In this review, the technologies and working principles of different materials used in supercapacitors are explained. The most important supercapacitor active materials are discussed from both research and application perspectives, together with brief explanations of their properties, such as specific surface area and capacitance values. A review of different supercapacitor electrolytes is given and their positive and negative features are discussed. Finally, cell configurations are considered, pointing out the advantages and drawbacks of each configuration.
Global warming and climate change concerns have triggered global efforts to reduce the concentration of atmospheric carbon dioxide (CO ). Carbon dioxide capture and storage (CCS) is considered a crucial strategy for meeting CO emission reduction targets. In this paper, various aspects of CCS are reviewed and discussed including the state of the art technologies for CO capture, separation, transport, storage, leakage, monitoring, and life cycle analysis. The selection of specific CO capture technology heavily depends on the type of CO generating plant and fuel used. Among those CO separation processes, absorption is the most mature and commonly adopted due to its higher efficiency and lower cost. Pipeline is considered to be the most viable solution for large volume of CO transport. Among those geological formations for CO storage, enhanced oil recovery is mature and has been practiced for many years but its economical viability for anthropogenic sources needs to be demonstrated. There are growing interests in CO storage in saline aquifers due to their enormous potential storage capacity and several projects are in the pipeline for demonstration of its viability. There are multiple hurdles to CCS deployment including the absence of a clear business case for CCS investment and the absence of robust economic incentives to support the additional high capital and operating costs of the whole CCS process.
The smart grid is conceived of as an electric grid that can deliver electricity in a controlled, smart way from points of generation to active consumers. Demand response (DR), by promoting the interaction and responsiveness of the customers, may offer a broad range of potential benefits on system operation and expansion and on market efficiency. Moreover, by improving the reliability of the power system and, in the long term, lowering peak demand, DR reduces overall plant and capital cost investments and postpones the need for network upgrades. In this paper a survey of DR potentials and benefits in smart grids is presented. Innovative enabling technologies and systems, such as smart meters, energy controllers, communication systems, decisive to facilitate the coordination of efficiency and DR in a smart grid, are described and discussed with reference to real industrial case studies and research projects.
Pyrolysis is one of the thermochemical technologies for converting biomass into energy and chemical products consisting of liquid bio-oil, solid biochar, and pyrolytic gas. Depending on the heating rate and residence time, biomass pyrolysis can be divided into three main categories slow (conventional), fast and flash pyrolysis mainly aiming at maximising either the bio-oil or biochar yields. Synthesis gas or hydrogen-rich gas can also be the target of biomass pyrolysis. Maximised gas rates can be achieved through the catalytic pyrolysis process, which is now increasingly being developed. Biomass pyrolysis generally follows a three-step mechanism comprising of dehydration, primary and secondary reactions. Dehydrogenation, depolymerisation, and fragmentation are the main competitive reactions during the primary decomposition of biomass. A number of parameters affect the biomass pyrolysis process, yields and properties of products. These include the biomass type, biomass pretreatment (physical, chemical, and biological), reaction atmosphere, temperature, heating rate and vapour residence time. This manuscript gives a general summary of the properties of the pyrolytic products and their analysis methods. Also provided are a review of the parameters that affect biomass pyrolysis and a summary of the state of industrial pyrolysis technologies.
Fossil fuel consumption in transportation system and energy-intensive sectors as the principal pillar of civilization is associated with progressive release of greenhouse gases. Hydrogen as a promising energy carrier is a perfect candidate to supply the energy demand of the world and concomitantly reduce toxic emissions. This article gives an overview of the state-of-the-art hydrogen production technologies using renewable and sustainable energy resources. Hydrogen from supercritical water gasification (SCWG) of biomass is the most cost effective thermochemical process. Highly moisturized biomass is utilized directly in SCWG without any high cost drying process. In SCWG, hydrogen is produced at high pressure and small amount of energy is required to pressurize hydrogen in the storage tank. Tar and char formation decreases drastically in biomass SCWG. The low efficiency of solar to hydrogen system as well as expensive photovoltaic cell are the most important barriers for the widespread commercial development of solar-based hydrogen production. Since electricity costs play a crucial role on the final hydrogen price, to generate carbon free hydrogen from solar and wind energy at a competitive price with fossil fuels, the electrical energy cost should be four times less than commercial electricity prices.
Large-scale deployment of intermittent renewable energy (namely wind energy and solar PV) may entail new challenges in power systems and more volatility in power prices in liberalized electricity markets. Energy storage can diminish this imbalance, relieving the grid congestion, and promoting distributed generation. The economic implications of grid-scale electrical energy storage technologies are however obscure for the experts, power grid operators, regulators, and power producers. A meticulous techno-economic or cost-benefit analysis of electricity storage systems requires consistent, updated cost data and a holistic cost analysis framework. To this end, this study critically examines the existing literature in the analysis of life cycle costs of utility-scale electricity storage systems, providing an updated database for the cost elements (capital costs, operational and maintenance costs, and replacement costs). Moreover, life cycle costs and levelized cost of electricity delivered by electrical energy storage is analyzed, employing Monte Carlo method to consider uncertainties. The examined energy storage technologies include pumped hydropower storage, compressed air energy storage (CAES), flywheel, electrochemical batteries (e.g. lead–acid, NaS, Li-ion, and Ni–Cd), flow batteries (e.g. vanadium-redox), superconducting magnetic energy storage, supercapacitors, and hydrogen energy storage (power to gas technologies). The results illustrate the economy of different storage systems for three main applications: bulk energy storage, T&D support services, and frequency regulation.
Dye-sensitized solar cell (DSSC) offers an efficient and easily implemented technology for future energy supply. Compared to conventional silicon solar cells, it provides comparable power conversion efficiency (PCE) at low material and manufacturing costs. DSSC materials such as titanium oxide (TiO ) are inexpensive, abundant and innocuous to the environment. Since DSSC materials are less prone to contamination and processable at ambient temperature, a roll-to-roll process could be utilized to print DSSCs on the mass production line. DSSCs perform better under lower light intensities, which makes them an excellent choice for indoor applications. Due to the advancement of molecular engineering, colored and transparent thin films have been introduced to enhance the aesthetic values. Up to now, such benefits have attracted considerable research interests and commercialization effort. Here, this review examines advanced techniques and research trends of this promising technology from the perspective of device modeling, state-of-art techniques, and novel device structures.
Electric energy security is essential, yet the high cost and limited sources of fossil fuels, in addition to the need to reduce greenhouse gasses emission, have made renewable resources attractive in world energy-based economies. The potential for renewable energy resources is enormous because they can, in principle, exponentially exceed the world׳s energy demand; therefore, these types of resources will have a significant share in the future global energy portfolio, much of which is now concentrating on advancing their pool of renewable energy resources. Accordingly, this paper presents how renewable energy resources are currently being used, scientific developments to improve their use, their future prospects, and their deployment. Additionally, the paper represents the impact of power electronics and smart grid technologies that can enable the proportionate share of renewable energy resources.
The paper reviews different approaches, technologies, and strategies to manage large-scale schemes of variable renewable electricity such as solar and wind power. We consider both supply and demand side measures. In addition to presenting energy system flexibility measures, their importance to renewable electricity is discussed. The flexibility measures available range from traditional ones such as grid extension or pumped hydro storage to more advanced strategies such as demand side management and demand side linked approaches, e.g. the use of electric vehicles for storing excess electricity, but also providing grid support services. Advanced batteries may offer new solutions in the future, though the high costs associated with batteries may restrict their use to smaller scale applications. Different “P2Y”-type of strategies, where P stands for surplus renewable power and Y for the energy form or energy service to which this excess in converted to, e.g. thermal energy, hydrogen, gas or mobility are receiving much attention as potential flexibility solutions, making use of the energy system as a whole. To “functionalize” or to assess the value of the various energy system flexibility measures, these need often be put into an electricity/energy market or utility service context. Summarizing, the outlook for managing large amounts of RE power in terms of options available seems to be promising.
With the rising demand for renewable energy and environmental protection, anaerobic digestion of biogas technology has attracted considerable attention within the scientific community. This paper presents a comprehensive review of research achievements on anaerobic digestion developments for biogas production. The review includes a discussion of factors affecting efficiency (temperature, pH, C/N ratio, OLR and retention time), accelerants (greenery biomass, biological pure culture and inorganic additives), reactors (conventional anaerobic reactors, sludge retention reactors and anaerobic membrane reactors) and biogas AD processes (lignocellulose waste, municipal solid waste, food waste, livestock manure and waste activated sludge) based on substrate characteristics and discusses the application of each forementioned aspect. The factors affecting efficiency are crucial to anaerobic digestion, because they play a major role in biogas production and determine the metabolic conditions for microorganism growth. As an additive, an accelerant is not only regarded as a nutrient resource, but can also improve biodegradability. The focus of reactor design is the sufficient utilization of a substrate by changing the feeding method and enhancing the attachment to biomass. The optimal digestion process balances the optimal digest conditions with the cost-optimal input/output ratio. Additionally, establishment of theoretical and technological studies should emphasize practicality based on laboratory-scale experiments because further development of biogas plants would allow for a transition from household to medium- and large-scale projects; therefore, improving stability and efficiency are recommended for advancing AD research.
Persistent organic pollutants (POPs) are carbon-based chemical substances that are resistant to environmental degradation and may not be completely removed through treatment processes. Their persistence can contribute to adverse health impacts on wild-life and human beings. Thus, the solar photocatalysis process has received increasing attention due to its great potential as a green and eco-friendly process for the elimination of POPs to increase the security of clean water. In this context, ZnO nanostructures have been shown to be prominent photocatalyst candidates to be used in photodegradation owing to the facts that they are low-cost, non-toxic and more efficient in the absorption across a large fraction of the solar spectrum compared to TiO . There are several aspects, however, need to be taken into consideration for further development. The purpose of this paper is to review the photo-degradation mechanisms of POPs and the recent progress in ZnO nanostructured fabrication methods including doping, heterojunction and modification techniques as well as improvements of ZnO as a photocatalyst. The second objective of this review is to evaluate the immobilization of photocatalyst and suspension systems while looking into their future challenges and prospects.
Due to increasing concerns about global warming, greenhouse gas emissions, and the depletion of fossil fuels, the electric vehicles (EVs) receive massive popularity due to their performances and efficiencies in recent decades. EVs have already been widely accepted in the automotive industries considering the most promising replacements in reducing CO emissions and global environmental issues. Lithium-ion batteries have attained huge attention in EVs application due to their lucrative features such as lightweight, fast charging, high energy density, low self-discharge and long lifespan. This paper comprehensively reviews the lithium-ion battery state of charge (SOC) estimation and its management system towards the sustainable future EV applications. The significance of battery management system (BMS) employing lithium-ion batteries is presented, which can guarantee a reliable and safe operation and assess the battery SOC. The review identifies that the SOC is a crucial parameter as it signifies the remaining available energy in a battery that provides an idea about charging/discharging strategies and protect the battery from overcharging/over discharging. It is also observed that the SOC of the existing lithium-ion batteries have a good contribution to run the EVs safely and efficiently with their charging/discharging capabilities. However, they still have some challenges due to their complex electro-chemical reactions, performance degradation and lack of accuracy towards the enhancement of battery performance and life. The classification of the estimation methodologies to estimate SOC focusing with the estimation model/algorithm, benefits, drawbacks and estimation error are extensively reviewed. The review highlights many factors and challenges with possible recommendations for the development of BMS and estimation of SOC in next-generation EV applications. All the highlighted insights of this review will widen the increasing efforts towards the development of the advanced SOC estimation method and energy management system of lithium-ion battery for the future high-tech EV applications.
Recently, Wireless Sensor Networks (WSNs) have attracted lot of attention due to their pervasive nature and their wide deployment in Internet of Things, Cyber Physical Systems, and other emerging areas. The limited energy associated with WSNs is a major bottleneck of WSN technologies. To overcome this major limitation, the design and development of efficient and high performance energy harvesting systems for WSN environments are being explored. We present a comprehensive taxonomy of the various energy harvesting sources that can be used by WSNs. We also discuss various recently proposed energy prediction models that have the potential to maximize the energy harvested in WSNs. Finally, we identify some of the challenges that still need to be addressed to develop cost-effective, efficient, and reliable energy harvesting systems for the WSN environment.
Climate change and global warming as the main human societies’ threats are fundamentally associated with energy consumption and GHG emissions. The residential sector, representing 27% and 17% of global energy consumption and CO emissions, respectively, has a considerable role to mitigate global climate change. Ten countries, including China, the US, India, Russia, Japan, Germany, South Korea, Canada, Iran, and the UK, account for two-thirds of global CO emissions. Thus, these countries’ residential energy consumption and GHG emissions have direct, significant effects on the world environment. The aim of this paper is to review the status and current trends of energy consumption, CO emissions and energy policies in the residential sector, both globally and in those ten countries. It was found that global residential energy consumption grew by 14% from 2000 to 2011. Most of this increase has occurred in developing countries, where population, urbanization and economic growth have been the main driving factors. Among the ten studied countries, all of the developed ones have shown a promising trend of reduction in CO emissions, apart from the US and Japan, which showed a 4% rise. Globally, the residential energy market is dominated by traditional biomass (40% of the total) followed by electricity (21%) and natural gas (20%), but the total proportion of fossil fuels has decreased over the past decade. Energy policy plays a significant role in controlling energy consumption. Different energy policies, such as building energy codes, incentives, energy labels have been employed by countries. Those policies can be successful if they are enhanced by making them mandatory, targeting net-zero energy building, and increasing public awareness about new technologies. However, developing countries, such as China, India and Iran, still encounter with considerable growth in GHG emissions and energy consumption, which are mostly related to the absence of strong, efficient policy.
How to effectively utilize low and medium temperature energy is one of the solutions to alleviate the energy shortage and environmental pollution problems. In the past twenty years, because of its feasibility and reliability, organic Rankine cycle has received widespread attentions and researches. In this paper, it reviews the selections of working fluids and expanders for organic Rankine cycle, including an analysis of the influence of working fluids' category and their thermodynamic and physical properties on the organic Rankine cycle's performance, a summary of pure and mixed working fluids' screening researches for organic Rankine cycle, a comparison of pure and mixture working fluids' applications and a discussion of all types of expansion machines' operating characteristics, which would be beneficial to select the optimal working fluid and suitable expansion machine for an effective organic Rankine cycle system.
Climate change and fossil fuel depletion are the main reasons leading to hydrogen technology. There are many processes for hydrogen production from both conventional and alternative energy resources such as natural gas, coal, nuclear, biomass, solar and wind. In this work, a comparative overview of the major hydrogen production methods is carried out. The process descriptions along with the technical and economic aspects of 14 different production methods are discussed. An overall comparison is carried out, and the results regarding both the conventional and renewable methods are presented. The thermochemical pyrolysis and gasification are economically viable approaches providing the highest potential to become competitive on a large scale in the near future while conventional methods retain their dominant role in H production with costs in the range of 1.34–2.27 $/kg. Biological methods appear to be a promising pathway but further research studies are needed to improve their production rates, while the low conversion efficiencies in combination with the high investment costs are the key restrictions for water-splitting technologies to compete with conventional methods. However, further development of these technologies along with significant innovations concerning H storage, transportation and utilization, implies the decrease of the national dependence on fossil fuel imports and green hydrogen will dominate over the traditional energy resources.
New heat conversion technologies need to be developed and improved to take advantage of the necessary increase in the supply of renewable energy. The Organic Rankine Cycle is well suited for these applications, mainly because of its ability to recover low-grade heat and the possibility to be implemented in decentralized lower-capacity power plants. In this paper, an overview of the different ORC applications is presented. A market review is proposed including cost figures for several commercial ORC modules and manufacturers. An in-depth analysis of the technical challenges related to the technology, such as working fluid selection and expansion machine issues is then reported. Technological constraints and optimization methods are extensively described and discussed. Finally, the current trends in research and development for the next generation of Organic Rankine Cycles are presented.
The conversion of biomass by thermochemical means is very promising for the substitution of fossil materials in many energy applications. Given the complexity of biomass the main challenge in its use is to obtain products with high yield and purity. For a better understanding of biomass thermochemical conversion, many authors have studied in TG analyzer or at bed scale the individual pyrolysis of its main constituents (i.e. cellulose, hemicelluloses and lignin). Based on these studies, this original work synthesizes the main steps of conversion and the composition of the products obtained from each constituent. Pyrolysis conversion can be described as the superposition of three main pathways (char formation, depolymerization and fragmentation) and secondary reactions. Lignin, which is composed of many benzene rings, gives the highest char yield and its depolymerization leads to various phenols. The depolymerization of the polysaccharides is a source of anhydro-saccharides and furan compounds. The fragmentation of the different constituents and the secondary reactions produce CO, CO and small chain compounds. For temperature higher than 500 °C, the residues obtained from the different constituents present a similar structure, which evolves towards a more condensed polyaromatic form by releasing CH , CO and H . As the aromatic rings and their substituent composition have a critical influence on the reactivity of pyrolysis products, a particular attention has been given to their formation. Some mechanisms are proposed to explain the formation of the main products. From the results of this study it is possible to predict the reactivity and energy content of the pyrolysis products and evaluate their potential use as biofuels in renewable applications.
This paper provides a comprehensive review of fuel cell science and engineering with a focus on hydrogen fuel cells. The paper provides a concise, up-to-date review of fuel cell fundamentals; history; competing technologies; types; advantages and challenges; portable, stationary, and transportation applications and markets; current status of research-and-development; future targets; design levels; thermodynamic and electrochemical principles; system evaluation factors; and prospects and outlook. The most current data from industry and academia have been used with the relation between fuel cell fundamentals and applications highlighted throughout the manuscript.
Torrefaction is a mild pyrolysis, which has been explored for the pretreatment of biomass to increase the heating value and hydrophobicity. Due to its potential applications for making torrefied pellets, which can be used as a high quality feedstock in gasification for high quality syngas production and as a substitute for coal in thermal power plants and metallurgical processes, torrefaction and densification have attracted great interest in recent years from both academia and bioenergy industry. This paper provides a comprehensive review of research progresses in this area, drawing on major contributions from two major research groups of the authors on torrefaction and densification at Canada and Taiwan as well as literatures. It is revealed that torrefaction of various biomass species and their major components, lignin, cellulose and hemicelluloses have been extensively studied in thermogravimetric apparatus (TGA) under both inert (N ) and oxidative (O , H O) environments to elucidate the weight loss as a function of temperature, particle size and time. It was found that the higher heating value and saturated water uptake of torrefied biomass were a strong function of weight loss, which represents the degree of torrefaction. When torrefied sawdust is compressed into torrefied pellets, more mechanical energy is consumed and higher die temperature is required to make torrefied pellets of similar density and hardness as regular pellets. Simple economics analyses based on laboratory scale experimental data showed that because of the potential savings from pellets transport, handling and storage logistics, the overall cost for torrefied pellets can be lower than regular pellets in European market for both European and Canadian pellets. The gasification could be improved in terms of both energy efficiency and syngas quality because of the removal of oxygenated volatile compounds from torrefied biomass.