of Environmental System)
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Open AccessReview
Hydrolytic Dehydrogenation of Ammonia Borane Attained by Ru-Based Catalysts: An Auspicious Option to Produce Hydrogen from a Solid Hydrogen Carrier Molecule
Energies 2021, 14(8), 2199; https://doi.org/10.3390/en14082199 (registering DOI) - 15 Apr 2021
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Abstract
Chemical hydrogen storage stands as a promising option to conventional storage methods. There are numerous hydrogen carrier molecules that afford satisfactory hydrogen capacity. Among them, ammonia borane has attracted great interest due to its high hydrogen capacity. Great efforts have been devoted to [...] Read more.
Chemical hydrogen storage stands as a promising option to conventional storage methods. There are numerous hydrogen carrier molecules that afford satisfactory hydrogen capacity. Among them, ammonia borane has attracted great interest due to its high hydrogen capacity. Great efforts have been devoted to design and develop suitable catalysts to boost the production of hydrogen from ammonia borane, which is preferably attained by Ru catalysts. The present review summarizes some of the recent Ru-based heterogeneous catalysts applied in the hydrolytic dehydrogenation of ammonia borane, paying particular attention to those supported on carbon materials and oxides. Full article
(This article belongs to the Special Issue Catalytic Hydrogen Generation and Use for Production of Fuels)
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Open AccessArticle
Static Reactive Power Compensator Design, Based on Three-Phase Voltage Converter
Energies 2021, 14(8), 2198; https://doi.org/10.3390/en14082198 (registering DOI) - 15 Apr 2021
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Abstract
At present, electrical network stability is of the utmost importance because of the increase in electric demand and the integration of distributed generation deriving from renewable energy. In this paper, we proposed a static reactive power compensator model with common direct current voltage [...] Read more.
At present, electrical network stability is of the utmost importance because of the increase in electric demand and the integration of distributed generation deriving from renewable energy. In this paper, we proposed a static reactive power compensator model with common direct current voltage sources. Converter parameters were calculated and designed to fulfill specifications. In order to ascertain the device response for different operating modes as reactive power consumer and generator, we developed the model’s power and control circuits in Matlab Simulink. Simulations were performed for different conditions, and as a result, the current and voltage waveforms and the circular power chart were obtained. This paper has theoretically proven it is possible to achieve the consumption or generation of purely active or reactive power by implementing a static reactive power compensator with common DC voltage sources. Full article
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Open AccessArticle
Using CFD to Evaluate Natural Ventilation through a 3D Parametric Modeling Approach
Energies 2021, 14(8), 2197; https://doi.org/10.3390/en14082197 - 15 Apr 2021
Viewed by 164
Abstract
Predicting building air change rates is a challenge for designers seeking to deal with natural ventilation, a more and more popular passive strategy. Among the methods available for this task, computational fluid dynamics (CFD) appears the most compelling, in ascending use. However, CFD [...] Read more.
Predicting building air change rates is a challenge for designers seeking to deal with natural ventilation, a more and more popular passive strategy. Among the methods available for this task, computational fluid dynamics (CFD) appears the most compelling, in ascending use. However, CFD simulations require a range of settings and skills that inhibit its wide application. With the primary goal of providing a pragmatic CFD application to promote wind-driven ventilation assessments at the design phase, this paper presents a study that investigates natural ventilation integrating 3D parametric modeling and CFD. From pre- to post-processing, the workflow addresses all simulation steps: geometry and weather definition, including incident wind directions, a model set up, control, results’ edition, and visualization. Both indoor air velocities and air change rates (ACH) were calculated within the procedure, which used a test house and air measurements as a reference. The study explores alternatives in the 3D design platform’s frame to display and compute ACH and parametrically generate surfaces where air velocities are computed. The paper also discusses the effectiveness of the reference building’s natural ventilation by analyzing the CFD outputs. The proposed approach assists the practical use of CFD by designers, providing detailed information about the numerical model, as well as enabling the means to generate the cases, visualize, and post-process the results. Full article
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Open AccessArticle
Nonequilibrium Entropy Conservation and the Transport Equations of Mass, Momentum, and Energy
Energies 2021, 14(8), 2196; https://doi.org/10.3390/en14082196 - 14 Apr 2021
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Abstract
Nonequilibrium statistical mechanics or molecular theory has put the transport equations of mass, momentum and energy on a firm or rigorous theoretical foundation that has played a critical role in their use and applications. Here, it is shown that those methods can be [...] Read more.
Nonequilibrium statistical mechanics or molecular theory has put the transport equations of mass, momentum and energy on a firm or rigorous theoretical foundation that has played a critical role in their use and applications. Here, it is shown that those methods can be extended to nonequilibrium entropy conservation. As already known, the “closure” of the transport equations leads to the theory underlying the phenomenological laws, including Fick’s Law of Diffusion, Newton’s Law of Viscosity, and Fourier’s Law of Heat. In the case of entropy, closure leads to the relationship of entropy flux to heat as well as the Second Law or the necessity of positive entropy generation. It is further demonstrated how the complete set of transport equations, including entropy, can be simplified under physically restrictive assumptions, such as reversible flows and local equilibrium flows. This analysis, in general, yields a complete, rigorous set of transport equations for use in applications. Finally, it is also shown how this basis set of transport equations can be transformed to a new set of nonequilibrium thermodynamic functions, such as the nonequilibrium Gibbs’ transport equation derived here, which may have additional practical utility. Full article
(This article belongs to the Special Issue The Concept of Entropy and Its Application in Thermal Engineering)
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Open AccessFeature PaperArticle
Life Cycle Assessment of Dynamic Water Flow Glazing Envelopes: A Case Study with Real Test Facilities
Energies 2021, 14(8), 2195; https://doi.org/10.3390/en14082195 - 14 Apr 2021
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Abstract
High initial costs hinder innovative technologies for building envelopes. Life Cycle Assessment (LCA) should consider energy savings to show relevant economic benefits and potential to reduce energy consumption and CO2 emissions. Life Cycle Cost (LCC) and Life Cycle Energy (LCE) should focus [...] Read more.
High initial costs hinder innovative technologies for building envelopes. Life Cycle Assessment (LCA) should consider energy savings to show relevant economic benefits and potential to reduce energy consumption and CO2 emissions. Life Cycle Cost (LCC) and Life Cycle Energy (LCE) should focus on investment, operation, maintenance, dismantling, disposal, and/or recycling for the building. This study compares the LCC and LCE analysis of Water Flow Glazing (WFG) envelopes with traditional double and triple glazing facades. The assessment considers initial, operational, and disposal costs and energy consumption as well as different energy systems for heating and cooling. Real prototypes have been built in two different locations to record real-world data of yearly operational energy. WFG systems consistently showed a higher initial investment than traditional glazing. The final Life Cycle Cost analysis demonstrates that WFG systems are better over the operation phase only when it is compared with a traditional double-glazing. However, a Life Cycle Energy assessment over 50 years concluded that energy savings between 36% and 66% and CO2 emissions reduction between 30% and 70% could be achieved. Full article
(This article belongs to the Special Issue Energy Efficiency and Indoor Environment Quality)
Open AccessArticle
Multiple Input Multiple Output Resonant Inductive WPT Link: Optimal Terminations for Efficiency Maximization
Energies 2021, 14(8), 2194; https://doi.org/10.3390/en14082194 - 14 Apr 2021
Viewed by 155
Abstract
In this paper a general-purpose procedure for optimizing a resonant inductive wireless power transfer link adopting a multiple-input-multiple-output (MIMO) configuration is presented. The wireless link is described in a general–purpose way as a multi-port electrical network that can be the result of either [...] Read more.
In this paper a general-purpose procedure for optimizing a resonant inductive wireless power transfer link adopting a multiple-input-multiple-output (MIMO) configuration is presented. The wireless link is described in a general–purpose way as a multi-port electrical network that can be the result of either analytical calculations, full–wave simulations, or measurements. An eigenvalue problem is then derived to determine the link optimal impedance terminations for efficiency maximization. A step-by-step procedure is proposed to solve the eigenvalue problem using a computer algebra system, it provides the configuration of the link, optimal sources, and loads for maximizing the efficiency. The main advantage of the proposed approach is that it is general: it is valid for any strictly–passive multi–port network and is therefore applicable to any wireless power transfer (WPT) link. To validate the presented theory, an example of application is illustrated for a link using three transmitters and two receivers whose impedance matrix was derived from full-wave simulations. Full article
(This article belongs to the Special Issue Modelling of Wireless Power Transfer II)
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Open AccessArticle
Simulation Verification of Overcurrent Protection Operation in Power Networks Integrating Renewable Energy Sources in Energy Communities
Energies 2021, 14(8), 2193; https://doi.org/10.3390/en14082193 (registering DOI) - 14 Apr 2021
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Abstract
This publication discusses the risks of further use of classical overcurrent protections in modern power systems. The increasing penetration of renewable energy sources has caused a lot of challenges, among other things, the development of energy communities that balance local generation and consumption. [...] Read more.
This publication discusses the risks of further use of classical overcurrent protections in modern power systems. The increasing penetration of renewable energy sources has caused a lot of challenges, among other things, the development of energy communities that balance local generation and consumption. Usually the interconnection line between the energy community and power systems are only used to balance the shortage or overflow of energy. As a result, most of the time these connections can be low loaded. Such a state can cause incorrect operation of power system protection approached, because the current level values are smaller than the required activation level for the protections. This article presents the potential incorrect operation of digital power system protection with overcurrent function. The obtained simulation results clearly show that the correctness of protection operation is strongly dependent on the level load of lines and the parameters and structure of the protection decision algorithms. These problems occur during low load line periods because these were not taken into account during the classical digital protection design stage. In the future this can cause problems with the fulfillment of the basic protection requirements of stability, speed, sensitivity. This publication suggests extra problems for power system protection research. Full article
(This article belongs to the Special Issue Protection and Communication Techniques in Modern Power Systems)
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Open AccessArticle
Ocean Thermal Energy Conversion—Flexible Enabling Technology for Variable Renewable Energy Integration in the Caribbean
Energies 2021, 14(8), 2192; https://doi.org/10.3390/en14082192 (registering DOI) - 14 Apr 2021
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Abstract
Many Caribbean island nations have historically been heavily dependent on imported fossil fuels for both power and transportation, while at the same time being at an enhanced risk from the impacts of climate change, although their emissions represent a very tiny fraction of [...] Read more.
Many Caribbean island nations have historically been heavily dependent on imported fossil fuels for both power and transportation, while at the same time being at an enhanced risk from the impacts of climate change, although their emissions represent a very tiny fraction of the global total responsible for climate change. Small island developing states (SIDSs) are among the leaders in advocating for the ambitious 1.5 °C Paris Agreement target and the transition to 100% sustainable, renewable energy systems. In this work, three central results are presented. First, through GIS mapping of all Caribbean islands, the potential for near-coastal deep-water as a resource for ocean thermal energy conversion (OTEC) is shown, and these results are coupled with an estimate of the countries for which OTEC would be most advantageous due to a lack of other dispatchable renewable power options. Secondly, hourly data have been utilized to explicitly show the trade-offs between battery storage needs and dispatchable renewable sources such as OTEC in 100% renewable electricity systems, both in technological and economic terms. Finally, the utility of near-shore, open-cycle OTEC with accompanying desalination is shown to enable a higher penetration of renewable energy and lead to lower system levelized costs than those of a conventional fossil fuel system. Full article
(This article belongs to the Special Issue Selected Papers from The 8th International OTEC Symposium)
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Open AccessArticle
Performance Assessment of a Building-Integrated Photovoltaic Thermal System in a Mediterranean Climate—An Experimental Analysis Approach
Energies 2021, 14(8), 2191; https://doi.org/10.3390/en14082191 (registering DOI) - 14 Apr 2021
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Abstract
The experimental investigation of building-integrated photovoltaic thermal (BIPVT) solar systems is essential to characterise the operation of these elements under real conditions of use according to the climate and building type they pertain. BIPVT systems can increase and ensure energy performance and readiness [...] Read more.
The experimental investigation of building-integrated photovoltaic thermal (BIPVT) solar systems is essential to characterise the operation of these elements under real conditions of use according to the climate and building type they pertain. BIPVT systems can increase and ensure energy performance and readiness without jeopardising the occupant comfort if correctly operated. The present work presents a case study’s experimental analysis composed of a BIPVT system for heat recovery located in a controlled test room. This work contribution focuses on the presentation of the obtained measured value results that correspond to the BIPVT main boundary conditions (weather and room characteristics) and the thermal behaviour and performance of the BIPVT system, located in the Solar XXI Building, a nZEB exposed to the mild Mediterranean climate conditions of Portugal. Full article
(This article belongs to the Special Issue Building Thermal Envelope - New Trends and Applications)
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Open AccessArticle
A Framework for Design and Operation Optimization for Utilizing Low-Grade Industrial Waste Heat in District Heating and Cooling
Energies 2021, 14(8), 2190; https://doi.org/10.3390/en14082190 - 14 Apr 2021
Viewed by 136
Abstract
In the process industry, a large amount of low-grade waste heat is discharged into the environment. Furthermore, district heating and cooling systems require considerable low-grade energy. The integration of the two systems has great significance for energy saving. Because the energy demand of [...] Read more.
In the process industry, a large amount of low-grade waste heat is discharged into the environment. Furthermore, district heating and cooling systems require considerable low-grade energy. The integration of the two systems has great significance for energy saving. Because the energy demand of consumers varies in periods, the design and operation of an industrial waste heat recovery system need to match with the fluctuations of district energy demand. However, the impact of the periodic changes on the integration schemes are not considered enough in existing research. In this study, a framework method for solving above problem is proposed. Industrial waste heat was integrated with a district heating and cooling system through a heat recovery loop. A three-step mathematical programming method was used in design and operation optimization for multiperiod integration. A case study was conducted, and the results show that the multiperiod optimization method can bring significant benefits to the system. By solving the mixed integer nonlinear programming model, the optimal operation plans of the integration in different periods can be obtained. Full article
Open AccessArticle
SPEAR (Solar Pyrolysis Energy Access Reactor): Theoretical Design and Evaluation of a Small-Scale Low-Cost Pyrolysis Unit for Implementation in Rural Communities
Energies 2021, 14(8), 2189; https://doi.org/10.3390/en14082189 - 14 Apr 2021
Viewed by 171
Abstract
Energy access and waste management are two of the most pressing developmental and environmental issues on a global level to help mitigate the accelerating impacts of climate change. They are particularly relevant in Sub–Saharan Africa where electrification rates are significantly below global averages [...] Read more.
Energy access and waste management are two of the most pressing developmental and environmental issues on a global level to help mitigate the accelerating impacts of climate change. They are particularly relevant in Sub–Saharan Africa where electrification rates are significantly below global averages and rural areas are lacking a formal waste management sector. This paper explores the potential of integrating solar energy into a biomass pyrolysis unit as a potentially synergetic solution to both issues. The full design of a slow pyrolysis batch reactor targeted at biochar production, following a strict cost minimization approach, is presented in light of the relevant considerations. SPEAR is powered using a Cassegrain optics parabolic dish system, integrated into the reactor via a manual tracking system and optically optimized with a Monte-Carlo ray tracing methodology. The design approach employed has led to the development an overall cost efficient system, with the potential to achieve optical efficiencies up 72% under a 1.5° tracking error. The outputs of the system are biochar and electricity, to be used for soil amendment and energy access purposes, respectively. There is potential to pyrolyze a number of agricultural waste streams for the region, producing at least 5 kg of biochar per unit per day depending on the feedstock employed. Financial assessment of SPEAR yields a positive Net Present Value (NPV) in nearly all scenarios evaluated and a reasonable competitiveness with small scale solar for electrification objectives. Finally, SPEAR presents important positive social and environmental externalities and should be feasibly implementable in the region in the near term. Full article
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Open AccessArticle
Multiple-Load Forecasting for Integrated Energy System Based on Copula-DBiLSTM
Energies 2021, 14(8), 2188; https://doi.org/10.3390/en14082188 - 14 Apr 2021
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Abstract
With the tight coupling of multi-energy systems, accurate multiple-load forecasting will be the primary premise for the optimal operation of integrated energy systems. Therefore, this paper proposes a Copula correlation analysis combined with deep bidirectional long and short-term memory neural network forecasting model. [...] Read more.
With the tight coupling of multi-energy systems, accurate multiple-load forecasting will be the primary premise for the optimal operation of integrated energy systems. Therefore, this paper proposes a Copula correlation analysis combined with deep bidirectional long and short-term memory neural network forecasting model. First, Copula correlation analysis is used to conduct correlation analysis on multiple loads and various influencing factors. The influencing factors that have a great correlation with multiple loads were screened out as the input feature set of the model to eliminate the influence of interfering factors. Then, a deep bidirectional long and short-term memory neural network was constructed. Combined with the input feature set screened by the Copula correlation analysis method, the useful information contained in the historical data was more comprehensively learned from the forward and backward directions for training and forecasting. Through the actual calculation example analysis and comparison with other models, the forecasting accuracy of the method presented in this paper was improved to a certain extent. Full article
(This article belongs to the Special Issue Computational Intelligence and Load Forecasting in Power Systems)
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Open AccessArticle
Numerical Investigation of Gravity-Driven Granular Flow around the Vertical Plate: Effect of Pin-Fin and Oscillation on the Heat Transfer
Energies 2021, 14(8), 2187; https://doi.org/10.3390/en14082187 - 14 Apr 2021
Viewed by 143
Abstract
In this paper, the heat transfer of pin-fin plate unit (PFPU) under static and oscillating conditions are numerically studied using the discrete element method (DEM). The flow and heat transfer characteristics of the PFPU with sinusoidal oscillation are investigated under the conditions of [...] Read more.
In this paper, the heat transfer of pin-fin plate unit (PFPU) under static and oscillating conditions are numerically studied using the discrete element method (DEM). The flow and heat transfer characteristics of the PFPU with sinusoidal oscillation are investigated under the conditions of oscillating frequency of 0–10 Hz, amplitude of 0–5 mm and oscillating direction of Y and Z. The contact number, contact time, porosity and heat transfer coefficient under the above conditions are analyzed and compared with the smooth plate. The results show that the particle far away from the plate can transfer heat with the pin-fin of PFPU, and the oscillating PFPU can significantly increase the contact number and enhance the temperature diffusion and heat transfer. The heat transfer coefficient of PFPU increases with the increase of oscillating frequency and amplitude. When the PFPU oscillates along the Y direction with the amplitude of 1 mm and the frequency of 10 Hz, the heat transfer coefficient of PFPU is increased by 28% compared with that of the smooth plate. Compared with the oscillation along the Z direction, the oscillation along the Y direction has a significant enhancement on the heat transfer of PFPU. Full article
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Open AccessArticle
“Green Energy” and the Standard of Living of the EU Residents
Energies 2021, 14(8), 2186; https://doi.org/10.3390/en14082186 - 14 Apr 2021
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Abstract
The author intended to present the relationship between the standard of living of EU citizens and the level of the development of renewable energy. It is particularly important in the context of the implementation of the sustainable development idea, by ensuring a high [...] Read more.
The author intended to present the relationship between the standard of living of EU citizens and the level of the development of renewable energy. It is particularly important in the context of the implementation of the sustainable development idea, by ensuring a high standard of living for both current and future generations, with rational use of available natural resources. The first, theoretical part of the article presents the problem related to the impact of renewable energy on the standard of living in a synthetic way. The second part involves empirical research conducted in all countries of the EU. To evaluate the level of renewable energy development and the standard of living, the author constructed original measures based on the TOPSIS method. Variables were selected on the basis of substantive, statistical and formal criteria (primarily the completeness and availability of data in 2019). Within the framework of the conducted study, the author obtained, among other things, a relatively high value of Spearman’s rank correlation coefficient between the constructed synthetic measures (0.47). Canonical analysis was used to identify the relationship between them. Numerous indicators, including canonical correlations, complete redundancy and extracted variances, were determined with the use of canonical analysis. Seven statistically significant canonical variables were identified. The value of the greatest and most statistically significant canonical correlation exceeded 0.94, and for the last statistically significant canonical variable, the value reached over 0.31. Statistical data were primarily obtained from the publicly available EUROSTAT database. Full article
(This article belongs to the Special Issue Green Economy and Sustainable Development)
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Open AccessArticle
Cellulosic Bioethanol from Industrial Eucalyptus globulus Bark Residues Using Kraft Pulping as a Pretreatment
Energies 2021, 14(8), 2185; https://doi.org/10.3390/en14082185 - 14 Apr 2021
Viewed by 170
Abstract
The pulp and paper industry faces an emerging challenge for valorising wastes and side-streams generated according to the biorefinery concept. Eucalyptus globulus bark, an abundant industrial residue in the Portuguese pulp and paper sector, has a high potential to be converted into biobased [...] Read more.
The pulp and paper industry faces an emerging challenge for valorising wastes and side-streams generated according to the biorefinery concept. Eucalyptus globulus bark, an abundant industrial residue in the Portuguese pulp and paper sector, has a high potential to be converted into biobased products instead of being burned. This work aimed to evaluate the ethanol production from E. globulus bark previously submitted to kraft pulping through separate hydrolysis and fermentation (SHF) configuration. Fed-batch enzymatic hydrolysis provided a concentrated hydrolysate with 161.6 g L−1 of cellulosic sugars. S. cerevisiae and Ethanol Red® strains demonstrated a very good fermentation performance, despite a negligible xylose consumption. S. passalidarum, a yeast known for its capability to consume pentoses, was studied in a simultaneous co-culture with Ethanol Red®. However, bioethanol production was not improved. The best fermentation performance was achieved by Ethanol Red®, which provided a maximum ethanol concentration near 50 g L−1 and fermentation efficiency of 80%. Concluding, kraft pulp from E. globulus bark showed a high potential to be converted into cellulosic bioethanol, being susceptible to implementing an integrated biorefinery on the pulp and paper industrial plants. Full article
(This article belongs to the Special Issue Latest Progress in Lignocellulosic Bioethanol Production)
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