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1 May 2013

Volume 5, Issue 3 (partial)

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Conventional and global maximum power point tracking techniques in photovoltaic applications: A review

A. Pallavee Bhatnagar and B. R. K. Nema

J. Renewable Sustainable Energy 5, 032701 (2013); http://dx.doi.org/10.1063/1.4803524 (22 pages)

Online Publication Date: 13 May 2013

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Maximum Power Point Tracking (MPPT) is a technique employed to extract maximum power available from a photovoltaic (PV) module under varying atmospheric conditions. It traces the PV operating voltage corresponding to the maximum power point (MPP) and operates the panel at MPP. However, if a PV array is partially shaded, the conventional MPPT techniques track local MPP and fail to track global MPP. Also, if modules with different optimal currents are connected in series—parallel local MPPs occur in the P-V curves and conventional MPPT techniques fail to search global maxima. A lot of literature is available on global MPPT techniques to increase overall system efficiency. The power conditioning unit should, therefore, be capable of searching global maximum power point also. This paper aims at presenting a number of conventional and global MPPT techniques; these methods are discussed in detail on the basis of certain performance parameters.
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84.30.Jc Power electronics; power supply circuits
85.60.-q Optoelectronic devices
88.40.H- Solar cells (photovoltaics)
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Transport and interfacial transfer of electrons in dye-sensitized solar cells based on a TiO2 nanoparticle/TiO2 nanowire “double-layer” working electrode

Aixiang Wei, Zhipeng Zuo, Jun Liu, Kangbao Lin, and Yu Zhao

J. Renewable Sustainable Energy 5, 033101 (2013); http://dx.doi.org/10.1063/1.4803525 (10 pages)

Online Publication Date: 3 May 2013

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Dye-sensitized solar cells (DSSCs) with different thickness TiO2 nanoparticle films and a “double-layer” working electrode of TiO2 nanoparticle/TiO2 nanowire are fabricated. The influence of the TiO2 nanoparticle films thickness and of a light-scattering layer of TiO2 nanowire on the photovoltaic performance of DSSCs are investigated. The transport and interfacial transfer of electrons in DSSCs are investigated using intensity modulated photocurrent spectroscopy (IMPS), intensity modulated photovoltage spectroscopy (IMVS), and electrochemical impedance spectroscopy (EIS) to determine the lifetime, diffusion coefficient, and diffusion length of the electrons. The results indicate that the optimum TiO2 nanoparticle films' thickness for DSSCs is about 14 μm. The introduction of the light-scattering layer leads to an obvious enhancement of the power conversion efficiency. This can mainly be attributed to the superior light-scattering ability, fast electron transport, and long electron lifetime, resulting in a larger electron diffusion coefficient and a higher charge collection efficiency, which are confirmed by IMPS, IMVS, and EIS.
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88.40.J- Types of solar cells
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.45.Fk Electrodes
82.80.Fk Electrochemical methods

Model study of combined wind and solar electricity production in Hungary

Imre M. Jánosi

J. Renewable Sustainable Energy 5, 033102 (2013); http://dx.doi.org/10.1063/1.4803528 (9 pages)

Online Publication Date: 3 May 2013

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Since large-scale and cheap energy storage is an unsolved problem, the main difficulty of using wind and solar electricity is caused by their intermittent nature. It is a widespread belief that the combination of the two renewable technologies generally improves the reliability and supply quality of electricity generation. Indeed, there are some locations where wind speeds are definitely larger during the nights because of the increased stability of the atmospheric boundary layer. However, a proper decision making requires to study the supposed benefits at the very location of designed installations. Here, we report on a model study, where the whole area of Hungary is evenly covered by wind generators and solar photovoltaic units of various composition and total rated power. The combined model output is compared to the recorded electricity consumption in Hungary. Our results indicate that the integrated output of combined renewable production can be definitely lower than the output of “pure” (either solar or wind) resource network of the same rated power. The main reasons are the lack of daily cycle of wind strength and the strong annual seasonality of insolation in the Carpathian basin. Benefits of combined production show up at unrealistically high rated power values which is a consequence of limited capacity factors of both renewable sources around Hungary.
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88.05.-b Energy analysis
88.40.-j Solar energy
88.80.-q Energy delivery and storage
88.50.J- Wind farms
88.80.F- Energy storage technologies

A comprehensive view on performance, emission, and combustion characteristics of biodiesel-diesel blends at advanced injection timings

A. Murugesan, D. Subramaniam, A. Avinash, and N. Nedunchezhian

J. Renewable Sustainable Energy 5, 033103 (2013); http://dx.doi.org/10.1063/1.4803745 (10 pages)

Online Publication Date: 3 May 2013

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In this article, an endeavor has been made to assess the operating characteristics of a diesel engine fuelled with methyl esters of pungamia, ethyl esters of pungamia, and ethyl esters of neem, added to diesel by percentage volume ranging from B20 to B80. The test runs on diesel fuel in the first phase of work were carried out under standard injection timing of 23° before top dead center (BTDC), so as to establish baseline for other parameters. The similar test procedures were repeated with an advanced injection timings of 26° BTDC and 28° BTDC fuelled with diesel and biodiesel–diesel blends varying from B20 to B100. Experimental results proved that the 3° advancement of injection timing from the standard injection timing proved promising outcomes for biodiesel operated engine, whereas 5° BTDC crank angle degree produced a higher exhaust gas temperature and higher levels of NOx formation.
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88.05.Np Environmental aspects
89.20.Bb Industrial and technological research and development
89.20.Kk Engineering
88.20.jj Combustion

Optimization of biohydrogen production by Enterobacter species using artificial neural network and response surface methodology

P. Karthic, Shiny Joseph, Naveenji Arun, and S. Kumaravel

J. Renewable Sustainable Energy 5, 033104 (2013); http://dx.doi.org/10.1063/1.4803746 (12 pages)

Online Publication Date: 3 May 2013

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Optimization studies on fermentative hydrogen production were investigated using a facultative bacteria namely, Enterobacter species (MTCC 7104). The present study emphasizes the application of mathematical tools such as response surface methodology (RSM) and artificial neural network (ANN) to predict the maximum yield of hydrogen from the optimized carbon and nitrogen source. The key components such as glucose, initial pH, xylose, tryptone, yeast extract, sucrose, and peptone were screened using the Plackett-Burman design. Furthermore, rotatable central composite design and analysis of variance were adopted to investigate the interactive effect of the significant variables (xylose concentration, initial pH, and peptone concentration). Maximum experimental hydrogen yield of 1.94 mol H2/mol xylose was achieved at the optimal points predicted by the RSM. Modeling ability of ANN and RSM has also been evaluated on predicting the maximum hydrogen yield with the estimated values of root mean square error (RMSE), multiple correlation coefficients (R2), and standard error of prediction (SEP). The estimated values of RMSE, R2, and SEP for ANN model and RSM model confirm that fitness and prediction accuracy of ANN model were higher when compared to RSM model. Energy conversion efficiency and energy recovery analysis were performed for hydrogen production process using xylose as the source material.
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87.85.M- Biotechnology
02.60.Pn Numerical optimization
02.70.Rr General statistical methods

Solar cell parameters estimation from illuminated I-V characteristic using linear slope equations and Newton-Raphson technique

Shubham Raj, Ankit Kumar Sinha, and Ashish K. Panchal

J. Renewable Sustainable Energy 5, 033105 (2013); http://dx.doi.org/10.1063/1.4803748 (8 pages)

Online Publication Date: 3 May 2013

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To extract maximum output power from a solar cell, it is essential to know the solar cell parameters such as the photo-current (Iph), the series resistance (Rse), the shunt resistance (Rsh), the reverse saturation current (I0), and the diode ideality factor (n). This paper presents new and simple methods for estimating the cell parameters. First, Rse and Rsh are estimated from the intercepts of the linear slope equations dV/dI and dI/dV at the open circuit voltage (Voc) and the short circuit current (Isc) regions, respectively. The slopes of these equations also give I0 and n, known as method-1. In method-2, using Rse and Rsh obtained by method-1, I0 and n are estimated using Newton-Raphson technique. The methods presented here are applied to the illuminated I-V characteristics of silicon solar cells, an organic solar cell, and a dye sensitized solar cell previously reported in the literatures. The studies show that method-1 is more suitable for the solar cells with 70% or above fill factor whereas method-2 is suitable for all kinds of solar cells irrespective of fill factor.
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88.40.jr Organic photovoltaics
02.60.-x Numerical approximation and analysis

The simultaneous effect of a fairing tower and increased blade flexibility on a downwind mounted rotor

M. Reiso and M. Muskulus

J. Renewable Sustainable Energy 5, 033106 (2013); http://dx.doi.org/10.1063/1.4803749 (11 pages)

Online Publication Date: 3 May 2013

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This is a parametric study on how blade and tower loads for a prototypical downwind offshore wind turbine are affected as the tower geometry and blade properties are changed. Downwind turbines have the potential to reduce the cost of energy, as blades can be more flexible and lighter, but the tower shadow induces additional structural vibrations. In order to reduce the latter, a fairing around the tower has been introduced. The length of the fairing is varied, adjusting the rotor overhang accordingly. Additionally, the blade weight and stiffness are adjusted. The blade and tower fatigue loads are, thereby, significantly decreased. In the first case, a maximum reduction of 8% and 28% (for the blade root bending and tower bottom moment, respectively) was achieved, compared to a downwind version of the National Renewable Energy Laboratory (NREL) 5 MW reference wind turbine on a monopile tower. Using softer and lighter blades resulted in loads even lower than for the conventional upwind rotor of the NREL turbine, up to 5% and 13% less for the blade and tower fatigue loads, respectively. The increased overhang increased the mean tower bending moments, suggesting that an optimal downwind turbine needs to be designed with a compromise between these fatigue and ultimate loads. The power production stayed approximately the same as that of a conventional wind turbine or was slightly higher.
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88.50.G- Wind turbines

Enhancement of efficiency of a conducting polymer P3HT:CdSe/ZnS quantum dots hybrid solar cell by adding single walled carbon nanotube for transporting photogenerated electrons

Shiv Kumar Dixit, Shikha Madan, Amandeep Kaur, Devinder Madhwal, Inderpreet Singh, P. K. Bhatnagar, P. C. Mathur, and C. S. Bhatia

J. Renewable Sustainable Energy 5, 033107 (2013); http://dx.doi.org/10.1063/1.4807475 (6 pages)

Online Publication Date: 21 May 2013

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Hybrid solar cells consisting of a composite of poly (3-hexylthiophene) (P3HT), single walled carbon nanotube (SWCNT), and cadmium selenide/zinc sulphide (CdSe/ZnS) coreshell quantum dots (QDs) have been fabricated in the present work. The bulk hetrojunction has been formed from the bilayer of P3HT:SWCNT composite and QDs using inter-diffusion process. Due to low percolation limit and high conductivity of SWCNT, the photo-generated electrons are collected at the electrode very fast (within few femto-seconds) enhancing the efficiency of the solar cell. The absorption measurements on the composite film show that the addition of SWCNT in the hybrid structure increases the absorption coefficient in the near infrared region and also makes the spectrum wider as compared to that of P3HT. The photoluminescence (PL) measurements show that the PL of hybrid P3HT, SWCNT, and QDs is quenched about ∼15 times as compared to that of P3HT film. This shows that a significant charge transfer of electrons occurs through SWCNT to the electrode. The morphology of P3HT:SWCNT:CdSe/ZnS was observed using atomic force microscopy. With this approach, we have been able to achieve power conversion efficiency of 5.4% using a standard solar simulator with an irradiance of 100 mW/cm2.
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88.40.H- Solar cells (photovoltaics)
81.05.Qk Reinforced polymers and polymer-based composites
82.45.Fk Electrodes
82.45.Wx Polymers and organic materials in electrochemistry
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Alumina reduction by laser sustained plasma for aluminum-based renewable energy cycling

Makoto Matsui, Naohiro Fukuji, Masakatsu Nakano, Kimiya Komurasaki, Yoshihiro Arakawa, Tetsuya Goto, and Hirofumi Shirakata

J. Renewable Sustainable Energy 5, 039101 (2013); http://dx.doi.org/10.1063/1.4807607 (5 pages)

Online Publication Date: 21 May 2013

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A novel alumina (Al2O3) reduction technique for a renewable energy cycling system based on aluminum is proposed. Al2O3 powder was fed into laser-sustained plasma and thermally dissociated. The produced Al was expanded to supersonic speeds through a nozzle. From the Al and argon line distributions in the flow direction, it was found that Al remained in the dissociated state. A water-cooled copper tube was inserted in the flow to collect Al. X-ray analysis indicated that elemental Al was observed on the surface of the tube. The maximum value of the estimated reduction efficiency was 5%.
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88.40.-j Solar energy
88.50.-k Wind energy
42.62.-b Laser applications
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