..... Vh"lUUU CONTRACTOR REPORT / DE83013143 vi SAN[t-81-7191 Integrated Structure Designs for Photovoltaic Arrays H. A. Franklin, Project Manager Bechtel Group, Inc. Research and Engineering Operation San Francisco, California Prepared bySandiaNational LaboratoriesAlbuquerque, NewMexico87185 andLivermore, California 94550fortheUnitedStatesDepartmentofEnergy underContract DE-AC04~76DPOQ789 Printed April 1983 RlPROOUCtO 6Y NATIONAL TECHNICAL /9 INFORMATION SERVICE us OEPARTMENT OF COMMERCE .2./17 ..SPRINGfIElD, VA 22161 .11 / r Issued by Sandia National Laboratories. operated for the United States DepartmentofEnergybySandiaCorporation. NOTICE: Thisreportwaspreparedasanaccountofworksponsoredbyan agencyoftheUnitedStatesGovernment.NeithertheUnitedStatesGovern mentnoranyagencythereof,Doranyoftheiremployees, noranyoftheir contractors,subcontractors,ortheiremployees,makesanywarranty,express orimplied,orasllUIDesanylegalliabilityorresponsibilityfortheaccuracy, completeness..orusefulnessofanyinformation,apparatus,product,orpro cessdisclosea,orrepresentsthatitsusewouldnotinfringeprivatelyowned rights. Reference herein to any specific commercial product, process, or service by trade DaIn6, trademark, manufacturer, or otherwise, does not necessarilyconstituteorimplyitsendorsement,recommendation,orfavoring by the United States Government, any agency thereof or any of their contractorsorsubcontractors.Theviewsandopinionsexpressedhereindo notnecessarilystateorreflectthoseoftheUnitedStatesGovernment,any agencythereoforanyoftheircontractorsorsubcontractors. PrintedintheUnitedStatesofAmerica Availablefrom NationalTechnicalInformationService U.S.DepartmentofCommerce 5285PortRoyalRoad Springfield,VA22161 NTISpricecodes Printedcopy:All Microfichecopy:A01 SAND81-7191 Distribution Unlimited Release Category UC- 63a Printed April 1983 Integrated Structure Designs for Photovoltaic Arrays H. A. Franklin, Project Manager Bechtel Group, Inc. Research and Engineering Operation San Francisco, California Work performed for Sandia National Laboratories Under Contract 62-9877 Abstract Thisreportdescribesthethirdphaseofa multi-yearprogramto investigatethedesign of low-cost support structures for solar photovoltaic arrays used for central power production. Earlier phases concerned conceptual designs, extensive surveys of solar system manufacturers, preliminary cost estimates, development of structural design criteria for arrays, and wind tunnel tests to provide needed wind design parameters. The presentfinal phasefocuses on two low-costcandidatesupportconcepts. Detailed design integration was investigated after some comparative costing was done for a selectionofpossibleconcepts.Designintegrationinvolveddetailingvariousfoundation and superstructure systems to reduce structural redundancy and improve system efficiencyfor fabrication and installation. Additionalwind-tunneltests ofthese fixed, flat-panel arrays extended earlier experimental results. The structural responses and aerodynamic stability of candidate designs were checked by wind dynamic analyses. This study led eventually to the fabrication and installation of a non-operative demonstrationarrayinAlbuquerque, NM, whichshowedthe simplicityand effective ness ofthe selected design for future large-scale applications. CONTENTS Section Page 1 INTEGRATED ARRAY DESIGNS - TASK I 1-1 1.1 Basis for Structural Concepts 1-2 1.1.1 Basic Plant Layout Principles 1-4 1.1.2 Materials, Codes, and Standards 1-7 1.1.3 Review of Available Concepts 1-10 1.2 Conceptual Array Designs 1-13 1.2.1 Panel Parameter Study 1-13 1.2.2 Concept 1 - Torque Tube W/Caisson 1-21 1.2.3 Concept 2 - Torque Tube W/Steel Pipe Pile 1-21 1.2.4 Concept 3 - Torque Tube W/H-Pile 1-25 1.2.5 Concept 4 - Torque Tube W/Wood Pile 1-25 1.2.6 Concept 5 - L-Shaped Corrugated Steel 1-28 1.2.7 Concept 6 - Half-Pipe Corrugated Steel 1-28 1.2.8 Selected Candidate Designs 1-33 1.3 Final Design Criteria 1-35 1.3.1 Loading Criteria 1-35 1.3.2 Load Combinations 1-42 1.3.3 Foundation Criteria 1-44 1.4 Design Optimizations 1-50 1.4.1 Panel/Module Integration 1-51 1.4.2 Single Supports versus Double Supports 1-58 1.4.3 Span Length Variations 1-59 1.4.4 Variation of Support Locations 1-60 1.5 Selected Final Designs 1-63 1.5.1 Integrated Superstructure Design 1-64 1.5.2 Substructure Designs 1-68 1.5.3 Connections and Details 1-73 1.6 Array Field Fence Study 1-77 v CONTENTS (Cont'd) Section 2 DYNAMIC WIND ANALYSIS - TASK II 2-1 2.1 General 2-1 2.1.1 Basic Approach 2-1 2.1.2 Scope of Investigation 2-3 2.2 Mathematical Models of Photovoltaic Arrays 2-3 2.3 Analysis For Steady-State Wind Loads 2-4 2.4 Modal Analysis 2-7 2.5 Dynamic Instability Evaluation 2-11 2.5.1 Flutter Instability 2-11 2.5.2 Vortex Shedding 2-13 2.6 Dynamic Response Analysis 2-14 2.6.1 Dynamic Wind Load 2-14 2.6.2 Dynamic Response Analysis Method and Results 2-18 2.6.3 Discussion of Results 2-21 2.6.4 Fatigue Considerations 2-26 2.7 Summary and Conclusions 2-26 2.8 Recommendations for Future Studies 2-28 3 SYSTEM COST ESTIMATES - TASK III 3-1 3.1 Bases for Construction Cost Estimates 3-2 3.1.1 Field Costs 3-4 3.1.2 Engineering Services 3-6 3.1.3 Allowance for Uncertainty 3-7 3.1.4 Qualifications 3-7 3.1.5 Exclusions 3-8 3.2 Preliminary Cost Estimate Analysis 3-8 vi CONTENTS (Cont'd) Section 3 (Cont'd) 3.2.1 Field Costs 3-9 3.2.2 Qualifications, Exclusions, and Assumptions 3-14 3.2.3 Evaluation 3-14 3.3 Final Cost Estimate Analysis 3-15 3.3.1 Field Costs 3-18 3.3.2 Qualifications, Exclusions, and Assumptions 3-22 3.3.3 Summary 3-22 4 PROTOTYPE HARDWARE - TASK IV 4-1 4.1 Prototype Array Design Criteria 4-2 4.2 Design of Demonstration Array 4-3 4.3 Dummy Solar Modules 4-4 4.4 Construction Specifications 4-4 4.5 Construction of Demonstration Array 4-5 4.6 Review of Construction 4-8 5 WIND TUNNEL TESTS - TASK V 5-1 5.1 Scope 5-1 5.2 Summary and Conclusions 5-2 REFERENCES R-1 vii CONTENTS (Cont'd) Section APPENDIX A - Drawings for Large Array Field and Construction of Demonstration Array APPENDIX B - Mode Shape Plots of Photovoltaic Structural Systems (Concrete Single-Post and Timber Double-Post Designs) APPENDIX C - Derivation of Fluctuating Wind Pressure Power Spectral-Density Functions in Reference 2-1 APPENDIX D- Technical Specifications for the Fabrication and Construction of Demonstration Dummy Photovoltaic Arrays APPENDIX E - CSU Wind Tunnel Study-Phase II vii i ILLUSTRATIONS Figure 1-1 Definitions of Terminology 1-3 1-2 Array Spacing and Roadway Allocations 1-6 1-3 A1 MW Array Fie1d Layout 1~8 1-4 JPL Array Support Structure 1-11 1-5 Single Supported Panel - Design A 1-14 1-6 Single Supported Panel - Design B 1-15 1-7 Single Supported Panel - Design C - Torque Tube 1-16 1-8 End-Supported Panel - Concept A 1-18 1-9 End-Supported Panel - Concept B 1-19 1-10 Foundation Concepts for Torque Tube System 1-20 1-11 Design Curves for Concrete Caissons 1-22 1-12 Connection of Torque Tube Pedestal to Concrete Caisson 1-23 1-13 Design Curves for Steel Pipe Supports 1-24 1-14 Conceptual Connection of Torque Tube to Steel Tube Pile 1-26 1-15 Conceptual Connection of Torque Tube to H-Pi1e 1-27 1-16 Conceptual Connection of Torque Tube to Wood Pile 1-29 1-17 L-Shaped Corrugated Steel Support System for PV Arrays 1-30 1-18 Corrugated Steel Half-Pipe Array Support 1-32 1-19 Resultant Wind Forces On Arrays 1-39 1-20 Assumed Soil Reactions due to Lateral Loads for a Short Rigid Pile in Granular Material 1-47 1-21 Framed Module Support-Concept A 1-52 1-22 Framed Module Support-Concept B 1-53 ix ILLUSTRATIONS (Cont'd) Figure 1-23 Framed Module Support Concept C 1-54 1-24(a) Conceptual 8' x 20' Panel for Frameless Modules 1-56 1-24(b) Sections For Conceptual Panel 1-57 1-25 Total Installed Direct Costs Versus Span Lengths 1-61 1-26 Typical Row of 8' x 36' Arrays - Double-Supported 1-62 Cantilever System 1-27 Typical Row of Prototype Arrays 1-65 1-28 Attachment of Photovoltaic Modul es to Panel Tees 1-66 1-29 Attachment of Photovoltaic Modules to Panel Tees 1-67 1-30 Embedment Depths of Caissons in Prototype Array Field 1-69 1-31 Extended Concrete Caisson for Prototype 1-71 Array Field 1-32 Connection of Torque Tube to Extended Concrete Caisson 1-74 1-33 Connection of Torque Tube to Timber Pole 1-75 1-34 Typical Connection Between Adjacent Torque Tubes 1-76 2-1 Finite Element Model of Single-Post 8' x 20' Array 2-5 2-2 Finite Element Model of Double-Post 8' x 20' Array 2-6 2-3 Steady-State Wind Pressure Loading for Extreme S-W Wind 2-8 2-4 Simplified Steady-State S-W Wind Pressure Loading 2-9 2-5 Wind Pressure Power-Spectral-Density Input 2-17 3-1 Cost Estimate Flow Diagram 3-3 3-2 Installation Scenario for a Prototype Array Field 3-19 4-1 Demonstration Reinforced Concrete Caisson 4-10 4-2 Demonstration Panel Fabrication 4-11 4-3 Lifting An 8' x 36' Panel Assembly 4-12 4-4 Completed 2 - Span Demonstration Array 4-13 5-1 Typical Corner of an Array Field 5-4 x