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1 May 2009

Volume 1, Issue 3, Articles (03xxxx)

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A molecular dynamics simulation study of hydrated sulfonated poly(ether ether ketone) for application to polymer electrolyte membrane fuel cells: Effect of water content

Giuseppe Brunello, Seung Geol Lee, Seung Soon Jang, and Yue Qi

J. Renewable Sustainable Energy 1, 033101 (2009); http://dx.doi.org/10.1063/1.3138922 (14 pages) | Cited 6 times

Online Publication Date: 21 May 2009

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Sulfonated poly(ether ether ketone) (S-PEEK) with 40% of degree of sulfonation was studied using full atomistic molecular dynamics simulation in order to investigate the nanophase-segregated structures, focusing on the sulfonate group and water phase at various water contents such as 10, 13, and 20 wt %. By analyzing the pair correlation function, it is found that as the water solvation of sulfonate groups proceeds more with increasing water content, the distance between sulfonate groups is increased from 4.4 Å (10 wt %) to 4.8 Å (13 wt %) to 5.4 Å (20 wt %), and the hydronium ions (H3O+) become farther apart from the sulfonate groups. The water coordination number for water and the water diffusion are enhanced with increasing water content because the internal structure of the water phase in S-PEEK approaches that of bulk water. Compared to the Nafion and Dendrion membranes, the S-PEEK membrane shows less internal structure in the water phase and smaller water diffusion, indicating that the S-PEEK has less nanophase segregation than the Nafion and Dendrion membranes.
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82.47.Nj Polymer-electrolyte fuel cells (PEFC)
88.30.pd Proton exchange membrane fuel cells (PEM)
82.45.Mp Thin layers, films, monolayers, membranes
64.75.Va Phase separation and segregation in polymer blends/polymeric solutions
82.35.Jk Copolymers, phase transitions, structure

Can large-scale advanced-adiabatic compressed air energy storage be justified economically in an age of sustainable energy?

William F. Pickard, Nicholas J. Hansing, and Amy Q. Shen

J. Renewable Sustainable Energy 1, 033102 (2009); http://dx.doi.org/10.1063/1.3139449 (10 pages) | Cited 2 times

Online Publication Date: 21 May 2009

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This article explores whether large-scale compressed air energy storage can be justified technically and economically in an era of sustainable energy. In particular, we present an integrated energy and exergy analysis of an idealized case of an advanced-adiabatic compressed air energy storage system and estimate its cycle efficiency. Based on our results, advanced-adiabatic compressed air energy storage (AA-CAES) seems to be technically feasible with a cycle efficiency of roughly 50% or better. However, our calculation shows that AA-CAES may not be as economically attractive as underground pumped hydro storage.
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84.60.Ve Energy storage systems, including capacitor banks
88.05.-b Energy analysis
88.30.R- Hydrogen storage

Analysis of delta-omega and fuzzy logic power system stabilizers under several operating conditions

R. Chopra, D. Joshi, and R. C. Bansal

J. Renewable Sustainable Energy 1, 033103 (2009); http://dx.doi.org/10.1063/1.3148273 (11 pages)

Online Publication Date: 2 June 2009

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Power system stabilizers (PSSs) have become very common in the operation of large electric power systems. The stability of electric power systems is increased by the use of power system stabilizers. It is a challenging task to design a stabilizer that delivers good performance in a wider range of operating conditions and under disturbances. This paper presents a fuzzy logic power system stabilizer (FLPSS) and demonstrates the good performance of this stabilizer under a wide range of operating conditions and disturbances. The performance of FLPSS is compared with that of a speed deviation (delta-omega) PSS in the variation of four different operating conditions, i.e., inertia constant (H), automatic voltage regulator (AVR) gain (Ka), internal reactance (Xe), and reactive power (Q).
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
84.35.+i Neural networks
89.20.Bb Industrial and technological research and development

Determining optimum tilt angles of photovoltaic panels at typical north-tropical latitudes

Emanuele Calabrò

J. Renewable Sustainable Energy 1, 033104 (2009); http://dx.doi.org/10.1063/1.3148272 (6 pages) | Cited 3 times

Online Publication Date: 9 June 2009

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An application of renewable energy technology is the installation of photovoltaic systems that generate power without emitting pollutants and requiring no fuel. Solar radiation varies with geographic latitude, season, and time of day due to the various sun positions in the sky. Hence, the problem of designing the optimal tilt angle and the orientation of a solar panel arises for maximizing solar radiation collection at a fixed latitude. An approach of employing sky radiance models for determining optimal tilt angle values of solar collectors with respect to a set of geographic latitudes was conducted by using a data archive of the daily global solar radiation collected by the Italian Institute of ENEA. The results provided a set of tilt angles for winter months that enables a solar panel to absorb the maximum amount of global solar radiation and another set of smaller tilt angle values for summer months, as well. The great difference between these two sets suggested to us to plan semifixed solar panels whose tilt angle can be changed twice a year. The relative gain in solar radiation collectable should not be negligible, as shown in Sec. 3.
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84.60.Jt Photoelectric conversion
42.79.Ek Solar collectors and concentrators
88.40.fc Modeling and analysis
88.40.hj Efficiency and performance of solar cells

Comparison of wind power estimates from the ECMWF reanalyses with direct turbine measurements

Péter Kiss, László Varga, and Imre M. Jánosi

J. Renewable Sustainable Energy 1, 033105 (2009); http://dx.doi.org/10.1063/1.3153903 (11 pages) | Cited 3 times

Online Publication Date: 11 June 2009

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Reanalysis data are rarely used for wind power estimates because of the limited spatial and temporal resolution. Here we report on a detailed comparison of wind speed and electric power time series recorded at a continental location in Hungary and estimates provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-40 and Interim databases at nearby grid points. The results show that the temporal behavior is adequately represented in reanalysis records with damped magnitudes, as expected. However, characteristic shape differences in the wind speed histograms for turbine measurements and reanalysis hinder a perfect match of statistics. A satisfying agreement of histograms for measured and modeled output powers is achieved by scaling up surface wind speeds to have the same long time average value as for the turbine records. The presented calibration permits us to provide wind power estimates for large geographic areas, where the wind field is similarly coherent as around the test site.
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02.50.-r Probability theory, stochastic processes, and statistics
88.50.-k Wind energy
88.05.-b Energy analysis

Design of solar beam collectors consisting of multilayer optical waveguide films for integrated solar energy conversion systems

Rina Shioya and Tetsuzo Yoshimura

J. Renewable Sustainable Energy 1, 033106 (2009); http://dx.doi.org/10.1063/1.3148276 (15 pages)

Online Publication Date: 11 June 2009

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To reduce consumption of semiconductor materials, to provide wide-angle solar beam collecting capability, and to make systems flexible and compact, we propose integrated solar energy conversion systems with waveguide-type solar beam collectors having film structures. We design structures of solar beam collectors consisting of multilayer optical waveguides with vertical mirrors and estimate the solar beam collecting efficiencies using the beam propagation method and the finite difference time domain method. The efficiencies for vertical incident light beams of 600 nm wavelength increase from 62% to 87% with increasing the layer counts from 1 to 3. The efficiency for incident angle of 45° is 1.5 times larger in solar beam collectors with 45° and 30° mirrors than in those with only 45° mirrors. Almost the same light-beam-collecting characteristics are obtained for wavelengths of 400 and 800 nm, achieving overall light beam collecting efficiency of more than 60%. These results suggest that the solar beam collector consisting of multilayer optical waveguides with mirrors of different angles enables wide-angle light beam collecting.
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42.79.Ek Solar collectors and concentrators
02.70.Bf Finite-difference methods
42.79.Gn Optical waveguides and couplers
88.40.fc Modeling and analysis
42.25.Bs Wave propagation, transmission and absorption

Synergetic pyrolysis of high density polyethylene and Jatropha and Karanj cakes: A thermogravimetric study

Dharmendra B. Parekh, Yogesh C. Rotliwala, and Parimal A. Parikh

J. Renewable Sustainable Energy 1, 033107 (2009); http://dx.doi.org/10.1063/1.3153904 (10 pages) | Cited 2 times

Online Publication Date: 15 June 2009

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Coprocessing behavior of mixtures of high density polyethylene (HDPE) and deoiled cakes of Jatropha and Karanja was studied by thermogravimetric analyses under dynamic conditions in the presence of nitrogen atmosphere and compared with those of individual materials. Experiments were carried out in the temperature range of ambient temperature to 900 °C at two heating rates (5 and 20 °C/min). Kinetic studies indicated activation energies for HDPE decomposition to be 235 and 258 kJ/mol at heating rates of 5 and 20 °C/min, respectively. Values of activation energy for pyrolysis of cakes of Jatropha and Karanj and those for cake-HDPE mixtures varied with the rate of heating as well as with the three temperature ranges. This variation has been explained based on the materials’ decomposition behavior. Reduction in activation energy for decomposition of the mixtures implies synergetic effects to be existing when two materials are coprocessed together.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
81.70.Pg Thermal analysis, differential thermal analysis (DTA), differential thermogravimetric analysis
88.20.mt Pyrolysis to liquids
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.05.Cy Elemental semiconductors

Thermal and daylighting evaluation of the effect of varying aspect ratios in urban canyons in Curitiba, Brazil

Eduardo Krüger and Mauro Suga

J. Renewable Sustainable Energy 1, 033108 (2009); http://dx.doi.org/10.1063/1.3153900 (17 pages) | Cited 1 time

Online Publication Date: 16 June 2009

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Urbanization is commonly associated with densification, which may lead to vertical growth or urban consolidation. The present study evaluates the daylighting potential as a function of urban morphology for the city of Curitiba (25°25′50″ S, 46°16′15″ W). It also presents a thermal analysis for a representative street axis orientation in this location, showing indoor conditions within a test office for different aspect ratios. In Curitiba, certain street axes were designated to allow densification (in the so-called structural sector of the city). As a consequence, there is a great risk of urban canyons being formed, as local legislation does not impose height restrictions to adjacent buildings. Daylight analysis was based on software simulations with LUZ DO SOL, DLN, ECOTECT, and RADIANCE. Thermal analysis was carried out by means of computer simulations with the IDA ICE software. It was verified that diagonal axial orientations relative to the north (rotated in 45°) provide higher daylighting potentials to buildings located in urban canyons. With regard to the thermal effect of varying the aspect ratio in an east-west street axis, results confirm daylighting simulations, showing the interrelation between both comfort parameters.
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89.65.Lm Urban planning and construction
92.60.Vb Radiative processes, solar radiation
02.70.-c Computational techniques; simulations

ZnO solid-state dye sensitized solar cells using composite electrolyte of poly(3-hexylthiophene-2,5-diyl) and carbon nanotubes

Seema Rani and R. M. Mehra

J. Renewable Sustainable Energy 1, 033109 (2009); http://dx.doi.org/10.1063/1.3156004 (12 pages) | Cited 7 times

Online Publication Date: 24 June 2009

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Solid-state dye sensitized solar cells (DSSCs) could become alternative to liquid electrolyte-based cells which suffer from several problems such as leakage, encapsulation, and cell interconnections within the module. In this paper we focus on ZnO solid-state DSSCs employing thiophene-based polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) as hole conducting agent. The effect of the addition of multiwalled carbon nanotubes (MWCNTs) in P3HT on the solar cell parameters was investigated. Current-voltage (I-V) characteristics of the different cells were obtained having different wt % of MWCNTs. Using the I-V characteristics and single diode model for the solar cell, various parameters such as the photocurrent, the saturation current of the diode, the series resistance, the shunt resistance, and the ideality factor were determined. The use of MWCNTs with polymer P3HT increased the photovoltaic performance of the solar cells. Highest device performance was achieved with 0.8 wt % of MWCNTs in P3HT. The role of MWCNTs for efficient hole transfer was discussed in terms of series and shunt resistances.
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84.60.Jt Photoelectric conversion
82.45.Gj Electrolytes
88.40.J- Types of solar cells
72.40.+w Photoconduction and photovoltaic effects
82.35.Rs Polyelectrolytes
82.35.Lr Physical properties of polymers

Computational fluid dynamics analysis of a combined three-bucket Savonius and three-bladed Darrieus rotor at various overlap conditions

Biplab Kumar Debnath, Agnimitra Biswas, and Rajat Gupta

J. Renewable Sustainable Energy 1, 033110 (2009); http://dx.doi.org/10.1063/1.3152431 (13 pages) | Cited 3 times

Online Publication Date: 29 June 2009

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In this paper, a computational fluid dynamics analysis using the FLUENT package 6.2 was carried out to predict the performance characteristics such as power coefficient (Cp), torque coefficient (Ct), and tip speed ratio of a combined three-bucket Savonius and three-bladed Darrieus rotor for various overlap conditions, namely, 16.2%, 20%, 25%, 30%, and 35%. In the upper part of the rotor model, there was a three-bucket Savonius rotor of bucket diameter of 8 cm and height of 10 cm, whereas, in the lower part, there was a three-bladed Darrieus rotor of blade diameter of 8 cm and height of 10 cm. A two-dimensional unstructured computational grid was developed for the combined Savonius–Darrieus rotor model. A k-ε turbulence closure model with enhanced wall treatment function was chosen. A first-order upwind discretization scheme was adopted for pressure-velocity coupling of the flow. The values of Cp and Ct obtained computationally were then compared with those of the values of Cp and Ct obtained experimentally for all the overlap conditions. The experimental values of Cp and Ct for different overlap conditions were obtained from the tests conducted previously in an open-circuit subsonic wind tunnel available in the department. The comparison of experimental and computational studies is quite encouraging.
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89.20.Kk Engineering
89.20.Bb Industrial and technological research and development
88.50.gj Modeling, design
47.85.Gj Aerodynamics
47.11.-j Computational methods in fluid dynamics

Biofuel contribution to mitigate fossil fuel CO2 emissions: Comparing sugar cane ethanol in Brazil with corn ethanol and discussing land use for food production and deforestation

Luiz Pinguelli Rosa, Christiano Pires de Campos, and Maria Silvia Muylaert de Araujo

J. Renewable Sustainable Energy 1, 033111 (2009); http://dx.doi.org/10.1063/1.3139803 (21 pages)

Online Publication Date: 30 June 2009

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This paper compares the use of sugar cane and corn for the production of ethanol, with a focus on global warming and the current international debate about land use competition for food and biofuel production. The indicators used to compare the products are CO2 emissions, energy consumption, sugar cane coproducts, and deforestation. The life cycle emission inventory as a methodological tool is taken into account. The sustainability of socioeconomic development and the developing countries’ need to overcome barriers form the background against which the Brazilian government energy plans are analyzed.
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88.20.ff Ethanol
89.60.-k Environmental studies
92.70.Mn Impacts of global change; global warming
89.65.-s Social and economic systems

Electrolysis of glycerol in subcritical water

Asli Yuksel, Hiromichi Koga, Mitsuru Sasaki, and Motonobu Goto

J. Renewable Sustainable Energy 1, 033112 (2009); http://dx.doi.org/10.1063/1.3156006 (11 pages) | Cited 2 times

Online Publication Date: 30 June 2009

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Recently, there has been a rising interest for the disposal of biorelated components that cannot be treated easily by biological processes. Because of the development of biodiesel production, the production of by-products such as crude glycerol has increased dramatically. Presently, in many biodiesel plants with low capacity, the aqueous phase containing produced/left glycerol, which is an important molecule in the context of renewable biomass resources to provide hydrogen energy and chemical intermediates, methanol and salts as by-products, is discharged as wastewater. In this manner, both environmental pollution and economical losses are created. Therefore, we developed a new hydrothermal electrolysis system, by which these organics can be converted into value added chemicals, under high-temperature and high-pressure aqueous conditions. In this study, hydrothermal electrolysis reactions of glycerol with an alkali were investigated systematically to determine the intermediate products and current efficiency. We next studied the effects of electricity loading on the molecular transformation of glycerol through the comparison of the product distribution obtained by hydrothermal electrolysis with that by hydrothermal degradation under alkaline conditions. As a gaseous product, hydrogen gas was generated, whereas lactic acid was produced as the main liquid product. The yield of lactic acid increased to 34.7% at 280 °C with 50 mM NaOH after 90 min reaction time.
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89.60.-k Environmental studies
82.45.Hk Electrolysis
84.60.-h Direct energy conversion and storage
89.30.-g Fossil fuels and nuclear power
82.47.Wx Electrochemical engineering
82.20.Hf Product distribution
88.20.fk Biodiesel
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