Amin Bennouna

Electrochromism in sputtered V2O5 thin films: structural and optical studies

Abstract Vanadium pentoxide thin films were successfully fabricated on indium–tin–oxide-coated glasses by r.f. sputtering in an Ar/O2 gas mixture. The films gave excellent cyclic voltammograms with a two-step electrochromism, yellow to green, and then green to blue. The effect of the Li+ concentration in the electrolyte on the voltammogram cycles was also studied. The thin films were characterized before and after coloration by X-ray diffraction. No significant changes in the crystallographic structure occurred after coloration. The optical properties of films colored at three different potentials were measured in the UV-vis near infra-red (NIR) wavelength range. The results showed that the changes in the optical absorption are consistent with the color changes of the films. In particular, when the potential increased the optical absorption decreased in the wavelength range 500–900 nm, and the optical absorption edge shifted towards lower energies. The optical density of each colored film was monitored continuously when the circuit was opened after coloration for 15 min. The green, yellow and blue colors were relatively stable for several tens of hours.

Optical characterization of low optical thickness thin films from transmittance and back reflectance measurements

In this work a method for the determination of the thickness and optical properties of low optical thickness films (D<600 nm), from the experimental transmittance (T) and back reflectance (R′) measurements, is proposed. An original analytical formulation without any kind of approximation is employed for the computations. The computing algorithm is presented in detail and an error study is given. The method is applied for the characterization of sputtered CdTe and a-Si thin films of optical thickness in the range of 250 nm.

STRUCTURAL, OPTICAL AND ELECTROCHROMIC PROPERTIES OF SOL-GEL V2O5 THIN FILMS

Vanadium pentoxide thin films are prepared by the sol–gel route by dissolving V2O5 powder (99.5% purity) in H2O2 solution. The solution is spin-coated on glass substrates for optical (UV–VIS–NIR) and XRD analysis, and on ITOcoated glass substrates for electrochromic measurements. The samples are then annealed at 150°C for 1 hour. The resulting films have a yellow-orange color, typical of polycrystalline V2O5. XRD measurements have shown that after annealing in air at 400°C the structure of the films has a c-axis preferred orientation, the (0 0 1)-type planes lying parallel to the substrate. SEM analysis revealed a smooth surface. The films’ optical and physical constants (n, α, Eg, the thickness d and the mean thickness inhomogeneity s) are calculated using a simple and accurate method based on the transmission spectrum alone. The films’ electrochromism is studied using cyclic voltammetry (CV) and chronoamperometry in propylene carbonate solution containing 1 mol/l LiCIO4. The films show reversible multichromism (yellow–green–blue) upon Li

Preparation and characterization of CdTeO3 thin films

Abstract Cadmium telluride oxide CdTeO3 thin films were prepared by r.f.-sputtering from a polycrystalline CdTe target in an atmosphere of nitrogen and oxygen. X-ray diffraction (XRD) analysis showed that the as-deposited samples were amorphous. X-ray photoelectron spectroscopy (XPS) measurements revealed that the films were nearly stoichiometric. The resistivity and the static dielectric constant of the as-deposited layers were found to be 3×106 Ω m and 16, respectively. Optical transmission measurements in the ultraviolet–visible–near-IR (UV–VIS–NIR) region allowed the determination of the optical constants of the prepared films. Post-deposition annealing of the layers at 420°C for 2 h favored their crystallization. Finally, we show that polycrystalline CdTO3 films can be grown on CdTe films, deposited on C7059 glass by an appropriate heat-treatment of the CdTeO3/CdTe/C7059 structure.

Surface wear damage of glass solar mirrors in Moroccan desert environment

Surface wear of mirrors used in Concentrated Solar Power Plants -CSP- is among phenomena that causes irreversible specular reflectivity losses and therefore, a decrease in the global performance of the plant. This phenomenon can be caused by mechanical contact cleaning or by direct impact by airborne sand particles. In order to evaluate the effect of desert environment on direct surface wear upon mirrors, second surface silvered glass mirrors were exposed in Moroccan desert site, near to Ouarzazate city. In addition and in order to focus on the effect of surface wear separately from other potential degradations, tests were made on sandblasting machine in controlled environment on laboratory. The originality of the present work is that the adjustable parameters were chosen according to global analysis made on climatic and geological parameters of the desert site. Sand particles used in these tests are representatively extracted from the natural site. The application of the outdoor parameters upon mirrors tested on laboratory gives strong similarity of the laboratorys obtained results with those observed during natural aging.

Performance of different silicon PV technologies based on experimental measurements: A case study in Marrakech

The scope of this paper is to compare a one year performance of three grid-connected PV module technologies systems, installed at the Faculty of Sciences Semlalia Marrakech (latitude 31.6497°N and longitude 8.0169°W). The studied silicon-based PV modules technologies are monocrystalline (mono-c-Si), amorphous silicon (a-Si) and polycrystalline (poly-c-Si). Monthly and annual evaluated performance elements include: energy output, reference yield, final yield and performance ratio. The results show that poly-Si system presents the best performance followed by mono-c-Si and by a-Si. To our knowledge, these are the first published performance of grid-connected PV systems in Marrakech.

RafriBAT: A project to introduce energy efficiency in buildings in Marrakech area by means of passive and low exergy air-conditioning systems

RafriBAT is a project funded by the Hassan II Academy of Sciences and Technology for the period 2012-2015. It aims to study the use of passive and hybrid systems in buildings for natural air refreshment and heating. The project also focuses on the building envelope in order to point out the synergy between an adapted envelope and the use of the passive/hybrid systems for cooling/heating. Specifically, some existing buildings with passive and hybrid systems for cooling/heating will be monitored and modeled. In the second part of the project, the passive and hybrid systems for cooling/heating will be tested individually in Outdoor Test-Cells. The dynamic response of these systems will be also calculated by means of TRNSYS software. The comparison of the monitoring results and the dynamic modeling will produce an efficient and well-validated simulation tool. This tool may be used for the design of energetically efficient buildings in an arid climate such as that of Marrakech. The final target, of this project is to accompany the elaboration of the building energy efficiency code in the frame of the national energy efficiency strategy.

Photovoltaic Discoloration and Cracks: Experimental Impact on the I-V Curve Degradation

Optical and mechanical failures are often reported in a PV installation. This paper presents the impact of two of the most prevalent failures: The discoloration and the cell cracks on the electrical parameters of the PV characteristic. The studied installation was exposed to a semi-arid climate for two years. Hence, discoloration and cracks are inspected in some modules. The aim of this paper is to correlate between the types of failure occurred and the affected electrical parameter basically through the I-V curve pattern. For this purpose I-V curve measurements are performed for the degraded modules and compared with reference I-V curves of the same system. Throughout this study, identification methods such electroluminescence imaging and I-V curve characterization are utilized to diagnosis these failures.

Mathematical Models Calculating PV Module Temperature Using Weather Data: Experimental Study

A portion of solar irradiance that reaches the surface of the Photovoltaic modules is transformed into heat, and this increases the temperature of the modules which causes a decrease in their performance. As a result, the evaluation of the Photovoltaic modules temperature has a great importance. In this study, we give an overview of different approaches for Photovoltaic module temperature prediction by comparing different theoretical models with experimental measurements. These temperature models are calculated using meteorological parameters such as environment temperature, incident solar irradiance and wind speed if necessary. Data collected from three grid-connected Photovoltaic systems based on three technologies: Monocrystalline, Polycrystalline and Amorphous are used in this work. The different results obtained in this study are: It is not obvious to give one formula correlation to describe all the modules temperatures behaviours. Models without wind effect gave the best simulations for the three technologies. Lasnier and PVsyst methods gave the best results, NOCT approach has overestimated the module temperature; among the models without wind. Akhsassi2 and Sandia correlations gave satisfying results while Mattei has overestimated the module temperature; among the models considering wind effect.

Production study of a grid connected PV plant

In this work we present a detailed description of a 6 kWp photovoltaic power plant installed in the roof of the Faculty of Science and Technology Beni Mellal (Center of Morocco). This plant is grid connected and contributes to reducing the burden of electricity consumption within the faculty. In addition, it consists of three silicon technologies. The results of the plant during the four seasons of the year are presented and discussed well in sunny and cloudy conditions. The weather conditions are measured using a meteorological station.