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姓名 戴振宇(Chen Yu Dai) 查詢紙本館藏 畢業系所 機械工程學系 論文名稱 2-kW級太陽追蹤器結構變形與追日偏差分析
(Analysis of Structural Deformation and Misalignment in a 2-kW Solar Tracker)相關論文 檔案 [Endnote RIS 格式]
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摘要(中) 本研究主旨在利用有限元素分析法(FEA)，探討一組2-kW級太陽光電系統之太陽追蹤器受到重力及風力作用下，其結構變形和PV模組的追日偏差量。分析的條件分別為無風之自重狀態，以及在風速為7 m/s、12 m/s和37.5 m/s之情況，在每個風速作用下又各別分為風從太陽追蹤器的正面(0o)至背面(180o)，以30o為一間隔吹來之七種風向；而在風速37.5 m/s的作用下，太陽追蹤器停止運作並以仰角0o插上安全插銷作為分析條件。此外，本研究亦分析此太陽追蹤器之自然振動頻率作為設計及安裝參考，避免結構共振之發生。同時藉由量測此太陽追蹤器二個選定位置在實際操作情況下之應變變化，與模擬結果作比對，以驗證本研究所建立有限元素分析模型之有效性。比對結果顯示，模擬結果之應變改變趨勢和實驗結果一致，此一致性證實本研究所建立之有限元素分析模型之有效性，可適用於分析太陽光電系統之結構變形。
根據von Mises破損準則，模擬結果顯示此太陽追蹤器在受到重力加上風速為7 m/s、12 m/s或37.5 m/s的作用下，預期各個組件將不會有永久變形之情形發生。模擬結果亦顯示此追蹤器在不同追日角度受重力及不同風力作用下，PV模組追日偏差量的變化趨勢與其總位移的變化趨勢一致。此外，產生較大追日偏差量的PV模組皆位於受風前緣面板中的一個。除了在風速37.5 m/s的作用下，在其他所有分析情況中，PV模組在風速為12 m/s並從其正面(0o)吹來的情況下會有最大的追日偏差量，其值為1.48o。由於此偏差角對於此PV模組發電效率影響很小，所以預期此太陽追蹤器在風速為12 m/s的作用下仍可以正常運作，不會有明顯的發電效率下降，同時在正常的運作之下，不會有結構破損之情形發生。自然振動頻率分析結果顯示其前六個振動模態的自然頻率值落在3.85 Hz至11.4 Hz之間，未來在架設此太陽追蹤器時應考慮所在地之風場的頻率。
摘要(英) The purpose of this study is using finite element analysis (FEA) to investigate the effects of gravity and wind loadings on the structural deformation and misalignment of solar radiation in a 2-kW photovoltaic (PV) system. Several loading conditions, including gravity alone and gravity plus wind speeds of 7 m/s, 12 m/s, and 37.5 m/s with blowing direction varying from front (wind direction of 0o) to back (wind direction of 180o) sides with an interval of 30o, are applied to calculate the stress distribution and structural deformation. The misalignment of solar radiation induced by structural deformation is calculated. Moreover, to avoid the damage caused by resonance, natural frequencies of vibration for the given PV system are also determined. A comparison of the simulation and measurement results of strain change at two selected locations in the given solar tracker during field operation is made to validate the constructed FEA model. A reasonable agreement of the simulation and measurement results is found such that the constructed FEA model is validated to be effective in assessment of the structural integrity of a PV system.
No structural failure is predicted for all components in the given solar tracker under all of the given loading conditions according to the von Mises failure criterion. An agreement in the trend of variation of misalignment and resultant displacement of PV modules is found. Moreover, the maximum misalignment for each wind direction occurs at the PV modules which touch the wind first. Considering the effects of gravity and wind speeds of 7 m/s and 12 m/s, the maximum misalignment of solar radiation is of 1.48o for a wind speed of 12 m/s with wind direction of 0o. It is expected that such a misalignment value will not cause a significant degradation of power generation for the given PV system. Consequently, the given PV system can operate safely under the effects of gravity and wind speeds of 7 m/s and 12 m/s with a good efficiency. The range of natural frequencies of the first six vibration modes for the given PV system is from 3.85 Hz to 11.4 Hz.
關鍵字(中) ★ 偏差角
★ 太陽光電
★ 太陽追蹤器
★ 結構變形關鍵字(英) ★ deformation
★ structural
★ photovoltaic
★ solar tracker
★ misalignment論文目次 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
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指導教授 林志光(Chih-Kuang Lin) 審核日期 2012-8-13 推文 plurk
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