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Solar panels can achieve the highest yield when they are oriented in the right way as the influence of the tilt angles can lead to a high impact on the performance. This paper demonstrates the effect of the tilt angle on the final yield and maximum utilization of solar energy. The annual optimal tilt angle of the solar panels for Pune was found out using the Liu and Jordan model. The optimal tilts yielding an increase of 7% was found out to be 0° on the months starting from April and lasting till September and 40° starting from October and holding at 40° till March. By changing the tilt angle every month, there was an increase in the yield by more than 8%. For better yield and maximum utilization of solar energy, optimizing the tilt angles of solar panels monthly or even twice a year is effective based on the study. Most of the panels are fixed at an angle equal to the latitude of the place and oriented towards the Southern sky in the northern hemisphere. Measurements of the monthly average global solar radiation, monthly average temperatures, and monthly average relative humidity were compared. Further ahead regression correlation for a linear model was carried and the regression coefficients a and b were found out to be 0.2804 and 0.3618 respectively.

The incident fraction of solar radiations on the photovoltaic (PV) panel converted into heat and electrical energy. The generated heat, reducing the performance of the photovoltaic system. The efficiency of the photovoltaic panel reduces approximately by 0.5% to 0.6% for every one-degree increase in temperature depending upon the type of solar cell material. Therefore, temperature regulations become a challenging task for improving the efficiency of the photovoltaic panel. The objective of the study to regulate the temperature photovoltaic system by using a passive cooling technique. This article presents an experimental investigation of three different PV systems under the same climatic conditions to ameliorate the performance of the system. The three panels of 40 W each are used; first conventional panel without any modification, the second photovoltaic panel with fins and PCM, a third water-based photovoltaic system with PCM. In a photovoltaic panel with fins system triangular shaped aluminum fins are used to improve the cooling system, water carrier Photovoltaic thermal (PVT) –PCM system copper pipe is used to flow the water. For both second and third system PCM, white petroleum jelly is used as phase change material. The experiment was performed by keeping all three panels at the same environmental conditions at Lonavala in Maharashtra. It has been observed from the analysis that the reduction in the temperature of the PVT - PCM panel 8.10% compared to the conventional panel. The electrical power of the water-based PVT-PCM system is 4.06% higher than that of a conventional PV panel. The enhancement in the electrical efficiency of the PVT-PCM system 4.24% more than conventional PV panel. It has been concluded that the water-based Photovoltaic thermal system could become the best configuration to give an electrical and thermal performance.

We report synthesis and characterization of hybrid photoanode made up of Titanium Dioxide (TiO2) and Zinc Oxide (ZnO) nanoparticles prepared by a co-precipitation process. Though TiO2 is the most preferred anode for Dye Sensitized Solar Cell (DSSC), the charge recombination between electrode and electrolyte poses a major challenge. ZnO photoelectrode is a potential alternative due to higher carrier mobility but has a slower electron injection than TiO2. To maximize the benefits of both, a co-precipitation synthesis of TiO2/ZnO is proposed in this work as a promising alternative. The co-precipitation process produces metal oxides TiO2 and ZnO and eventually yields the Anatase TiO2 and Wurtzite ZnO. The experimental investigations of the new co-precipitation process show improved control of particle size, shape, and uniform distribution of ZnO and yet preserve the economy and simplicity of synthesis. The study shows an average crystallite size of 10 nm to 22 nm for TiO2 and 17 nm to 35 nm for ZnO. Wurtzite phase varies from 4.5% to 10.8% in a co-precipitated photoanode. The deconvolution of the typical Photoluminescence (PL) curve shows two distinct bands for ZnO and TiO2 cantered around 390 nm and 460 nm. The study shows that the co-precipitated TiO2/ZnO has a bandgap of less than 3.2 eV, this paves the way for reduced recombination and improved device performance. Further, we fabricated a prototype of a DSSC using photoanode of TiO2/ZnO and a sensitizer of natural plant pigment extracted from Phyllanthus reticulatas and successfully tested the prototype DSSC.

In this article, we present highly sensitive and reliable nitrogen gas flow sensors based on surface modified n-type (n-Si) and p-type (p-Si) silicon wafers. The surfaces of n-Si and p-Si wafers were coated with octyltrichlorosilane (OTS) molecules. The surface modified n-Si and p-Si wafers were used as sensing elements. The sensing elements were kept on the 45° angle inclined to the experimental mount and nitrogen gas was flown over the inclined surface at subsonic velocities. The flow induced voltage generation is caused by the interplay between the mechanisms of Bernoulli's principle and Seebeck effect. The experimental results show that the half coated and full coated n-Si and p-Si wafers generate more voltage than that of the uncoated at a given velocity. In the case of n-Si wafers, the half coated surface generated voltage was ≈4.80 times than that of the uncoated surface. In the case of p-Si wafers, the half coated surface generated voltage was ≈3.83 times than that of the full coated. The surface analysis of the half and full coated surfaces show that the OTS SAM molecules on n-Si surfaces were homogeneous and well ordered, however on p-Si surfaces, the OTS SAM molecules were heterogeneous and disordered. The enhanced voltage generations and high sensitivities are caused by an effective change in the gradient of Fermi energy (EF) due to OTS SAM coating. The experimental observations and theoretical analysis of enhanced voltage generation show that the OTS surface modification causes synergism of different mechanisms, contributing to the cumulative increase of flow induced voltage. The effect of aging process on the reliability of the half coated OTS/n-Si and OTS/p-Si sensors were tested for 24 h, 30 days and 90 days, the experimental results confirm that the flow induced voltages are consistent and reproducible and both the OTS/n-Si and OTS/p-Si sensors are very reliable. The investigation of the effects of the coverage of the OTS SAM and the angle of inclination on the flow induced voltage shows that the 50% coverage of the OTS/n-Si, OTS/p-Si and the 45° angle of inclination produced a maximum flow induced voltage at any given velocity.

A method for the large scale fabrication of nano/micro array patterned structure for solar Photovoltaics (PV) is demonstrated by the use of laser interference lithography (LIL) technique. Since micro/nano array patterned structures for photonic arrangement are of increasing importance in higher efficiency solar PV cell concepts, structuring technique and miniaturization in size play a vital role in their realization/fabrication. In this paper, we have designed and modelled multi-beam interference lithography technique (MBIL) for the fabrication of solar PV cells. The generated periodic 1D, 2D and 3D micro/nano array structures are done using MATLAB. The obtained results show that the complexity of the pattern structures varies with the variation in position of beams and angle of incidence. The interference parameters such as wavelength, slit separation, distance between slit and screen influence in generation of periodic array pattern structures. The maximum intensity occurs at an angle of incidence 45 degree. The obtained pattern structures have the periodicity of 0.19 µm for 1064 nm, 0.18 µm for 1024 nm, 0.14 µm for 780 nm, 0.12 µm for 650 nm and 0.07 µm for 565 nm. Depth of the focus is found to be 0.029 µm for 1064 nm, 0.028 µm for 1024 nm, 0.024 µm for 780 nm, 0.020 µm for 650 nm and 0.015 µm for 565 nm. MBIL can be applied in fabrication of 3D photonic crystals, magnetic storage, solar cells, waveguides, calibration grids, Organic Light Emitting Diodes (OLEDs) and functional surfaces of sensors.

In this work, we studied photocatalytic and thermolytic “attenuation-degradation” mechanisms of 1H, 1H, 2H, 2H - perfluorooctyltrichlorosilane (FOTS-SAM) coated titanium dioxide nanoparticles (TiO2-NPs). During thermolytic analysis, FOTS-SAM on TiO2-NPs was very stable up to 300 °C and further increase of temperature to 450 °C caused conformational disorders and the disorders increased up to 550 °C and complete degradation and desorption of FOTS-SAM from TiO2-NPs occurred above 550 °C. During photocatalytic analysis, FOTS-SAM on TiO2-NPs was stable up to 3 hrs and further UV exposure caused increase of conformational disorders up to 12 hrs and after 15 hrs complete degradation and desorption of FOTS-SAM from the TiO2-NPs. It is observed that FOTS-SAM surface modification (i) passivates TiO2-NPs (ii) increases band gap from 3.2 eV to 5.7 eV and (iii) attenuates UV induced electron-hole pair (e−, h+) generation. Further observed that the FOTS-SAM-TiO2-NPs were superhydrophobic but under long UV exposure and high temperature they became hydrophilic. PLLA-nanocomposites filled with FOTS-SAM-TiO2-NPs show excellent mechanical properties and stability compared to PLLA-nanocomposites filled with uncoated TiO2-NPs. Experimental investigations confirm that FOTS-SAM on TiO2-NPs acts as photocatalytic and thermolytic attenuation layer, super hydrophobic layer and enhances stability and mechanical properties of nanocomposites.

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International audience

We report a study of techno economic evaluation of solar thermal power generation in India. Generation of quality and useful thermal energy by Concentrating Solar Power (CSP) is an advancement that uses direct daylight to solar thermal concentrating systems for power generation. A solar parabolic trough plant located in Jodhpur, India is selected for the sensitivity analysis of solar power plants and solar parabolic troughs along with the total solar radiation data. In this work we have studied the cost of connectivity to the grid, Internal Rate of Return (IRR) calculations and Levelized Cost of Energy (LCOE). We observed that a small change in the percentage of power blocks causes significant changes in the capital cost, LCOE, IRR, loan rate and which eventually affecting the final tariff of the plant. In the present study, we have identified important parameters, which are required for the commissioning of the CSP plants in India. The primary reason for this study is to analyze the best accessible technology from the available technologies. The technologies should also encounter diverse market necessities such as centralized versus decentralized applications or global versus regional/local scope.

In this paper, we study the Einstein relation for the diffusivity to mobility ratio (DMR) in n-channel inversion layers of non-linear optical materials on the basis of a newly formulated electron dispersion relation by considering their special properties within the frame work of k.p formalism. The results for the n-channel inversion layers of III-V, ternary and quaternary materials form a special case of our generalized analysis. The DMR for n-channel inversion layers of II-VI, IV-VI and stressed materials has been investigated by formulating the respective 2D electron dispersion laws. It has been found, taking n-channel inversion layers of CdGeAs2, Cd(3)AS(2), InAs, InSb, Hg1-xCdxTe, In1-xGaxAsyP1-y lattice matched to InP, CdS, PbTe, PbSnTe, Pb1-xSnxSe and stressed InSb as examples, that the DMR increases with the increasing surface electric field with different numerical values and the nature of the variations are totally band structure dependent. The well-known expression of the DMR for wide gap materials has been obtained as a special case under certain limiting conditions and this compatibility is an indirect test for our generalized formalism. Besides, an experimental method of determining the 2D DMR for n-channel inversion layers having arbitrary dispersion laws has been suggested.

Nanoscale energy dissipation and failure mechanics of silica nano- and micro-particle-filled polymer composite have been evaluated using advanced electron microscopy, scanning probe microscopy and nanoindentation techniques. Objective of this study is to understand the role of nano-microstructure and strength of particle–matrix interface and effects of geometrical gradient (spatial variation of surface height) and mechanical gradient (spatial variation of effective modulus) on energy dissipation process and subsequent failure mechanisms. In order to understand the role of geometrical gradient and mechanical gradient during the energy dissipation process, we carried out amplitude modulation simulation of soft–hard–soft surfaces with zero initial height and with 10 nm initial height of the hard material. Nanoindentation results show hardness and reduced modulus of the nanocomposite are homogeneous; however, the hardness and reduced modulus of the microcomposite were found to be heterogeneous. In the microcomposite, the sharp edges of particles increase friction, and heterogeneous mechanical properties result in high-energy dissipation. Large particles with weak interfacial bonding were easily removed, it resulting in defects on the sliding surface that acted as failure “hot-spots”. These characteristics result in relatively high friction and wear of the microcomposite. The nanocomposite showed better tribo-mechanical performance compared with that of the micro-particle-filled composite.

Lateral force microscopy is used to measure the frictional forces generated in sliding a silicon nitride tip on perflurooctyl trichlorosilane (FOTS) and octadecyltrichlorosilane (ODTS) monolayers self-assembled (SAM) on silicon wafer. The work is motivated by a need to rationalize the high friction of FOTS in comparison to that found for ODTS, inspite of the former having a low surface energy compared to that of the latter. Having first established that the tribology here is a thermally activated process, we use the Eyring equation to estimate the energetic barrier height to sliding motion, system activation energy, shear coordination and pressure activation volumes. For a molecular species when the velocity and temperature are unchanged in a sliding experiment and the activation energy remains unchanged the change in shear coordination with increasing normal load controls the friction coefficient. In comparing the performance of the two test molecules the friction coefficient of the FOTS is found to be three times greater than that of the ODTS; the corresponding difference in barrier height is about 10%. Our results indicate that when the two molecules are well ordered, the shear coordination modulates the frictional differential but it is the difference in their system activation energy, principally determined by electrostatic repulsion between the neighbouring molecules which is a dominant influence on their friction differential.

The tribology of two potential additive molecules for aluminium has been studied in the self assembled monolayer state at low loads $(10^{-9}-10^{-2} N)$ and in dispersion state in n-hexadecane at high load (60 N). The two additive molecules are 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (FOTS), which has a rigid rod-like helical structure and octadecyltrichlorosilane (OTS), which has a zigzag backbone configuration. The adhesion, friction and wear performance have been investigated. Molecular conformational order and stiffness were found to play major roles in frictional dissipation and wear resistance, recorded in a nanotribometer and a pin-on-disc machine, while for very low load measurements (LFM), adhesion was found to have a significant role on friction along with molecular entropy.

We report the design of a variation of a double cantilever flexure system used for the measurement of displacement and force in surface force apparatus (SFA). The new force sensor is called dual double cantilever. The simple cantilever flexure suffers rotation, sideways deflection, and thermal expansion at the free end when loaded normally and asymmetrically. In the double cantilever these errors are minimized to a second order. In the dual double cantilever flexure the stiffness is enhanced 16 times as that of a single cantilever flexure but the rotation, sideways deflection, and thermal expansion at the free end are brought to many orders below the instrument resolutions. The new design enables the measurement of deflection by optical and capacitive sensing methods. The stiffness and the strain of the aluminum alloy [AUG1(2024)] flexure were estimated [dimensions, length (l=50.5 mm), breadth (b=10.5 mm), and thickness (t=1.2 mm)] by finite element method and were also validated experimentally. The finite element method was also used to create a map for the selection of a flexure geometry relevant to the properties of material under investigation by a SFA or a nanoindenter.

Interference Lithography is a developing technique for producing micro/nano array pattern structures over large areas. This paper focus on generation of nano/micro feature size patterns using four-beam interference lithography technique. The generated periodic array pattern structures are developed using MATLAB. The interference parameters in FBIL include wavelength (λ), slit separation (d), angle of incidence (Θ), distance between slit and screen (L) and depth of penetration (DOP). We have simulated and modelled the four beam interference lithography technique by varying interference parameters to produce various feature size patterns over the surface of the substrate. The obtained pattern structures have the periodicity of 0.75 μm for 1064 nm, 0.39 μm for 565 nm. Depth of the focus is found to be 0.235 μm for 1064 nm and 0.125μm for 565 nm. Highest value of depth of penetration is observed to be 0.552 mm and 0.586 mm for 1064 nm and 565 nm respectively. The study of FBIL shows depth of penetration increases with decrease in slit separation. More complex patterns can also be produced on varying the position of beams, angle of incidence and number of beams. FBIL can be applied in fabrication of 3D photonic crystals, magnetic storage, solar cells, waveguides, calibration grids, OLEDs and functional surfaces of sensors.

Report here a gas flow driven voltage production over a modified surface of doped p-type and n-type Silicon (Si) wafer at a modest velocities of subsonic regime where Mach number

We report the effects of surface modifications on (i) Seebeck coefficients and (ii) flow induced voltage generations of the n-type (n-Si) and p-type (p-Si) silicon wafers. The surfaces of n-Si and p-Si wafers were coated with 1H,1H,2H,2H- perfluorooctyltrichlorosilane (FOTS) molecules. The surface modified n-Si and p-Si of size 12 mm×4 mm were mounted on the π/4 angle inclined experimental mount, and nitrogen gas was flown over the inclined surface at the subsonic velocities, 5.3, 10.61, 15.91, 21.22, and 26.52 ms−1, and the voltage difference between the lead and rear ends of pristine and surface modified n-Si and p-Si was measured. The experimental results and theoretical relations are presented. The flow induced voltage generation is caused by the interplay between the Bernoulli flow and Seebeck effect. The flow-voltage response results show that the half coated and full coated n-Si and p-Si wafers generate more voltage than that of the uncoated at a given velocity. The band theory reveals that the flo...

The objective of this work is to quantify nanomechanical and nanotribological properties of nano- and micro-particles filled polymer composites used for the dental restorative applications. Nanotribological performances of the two polymer composites with different reinforcing particulates were investigated using advanced microscopy techniques. Both the polymer composites composed of same dimethacrylate based monomeric mixture, Bisphenol-A-glycidyldimethacrylate (Bis-GMA), triethylene glycoldimethacrylate (TEGDMA), urethane dimethacrylate (UDMA), as matrix. It was found that the elastic modulus, hardness, particle size, shape, distribution and agglomeration significantly influence the friction and wear characteristics of the polymer composites. The results show that nanotribological performance of nanoparticle reinforced polymer composites is better than the microparticle reinforced polymer composites.Copyright © 2007 by ASME

We have measured the frictional responses of two silane molecules (Octadecyltrichlorosilane; OTS and 1H, 1H, 2H, 2H-Perfluorooctyltrichlorosilane; FOTS) self-assembled on an aluminium substrate in their non heat-treated and heat-treated states. We varied the contact length scale by performing the experiments in atomic force microscope, nanotribometer and macro scale pin-on-disc machine. We have found that conformational disorder and molecular stiffness have major influences on friction in strongly distinguishing the response of OTS from that of the FOTS molecules. The frictional identity between the two molecules before and after heat treatment, though somewhat contrary to that suggested from purely surface energy considerations, is found to hold over six orders of contact length scales, ten orders of normal load and in three vastly different contact conditions; (a) the probe penetrates about 25% of the molecular backbone of a SAM; no substrate deformation, (b) the contact of the probe with the SAM is conformal and the substrate is plastically deformed and (c) the molecule is dispersed in 5% (v/v) concentration in n-hexadecane to lubricate a pin-on-disc contact.

We use a displacement-controlled dual double-cantilever-based surface-force-type apparatus to dynamically probe perfluorooctyl trichlorosilane monolayers self-assembled on aluminum and silicon substrates of 1 nm and 0.7 nm rms (root mean square) roughness,respectively, using a 1.12 mm diameter ruby sphere of 0.25 nm rms roughness. We record stiffness and damping constant as a function of compression load and deconvolute the elastic modulus using contact mechanical formulations. When mechanical intervention is limited to the terminal end of the molecule there is a strong viscous response and a low level of elastic response in consonance with the ability of the molecule to generate conformational defects freely. When the intervention penetrates into the molecular backbone the damping disappears dramatically and the molecule registers at a contact mean pressure of about 0.2 GPa a monotonic and steep rise in elastic resistance in response to further intervention by the probe. We offer a physical explanation of the process and describe this change as due to a phase transition from a liquid like to a solidlike state as indicated by a large increase in relaxation time constant.

We control the stiffnesses of two dual double cantelevers placed in series to control penetration into a perflurooctyltrichlorosilane monolayer self assembled on aluminium and silicon substrates. The top cantilever which carries the probe is displaced with respect to the bottom cantilever which carries the substrate, the difference in displacement recorded using capacitors gives penetration. We further modulate the input displacement sinusoidally to deconvolute the viscoelastic properties of the monolayer. When the intervention is limited to the terminal end of the molecule there is a strong viscous response in consonance with the ability of the molecule to dissipate energy by the generation of gauche defects freely. When the intervention reaches the backbone, at a contact mean pressure of 0.2GPa the damping disappears abruptly and the molecule registers a steep rise in elastic modulus and relaxation time constant, with increasing contact pressure. We offer a physical explanation of the process and describe this change as due to a phase transition from a liquid like to a solid like state.

Thermal stability behavior of 1H, 1H,2H,2H-perfluorooctyl trichlorosilane self-assembled on aluminum substrates is characterized using a grazing-angle Fourier transform infrared spectrometer, Fourier transform-Raman spectroscopy, and contact angle measurements. The self-assembled monolayer (SAM) is heated quasi-statically from room temperature to above 633 K with a heating rate of 1 K/s. Variations in peak frequencies, integrated areas of intensities of symmetric and antisymmetric CF2 stretches, and the relative tilt angle of the SAM are reported. We find that the conformational order in the SAM is not disrupted because of thermal cycling when the peak temperature is below 423 K. When the peak temperature is between 423 and 603 K, the cycling results in only a partial retention of the original order. When the peak temperature is above 603 K, the process is completely irreversible. Surface-enhanced Raman spectroscopy and contact angle measurements support these observations. We confirm these trends for a longer chain (1H,1H,2H,2H-perfluordecyl trichlorosilane) molecule of the same family using the same techniques. We discuss the possible reasons for the changes in light of the tilting-untilting and uncoiling-coiling of the helical silane monolayer.

We design and fabricate an apparatus which uses two dual double cantilever flexures to probe mechanical properties of self-assembled monolayers (SAM) under compression. The cantilevers were designed to give stiffness of the same order as the SAM. One of the cantilevers carrying the probe is vibrated sinusoidally at subresonance frequency and subnanometric amplitude while the dynamic response of the other carrying the SAM is recorded in the contact mode to yield data which could be deconvoluted to give stiffness and damping constant of the SAM under compression using a model of viscoelasticity. We validate the apparatus as well as the method of deconvolution by indenting bulk polytetrafluoroethylene and estimate mechanical properties of SAMs of different chain length and head group. The approach adopted here is able to distinguish in terms of mechanical properties a bulk polymer from a SAM and also between two SAMs of similar but subtly different structure.