Showing papers in "Journal of Renewable and Sustainable Energy in 2012"
TL;DR: In this article, a study was conducted to explore those areas which are most suitable for solar energy potential using fifty eight meteorological stations covering the whole country Angstrom equation and Hargreaves formula was used to calculate monthly solar power potential by utilizing monthly climatical data of bright sunshine hours, mean maximum and minimum temperatures.
Abstract: In view of the growing needs of energy in Pakistan, the efficient use and development of renewable energy sources has become a major issue in the country This has brought the intention of several national and multinational companies to design and implement a major work plan for energy conservation and construction of renewable energy sources like wind mills and solar panels Fortunately, Pakistan is among those countries in which sun warms the surface throughout the year and therefore has a strong potential for solar power generation This study was conducted to explore those areas which are most suitable for solar energy potential using fifty eight meteorological stations covering the whole country Angstrom equation and Hargreaves formula was used to calculate monthly solar energy potential by utilizing monthly climatical data of bright sunshine hours, mean maximum and minimum temperatures The lowest solar radiation intensity 7649 W/m2 observed at Cherat during December and highest 33925 W/m2 at Gilgit The average monthly solar radiation intensity remains 13605 to 28736 W/m2 in the country The results indicate that the values of solar radiation intensity greater than 200 W/m2 were observed in the months: February to October in Sindh, March to October in almost all regions of Balochistan, April to September in NWFP, Northern Areas and Kashmir regions while March to October in Punjab For 10 h a day, average solar radiation intensity ranges from 1500 W/m2/day to 2750 W/m2/day in Pakistan especially in southern Punjab, Sindh and Balochistan regions throughout the year In an area of 100 m2, 45 MW to 83 MW power per month may be generated in the above mentioned regions
92 citations
TL;DR: In this paper, the authors present a historical perspective on the Savonius turbines and discuss recent developments in analysis methods which intend to optimize the turbines for powering cellular communication towers in developing parts of the world.
Abstract: Wind turbine use is expanding throughout the world as a means to provide electricity without contributing to the increase in global-warming gases. Most commonly, very large, horizontal-axis turbines are constructed in fleets that are connected to national-level electrical grid systems. More recently, there has been a desire for more local, small-scale power production that can be used to power very specific pieces of equipment or buildings. Some of the small-scale turbines are designed differently from their larger counterparts—they are driven by drag forces rather than by lift. Drag-driven turbines are typically called Savonius turbines. This paper, which presents a historical perspective on Savonius turbines, will illustrate their potential for providing local power. Finally, we will discuss recent developments in analysis methods which intend to optimize Savonius turbines for powering cellular communication towers in developing parts of the world.
82 citations
TL;DR: In this article, the authors used the National Renewable Energy Laboratory's hybrid optimization model for electric renewables simulation software has been used to carry out the optimal design and techno-economic viability of energy system in this study.
Abstract: In respect to increasing demand for energy in the world and limited fossil fuel resources, there is a great need for using renewable energies (REs). One of the most attractive applications of RE technology is the application of hybrid energy systems in remote areas. An alternative to overcoming the intermittence of RE sources, such as the sun and wind (are freely available and environmental friendly), is to develop the hybrid energy system where excess electrical energy could be converted and stored. These sources combined with energy storage would provide a better system reliability making it suitable for stand-alone applications. They have been integrated and worked at the Taleghan renewable energies site in Iran. The National Renewable Energy Laboratory's hybrid optimization model for electric renewables simulation software has been used to carry out the optimal design and techno-economic viability of energy system in this study. The simulation results demonstrate that for hybrid energy system is consists of 0.8 kW PV modules, two wind turbines (0.4 kW each), 2.5 kW inverter, and 8 batteries (200 Ah and 12 V). The cost of energy is 1.655 US$/kWh, whereas the initial capital required, and net present costs are, 22998 US$ and 24623 US$, respectively.
80 citations
TL;DR: In this article, a comparative spectral characterization of zirconium, hafnium, and tantalum carbides for concentrating solar power applications is presented, where they are evaluated as sunlight absorbers in receivers for high-temperature thermodynamic solar plants.
Abstract: Ultra-high temperature ceramics are the ideal materials for extreme conditions owing to their very high melting points and good thermo-mechanical properties at high temperatures. For these reasons, they are widely known as materials for aerospace applications. This paper presents a comparative spectral characterization of zirconium, hafnium, and tantalum carbides ultra-high temperature ceramics for concentrating solar power applications. Room-temperature reflectance spectra have been measured from the ultraviolet wavelength region to the mid-infrared band. Using these spectral properties, the ceramics were evaluated as sunlight absorbers in receivers for high-temperature thermodynamic solar plants.
77 citations
TL;DR: In this paper, various statistical features of turbulence causing vertical entrainment of mean-flow kinetic energy are studied using hot-wire velocimetry data taken in a model wind farm in a scaled wind tunnel experiment.
Abstract: For large wind farms, kinetic energy must be entrained from the flow above the wind turbines to replenish wakes and enable power extraction in the array. Various statistical features of turbulence causing vertical entrainment of mean-flow kinetic energy are studied using hot-wire velocimetry data taken in a model wind farm in a scaled wind tunnel experiment. Conditional statistics and spectral decompositions are employed to characterize the most relevant turbulent flow structures and determine their length-scales. Sweep and ejection events are shown to be the largest contributors to the vertical kinetic energy flux, although their relative contribution depends upon the location in the wake. Sweeps are shown to be dominant in the region above the wind turbine array. A spectral analysis of the data shows that large scales of the flow, about the size of the rotor diameter in length or larger, dominate the vertical entrainment. The flow is less incoherent below the array, causing decreased vertical fluxes there. The results show that improving the rate of vertical kinetic energy entrainment into wind turbine arrays is a standing challenge and would require modifying the large-scale structures of the flow. Such an optimization would in the future aid recovery of the wind turbine wake towards conditions corresponding to the undisturbed atmospheric boundary layer.
74 citations
TL;DR: A comprehensive review of frequency tuning methods for piezoelectric energy harvesting systems is presented in this paper, where the recent developments of many tuning strategies are discussed and summarized, including manual and autonomous tuning methods.
Abstract: Piezoelectric energy harvesting technologies have received a great attention during the last decade to design self-powered microelectronic devices such as wireless sensor nodes. Piezoelectric energy harvester is a resonant system that produces maximum power output when its resonant frequency matches the ambient vibration frequency. The deviation from the resonance causes significant decrease in the power output. There are two possible solutions to compensate the effect of frequency deviation: widening the operating frequency bandwidth and tuning the resonant frequency. Tuning the resonant frequency is a more efficient technique for applications with single time varying dominant frequency. This paper presents a comprehensive review of frequency tuning methods for piezoelectric energy harvesting systems. Two categories generally investigated in the literature include manual and autonomous tuning methods. The recent developments of many tuning strategies are discussed and summarized.
73 citations
TL;DR: In this article, a solar parabolic trough concentrator (PTC) with a rim angle of 45°, a length of 4.88m, and an aperture area of 5.8 m2 was designed for low enthalpy steam generation and hot water.
Abstract: This paper reports the design, construction, and evaluation of a solar parabolic trough concentrator (PTC) with a rim angle of 45°, a length of 4.88 m, and an aperture area of 5.8 m2. The PTC is made of aluminium in such a way that both the manufacturing and assembly processes do not require complicated technology or skilled labour. Since the PTC is for low enthalpy steam generation and hot water, it is designed with an unshielded receiver and without a glass cover in order to reduce both production and transportation costs. A finite element stress analysis is conducted to determine the mechanical behaviour of the PTC under various simulated wind loads on the structure. A simple solar tracking system is employed when it is oriented in a North-to-South direction. The optical efficiency of the collector is also reported. Said efficiency depends on the optical properties of the materials involved, the geometry of the collector, and the various imperfections arising from the construction of the collector. The thermal performance of the PTC was determined according to the Standard ASHRAE 93-1986 (RA 91). Peak efficiencies close to 60% were obtained.
50 citations
TL;DR: In this article, the evaluation of five planetary boundary layer (PBL) schemes in the Weather Research and Forecasting model for offshore wind energy purposes is focused on evaluating the ability of different PBL schemes to forecast turbulent fluxes of heat and momentum and surface stability.
Abstract: This paper is focused on the evaluation of five planetary boundary layer (PBL) schemes in the Weather Research and Forecasting model for offshore wind energy purposes. One first order scheme: Yonsey University and four one-and-a-half order schemes: Mellor-Yamada-Janic, Quasi-Normal Scale Elimination, Mellor-Yamada-Nakanishi-Niino, and Bougeault-Lacarrere, are considered. Turbulent flux measurements from the FINO1 platform in the North Sea are used to estimate the Obukhov length, allowing the sorting of the data into different stability classes. In addition, wind LiDAR measurements are used to analyze wind profiles up to 251.5 m, encompassing the heights where today's wind turbines operate. The ability of the different PBL schemes to forecast turbulent fluxes of heat and momentum and surface stability is evaluated. Obukhov length results show that in general, PBL schemes forecast more moderated stable stratifications and a reinforcement of the instability for neutral and convective conditions, compared to FINO1 observations. The vertical structure of the wind speed profile is thoroughly analyzed for stable, near-neutral, unstable, and very unstable conditions by using total shear stresses, eddy diffusivities, and wind speed shears. The Mellor-Yamada-Nakanishi-Niino scheme presents the best agreement with measurements considering the different atmospheric stabilities analyzed. Stable conditions are the most complicated scenario for the PBL schemes to reproduce due to their overdiffusive formulations, which effect is to lower the vertical wind shear. Under such conditions, Quasi-Normal Scale Elimination and Yonsey University outperform the rest of the PBL schemes, the latest using a revised diffusion formulation.
47 citations
TL;DR: In this article, the optimum tilt angle for south facing flat-plate solar collectors in Iran was determined by applying an empirical method and employing meteorological data from 80 selected cities, and the average benefits of annual solar radiation for 80 cities were 21.3% for daily, 21% for monthly, 19.6% for seasonal, 19% for bi-annual, and 13.3 % for yearly adjustments compared with the radiation on the horizontal collector.
Abstract: This paper aims at determining the optimum tilt angle for south facing flat-plate solar collectors in Iran. Solar radiation on a horizontal surface was estimated by applying an empirical method and employing meteorological data from 80 selected cities. A mathematical model was used for estimating the solar radiation at different tilt angles. Daily, monthly, seasonally, bi-annually, and yearly optimum tilt angles and solar radiations were determined for 80 selected cities. Recommendations were made on the optimum tilt angle adjustment for different places in the country in order to benefit the best solar radiation available. The averaged benefits of annual solar radiation for 80 cities were 21.3% for daily, 21% for monthly, 19.6% for seasonal, 19.3% for bi-annual, and 13.3% for yearly adjustments compared with the radiation on the horizontal collector. Based on these results, adjusting tilt angles, at least twice a year, is recommended. Optimum tilt angles for cloudy sky cities with a low clearness index are lower than those for cities at the same latitude angle having a higher clearness index. In addition to latitude angle, the climate conditions are also important for determining the optimum tilt angle.
47 citations
TL;DR: In this article, the fabrication of Zinc Oxide (ZnO) based quantum dot sensitized solar cell using Cadmium Sulphide (CdS) quantum dots (QDs) capped by poly vinyl alcohol (PVA).
Abstract: This paper reports the fabrication of Zinc Oxide (ZnO) based quantum dot sensitized solar cell using Cadmium Sulphide (CdS) quantum dots (QDs) capped by poly vinyl alcohol (PVA). Chemical route was used to synthesize ZnO nanoparticles (NPs) as well as CdS QDs. The crystallite size of ZnO NPs was obtained to be 28 nm at 7 pH. The size of QDs decreased from 5.6 to 2.6 nm with increase in the PVA concentration from 2 to 10 wt. %. There is a blue shift in the band gap of QDs with increase in the concentration of PVA. Current-Voltage characteristic of the cell was obtained and various solar cell parameters were estimated. The efficiency of quantum dot sensitized solar cells was found to be 1.3% at AM 1.5.
45 citations
TL;DR: In this article, the x-ray photoelectron spectroscopy results indicate that sulfur-doped TiO2 are locally distorted by incorporating S6+ species into TiO 2 and substitutes for some of the lattice titanium (Ti4+).
Abstract: Sulfur-doped TiO2 is prepared by a mechanical process with ball milling the thiourea with commercial P25 TiO2 nanoparticles and successfully used as photoanode of dye-sensitized solar cells (DSSCs). The x-ray photoelectron spectroscopy results indicate that sulfur-doped TiO2 are locally distorted by incorporating S6+ species into TiO2 and substitutes for some of the lattice titanium (Ti4+); meanwhile, a clear reduction in the band gap energy of the sulfur-doped TiO2 photoanode compared to the band gap value for P25. The linear sweep voltammetry indicate that the edge of the conduction band of sulfur-doped TiO2 move positively toward the vacuum level. A conversion efficient of 6.91% was achieved for a DSSC based on sulfur-doped solar cell, which was 24% higher than that of the un-doped solar cell. The improved performance was ascribed to the improved charge injection from the dye to the sulfur doped TiO2 electrode, as evidence by an improved spectral response in the whole wavelength range.
TL;DR: In this article, the level of energy security in the Nordic countries with comparison to other developed countries and their neighbors is discussed and the support schemes and policies to achieve the energy security and diversification are reviewed based on the system thinking approach with especial focus on the renewable energy resources.
Abstract: Security of energy supply has been one of the important debates among citizens and governments of the Nordic countries after the first energy crisis. In response, diversification was defined as the heart strategy to reach a certain level of energy supply. This article discusses about the level of energy security in the Nordic countries with comparison to other developed countries and their neighbors. Then, the support schemes and policies to achieve the energy security and diversification are reviewed based on the system thinking approach with especial focus on the renewable energy resources. This approach provides a unique and powerful tool to explain the complexity and the relationships among the elements of the support schemes in the energy security analysis.
TL;DR: In this article, the authors examined the relationship between inputs and outputs of cotton production in Iran using the Cobb-Douglas production function and found that machinery, fertilizer, diesel fuel, and biocide energies had significant effect on cotton yield.
Abstract: This study examined the energy use, greenhouse gas (GHG) emission and the relationship between energy inputs and yield of cotton production in Iran. Data were collected randomly from 57 cotton farms using a face to face questionnaire. The results revealed the total energy of 31 237 MJ ha−1 which fertilizer, diesel fuel, and machinery were the main energy consuming inputs. Total GHG emission was 1195 kg CO2eq ha−1, and machinery, diesel fuel, and irrigation had the highest emissions. Energy ratio and energy productivity were 1.85 and 0.11 kg MJ−1, respectively. In order to explore the relationship between inputs and outputs, the Cobb-Douglas production function was applied and it was deduced that machinery, fertilizer, diesel fuel, and biocide energies had significant effect on cotton yield. Also, the results of marginal physical productivity technique indicated that an additional use of 1 MJ ha−1 from each of the biocide, machinery, and diesel fuel would lead to an increase in production by 1.68, 0.45, an...
TL;DR: In this article, the authors utilized three hourly measured values of wind speed and direction from seven buoys data collection stations in the Aegean Sea to study the wind speeds and power characteristics applying the Weibull shape and scale parameters.
Abstract: This paper utilizes three hourly measured values of wind speed and direction from seven buoys data collection stations in Aegean Sea to study the wind speed and power characteristics applying the Weibull shape and scale parameters. Specifically, the site dependent, annual and monthly mean patterns of mean wind speed, Weibull parameters, frequency distribution, most probable wind speed, maximum energy carrying wind speed, wind power density and wind energy density characteristics have been studied. The Weibull distribution was found to represent the wind speed distribution with more than 90% accuracy in most of the cases. Slightly decreasing trends were observed in annual mean wind speed values at Lesvos and increasing at Mykonos. The mean values of wind speed, scale parameter, most probable wind speed, maximum energy carrying wind speed, wind power and wind energy density values showed higher values during winter time and lower in summer time. Mykonos was found to be the best site from wind power harnessing point of view. Moreover, the correlation between the percentages of times the wind speed was above cut-in-speed and the measured mean wind speed for the three selected sites and the correlation between the aforementioned percentages and the scale parameter c were examined and were found linear.
TL;DR: In this paper, the authors numerically examined the interactions among multiple Savonius turbines with the help of the commercial computational fluid dynamics software fluent and found that these coupling effects can effectively increase the overall power output of a turbine farm.
Abstract: A Savonius rotor can be used as a wind or water current energy conversion device that produces electricity. In spite of their simple structure and assembly, Savonius turbines have less commercial appeal than other types of turbines due to their relatively low energy conversion efficiency. In order to increase the output power of a Savonius turbine, most studies have only focused on optimization of the rotor configuration or installation of ancillary equipment around the rotor. However, previous research has found that a beneficial interaction that existed between two parallel Savonius turbines can also augment the power output of each rotor if they are rotating side by side. This paper numerically examines the interactions among multiple Savonius turbines with the help of the commercial computational fluid dynamics software fluent and finds that these coupling effects can effectively increase the overall power output of a Savonius turbine farm, especially when Savonius turbines are arranged relatively clo...
TL;DR: In this paper, the authors investigated the relationship analysis between biomass energy consumption and economic growth by using Autoregressive Distributed Lag (ARDL) bounds testing approach of cointegration and vector error-correction models.
Abstract: This paper investigates the relationship analysis between biomass energy consumption and economic growth by using Autoregressive Distributed Lag (ARDL) bounds testing approach of cointegration and vector error-correction models. The cointegration test results show that there is cointegration between the biomasss energy consumption and the economic growth in five of the seven countries (Bolivia, Brazil, Chile, Colombia, and Guatemala) and there is no cointegration between the biomasss energy consumption and the economic growth in two of the seven countries (Argentina and Jamaica).
TL;DR: In this article, the effect of roughness on the Nusselt number and friction factor of a V-down rib roughened solar air heater duct was investigated.
Abstract: Artificial roughening of a broad wall of solar air heater leads to significant enhancement in heat transfer besides comparable rise in friction losses. This paper presents the outcome of experimental study on heat transfer and fluid friction characteristics of solar air heater duct roughened with broken V-down rib combined with staggered rib piece. Experimental data were collected on a high aspect ratio rectangular duct by varying the Reynolds number from 3000 to 17 000, relative gap position (s′/s) 0.2–0.8, relative staggered rib position (p′/p) 0.2–0.8, relative staggered rib size (r/e) 1–2.5, for the fixed values of relative roughness pitch (p/e) of 10, relative roughness height (e/Dh) of 0.043, relative gap size (g/e) of 1, and angle of attack (α) of 60°. The effect of flow Reynolds number and roughness parameters on Nusselt number and friction factor has been explored and the results are compared with continuous V-down rib roughened duct and smooth duct under similar flow conditions. Correlations for the Nusselt number and friction factor as a function of Reynolds number and roughness parameters have been developed.
TL;DR: In this article, the effects of arbitrary waveforms on magnetic core loss in high frequency high power transformers were studied and the capabilities of nanocrystalline and amorphous magnetic materials were compared.
Abstract: High frequency high power transformers used in power electronic converters are frequently subjected to non-sinusoidal excitations. The main purpose of this paper is to study the effects of some general arbitrary waveforms on magnetic core loss in these transformers. First, using well-known empirical equations, general expressions were derived based on the parameters of the waveforms. Second, the impacts of different orders of voltage harmonics were investigated. Finally, capabilities of nanocrystalline and amorphous magnetic materials were compared. It is shown that the loss inside the core is highly sensitive to the rise time and duty cycle of trapezoidal and rectangular waveforms, respectively. Furthermore, although amorphous materials have higher saturation flux density, the total core loss inside the transformer designed using nanocrystalline material is considerably lower than the similar transformer with amorphous materials.
TL;DR: In this paper, the structural, electronic, and phonon properties of Na2ZrO3 and M2CO3 were investigated by combining the density functional theory with lattice phonon dynamics.
Abstract: Alkali metal zirconates could be used as solid sorbents for CO2 capture. The structural, electronic, and phonon properties of Na2ZrO3, K2ZrO3, Na2CO3, and K2CO3 are investigated by combining the density functional theory with lattice phonon dynamics. The thermodynamics of CO2 absorption/desorption reactions of these two zirconates are analyzed. The calculated results show that their optimized structures are in a good agreement with experimental measurements. The calculated band gaps are 4.339 eV (indirect), 3.641 eV (direct), 3.935 eV (indirect), and 3.697 eV (direct) for Na2ZrO3, K2ZrO3, Na2CO3, and K2CO3, respectively. The calculated phonon dispersions and phonon density of states for M2ZrO3 and M2CO3 (M = K, Na, Li) revealed that from K to Na to Li, their frequency peaks are shifted to high frequencies due to the molecular weight decreased from K to Li. From the calculated reaction heats and relationships of free energy change versus temperatures and CO2 pressures of the M2ZrO3 (M = K, Na, Li) reacting...
TL;DR: In this article, the physical properties of tin sulphide are affected by indium concentration, and it is found that better crystallinity in zinc blend structure with preferential orientations was obtained for y equal to 6%.
Abstract: SnS:In thin films have been successfully prepared on Pyrex substrates using low cost chemical bath deposition technique with different indium concentrations (y=[In][Sn]=4%,6%,8%,and10%). The structure, the surface morphology, and the optical properties of the SnS:In films were studied by x-ray diffraction, scanning electron microscope, atomic force microscopy, and spectrophotometer measurements. In order to obtain a thickness of the order of 308 ± 10 nm for potential applications in solar cell devices, a multilayer deposition has been prepared. It is found that the physical properties of tin sulphide are affected by indium concentration. In fact, x-ray diffraction study showed that better crystallinity in zinc blend structure with preferential orientations (111)ZB and (200)ZB was obtained for y equal to 6%. According to the AFM analysis, we remark that low average surface roughness value of SnS(ZB) thin film is obtained with In concentrations equal to y = 6%. Energy dispersive spectroscopy showed the exis...
TL;DR: In this article, the effect of broken V-rib roughness combined with staggered ribs on heat transfer and friction in a flow through artificially roughened solar air heater duct was investigated.
Abstract: Thermal performance of solar air heater has been found to be substantially improved by the application of artificial roughness provided on underside of absorber surface. The present investigation was taken up to study the effect of broken V-rib roughness combined with staggered ribs on heat transfer and friction in a flow through artificially roughened solar air heater duct. This work covered a range of Reynolds number (Re) 3000–17 000, relative staggered rib pitch (p′/p) 0.2–0.8, relative staggered rib size (r/e) 1–2.5, relative gap position (s′/s) 0.2–0.8 for the fixed values of relative roughness pitch (p/e) of 10, relative roughness height (e/Dh) of 0.043, relative gap size (g/e) of 1, and angle of attack (α) of 60°. Experimental data pertinent to heat transfer and friction was generated and thermohydraulic performance was determined for different sets of roughness and flow parameters.
TL;DR: In this paper, the optimization of transesterification process for different varieties of biodiesel by considering the factors such as alcohols, fatty acid content, molar ratio of alcohols to oil, catalyst concentration, reaction temperature, and reaction time is discussed.
Abstract: Biodiesel is an alternative fuel to diesel engine that can replace or reduce the use of petroleum diesel. Biodiesel is derived from vegetable oils, animal fats, and waste cooking oils through transesterification reaction. This paper reviews the optimization of transesterification process for different varieties of biodiesel by considering the factors such as alcohols, fatty acid content, molar ratio of alcohols to oil, catalyst concentration, reaction temperature, and reaction time. The review also addresses various technical aspects of biodiesel usage in diesel engine to improve the cold flow properties, performance, combustion characteristics and reduce the emission characteristics, particularly nitric oxide and smoke compared to diesel through either modifying engine parameters like fuel injection pressure and timing or fuel modification by blending with alcohols, diesel, and metal based additives.
TL;DR: In this paper, an energy and exergy analysis of a domestic size parabolic solar cooker in actual use was carried out and the experimental time period was from 10:00 to 13:30 solar time.
Abstract: This paper deals with an energy and exergy analysis of a domestic size parabolic solar cooker in actual use. The experimental time period was from 10:00 to 13:30 solar time. During the experiment, it was found that the maximum temperature of water was 368 K. The energy out of the cooker varied between 46.67 and 653.33 W, whereas its exergy output was in the range, 7.37-46.46 W. Maximum energy and exergy efficiencies of the cooker were experimentally evaluated, and it was about 46.82% and 32.97%, respectively. Over the time, both efficiencies were decreased because of the optical and thermal losses from the reflector and pot. By using properly insulated cooking pot, the considerable amount of conventional energy can be saved. Regular use of a solar cooker helps in CO2 mitigation and provides clean and safe cooking.
TL;DR: In this article, a hierarchical control scheme is used for maximizing the power production output of local distributed generators, and optimizing power exchanges among the microgrids as well as power exchange between the main distribution system and the integrated microgrid.
Abstract: Operation of modern power system has become a complex problem, as its focus has shifted to implementing smart grid techniques and integrating distributed renewable energy sources. Integrated microgrid is an innovative control and management architecture at distribution network level, where several microgrids are electrically interconnected with each other. This paper presents a multi-agent system (MAS) for the operation of an integrated microgrid. A hierarchical control scheme is used for maximizing the power production output of local distributed generators, and optimizing power exchanges among the microgrids as well as power exchange between the main distribution system and the integrated microgrid. This scheme was implemented on the multi-agent system. Simulation studies carried out on the developed system demonstrate the effectiveness of the proposed multi-agent system for the operation of an integrated microgrid.
TL;DR: In this article, the authors consider only two great transformations in the history of human mankind to be comparable to the Great Transformation towards a global low-carbon economy faced now: the Neolithic Revolution and the Industrial Revolution, and argue that the technological, economic, and social main elements which will permit the transformation to be made to climate compatibility are already emerging.
Abstract: The authors consider only two great transformations in the history of human mankind to be comparable to the Great Transformation towards a global low-carbon economy faced now: the Neolithic Revolution and the Industrial Revolution. This paper discusses different social, economic, and cultural theories which might help to understand this far reaching socio-economic transformation and focus on specific arenas of change in which low-carbon dynamics occur. The authors argue that the technological, economic, and social main elements which will permit the transformation to be made to climate compatibility are already emerging. On the other hand the speed and geographical spread of the low-carbon dynamics are still not sufficient to avoid dangerous climate change.
TL;DR: In this paper, an evacuated solar heat pipe collector is investigated theoretically and experimentally, and a test method was adopted from ISO 9806-1 to compare the theoretical model with the experimental results.
Abstract: In this paper, an evacuated solar heat pipe collector is investigated theoretically and experimentally. Heat transfer formulas were used for theoretical modeling, and a test method was adopted from ISO 9806-1 to compare the theoretical model with the experimental results. The collector efficiency and useful heat gain were compared between the theoretical and experimental methods. The effect of the working fluid flow rates and collector area were also investigated and discussed. The comparison shows that the theoretical model is in good agreement with the experimental results and is capable of predicting the efficiency, useful heat gain, and working fluid outlet temperature of an evacuated heat pipe collector with good accuracy.
TL;DR: LiFePO4/graphene/C composite nanofibers were synthesized by using a combination of electrospinning and sol-gel techniques in this paper, in which LiFePO 4 nanoparticles were encapsulated in graphene-containing carbon nanofiber matrix, and the carbon source Graphene was incorporated in order to increase the conductivity of the composite PAN.
Abstract: LiFePO4/graphene/C composite nanofibers, in which LiFePO4 nanoparticles were encapsulated in graphene-containing carbon nanofiber matrix, were synthesized by using a combination of electrospinning and sol-gel techniques Polyacrylonitrile (PAN) was used as the electrospinning media and the carbon source Graphene was incorporated in order to increase the conductivity of the composite PAN was dissolved in N,N–dimethylformamide (DMF) LiFePO4 precursor and graphene were dispersed in DMF separately and were mixed with PAN solution before electrospinning Electrospun fibers were heat-treated to obtain LiFePO4/graphene/C composite nanofibers The structure of LiFePO4/graphene/C composite nanofibers was determined by X–ray diffraction analysis The surface morphology and microstructure of LiFePO4/graphene/C composite nanofibers were characterized using scanning electron microscopy and transmission electron microscopy Electrochemical performance of LiFePO4/graphene/C composite nanofibers was evaluated in coin-
TL;DR: A molybdenum diffusion layer has been prepared on the surface of AISI 304 stainless steel (Mo-304 SS) by means of plasma surface diffusion alloying method as mentioned in this paper.
Abstract: A molybdenum diffusion layer has been prepared on the surface of AISI 304 stainless steel (Mo-304 SS) by means of plasma surface diffusion alloying method. X-ray diffraction data show that the molybdenum modified layer of 304 SS mainly consists of cubic Mo. The results of scanning electron microscopy in combination with energy-dispersive X-ray analysis spectrometer indicate that the as-prepared molybdenum diffusion layer is ∼3 μm with dominant molybdenum element. A series of electrochemical evaluation tests were conducted on the Mo-304 SS specimens to determine if the Mo-304 SS is suitable to be used as proton exchange membrane fuel cell (PEMFC) bipolar plate. The corrosion resistance and the passivated behavior of the Mo-304 SS are improved, which yield better results than those found in the untreated 304 SS after the potentiodynamic and potentiostatic polarization under simulated typical PEMFC operating conditions (0.05 M H2SO4 +2 ppm F− solution at 70 °C purged with either hydrogen or air). Also, the i...
TL;DR: In this article, a mathematical model of a parabolic trough collector (PTC) is described in detail and tested by comparing the efficiency predicted by the model with the efficiency measured through outdoor tests on a PTC prototype.
Abstract: In this paper, a mathematical model of a parabolic trough collector (PTC) is described in detail and tested by comparing the efficiency predicted by the model with the efficiency measured through outdoor tests on a PTC prototype. The model accounts for optical and thermal losses, thus allowing the calculation of optical, thermal, and global efficiencies, and of all working parameters such as temperatures or heat fluxes on all parts of the receiver. The model is presented in detail and its implementation in a specific ambient for technical computation is also described. The application of the model to a specific prototype of parabolic trough collector is described: this prototype has been developed and tested at Universita Politecnica delle Marche and is intended for industrial process heat production. The comparison between experimental and calculated results shows an average error of about 3.82% and a maximum error of 14% on global efficiencies for tests with water in the temperature range 25–75 °C.
TL;DR: In this article, the effects of transition metal doping on Li-vacancy formation energies and electrode potentials of Li2S cathode materials for lithium batteries are investigated using first-principles calculations with density functional theory.
Abstract: The effects of transition metal (TM) doping on Li-vacancy formation energies and electrode potentials of Li2S cathode materials for lithium batteries are investigated using first-principles calculations with density functional theory. In addition, the geometric and electronic structures for 1.56 at. % Fe-doped lithium sulfide are analyzed to further reveal the TM-doping effect. We find that Evac can be only moderately enhanced by the increasing atomic number of TM dopant. The Evac is lowered from 3.37 eV in pure Li2S to about 1.11–1.23 eV in the Fe-doped compounds. Such decrease can be mainly attributed to the electronic structures. Compared with Li2S, the downtrend of reversible electrode potential (U) value in the Cu-doped systems is indistinctive with increase in the dopant contents.