Paradigm shift in urban energy systems through distributed generation: Methods and models

The path towards energy sustainability is commonly referred to the incremental adoption of available technologies, practices and policies that may help to decrease the environmental impact of energy sector, while providing an adequate standard of energy services. The evaluation of trade-offs among technologies, practices and policies for the mitigation of environmental problems related to energy resources depletion requires a deep knowledge of the local and global effects of the proposed solutions. While attempting to calculate such effects for a large complex system like a city, an advanced multidisciplinary approach is needed to overcome difficulties in modeling correctly real phenomena while maintaining computational transparency, reliability, interoperability and efficiency across different levels of analysis. Further, a methodology that rationally integrates different computational models and techniques is necessary to enable collaborative research in the field of optimization of energy efficiency strategies and integration of renewable energy systems in urban areas. For these reasons, a selection of currently available models for distributed generation planning and design is presented and analyzed in the perspective of gathering their capabilities in an optimization framework to support a paradigm shift in urban energy systems. This framework embodies the main concepts of a local energy management system and adopts a multicriteria perspective to determine optimal solutions for providing energy services through distributed generation.     

A bibliometric analysis of the hydrogen production from dark fermentation

Hydrogen energy plays an important role in solving the environmental problems caused by the fuel crisis and greenhouse gas emissions. However, hydrogen application on an industrial scale still requires technological advances, especially in choosing the best technological route for the recovery of renewable and cost-effective hydrogen. Therefore, this bibliometric review evaluated the research progress, trends, updates, and hotspots on hydrogen production from dark fermentation. The Web of Science© database was used to select the documents from 2000 to 2021, and the VOSviewer© and Bibliometrix softwares were used to carry out the bibliometric investigation. The results demonstrated that 3071 documents (2755 articles and 316 reviews) studied the hydrogen production from dark fermentation over the last 21 years. The number of publications exponentially increased in the last five years, which can be associated with the demand for new technologies to produce clean energy sources and decrease the environmental impacts caused by petroleum-based fuel. Keyword analysis revealed that the studies focused on the operational parameters, process optimization, pretreatment, and microbial community, aiming to increase the hydrogen yield during dark fermentation. Finally, this comprehensive review provides future directions for applying dark fermentation to produce hydrogen as a sustainable and renewable fuel in a biorefiney concept.     

Hydrogen energy storage integrated hybrid renewable energy systems: A review analysis for future research directions

Hydrogen energy storage systems (HydESS) and their integration with renewable energy sources into the grid have the greatest potential for energy production and storage while controlling grid demand to enhance energy sustainability. This paper presents a bibliometric analysis based on a comprehensive review of the highly cited articles on HydESS to provide a detailed insight into future directions and applications. The study was carried out by using the Scopus database search engine to look for filtered keywords in the HydESS and related research. It can be demonstrated that the HydESS literature expanded rapidly from 2016 to 2021 compared to 2011 to 2015. It is found that 89.17% of published articles explained control and test systems-based methods, whereas 10.83% of publications discuss review assessments. Our analysis of highly cited articles on HydESS highlights several aspects, such as methods and systems, issues, difficulties, and challenges to establishing current constraints and research gaps. This evaluation can enhance operational performance, environmental friendliness, energy savings, uninterrupted power supply service, cost benefits, on-site generation, and adaptability. It would be beneficial for technology development and the growth of the hydESS industry. This study may act as a guideline not only for academics in determining the line of research and generating additional discoveries, but also for the government in formulating financial strategies.     

Waste-to-hydrogen technologies: A critical review of techno-economic and socio-environmental sustainability

Hydrogen is a fuel with immense potential of satisfying the need for environmentally benign energy sources, and waste-derived hydrogen is promising in diverting waste streams away from landfills and other costly treatment. Nonetheless, many waste-to-hydrogen pathways are incipient and require significant efforts to be established as an indispensable element of the path towards sustainability. This review comprehensively evaluates waste-to-hydrogen technologies from technological, economic, environmental, and societal viewpoints. State-of-the-art of five technologies was summarized, focusing on emerging trends in published literature. Several knowledge gaps, future research prospects, and possible improvements related to performance, greenhouse gas emissions, production costs, hydrogen-based transportation, and public acceptance were also identified. Fulfilling the lack of techno-economic and environmental studies of waste-to-hydrogen routes, incorporation of renewable energy into processes, and necessities of scaling-up and production cost reduction are prominent among research needs recognized through this review. Conclusions of this study will be beneficial towards sustainably integrating hydrogen into large-scale energy systems.     

The sustainability indicators of power production systems

One of the most important elements of economical and social development is to provide uninterrupted electric energy to consumers. The increasing world population and technological developments rapidly increase the demand on electric energy. In order to meet the increasing demand for sustainable development, it is necessary to use the consumable resources of the world in the most productive manner and minimum level and to keep its negative effects on human health and environment in the lowest level as much as possible. In this study, alignment of hydrogen fuel cells, hydroelectric, wind, solar and geothermal sourced electric energy systems, in addition to fossil fueled coal, natural gas and nuclear power plants, in respect to sustainability parameters such as CO₂ emission, land use, energy output, fresh water consumption and environmental and social effects is researched. Consequently, it has been determined that the wind and nuclear energy power plants have the highest sustainability indicators. The fuel cells that use hydrogen obtained by using coal and natural gas are determined as the most disadvantageous transformation technologies in respect to sustainability. This study contains an alignment related to today's technologies. Using of renewable energy resources especially in production of hydrogen, output increases to be ensured with nanotechnology applications in photovoltaic systems may change this alignment.     

Fuzzy Multi-actor Multi-criteria Decision Making for sustainability assessment of biomass-based technologies for hydrogen production

The purpose of this paper is to develop a sustainability assessment method to rank the prior sequence of biomass-based technologies for hydrogen production. A novel fuzzy Multi-actor Multi-criteria Decision Making method which allows multiple groups of decision-makers to use linguistic variables to assess the biomass-based technologies for hydrogen production has been developed. Fifteen criteria relevant to in economic, environmental, technological and social-political aspects have been used in sustainability assessment. Four biomass-based technologies including pyrolysis, conventional gasification, supercritical water gasification and fermentative hydrogen production have been studied by the proposed method, and biomass gasification has been considered as the most sustainable scenario and can be chosen for further development.     

A novel multicriteria sustainability investigation of energy storage systems

Affordable, clean, efficient, flexible, and reliable energy storage is an important component of sustainable energy systems. There are several studies in the literature concentrating on improving the sustainability performance of energy storage systems from economic and technical perspectives. However, a comprehensive performance investigation of energy storage systems that take economic, environmental, social, and technical criteria into account is still needed. For that reason, in the present study, it is aimed to perform a complete assessment and analysis of the sustainability of energy storage systems for residential applications in communities and cities. Pumped hydro, conventional batteries, high‐temperature batteries, flow batteries, and hydrogen are the selected energy storage systems. In order to handle the vagueness and ambiguity during the assessment and to eliminate the perceived hesitancy in the decision makers' preferences, an innovative method, a hybrid hesitant fuzzy multicriteria decision‐making (MCDM) methodology composed of hesitant fuzzy analytic hierarchy process (HFAHP) and hesitant fuzzy technique for order preference by similarity to ideal solution (HFTOPSIS), is utilized to assess the sustainability of the selected systems. In this study, four different performance criteria: economic (power cost and energy cost), environmental (pollutant emissions, area requirement, wastewater quality, and solid waste production), social (safety, accessibility, ease of use, and public acceptance), and technical (efficiency, storage capacity, cycling limit, and performance degradation) are taken into consideration. The performance evaluation results indicate that technical performance has the highest influence and social performance has the lowest influence when evaluating the sustainability of the selected energy storage systems. And hydrogen has the highest sustainability performance compared with the other selected energy storage options.     

Sustainability improvement in combined electricity and freshwater generation systems via biomass: A comparative emergy analysis and multi-objective optimization

For energy systems, sustainability is a major concern that must be carefully considered when designed and established. Emergy analysis is an effective technique to scrutinize the sustainability of these systems. On the other hand, water shortage is seen to become a big problem in the close future; however, this problem can be effectively alleviated by combined electricity/water production plants, where waste heat is recovered to generate freshwater. This study applies emergy analysis to evaluate and improve the sustainability, renewability, environmental impacts, and economic aspect of such a plant, in which a multi-stage desalination (MSF) system is employed to recover the waste heat from a gas turbine (GT). The plant is fueled by biomass/natural gas (system I), natural gas (system II), and biomass (system III), and the above-mentioned features are compared for the different fuel types. To estimate chemical equilibrium state inside the gasifier, Lagrange's method of undetermined multipliers is applied. Also, considering exergy efficiency and emergy sustainability index as objective functions, biomass/natural gas-fueled system is optimized by adopting a multi-objective optimization approach based on the non-dominated sorting genetic algorithm II (NSGA II). To predict the optimized points' behavior, the Pareto optimal frontier of the system is utilized. The results reveal that using biomass as inlet fuel remarkably improves the sustainability index and reduces environmental impacts. The optimization results show that as sustainability index increases, exergy efficiency decreases. Also, the two optimized points of the system are found to have exergy efficiencies of 20.14% and 25.09% and sustainability indices of 24.67% and 13.60%.     

Prioritizing sustainable electricity production technologies: MCDM approach

Economic, technological, social, and political developments stressed the need for shifts in energy-mix. Therefore it is important to provide a rationale for sustainable decision making in energy policy. The aim of this paper is to develop the multi-criteria decision support framework for choosing the most sustainable electricity production technologies. Given selection of sustainable energy sources involves many conflicting criteria, multi-criteria decision methods MULTIMOORA and TOPSIS were employed for the analysis. The indicator system covering different approaches of sustainability was established. The analysis proved that the future energy policy should be oriented towards the sustainable energy technologies, namely water and solar thermal ones. It is the proposed multi-criteria assessment framework that can constitute a basis for further sub-regional optimization of sustainable energy policy.     

Hydrogen energy storage integrated battery and supercapacitor based hybrid power system: A statistical analysis towards future research directions

Environmentally friendly and pollution-free hydrogen cell, battery and supercapacitor hybrid power system has taken the attention of scientists in recent years. Several notable advancements in energy storage mechanisms with hybrid power systems have been made during the last decade, influencing innovation, research, and the possible direction for improving energy storage technologies. This paper represents a quantitative analysis of all knowledge carriers with mathematical and statistical methods of hydrogen energy storage to establish a hybrid power system. For selecting the top cited papers in this topic, related articles on energy storage mechanisms for hybrid power systems were searched in the Scopus database under specified predetermined parameters. The selection technique of the most cited paper was based on filtered keywords in the hybrid hydrogen energy storage-based hybrid power system and related research during 2008–2021. About 48% of all articles have been published between 2016 and 2019; 21% will have originated from China; and 29% of the papers have used batteries as a form of energy storage in the application of electric vehicles. Most of the articles contain experimental work (25.11%) followed by simulation analysis (25%) and systematic and nonsystematic review (18.75%). Related publications with the most citations were published in 35 different impactful journals from different publishers and nations. This research found that integrating hydrogen energy storage with battery and supercapacitor to establish a hybrid power system has provided valuable insights into the field's progress and development. Moreover, it is a thriving and expanding subject of study. Bibliometric analysis was used to identify the most significant research publications on the subject of hybrid energy storage, mapping the multidisciplinary character, illustrating nature and trends, and outlining areas for further research. The process of collecting, selecting, and analyzing the most cited articles is expected to contribute to a methodical foundation for future developments of hydrogen energy storage systems and provide viable research paths toward attaining a hybrid power system.     

Mexican contributions for the improvement of electrocatalytic properties for the oxygen reduction reaction in PEM fuel cells

Like the rest of the world, Mexico faces severe environmental challenges due to its energy dependence on fossil fuels, for that reason Mexican researchers have conducted studies related to the development of renewable energy technologies. In this sense, different research groups have contributed top quality results in the design, synthesis, characterization, and evaluation of the performance of electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). This review describes Mexican contributions to the design of new nanocatalysts for the cathodic reaction in fuel cells. Two categories of nanocatalysts are discussed, those based on Pt and those which are Pt-free, with special attention given to Pd and Ru-based materials, whose catalytic activities are noteworthy. Mexican scientific groups have published more than 100 articles on the ORR in the last 20 years, with over 50% of those publications focused on the performance of Pt-based catalytic compounds which have shown high active and stable surface area, and low catalyst loading. The remaining publications address Pt-free nanoparticles that present catalytic activity for the ORR.     

中国低碳能源与环境污染控制研究现状

本文阐述了中国能源结构现状并归纳分析集中式低碳能源、分布式低碳能源与单项低碳能源研究技术进展;从大气、固废、水环境及煤矿油田角度分析了与低碳能源相关的环境污染控制研究现状;系统汇集分析了我国低碳能源与环境污染控制方面的立法、政策与保障措施;提出了中国低碳能源与环境污染控制的技术发展趋势。     

Sustainability issues for promotion of Jatropha biodiesel in Indian scenario: A review

Jatropha, a non-edible oil seed yielding plant has been identified by the Government of India to produce biodiesel under National Biodiesel Mission. Failure of National Biodiesel Mission Phase-I requires critical analysis of all the possible facts related to its long-term sustainability. Present work identifies important sustainability issues related to promotion of Jatropha biodiesel in India. These sustainability issues have been regrouped in four major categories: technological, environmental, economic and social. This paper attempts to explore various sustainability issues taking into account the recent Indian experiences with possible government support/initiatives for successful adoption of Jatropha biodiesel in Indian scenario.     

Exploring the impact of technology development and adoption for sustainable hydroelectric power and storage technologies in the Pacific Northwest United States

A wide range of literature streams and methods were examined for this research, including sustainability, integrated resource planning, and construction of portfolios of electricity generation technologies. The research then focused on current and emerging HPSTs (hydropower generation and storage technologies), and technical, economic, social, and environmental sustainability objectives associated with those technologies in the PNW (Pacific Northwest) region of the United States. Candidate technologies obtained from the literature were examined using the Delphi Method, and then rated according to their perceived impacts using the AHP (Analytical Hierarchy Process). GP (Goal Programming) was then used to determine an optimal mix of technologies to achieve sustainability objectives, using these weightings and assumptions related to specific scenarios regarding technology development, adoption, and availability. This research is important because few previous studies have systematically considered multiple objectives and criteria from multiple stakeholder experts for creating portfolios of sustainable electricity generation technologies. Previous research has also not comprehensively investigated the manner in which changing scenarios of technology development and availability rates may lead to various technological, economic, environmental, and social sustainability impacts with regard to planning of regional electrical generation and storage systems.     

Life cycle analysis for future photovoltaic systems using hybrid solar cells

Global climate change concerns have lead to growing demand for renewable energy sources (RES). However the viability of these sources is critically dependent on environmental, economic and technological considerations. This paper focuses on the environmental aspect of future photovoltaic (PV) systems which are assessed through life cycle analysis (LCA). Previous LCA studies on commercially available PV systems are reviewed. The sustainable evaluation methods used in these studies are also discussed. These methods are applied to the hybrid quantum dot (QD)-based solar cells currently under development within a project between the University of Manchester and Imperial College London. The aim of this project is to develop affordable solar cells with efficiencies up to 10% for micro-generation applications. Presently hybrid QD-based solar cells are not commercially fabricated; therefore the study is mostly based on very small laboratory-scale production. For easy comparability 10% conversion efficiency and 25 years lifetime are initially assumed. Lower conversion efficiencies and shorter lifetimes likely to initially characterise emerging PV technologies such as the hybrid QD-based solar cells are discussed. Comparable criteria for sustainability of electricity-generating systems namely net energy ratio (NER), energy pay-back time (EPB-T) and CO₂ emissions per unit generated during lifetime are found to be lower than current commercially available PV modules.     

A bibliometric analysis of recent energy efficiency literatures: an expanding and shifting focus

To meet the energy requirements of sustainable economic growth, policymakers, analysts, and business leaders have increasingly turned to the role that energy efficiency might play. This has resulted in a growing energy efficiency literature, which is examined in this paper. Using bibliometric techniques, we analyze the database of Science Citation Index Expanded and Social Sciences Citation Index covering the 1991–2010 period. Of the 8,244 publications, 78.8 % were journal articles, and about 95.5 % were published in English. Based on the h-index, an evaluative indicator, the USA has produced the most influential set of publications on energy efficiency, followed by Canada, UK, Japan, and China. In contrast, China is second to the USA in the volume of its publications. Correspondingly, the University of California at Berkeley, Chinese Academy of Sciences, and Tsinghua University were the most productive research organizations. The three most common subjects examined in this body of research were “energy and fuels”, “environmental sciences”, and “electrical and electronic engineering”. Energy Policy has been the most productive journal, and “A water and heat management model for proton-exchange-membrane fuel-cells”, has had the most citations (587 through May 2012). Based on an analysis of article titles and keywords, we conclude that the hotspots of energy efficiency research have been green communications, renewable energy, and energy sustainability; green communications, in particular, has developed rapidly as a focus of energy efficiency publications in recent years.     

Multi-criteria assessment of new and renewable energy power plants

The multi-criteria evaluation of new and renewable technologies demonstrates the potential analysis of complex systems. Every energy system under consideration is an entity by itself, defined by the respective number of parameters which are deterministically interrelated according to the physical laws. Sustainability indicators take into account the economic and environmental resources parameters. This paper presents selection of criteria and options for the new and renewable energy technologies assessment based on the analysis and synthesis of parameters under the information deficiency method. In order to present an evaluation of the new energy technologies, a number of options featuring some of the characteristics measured by the selected sustainability indicators are taken into consideration. For each option under consideration, the sustainability indicators are defined in order to verify their rating under the specific constraints and to obtain the generalised index of sustainability rating of all options. The aim of this paper is to define energy indicators used in the assessment of energy systems which meet the sustainability criterion. In this respect, the following indicators are taken into consideration: energy resources, environment capacity, social indicators and economic indicators.     

Thermochemical conversion of sewage sludge: A critical review

The increasing levels of sewage sludge production demands research and development to introduce more commercially feasible options for reducing socio-economic and environmental problems associated with its current treatment. Sewage sludge may be processed to produce useful products or as a feedstock for energy generation. Initially, the characteristics of sewage sludge are discussed in terms of composition and the current options for its treatment with the associated environmental impacts. Processes to valorize sewage sludge are discussed, including heavy metal removal from sewage sludge, production of bio-char, production and use of activated carbon and use of sewage sludge combustion ash in cement and concrete. Thermochemical processes i.e., pyrolysis, co-pyrolysis and catalytic pyrolysis, also gasification and combustion for process intensification, energy and resource recovery from sewage sludge are then critically reviewed in detail. The pyrolysis of sewage sludge to produce a bio-oil is covered in relation to product bio-oil composition, reactor type and the use of catalysts. Gasification of sewage sludge focusses on the characteristics of the different available reactor types and the influence of a range of process parameters and catalysts on gas yield and composition. The selection and design of catalysts are of vital importance to enhance the selectivity of the selected thermochemical pyrolysis or gasification process. The catalysts used for sewage sludge treatment need more research to enable selectivity towards the targeted desired end-products along with optimization of parametric conditions and development of innovative reactor technologies. The combustion of sewage sludge is reviewed in terms of reactor technologies, flue gas cleaning systems and pollutant emissions. In addition, reactor technologies in terms of technological strength and market competitiveness with the particular application to sewage sludge are compared for the first time for thermochemical conversion. A critical comparison is made of the drying techniques, co-feedstocks and catalytic processes, reaction kinetics, reactor technologies, operating conditions to be optimized, removal of impurities, fuel properties, their constraints and required improvements. The emphasis of this review is to promote environmental sustainability for process intensification, energy and resource recovery from pyrolysis, gasification and combustion involving the use of catalysts.     

General sustainability indicator of renewable energy system based on grey relational analysis

This research answers the question of how to measure the sustainability of a renewable energy systems (RESs) as a physical parameter. Renewable energy is considered as a solution for mitigating the energy crisis, climate change and environmental pollution; however, an important problem of its application is that it is very difficult to evaluate the sustainability of RESs. This study develops a general sustainability indicator which is a tool to evaluate sustainability of RESs precisely and comprehensively. Based on the Triple Bottom Line approach, 11 Basic Sustainability Indicators with different dimensions and various units are selected from environmental, economic and social sustainability assessment criteria. In order to deal with the uncertainties in the definition and the assessment of sustainability, the grey regression analysis method is employed to quantify the basic indicators and to aggregate them into the general indicator. In addition, for explaining application of the general indicator, the cases of four RESs in hot‐arid Australia are presented. In the case study, the grey indicator is used to assess the sustainability of four systems with different combinations of grid, solar photovoltaic and wind renewable energy. The final results are compared with the general indicator based on fuzzy sets theory developed in previous studies. It is found that for the case of Australian system, the grey sustainability indicator has a good linear correlation to the fuzzy indicator results. The grey indicator is an effective way to assess the sustainability of RESs and provides a good tool for designers, users, decision makers and researchers. Copyright © 2013 John Wiley & Sons, Ltd.     

Should a small combined heat and power plant (CHP) open to its regional power and heat networks? Integrated economic,energy, and emergy evaluation of optimization plans for Jiufa CHP

The development of industrial ecology has led company managers to increasingly consider their company's niche in the regional system, and to develop optimization plans. We used emergy-based, ecological-economic synthesis to evaluate two optimization plans for the Jiufa Combined Heat and Power (CHP) Plant, Shandong China. In addition, we performed economic input–output analysis and energy analysis on the system. The results showed that appropriately incorporating a firm with temporary extra productivity into its regional system will help maximize the total productivity and improve ecological-economic efficiency and benefits to society, even without technical optimization of the firm itself. In addition, developing a closer relationship between a company and its regional system will facilitate the development of new optimization opportunities. Small coal-based CHP plants have lower-energy efficiency, higher environmental loading, and lower sustainability than large fossil fuel and renewable energy-based systems. The emergy exchange ratio (EER) proved to be an important index for evaluating the vitality of highly developed ecological-economic systems.