Showing papers on "Electricity generation published in 2015"

Overview of Power Management Strategies of Hybrid AC/DC Microgrid

Abstract: Today, conventional power systems are evolving to modern smart grids, where interconnected microgrids may dominate the distribution system with high penetration of renewable energy and energy storage systems. The hybrid ac/dc systems with dc and ac sources/loads are considered to be the most possible future distribution or even transmission structures. For such hybrid ac/dc microgrids, power management strategies are one of the most critical operation aspects. This paper presents an overview of power management strategies for a hybrid ac/dc microgrid system, which includes different system structures (ac-coupled, dc-coupled, and ac–dc-coupled hybrid microgrids), different operation modes, a thorough study of various power management and control schemes in both steady state and transient conditions, and examples of power management and control strategies. Finally, discussion and recommendations of power management strategies for the further research are presented.

Research progress of perovskite materials in photocatalysis- and photovoltaics-related energy conversion and environmental treatment.

Abstract: Meeting the growing global energy demand is one of the important challenges of the 21st century. Currently over 80% of the world's energy requirements are supplied by the combustion of fossil fuels, which promotes global warming and has deleterious effects on our environment. Moreover, fossil fuels are non-renewable energy and will eventually be exhausted due to the high consumption rate. A new type of alternative energy that is clean, renewable and inexpensive is urgently needed. Several candidates are currently available such as hydraulic power, wind force and nuclear power. Solar energy is particularly attractive because it is essentially clean and inexhaustible. A year's worth of sunlight would provide more than 100 times the energy of the world's entire known fossil fuel reserves. Photocatalysis and photovoltaics are two of the most important routes for the utilization of solar energy. However, environmental protection is also critical to realize a sustainable future, and water pollution is a serious problem of current society. Photocatalysis is also an essential route for the degradation of organic dyes in wastewater. A type of compound with the defined structure of perovskite (ABX3) was observed to play important roles in photocatalysis and photovoltaics. These materials can be used as photocatalysts for water splitting reaction for hydrogen production and photo-degradation of organic dyes in wastewater as well as for photoanodes in dye-sensitized solar cells and light absorbers in perovskite-based solar cells for electricity generation. In this review paper, the recent progress of perovskites for applications in these fields is comprehensively summarized. A description of the basic principles of the water splitting reaction, photo-degradation of organic dyes and solar cells as well as the requirements for efficient photocatalysts is first provided. Then, emphasis is placed on the designation and strategies for perovskite catalysts to improve their photocatalytic activity and/or light adsorption capability. Comments on current and future challenges are also provided. The main purpose of this review paper is to provide a current summary of recent progress in perovskite materials for use in these important areas and to provide some useful guidelines for future development in these hot research areas.

Integrated life-cycle assessment of electricity-supply scenarios confirms global environmental benefit of low-carbon technologies.

Abstract: Decarbonization of electricity generation can support climate-change mitigation and presents an opportunity to address pollution resulting from fossil-fuel combustion. Generally, renewable technologies require higher initial investments in infrastructure than fossil-based power systems. To assess the tradeoffs of increased up-front emissions and reduced operational emissions, we present, to our knowledge, the first global, integrated life-cycle assessment (LCA) of long-term, wide-scale implementation of electricity generation from renewable sources (i.e., photovoltaic and solar thermal, wind, and hydropower) and of carbon dioxide capture and storage for fossil power generation. We compare emissions causing particulate matter exposure, freshwater ecotoxicity, freshwater eutrophication, and climate change for the climate-change-mitigation (BLUE Map) and business-as-usual (Baseline) scenarios of the International Energy Agency up to 2050. We use a vintage stock model to conduct an LCA of newly installed capacity year-by-year for each region, thus accounting for changes in the energy mix used to manufacture future power plants. Under the Baseline scenario, emissions of air and water pollutants more than double whereas the low-carbon technologies introduced in the BLUE Map scenario allow a doubling of electricity supply while stabilizing or even reducing pollution. Material requirements per unit generation for low-carbon technologies can be higher than for conventional fossil generation: 11-40 times more copper for photovoltaic systems and 6-14 times more iron for wind power plants. However, only two years of current global copper and one year of iron production will suffice to build a low-carbon energy system capable of supplying the world's electricity needs in 2050.

A review on clean energy solutions for better sustainability

Abstract: Summary This paper focuses on clean energy solutions in order to achieve better sustainability, and hence discusses opportunities and challenges from various dimensions, including social, economic, energetic and environmental aspects. It also evaluates the current and potential states and applications of possible clean-energy systems. In the first part of this study, renewable and nuclear energy sources are comparatively assessed and ranked based on their outputs. By ranking energy sources based on technical, economic, and environmental performance criteria, it is aimed to identify the improvement potential for each option considered. The results show that in power generation, nuclear has the highest (7.06/10) and solar photovoltaic (PV) has the lowest (2.30/10). When nonair pollution criteria, such as land use, water contamination, and waste issues are considered, the power generation ranking changes, and geothermal has the best (7.23/10) and biomass has the lowest performance (3.72/10). When heating and cooling modes are considered as useful outputs, geothermal and biomass have approximately the same technical, environmental, and cost performances (as 4.9/10), and solar has the lowest ranking (2/10). Among hydrogen production energy sources, nuclear gives the highest (6.5/10) and biomass provides the lowest (3.6/10) in ranking. In the second part of the present study, multigeneration systems are introduced, and their potential benefits are discussed along with the recent studies in the literature. It is shown that numerous advantages are offered by renewable energy-based integrated systems with multiple outputs, especially in reducing overall energy demand, system cost and emissions while significantly improving overall efficiencies and hence output generation rates. Copyright © 2015 John Wiley & Sons, Ltd.

Maximum Energy Efficiency Tracking for Wireless Power Transfer Systems

Abstract: A method for automatic “maximum energy efficiency tracking” operation for wireless power transfer (WPT) systems is presented in this paper. Using the switched-mode converter in the receiver module to emulate the optimal load value, the proposed method follows the maximum energy efficiency operating points of a WPT system by searching for the minimum input power operating point for a given output power. Because the searching process is carried out on the transmitter side, the proposal does not require any wireless communication feedback from the receiver side. The control scheme has been successfully demonstrated in a two-coil system under both weak and strong magnetic coupling conditions. Experimental results are included to confirm its feasibility.

A review of key power system stability challenges for large-scale PV integration

Abstract: Global warming is the main driving force behind worldwide interest for the generation of bulk electrical energy from renewable sources. As a consequence of advancements in solar cell fabrication and converter technology, solar PV has emerged as one of the most promising renewable sources for bulk power generation. If the current commissioning rate continues, PV power would lead to the modification of several aspects of power system and could influence the stability of the system. This paper extensively reviews the technical challenges, on particular, the stability issues associated with the integration of large-scale PV into the power system. In addition, the paper also reviews the dynamic model of large-scale PV for stability studies as well as the grid codes for large-scale PV integration into the system. Finally, this paper summarizes the research findings about the technical solutions to overcome the power system stability challenges regarding the large-scale PV integration into the transmission and sub-transmission or medium voltage distribution system.

Direct Power Generation from a Graphene Oxide Film under Moisture.

Abstract: An efficient moisture-electric-energy transformation is discovered by means of establishing an oxygen functional group gradient in a graphene oxide film. The moisture variation serves as an energy source to generate electric power with an energy-conversion efficiency of up to ≈62%. Based on this finding, a prototype power generator and a self-powered respiratory monitor are demonstrated under the stimulus of the human breath.

A Double-Sided LCLC -Compensated Capacitive Power Transfer System for Electric Vehicle Charging

Abstract: A double-sided LCLC -compensated capacitive power transfer (CPT) system is proposed for the electric vehicle charging application. Two pairs of metal plates are utilized to form two coupling capacitors to transfer power wirelessly. The LCLC -compensated structure can dramatically reduce the voltage stress on the coupling capacitors and maintain unity power factor at both the input and output. A 2.4-kW CPT system is designed with four 610-mm × 610-mm copper plates and an air gap distance of 150 mm. The experimental prototype reaches a dc–dc efficiency of 90.8% at 2.4-kW output power. At 300-mm misalignment case, the output power drops to 2.1 kW with 90.7% efficiency. With a 300-mm air gap distance, the output power drops to 1.6 kW with 89.1% efficiency.

A review on the applications of nanofluids in solar energy systems

Abstract: The negative impact of human activities on the environment receives tremendous attention, especially on the increased global temperature. To combat climate change, clean and sustainable energy sources need to be rapidly developed. Solar energy technology is considered as one of the ideal candidates, which directly converts solar energy into electricity and heat without any greenhouse gas emissions. In both areas, high-performance cooling, heating and electricity generation is one of the vital needs. Modern nanotechnology can produce metallic or nonmetallic particles of nanometer dimensions which have unique mechanical, optical, electrical, magnetic, and thermal properties. Studies in this field indicate that exploiting nanofluid in solar systems, offers unique advantages over conventional fluids. In this paper, the applications of nanofluids on different types of solar collectors, photovoltaic systems and solar thermoelectrics are reviewed. Beside the wide range of energy conversion, the efforts done on the energy storage system (ESS) have been reviewed. In the field of economics, nanotech reduces manufacturing costs as a result of using a low temperature process.

Optimal Power Dispatch of Multi-Microgrids at Future Smart Distribution Grids

Abstract: In this paper, future distribution network operation is discussed under assumption of multimicrogrids (MMGs) concept. The economic operation of MMGs is formulated as an optimization problem. A stochastically and probabilistic modeling of both small-scale energy resources (SSERs) and load demand at each microgrids (MGs) is done to determine the optimal economic operation of each MGs with minimum cost based on the power transaction between the MGs and main grids. The balance between the total power generation in each MGs and the load demand is determined regarding the sold or purchase power either by MG or by main grid. Based on the results, the mean, standard deviation, and probability density function of each generated power with SSERs is determined considering optimization constraints. A statistical analysis for generated power and costs is given. The power interchange between MGs is considered. The particle swarm optimization is applied to minimize the cost function as an optimization algorithm. Results show that it is possible to regulate the power demand and power transaction between each MGs and the main grid. Moreover, it is indicated that the power sharing between MGs with main grid can reduce the total operation cost of the future distribution network.

An Improved Photovoltaic Power Forecasting Model With the Assistance of Aerosol Index Data

Abstract: Due to the intermittency and randomness of solar photovoltaic (PV) power, it is difficult for system operators to dispatch PV power stations. In order to find a precise expectation for day-ahead PV power generation, conventional models have taken into consideration the temperature, humidity, and wind speed data for forecasting, but these predictions were always not accurate enough under extreme weather conditions. Aerosol index (AI), which indicates the particulate matter in the atmosphere, has been found to have strong linear correlation with solar radiation attenuation, and might have potential influence on the power generated by PV panels. A novel PV power forecasting model is proposed in this paper, considering AI data as an additional input parameter. Based on seasonal weather classification, the back propagation (BP) artificial neural network (ANN) approach is utilized to forecast the next 24-h PV power outputs. The estimated results of the proposed PV power forecasting model coincide well with measurement data, and the proposed model has shown the ability of improving prediction accuracy, compared with conventional methods using ANN.

Historical development of concentrating solar power technologies to generate clean electricity efficiently – A review

Abstract: The conventional ways for generating electricity around the world face two main problems, which are gradual increase in the earth׳s average surface temperature (global warming) and depleting fossil fuel reserves. So switching to renewable energy technologies is an urgent need. Concentrating solar power (CSP) technologies are one of renewable technologies that are able to solve the present and future electricity problems. In this paper the historical evolution for the cornerstone plants of CSP technologies to generate clean electricity was reviewed and the current projects worldwide of CSP technologies were presented to show that the CSP technologies are technically and commercially proven and have the possibility for hybridization with fossil fuel or integration with storage systems to sustain continuous operation similar to conventional plants. Among all solar thermal technologies parabolic trough is the most technically and commercially proven. It also has the possibility for hybridization since it is proven by operating in several commercial projects for more than 28 years. It has a high maturity level and able to provide the required operating heat energy either as a stand-alone or in hybrid systems at the lowest cost and lower economic risks. For this reason, this technology is dominant in the operational and under-construction projects. However, currently there is a trend toward employing the other CSP technologies in the future projects as a result of the improvement in their performance. The use of PTC technology in the operational CSP projects is 95.7% and has decreased to 73.4% for the under-construction projects. Meanwhile, the uses of Fresnel collector (LFC), Tower power (TSP) and Stirling dish (SDC) technologies in the operational projects are 2.07%, 2.24%, and 0% respectively and have increased to 5.74%, 20.82% and 0.052% respectively for the under-construction projects. For the development projects, the use of TSP technology has reached to 71.43%, compared to 28.57% for PTC.

Fuel cell technology for domestic built environment applications: State of-the-art review

Abstract: Fuel cells produce heat when generating electricity, thus they are of particular interest for combined heat and power (CHP) and combined cooling heat and power (CCHP) applications, also known as tri-generation systems. CHP and tri-generation systems offer high energy conversion efficiency and hence the potential to reduce fuel costs and CO2 emissions. This article serves to provide a state-of-the-art review of fuel cell technology operating in the domestic built environment in CHP and tri-generation system applications. The review aims to carry out an assessment of the following topics: (1) the operational advantages fuel cells offer in CHP and tri-generation system configurations, specifically, compared to conventional combustion-based technologies such as Stirling engines, (2) how decarbonisation, running cost and energy security in the domestic built environment may be addressed through the use of fuel cell technology, and (3) what has been done to date and what needs to be done in the future. The article commences with a review of fuel cell technology, then moves on to examine fuel cell CHP systems operating in the domestic built environment, and finally explores fuel cell tri-generation systems in domestic built environment applications. The article concludes with an assessment of the present development of, and future challenges for, domestic fuel cells operating in CHP and tri-generation systems. As fuel cells are an emergent technology the article draws on a breadth of literature, data and experience, mostly from the United Kingdom, Germany, Japan, America and Australia. Fuel cells are a technology of the future here today, providing a change in the way heat and power are supplied to end users. Fuel cells operating in CHP and tri-generation systems in domestic built environment applications could finally provide the means by which energy generation can transfer from centralised to decentralised locales in a sustainable and effective manner.

Life cycle assessment of electricity production from renewable energies: Review and results harmonization

Abstract: A significant number of Life Cycle Assessment (LCA) analyses of renewable energy technologies is available in the literature, even though there is a lack of consistent conclusions about the life cycle impacts of the different technologies. The reported results vary consistently, according to the size and the technology of the considered plant, thus limiting the utility of LCA to inform policy makers and constituting a barrier to the deployment of a full awareness on sustainable energies. This variability in LCA results, in fact, can generate confusion regarding the actual environmental consequences of implementing renewable technologies. The article reviews approximately 50 papers, related to more than 100 different case studies regarding solar energy (Concentrated Solar Power, Photovoltaic), wind power, hydropower, and geothermal power. A methodology for the harmonization of the results is presented. The detailed data collection and the results normalization and harmonization allowed a more reliable comparison of the various renewable technologies. For most of the considered environmental indicators, wind power technologies turn out to be the low end while geothermal and PV technologies the high end of the impact range where all the other technologies are positioned.

Geothermal energy for sustainable development: A review of sustainability impacts and assessment frameworks

Abstract: Sustainable development calls for the use of sustainable energy systems. However, the way in which a geothermal resource is utilized will ultimately determine whether or not the utilization is sustainable. Energy usage is set to increase worldwide, and geothermal energy usage for both electricity generation and heating will also increase significantly. The world׳s geothermal resources will need to be used in a sustainable manner. The sustainable utilization of geothermal energy means that it is produced and used in a way that is compatible with the well-being of future generations and the environment. This paper provides a literature review of the linkages between geothermal energy developments for electricity generation and sustainable development, as well as a review of currently available sustainability assessment frameworks. Significant impacts occur as a result of geothermal energy projects for electricity generation and these impacts may be positive or negative. The need for correct management of such impacts through a customized sustainability assessment framework is identified and the foundation for sustainability assessment framework for geothermal energy development is built in this paper.

A review of developments in pilot-plant testing and modelling of calcium looping process for CO2 capture from power generation systems

Abstract: A nearly complete decarbonisation of the power sector is essential to meet the European Union target for greenhouse gas emissions reduction. Carbon capture and storage technologies have been identified as a key measure in reducing the carbon-intensity of the power sector. However, no cost-effective technology has yet been developed on a commercial scale, which is mostly due to high capital cost. Moreover, the mature technologies, such as amine scrubbing or oxy-combustion technologies, impose a high projected efficiency penalty (8–12.5% points) upon integration to the power plant. The calcium looping process, which is currently being tested experimentally in bench- and pilot-scale plants worldwide, is regarded as a promising alternative to the chemical solvent scrubbing approach, as it leads to the projected efficiency penalty of 6–8% points. The calcium looping concept has been developing rapidly due to the introduction of new test facilities, new correlations for process modelling, and process configurations for improved performance. The first part of this review provides an overview of the bench- and pilot-plant test facilities available worldwide. The focus is put on summarising the characteristics and operating conditions of the test facilities, as well as extracting the key experimental findings. Additionally, the experimental data suitable for validation or verification of the process models are presented. In the second part, the approaches to the carbonator and the calciner reactor modelling are summarised and classified in five model complexity levels. Moreover, the model limitations are assessed and the needs for modelling baselines for further process analyses are identified. Finally, in the third part the approaches for the integration of calcium looping to the power generation systems and for the improvement of the process performance are identified and evaluated. This review indicates that calcium looping integration resulted in the projected efficiency penalty of 2.6–7.9% points for the coal-fired power plants and 9.1–11.4% points for the combined-cycle power plants. Also, it was found that the calcium looping process can be used to develop a novel high-efficiency (46.7%LHV) coal-fired power generation system, making this technology even more promising compared to the other CO2 capture technologies.

A review on electric vehicles interacting with renewable energy in smart grid

Abstract: Electric vehicles (EVs) represent one of the most promising technologies to green the transportation systems. An important issue is that high penetration of EVs brings heavy electricity demand to the power grid. One effective way to alleviate the impact is to integrate local power generation such as renewable energy sources (RESs) into charging infrastructure. Because of the intermittent and indispatchable nature of RESs, it becomes very challenging to coordinate EVs charging with other grid load and renewable generation. In this paper, EVs charging problem in the presence of smart grid technologies is investigated, and the interaction with renewable energy is reviewed. An overview about EVs and RESs is first presented, which mainly introduces major types of EVs and renewable energy estimation methods. Then, according to the objectives, the existing research works are divided into three categories: cost-aware, efficiency-aware, and emissions-aware interactions between EVs and RESs. Each category׳s discussion includes the description of core ideas, summarization of solutions, and comparison between different works. Finally, some key open issues about EVs interacting with RESs are given and some possible solutions are also discussed.

Biomass gasification models for downdraft gasifier: A state-of-the-art review

Abstract: Among the different methods of energy production from biomass, gasification is considered as the most suitable option as it is a simple and economically viable process to produce thermal energy or decentralized electricity generation. Downdraft gasifiers are typically small-scale units having maximum power production capacity up to 5 MW. This feature makes it more suitable for decentralized power generation and distribution to the remote villages/islands deprived of grid electricity. Mathematical models can be helpful for the design of gasifiers, prediction of operational behavior, emissions during normal conditions, startup, shutdown, change of fuel, change of loading, and to alleviate the type of problems mentioned above. It has been observed that although many researchers have developed models of various types and degrees of complexity, reviews of these modeling and simulation studies are scarce. Largely, it is observed that the review articles reported in the literature fail to address the basic understanding of each model types and their applicability to design different gasifiers for a certain feedstock and variation of operating parameters. This review article discusses different models available for downdraft gasifiers such as thermodynamic equilibrium, kinetic, CFD, ANN and ASPEN Plus models. A comparative analysis of each model and its output is carried out. A critical analysis of the effect of different modeling parameters and finally the advantages and disadvantages of each modeling technique is outlined.

The consumptive water footprint of electricity and heat: a global assessment

Abstract: Water is essential for electricity and heat production. This study assesses the consumptive water footprint (WF) of electricity and heat generation per world region in the three main stages of the production chain, i.e. fuel supply, construction and operation. We consider electricity from power plants using coal, lignite, natural gas, oil, uranium or biomass as well as electricity from wind, solar and geothermal energy and hydropower. The global consumptive WF of electricity and heat is estimated to be 378 billion m3 per year. Wind energy (0.2–12 m3 TJe−1), solar energy through PV (6–303 m3 TJe−1) and geothermal energy (7–759 m3 TJe−1) have the smallest WFs, while biomass (50000–500000 m3 TJe−1) and hydropower (300–850000 m3 TJe−1) have the largest. The WFs of electricity from fossil fuels and nuclear energy range between the extremes. The global weighted-average WF of electricity and heat is 4241 m3 TJe−1. Europe has the largest WF (22% of the total), followed by China (15%), Latin America (14%), the USA and Canada (12%), and India (9%). Hydropower (49%) and firewood (43%) dominate the global WF. Operations (global average 57%) and fuel supply (43%) contribute the most, while the WF of construction is negligible (0.02%). Electricity production contributes 90% to the total WF, and heat contributes 10%. In 2012, the global WF of electricity and heat was 1.8 times larger than that in 2000. The WF of electricity and heat from firewood increased four times, and the WF of hydropower grew by 23%. The sector's WF can be most effectively reduced by shifting to greater contributions of wind, PV and geothermal energy.

A review of Safety, Health and Environmental (SHE) issues of solar energy system

Abstract: Solar energy is one of the cleanest forms of energy sources and considered as a green source of energy. Solar energy benefit ranges from low carbon emission, no fossil fuel requirement, long term solar resources, less payback time and other. However like other power generation sources, solar energy has also some Safety, Health and Environmental (SHE) concerns. This paper presents the overview of solar energy technologies and addresses the SHE impact of solar energy technologies to the sustainability of human activities. This paper will also recommend the possible ways to reduce the effect of potential hazards of widespread use of solar energy technologies.

The U.S. Electricity Industry After 20 Years of Restructuring

Abstract: Prior to the 1990s, most electricity customers in the US were served by regulated, vertically-integrated, monopoly utilities that handled electricity generation, transmission, local distribution and billing/collections Regulators set retail electricity prices to allow the utility to recover its prudently incurred costs, a process known as cost-of-service regulation During the 1990s, this model was disrupted in many states by "electricity restructuring," a term used to describe legal changes that allowed both non-utility generators to sell electricity to utilities — displacing the utility generation function — and/or "retail service providers" to buy electricity from generators and sell to end-use customers — displacing the utility procurement and billing functions We review the original economic arguments for electricity restructuring, the potential winners and losers from these changes, and what has actually happened in the subsequent years We argue that the greatest political motivation for restructuring was rent shifting, not efficiency improvements, and that this explanation is supported by observed waxing and waning of political enthusiasm for electricity reform While electricity restructuring has brought significant efficiency improvements in generation, it has generally been viewed as a disappointment because the price-reduction promises made by some advocates were based on politically-unsustainable rent transfers In reality, the electricity rate changes since restructuring have been driven more by exogenous factors — such as generation technology advances and natural gas price fluctuations — than by the effects of restructuring We argue that a similar dynamic underpins the current political momentum behind distributed generation (primarily rooftop solar PV) which remains costly from a societal viewpoint, but privately economic due to the rent transfers it enables