TABLE OF CONTENTS Page LIST OF TABLES VII LIST OF FIGURES VIII NOMENCLATURE XI 1. INTRODUCTION 1 1.1 Photovoltaic System 1 1.2 Solar Tracker 2 1.3 Literature Review for Wind Effects on Solar Tracker Structure 4 1.4 Purpose and Scope 7 2. MODELING 9 2.1 Modeling for Structural Deformation 9 2.1.1 Finite element model and material properties 9 2.1.2 Loads and boundary conditions 10 2.2 Modeling for Wind Loads 12 2.2.1 Finite element model 12 2.2.2 Physical properties and boundary conditions 13 2.3 Definition of Misalignment of Solar Radiation 13 3. EXPERIMENTAL SETUP AND PROCEDURE 15 3.1 Experimental Setup 15 3.2 Experimental Procedure 15 4. RESULTS AND DISCUSSION 17 4.1 Effect of Gravity Only 17 4.2 Effect of a Wind Speed of 7 m/s 20 4.3 Effect of a Wind Speed of 12 m/s 22 4.4 Effect of a Wind Speed of 37.5 m/s 26 4.5 Overall Comparison 27 4.6 Vibration Analysis of PV System 29 5. CONCLUSIONS 32 REFERENCES 34 TABLES................................................................................................................................. 36 FIGURES............................................................................................................................... 40 LIST OF TABLES Page Table 1　 Material properties of a highly transparent solar glass 36 Table 2　 Material properties of A5052 aluminum alloy 36 Table 3　 Material properties of A6063-T6 aluminum alloy 36 Table 4　 Material properties of AISI 1053 steel 36 Table 5　 Material properties of AISI 4140 steel 37 Table 6　 Material properties of SUJ2 steel 37 Table 7　 Material properties of SS400 steel 37 Table 8　 Physical properties of air at an atmospheric pressure 37 Table 9 Overall comparison of maximum stress, resultant displacement, and misalignment for various wind loadings 38 Table 10　Natural frequency of the given PV system at various elevation angles 39 LIST OF FIGURES Page Fig. 1 Schematic of a solar cell. [1] 40 Fig. 2 Evolution of photovoltaic electricity generation by end-use sectors. [4] 40 Fig. 3 Projection of installation for different PV systems by 2020. [5] 41 Fig. 4 Comparison of solar radiation for a fixed and dual-axis tracker. [10] 41 Fig. 5 Typical structures of dual-axis solar trackers: (a) pedestal form; (b) roll-tilt form; (c) roll-tilt form with box frame; (d) turntable form. [2] 42 Fig. 6 Shade balancing principle: (a) sun-pointing sensor; (b) tilted mount of photo sensor; (c) photo sensor in a collimator. [13] 44 Fig. 7 Schematic of one PV module: (a) front side; (b) back side. 45 Fig. 8 Schematic of the PV system model at elevation angles of (a) 0o and (b) 75o. 46 Fig. 9 Schematic of boundary conditions for the given PV model. 48 Fig. 10 Schematic of wind directions. 49 Fig. 11 Schematic of the PV model at elevation angles of (a) 0o and (b) 75o. 50 Fig. 12 Schematic of wind loading for the given PV model with wind blowing toward (a) the front (0o) and (b) rear (180o) sides of the PV modules. 51 Fig. 13 (a) Schematic of the CFD model for the simplified PV structure; (b) Schematic of the CFD model for the wind field; (c) Meshes of the CFD model for the wind field.. 53 Fig. 14 Schematic of the boundary conditions in the CFD model for wind blowing directions of (a) 0o and (b) 180o. 55 Fig. 15 Schematic of structural deformation in a PV module for calculating the misalignment: (a) iso view; (b) a cross-sectional view. 56 Fig. 16 Definition of the deviation angle between the undeformed plane P and deformed plane. 57 Fig. 17 Two selected locations for strain measurement: (a) a highlighted view from the FEA model; (b) the corresponding photograph. 58 Fig. 18 Photographs of experimental setup for strain measurement. 60 Fig. 19 Comparison of simulated and measured strain changes at (a) S1 and (b) S2 for various elevation angles. 61 Fig. 20 Schematic of normal and parallel force components of the weight of the upper part of the PV system, including PV modules, PSD, and beams, at elevation angles of (a) 45o, (b) 60o, and (c) 75o. (C: center of gravity) 62 Fig. 21 Locations of the bushing and ball bearings in the FEA model. 64 Fig. 22 Distributions of von Mises equivalent stress in the bushing and a ball bearing at elevation angles of (a) 0o, (b) 45o, (c) 60o, and (d) 75o for gravity only. 65 Fig. 23 Maximum von Mises equivalent stresses in the bushing and ball bearings at various elevation angles under the effect of gravity alone. 69 Fig. 24 Maximum misalignment and displacement of PV modules at various elevation angles under the effect of self-weight. 70 Fig. 25 Distributions of resultant displacement in PV modules at elevation angles of (a) 0o, (b) 30o, (c) 45o, and (d) 60o under the effect of self-weight. 71 Fig. 26 Distributions of von Mises equivalent stress in the bushing and a ball bearing at elevation angle of 75o for a wind speed of 7 m/s with blowing directions of (a) 0o, (b) 30o, and (c) 180o. 73 Fig. 27 Maximum von Mises equivalent stresses in the (a) bushing and (b) ball bearings at various elevation angles under the effect of gravity alone and a wind speed of 7 m/s with various blowing directions. 76 Fig. 28 Examples of distributions of wind pressure on the PV system at elevation of 75o under a wind speed of 7 m/s with blowing directions of (a) 0o, (b) 30o, (c) 90o, and (d) 180o. 77 Fig. 29 Variations of (a) resultant displacement and (b) maximum misalignment of PV modules with elevation angle for a wind speed of 7 m/s in various directions. 79 Fig. 30 Distributions of von Mises equivalent stress in the bushing and a ball bearing at elevation angle of 75o for a wind speed of 12 m/s with blowing directions of (a) 0o, (b) 30o and (c) 180o. 80 Fig. 31 Maximum von Mises equivalent stress in the (a) bushing and (b) ball bearings at various elevation angles under the effect of gravity alone and a wind speed of 12 m/s with various blowing directions. 83 Fig. 32 Example of distribution of wind pressure on the PV system at elevation of 15o under a wind speed of 12 m/s with blowing direction of 0o. 84 Fig. 33 Examples of distributions of wind pressure on the PV system at elevation of 75o under a wind speed of 12 m/s with blowing directions of (a) 0o, (b) 30o, (c) 90o, and (d) 180o 85 Fig. 34 Variations of (a) resultant displacement and (b) maximum misalignment of PV modules with elevation angle for a wind speed of 12 m/s in various directions. 87 Fig. 35 Distributions of resultant displacement in PV modules at elevation angle of 45o for a wind speed of 12 m/s and blowing directions of (a) 30o and (b) 60o. 88 Fig. 36 Maximum von Mises equivalent stress in the bushing, ball bearings, and frames of the PV modules at elevation angle of 0o under the effect of a wind speed of 37.5 m/s with various blowing directions. 89 Fig. 37 Comparisons of the maximum resultant displacement and misalignment at various elevation angles under the effects of gravity alone, and wind speeds of 7 m/s and 12 m/s with blowing directions of (a) 0o, (b) 90o, and (c) 180o. 90 Fig. 38 Calculated vibration mode shapes of the given PV system at elevation angle of 75o: (a) first mode; (b) second mode; (c) third mode; (d) fourth mode; (e) fifth mode; (f) sixth mode. 92