DOE/NASA/01 95-1 NASA CR-1 65352 M206 Photovoltaic Stand-Alone Systems Preliminary Engineering Design Handbook H. L. Macomber and John B. Ruzek Monegon, Ltd. Gaithersburg, Maryland Frederick A. Costello F.A. Costello, Inc. Herndon, Virginia and Staff of Bird Engineering Research Associates, Inc. Vienna, Virginia August 1981 Prepared for National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135 Under Contract DEN 3-195 for U.S. DEPARTMENT OF ENERGY Conservation and Renewable Energy Division of Solar Thermal Energy Systems Washington, D.C. 20545 Under Interagency Agreement DE-AI01-79ET20485 ACKNOWLEDGEMENT This handbook was prepared by MONEGON, LTD., of Gaithersburg, Maryland under Contract DEN3-195 with the National Aeronautics and Space Administration, Lewis Research Center. John B. Ruzek served as Project Engineer with management support by Dr. Harold L. Macomber. Valuable assistance was provided by two subcontractors, Frederick A. Costello, Inc., Consulting Engineers, and Bird Engineering-Research Associates, Inc. NOTE: Throughout this handbook, reference is made to Loss of Load Probability (LOLP) estimation procedures. According to the 1970 National Power Survey of the Federal Power Commission, these estimating procedures may be more correctly defined as Loss of Energy Probability (LOEP) procedures. This definitional difference in no way affects the accuracy or usefulness of these procedures. / CONTENTS Section Title Page 1 INTRODUCTION 1-1 2 GUIDE TO HANDBOOK USAGE 2-1 3 TYPICAL STAND-ALONE PHOTOVOLTAIC SYSTEM CONFIGURATIONS 3-1 4 COMPONENT DESIGN AND ENGINEERING INFORMATION 4-1 4.1 Electrical Loads 4-1 4.1.1 Estimating the Load 4-1 4.1.2 Load Reduction Strategies 4-4 4.1.3 Merits and Disadvantages of Both Ac and Dc Power 4-5 4.2 Photovoltaic Arrays 4-7 4.2.1 Photovoltaic Terminology 4-7 4.2.2 Ideal Solar-Cell Current-Voltage Characteristics 4-12 4.2.3 Current-Voltage Characteristics of Arrays in the Field 4-21 4.2.4 Available Modules 4-24 4.3 Lead-Acid Storage Batteries 4-27 4.3.1 Advantages and Disadvantages of Batteries in Photovoltaic Systems 4-27 4.3.2 Battery Operation 4-28 4.3.3 Battery Current/Voltage Characteristics 4-28 4.3.4 Battery-System Design 4-32 4.3.5 Battery Life 4-33 4.3.6 Lead-Acid Storage Battery Safety 4-36 4.4 Power Handling 4-40 4.4.1 Dc Power Conditioning 4-40 4.4.2 Control Schemes 4-43 4.4.3 Electrical Wiring 4-46 4.5 Emergency Backup Systems 4-51 4.5.1 Load Analysis 4-51 4.5.2 Basic PVPS Design Margin 4-52 4.5.3 Types and Suitability of Backup Systems 4-53 4.5.4 Incorporation of Backup Into the PV System 4-56 iii CONTENTS (Continued) Section Title Page 5 INFORMATION NEEDED TO START THE DESIGN PROCESS 5-1 6 PRELIMINARY SYSTEM DESIGN CONSIDERATIONS 6-1 6.1 Insolation and Siting 6-1 6.2 Operation of PV Systems Under Varying Loads 6-7 6.2.1 Array and Battery Quick-Sizing Method 6-7 6.2.2 Component Sizing 6-9 6.3 Basic Approach to Feasibility Assessment of Photovoltaic Power Systems 6-13 6.3.1 Preliminary Estimate 6-13 6.3.2 Life Cycle Cost Determination 6-15 6.4 Reliability Engineering Approach 6-18 6.4.1 Definition and Specification of PV System R & M Requirements 6-18 6.4.2 R & M Networks and Block Diagrams 6-24 6.4.3 Reliability Prediction and Feasibility Requirements 6-29 6.4.4 Failure Mode and Effects Analysis 6-30 6.5 Advantages and Disadvantages of PV Power Systems 6-34 7 SYSTEM DESIGN 7-1 7.1 Design Philosophy 7-1 7.2 System Design Procedure 7-2 7.3 Codes and Standards 7-15 7.3.1 Codes 7-15 7.3.2 Standards 7-16 7.3.3 Manuals 7-17 7.3.4 Approved Equipment Listings 7-17 7.3.5 Notes 7-18 7.3.6 Applicable Document List 7-18 7 iv CONTENTS (Continued) Section Title Page 8 INSTALLATIONS, OPERATION AND MAINTENANCE 8-1 8.1 Introduction 8-1 8.2 Power Outages 8-1 8.3 Reliability and Maintainability 8-2 8.4 Operation and Maintenance Tradeoffs 8-3 8.4.1 Operation and Preventive Maintenance 8-3 8.4.2 Corrective Maintenance 8-5 8.5 System Maintenance 8-8 8.5.1 Maintenance Concept 8-8 8.5.2 Maintainability Design 8-9 8.6 Logistics Design 8-11 8.6.1 Supply Support 8-11 8.6.2 Power System Drawings 8-13 8.6.3 Tools, Test Equipment, and Maintenance Aids 8-13 8.6.4 Technical Mannuals 8-14 8.6.5 Training 8-15 8.7 Installation Design Considerations 8-15 8.7.1 Physical Considerations 8-15 8.7.2 Equipment Housing and Structure Considerations 8-16 8.7.3 Installation Checkout and Acceptance Testing 8-16 9 SITE SAFETY 9-1 9.1 Personnel Safety Checklist 9-1 9.1.1 Safety & Health Standards 9-1 9.1.2 Electric Shock 9-2 9.1.3 Toxic &-Flammable Materials 9-2 9.1.4 Fire Safety 9-2 9.1.5 Excessive Surface Temperatures 9-3 9.1.6 Equipment Identification Labeling 9-3 9.1.7 Physical Barriers 9-3 V CONTENTS (Continued) Section Title Page 9.2 Facility Safety Checklist 9-4 9.2.1 PVPS Safety Protection from Environmental Conditions 9-4 9.2.2 PVPS Safety Protection from Man-Made Conditions 9-5 9.2.3 PVPS Safety Protection from Component Failure 9-6 9.3 References 9-6 10 DESIGN EXAMPLES 10-1 10.1 Remote Multiple-Load Application 10-i 10.1.1 Northern Hemisphere Location 10-1 10.1.2 Southern Hemisphere Location 10-2 11 INSOLATION 11-1 11.1 Introduction II-I 11.2 Insolation Calculation Programs 11-5 11.3 Statistical Insolation Computations 11-13 11.4 Sun Angle Charts 11-15 11.5 Row-to-Row Shading 11-15 12 PHOTOVOLTAIC SYSTEM COMPONENTS 12-1 12.1 Solar Cell Modules 12-1 12.2 Batteries 12-7 12.3 Dc Regulators 12-9 12.4 Dc Motors 12-10 13 GLOSSARY OF TERMS 13-1 13.1 Definitions of Photovoltaic Terminology 13-1 13.2 Conversion Factors 13-3 14 PHOTOVOLTAIC POWER SYSTEM EQUIPMENT SUPPLIERS 14-1 14.1 Photovoltaic Cells, Modules 14-1 14.2 Batteries 14-2 14.3 Power Conditioning Equipment 14-3 14.4 Direct Current Motor-, and Load Devices 14-5 vi CONTENTS (Continued) Section Title Page APPENDIX A WORLDWIDE INSOLATION DATA A-1 APPENDIX B FAILURE RATES FOR RELIABILITY ESTIMATION B-i B.I Failure-Rate Trends B-i B.2 Sources of Failure-Rate Data B-2 B.3 Estimated Failure Rates for Certain Items in the Typical PV System B-3 APPENDIX C LISTING OF SPONSORS OF CODES AND STANDARDS C-i C.I List of Codes and Standards Agencies and Their Addresses C-I C.2 Listing of Codes and Standards by Agencies C-2 REFERENCES R-I ERRATA SHEET o InExhibit 11.2-4, "Listing of an HP-67 Insolation Computation Program", corrections shown parentheticallY in the following tabulation of affected steps should be made: Step No. Key Strokes Key ode 001 f LBLA (31) 25 11 043 g x (>) Y 31 (63) 110 f cos 35 73 138 hT (35) 73 152 hT (35) 22 200 h RTN (35) 22 o In Exi~bit 11.2-3. ~~pagraph 4 ("Example"), the tilt angle should be 30 instead of 20 . The paragraph which follows is also numbered "4" and !,huld be changed to "V". V1 EXHIBITS Exhibit Page 2-1 Flow Chart, Photovoltaic Stand-Alone Systems Preliminary Engineering Design Handbook 2-2 3-1 Generalized Stand-Alone Direct Current Photovoltaic Power System Block Diagram 3-2 4.1-1 Load Diversity 4-3 4.1-2 Load-Reduction Strategies 4-4 4.1-3 Disadvantages of Dc and Ac 4-6 4.2-1 Terminology for Large-Scale Photovoltaic Installations 4-8 4.2-2 Series/Parallel Circuit Nomenclature 4-10 4.2-3 Module Output and Intermediate Loss Mechanisms 4-11 4.2-4 Operation of a Solar Cell 4-13 4.2-5 Equivalent Circuit of a Solar Cell 4-15 4.2-6 Typical Array Characteristics 4-16 4.2-7 Current-11oltage Characteristics of Cells in Series and Parallel 4-18 4.2-8 Protection From Open Circuit Failures 4-20 4.2-9 Array Power Loss Fraction Vs. Substring Failure Density 4-23 4.2-10 Typical Available Silicon Solar Modules 4-25 4.2-11 Nominal Array Costs (1975 Cost Levels) 4-26 4.3-1 Characteristics Summary Table: Commercially Available Batteries 4-29 4.3-2 Lead-Acid Battery Characteristic Curves 4-30 4.3-3 Lead-Acid Battery Failure Mechanisms 4-34 4.3-4 Typical Battery State of Charge (SOC) History 4-35 viii EXHIBITS (Continued) Exhibit Page 4.4-1 Self-Regulated PV System 4-42 4.4-2 I-V Curve of PV Module Exhibiting Self-Regulation 4-42 4.4-3 Voltage-Regulated PV System 4-42 4.4-4 Simplified Block Diagram For a Maximum Power Tracking Controller 4-45 4.5-1 Summary Descriptions of Backup Systems 4-55 5-1 Minimum Data Requirements to Establish Feasibility 5-2 5-2 General Checklist for Detailed Design 5-3 6.1-1 Average Monthly Insolation (kWh/m2-day) and the Ratio of Standard Deviation (Sigma 1) to Average 6-3 6.1-2 Horiz-n Profiles for Two Candidate Sites 6-6 6.2-1 Quick Sizing Computational Procedure for Array and Storage 6-10 6.2-2 Battery Storage Requirements for 1% LOLP 6-11 6.2-3 Effect of Depth of Discharge on Battery Life on Typical Lead-Acid Motive Power Type Cell 6-12 6.3-1 Components, System Costs and Ecooomic Parameters 6-16 6.3-2 Photovoltaic Power System Preliminary Design Life Cycle Cost Computation 6-17 6.4-1 Reliability Functions for Exponential (Random) and Gaussian (Wearout) Facilities 6-19 6.4-2 Partial Description of Requirements for Hypothetical Customer Application 6-22 6.4-3 Example Reliability Allocation for a Hypothetical System 6-23 6.4-4 Functional Rleliability Block Diagram 6-25 6.4-5 Functional Oriented lieliability Block Diagram 6-25 6.4-6 Optional Module Configurations: (A) Series: (B) S !'ci I6-26 EXHIBITS (Continued) Exhibit Page 7.2-1 Loss-cf-Load Probability Computational Procedure 7-3 7.2-2 Cumulative Distribution Function for the Normal Curve 7-4 7.2-3 Example of Loss-of-Load Probability Computation 7-7 7.2-4 Listing of a TI-59 Program for Calculating Loss-of-Load Probability 7-8 7.2-5 Instructions for the Operation of the TI-59 Program for Computing the Loss-of-Load Probability 7-9 7.2-6 Listing of an HP-67 Program for Calculating Loss-of-Load Probability 7-10 7.2-7 Instructions for the Use of the HP-67 Program for Calculating Loss-of-Load Probability 7-13 7.2-8 Typical Cases for the Loss-of-Load Probability 7-14 8.2-1 Causes of Power Loss in PV Systems 8-1 8.4-1 Reliability Improvement with Standby Redundancy 8-7 10.1-1 Multiple Load Application Monthly Load Summary 10-3 10.1-2 Multiple Load Application Equipment Sizing 10-4 11.1-1 Insolation Computation for a South-Facing Array 11-2 11.1-2 Insolation Computation Example: Washington, D.C. 11-3 11.1-3 Ground Reflectances for Various Surfaces 11-4 11.2-1 Instructions for Operating the TI-59 Insolation Computation Program 11-6 11.2-2 Listing of a TI-59 Insolation Computation Program 11-7 11.2-3 Instruetions for Operating the I-IP-67 Insolation Computation Program 11-9 11.2-4 Listing of an IIP-67 Insolation Computation Program 11-10 11.3-1 Generalized KH Distribution Curves 11-14 x