M. BOULECHFAR Hichem

This work concerns a numerical simulation of the natural convection in a solar chimney. The differential equations of natural convection used in this work are the continuity equation, the equation of motion and the equation of heat in Cartesian coordinates with taking in consideration the Boussinesq approximation. We performed the numerical simulation using Ansys Fluent which is computing software based on the finites volumes method that solve the dimensionless equations with consideration of some simplifying hypotheses. The airflow is considered laminar, stationary and incompressible and the temperatures of the hot and the cold walls that correspond respectively to the ground and the collector are considered constants. The results of the simulation showed that the airflow motion inside the solar chimney depends mainly on the value of the temperature difference between horizontal surfaces of the solar chimney. The main objective of this work is to find out at which value of the temperature difference the airflow is fully developed inside the chimney which helps to define the temperature ranges where the efficiency of this technology is pronounced.

This paper presents a numerical study of buoyancy-driven double-diffusive convection within an elliptical annulus enclosure filled with a saturated porous medium. An in-house built FORTRAN code has been developed, and computations are carried out in a range of values of Darcy–Rayleigh number Ram (10 ≤ Ram ≤ 500), Lewis number Le (0.1 ≤ Le ≤ 10), and the ratio of buoyancy forces N (−5 ≤ N ≤ 5). In addition, three methods are used, namely the multi-variable polynomial regression, the group method of data handling (GMDH), and the artificial neural network (ANN) for the predictions of heat and mass transfer rates. First, results are successfully validated with existing numerical and experimental data. Then, the results indicated that temperature and concentration distributions are sensitive to the Lewis number and thermal and mass plumes are developing in proportion to the Lewis number. Two particular values of Lewis number Le = 2.735 and Le = 2.75 captured the flow's transition toward an asymmetric structure with a bifurcation of convective cells. The average Nusselt number tends to have an almost asymptotic value for Le » 5. For the case of aiding buoyancies N > 1.

The presented work concerned a computation of two-dimensional heat transfer by
laminar natural convection in a heat pipe cross section. The cylindrical annular space
was categorized into two cases, in the first case the space was filled with a
Newtonian fluid and the second case filled with a fluid-saturated porous medium.
The mathematical model was described by continuity, momentum and energy
equations in the cylindrical coordinates system using Boussinesq’s approximation and
Brinkman’s equation. The numerical simulation was carried out using Comsol
Multiphysics software. The effects of Rayleigh number, aspect ratio and permeability
on the temperature and the velocity fields were examined and results obtained were
validated and found to be qualitatively in a good agreement with those in the
literature.

The solar chimney system is one of the applications that interest several countries it is already implemented and has shown success in the field. But the increase in the efficiency of the solar chimney has always been the subject of several studies. [1] Presented a numerical analysis on the performance of a solar chimney power plant using steady state Navier–Stokes and energy equations in cylindrical coordinate system. The fluid flow inside the chimney is assumed to be turbulent and simulated with the k-ε turbulent model, using the FLUENT software package.

The two-dimensional laminar and permanent natural thermal convection in a solar chimney has been studied numerically using the CFD calculation code. The effect of the Rayleigh number, which is characterized by a temperature gradient on heat transfer within the solar chimney, was analyzed. For this, we have a fluid conveyed inside which is Newtonian and the flow is two-dimensional, laminar and permanent. We have chosen the Boussinesq approximation for the variation of the density of the fluid. The mathematical model is represented by the equations of continuity, momentum and the equation of heat. The finite volume method was used for the discretization of the equations performed by the simulation tool. Simulation results show that for low temperature gradients that are lower than KT5≤Δwhich correspond to low Rayleigh number values, the isotherms represent parallel lines and the temperature is simply decreasing from the ground to the collector roof where the heat within the solar chimney is mainly transferred by pseudo conduction. For temperature gradientsKTK105Δ, the results show the simultaneous presence of two modes of heat transfer. In the right part of the collector the heat transfer is dominated by pseudo conduction. On the other hand, at the entrance of the vertical chimney, the natural convection intensifies but remains relatively weak. As the temperature gradient increases furthermoreKT10Δ, the natural convection increases significantly and the rise of warm air in the chimney becomes obvious, the isotherms deform further throughout the solar chimney space and the heat transfer is mainly by natural convection.

Table de matières
Chapitre 1 : Généralité sur l’énergie solaire
1- Introduction…………………………………………………………………………....3
2- Le soleil ………………………………………………………………………….……3
3- L’énergie solaire ………………………………………………………………………4
a. Le spectre solaire……………………………………………………………....5
b. Rayonnement d'un corps noir …………………………………………..……..6
c. Couleur et longueur d’onde……………………………………………………7
4- Eléments du rayonnement solaire …………………………………………………..…9
a. Constante solaire ……………………………………………………………...9
b. Rayonnement global………………………………………………………..….9
c. La convention air-mass……………………………………………………....10
d. Angles permettant de projeter le flux incident ……………….…………...…11
e. Le mouvement apparent du Soleil……………………………………………12
f. Irradiance sur la surface de la terre…………………………………………..13
i. Capacité d’irradiation solaire en Afrique ……………………………13
ii. Capacité d’irradiation solaire en Algérie ………………………….....14
5- Techniques d’exploitation de l’énergie solaire …………………………………...…15
a. Le solaire thermique……………………………………………….…………15
b. Le solaire thermodynamique…………………………………………………16
i. La centrale solaire cylindro-parabolique …………………………….16
ii. La cheminée (Tour) solaire…………………………………………..17
c. Le solaire photovoltaïque…………………………………………………….18
6- Références………………………………………………………………………..…..19
Chapitre 2 : L’effet photovoltaïque
1- Historique……………………………………………………………………………22
2- L’effet photovoltaïque……………………………………………………………….23
a- Etymologie…………………………………………………………………...23
b- L’effet photoélectrique……………………………………………………….23
i. L’émission photoélectrique (effet Compton)………………………..24
i
Table de matières
ii. L’effet de la photoconductivité………………………………………25
iii. L’effet photovoltaïque……………………………………………….25
c- Les semi-conducteurs ……………………………………………………….27
i. Semi-conducteur intrinsèque…………………………………………28
ii. Semi-conducteur extrinsèque ………………………………………..28
iii. Le dopage des semi-conducteurs……………………………………..28
• Dopage de type N…………………………………………………..28
• Dopage de type P…………………………………………………...29
• Jonction P-N………………………………………………………..30
3- Le silicium……………………………………………………………………………31
a- Classement et propriétés……………………………………………………...31
b- Point de vue cristallographique………………………………………………33
c- Différents types de silicium…………………………………………………..33
i. Silicium polycristallin poly-Si……………………………………….33
ii. Silicium monocristallin mono-Si…………………………………….34
iii. Silicium amorphe a-Si………………………………………………..34
d- Les différents procédés de fabrication du Si…………………………………35
i. La méthode Czochralski……………………………………………...35
ii. La méthode de fusion de zone (FZ) et tirage piédestal………………36
iii. Procédé de tirage EMCP……………………………………………..37
iv. Technique de fabrication pour le silicium amorphe…………………38
e- Degré de pureté du silicium………………………………………………….38
f- La chaine de production du photovoltaïque………………………………….38
4- Références …………………………………………………………………………...40
Chapitre 3 : La cellule photovoltaïque (la photopile)
1- La structure de la cellule photovoltaïque (La photopile) ……………………………43
a. Les différentes étapes de préparation de la cellule …………………………..43
b. Les éléments qui constituent la cellule PV…………………………………...44
c. Le principe de fonctionnement d’une cellule PV…………………………….45
2- Les différentes technologies des cellules PV………………………………………...46
a. Cellule solaire monocristalline……………………………………………….46
b. Cellule solaire polycristalline………………………………………………...47
ii
Table de matières
c. Cellule solaire à couches minces …………………………………………….48
3- Représentation et caractéristiques électriques d’une cellule PV……………………..48
a. Schéma équivalent d´une cellule PV…………………………………………48
b. Courbe courant-tension d’une cellule PV……………………………………50
4- Fonctionnement et performance d’une cellule PV…………………………………...51
a. Puissance caractéristique d'une cellule PV…………………………………...51
b. Influence de l’ensoleillement………………………………………………...52
c. Influence de la température…………………………………………………..53
d. Facteur de forme d’une cellule PV…………………………………………...55
5- Rendement des cellules photovoltaïques ……………………………………………55
6- Association de cellules en série et en parallèle………………………………………56
a. Association de cellule PV en série…………………………………………...57
b. Association de cellule PV en parallèle……………………………………….57
c. Combinaison d’association de cellules ………………………………………58
d. Les diodes de by-pass (diode de protection)…………………………………58
7- Références……………………………………………………………………………60
Chapitre 4 : Le module photovoltaïque
1- Assemblage des modules Photovoltaïque……………………………………………63
a. La phase interconnections …………………………………………………...63
b. La phase encapsulation………………………………………………………64
c. La phase d’encadrement……………………………………………………...66
2- Différentes technologies de modules………………………………………………...67
3- Association des modules PV…………………………………………………………67
4- L’installation photovoltaïque………………………………………………………...69
a. Les différents constituants dans une installation PV…………………………69
b. Différents systèmes d’installation photovoltaïque………………………..…69
i. Système de pompage…………………………………………………69
ii. Système automne…………………………………………………….70
iii. Système hybride……………………………………………………...70
iv. Système raccordée au réseau…………………………………………71
5- Exemple de fiche technique d’un module PV……………………………………..…72
6- Références …………………………………………………………………………...