Most Downloaded Energy Articles
Govinda R. Timilsina | Ashish Shrestha
Abstract: This paper revisits the recent developments in biofuel markets and their economic, social and environmental impacts. Several countries have introduced mandates and targets for biofuel expansion. Production, international trade and investment have increased sharply in the last few years. However, some analysts linked biofuels to the 2007–2008 global food crisis. Existing studies diverge on the magnitude of the projected long-term impacts of biofuels on food prices and supply, with studies that model only the agricultural sector showing higher impacts and studies that model the entire economy showing relatively lower impacts. In terms of climate change mitigation, biofuels reduces GHG emissions only if GHG emissions related to land-use change are avoided. When biofuel production entails conversion of forest to cropland, net reduction of GHG would not be realized for many years. Existing literature does not favor the diversion of food for large-scale biofuels production, but the regulated expansion of biofuels in countries with surplus lands and a strong biofuel industry cannot be ruled out. Developments in non-food based or cellulosic (or second generation) biofuels may offer some hope, yet they still compete with food supply through land use and are currently constrained by a number of technical and economic barriers.
Abstract: This paper discusses the perspective of renewable energy (wind, solar, wave and biomass) in the making of strategies for a sustainable development. Such strategies typically involve three major technological changes: energy savings on the demand side, efficiency improvements in the energy production, and replacement of fossil fuels by various sources of renewable energy. Consequently, large-scale renewable energy implementation plans must include strategies for integrating renewable sources in coherent energy systems influenced by energy savings and efficiency measures. Based on the case of Denmark, this paper discusses the problems and perspectives of converting present energy systems into a 100% renewable energy system. The conclusion is that such development is possible. The necessary renewable energy sources are present, and if further technological improvements of the energy system are achieved the renewable energy system can be created. Especially technologies of converting the transportation sector and the introduction of flexible energy system technologies are crucial.
Saqib Sohail Toor | Lasse Rosendahl | Andreas Rudolf
Abstract: This article reviews the hydrothermal liquefaction of biomass with the aim of describing the current status of the technology. Hydrothermal liquefaction is a medium-temperature, high-pressure thermochemical process, which produces a liquid product, often called bio-oil or bi-crude. During the hydrothermal liquefaction process, the macromolecules of the biomass are first hydrolyzed and/or degraded into smaller molecules. Many of the produced molecules are unstable and reactive and can recombine into larger ones. During this process, a substantial part of the oxygen in the biomass is removed by dehydration or decarboxylation. The chemical properties of bio-oil are highly dependent of the biomass substrate composition. Biomass constitutes of various components such as protein; carbohydrates, lignin and fat, and each of them produce distinct spectra of compounds during hydrothermal liquefaction. In spite of the potential for hydrothermal production of renewable fuels, only a few hydrothermal technologies have so far gone beyond lab- or bench-scale.
Abstract: Rapidly growing fossil energy consumption in the transport sector in the last two centuries caused problems such as increasing greenhouse gas emissions, growing energy dependency and supply insecurity. One approach to solve these problems could be to increase the use of biofuels.Preferred feedstocks for current 1st generation biofuels production are corn, wheat, sugarcane, soybean, rapeseed and sunflowers. The major problem is that these feedstocks are also used for food and feed production.The core objective of this paper is to investigate whether the recent increase of biofuels production had a significant impact on the development of agricultural commodity (feedstock) prices. The most important impact factors like biofuels production, land use, yields, feedstock and crude oil prices are analysed.The major conclusions of this analysis are: In recent years the share of bioenergy-based fuels has increased moderately, but continuously, and so did feedstock production, as well as yields. So far, no significant impact of biofuels production on feedstock prices can be observed. Hence, a co-existence of biofuel and food production seems possible especially for 2nd generation biofuels. However, sustainability criteria should be seriously considered. But even if all crops, forests and grasslands currently not used were used for biofuels production it would be impossible to substitute all fossil fuels used today in transport.
1 June 2013
Danny H.W. Li | Liu Yang | Joseph C. Lam
Abstract: Buildings account for a significant proportion of the total energy and carbon emissions worldwide, and play an important role in formulating sustainable development strategies. There is a growing interest in ZEBs (zero energy buildings) in recent years. Several countries have adopted or considering establishing ZEBs as their future building energy targets to help alleviate the problems concerning the depletion of energy resources and the deterioration of the environment. Broadly speaking, ZEBs involve two design strategies – minimizing the need for energy use in buildings (especially for heating and cooling) through EEMs (energy-efficient measures) and adopting RETs (renewable energy and other technologies) to meet the remaining energy needs. This paper reviews the works related to these two strategies. EEMs include building envelopes, internal conditions, and building services systems; RETs cover photovoltaic/building-integrated photovoltaic, wind turbines, solar thermal (solar water heaters), heat pumps, and district heating and cooling. Issues pertaining to sustainable development implications and further research work required are also highlighted. These include life-cycle cost and environmental impacts, climate change and social policy issues.
Jasmina Vujić | Dragoljub P. Antić | Zorka Vukmirović
Abstract: With all energy production systems there are environmental issues to be considered, risks to be assessed, and challenges to be addressed. It must be emphasized that an ideal energy source that is at the same time efficient, cost-effective, environment-friendly, and risk-free does not exist. There are always some necessary trade-offs to be made, in order to ensure optimal use of energy resources, while limiting environmental and health impacts. Nuclear energy is currently the only technology with a secure base-load electricity supply and no greenhouse gas emissions that has the potential to expand at a large scale. However, the spent fuel and safety issues must be addressed. Another base-load electricity source – the fossil-burning power plants – although affordable, emits various air pollutants (chemical and radioactive effluents, dust, ash, etc.), which are dispersed from a power source and transported through various pathways that could lead to the general population exposure. This paper summarizes current status and future trends in base-load electricity sources in the U.S., including environmental footprints, new regulatory requirements, and cost issues. It also presents an analysis of challenges that need to be overcome and opportunities that could us lead us closer to a sustainable energy future.
1 May 2013
Abstract: The various forms of solar energy – solar heat, solar photovoltaic, solar thermal electricity, and solar fuels offer a clean, climate-friendly, very abundant and in-exhaustive energy resource to mankind. Solar power is the conversion of sunlight into electricity, either directly using photovoltaic (PV), or indirectly using concentrated solar power (CSP). The research has been underway since very beginning for the development of an affordable, in-exhaustive and clean solar energy technology for longer term benefits. This paper, therefore, reviews the progress made in solar power generation research and development since its inception. Attempts are also made to highlight the current and future issues involved in the generation of quality and reliable solar power technology for future applications. A list of 121 research publications on the subject is also appended for a quick reference.
8. Life cycle assessment (LCA) of waste management strategies: Landfilling, sorting plant and incineration
Francesco Cherubini | Silvia Bargigli | Sergio Ulgiati
Abstract: This paper focuses on a Life Cycle Assessment (LCA) of four waste management strategies: landfill without biogas utilization; landfill with biogas combustion to generate electricity; sorting plant which splits the inorganic waste fraction (used to produce electricity via Refuse Derived Fuels, RDF) from the organic waste fraction (used to produce biogas via anaerobic digestion); direct incineration of waste. These scenarios are applied to the waste amount and composition of the Municipality of Roma (Italy) and are evaluated under different points of view: global and local emissions, total material demands, total energy requirements and ecological footprints. Results, reliable for most of the European big cities, show landfill systems as the worst waste management options and significant environmental savings at global scale are achieved from undertaking energy recycling. Furthermore, waste treatments finalized to energy recovery provide an energy output that, in the best case, is able to meet the 15% of Roma electricity consumption.
Helena M. Amaro | Ângela C. Macedo | F. Xavier Malcata
Abstract: In recent decades, the world has been confronted with an energy crisis associated with irreversible depletion of traditional sources of fossil fuels, coupled with atmospheric accumulation of greenhouse gases that cause global warming. The urgent need to replace traditional fuels led to emergence of biodiesel and biohydrogen as interesting alternatives, both of which can be obtained via microalga-mediated routes.Microalgae are ubiquitous eukaryotic microorganisms, characterized by a remarkable metabolic plasticity. Their oil productivities are much higher than those of higher terrestrial plants, and they do not require high quality agricultural land. Microalgae may indeed be cultivated in brackish and wastewaters that provide suitable nutrients (e.g. NH4+,NO3−andPO43−), at the expense of only sunlight and atmospheric CO2. On the other hand, metabolic engineering permits release of molecular hydrogen also via photosynthetic routes, which will easily be converted to electricity in fuel cells or mechanical power in explosion engines, with only water vapor as exhaust product in both cases.However, large-scale implementation of microalga-based systems to manufacture biodiesel and biohydrogen has been economically constrained by their still poor volumetric efficiencies, which imply excessively high costs when compared with current petrofuel prices. Technological improvements are accordingly critical, both on the biocatalyst and the bioreactor levels. The current bottlenecks that have apparently precluded full industrial exploitation of microalgae cells are critically discussed here, viz. those derived from the scarce knowledge on the mechanisms that control regulation of gene expression, the reduced number of species subjected to successful genetic transformation, the relatively low cell density attainable, the poor efficiency in harvesting, and the difficulties in light capture and use.Therefore, this paper provides an overview of the feasibility of microalgae for production of biofuels via synthesis of liquid endocellular metabolites (i.e. triglycerides) and gaseous extracellular ones (i.e. molecular hydrogen), and addresses technical and economic shortcomings and opportunities along the whole processing chain, at both microorganism and reactor levels.
Xiaojing Sun | Diangui Huang | Guoqing Wu
Abstract: Wind power has been the fastest growing form of renewable energy for the last few years. According to Intergovernmental Panel on Climate Change (IPCC) report, 80% of the world's energy supply could come from renewable sources by 2050 and wind energy will play a major role in electricity generation in 2050. In the growing market for wind energy and the limited available space onshore, the development of offshore wind farms become more and more important. With a rapid development of technology, the offshore wind power projects have become a trend in many countries like Europe now. Therefore, this paper aims to provide a brief overview of the current development status of offshore wind power in different countries and also explore the technical, economic and environmental issues around its development. Without doubt, offshore wind will lead technology advances in the wind sector in a near future as it seeks to exploit resources further offshore.
11. Photovoltaic and wind energy systems monitoring and building/home energy management using ZigBee devices within a smart grid
1 January 2013
N.C. Batista | R. Melício | J.C.O. Matias | J.P.S. Catalão
Abstract: The actual electric grid was developed to offer electricity to the clients from centralized generation, so with large-scale distributed renewable generation there is an urgent need for a more flexible, reliable and smarter grid. The wireless technologies are becoming an important asset in the smart grid, particularly the ZigBee devices. These smart devices are gaining increased acceptance, not only for building and home automation, but also for energy management, efficiency optimization and metering services, being able to operate for long periods of time without maintenance needs. In this context, this paper provides new comprehensive field tests using open source tools with ZigBee technologies for monitoring photovoltaic and wind energy systems, and also for building and home energy management. Our experimental results demonstrate the proficiency of ZigBee devices applied in distributed renewable generation and smart metering systems.
Monoj Kumar Mondal | Hemant Kumar Balsora | Prachi Varshney
Abstract: Coal-fired thermal power plants are the major source of CO2 emission among fossil fuel power plants. In thermal power plants, coal combustion produces flue gas containing a number of gases including hazardous pollutants, such as CO2, mercury (Hg), sulfur dioxide (SO2), and oxides of nitrogen (NOx). Among all, CO2 is the largest contributor to global warming. CO2 capture and separation are therefore essential to keep the environment safe and secure. The present paper delineates the existing literature to examine the current status of various methods and technologies used for CO2 capture and separation from thermal power plant flue gas. Various emerging technologies like, chemical-looping combustion, integrated gasification combined cycle, enzyme based separation, dual-alkali absorption approach, facilitated transport membrane, hydrate based separations, mixed matrix membrane and, calcium looping are also thoroughly discussed.
M.M. Gui | K.T. Lee | S. Bhatia
Abstract: Biodiesel has high potential as a new and renewable energy source in the future, as a substitution fuel for petroleum-derived diesel and can be used in existing diesel engine without modification. Currently, more than 95% of the world biodiesel is produced from edible oil which is easily available on large scale from the agricultural industry. However, continuous and large-scale production of biodiesel from edible oil without proper planning may cause negative impact to the world, such as depletion of food supply leading to economic imbalance. A possible solution to overcome this problem is to use non-edible oil or waste edible oil (WEO). In this context, the next question that comes in mind would be if the use of non-edible oil overcomes the short-comings of using edible oil. Apart from that, if WEO were to be used, is it sufficient to meet the demand of biodiesel. All these issues will be addressed in this paper by discussing the advantages and disadvantages of using edible oil vs. non-edible vs. WEO as feedstock for biodiesel production. The discussion will cover various aspects ranging from oil composition, oil yield, economics, cultivation requirements, land availability and also the resources availability. Finally, a proposed solution will be presented.
Abstract: The present paper reviews the reactions and the path of acceptance of the theory known as “peak oil”. The theory was proposed for the first time by M.K. Hubbert in the 1950s as a way to describe the production pattern of crude oil. According to Hubbert, the production curve is “bell shaped” and approximately symmetric. Hubbert's theory was verified with good approximation for the case of oil production in the United States that peaked in 1971, and is now being applied to the worldwide oil production. It is generally believed that the global peak of oil production (“peak oil”) will take place during the first decade of the 21st century, and some analysts believe that it has already occurred in 2005 or 2006. The theory and its consequences have unpleasant social and economical implications. The present paper is not aimed at assessing the peak date but offers a discussion on the factors that affect the acceptance and the diffusion of the concept of “peak oil” with experts and with the general public. The discussion is based on a subdivision of “four stages of acceptance”, loosely patterned after a sentence by Thomas Huxley.
S.H. Shuit | K.T. Tan | K.T. Lee | A.H. Kamaruddin
Abstract: It has been widely accepted worldwide that global warming is by far the greatest threat and challenge in the new millennium. In order to stop global warming and to promote sustainable development, renewable energy is a perfect solution to achieve both targets. Presently million hectares of land in Malaysia is occupied with oil palm plantation generating huge quantities of biomass. In this context, biomass from oil palm industries appears to be a very promising alternative as a source of raw materials including renewable energy in Malaysia. Thus, this paper aims to present current scenario of biomass in Malaysia covering issues on availability and sustainability of feedstock as well as current and possible utilization of oil palm biomass. This paper will also discuss feasibility of some biomass conversion technologies and some ongoing projects in Malaysia related to utilization of oil palm biomass as a source of renewable energy. Based on the findings presented, it is definitely clear that Malaysia has position herself in the right path to utilize biomass as a source of renewable energy and this can act as an example to other countries in the world that has huge biomass feedstock.
E.H. Wang | H.G. Zhang | B.Y. Fan | M.G. Ouyang | Y. Zhao | Q.H. Mu
Abstract: Organic Rankine Cycle (ORC) could be used to recover low-grade waste heat. When a vehicle is running, the engine exhaust gas states have a wide range of variance. Defining the operational conditions of the ORC that achieve the maximum utilization of waste heat is important. In this paper the performance of different working fluids operating in specific regions was analyzed using a thermodynamic model built in Matlab together with REFPROP. Nine different pure organic working fluids were selected according to their physical and chemical properties. The results were compared in the regions when net power outputs were fixed at 10kW. Safety levels and environmental impacts were also evaluated. The outcomes indicate that R11, R141b, R113 and R123 manifest slightly higher thermodynamic performances than the others; however, R245fa and R245ca are the most environment-friendly working fluids for engine waste heat-recovery applications. The optimal control principle of ORC under the transient process is discussed based on the analytical results.
17. Which is the best solar thermal collection technology for electricity generation in north-west India? Evaluation of options using the analytical hierarchy process
J.D. Nixon | P.K. Dey | P.A. Davies
Abstract: This study of concentrating solar thermal power generation sets out to evaluate the main existing collection technologies using the framework of the Analytical Hierarchy Process (AHP). It encompasses parabolic troughs, heliostat fields, linear Fresnel reflectors, parabolic dishes, compound parabolic concentrators and linear Fresnel lenses. These technologies are compared based on technical, economic and environmental criteria. Within these three categories, numerous sub-criteria are identified; similarly sub-alternatives are considered for each technology. A literature review, thermodynamic calculations and an expert workshop have been used to arrive at quantitative and qualitative assessments. The methodology is applied principally to a case study in Gujarat in north-west India, though case studies based on the Sahara Desert, Southern Spain and California are included for comparison. A sensitivity analysis is carried out for Gujarat. The study concludes that the linear Fresnel lens with a secondary compound parabolic collector, or the parabolic dish reflector, is the preferred technology for north-west India.
18. Energy system analysis of 100% renewable energy systems—The case of Denmark in years 2030 and 2050
H. Lund | B.V. Mathiesen
Abstract: This paper presents the methodology and results of the overall energy system analysis of a 100% renewable energy system. The input for the systems is the result of a project of the Danish Association of Engineers, in which 1600 participants during more than 40 seminars discussed and designed a model for the future energy system of Denmark. The energy system analysis methodology includes hour by hour computer simulations leading to the design of flexible energy systems with the ability to balance the electricity supply and demand. The results are detailed system designs and energy balances for two energy target years: year 2050 with 100% renewable energy from biomass and combinations of wind, wave and solar power; and year 2030 with 50% renewable energy, emphasising the first important steps on the way. The conclusion is that a 100% renewable energy supply based on domestic resources is physically possible, and that the first step towards 2030 is feasible to Danish society. However, Denmark will have to consider to which degree the country shall rely mostly on biomass resources, which will involve the reorganisation of the present use of farming areas, or mostly on wind power, which will involve a large share of hydrogen or similar energy carriers leading to certain inefficiencies in the system design.
George Cristian Lazaroiu | Mariacristina Roscia
Abstract: Nowadays, the large and small districts are proposing a new city model, called “the smart city”, which represents a community of average technology size, interconnected and sustainable, comfortable, attractive and secure. The landscape requirements and the solutions to local problems are the critical factors. The cities consume 75% of worldwide energy production and generate 80% of CO2 emissions. Thus, a sustainable urban model, “the smart city”, is sustained by the European Commission. In this paper, a model for computing “the smart city” indices is proposed. The chosen indicators are not homogeneous, and contain high amount of information. The paper deals with the computation of assigned weights for the considered indicators. The proposed approach uses a procedure based on fuzzy logic and defines a model that allows us to estimate “the smart city”, in order to access European funding. The proposed innovative system results in a more extended comprehension and simple use. Thus, the model could help in policy making process as starting point of discussion between stakeholders, as well as citizens in final decision of adoption measures and best evaluated options.
H. Lund | B. Möller | B.V. Mathiesen | A. Dyrelund
Abstract: Based on the case of Denmark, this paper analyses the role of district heating in future Renewable Energy Systems. At present, the share of renewable energy is coming close to 20 per cent. From such point of departure, the paper defines a scenario framework in which the Danish system is converted to 100 per cent Renewable Energy Sources (RES) in the year 2060 including reductions in space heating demands by 75 per cent. By use of a detailed energy system analysis of the complete national energy system, the consequences in relation to fuel demand, CO2 emissions and cost are calculated for various heating options, including district heating as well as individual heat pumps and micro CHPs (Combined Heat and Power). The study includes almost 25 per cent of the Danish building stock, namely those buildings which have individual gas or oil boilers today and could be substituted by district heating or a more efficient individual heat source. In such overall perspective, the best solution will be to combine a gradual expansion of district heating with individual heat pumps in the remaining houses. Such conclusion is valid in the present systems, which are mainly based on fossil fuels, as well as in a potential future system based 100 per cent on renewable energy.
J.A. Quintero | M.I. Montoya | O.J. Sánchez | O.H. Giraldo | C.A. Cardona
Abstract: The Colombian government has defined the use of bioethanol as a gasoline enhancer to reduce greenhouse gases, gasoline imports, and to boost the rural economy. To meet the projected fuel ethanol demand needed to oxygenate the gasoline in the whole country, the construction of about five additional ethanol production plants is required. For this, a comparative analysis of the technological options using different feedstocks should be performed. In this work, a comparison of the economical and environmental performance of the ethanol production process from sugarcane and corn under Colombian conditions has been carried out. Net present value and total output rate of potential environmental impact were used as the economical and environmental indicators, respectively. Through the integration of these indicators into one index by using the analytical hierarchy process (AHP) approach, sugarcane ethanol process was determined as the best choice for Colombian ethanol production facilities. AHP scores obtained in this study for sugarcane and corn ethanol were 0.571 and 0.429, respectively. However, starchy crops like corn, cassava or potatoes used as feedstock for ethanol production could potentially cause a higher impact on the rural communities and boost their economies if social matters are considered.
Abstract: The status of nuclear energy today and its potential evolution during the next 10–20 years is discussed. Nuclear energy contributes only about 14% of the world’s electric energy mix today, and as electric energy contributes itself only about 16% to the end energy use, its contribution is essentially negligible. Still, nuclear energy is plagued already with a long list of unsolved problems. Among the less known problems one finds the difficulties that nuclear plants cannot provide power according to needs, but have to be operated at full power also during times of low demand and regions with large contributions from nuclear power need some backup hydropower storage systems. The better known problems, without solutions since at least 40 years, are the final safe storage of the accumulated highly radioactive nuclear waste, that uranium itself is a very limited and non renewable energy resource and that enormous amounts of human resources, urgently needed to find a still unknown path towards a low energy future, are blocked by useless research on fusion energy. Thus, nuclear energy is not a solution to our energy worries but part of the problem.
23. Optimization of diesel engine performances for a hybrid wind–diesel system with compressed air energy storage
H. Ibrahim | R. Younès | T. Basbous | A. Ilinca | M. Dimitrova
Abstract: Electricity supply in remote areas around the world is mostly guaranteed by diesel generators. This relatively inefficient and expensive method is responsible for 1.2 million tons of greenhouse gas (GHG) emission in Canada annually. Some low- and high-penetration wind–diesel hybrid systems (WDS) have been experimented in order to reduce the diesel consumption. We explore the re-engineering of current diesel power plants with the introduction of high-penetration wind systems together with compressed air energy storage (CAES). This is a viable alternative to major the overall percentage of renewable energy and reduce the cost of electricity. In this paper, we present the operative principle of this hybrid system, its economic benefits and advantages and we finally propose a numerical model of each of its components. Moreover, we are demonstrating the energy efficiency of the system, particularly in terms of the increase of the engine performance and the reduction of its fuel consumption illustrated and supported by a village in northern Quebec.
Abass A. Olajire
Abstract: Carbon capture from point source emissions has been recognized as one of several strategies necessary for mitigating unfettered release of greenhouse gases (GHGs) into the atmosphere. To keep GHGs at manageable levels, large decreases in CO2 emissions through capturing and separation will be required. This article reviews the possible CO2 capture and separation technologies for end-of-pipe applications. The three main CO2 capture technologies discussed include post-combustion, pre-combustion and oxyfuel combustion techniques. Various separation techniques, such as chemical absorption, physical absorption, physical adsorption, cryogenics, membrane technology, membranes in conjunction with chemical absorption and chemical-looping combustion (CLC) are also thoroughly discussed. Future directions are suggested for application by oil and gas industry. Sequestration methods, such as geological, mineral carbonation techniques, and ocean dump are not covered in this review.
25. World geothermal power production status: Energy, environmental and economic study of high enthalpy technologies
César R. Chamorro | María E. Mondéjar | Roberto Ramos | José J. Segovia | María C. Martín | Miguel A. Villamañán
Abstract: The current world status of geothermal electricity production, including installed capacities, number of units and energy produced by exploitation technology, is presented in this paper. Four geothermal model plants based on different modes of high enthalpy technologies are analyzed from energy, environmental and economic points of view for specific reservoir characteristics. Once process parameters are optimized for the best plant operation, a cost and financial analysis is performed within a given economic frame. This analysis shows that Dry Steam power plants are the most efficient. Flash steam power plants increase their exergy efficiency with increasing reservoir temperature. Double Flash technology raises the energy produced with respect to Single Flash between 17 and 25%, and economic parameters become better. An additional third flash process increases power production by 10%, but economic parameters are not improved unless a reservoir of very high temperatures is considered. The energy and economic study conclude that the choice of the best flash technology depends on the resource characteristics, the financial frame and the technology costs.