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Special Issue "Sustainable Energy Systems"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Sustainable Energy".

Deadline for manuscript submissions: closed (15 December 2018)

Special Issue Editors

Guest Editor
Prof. Nídia Caetano

Laboratory for Process Engineering, Environment, Biotechnology and Energy (LEPABE), Faculty of Engineering, University of Porto (FEUP), R. Dr. Roberto Frias S/N, 4200-465 Porto, Portugal
School of Engineering (ISEP), Polytechnic of Porto, R. Dr. António Bernardino de Almeida 431, 4249-015 Porto, Portugal
Website 1 | Website 2 | Website 3 | E-Mail
Interests: biofuels and biorefineries; energy storage systems; sustainability; waste valorization; wastewater treatment; waste-to-energy
Guest Editor
Prof. Dr. Zita A. Vale

Polytechnic of Porto, Portugal
Website | E-Mail
Interests: demand response; electric vehicles; electricity markets; power and energy systems; renewables; smart grids
Guest Editor
Dr. Bo Nørregaard Jørgensen

Center for Energy Informatics, Mærsk Mc-Kinney Møller Institute, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
E-Mail
Interests: Multi-agent systems; Demand response; Energy flexibility; Multi-objective optimization
Guest Editor
Prof. Carlos Felgueiras

Department of Electrical Engineering, School of Engineering (ISEP), Polytechnic Institute of Porto (IPP), Porto, Portugal
Website | E-Mail
Interests: energy quality; energy and buildings; energy and environmental Indicators; renewable energy systems; sustainable energy systems

Special Issue Information

Dear Colleagues,

Energy is a crucial resource for nation and society development. Sustainable energy production and use is still a distant target, in spite of all the efforts and advancements achieved so far. Although renewable energy use has been increasing significantly, a large share of the energy currently used around the world is still based on fossil resources (oil and coal).

Renewable energy use brings along technical and business challenges. Geographically distributed by nature, renewables contribute to increasingly distributed generation of electricity. Ensuring the required reliability and efficiency with the spreading of small-scale electricity generation is a huge challenge that must be overcome. Energy storage systems and active participation from the demand side, with efficient use of the available energy, demand flexibility must be intelligently used to compensate for the intermittency of the most attractive renewable energy sources, such as wind and sun.

This Special Issue, therefore, aims to contribute to the “Sustainable Energy Systems” agenda through advanced scientific and multi-disciplinary knowledge, combined to improve energy security and performance.

We therefore invite papers on innovative technical developments, reviews, case studies, analytical, as well as assessments, from different disciplines, which are relevant to “Sustainable Energy Systems”. These include smart grids, renewable energy systems, energy storage systems, life cycle analysis of energy systems, zero energy buildings, electric and hybrid vehicles, financial and economic analysis of energy systems, smart systems, energy management and big data, energy policy, novel energy sources, and renewable-based generation, among others.

Dr. Nídia Caetano
Dr. Zita Vale
Dr. Bo Nørregaard Jørgensen
Dr. Carlos Felgueiras
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • electric and hybrid vehicles
  • energy efficiency
  • energy management and policy
  • energy storage
  • life cycle assessment
  • renewable energy
  • renewable energy systems
  • smart grids
  • waste-to-energy
  • zero energy buildings

Published Papers (29 papers)

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Research

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Open AccessArticle Battery Characterization and Dimensioning Approaches for Micro-Grid Systems
Energies 2019, 12(7), 1305; https://doi.org/10.3390/en12071305
Received: 15 December 2018 / Revised: 21 February 2019 / Accepted: 22 March 2019 / Published: 4 April 2019
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Abstract
Micro-Grid (MG) systems have been extensively studied and deployed to lower the power consumption while reducing the greenhouse gas emissions. Although, the challenge with Renewable Energy Sources (RES) is their uncertain and intermittent nature, things that led the researchers to think about integrating [...] Read more.
Micro-Grid (MG) systems have been extensively studied and deployed to lower the power consumption while reducing the greenhouse gas emissions. Although, the challenge with Renewable Energy Sources (RES) is their uncertain and intermittent nature, things that led the researchers to think about integrating storage devices, especially batteries, into MG systems. The main aim is to store the excess of produced energy for further usage when not enough energy is available. Nevertheless, batteries modeling and characterization is mandatory to identify their parameters and study their performance within MG systems. Moreover, in order to continuously supply electricity to the building, it is required to figure out the optimum size of energy production systems and storage devices. This paper introduces a methodology for MG modeling and performance evaluation. Its main contribution is twofold, (i) battery’s parameters identification, and (ii) modeling and dimensioning method for both standalone and MG systems. An instrumentation platform, composed of recent sensing and actuating equipment, for MG energy management and battery characterization is developed. Simulation and experimental results show the effectiveness of the proposed methodology. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Analysis of Fossil Fuel Energy Consumption and Environmental Impacts in European Countries
Energies 2019, 12(6), 964; https://doi.org/10.3390/en12060964
Received: 15 January 2019 / Revised: 19 February 2019 / Accepted: 8 March 2019 / Published: 13 March 2019
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Abstract
The use of fossil fuels as the main source of energy for most countries has caused several negative environmental impacts, such as global warming and air pollution. Air pollution causes many health problems, causing social and economic negative effects. Worldwide efforts are being [...] Read more.
The use of fossil fuels as the main source of energy for most countries has caused several negative environmental impacts, such as global warming and air pollution. Air pollution causes many health problems, causing social and economic negative effects. Worldwide efforts are being made to avoid global warming consequences through the establishment of international agreements that then lead to local policies adapted to the development of each signing nation. In addition, there is a depletion of nonrenewable resources which may be scarce or nonexistent in future generations. The preservation of resources, which is a common goal of the Circular Economy strategy and of sustainable development, is not being accomplished nowadays. In this work, the calculation of indicators and mathematical and statistical analysis were applied to clarify and evidence the trends, provide information for the decision-making process, and increase public awareness. The fact that European countries do not possess abundant reserves of fossil fuels will not change, but the results of this analysis can evolve in the future. In this work, fossil fuel energy consumption, fossil fuel depletion, and their relationship with other variables, such as energy dependence and share of renewable energy in gross final energy consumption, were analyzed for 29 European countries. Furthermore, it was possible to conclude that many European countries still depend heavily on fossil fuels. Significant differences were not found in what concerns gross inland consumption per capita when the Kruskal–Wallis test was applied. It was possible to estimate that by 2050 (considering Jazz scenario) it will only remain approximately 14% of oil proven reserves, 72% of coal proven reserves and 18% of gas proven reserves. Given the small reserves of European countries on fossil fuels, if they need to use them, they will fast disappear. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Driving Forces of Energy-Related CO2 Emissions Based on Expanded IPAT Decomposition Analysis: Evidence from ASEAN and Four Selected Countries
Energies 2019, 12(4), 764; https://doi.org/10.3390/en12040764
Received: 12 December 2018 / Revised: 6 February 2019 / Accepted: 12 February 2019 / Published: 25 February 2019
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Abstract
ASEAN is a dynamic and diverse region which has experienced rapid urbanization and population growth. Their energy demand grew by 60% in the last 15 years. In 2013, about 3.6% of global greenhouse-gas emissions was emitted from this region and the share is [...] Read more.
ASEAN is a dynamic and diverse region which has experienced rapid urbanization and population growth. Their energy demand grew by 60% in the last 15 years. In 2013, about 3.6% of global greenhouse-gas emissions was emitted from this region and the share is expected to rise substantially. Hence, a better understanding of driving forces of the changes in CO2 emissions is important to tackle global climate change and develop appropriate policies. Using IPAT combined with variance analysis, this study aims to identify the main driving factors of CO2 emissions for ASEAN and four selected countries (Indonesia, Malaysia, Philippines and Thailand) during 1971–2013. The results show that population growth and economic growth were the main driving factors for increasing CO2 emissions for most of the countries. Fossil fuels play an important role in increasing CO2 emissions, however the growth in emissions was compensated by improved energy efficiency and carbon intensity of fossil energy. The results imply that to decouple energy use from high levels of emissions is important. Proper energy management through fuel substitution and decreasing emission intensity through technological upgrades have considerable potential to cut emissions. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Influence on CO and PM Emissions of an Innovative Burner Pot for Pellet Stoves: An Experimental Study
Energies 2019, 12(4), 590; https://doi.org/10.3390/en12040590
Received: 10 December 2018 / Revised: 28 January 2019 / Accepted: 4 February 2019 / Published: 13 February 2019
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Abstract
In this study, an extensive set of experiments has been performed to investigate how the emissions of carbon monoxide (CO) and particulate matter (PM) from wood pellet combustion are correlated with the different layout of air inlets in the two burner pots of [...] Read more.
In this study, an extensive set of experiments has been performed to investigate how the emissions of carbon monoxide (CO) and particulate matter (PM) from wood pellet combustion are correlated with the different layout of air inlets in the two burner pots of pellet stoves. In particular, emissions generated using a “traditional” burner pot are compared with those produced with an innovative one. Tests were carried out on four pellet stoves (8–11 kW burning power). Tests show that CO emissions can be reduced close to zero using the innovative burner pot. PM emissions are also reduced, but not as much as those of CO. This phenomenon is explained assuming that CO reduction implies a reduction of the organic part of PM, but not of the inorganic matter. Experiments also show an apparent dependence of PM release on the time from ignition for both burner pot models: PM emissions increase and the color of PM deposited on filters varies over a wide range. It is argued that this effect is due to ash accumulation on the bottom of the burner pot and to its interaction with the primary air stream that flows over it. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Analysis of the Reduction of CO2 Emissions in Urban Environments by Replacing Conventional City Buses by Electric Bus Fleets: Spain Case Study
Energies 2019, 12(3), 525; https://doi.org/10.3390/en12030525
Received: 14 December 2018 / Revised: 29 January 2019 / Accepted: 1 February 2019 / Published: 7 February 2019
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Abstract
The emissions of CO2 gas caused by transport in urban areas are increasingly serious, and the public transport sector plays a vital role in society, especially when considering the increased demands for mobility. New energy technologies in urban mobility are being introduced, [...] Read more.
The emissions of CO2 gas caused by transport in urban areas are increasingly serious, and the public transport sector plays a vital role in society, especially when considering the increased demands for mobility. New energy technologies in urban mobility are being introduced, as evidenced by the electric vehicle. We evaluated the positive environmental effects in terms of CO2 emissions that would be produced by the replacement of conventional urban transport bus fleets by electric buses. The simulation of an electric urban bus conceptual model is presented as a case study. The model is validated using the speed and height profiles of the most representative route within the city of Madrid—the C1 line. We assumed that the vehicle fleet is charged using the electric grid at night, when energy demand is low, the cost of energy is low, and energy is produced with a large provision of renewable energy, principally wind power. For the results, we considered the percentage of fleet replacement and the Spanish electricity mix. The analysis shows that by gradually replacing the current fleet of buses by electric buses over 10 years (2020 to 2030), CO2 emissions would be reduced by up to 92.6% compared to 2018 levels. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle A Real-Time Layer-Adaptive Wavelet Transform Energy Distribution Strategy in a Hybrid Energy Storage System of EVs
Energies 2019, 12(3), 440; https://doi.org/10.3390/en12030440
Received: 15 December 2018 / Revised: 19 January 2019 / Accepted: 22 January 2019 / Published: 30 January 2019
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Abstract
In this paper, a real-time energy distribution strategy is designed by a layer-adaptive wavelet transform algorithm and proposed to meet the load power demand while distributing the high-frequency component to supercapacitors and the low-frequency component to batteries in a hybrid energy storage system. [...] Read more.
In this paper, a real-time energy distribution strategy is designed by a layer-adaptive wavelet transform algorithm and proposed to meet the load power demand while distributing the high-frequency component to supercapacitors and the low-frequency component to batteries in a hybrid energy storage system. In the proposed method, the number of decomposition layers of wavelet transform corresponding to the load power is adaptively determined by dividing the operation zone of supercapacitors into eight cases to respectively distribute the low frequency component to batteries and the remaining high frequency component to supercapacitors. Firstly, since the state of charge of supercapacitors decreases faster as the decomposition layers increases, the state of charge of supercapacitors is divided into eight cases of operation zones. Secondly, since supercapacitors act as the peak power buffer unit, the corresponding number of decomposition layers is finally adaptively determined according to the operation zone of supercapacitors. An experiment testbed is built to verify the effectiveness of the proposed method. Extensive experiment results show that the proposed method provides a better real-time energy sharing between supercapacitors and batteries when compared with the conditional method. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle N-Doped Porous Carbon from Sargassum spp. as Efficient Metal-Free Electrocatalysts for O2 Reduction in Alkaline Fuel Cells
Energies 2019, 12(3), 346; https://doi.org/10.3390/en12030346
Received: 16 November 2018 / Revised: 5 January 2019 / Accepted: 10 January 2019 / Published: 23 January 2019
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Abstract
This work reports the synthesis of N-doped porous carbon (NPC) with a high surface area from Sargassum spp. as a low-cost alternative for electrocatalyst production for the oxygen reduction reaction (ORR). Sargassum spp. was activated with potassium hydroxide at different temperatures (700, 750, [...] Read more.
This work reports the synthesis of N-doped porous carbon (NPC) with a high surface area from Sargassum spp. as a low-cost alternative for electrocatalyst production for the oxygen reduction reaction (ORR). Sargassum spp. was activated with potassium hydroxide at different temperatures (700, 750, and 800 °C) and then doped with pyridine (N700, N750, and N800). As a result of the activation process, the 800 °C sample showed a high surface area (2765 m2 g−1) and good onset potential (0.870 V) and current density (4.87 mA cm−2). The ORR performance of the electrocatalysts in terms of their current density was N800 > N750 > N700 > 750 > 800 > 700, while the onset potential decreased in the following order: N800 > 800 > 750 > 700 > N700 > N750. The fuel cell performance of the membrane electrode assembly (MEA) prepared with electrocatalyst synthesized at 750 °C and doped with pyridine was 12.72 mW cm−2, which was close to that from Pt/C MEA on both the anode and cathode (14.42 mW cm−2). These results indicate that NPCs are an alternative to the problem of Sargassum spp. accumulation in the Caribbean due to their high efficiency as electrocatalysts for ORR. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessFeature PaperArticle The Energy System and the Sharing Economy: Interfaces and Overlaps and What to Learn from Them
Energies 2019, 12(3), 339; https://doi.org/10.3390/en12030339
Received: 13 December 2018 / Revised: 18 January 2019 / Accepted: 19 January 2019 / Published: 22 January 2019
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Abstract
The dissemination of decentralized renewable energy generation, storage and smart metering devices has led to the need for new business models and coordination mechanisms in the energy sector. At the same time, the emerging sharing economy focuses on using digital platforms to coordinate [...] Read more.
The dissemination of decentralized renewable energy generation, storage and smart metering devices has led to the need for new business models and coordination mechanisms in the energy sector. At the same time, the emerging sharing economy focuses on using digital platforms to coordinate value creation on a decentralized level. While sharing concepts have already been applied to specific energy technologies and microgrids, a more general understanding of what the sharing economy means in the context of the energy sector is still missing. This paper aims to bring these two topics together and to analyze their interfaces and overlaps. For this purpose, this paper draws from existent scientific publications, reports, blog posts, and websites as well as company workshops to discuss which activities and characteristics of the sharing economy might be applicable to the energy sector. Results show that there are significant overlaps in characteristics of the sharing economy and of the transitioning energy system. Furthermore, a broad range of business models within the energy system were found to be based on sharing resources. The findings of this study open up a range of new research and business opportunities at the interface of the sharing economy and the transitioning energy system. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Analysis of a Control System for DFIG Wind Generators Based on the Transmission of Power References through a GSM Wireless Network: A Smart Grid Experimental Approach
Energies 2019, 12(2), 241; https://doi.org/10.3390/en12020241
Received: 26 October 2018 / Revised: 16 December 2018 / Accepted: 27 December 2018 / Published: 14 January 2019
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Abstract
This work proposes the use of the automatic Short Message Service (SMS) of a Global System for Mobile Communication (GSM) network to transmit the control information to a Doubly Fed Induction Generator (DFIG) of a wind turbine, according to the Smart Grid (SG) [...] Read more.
This work proposes the use of the automatic Short Message Service (SMS) of a Global System for Mobile Communication (GSM) network to transmit the control information to a Doubly Fed Induction Generator (DFIG) of a wind turbine, according to the Smart Grid (SG) concept. In the proposed strategy, the Control Center (CC) can remotely transmit the required power references (active and reactive) to the DFIG controller, in order to manage the power generation of the wind turbine dynamically. The proposed wireless network was developed in a Software Defined Radio (SDR) transceiver connected to an OpenBTS platform. The control information can be directly inserted in the Open Base Transceiver Station (OpenBTS) server (located at the CC) or sent by a wireless device (e.g., mobile phone) connected to the GSM network, and then transmitted to the wireless receiver at the wind turbine. The receiver on the turbine side was developed in a microcontroller board with a GSM card, and the DFIG controller was implemented in a Digital Signal Processor (DSP) board. The results of the tests showed that the DFIG can be satisfactorily controlled according to the power references, considering that they vary at low rates. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Partial Shading Detection and Global Maximum Power Point Tracking Algorithm for Photovoltaic with the Variation of Irradiation and Temperature
Energies 2019, 12(2), 202; https://doi.org/10.3390/en12020202
Received: 7 November 2018 / Revised: 5 January 2019 / Accepted: 5 January 2019 / Published: 9 January 2019
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Abstract
Photovoltaic (PV) technology has been the focus of interest due to its nonpolluting operation and good installation flexibility. Irradiation and temperature are the two main factors which impact the performance of the PV system. Accordingly, when partial shading from surroundings occurs, its incident [...] Read more.
Photovoltaic (PV) technology has been the focus of interest due to its nonpolluting operation and good installation flexibility. Irradiation and temperature are the two main factors which impact the performance of the PV system. Accordingly, when partial shading from surroundings occurs, its incident shadow diminishes the irradiation and reduces the generated power. Since the conventional maximum power point tracking methods (MPPT) could not distinguish the global maximum power of the power-voltage (P-V) characteristic curve, a new tracking method needs to be developed. This paper proposes a global maximum power point tracking method using shading detection and the trend of slopes from each section of the curve. Full mathematical equations and algorithms are presented. Simulations based on real weather data were performed both in short-term and long-term studies. Moreover, this paper also presents the experiment using the DC-DC synchronous and interleaved boost converter. Results from the simulation show an accurate tracking result and the system can enhance the total energy generated by 8.55% compared to the conventional scanning method. Moreover, the experiment also confirms the success of the proposed tracking algorithm. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Multi-Step-Ahead Carbon Price Forecasting Based on Variational Mode Decomposition and Fast Multi-Output Relevance Vector Regression Optimized by the Multi-Objective Whale Optimization Algorithm
Energies 2019, 12(1), 147; https://doi.org/10.3390/en12010147
Received: 3 December 2018 / Revised: 24 December 2018 / Accepted: 28 December 2018 / Published: 2 January 2019
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Abstract
The accurate and stable forecasting of carbon prices is vital for governors to make policies and essential for market participants to make investment decisions, which is important for promoting the development of carbon markets and reducing carbon emissions in China. However, it is [...] Read more.
The accurate and stable forecasting of carbon prices is vital for governors to make policies and essential for market participants to make investment decisions, which is important for promoting the development of carbon markets and reducing carbon emissions in China. However, it is challenging to improve the carbon price forecasting accuracy due to its non-linearity and non-stationary characteristics, especially in multi-step-ahead forecasting. In this paper, a hybrid multi-step-ahead forecasting model based on variational mode decomposition (VMD), fast multi-output relevance vector regression (FMRVR), and the multi-objective whale optimization algorithm (MOWOA) is proposed. VMD is employed to extract the primary mode for the carbon price. Then, FMRVR, which is used as the forecasting module, is built on the preprocessed data. To achieve high accuracy and stability, the MOWOA is utilized to optimize the kernel parameter and input the lag of the FMRVR. The proposed hybrid forecasting model is applied to carbon price series from three major regional carbon emission exchanges in China. Results show that the proposed VMD-FMRVR-MOWOA model achieves better performance compared to several other multi-output models in terms of forecasting accuracy and stability. The proposed model can be a potential and effective technique for multi-step-ahead carbon price forecasting in China’s three major regional emission exchanges. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Minimization of Losses in Solar Photovoltaic Modules by Reconfiguration under Various Patterns of Partial Shading
Energies 2019, 12(1), 24; https://doi.org/10.3390/en12010024
Received: 15 November 2018 / Revised: 13 December 2018 / Accepted: 16 December 2018 / Published: 22 December 2018
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Abstract
Configurations of photovoltaic (PV) modules, such as series-parallel (SP), bridge-linked (BL), and total cross-tied (TCT) configurations, always utilize a number of connecting switches. In a simulation, the ideal switch with no loss is used to optimize the reconfiguration method for a solar PV [...] Read more.
Configurations of photovoltaic (PV) modules, such as series-parallel (SP), bridge-linked (BL), and total cross-tied (TCT) configurations, always utilize a number of connecting switches. In a simulation, the ideal switch with no loss is used to optimize the reconfiguration method for a solar PV array. However, in practice, the switches are non-ideal, causing losses and resulting in a decrease in the total output power of the PV array. In this work, MATLAB/Simulink (R2016a) was employed to simulate nine PV modules linked in a 3 × 3 array, and they were reconfigured using series-parallel (SP), bridge-linked (BL), and total cross-tied (TCT) configurations for both ideal and non-ideal switch cases. It was not surprising that non-ideal switches deteriorated the output power compared with ideal cases. Then, the minimization of losses (ML) configuration was proposed by minimizing the number of switches to give the highest output power. A 5% higher power output was set as the criterion to reconfigure the PV modules when partial shading occurred. The results showed that if 50% or more of the area was partially shaded, reconfiguration was unnecessary. On the other hand, when the shaded area was less than 50%, reconfiguration gave a significant increase in power. Finally, the ML method had different configurations for various shading patterns, and provided better results than those of the TCT method. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Experimental Comparison of Three Real-Time Optimization Strategies Applied to Renewable/FC-Based Hybrid Power Systems Based on Load-Following Control
Energies 2018, 11(12), 3537; https://doi.org/10.3390/en11123537
Received: 19 November 2018 / Revised: 13 December 2018 / Accepted: 17 December 2018 / Published: 19 December 2018
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Abstract
Besides three different real-time optimization strategies analyzed for the Renewable/Fuel Cell Hybrid Power Systems (REW/FC-HPS) based on load-following (LFW) control, a short but critical assessment of the Real-Time Optimization (RTO) strategies is presented in this paper. The advantage of power flow balance on [...] Read more.
Besides three different real-time optimization strategies analyzed for the Renewable/Fuel Cell Hybrid Power Systems (REW/FC-HPS) based on load-following (LFW) control, a short but critical assessment of the Real-Time Optimization (RTO) strategies is presented in this paper. The advantage of power flow balance on the DC bus through the FC net power generated using the LFW control instead of using the batteries’ stack is highlighted in this study. As LFW control consequence, the battery operates in charge-sustained mode and many advantages can be exploited in practice such as: reducing the size of the battery and maintenance cost, canceling the monitoring condition of the battery state-of-charge etc. The optimization of three FC-HPSs topologies based on appropriate RTO strategy is performed here using indicators such as fuel economy, fuel consumption efficiency, and FC electrical efficiency. The challenging task to optimize operation of the FC-HPS under unknown profile of the load demand is approached using an optimization function based on linear mix of the FC net power and the fuel consumption through the weighting coefficients knet and kfuel. If optimum values are chosen, then a RTO switching strategy can improve even further the fuel economy over the entire range of load. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Stochastic Dynamic Response Analysis of a 10 MW Tension Leg Platform Floating Horizontal Axis Wind Turbine
Energies 2018, 11(12), 3341; https://doi.org/10.3390/en11123341
Received: 2 October 2018 / Revised: 9 November 2018 / Accepted: 23 November 2018 / Published: 30 November 2018
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Abstract
The dynamic response of floating horizontal axis wind turbines (FHWATs) are affected by the viscous and inertia effects. In free decay motion, viscous drag reduces the amplitude of pitch and roll fluctuation, the quasi-static mooring system overestimates the resonant amplitude values of pitch [...] Read more.
The dynamic response of floating horizontal axis wind turbines (FHWATs) are affected by the viscous and inertia effects. In free decay motion, viscous drag reduces the amplitude of pitch and roll fluctuation, the quasi-static mooring system overestimates the resonant amplitude values of pitch and roll. In this paper, the quasi-static mooring system is modified by introducing linear damping and quadratic damping. The dynamic response characteristics of the FHAWT modified model of the DTU 10 MW tension leg platform (TLP) were studied. Dynamic response of the blade was mainly caused by wind load, while the wave increased the blade short-term damage equivalent load. The tower base bending moment was affected by inclination of the tower and the misaligned angle βwave between wind and wave. Except the yaw motion, other degrees of freedom motions of the TLP were substantially affected by βwave. Ultimate tension of the mooring system was related to the displacement caused by pitch and roll motions, and standard deviation of the tension was significantly affected by the wave frequency response. Under the action of wave load, the viscous drag would stimulate the mooring system and increase the resonance of the platform motion. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Wind Power Interval Forecasting Based on Confidence Interval Optimization
Energies 2018, 11(12), 3336; https://doi.org/10.3390/en11123336
Received: 17 October 2018 / Revised: 22 November 2018 / Accepted: 27 November 2018 / Published: 30 November 2018
Cited by 1 | PDF Full-text (4812 KB) | HTML Full-text | XML Full-text
Abstract
Most of the current wind power interval forecast methods are based on the assumption the point forecast error is subject to a known distribution (such as a normal distribution, beta distribution, etc.). The interval forecast of wind power is obtained after solving the [...] Read more.
Most of the current wind power interval forecast methods are based on the assumption the point forecast error is subject to a known distribution (such as a normal distribution, beta distribution, etc.). The interval forecast of wind power is obtained after solving the confidence interval of the known distribution. However, this assumption does not reflect the truth because the distribution of error is random and does not necessary obey any known distribution. Moreover, the current method for calculating the confidence interval is only good for a known distribution. Therefore, those interval forecast methods cannot be applied generally, and the forecast quality is not good. In this paper, a general method is proposed to determine the optimal interval forecast of wind power. Firstly, the distribution of the point forecast error is found by using the non-parametric Parzen window estimation method which is suitable for the distribution of an arbitrary shape. Secondly, an optimal method is used to find the minimum confidence interval of arbitrary distribution. Finally the optimal forecast interval is obtained. Simulation results indicate that this method is not only generally applicable, but also has a better comprehensive evaluation index. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Prototype Co-Pyrolysis of Used Lubricant Oil and Mixed Plastic Waste to Produce a Diesel-Like Fuel
Energies 2018, 11(11), 2973; https://doi.org/10.3390/en11112973
Received: 8 October 2018 / Revised: 26 October 2018 / Accepted: 29 October 2018 / Published: 1 November 2018
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Abstract
The co-pyrolysis of used lubricant oil blended with plastic waste, namely high-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS), to produce a diesel-like fuel was studied. The proportions of the raw materials were optimized using laboratory scale pyrolysis at atmospheric pressure at a [...] Read more.
The co-pyrolysis of used lubricant oil blended with plastic waste, namely high-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS), to produce a diesel-like fuel was studied. The proportions of the raw materials were optimized using laboratory scale pyrolysis at atmospheric pressure at a final temperature of 450 °C without a catalyst. The ratios of used lubricant oil (Oil) and plastic waste (Oil:HDPE:PP:PS) investigated were 50:30:20:0, 50:30:0:20, 50:0:30:20, and 50:30:10:10 by weight. It was found that the oil produced using an Oil:HDPE:PP:PS ratio of 50:30:20:0 exhibited most of the properties of standard diesel oil as specified by the Ministry of Energy (Thailand), except for its flash point, which was lower than the standard. Therefore, this proportion was utilized for the scaled-up testing in the co-pyrolysis prototype (10 kg/day). Three reactor temperature ranges (less than 400 °C, 400–425 °C, and 425–450 °C) were studied, and the properties of the oil products were analysed. The oil products produced at 400–425 °C exhibited diesel-like fuel properties. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessFeature PaperArticle A Review and New Problems Discovery of Four Simple Decentralized Maximum Power Point Tracking Algorithms—Perturb and Observe, Incremental Conductance, Golden Section Search, and Newton’s Quadratic Interpolation
Energies 2018, 11(11), 2966; https://doi.org/10.3390/en11112966
Received: 22 September 2018 / Revised: 13 October 2018 / Accepted: 24 October 2018 / Published: 1 November 2018
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Abstract
Maximum Power Point Tracking (MPPT) enables photovoltaic (PV) systems to extract as much solar energy as possible. Depending on which type of controller is used, PV systems can be classified as centralized MPPT (CMPPT) or decentralized MPPT (DMPPT). In substring-level systems, it is [...] Read more.
Maximum Power Point Tracking (MPPT) enables photovoltaic (PV) systems to extract as much solar energy as possible. Depending on which type of controller is used, PV systems can be classified as centralized MPPT (CMPPT) or decentralized MPPT (DMPPT). In substring-level systems, it is known that the energy yield of DMPPT can outweigh the power electronics cost. At the substring level, it is usually assumed that the PV curve exhibits a single peak, even under partial shading. Thus, the control algorithms for DMPPT are usually less complicated than those employed in CMPPT systems. This paper provides a comprehensive review of four simple DMPPT algorithms, which are perturb and observe (P&O), incremental conductance (INC), golden section search (GSS), and Newton’s quadratic interpolation (NQI). The comparison of these algorithms are done from the perspective of numerical analysis. Guidelines on how to set initial conditions and convergence criteria are thoroughly explained. This is of great interest to PV engineers when selecting algorithms for use in MPPT implementations. In addition, various problems that have never previously been identified before are highlighted and discussed. For instance, the problems of NQI trap is identified and methods on how to mitigate it are also discussed. All the algorithms are tested under various conditions including static, dynamic, and rapid changes of irradiance. Both simulation and experimental results indicate that P&O and INC are the best algorithms for DMPPT. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Benefits of Medium Temperature Solar Concentration Technologies as Thermal Energy Source of Industrial Processes in Spain
Energies 2018, 11(11), 2950; https://doi.org/10.3390/en11112950
Received: 31 July 2018 / Revised: 2 October 2018 / Accepted: 23 October 2018 / Published: 29 October 2018
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Abstract
This paper analyses the possible applications of medium temperature solar concentration technologies, Compound Parabolic Collector, Linear Fresnel Collector and Parabolic Trough Collector in the Spanish industrial sector. Results of this study allow evaluating whether or not solar technologies are an alternative to conventional [...] Read more.
This paper analyses the possible applications of medium temperature solar concentration technologies, Compound Parabolic Collector, Linear Fresnel Collector and Parabolic Trough Collector in the Spanish industrial sector. Results of this study allow evaluating whether or not solar technologies are an alternative to conventional sources. This possibility is analyzed energetically, economically and environmentally. Results show that the percentage of solar use is decisive in determining the true thermal energy generation cost. The other essential parameter is the solar field area due to produce economy of scale that reduces investment costs. Fluid temperature has significant influence mainly in Compound Parabolic Collector technology. Results obtained in this paper collect multiple alternatives and allow comparing for different scenarios the suitability to replace conventional energy sources by thermal energy obtained from medium temperature solar concentration technologies from an economic perspective. For instance, for percentage of solar use equal to 100%, the lowest thermal energy generation costs for each technology are 1.3 c€/kWh for Compound Parabolic Collector technology, fluid temperature of 100 °C and industrial process located in Seville, 2.4 c€/kWh for Linear Fresnel Collector technology, fluid temperature of 170 °C and industrial process located in Jaen, 3.3 c€/kWh for technology, fluid temperature of 350 °C and industrial process located in Jaen. These costs are lower than conventional energy sources costs. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Consequences of the National Energy Strategy in the Mexican Energy System: Analyzing Strategic Indicators with an Optimization Energy Model
Energies 2018, 11(10), 2837; https://doi.org/10.3390/en11102837
Received: 28 August 2018 / Revised: 16 October 2018 / Accepted: 16 October 2018 / Published: 20 October 2018
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Abstract
This paper presents an approach to the assessment of the Mexican energy system’s evolution under the climate and energy objectives set by the National Climate Change Strategy using an energy optimization model. Some strategic indicators have been chosen to analyze the performance of [...] Read more.
This paper presents an approach to the assessment of the Mexican energy system’s evolution under the climate and energy objectives set by the National Climate Change Strategy using an energy optimization model. Some strategic indicators have been chosen to analyze the performance of three integration elements: sustainability, efficiency, and energy security. Two scenarios have been defined in the medium and long-term: the business as usual scenario, with no energy or climate targets, and the National Climate Change Strategy scenario, where clean energy technologies and CO2 emissions objectives are considered. The aim of this work is the analysis of some of those strategic indicators’ evolution using the EUROfusion Times Model. Results show that reaching the strategy targets leads to improvements in the integration elements in the medium and long term. Besides, meeting the CO2 emission limits is achievable in terms of technologies and resources availability but at a high cost, while clean technologies targets are met with no extra costs even in the business as usual scenario. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessFeature PaperArticle Circular Statistics Applied to the Study of the Solar Radiation Potential of Rooftops in a Medium-Sized City
Energies 2018, 11(10), 2813; https://doi.org/10.3390/en11102813
Received: 15 September 2018 / Revised: 12 October 2018 / Accepted: 16 October 2018 / Published: 18 October 2018
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Abstract
Solar energy constitutes one of the most effective alternative energy sources for combating climate change. However, the solar potential in a city can vary depending on the urban morphology. The purpose of this paper is to perform a directional statistical analysis of the [...] Read more.
Solar energy constitutes one of the most effective alternative energy sources for combating climate change. However, the solar potential in a city can vary depending on the urban morphology. The purpose of this paper is to perform a directional statistical analysis of the distribution of the monthly solar potential of rooftops in the city of Cáceres, Spain, in relation to the orientations and slopes of the rooftops. Two residential areas, one in the city center and one on the outskirts of the city, and an industrial zone, all of which exhibit different urban morphologies, have been evaluated. Statistics have been assessed in consideration of the orientation and slope values of the rooftops as circular data, and the radiation values as linear data. The three dissimilar urban morphologies result in different solar potential values, and the monthly disaggregation of the data enables the ability to detect the differences existing in the solar potential between each zone, during each month. The proposed analysis could also be extrapolated to urban planning for the design of more sustainable cities to face the challenges associated with climate change. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Heat Removal Factor in Flat Plate Solar Collectors: Indoor Test Method
Energies 2018, 11(10), 2783; https://doi.org/10.3390/en11102783
Received: 9 August 2018 / Revised: 20 September 2018 / Accepted: 4 October 2018 / Published: 17 October 2018
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Abstract
This paper presents a couple of methods to evaluate the heat removal factor FR of flat plate solar collectors, as well as a parametric study of the FR against the tilt angle β, and (TiTa [...] Read more.
This paper presents a couple of methods to evaluate the heat removal factor FR of flat plate solar collectors, as well as a parametric study of the FR against the tilt angle β, and (TiTa)/G, and its effects on the a0-factor (FRτα) and the a1-factor (FRULmin). The proposed methods were based on indoor flow calorimetry. The first method considers the ratio of the actual useful heat to the maximum useful heat. The second takes into account the slopes of the family of efficiency curves (FRULmin) according to ANSI/ASHRAE 93-2010, and the minimum overall heat loss coefficient, ULmin. In both methods, a feedback temperature control at collector inclinations from horizontal to vertical allows the inlet temperature and the emulating of the solar radiation to be established by electrical heating. The performance of the methods was determined in terms of the uncertainty of the FR. Method 1 allowed a three-fold improved precision compared to Method 2; however, this implied a more detailed experimental setup. According to the first method, the effects of the tilt angle β, and the (TiTa)/G, on the a0-factor were considerable, since FR is directly proportional to the a0-factor. The changes in (TiTa)/G caused an average change in FR of 32% The FR shows almost linear behavior for inclinations from horizontal to vertical with a 14.5% change. The effects of β on the a1-factor were not considerable, due to the compensation between the increase in FR and the decrease in ULmin as β increased. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle A Sketch of Bolivia’s Potential Low-Carbon Power System Configurations. The Case of Applying Carbon Taxation and Lowering Financing Costs
Energies 2018, 11(10), 2738; https://doi.org/10.3390/en11102738
Received: 22 August 2018 / Revised: 28 September 2018 / Accepted: 8 October 2018 / Published: 12 October 2018
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Abstract
This paper considers hypothetical options for the transformation of the Bolivian power generation system to one that emits less carbon dioxide. Specifically, it evaluates the influence of the weighted average cost of capital (WACC) on marginal abatement cost curves (MACC) when applying carbon [...] Read more.
This paper considers hypothetical options for the transformation of the Bolivian power generation system to one that emits less carbon dioxide. Specifically, it evaluates the influence of the weighted average cost of capital (WACC) on marginal abatement cost curves (MACC) when applying carbon taxation to the power sector. The study is illustrated with a bottom-up least-cost optimization model. Projections of key parameters influence the shape of MACCs and the underlying technology configurations. These are reported. Results from our study (and the set of assumptions on which they are based) are country-specific. Nonetheless, the methodology can be replicated to other case studies to provide insights into the role carbon taxes and lowering finance costs might play in reducing emissions. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessFeature PaperArticle Performance Evaluation of a PID-Controlled Synchronous Buck Converter Based Battery Charging Controller for Solar-Powered Lighting System in a Fishing Trawler
Energies 2018, 11(10), 2722; https://doi.org/10.3390/en11102722
Received: 28 September 2018 / Revised: 1 October 2018 / Accepted: 2 October 2018 / Published: 11 October 2018
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Abstract
A Proportional-Integral-Derivative (PID)-controlled synchronous buck converter (SBC)-based battery charging system was designed to charge a lead-acid cell battery using commercially available Photovoltaic (PV) panel. The proposed system was installed aboard a fishing trawler to power its electrical system replacing the conventional system, which [...] Read more.
A Proportional-Integral-Derivative (PID)-controlled synchronous buck converter (SBC)-based battery charging system was designed to charge a lead-acid cell battery using commercially available Photovoltaic (PV) panel. The proposed system was installed aboard a fishing trawler to power its electrical system replacing the conventional system, which uses a diesel generator and a few kerosene lamps for lighting purposes. A PID algorithm instead of traditional Maximum power point tracker (MPPT) is used in the proposed system since the charging process of the battery requires a maximum current instead of maximum power. The proposed control algorithm is compared with the popular MPPT technique Perturb and Observation (P&O) to validate its dynamic performance at different solar irradiance levels using MATLAB/Simulink®. The simulation and the experimental results have demonstrated that the dynamic response of the proposed algorithm is significantly improved by considering higher charging current, the capability to charge the battery at low irradiance, high stability, and lower cost. Finally, a successful 15-day field trial was conducted at sea using the proposed system, and a maximum charging current output of 6.5 A was achieved by the SBC during noon time; it was sufficient to charge a 12 V, 100 Ah battery, with a state of charge (SoC) of 33%, at a voltage charging rate of +0.3 V/h. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle High Performances Design of a Six-Phase Synchronous Reluctance Motor Using Multi-Objective Optimization with Altered Bee Colony Optimization and Taguchi Method
Energies 2018, 11(10), 2716; https://doi.org/10.3390/en11102716
Received: 24 August 2018 / Revised: 13 September 2018 / Accepted: 10 October 2018 / Published: 11 October 2018
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Abstract
A two-step optimal design with multi-objective functions by using two kinds of optimization methods for a six-phase synchronous reluctance motor is applied in a centrifugal compressor to achieve minimum cost, lower torque ripple, maximum efficiency and higher power factor. In the first-step procedure, [...] Read more.
A two-step optimal design with multi-objective functions by using two kinds of optimization methods for a six-phase synchronous reluctance motor is applied in a centrifugal compressor to achieve minimum cost, lower torque ripple, maximum efficiency and higher power factor. In the first-step procedure, the optimal design with multi-objective functions by use of the altered bee colony optimization (BCO) and the Taguchi method combined with finite element analysis (FEA) is used for optimizing the barrier shape and size in the rotor to reduce torque ripple, raise power factor, maximum efficiency and raise output torque. In the second-step procedure, the optimal design with multi-objective functions by means of the altered BCO and the Taguchi method combined with FEA is applied for optimizing the geometry of stator to reduce manufacturing cost, stator iron weight and stator winding weight. Finally, some experimental results show the effectiveness of the proposed techniques. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Correlation Analysis between Wind Speed/Voltage Clusters and Oscillation Modes of Doubly-Fed Induction Generators
Energies 2018, 11(9), 2370; https://doi.org/10.3390/en11092370
Received: 13 August 2018 / Revised: 28 August 2018 / Accepted: 5 September 2018 / Published: 8 September 2018
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Abstract
Potential machine-grid interactions caused by large-scale wind farms have drawn much attention in recent years. Previous work has been done by analyzing the small–signal modeling of doubly-fed induction generators (DFIGs) to obtain the oscillation modes. This paper, by making use of the metered [...] Read more.
Potential machine-grid interactions caused by large-scale wind farms have drawn much attention in recent years. Previous work has been done by analyzing the small–signal modeling of doubly-fed induction generators (DFIGs) to obtain the oscillation modes. This paper, by making use of the metered power data of wind generating sets, studies the correlation between oscillation modes of the DFIG system and influence factors which includes wind speed and grid voltage. After the metered data is segmented, the Prony algorithm is used to analyze the oscillation modes contained in the active power. Then, the relevant oscillation modes are extracted in accordance with the small-signal analysis results. Meanwhile, data segments are clustered according to wind speed and grid voltage. The Apriori algorithm is finally used to discuss the association rules. By training the mass of data of wind generating sets, the inevitable association rules between oscillation modes and influence factors can be mined. Therefore, the prediction of oscillation modes can be achieved based on the rules. The results show that the clustering number quite affects the association rules. When the optimal cluster number is adopted, part of the wind speed/voltage clusters can analyze the certain oscillation modes. The predicted results are quite consistent with the practical data. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Scrutinising the Gap between the Expected and Actual Deployment of Carbon Capture and Storage—A Bibliometric Analysis
Energies 2018, 11(9), 2319; https://doi.org/10.3390/en11092319
Received: 29 July 2018 / Revised: 24 August 2018 / Accepted: 28 August 2018 / Published: 3 September 2018
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Abstract
For many years, carbon capture and storage (CCS) has been discussed as a technology that may make a significant contribution to achieving major reductions in greenhouse gas emissions. At present, however, only two large-scale power plants capture a total of 2.4 Mt CO [...] Read more.
For many years, carbon capture and storage (CCS) has been discussed as a technology that may make a significant contribution to achieving major reductions in greenhouse gas emissions. At present, however, only two large-scale power plants capture a total of 2.4 Mt CO2/a. Several reasons are identified for this mismatch between expectations and realised deployment. Applying bibliographic coupling, the research front of CCS, understood to be published peer-reviewed papers, is explored to scrutinise whether the current research is sufficient to meet these problems. The analysis reveals that research is dominated by technical research (69%). Only 31% of papers address non-technical issues, particularly exploring public perception, policy, and regulation, providing a broader view on CCS implementation on the regional or national level, or using assessment frameworks. This shows that the research is advancing and attempting to meet the outlined problems, which are mainly non-technology related. In addition to strengthening this research, the proportion of papers that adopt a holistic approach may be increased in a bid to meet the challenges involved in transforming a complex energy system. It may also be useful to include a broad variety of stakeholders in research so as to provide a more resilient development of CCS deployment strategies. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessArticle Variable Parameters for a Single Exponential Model of Photovoltaic Modules in Crystalline-Silicon
Energies 2018, 11(8), 2138; https://doi.org/10.3390/en11082138
Received: 18 July 2018 / Revised: 8 August 2018 / Accepted: 13 August 2018 / Published: 16 August 2018
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Abstract
The correct approximation of parallel resistance (Rp) and series resistance (Rs) poses a major challenge for the single diode model of the photovoltaic module (PV). The bottleneck behind the limited accuracy of the model is the static [...] Read more.
The correct approximation of parallel resistance (Rp) and series resistance (Rs) poses a major challenge for the single diode model of the photovoltaic module (PV). The bottleneck behind the limited accuracy of the model is the static estimation of resistive parameters. This means that Rp and Rs, once estimated, usually remain constant for the entire operating range of the same weather condition, as well as for other conditions. Another contributing factor is the availability of only standard test condition (STC) data in the manufacturer’s datasheet. This paper proposes a single-diode model with dynamic relations of Rp and Rs. The relations not only vary the resistive parameters for constant/distinct weather conditions but also provide a non-iterative solution. Initially, appropriate software is used to extract the data of current-voltage (I-V) curves from the manufacturer’s datasheet. By using these raw data and simple statistical concepts, the relations for Rp and Rs are designed. Finally, it is proved through root mean square error (RMSE) analysis that the proposed model holds a one-tenth advantage over numerous recently proposed models. Simultaneously, it is low complex, iteration-free (0 to voltage in maximum power point Vmpp range), and requires less computation time to trace the I-V curve. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessFeature PaperReview A Systematic Literature Review of Methods for Improved Utilisation of the Non-Energy Benefits of Industrial Energy Efficiency
Energies 2018, 11(12), 3241; https://doi.org/10.3390/en11123241
Received: 29 October 2018 / Revised: 12 November 2018 / Accepted: 19 November 2018 / Published: 22 November 2018
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Abstract
Improvements in industrial energy efficiency demonstrated various additional effects beyond pure energy savings and energy cost savings. Observed on many levels, these additional effects, often denoted as non-energy benefits, constitute a diverse collection, for instance, effects related to firms’ production or improvements in [...] Read more.
Improvements in industrial energy efficiency demonstrated various additional effects beyond pure energy savings and energy cost savings. Observed on many levels, these additional effects, often denoted as non-energy benefits, constitute a diverse collection, for instance, effects related to firms’ production or improvements in the work environment and the external environment. Previous studies showed the potential of including quantified and monetised non-energy benefits in energy efficiency investments. However, there seems to be a lack of methodological overview, including all the steps from observation to monetisation and inclusion in investments. This study systematically reviews the academic literature on non-energy benefits relating to methods for observation, measuring, quantification, and monetisation of the benefits. The most commonly applied research design was a case study approach, in which data on non-energy benefits were collected by conducting interviews. Furthermore, the primary methods used to enable quantification and monetisation of observed non-energy benefits were based on classifications, indexes in relation to the energy savings, or frameworks. Calculation methods, databased tools, classification frameworks, and ranking were applied to evaluate the benefits’ potential in relation to energy efficiency investments. Based on a synthesis of the review findings, this article contributes a novel scheme for improved utilisation of the non-energy benefits of industrial energy efficiency. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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Open AccessReview Frosting Phenomenon and Frost-Free Technology of Outdoor Air Heat Exchanger for an Air-Source Heat Pump System in China: An Analysis and Review
Energies 2018, 11(10), 2642; https://doi.org/10.3390/en11102642
Received: 18 August 2018 / Revised: 19 September 2018 / Accepted: 30 September 2018 / Published: 3 October 2018
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Abstract
Frost layer on the outdoor air heat exchanger surface in an air-source heat pump (ASHP) can decrease the system coefficient of performance (COP). Although the common defrosting and anti-frosting methods can improve the COP, the periodic defrosting not only reduces the system energy [...] Read more.
Frost layer on the outdoor air heat exchanger surface in an air-source heat pump (ASHP) can decrease the system coefficient of performance (COP). Although the common defrosting and anti-frosting methods can improve the COP, the periodic defrosting not only reduces the system energy efficiency but also deteriorates the indoor environment. To solve these problems, it is necessary to clearly understand the frosting phenomenon and to achieve the system frost-free operation. This paper focused firstly on the analyses of frosting pathways and frosting maps. Followed by summarizing the characteristics of frost-free technologies. And then the performances of two types of frost-free ASHP (FFASHP) systems were reviewed, and the exergy and economic analysis of a FFASHP heating system were carried out. Finally, the existing problems related to the FFASHP technologies were proposed. Results show that the existing frosting maps need to be further improved. The FFASHP systems can not only achieve continuous frost-free operation but reduce operating cost. And the total COP of the FFASHP heating system is approximately 30–64% higher than that of the conventional ASHP system under the same frosting conditions. However, the investment cost of the FFASHP system increases, and its reliability also needs further field test in a wider frosting environment. In the future, combined with a new frosting map, the control strategy for the FFASHP system should be optimized. Full article
(This article belongs to the Special Issue Sustainable Energy Systems)
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