Solar rechargeable battery—principle and materials

A brief survey of the historical development of a photoelectrochemical solar cell is given. The principle and future of solar chargeable battery is compared with a wet and a dry type photovoltaic cell. A solar chargeable battery, with or without a membrane and with an aqueous solution or with solid-state electrolytes is discussed. A new unique type of configuration “Sharon-Schottky” junction solar cell is described which can be used either as a charger for any secondary batteries or could be used for photoelectrolysis of water. All these configurations and their relative merits are discussed. A review on the various semiconductors and types of solar chargeable batteries is made. Finally, a conclusion is drawn for future direction of research for developing an economically viable photoelectrochemical (PEC) solar cell based on either the principle of a solar charger (to charge a Ni---Cd battery or lead—acid battery) and/or solar chargeable battery with or without without a membrane. Some new innovative ideas for the preparation of materials is discussed. The entire discussion is geared towards answering a relevant question: what has gone wrong to result in the stagnation and failure in commercialization of a PEC based solar cell?

Polarization studies in electromagnetic scattering by small Solar-system particles

In remote-sensing studies, particles that are comparable to the wavelength exhibit characteristic features in electromagnetic scattering, especially in the degree of linear polarization. These features vary with the physical properties of the particles, such as shape, size, refractive index, and orientation. In the thesis, the direct problem of computing the unknown scattered quantities using the known properties of the particles and the incident radiation is solved at both optical and radar spectral regions in a unique way. The internal electromagnetic fields of wavelength-scale particles are analyzed by using both novel and established methods to show how the internal fields are related to the scattered fields in the far zone. This is achieved by using the tools and methods that were developed specifically to reveal the internal field structure of particles and to study the mechanisms that relate the structure to the scattering characteristics of those particles. It is shown that, for spherical particles, the internal field is a combination of a forward propagating wave with the apparent wavelength determined by the refractive index of the particle, and a standing wave pattern with the apparent wavelength the same as for the incident wave. Due to the surface curvature and dielectric nature of the particle, the incident wave front undergoes a phase shift, and the resulting internal wave is focused mostly at the forward part of the particle similar to an optical lens. This focusing is also seen for irregular particles. It is concluded that, for both spherical and nonspherical particles, the interference at the far field between the partial waves that originate from these concentrated areas in the particle interior, is responsible for the specific polarization features that are common for wavelength-scale particles, such as negative values and local extrema in the degree of linear polarization, asymmetry of the phase function, and enhancement of intensity near the backscattering direction. The papers presented in this thesis solve the direct problem for particles with both simple and irregular shapes to demonstrate that these interference mechanisms are common for all dielectric wavelength-scale particles. Furthermore, it is shown that these mechanisms can be applied to both regolith particles in the optical wavelengths and hydrometeors at microwave frequencies. An advantage from this kind of study is that it does not matter whether the observation is active (e.g., polarimetric radar) or passive (e.g., optical telescope). In both cases, the internal field is computed for two mutually perpendicular incident polarizations, so that the polarization characteristics can then be analyzed according to the relation between these fields and the scattered far field.

A Comparative Study of the Effect of Metallic Au and ReO3 Nanoparticles on the Performance of Silicon Solar Cells

The influence of gold (similar to 35 nm diameter) as well as ReO3 (similar to 17 nm diameter) nanoparticles placed atop silicon photovoltaic devices on absorption and photocurrent generation has been investigated. The nanoparticles improve the power transmission into the semiconductor and consequently, the photocurrent response at wavelengths corresponding to plasmon absorption. An increase in short circuit current up to 4.5% under simulated solar irradiation was observed with the ReO3 nanoparticles, while the gold nanoparticles showed enhancements up to 6.5%. The increase in photocurrent is observed at wavelengths corresponding to the maxima in the surface plasmon resonance absorption spectra. (C) 2010 The Japan Society of Applied Physics

Hybrid Solar Cooking

In the existing traditional solar cookers, the cooking is performed near the collector which may be at an inconvenient location for cooking purposes. This paper proposes a hybrid solar cooking system where the solar energy is brought to the kitchen. The energy source is a combination of the solar thermal energy and the Liquefied Petroleum Gas (LPG) that is very common in kitchens. The solar thermal energy is transferred to the kitchen by means of a circulating fluid like oil. The transfer of solar heat is a two fold process wherein the energy from the collector is transferred first to an intermediate energy storage tank and then the energy is subsequently transferred from the tank to the cooking load. There are three parameters that are controlled in order to maximize the energy transfer from the collector to the load viz. the fluid flow rate from collector to tank, fluid flow rate from tank to load and the diameter of the pipes. The entire system is modeled using the bond graph approach. This paper discusses the implementation of such a system.

Performance of a small solar pond in the tropics

The performance of the 240 m2 solar pond in Bangalore is discussed. The problems of erosion of gradient zone and formation of internal convective zones is highlighted. The technique of passive salt addition is shown to be a viable alternative for salt recycling. Different techniques of heat extraction are discussed and the use of an immersed copper heat exchanger is shown to be most convenient. A two-zone model for prediction of the seasonal structure of the solar pond performance is proposed. The model is shown to simulate the seasonal structure of the observed variation of the temperature in the storage zone.

Locating the seat of the solar dynamo

The hypothesis that the solar dynamo operates in a thin layer at the bottom of the convection zone is addressed. Recent work on the question whether the magnetic flux can be made to emerge at sunspot latitudes is reviewed. It is concluded that this hypothesis can fit the observational facts only if there is turbulence with a length scale of a few hundred kilometers in and around the dynamo region.

Local variability and base sequence effects in DNA crystal structures.

The importance and usefulness of local doublet parameters in understanding sequence dependent effects has been described for A- and B-DNA oligonucleotide crystal structures. Each of the two sets of local parameters described by us in the NUPARM algorithm, namely the local doublet parameters, calculated with reference to the mean z-axis, and the local helical parameters, calculated with reference to the local helix axis, is sufficient to describe the oligonucleotide structures, with the local helical parameters giving a slightly magnified picture of the variations in the structures. The values of local doublet parameters calculated by NUPARM algorithm are similar to those calculated by NEWHELIX90 program, only if the oligonucleotide fragment is not too distorted. The mean values obtained using all the available data for B-DNA crystals are not significantly different from those obtained when a limited data set is used, consisting only of structures with a data resolution of better than 2.4 A and without any bound drug molecule. Thus the variation observed in the oligonucleotide crystals appears to be independent of the quality of their crystallinity. No strong correlation is seen between any pair of local doublet parameters but the local helical parameters are interrelated by geometric relationships. An interesting feature that emerges from this analysis is that the local rise along the z-axis is highly correlated with the difference in the buckle values of the two basepairs in the doublet, as suggested earlier for the dodecamer structures (Bansal and Bhattacharyya, in Structure & Methods: DNA & RNA, Vol. 3 (Eds., R.H. Sarma and M.H. Sarma), pp. 139-153 (1990)). In fact the local rise values become almost constant for both A- and B-forms, if a correction is applied for the buckling of the basepairs. In B-DNA the AA, AT, TA and GA basepair sequences generally have a smaller local rise (3.25 A) compared to the other sequences (3.4 A) and this seems to be an intrinsic feature of basepair stacking interaction and not related to any other local doublet parameter. The roll angles in B-DNA oligonucleotides have small values (less than +/- 8 degrees), while mean local twist varies from 24 degrees to 45 degrees. The CA/TG doublet sequences show two types of preferred geometries, one with positive roll, small positive slide and reduced twist and another with negative roll, large positive slide and increased twist.(ABSTRACT TRUNCATED AT 400 WORDS)

Conformational Variability in Modified Nucleosides. Crystal and Molecular Structure of 2',3'-O-Isopropylidene Inosine

The crystal structure of 2',3'-O-isopropylidene inosine shows a number of interesting features. The four independent molecules in the asymmetric unit exhibit significant conformational variations. Ribose puckers fall in the O(4')-exo region, unfavourable in unsubstituted nucleosides. Hypoxanthine bases show base-pairing (I.I) in a manner analogous to the guanine self pairs (G.G) in 2',3'-O-isopropylidene guanosine but with a C(2)-H…O(6) hydrogen bond instead of N(2)-H…O(6).

Aperiodic Variability in the Cane-Zebiak Model: A Diagnostic Study

The finite predictability of the coupled ocean-atmosphere system is determined by its aperiodic variability. To gain insight regarding the predictability of such a system, a series of diagnostic studies has been carried out to investigate the role of convergence feedback in producing the aperiodic behavior of the standard version of the Cane-Zebiak model. In this model, an increase in sea surface temperature (SST) increases atmospheric heating by enhancing local evaporation (SST anomaly feedback) and low-level convergence (convergence feedback). The convergence feedback is a nonlinear function of the background mean convergence field. For the set of standard parameters used in the model, it is shown that the convergence feedback contributes importantly to the aperiodic behaviour of the model. As the strength of the convergence feedback is increased from zero to its standard value, the model variability goes from a periodic regime to an aperiodic regime through a broadening of the frequency spectrum around the basic periodicity of about 4 years. Examination of the forcing associated with the convergence feedback reveals that it is intermittent, with relatively large amplitude only during 2 or 3 months in the early part of the calendar year. This seasonality in the efficiency of the convergence feedback is related to the strong seasonality of the mean convergence over the eastern Pacific. It is shown that if the mean convergence field is fixed at its March value, aperiodic behavior is produced even in the absence of annual cycles in the other mean fields. On the, other hand, if the mean convergence field is fixed at its September value, the coupled model evolution remains close to periodic, even in the presence of the annual cycle in the other fields. The role of convergence feedback on the aperiodic variability of the model for other parameter regimes is also examined. It is shown that a range exists in the strength of the SST anomaly feedback for which the model variability is aperiodic even without the convergence feedback. It appears that in the absence of convergence feedback, enhancement of the strength of the air-sea coupling in the model through other physical processes also results in aperiodicity in the model.

Mechanisms of variability and predictability of the tropical coupled ocean-atmosphere system

A conceptual model is proposed to explain the observed aperiodicity in the short term climate fluctuations of the tropical coupled ocean-atmosphere system. This is based on the evidence presented here that the tropical coupled ocean-atmosphere system sustains a low frequency inter-annual mode and a host of higher frequency intra-seasonal unstable modes. At long wavelengths, the low frequency mode is dominant while at short wavelengths, the high frequency modes are dominant resulting in the co-existence of a long wave low frequency mode with some short wave intra-seasonal modes in the tropical coupled system. It is argued that due to its long wavelength, the low frequency mode would behave like a linear oscillator while the higher frequency short wave modes would be nonlinear. The conceptual model envisages that an interaction between the low frequency linear oscillator and the high frequency nonlinear oscillations results in the observed aperiodicity of the tropical coupled system. This is illustrated by representing the higher frequency intra-seasonal oscillations by a nonlinear low order model which is then coupled to a linear oscillator with a periodicity of four years. The physical mechanism resulting in the aperiodicity in the low frequency oscillations and implications of these results on the predictability of the coupled system are discussed.

Solar pond technology

Solar pond technology has made substantial progress in the last fifteen years. This paper reviews the basic principles of solar ponds and the problems encountered in their operation and maintenance. The factors which influence the technical and economic viability of solar ponds for thermal applications and power generation have been discussed.

The Waldmeier effect and the flux transport solar dynamo

We confirm that the evidence for the Waldmeier effect WE1 (the anticorrelation between rise times of sunspot cycles and their strengths) and the related effect WE2 (the correlation between rise rates of cycles and their strengths) is found in different kinds of sunspot data. We explore whether these effects can be explained theoretically on the basis of the flux transport dynamo models of sunspot cycles. Two sources of irregularities of sunspot cycles are included in our model: fluctuations in the poloidal field generation process and fluctuations in the meridional circulation. We find WE2 to be a robust result which is produced in different kinds of theoretical models for different sources of irregularities. The Waldmeier effect WE1, on the other hand, arises from fluctuations in the meridional circulation and is found only in the theoretical models with reasonably high turbulent diffusivity which ensures that the diffusion time is not more than a few years.

Proposed visible emission line space solar coronagraph

The outer atmosphere of the sun called the corona has been observed during total solar eclipse for short periods (typically <6 min), from as early as the eighteenth century. In the recent past, space-based instruments have permitted us to study the corona uninterruptedly. In spite of these developments, the dynamic corona and its high temperature (1-2 million K) are yet to be Ally understood. It is conjectured that their dynamic nature and associated energetic events are possible reasons behind the high temperature. In order to study these in detail, a visible emission line space solar coronagraph is being proposed as a payload under the small-satellite programme of the Indian Space Research Organisation. The satellite is named as Aditya-1 and the scientific objectives of this payload are to study: (i) the existence of intensity oscillations for the study of wave-driven coronal heating; (ii) the dynamics and formation of coronal loops and temperature structure of the coronal features; (iii) the origin, cause and acceleration of coronal mass ejections (CMEs) and other solar active features, and (iv) coronal magnetic field topology and three-dimensional structures of CMEs using polarization information. The uniqueness of this payload compared to previously flown space instruments is as follows: (a) observations in the visible wavelength closer to the disk (down to 1.05 solar radii); (b) high time cadence capability (better than two-images per second), and (c) simultaneous observations of at least two spectral windows all the time and three spectral windows for short durations.

Nanoscale ZnO/CdS heterostructures with engineered interfaces for high photocatalytic activity under solar radiation

Semiconductor based nanoscale heterostructures are promising candidates for photocatalytic and photovoltaic applications with the sensitization of a wide bandgap semiconductor with a narrow bandgap material being the most viable strategy to maximize the utilization of the solar spectrum. Here, we present a simple wet chemical route to obtain nanoscale heterostructures of ZnO/CdS without using any molecular linker. Our method involves the nucleation of a Cd-precursor on ZnO nanorods with a subsequent sulfidation step leading to the formation of the ZnO/CdS nanoscale heterostructures. Excellent control over the loading of CdS and the microstructure is realized by merely changing the initial concentration of the sulfiding agent. We show that the heterostructures with the lowest CdS loading exhibit an exceptionally high activity for the degradation of methylene blue (MB) under solar irradiation conditions; microstructural and surface analysis reveals that the higher activity in this case is related to the dispersion of the CdS nanoparticles on the ZnO nanorod surface and to the higher concentration of surface hydroxyl species. Detailed analysis of the mechanism of formation of the nanoscale heterostructures reveals that it is possible to obtain deterministic control over the nature of the interfaces. Our synthesis method is general and applicable for other heterostructures where the interfaces need to be engineered for optimal properties. In particular, the absence of any molecular linker at the interface makes our method appealing for photovoltaic applications where faster rates of electron transfer at the heterojunctions are highly desirable.