Handbook of Concentrator Photovoltaic Technology

Carlos Algora received his B.Sc. degree in Physics in 1986 and his PhD in Physics in 1990, both from the Universidad Complutense de Madrid. He joined the Solar Energy Institute of the Technical University of Madrid in 1985 where he became Associate Professor in 1991 and a Full Professor in 2008. Since 1996 he has been the head of the III-V Semiconductors Group, which is devoted to the modelling, technology, characterization and reliability of III-V solar cells. Together with his team he has helped to develop several World efficiency record concentrator cells. He has been the main researcher of more than 40 R&D projects, has published more 230 scientific papers and has authored several book chapters. Ignacio Rey-Stolle is an Associate Professor at the Solar Energy Institute of the Technical University of Madrid, where he obtained his PhD in 2001. During his scientific career he has accumulated more than 17 years working in the field of high efficiency concentrator solar cells, during which he has contributed to several efficiency records. His research activities encompass the whole life cycle of concentrator solar cells, including design and simulation, epitaxial growth, fabrication, characterization and reliability studies. Ignacio Rey-Stolle has co-authored more than 100 scientific papers, three book chapters and one patent.

List of Contributors xix Preface xxiii 1 Direct Normal Radiation 1 Daryl R. Myers 1.1 Concepts and Definitions 1 1.1.1 Orbital and Geometrical Considerations 1 1.1.2 The Solar Constant 2 1.1.3 Temporal Variations in Extraterrestrial Radiation (ETR) 3 1.1.4 Extraterrestrial Radiation Spectral Power Distribution 4 1.1.5 The Atmospheric Filter 6 1.2 Measuring Broadband Direct Solar Radiation 8 1.2.1 Pyrheliometers 8 1.2.2 Rotating Shadow Band Radiometers 11 1.2.3 Reference Standards, the World Radiometric Reference (WRR) 13 1.2.4 Calibration of Pyrheliometers 16 1.2.5 Accuracy and Uncertainty 17 1.2.6 Summary of Guide to Uncertainty in Measurement (GUM) Approach 18 1.2.7 Measurement Data Quality 20 1.3 Modeling Broadband Direct Solar Radiation 21 1.3.1 Models for Direct Beam Irradiance 21 1.3.2 Atmospheric Component Transmittance 22 1.3.3 Estimating Direct Beam Radiation from Hemispherical Data 25 1.4 Modeling Spectral Distributions 26 1.4.1 Bird Simple Spectral Model (SPCTRL2) 27 1.4.2 Simple Model for Atmospheric Transmission of Sunshine (SMARTS) 28 1.4.3 Spectral Distributions from Broadband Data 28 1.5 Resources for Broadband Estimates of CPV Performance 29 1.5.1 Broadband Direct Beam Radiation Data Resources 29 1.5.2 Typical Meteorological Year Data for CPV Performance Estimates 31 1.5.3 CPV Spectral Performance Issues 33 1.6 Sunshape 33 1.6.1 The Solar Disk 33 1.6.2 Circumsolar Radiation 36 1.6.3 Recent Circumsolar Radiation Research 39 1.7 Direct Solar Radiation Climates 40 1.7.1 Measurement Networks and Data 41 1.7.2 Concentrating Solar Power Site Selection 41 1.7.3 Concentrating Solar Power Resource Map Examples 43 1.7.4 Solar Resource Maps and Data Internet Resources 47 1.8 Consensus Standards for Direct Solar Radiation Applications 48 1.8.1 World Radiometric Reference 48 1.8.2 Solar Radiometric Instrumentation Calibration 48 1.8.3 Spectral Calibration Standards 49 1.8.4 Standard and Reference Spectral Distributions 49 Glossary 50 List of Acronyms 50 List of Symbols 51 References 53 2 Concentrator Multijunction Solar Cells 59 Ignacio Rey-Stolle, Jerry M. Olson, and Carlos Algora 2.1 Introduction 59 2.2 Fundamentals 60 2.2.1 Fundamentals of Photovoltaic Cells 60 2.2.2 Fundamentals of Multijunction Solar Cells 63 2.3 Multijunction Solar Cell Structures 67 2.3.1 Historical Development of Multijunction PV Converters 68 2.3.2 Designing Multijunction Solar Cell Structures 73 2.4 Multijunction Solar Cell Modeling 79 2.4.1 Numerical Modeling of Multijunction Solar Cell Structures 79 2.4.2 Analytical Modeling of Multijunction Solar Cells 81 2.4.3 Further Steps: Distributed Circuit-based Modeling 98 2.5 Concentrator Requirements 103 2.5.1 High Efficiency 103 2.5.2 Series Resistance. Grid Designs 107 2.5.3 Tunnel Junctions 110 2.5.4 Distributed Effects 113 2.5.5 Atmospheric Spectral Variations and Impact on Energy Yield 116 2.5.6 Temperature Effects 118 2.6 Description of Different Cell Approaches 118 2.6.1 Lattice-matched GaInP/GaAs/Ge 118 2.6.2 Metamorphic GaInP/GaInAs/Ge 119 2.6.3 Inverted Metamorphic GaInP/GaAs/GaInAs 120 2.6.4 Double Sided Epi 122 2.6.5 Lattice Matched GaInP/GaAs/GaInNAs 122 2.6.6 Quantum Dot and Quantum Well Multijunction Solar Cells 123 2.6.7 More Junctions (4, 5, 6) 123 2.6.8 Stacked Multijunction Cells 124 2.6.9 III-Vs on Silicon 124 2.6.10 Epitaxial Liftoff 126 Acknowledgements 127 Glossary 127 List of Acronyms 127 List of Symbols 127 References 129 3 Emerging High Efficiency Concepts for Concentrator Solar Cells 137 Ignacio Tobias and Antonio Luque 3.1 Introduction 137 3.2 Thermodynamic Efficiency Limits 138 3.2.1 Disequilibria and Energy Conversion in Solar Cells 140 3.2.2 Thermodynamic Efficiencies 142 3.3 Detailed Balance Modeling of Solar Cells 143 3.3.1 Shockley Queisser Model of a Solar Cell 144 3.3.2 The System with Infinite Monochromatic Solar Cells 146 3.4 Solar Cell Concepts Exceeding the Single Junction Shockley Queisser Limit 148 3.4.1 Multijunction Solar Cells 148 3.4.2 Hot Carrier Solar Cells 149 3.4.3 Carrier Multiplication or Multi-Exciton Generation Solar Cells 152 3.4.4 Intermediate Band Solar Cells 155 3.5 Other Concepts 159 3.5.1 Light Management for High Efficiency Photovoltaics 160 3.5.2 Spectrum Conversion 161 3.6 Nanostructures in Solar Cells 162 3.6.1 Electron States in Nanostructures 162 3.6.2 Light Absorption by Nanostructures 173 3.6.3 Relaxation, Capture and Recombination in Nanostructures 176 3.6.4 Nanostructures for Multijunction Solar Cells 177 3.6.5 Fabrication Techniques 178 Glossary 179 List of Acronyms 179 References 179 4 CPV Optics 187 Ruben Mohedano and Ralf Leutz 4.1 Introduction 187 4.2 Light, Optics and Concentration 188 4.2.1 Light and Optics 189 4.2.2 Optics for Concentration Photovoltaics 190 4.3 Optical Background 192 4.3.1 Basic Concepts in Geometrical Optics 192 4.3.2 Basic Concepts in Nonimaging Optics 196 4.4 Design of the Optical Train: Calculation of Surfaces 202 4.4.1 Types of Concentrators as a Function of Concentration Level 203 4.4.2 Design Examples 204 4.4.3 Secondary Optical Elements: Design Details 210 4.5 Performance Analysis and Optimization of the Optical Train 213 4.5.1 Efficiency. Sources of Losses 215 4.5.2 Ray Trace Modeling 220 4.6 Optics Manufacturing 224 4.6.1 Optical Materials for CPV 224 4.6.2 Tolerance Budget 226 4.6.3 Manufacturing of Primary Optical Elements 227 4.6.4 Manufacturing of Secondary Optic Elements 231 4.7 Impact of CPV Optics in a Nutshell 232 Glossary 233 List of Acronyms 233 List of Symbols 234 References 235 Annex 4-I: Etendue Calculation 239 Annex 4-II: 2D Treatment of Rotational and Linear 3D Optical Systems 241 Annex 4-III: Design of the XR Concentrator 242 5 Temperature Effects on CPV Solar Cells, Optics and Modules 245 Ivan Garcia, Marta Victoria, and Ignacio Anton 5.1 Introduction 245 5.2 Effects of Temperature on CPV Solar Cells 246 5.2.1 Dependence of the Bandgap on Temperature 246 5.2.2 Dependence of the Solar Cell Parameters on Temperature 248 5.2.3 Influence of Concentration on the Sensitivity to Temperature 260 5.2.4 Experimental Measurements on Real Solar Cells 261 5.2.5 Summary of Temperature Effects in CPV Multijunction Solar Cells 264 5.3 Temperature Effects and Thermal Management in CPV Optics and Modules 266 5.3.1 Temperature Effects on CPV Optics and Modules 266 5.3.2 Thermal Coefficients of CPV Modules 270 5.3.3 Heat Extraction Strategies 274 Glossary 286 List of Acronyms 286 List of Symbols 286 References 287 6 CPV Tracking and Trackers 293 Ignacio Luque-Heredia, Pedro Magalhaes, and Matthew Muller 6.1 Introduction 293 6.2 Requirements and Specifications 294 6.3 Basic Taxonomy of CPV Trackers 297 6.4 Design of CPV Trackers Structural Considerations 300 6.5 Sun Tracking Control 307 6.5.1 Background 307 6.5.2 The Autocalibrated Sun Tracking Control Unit 311 6.6 Sun Tracking Accuracy 315 6.6.1 The Tracking Accuracy Sensor 315 6.6.2 The Monitoring System 316 6.6.3 Accuracy Assessment: Example of the Autocalibrated Tracking Strategy 318 6.7 Designing for Optimal Manufacturing and Field Works 322 6.7.1 Manufacturing Considerations 322 6.7.2 Field Works Considerations 324 6.8 Description and Performance of Current Tracker Approaches 327 6.8.1 Parabolic Trough 327 6.8.2 Single-Pole Az.-El. Trackers 328 6.8.3 Tilt-Roll Trackers 330 6.8.4 Carrousel Trackers 331 6.8.5 Variations to Main Architectures in the Field 332 6.9 International Standards for Solar Trackers 334 References 337 7 CPV Modules 339 Stephen Askins and Gabriel Sala Pano 7.1 Introduction 339 7.2 What is a CPV Module? 339 7.3 Definition, Functions, and Structure of a CPV Module 341 7.3.1 Functions of a CPV Module 342 7.3.2 General Terms and Definitions 343 7.3.3 Structure of a CPV Module 343 7.4 Design Process and Prototyping Stages 349 7.5 Concentration Ratio and Cell Size 353 7.5.1 Concentration Ratio 353 7.5.2 Cell Size Selection 353 7.5.3 Module Size and Length 356 7.5.4 Market Survey 357 7.6 Opto-Mechanics of CPV Modules 359 7.6.1 Acceptance Angle 359 7.6.2 Acceptance Angle Budget 361 7.6.3 External Tolerances 362 7.6.4 Internal Tolerances 363 7.7 Electrical Design 372 7.7.1 Module Voltages and Dielectric Strength 372 7.7.2 Series Connections and Bypass Diodes 373 7.7.3 Parallel Connections and Blocking Diodes 374 7.8 Thermal Design 375 7.8.1 Target Cell Temperature 376 7.8.2 Simplified Thermal Model 377 7.9 Venting Considerations 389 7.10 Manufacturing Processes for CPV Modules 390 7.10.1 Chassis and Backplane Fabrication 390 7.10.2 Heat Sink Fabrication 395 7.10.3 Module Assembly 398 7.11 Standards Applicable to CPV Modules 399 Glossary 401 References 403 Annex 7-I: Abengoa s CPV Modules and Systems 406 Jose A. Perez, Sebastian Caparros, Justo Albarran, and Antonio de Dios Annex 7-II: CPV Modules and Systems from Daido Steel 413 Kenji Araki Annex 7-III: Soitec CPV Modules and Systems 419 Francisca Rubio, Sven T. Wanka, and Andreas Gombert Annex 7-IV: Suncore Photovoltaics CPV Modules 426 James Foresi 8 CPV Power Plants 433 Maria Martinez, Daniel Sanchez, Francisca Rubio, Eduardo F. Fernandez, Florencia Almonacid, Norman Abela, Tobias Zech, and Tobias Gerstmaier 8.1 Introduction 433 8.2 Construction of CPV Plants 434 8.2.1 Preliminary Works 434 8.2.2 Basic Engineering Study 436 8.2.3 Detailed Engineering 437 8.2.4 Construction Phase 440 8.3 CPV Inverters: Configurations and Sizing 445 8.3.1 Types of Configurations 446 8.3.2 Sizing of the Inverter 448 8.4 Optimized Distribution of Trackers 450 8.4.1 State of the Art 451 8.4.2 Procedure for Optimizing the Distribution of Trackers 452 8.5 Considerations of Environmental Impact and Dual Use of the Land 456 8.6 CPV Plant Monitoring and Production Data Analysis 458 8.6.1 Monitoring System: Registering the Operating Parameters 459 8.6.2 Monitoring System: Controlling a CPV Plant 460 8.6.3 Analysis of Production Data 461 8.7 Operation and Maintenance 464 8.7.1 Operation 465 8.7.2 Maintenance 467 8.8 Power Rating of a CPV Plant 470 8.8.1 ISFOC Approach 470 8.8.2 International ASTM Standards 471 8.8.3 International IEC Standards 472 8.9 Modeling the Energy Production of CPV Power Plants 477 8.9.1 Basic Models 477 8.9.2 Input Data and Quality Checks 478 8.9.3 Loss Mechanisms 479 Glossary 484 List of Acronyms 484 List of Symbols 485 References 486 Annex 8-I: Software Tools for CPV Plant Design and Analysis 491 Annex 8-II: CPV Power Plants at ISFOC 501 Maria Martinez, Daniel Sanchez, Oscar de la Rubia, and Francisca Rubio Annex 8-III: Soitec Power Plants 513 Andreas Gombert, Norman Abela, Tobias Gerstmeier, Shelley Bambrook, and Francisca Rubio 9 Reliability 521 Carlos Algora, Pilar Espinet-Gonzalez, Manuel Vazquez, Nick Bosco, David Miller, Sarah Kurtz, Francisca Rubio, and Robert McConnell 9.1 Introduction 521 9.2 Fundamentals of Reliability 521 9.2.1 Reliability Functions 522 9.2.2 Statistical Distribution Functions 524 9.2.3 Accelerated Life Tests 529 9.2.4 Reliability Versus Qualification 532 9.3 Reliability of Solar Cells 533 9.3.1 Issues in Accelerated Aging Tests in CPV Solar Cells 533 9.3.2 Types of Failure 538 9.3.3 Failures in Real Time Operation 539 9.3.4 Accelerated Life Tests 539 9.3.5 Reliability of Similar Devices 546 9.3.6 Links Among Degradation Studies, Reliability and Qualification Standards 548 9.4 Reliability of Modules 549 9.4.1 Introduction 549 9.4.2 Die-attach 549 9.4.3 CPV Encapsulation 552 9.4.4 CPV Optics 555 9.4.5 Other CPV Module Reliability Issues 562 9.5 Reliability of Systems and Plants 562 9.5.1 Performance Degradation in Power Plants 563 9.5.2 Failures of Components 568 9.5.3 Qualification Tests on Power Plants Components 572 9.5.4 Aging Tests 575 9.6 Standards Development for CPV 577 9.6.1 Standards as the Mark of a Mature Industry 577 9.6.2 History of CPV Standards Development 577 Acknowledgement 582 References 582 10 CPV Multijunction Solar Cell Characterization 589 Carl R. Osterwald and Gerald Siefer 10.1 Introduction 589 10.2 Basic Concepts About Multijunction Solar Cells for Characterization Purposes 590 10.2.1 Review of Multijunction Solar Cell Theory 590 10.2.2 Definition of CPV Cell Efficiency 592 10.2.3 Current-Voltage as a Function of Concentration 593 10.3 Spectral Matching and Adjustment 594 10.3.1 Isotype Method 594 10.3.2 Reference Cell Method 594 10.3.3 Rij Method and Linear Equation System Method 595 10.3.4 Effects of Subcell Mismatching 597 10.4 Flash Solar Simulators: Description and Limitations 600 10.4.1 Sources and Optics 600 10.4.2 Adjusting Total Intensity 600 10.4.3 Irradiance Versus Time 600 10.4.4 Spectral Irradiance Adjustment 601 10.4.5 Spectral Irradiance Measurement 602 10.5 Concentrator Solar Cell Characterization 603 10.5.1 Overview 603 10.5.2 Area Measurement 603 10.5.3 External Quantum Efficiency 604 10.5.4 One-Sun Light I-V and One-Sun Short Circuit Current Calibration 607 10.5.5 Concentration I-V 608 10.5.6 Uncertainty Analysis 608 10.5.7 Open Challenges 610 Acknowledgments 611 Glossary 611 List of Acronyms 611 List of Symbols 611 References 612 11 Characterization of Optics for Concentrator Photovoltaics 615 Maikel Hernandez 11.1 Introduction 615 11.2 Geometrical Characterization 616 11.2.1 Faceted Optics 617 11.2.2 Non-faceted Optics 620 11.3 Optical Characterization 624 11.3.1 Measurement of the Optical Efficiency 624 11.3.2 POE Scattering Basic Measurements 628 11.3.3 Acceptance Angle Measurement 629 11.3.4 Spectral Irradiance Distribution Measurement at the Solar Cell Plane 633 11.3.5 Angular Power Distribution at the Solar Cell Plane 634 11.3.6 In-line Characterization of Optics in Production 634 Glossary 636 List of Acronyms 636 List of Symbols 636 References 637 12 Characterization of CPV Modules and Receivers 639 Cesar Dominguez, Rebeca Herrero, and Ignacio Anton 12.1 Introduction 639 12.2 Figures of Merit of PV Concentrators 640 12.2.1 Reporting CPV Module Performance 640 12.2.2 Performance Indicators for Concentrator Optics 642 12.3 Instruments and Methods for CPV Characterization 643 12.3.1 Indoors versus Outdoors 643 12.3.2 Operating Conditions Relevant to CPV 644 12.3.3 Tracker Requirements 650 12.3.4 Alignment Procedures 651 12.3.5 Rating CPV Module Performance 652 12.3.6 Spectral Characterization of CPV Modules and Receivers 656 12.3.7 Angular Transmission Curve 660 12.3.8 Uncertainties of Instruments and Methods for CPV Characterization 662 12.4 Indoor Measurements of CPV Modules 663 12.4.1 Solar Simulators for CPV Modules 663 12.4.2 Reference Sensor 668 12.4.3 Caveats on Indoor Measurements 672 12.4.4 Angular Transmission Curve: Direct and Inverse Methods 674 12.4.5 Uncertainties in the Indoor Measurement of I-V Curves 678 Glossary 678 List of Acronyms 678 List of Symbols 678 References 679 13 Life Cycle Analysis of CPV Systems 685 Vasilis Fthenakis 13.1 Introduction 685 13.2 Case Study Description 686 13.3 Methodology 687 13.4 Life-Cycle Inventory Analysis 688 13.4.1 Production of Materials and Associated Emissions 688 13.4.2 Solar Cell Manufacturing 690 13.4.3 Primary Energy Demand 692 13.4.4 End-of-Life Processing 693 13.5 System Performance Data and Estimates 694 13.6 Energy Payback Time 695 13.7 Greenhouse and Toxic Gas Emissions 696 13.7.1 Emissions in the Life-Cycle of Amonix 7700 696 13.7.2 Reduction of Emissions from PV Replacing Electricity from the Grid 697 13.8 Land and Water Use in CPV Systems 699 13.9 Discussion and Comparison with Other CPV and PV Systems 700 13.9.1 Comparison with Other CPV Systems 700 13.9.2 Comparison with Other PV Systems 701 Glossary 702 List of Acronyms 702 List of Symbols 702 References 703 Annex 13-I: Energy Flow Diagrams for Amonix 7700 System Components 705 14 Cost Analysis 711 Carlos Algora, Diego L. Talavera, and Gustavo Nofuentes 14.1 Introduction 711 14.2 Basic Concepts of Cost and Profitability Analysis 711 14.2.1 Elements of the Investment 712 14.2.2 Present and Future Worth of Sums. The Impact of Inflation 712 14.2.3 The Discount Rate 713 14.2.4 Effect of Inflation 713 14.2.5 Impact of Taxation 714 14.2.6 Financing 714 14.3 Review of Profitability Analysis 715 14.3.1 The Life Cycle Cost of a CPV System 715 14.3.2 The Present Worth of the Cash Inflows Generated by a CPV System 717 14.3.3 Assessment of the Profitability of a CPV System 718 14.3.4 Sensitivity Analysis on the Profitability of CPV Systems 720 14.4 The Cost of CPV 728 14.4.1 The Cost of CPV Systems 728 14.4.2 Levelized Cost of Electricity (LCOE) of CPV 735 14.4.3 Towards the CPV Grid Parity 746 Glossary 754 References 756 Index 759