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Student Number 983203001 Author June-Yuan Fang(¤è§g¤¸) Author's Email Address doyoulm@hotmail.com Statistics This thesis had been viewed 824 times. Download 391 times. Department Mechanical Engineering Year 2010 Semester 2 Degree Master Type of Document Master's Thesis Language English Title Analysis of Structural Deformation and Concentrator Misalignment in a 1-kW Solar Tracker Date of Defense 2011-07-15 Page Count 120 Keyword finite element analysis solar tracker Abstract The purpose of this study is to investigate the effects of gravity and wind loadings on structural deformation and concentrator misalignment in a 1-kW high concentrator photovoltaic (HCPV) system using finite element analysis (FEA) approach. A three-dimensional (3-D) FEA model was constructed for a roll-tilt form of solar tracker in an HCPV system developed at the National Central University. Several loading conditions, including gravity only and gravity plus wind speeds of 7 and 12 m/s blowing toward the front (wind direction of 0o), lateral (wind direction of 90o), and rear (wind direction of 180o) sides of the solar tracker, were applied to calculate the stress distribution and structural deformation. Three changeable tilt angles of 24.5o (the spring/autumn equinox), 1o (the summer solstice), and 48o (the winter solstice) for the concentrator modules were also taken into account. Meanwhile, the concentrator misalignment induced by the structural deformation was calculated. A comparison of the simulation and measurement results of strain change at two selected locations in the given solar tracker during field operation was made to validate the constructed FEA model. A reasonable agreement of the simulation and measurement results was found such that the constructed FEA model was validated to be effective in assessment of the structural integrity of an HCPV system.

No structural failure was predicted for all components in the given solar tracker under all the given loading conditions according to von Mises failure criterion. An agreement in the trend of variation of concentrator misalignment and normal displacement of Fresnel lens in each concentrator module was found. Therefore, the concentrator with a greater misalignment could be readily identified from the corresponding normal displacement distribution. For all the cases investigated, the maximum concentrator misalignment was of 0.142o for a wind speed of 12 m/s with wind direction of 90o for the tilt angle of 1o (the summer solstice) and it was within the range of an acceptance angle of 0.5o for the given concentrator module. Consequently, the given HCPV system can operate safely under the effects of wind speeds of 7 and 12 m/s with a good efficiency in power generation.Table of Content LIST OF TABLESVII

LIST OF FIGURESVVIII

1.INTRODUCTION1

1.1High Concentrator Photovoltaic System1

1.1.1Concentrator module2

1.1.2Solar tracker3

1.2Literature Review for Wind Effects on Solar Tracker Structure5

1.3Purpose and Scope7

2.MODELING10

2.1Modeling for Structural Deformation10

2.1.1Finite element model and material properties10

2.1.2Loads and boundary conditions11

2.2Modeling for Wind Loads13

2.2.1Finite element model13

2.2.2Physical properties and boundary conditions14

2.3Definition of Concentrator Misalignment15

3.EXPERIMENTAL SETUP AND PROCEDURE17

3.1Experimental Setup17

3.2Experimental Procedure17

4.RESULTS AND DISCUSSION19

4.1Effect of Gravity Only19

4.2Effect of a Low Wind Speed of 7 m/s22

4.3Effect of a Wind Speed of 12 m/s for the Tilt Angle of 24.5o23

4.4Effect of a Wind Speed of 12 m/s for the Tilt Angle of 1o26

4.5Effect of a Wind Speed of 12 m/s for the Tilt Angle of 48o28

4.6Overall Comparison31

5.CONCLUSIONS34

REFERENCES36

TABLES40

FIGURES42

Table 1¡@Material properties of PMMA Fresnel lenses40

Table 2¡@Material properties of A6N01S-T5 aluminum alloy40

Table 3Material properties of the aluminum frame used in the concentrator modules40

Table 4¡@Material properties of C2200 copper alloy40

Table 5¡@Material properties of SS400 steel40

Table 6¡@Physical properties of air at an atmospheric pressure41

Table 7¡@Overall comparisons of maximum stress, normal displacement, and misalignment for various combinations of wind loading and tracking angle41

Fig. 1Schematic of a GaInP/GaInAs/Ge triple-junction solar cell structure. [7]42

Fig. 2The principle of PV concentration, using Fresnel lens optics. [11]43

Fig. 3Major parts in an HCPV system. [10]44

Fig. 4Schematic of primary optics: (a) refractive lens; (b) reflective dish. [4]45

Fig. 5Two types of secondary optics in which the primary optics is a Fresnel lens: (a) non-imaging mirror; (b) imaging lens. [21]46

Fig. 6Typical structures of dual-axis solar trackers: (a) pedestal form; (b) roll-tilt form; (c) roll-tilt form with box frame; (d) turntable form. [4]47

Fig. 7Shade balancing principle: (a) sun-pointing sensor; (b) tilted mount of photo sensor; (c) photo sensor in a collimator. [11]49

Fig. 8Schematic of a concentrator module50

Fig. 9Schematic of the HCPV system model: (a) front view; (b) rear view51

Fig. 10Schematic of three selected wind directions52

Fig. 11Schematic of the HCPV model at hour angles of (a) 0o and (b) 75o53

Fig. 12Schematic of three selected tilt angles of the concentrator modules: (a) 24.5o (the spring/autumn equinox); (b) 1o (the summer solstice); (c) 48o (the winter solstice)54

Fig. 13Schematic of wind loading for the given HCPV model with wind blowing toward (a) the front (0o), (b) lateral (90o), and (c) rear (180o) sides of the concentrator modules55

Fig. 14(a) Schematic of the simplified HCPV FEA model for calculating the wind pressure; (b) schematic of the computational domain in FEA analysis57

Fig. 15Schematic of the computational domain and boundary conditions with wind blowing toward (a) the front (0o), (b) lateral (90o), and (c) rear (180o) sides of the concentrator modules58

Fig. 16(a) Wind pressure distributions on the concentrator modules and a cross-sectional view of wind vorticity and (b) velocity field of wind flow around the concentrator modules at hour angle of 60o under the effect of a wind speed of 12 m/s with direction of 90o for the tilt angle of 24.5o60

Fig. 17Schematic of structural deformation in a Fresnel lens for calculating the misalignment: (a) iso view; (b) a cross-sectional view61

Fig. 18Definition of the angle between the undeformed plane P and deformed plane P'62

Fig. 19Two selected locations for strain measurement: (a) a highlighted view from the FEA model; (b) the corresponding photograph63

Fig. 20Experimental setup for strain measurement65

Fig. 21Comparison of simulated and measured strain variations at various hour angles at locations S1 and S266

Fig. 22Schematic of normal and parallel force components of the weight of concentrator modules67

Fig. 23Distributions of von Mises equivalent stress in the lower long steel beam at hour angles of (a) 0o, (b) 30o, (c) 60o, and (d) 75o for the tilt angle of 24.5o under the effect of gravity alone68

Fig. 24Comparisons of calculated maximum von Mises stresses in the long steel beam under the effect of gravity alone at various hour angles for three different tilt angles70

Fig. 25Comparisons of maximum misalignment and normal displacement of concentrator modules under the effect of gravity only at various tilt angles: (a) 24.5o; (b) 1o; (c) 48o71

Fig. 26Distributions of normal displacement in Fresnel lenses at hour angles of (a) 0o, (b) 30o, (c) 60o, and (d) 75o for the tilt angle of 24.5o under the effect of gravity alone73

Fig. 27Distributions of normal displacement in Fresnel lenses under the effect of gravity alone: (a) at hour angle of 40o for the tilt angle of 1o; (b) at hour angle of 30o for the tilt angle of 48o75

Fig. 28Distributions of maximum von Mises equivalent stress in the long steel beam under the effect of a wind speed of 7 m/s with wind direction of 0o for tilt angles of (a) 24.5o, (b) 1o, and (c) 48o76

Fig. 29Distributions of maximum von Mises equivalent stress in the long steel beam under the effect of a wind speed of 12 m/s with wind directions of (a) 0o (hour angle of 20o), (b) 90o (hour angle of 30o), and (c) 180o (hour angle of 20o) for the tilt angle of 24.5o78

Fig. 30Comparison of calculated maximum von Mises stresses in the long steel beam at various hour angles under the effect of gravity alone and a wind speed of 12 m/s with three specified wind directions for the tilt angle of 24.5o80

Fig. 31Distributions of wind pressure on the concentrator modules under the effect of a wind speed of 12 m/s with directions of (a) 0o (hour angle of 0o), (b) 90o (hour angle of 50o), and (c) 180o (hour angle of 0o) for the tilt angle of 24.5o81

Fig. 32Comparisons of maximum misalignment and normal displacement of concentrator modules under the effect of a wind speed of 12 m/s with directions of (a) 0o, (b) 90o, and (c) 180o for the tilt angle of 24.5o83

Fig. 33Distributions of normal displacement in Fresnel lenses at hour angles of (a) 0o, (b) 30o, (c) 60o, and (d) 75o for the tilt angle of 24.5o under the effect of a wind speed of 12 m/s with direction of 90o85

Fig. 34Distributions of maximum von Mises equivalent stress in the long steel beam under the effect of a wind speed of 12 m/s with wind directions of (a) 0o (hour angle of 20o), (b) 90o (hour angle of 40o), and (c) 180o (hour angle of 30o) for the tilt angle of 1o87

Fig. 35Comparison of calculated maximum von Mises stresses in the long steel beam at various hour angles under the effect of gravity alone and a wind speed of 12 m/s with three specified wind directions for the tilt angle of 1o89

Fig. 36Distributions of wind pressure on the concentrator modules under the effect of a wind speed of 12 m/s with wind directions of (a) 0o (hour angle of 0o) and (b) 180o (hour angle of 75o) for the tilt angle of 1o90

Fig. 37Comparisons of maximum misalignment and normal displacement of concentrator modules under the effect of a wind speed of 12 m/s with directions of (a) 0o, (b) 90o, and (c) 180o for the tilt angle of 1o91

Fig. 38Distributions of normal displacement in Fresnel lenses at hour angles of (a) 0o, (b) 30o, (c) 60o, and (d) 75o for the tilt angle of 1o under the effect of a wind speed of 12 m/s with direction of 0o93

Fig. 39Distributions of normal displacement in Fresnel lenses at hour angles of (a) 0o, (b)330o, (c) 60o, and (d) 75o for the tilt angle of 1o under the effect of a wind speed of 12 m/s with direction of 90o95

Fig. 40Distributions of maximum von Mises equivalent stress in the long steel beam under the effect of a wind speed of 12 m/s with wind directions of (a) 0o (hour angle of 20o), (b) 90o (hour angle of 40o), and (c) 180o (hour angle of 30o) for the tilt angle of 48o97

Fig. 41Comparison of calculated maximum von Mises stresses in the long steel beam at various hour angles under the effect of gravity alone and a wind speed of 12 m/s with three specified wind directions for the tilt angle of 48o99

Fig. 42Distribution of wind pressure on the concentrator modules at hour angle of 0o under the effect of a wind speed of 12 m/s with wind direction of 180o for the tilt angle of 48o100

Fig. 43Comparisons of maximum misalignment and normal displacement of concentrator modules under the effect of a wind speed of 12 m/s with directions of (a) 0o, (b) 90o, and (c) 180o for the tilt angle of 48o101

Fig. 44Distributions of normal displacement in Fresnel lenses at hour angles of (a) 0o, (b)630o, (c) 60o, and (d) 75o for the tilt angle of 48o under the effect of a wind speed of 12 m/s with direction of 180o103

Fig. 45Schematic of (a) boundary conditions of the bottom surface and (b) an example of wind loadings on the selected concentrator module105Reference 1.R. A. Messenger and J. Ventre, Photovoltaic Systems Engineering, 2nd Ed., CRC Press, Boca Raton, FL, USA, 2003.

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