Konrad Mertens, PhD, is Professor at Münster University of Applied Sciences, Germany, where he covers the subjects of photovoltaics, sensor technology, and optoelectronics. He is also the founder and head of the university's photovoltaic test lab and head of the lab of sensor technology and optoelectronics.

Preface to the First International Edition xv

Preface to the Second International Edition xvii

Abbreviations xix

1 Introduction 1

1.1 Introduction 1

1.1.1 Why Photovoltaics? 1

1.1.2 Who Should Read This Book? 2

1.1.3 Structure of the Book 2

1.2 What Is Energy? 3

1.2.1 De¿nition of Energy 3

1.2.2 Units of Energy 4

1.2.3 Primary, Secondary, and End Energy 5

1.2.4 Energy Content of Various Substances 6

1.3 Problems with Today's Energy Supply 7

1.3.1 Growing Energy Requirements 7

1.3.2 Tightening of Resources 8

1.3.3 Climate Change 9

1.3.4 Hazards and Disposal 11

1.4 Renewable Energies 11

1.4.1 The Family of Renewable Energies 11

1.4.2 Advantages and Disadvantages of Renewable Energies 12

1.4.3 Previous Development of Renewable Energies 13

1.5 Photovoltaics - The Most Important in Brief 13

1.5.1 What Does "Photovoltaics" Mean? 13

1.5.2 What Are Solar Cells and Solar Modules? 14

1.5.3 How Is a Typical Photovoltaic Plant Structured? 14

1.5.4 What Does a Photovoltaic Plant "Bring?" 15

1.6 History of Photovoltaics 16

1.6.1 How It all Began 16

1.6.2 The First Real Solar Cells 17

1.6.3 From Space to Earth 19

1.6.4 From Toy to Energy Source 20

2 Solar Radiation 23

2.1 Properties of Solar Radiation 23

2.1.1 Solar Constant 23

2.1.2 Spectrum of the Sun 23

2.1.3 Air Mass 25

2.2 Global Radiation 25

2.2.1 Origin of Global Radiation 25

2.2.2 Contributions of Di¿use and Direct Radiation 26

2.2.3 Global Radiation Maps 28

2.3 Calculation of the Position of the Sun 30

2.3.1 Declination of the Sun 30

2.3.2 Calculating the Path of the Sun 32

2.4 Radiation on Tilted Surfaces 35

2.4.1 Radiation Calculation with the Three-component Model 35

2.4.1.1 Direct Radiation 35

2.4.1.2 Di¿use Radiation 36

2.4.1.3 Re¿ected Radiation 37

2.4.2 Radiation Estimates with Diagrams and Tables 38

2.4.3 Yield Gain through Tracking 41

2.5 Radiation Availability and World Energy Consumption 41

2.5.1 The Solar Radiation Energy Cube 41

2.5.2 The Sahara Miracle 45

3 Fundamentals of Semiconductor Physics 47

3.1 Structure of a Semiconductor 47

3.1.1 Bohr's Atomic Model 47

3.1.2 Periodic Table of Elements 49

3.1.3 Structure of the Silicon Crystal 49

3.1.4 Compound Semiconductors 49

3.2 Band Model of a Semiconductor 51

3.2.1 Origin of Energy Bands 51

3.2.2 Di¿erences in Isolators, Semiconductors, and Conductors 53

3.2.3 Intrinsic Carrier Concentration 53

3.3 Charge Transport in Semiconductors 55

3.3.1 Field Currents 55

3.3.2 Di¿usion Currents 56

3.4 Doping of Semiconductors 57

3.4.1 n-Doping 57

3.4.2 p-Doping 58

3.5 The p-n Junction 59

3.5.1 Principle of Method of Operation 59

3.5.2 Band Diagram of the p-n Junction 61

3.5.3 Behavior with Applied Voltage 62

3.5.4 Diode Characteristics 63

3.6 Interaction of Light and Semiconductors 64

3.6.1 Phenomenon of Light Absorption 64

3.6.1.1 Absorption Coe¿cient 65

3.6.1.2 Direct and Indirect Semiconductors 65

3.6.2 Light Re¿ection on Surfaces 67

3.6.2.1 Re¿ection Factor 67

3.6.2.2 Antire¿ection Coating 69

4 Structure and Method of Operation of Solar Cells 71

4.1 Consideration of the Photodiode 71

4.1.1 Structure and Characteristics 71

4.1.2 Equivalent Circuit 73

4.2 Method of Function of the Solar Cell 73

4.2.1 Principle of the Structure 73

4.2.2 Recombination and Di¿usion Length 74

4.2.3 What Happens in the Individual Cell Regions? 75

4.2.3.1 Absorption in the Emitter 75

4.2.3.2 Absorption in the Space Charge Region 76

4.2.3.3 Absorption Within the Di¿usion Length of the Electrons 76

4.2.3.4 Absorption Outside the Di¿usion Length of the Electrons 76

4.2.4 Back-surface Field 77

4.3 Photocurrent 77

4.3.1 Absorption E¿ciency 78

4.3.2 Quantum E¿ciency 79

4.3.3 Spectral Sensitivity 79

4.4 Characteristic Curve and Characteristic Parameters 80

4.4.1 Short-circuit Current ISC 81

4.4.2 Open-circuit Voltage V OC 82

4.4.3 Maximum Power Point (MPP) 82

4.4.4 Fill Factor (FF) 82

4.4.5 E¿ciency ¿ 83

4.4.6 Temperature Dependence of Solar Cells 83

4.5 Electrical Description of Real Solar Cells 85

4.5.1 Simpli¿ed Model 85

4.5.2 Standard Model (Single-diode Model) 86

4.5.3 Two-diode Model 86

4.5.4 Determining the Parameters of the Equivalent Circuit 88

4.6 Considering E¿ciency 90

4.6.1 Spectral E¿ciency 91

4.6.2 Theoretical E¿ciency 94

4.6.3 Losses in Real Solar Cells 96

4.6.3.1 Optical Losses, Re¿ection on the Surface 96

4.6.3.2 Electrical Losses and Ohmic Losses 98

4.7 High-e¿ciency Cells 99

4.7.1 Buried-contact Cell 99

4.7.2 Point-contact Cell (IBC Cell) 99

4.7.3 PERL and PERC Cell 101

5 Cell Technologies 103

5.1 Production of Crystalline Silicon Cells 103

5.1.1 From Sand to Silicon 103

5.1.1.1 Production of Polysilicon 103

5.1.1.2 Production of Monocrystalline Silicon 105

5.1.1.3 Production of Multicrystalline Silicon 106

5.1.2 From Silicon to Wafer 107

5.1.2.1 Wafer Production 107

5.1.2.2 Wafers from Ribbon Silicon 107

5.1.3 Production of Standard Solar Cells 108

5.1.4 Production of Solar Modules 111

5.2 Cells of Amorphous Silicon 112

5.2.1 Properties of Amorphous Silicon 112

5.2.2 Production Process 113

5.2.3 Structure of the Pin Cell 113

5.2.4 Staebler-Wronski E¿ect 115

5.2.5 Stacked Cells 116

5.2.6 Combined Cells of Micromorphous Material 118

5.2.7 Integrated Series Connection 119

5.3 Further Thin Film Cells 120

5.3.1 Cells of Cadmium-Telluride 120

5.3.2 CIS Cells 121

5.4 Hybrid Wafer Cells 123

5.4.1 Combination of c-Si and a-Si (HIT Cell) 123

5.4.2 Stacked Cells of III/V Semiconductors 124

5.5 Other Cell Concepts 125

5.6 Concentrator Systems 126

5.6.1 Principle of Radiation Bundling 126

5.6.2 What Is the Advantage of Concentration? 127

5.6.3 Examples of Concentrator Systems 128

5.6.4 Advantages and Disadvantages of Concentrator Systems 128

5.7 Ecological Questions on Cell and Module Production 129

5.7.1 Environmental E¿ects of Production and Operation 129

5.7.1.1 Example of Cadmium-Telluride 129

5.7.1.2 Example of Silicon 129

5.7.2 Availability of Materials 130

5.7.2.1 Silicon 130

5.7.2.2 Cadmium-Telluride 131

5.7.2.3 Cadmium Indium Selenide 131

5.7.2.4 III/V Semiconductors 132

5.7.3 Energy Amortization Time and Yield Factor 132

5.8 Summary 135

6 Solar Modules and Solar Generators 139

6.1 Properties of Solar Modules 139

6.1.1 Solar Cell Characteristic Curve in All Four Quadrants 139

6.1.2 Parallel Connection of Cells 139

6.1.3 Series Connection of Cells 141

6.1.4 Use of Bypass Diodes 142

6.1.4.1 Reducing Shading Losses 142

6.1.4.2 Prevention of Hotspots 144

6.1.5 Typical Characteristic Curves of Solar Modules 147

6.1.5.1 Variation of the Irradiance 147

6.1.5.2 Temperature Behavior 147

6.1.6 Special Case Thin-¿lm Modules 149

6.1.7 Examples of Data Sheet Information 150

6.2 Connecting Solar Modules 150

6.2.1 Parallel Connection of Strings 150

6.2.2 What Happens in Case of Cabling Errors? 152

6.2.3 Losses Due to Mismatching 153

6.2.4 Smart Installation in Case of Shading 153

6.3 Direct Current Components 156

6.3.1 Principle of Plant Construction 156

6.3.2 Direct Current Cabling 156

6.4 Types of Plants 158

6.4.1 Ground-mounted Plants 158

6.4.2 Flat-roof Plants 161

6.4.3 Pitched-roof Systems 162

6.4.4 Facade Systems 164

7 System Technology of Grid-connected Plants 165

7.1 Solar Generator and Load 165

7.1.1 Resistive Load 165

7.1.2 DC/DC Converter 166

7.1.2.1 Idea 166

7.1.2.2 Buck Converter 166

7.1.2.3 Boost Converter 169

7.1.3 MPP Tracker 171

7.2 Construction of Grid-connected Systems 172

7.2.1 Feed-in Variations 172

7.2.2 Plant Concepts 173

7.3 Construction of Inverters 174

7.3.1 Tasks of the Inverter 175

7.3.2 Line-commutated and Self-commutated Inverter 175

7.3.3 Inverters Without Transformers 175

7.3.4 Inverters with Mains Transformer 177

7.3.5 Inverters with HF Transformer 178

7.3.6 Three-phase Feed-in 179

7.3.7 Further Clever Concepts 180

7.4 E¿ciency of Inverters 181

7.4.1 Conversion E¿ciency 181

[...]opean E¿ciency 184

7.4.3 Clever MPP Tracking 185

7.5 Dimensioning of Inverters 186

7.5.1 Power Dimensioning 186

7.5.2 Voltage Dimensioning 187

7.5.3 Current Dimensioning 188

7.6 Requirements of the Grid Operators 188

7.6.1 Prevention of Stand-Alone Operation 188

7.6.2 Maximum Feed-in Power 190

7.6.3 Reactive Power Provision 191

7.7 Safety Aspects 194

7.7.1 Earthing of the Generator and Lightning Protection 194

7.7.2 Fire Protection 194

8 Storage of Solar Energy 197

8.1 Principle of Solar Storage 197

8.2 Batteries 198

8.2.1 Lead-acid Battery 199

8.2.1.1 Principle and Build-up 199

8.2.1.2 Types of Lead...