Center for Study of Science

Bangalore, India

Center for Study of Science

Bangalore, India
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Lavania C.,Soliton Technologies | Rao S.,International Institute of Information Technology Bangalore | Subrahmanian E.,Center for Study of Science
IEEE Systems Journal | Year: 2012

Solar irradiation tends to vary greatly throughout the day. The difference is very large especially between the early hours of sunshine, and during the peak hours of the day. Yet, it is desirable to supply a nearly constant amount of power to loads or power grids for high reliability. Hence, we propose a technique aimed at reducing the variation in solar power generation. Solar irradiation data is considered as a time-series data and the approach involves conversion of this data to the frequency domain through Fourier analysis. A more balanced supply by a set of plants is devised by interconnecting the plants, which also requires finding the optimum number of plants to connect using the above analysis. The effectiveness of the procedure is demonstrated by applying a suitable supply prediction algorithm over the individual plants and the effective data for the plants, using real data from Nevada, Texas, and California. © 2011 IEEE.


Das A.K.,Center for Study of Science
Solar Energy | Year: 2011

The J-V equation of a solar cell is implicit and requires iterative calculation to determine the fill factor and the maximum power point. Here an explicit model for J-V characteristic is proposed which is applicable to a large variety of solar cell. This model allows an easy estimation of fill factor from four simple measurements of the bias points corresponding to V oc, J sc, and any two voltage values lying between 0 and V oc, where V oc is the open circuit voltage and J sc is the short circuit current density. © 2011 Elsevier Ltd.


Das A.K.,Center for Study of Science
2012 International Conference on Devices, Circuits and Systems, ICDCS 2012 | Year: 2012

A simple power law model (PLM) of J-V equation to characterize an illuminated solar cell can be represented as j = 1 - (1 - γ)ν - γν m where the normalized voltage, v and normalized current density j can be represented as v=V/V oc and j=J/J sc and γ and m are parameters related to the physical parameters of the solar cell. Using this model, the empirical equation for the peak power voltage works only for good quality solar cells. Here in this paper, a semi-empirical approach is considered to determine the peak power voltage for any illuminated solar cell. © 2012 IEEE.


Das A.K.,Center for Study of Science
Solar Energy | Year: 2012

Recently a simple explicit model was introduced to represent the J-V characteristics of an illuminated solar cell with parasitic resistances and bias dependent photocurrent as v m+j n=1. Here the normalized voltage, v and normalized current density j can be represented as v=V/V oc and j=J/J sc respectively, where V oc is the open circuit voltage and J sc is the short circuit current density. This model is useful for design, characterization and simple fill factor calculation and its applicability was demonstrated with the measured data of a wide variety of solar cells. This explicit form is intuitive and hence the model lacks the analytical support. In this paper an analytical derivation of this closed form explicit model is presented, which is derived from the physics based implicit J-V equation. The derivation expands the scope of model applicability and provides a new insight of analytical modeling of the solar cell. © 2011 Elsevier Ltd.


Srilakshmi G.,Center for Study of Science | Venkatesh V.,Center for Study of Science | Thirumalai N.C.,Center for Study of Science | Suresh N.S.,Center for Study of Science
Renewable and Sustainable Energy Reviews | Year: 2015

Solar Tower technology has gained considerable momentum over the past decade. Unlike the parabolic trough, Solar Tower has a lot of variants in terms of type of receivers, working fluids, power cycles, size of heliostats, etc. Most of the literature available on this technology does not address in great depths, details of various parameters associated with tower technology. A detailed examination of plant parameters is required in order to perform a potential assessment, design basis or feasibility analysis. This paper aims to assess the principal parameters of existing plants, namely, solar to electric conversion efficiency, mirror and land area per MWe of equivalent capacity, packing density, field layout configuration, receiver size, tower height and gross costs of plants, wherever data is available. Based on this global review of existing plants, it is observed that, the annual solar to electric conversion efficiencies has an average value of 16% and the packing density has an average value of about 20%. Since most of the existing plants have been constructed for demonstration purposes, the true potential of this technology has not yet been realised. Using this assessment as a basis, the technical, financial and policy drivers and barriers for adopting tower technology in India are discussed. It is seen that based on indigenisation prospects, tower technology with external cylindrical or cavity receivers with storage could be adopted. The role and significance of this technology is brought out in the context of the Jawaharlal Nehru National Solar Mission (JNNSM) in order to achieve grid-connected solar power. It is estimated that around 1800 MW of grid connected Solar Tower plants could come up under this mission by 2022. © 2015 Elsevier Ltd. All rights reserved.


Das A.K.,Center for Study of Science
Energy Systems | Year: 2014

The power curve of a wind turbine grows exponentially as a function of wind-velocity if the measured wind-velocity varies between the cut-in velocity and the rated velocity. In this study, we propose an empirical, two-parameter explicit model of the power curve for a wind turbine. The model generalizes different turbine power curves and provides an easy estimate to compare various turbine characteristics. The energy analysis of the wind turbine is done using the (proposed) functional relationship and demonstrates how the capacity factor of a wind turbine varies with these empirical factors. © 2014 Springer-Verlag Berlin Heidelberg.


Recently a simple explicit model was introduced to represent the J - V characteristics of an illuminated solar cell with parasitic resistances and bias dependent photocurrent as j=. (1. vm)/(1. +. αv), here the normalized voltage, v and normalized current density j can be represented as v=V/Voc and j=J/Jsc respectively, where Voc is the open circuit voltage and Jsc is the short circuit current density. The model is an equivalent rational function form and useful for design, characterization and calculation of maximum power point voltage. The model is intuitive and lacks the analytical support. In this paper an analytical derivation of the model is presented using the physics based implicit J - V equation. © 2014 Elsevier Ltd.


Sarkar S.,Indian Institute of Technology Bombay | Bhowmik A.,Center for Study of Science | Bharadwaj M.D.,Center for Study of Science | Mitra S.,Indian Institute of Technology Bombay
Journal of the Electrochemical Society | Year: 2014

Structural and kinetic behavior of lithium-vanadium-oxide (Li xVO8) cathode is studied as lithium-ion battery electrode. The morphology of LixV3O8 is found to be nanoplates with nanorods as minor constituents. Theoretical prediction shows such a nanoplate morphology will have almost thirty four times faster lithium diffusion than spherical particle of same volume. In the present study, experimental and theoretical observation of Fourier transform infrared spectroscopy (FT-IR) is compared to investigate the vibrational mode of V-O bond. LixV3O8 cathode, delivers a high discharge capacity of 270 mAh g-1 at 200 mA g-1 and as high as 200 mAh g-1, 135 mAh g-1, and 100 mAh g -1 at 1000 mA g-1, 2000 mA g-1, and 3000 mA g-1 current rates respectively. A detailed electrode kinetic study using galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) are performed to establish the relationship between high rate capability with kinetic parameters. The diffusion co-efficient (DLithium) value of LixV3O8 is estimated to be ̃ 10-15-10 -13 cm2 s-1 and 10-13-10 -11 cm2 s-1 in the single phase region (0 ≤ x ≤ 1.7) during discharge and charge processes respectively. Further, ex situ XRD is performed on LixV3O8 cathode material to study the phase transformation during charge/discharge process. © 2013 The Electrochemical Society.


The J-. V equation of an illuminated solar cell is implicit and recently it is shown that this equation can be expressed explicitly using rational function considering padé approximants. Here an explicit model for J-. V characteristic is proposed using equivalent rational function form having two shape parameters. This model allows a simple closed form estimation of maximum power point voltage. The proposed explicit model is validated using wide variety of solar cells. © 2013 Elsevier Ltd.


Das A.K.,Center for Study of Science
Renewable Energy | Year: 2013

The J-V characteristics of an illuminated solar cell can be represented as a simple explicit form of vη+jξ=1, here the normalized voltage, v and normalized current density j can be represented as v = V/Voc and j = J/Jsc respectively, where Voc is the open circuit voltage and Jsc is the short circuit current density. Here η and ξ are the shape parameters of the J-V curve which can be obtained from the experimental data. In this paper it is shown that the model parameters, η and ξ can be used for the analytical representation of the single exponential model parameters of an illuminated solar cell, namely ideality factor n, parasitic series resistance Rs, parasitic shunt resistance Rsh, dark-current density J0, and photo-generated current density Jph. The simple measurement of voltage (V) and corresponding current density (J) of an illuminated solar cell experimentally determines the parameters η and ξ, with which the physical parameters of the illuminated solar cells can be determined. The proposed analytical expression is used to determine the physical parameters for wide variety of solar cells and gives satisfactory results. © 2012 Elsevier Ltd.

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