Indoor Photovoltaics Materials, Modeling, and Applications

This is the first and most comprehensive guide on the modeling, engineering and reliable design of indoor photovoltaics which currently is the most promising and energy efficient power supply for edge nodes for the Internet of Things and other indoor devices.

Indoor photovoltaics (IPV) has grown in importance over recent years. This can in part be attributed to the creation of the Internet of Things (IoT) and Artificial Intelligence (AI) along with the vast amounts of data being processed in the field, which has been a massive accelerator for this development. Moreover, since energy conservation is being imposed as the national strategy of many countries and is being set as a top priority throughout the world, understanding and promoting IPV as the most promising indoor energy harvesting source is considered by many to be essential these days.

The book provides the engineer and researcher with guidelines, and presents a comprehensive overview of theoretical models, efficiencies, and application design. This unique and groundbreaking book has chapters by leading researchers on:

• Introduction to micro energy harvesting
• Introduction to indoor photovoltaics
• Modeling indoor irradiance
• Characterization and power measurement of IPV cells
• Luminescent solar concentrators
• Organic photovoltaic cells and modules for applications under indoor lighting conditions
• High-efficiency indoor photovoltaic energy harvesting
• Indoor photovoltaics based on ALGAAs alloys

Monika Freunek Müller studied Mechatronic and Product Engineering at the Universities of Applied Sciences of Bielefeld and Furtwangen, Germany from 2002-2006. After graduation and postdoctoral research at IBM Research Zurich, she worked as a researcher and co-founder of a start-up. Monika Freunek is now at BKW, Switzerland, as an energy specialist. Her main focus in research is modeling of energy and photovoltaic systems under different application conditions. She is an expert in indoor photovoltaics.

Preface xi

1 Will Photovoltaics Stay Out of the Shadows? 1
Joseph A. Paradiso

1.1 Introduction 1

References 6

2 Introduction to Micro Energy Harvesting 9
Monika Freunek (Müller)

2.1 Introduction and History 9

2.1.1 Brief History of Electric Generators and Loads 10

2.1.2 Forms of Energies and Energy Converters 10

2.2 Kinetic Energy 11

2.2.1 Oscillating Solid Objects 12

2.2.1.1 Human Motion 13

2.2.1.2 Vibrations 13

2.2.1.3 Flow of Gas and Fluids 14

2.2.1.4 Acoustic Vibrations 15

2.2.1.5 Elastic Energy 16

2.3 Thermoelectric Conversion 16

2.4 Electrochemical Potential 18

2.5 Electromagnetic Transmission 19

2.6 Atomic Batteries 19

2.7 Challenges 20

2.8 Conclusions and Outlook 20

Acknowledgment 21

References 21

3 Introduction to Indoor Photovoltaics 25
Monika Freunek (Müller)

3.1 Introduction 25

3.2 Indoor Spectra and Efficiencies 28

3.3 State of IPV Design, Issues, Approaches 31

3.4 Fields of Application 32

3.4.1 Customer and Office Applications 32

3.4.2 Ambient Assisted Living and Building Automatization 32

3.4.3 Industry, Agriculture, Horticulture, Retail, and Logistics 33

3.4.4 Relation of IPV to Outdoor Applications – Hiking, Emergency Kits 34

3.5 Degradation and Lifetime Issues 34

3.6 Conclusions and Outlook 35

References 35

4 Modeling Indoor Irradiance 39
Monika Freunek (Müller)

4.1 Introduction 39

4.2 Fundamentals 40

4.2.1 Photometry and Its Impact on IPV 41

4.2.2 Comparison Measurements of Different Luxmeter Products and Settings 44

4.2.3 Conclusions for Indoor Irradiance Measurements 45

4.2.4 Available Data on Indoor Irradiance 45

4.3 Radiometric Solutions 47

4.3.1 Structure 47

4.3.2 Settings of the Studied Rooms 48

4.3.3 Investigated Installation Points 49

4.4 Analytical Model 52

4.4.1 Solar Radiation 52

4.4.2 Artifical Lighting 56

4.4.3 Interaction with Objects 60

4.4.4 Indirect Contributions of Solar Radiation 61

4.4.5 Final Results and Limits of Analytical Models 62

4.5 Simulations 62

4.5.1 Ray Tracing: Fundamental Principles 62

4.5.2 Radiance 64

4.5.3 DAYSIM 65

4.5.4 Calculation Methods and Parameters 66

4.5.5 Daylight Coefficient in DAYSIM 68

4.5.6 Environmental Parameters 69

4.5.7 Model Parameters 71

4.5.8 Results 73

4.5.9 Summary and Conclusion 85

4.6 Measurements 86

4.6.1 Available Measurement Methods 86

4.6.2 Long-Term Measurements Reference Year 89

4.6.3 Validating Simulation 94

4.6.4 Comparison Measurement Methods under Controlled Conditions 100

4.7 Discussion and Recommendation 103

4.8 Conclusion and Outlook 104

4.8.1 Autarky Factors 105

4.9 Acknowledgements 106

4.10 Symbols and Abbreviations 106

4.11 Constants 109

4.12 Abbreviations 109

Appendix 110

References 112

5 Characterization and Power Measurement of IPV Cells 115
Stefan Winter

5.1 Features of IPV Compared to Outdoor PV 115

5.1.1 Irradiance 116

5.1.2 Spectrum 116

5.1.2.1 Consequences of the Different Spectra Regarding Efficiency 117

5.1.3 Incident Angle Distribution 117

5.1.4 Modulated Light Sources 117

5.1.5 Further Effects 118

5.1.6 Standardization 118

5.2 Calibration Chain and Quality Management 119

5.2.1 Basic Laboratory Measurement Methods for the Secondary Calibration of IPV Cells 119

5.3 Flexible and Precise Method for Comprehensive and Primary Calibration of IPV Devices 122

5.3.1 Lamp-Based Facility 124

5.3.2 Laser-Based Facility 124

5.4 DSR Calibration of IPV Cells 128

5.4.1 Self-Referenced IV Characteristic 129

Acknowledgment 130

References 131

6 Luminescent Solar Concentrators 133
Evert P.J. Merkx and Erik van der Kolk

6.1 Introduction 134

6.2 A Crash Course in Luminescence 135

6.2.1 Luminescence in Organic Dyes 136

6.2.2 Luminescence in Rare Earth Ions 138

6.2.3 Luminescence in Quantum Dots 142

6.2.4 Hybrid Combinations 143

6.3 Principle of Operation 144

6.3.1 Absorption of Light 144

6.3.2 Emission within the LSC 145

6.3.3 Effects of Self-Absorption 146

6.3.4 Influence of the Waveguide 147

6.3.5 Conversion of Concentrated Light to Electricity 147

6.4 Calculating LSC Performance 148

6.4.1 Figures of Merit 148

6.4.2 Upper Bound for LSC Efficiency 149

6.4.3 Analytical Approach for Simple Geometries 152

6.4.4 Semi-Analytical Optimization Calculations for Arbitrary Geometries 153

6.4.5 Monte Carlo Simulations for Ray-Traced Complex Geometries 157

6.4.6 Considerations for Thin-Film LSCs 162

6.5 State-of-the-Art LSC Materials 163

6.5.1 Measures for the Visual Performance of LSC Materials 163

6.5.2 Evaluating the Performance of State-of-the-Art LSCs 165

6.5.3 Dye-Based Luminescent Solar Concentrators 167

6.5.4 Rare Earth-Based Luminescent Solar Concentrators 168

6.5.5 Quantum Dot and Doped Quantum Dot-Based Luminescent Solar Concentrators 169

6.6 Tm²⁺-Doped Halide Luminescent Solar Concentrators 174

6.7 LSC for an IPV Perspective 177

6.7.1 Performance Assessment 177

6.7.2 Application Examples 179

6.8 Conclusion 180

Acknowledgements 181

References 181

7 Organic Photovoltaic Cells and Modules for Applications under Indoor Lighting Conditions 189
Birger Zimmermann and Uli Würfel

7.1 Introduction 190

7.2 Implications of Indoor Lighting 192

7.3 OPV Modules 198

7.4 OPV Devices and Applications 201

7.5 Acceptance and Safety Considerations 202

References 203

8 High-Efficiency Indoor Photovoltaic Energy Harvesting 213
Matthias Kauer and Mathieu Bellanger

8.1 Introduction 214

8.2 Approaches for Efficient Indoor PV Energy Harvesting 216

8.2.1 PV Energy Harvesting Technologies 216

8.2.2 Commercial PV Energy Harvesting Devices 217

8.2.3 Recent Research Results for PV Energy Harvesting Devices 217

8.3 Lightricity’s PV Energy Harvesting Technology 221

8.3.1 Introduction 221

8.3.2 Energy Harvester Device Fabrication and Device Characteristics 222

8.4 High-Efficiency PV Energy Harvesting Power Supplies 225

8.4.1 Introduction 225

8.4.2 Energy Harvesting Power Management Solutions 226

8.4.3 System Integration and Performance Testing 230

8.5 Applications of Light Indoor Energy Harvesting 233

8.5.1 Watches and Wearable Devices 233

8.5.2 Wireless Building Automation Sensors 233

8.5.3 Wireless Beacons 236

8.6 Summary and Concluding Remarks 237

Acknowledgments 238

References 238

9 Indoor Photovoltaics Based on AlGaAs 241
Jamie Phillips, Eunseong Moon and Alan Teran

9.1 Importance of AlGaAs for Indoor Photovoltaics 242

9.2 Design Consideration for AlGaAs III-V Photovoltaic Cells 245

9.2.1 Base/Absorber 246

9.2.2 Contact 247

9.2.3 Window 248

9.2.4 Emitter 248

9.2.5 Back Surface Field 248

9.3 Large-Area AlGaAs III-V Photovoltaics 249

9.4 Small-Area AlGaAs Photovoltaics 252

9.4.1 Model of J-V Characteristics 254

9.4.2 Performance of mm-Scale AlGaAs Photovoltaics 257

9.4.3 Dark Current Limitations 260

9.5 Monolithic GaAs PV Cell Arrays 262

9.6 Conclusion 267

References 268

Index 273

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