Contents
Foreword to the World Scientific Series on Current Energy Issues xv
1. Introduction to Solar Energy 1
R. Corkish, W. Lipi´nski and R. J. Patterson
1 What is Solar Energy? . . . . . . . . . . . . . . . . . . . . . 1
2 Advantages and Disadvantages Associated with Solar
Energy Use . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 History of Solar Energy Use . . . . . . . . . . . . . . . . . . 7
4 Modern Applications of Solar Energy . . . . . . . . . . . . . 10
4.1 Photovoltaics for Large-Scale Electricity Production . . 10
4.2 Photovoltaics for Small Scale on Homes and
Commercial Buildings . . . . . . . . . . . . . . . . . . . 11
4.3 Photovoltaics for Small-Scale Off-grid Applications . . 12
4.4 Concentrating Solar Thermal Electricity . . . . . . . . 13
4.5 Solar Thermochemical Processes . . . . . . . . . . . . . 14
4.6 SolarWater Heating . . . . . . . . . . . . . . . . . . . . 14
4.7 Passive Heating of Buildings and Solar Architecture . . 15
4.8 Evaporative Cooling . . . . . . . . . . . . . . . . . . . . 16
4.9 Biomass and Biofuels . . . . . . . . . . . . . . . . . . . 16
4.10 Artificial Photosynthesis . . . . . . . . . . . . . . . . . 17
5 Economics of Solar Energy Use . . . . . . . . . . . . . . . . 17
6 Social and Policy Aspects . . . . . . . . . . . . . . . . . . . 21
7 Summary/Conclusions . . . . . . . . . . . . . . . . . . . . . 25
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2. Fundamentals of Photovoltaic Cells and Systems 31
Ignacio Rey-Stolle
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2 Solar Radiation . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.1 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . 32
2.2 Basic PV Terminology and Notation for Solar
Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.3 Components of the Solar Radiation . . . . . . . . . . . 33
2.4 World Distribution of Solar Radiation . . . . . . . . . . 35
2.5 Solar Radiation Collected by PV Systems . . . . . . . . 35
3 Solar Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.2 Basic Solar Cell Equations and Equivalent Circuits . . 37
3.2.1 Simple equivalent circuit for a solar cell
and I–V characteristic . . . . . . . . . . . . . . . 37
3.2.2 General equivalent circuit for a solar cell
and I–V characteristic . . . . . . . . . . . . . . . 38
3.3 The I–V Curve of a Solar Cell . . . . . . . . . . . . . . 38
3.3.1 General look and key parameters . . . . . . . . . 38
3.3.2 Effect of variations in series and parallel resistance
on the I–V curve . . . . . . . . . . . . . . . . . . 39
3.3.3 Effect of variations in irradiance on the
I–V curve . . . . . . . . . . . . . . . . . . . . . . 40
3.3.4 Effect of variations in temperature . . . . . . . . 41
3.3.5 Standard test conditions for solar cells . . . . . . 41
3.4 Overview of Solar Cell Technologies . . . . . . . . . . . 42
4 PVModules . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.1 Fundamentals . . . . . . . . . . . . . . . . . . . . . . . 42
4.1.1 Concept and mission . . . . . . . . . . . . . . . . 42
4.1.2 Construction . . . . . . . . . . . . . . . . . . . . 43
4.2 Characteristic Equation and I–V Curve . . . . . . . . . 44
4.2.1 I–V characteristic of a PV module . . . . . . . . 44
4.3 Electrical Performance . . . . . . . . . . . . . . . . . . 46
4.3.1 Standard test conditions . . . . . . . . . . . . . . 46
4.3.2 Factors affecting the electrical power of solar
panels under real operation . . . . . . . . . . . . 47
4.3.3 Modeling the equilibrium cell temperature
in a PVmodule . . . . . . . . . . . . . . . . . . . 47
4.3.4 Electrical power of solar panels at any irradiance
and temperature . . . . . . . . . . . . . . . . . . 48
4.3.5 Electrical Energy from a PV module . . . . . . . 48
5 PV Arrays and Systems . . . . . . . . . . . . . . . . . . . . 49
5.1 Basic Definitions . . . . . . . . . . . . . . . . . . . . . . 49
5.2 Balance of System Components of PV Systems . . . . . 49
5.2.1 Power conditioning . . . . . . . . . . . . . . . . . 49
5.2.2 Storage . . . . . . . . . . . . . . . . . . . . . . . 50
5.2.3 Electric components . . . . . . . . . . . . . . . . 50
5.2.4 Mounting structures . . . . . . . . . . . . . . . . 50
5.3 Types of PV Systems . . . . . . . . . . . . . . . . . . . 51
5.4 Designing a PV System . . . . . . . . . . . . . . . . . . 52
5.4.1 Location . . . . . . . . . . . . . . . . . . . . . . . 52
5.4.2 Orientation and tilt . . . . . . . . . . . . . . . . 52
5.4.3 Sizing . . . . . . . . . . . . . . . . . . . . . . . . 53
5.5 PV System Performance . . . . . . . . . . . . . . . . . 54
5.5.1 Output power of PV systems . . . . . . . . . . . 54
5.5.2 Energy rating of PV systems . . . . . . . . . . . 55
5.5.3 Alternative (simpler) energy rating
of PV systems . . . . . . . . . . . . . . . . . . . 55
6 Uses and World Market of PV Solar Energy . . . . . . . . . 57
6.1 Overview on the Uses of PV Energy . . . . . . . . . . . 57
6.2 World PVMarket . . . . . . . . . . . . . . . . . . . . . 57
6.2.1 Size and historic evolution of the world
PVmarket . . . . . . . . . . . . . . . . . . . . . 57
6.2.2 PV cell production by technology . . . . . . . . . 59
6.2.3 Evolution of costs of PV modules and PV
electricity . . . . . . . . . . . . . . . . . . . . . . 59
7 Material Usage and Environmental Impact
of PV Solar Energy . . . . . . . . . . . . . . . . . . . . . . . 61
7.1 The Value Chain of PV Technology . . . . . . . . . . . 61
7.2 Material Usage of PV Technology . . . . . . . . . . . . 61
7.3 Energy Payback Time of PV Systems . . . . . . . . . . 61
7.4 Greenhouse (GHG) Gas Emissions of PV Systems . . . 62
7.5 Operational Hazards of PV Systems . . . . . . . . . . . 63
7.6 PV Module Decommissioning and Recycling . . . . . . 64
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3. Large-Scale Solar Thermal Plants (CSP) 69
Manfred Becker, Robert Pitz-Paal and Wes Stein
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
2 Solar Radiation and Concentration . . . . . . . . . . . . . . 71
3 Receiving and Absorbing Solar Radiation . . . . . . . . . . . 72
3.1 Energy Balance . . . . . . . . . . . . . . . . . . . . . . 72
3.2 Selective Surface Theory . . . . . . . . . . . . . . . . . 73
4 Types of Solar Collectors for Power and Fuels . . . . . . . . 75
4.1 Solar Pond . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.2 Solar Chimney . . . . . . . . . . . . . . . . . . . . . . . 77
4.3 Parabolic Trough . . . . . . . . . . . . . . . . . . . . . 78
4.3.1 Trough technology . . . . . . . . . . . . . . . . . 78
4.3.2 Heat transfer field . . . . . . . . . . . . . . . . . 82
4.4 Linear Fresnel . . . . . . . . . . . . . . . . . . . . . . . 86
4.5 Central Receiver (Power Tower) . . . . . . . . . . . . . 87
4.5.1 Heliostats and field layout . . . . . . . . . . . . . 87
4.5.2 Receivers . . . . . . . . . . . . . . . . . . . . . . 90
4.6 Dish Concentrators . . . . . . . . . . . . . . . . . . . . 91
5 Thermal Storage . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.1 Two-TankMolten Salt . . . . . . . . . . . . . . . . . . 96
5.2 Single Tank Molten Salt . . . . . . . . . . . . . . . . . 97
5.3 Alternative Thermal Storage Options . . . . . . . . . . 97
5.4 Thermochemical Storage . . . . . . . . . . . . . . . . . 99
5.5 Cost Reduction of Thermal Storage Through Higher
Temperatures . . . . . . . . . . . . . . . . . . . . . . . 99
6 CSP Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 100
6.1 Rankine Cycle Based . . . . . . . . . . . . . . . . . . . 101
6.2 Brayton Cycle . . . . . . . . . . . . . . . . . . . . . . . 102
6.3 Stirling Cycle . . . . . . . . . . . . . . . . . . . . . . . 104
7 New Commercial Power Stations . . . . . . . . . . . . . . . 105
7.1 Parabolic Troughs . . . . . . . . . . . . . . . . . . . . . 105
7.2 Central Receivers (Power Towers) . . . . . . . . . . . . 107
8 Economy and Cost Reductions . . . . . . . . . . . . . . . . . 112
8.1 CSP in theMarket . . . . . . . . . . . . . . . . . . . . 112
8.2 Cost Developments and Cost Reductions . . . . . . . . 115
8.2.1 Cost reduction . . . . . . . . . . . . . . . . . . . 116
8.2.2 Scaling up . . . . . . . . . . . . . . . . . . . . . . 116
8.2.3 Volume production . . . . . . . . . . . . . . . . . 117
8.2.4 Technology innovations . . . . . . . . . . . . . . 117
9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
4. Large-Scale Photovoltaic Power Plants 125
G. Almonacid Puche, P. G. Vidal and E. Mu˜noz-Cer´on
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
2 Electrical Engineering: Key Points in Large
PV Generators . . . . . . . . . . . . . . . . . . . . . . . . . . 127
2.1 Layout of a Large-Scale PV Plant . . . . . . . . . . . . 127
2.2 Inverter Topology . . . . . . . . . . . . . . . . . . . . . 130
2.3 Capacitive Leakage Current . . . . . . . . . . . . . . . 131
2.4 Grounding . . . . . . . . . . . . . . . . . . . . . . . . . 132
2.5 Insulation Resistance . . . . . . . . . . . . . . . . . . . 134
2.6 Electrical Hazards . . . . . . . . . . . . . . . . . . . . . 134
3 Grid Connection . . . . . . . . . . . . . . . . . . . . . . . . . 136
3.1 Grid-Connection Requirements for Large-Scale
PV Plants . . . . . . . . . . . . . . . . . . . . . . . . . 137
3.1.1 Voltage control under normal operating
conditions — Static voltage support . . . . . . . 137
3.1.2 Dynamic grid support in fault operation . . . . . 137
3.1.3 Active power output . . . . . . . . . . . . . . . . 139
3.1.4 Unintentional islanding . . . . . . . . . . . . . . 140
3.2 Power Quality . . . . . . . . . . . . . . . . . . . . . . . 141
3.2.1 Voltage fluctuations at the PPC . . . . . . . . . 141
3.2.2 Limitation of DC injection . . . . . . . . . . . . 142
3.2.3 Harmonics . . . . . . . . . . . . . . . . . . . . . 142
3.2.4 Limitation of flicker induced by the
PV generator . . . . . . . . . . . . . . . . . . . . 143
4 Energy Yields and Efficiencies . . . . . . . . . . . . . . . . . 143
4.1 Efficiency and Productivity . . . . . . . . . . . . . . . . 143
4.2 Losses in Large-Scale PV Plants . . . . . . . . . . . . . 145
4.3 Software Simulation Tools . . . . . . . . . . . . . . . . 148
5 Commissioning. Operation & Maintenance . . . . . . . . . . 149
5.1 List of Procedures for the Commission of a Large
PV Plant . . . . . . . . . . . . . . . . . . . . . . . . . . 150
5.1.1 Visual inspection . . . . . . . . . . . . . . . . . . 150
5.1.2 Testing and initial startup . . . . . . . . . . . . . 151
5.1.3 System documentation . . . . . . . . . . . . . . . 152
5.2 Operation and Maintenance of a PV Plant . . . . . . . 152
6 Promotion Policies — Planning and Regulation . . . . . . . 155
7 Economic Analysis: Financing and Due Diligence . . . . . . 158
7.1 Economic Parameters: Grid Parity, Life-Cycle Cost
(LCC) and Levelized Cost of Electricity (LCOE) . . . . 158
7.2 Financing . . . . . . . . . . . . . . . . . . . . . . . . . . 162
7.3 Technical Due Diligence . . . . . . . . . . . . . . . . . . 162
8 The Future of Large-Scale PV Power Plants . . . . . . . . . 163
8.1 European Stand-by Future in Large-Scale PV Power
Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
8.2 The Asia Pacific and Middle East and
North Africa (MENA) Countries Boosting
Future in Large PV Plants . . . . . . . . . . . . . . . . 164
8.3 North and South American Deployment
of PV Plants . . . . . . . . . . . . . . . . . . . . . . . . 165
8.4 Africa’s Increasing Development of Large PV
Plant Projects . . . . . . . . . . . . . . . . . . . . . . . 165
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 166
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
5. Biomass 171
Anthony Turhollow
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
2 Biomass Products . . . . . . . . . . . . . . . . . . . . . . . . 172
2.1 Ethanol . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
2.1.1 Ethanol production in Brazil . . . . . . . . . . . 172
2.1.2 Ethanol production in the United States . . . . . 174
2.1.3 Second-generation Ethanol production . . . . . . 175
2.2 Biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . 175
2.3 Electricity . . . . . . . . . . . . . . . . . . . . . . . . . 176
2.4 Biochemicals . . . . . . . . . . . . . . . . . . . . . . . . 177
2.4.1 Nitrogen fertilizer produced from biomass . . . . 178
2.5 Wood Pellets . . . . . . . . . . . . . . . . . . . . . . . . 178
3 Thermal Processes . . . . . . . . . . . . . . . . . . . . . . . 179
3.1 Pyrolysis and Hydropyrolysis . . . . . . . . . . . . . . . 180
3.2 Gasification . . . . . . . . . . . . . . . . . . . . . . . . 182
3.3 Combustion . . . . . . . . . . . . . . . . . . . . . . . . 182
4 Biological Processes . . . . . . . . . . . . . . . . . . . . . . . 183
4.1 Anaerobic Digestion . . . . . . . . . . . . . . . . . . . . 183
4.2 Fermentation . . . . . . . . . . . . . . . . . . . . . . . . 184
5 Dedicated Energy Crops . . . . . . . . . . . . . . . . . . . . 185
5.1 Switchgrass . . . . . . . . . . . . . . . . . . . . . . . . . 186
5.2 Sorghum . . . . . . . . . . . . . . . . . . . . . . . . . . 187
5.3 Miscanthus . . . . . . . . . . . . . . . . . . . . . . . . . 188
5.4 Sugarcane and Energy Cane . . . . . . . . . . . . . . . 188
5.5 Hybrid Poplar . . . . . . . . . . . . . . . . . . . . . . . 189
5.6 Willow . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
5.7 Eucalyptus . . . . . . . . . . . . . . . . . . . . . . . . . 191
5.8 Oilseeds . . . . . . . . . . . . . . . . . . . . . . . . . . 191
5.9 Algae . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
6 Policies Affecting Biofuels . . . . . . . . . . . . . . . . . . . 193
7 Conclusions and Outlook . . . . . . . . . . . . . . . . . . . . 195
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 196
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
6. Artificial Photosynthesis 205
Nathan Skillen and Peter K. J. Robertson
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
2 Natural Photosynthesis . . . . . . . . . . . . . . . . . . . . . 207
2.1 Key Features . . . . . . . . . . . . . . . . . . . . . . . . 208
2.1.1 Energy absorption . . . . . . . . . . . . . . . . . 208
2.1.2 Electron transfer and ATP generation . . . . . . 210
2.1.3 Carbon fixation . . . . . . . . . . . . . . . . . . . 211
3 Artificial Photosynthesis . . . . . . . . . . . . . . . . . . . . 213
3.1 Light Harvesting . . . . . . . . . . . . . . . . . . . . . . 213
3.1.1 Photosensitizers . . . . . . . . . . . . . . . . . . 214
3.1.1.1 Dye sensitized solar cells . . . . . . . . . 214
3.1.1.2 Photocatalysts . . . . . . . . . . . . . . . 216
3.2 Electron Separation and Transfer . . . . . . . . . . . . 218
3.2.1 Single oxide photocatalysts . . . . . . . . . . . . 218
3.2.2 Z-scheme photocatalysts . . . . . . . . . . . . . . 222
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3.2.3 Nanobiocatalytic assemblies . . . . . . . . . . . 224
3.2.3.1 Mimicking PS I . . . . . . . . . . . . . . 224
3.2.3.2 Mimicking PS II . . . . . . . . . . . . . . 226
3.3 Carbon Fixation . . . . . . . . . . . . . . . . . . . . . . 227
3.3.1 Heterogenous catalysts . . . . . . . . . . . . . . . 228
3.3.2 Homogenous catalysts . . . . . . . . . . . . . . . 232
4 Artificial Photosynthesis Institutes . . . . . . . . . . . . . . 234
4.1 Swedish Consortium for Artificial Photosynthesis . . . 234
4.2 Joint Centre for Artificial Photosynthesis (JCAP) . . . 234
5 Future Outlook and Challenges . . . . . . . . . . . . . . . . 235
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
7. Small-Scale PV Applications in Home and Business 243
Estefan´ıa Caama˜no-Mart´ın, Miguel ´Angel Egido
and Jorge Sol´orzano
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
1.1 PV Applications in the Built Environment . . . . . . . 244
1.2 Stand-Alone PV Applications . . . . . . . . . . . . . . 246
2 Solar Resource Availability . . . . . . . . . . . . . . . . . . . 247
2.1 MeteorologicalResources andModeling . . . . . . . . . 247
2.2 On the Positioning of PVModules . . . . . . . . . . . . 249
2.3 Shading Losses . . . . . . . . . . . . . . . . . . . . . . . 252
3 Performance Assessment of Small-Scale PV Systems . . . . . 255
3.1 PV Systems Losses . . . . . . . . . . . . . . . . . . . . 260
4 PVs in Buildings . . . . . . . . . . . . . . . . . . . . . . . . 262
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 262
4.2 Types of PV Systems . . . . . . . . . . . . . . . . . . . 263
4.3 Design and Sizing . . . . . . . . . . . . . . . . . . . . . 266
4.3.1 PV generator . . . . . . . . . . . . . . . . . . . . 267
4.3.2 Inverter . . . . . . . . . . . . . . . . . . . . . . . 268
4.3.3 Operation and maintenance . . . . . . . . . . . . 270
4.4 Business Models and International Experiences . . . . . 270
5 SAPVS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 274
5.2 Types of SAPVS . . . . . . . . . . . . . . . . . . . . . . 274
5.3 Design and Sizing . . . . . . . . . . . . . . . . . . . . . 282
5.4 Operation and Management . . . . . . . . . . . . . . . 285
5.5 Business Models and International Experiences . . . . . 289
Contents xiii
6 Safety and Protections . . . . . . . . . . . . . . . . . . . . . 291
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
8. Low Temperature Solar Thermal Applications 299
Brian Norton, Hans Martin Henning and Daniel Mugnier
1 Outline of the Chapter . . . . . . . . . . . . . . . . . . . . . 299
2 Brief History of the Low Temperature Uses of Solar
Thermal Energy . . . . . . . . . . . . . . . . . . . . . . . . . 300
3 SolarWater Heating . . . . . . . . . . . . . . . . . . . . . . 302
4 Building Heating and Cooling with Solar Energy . . . . . . 307
5 Low Temperature Solar Heating in Industrial
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
6 Use of Solar Energy to Dry Crops . . . . . . . . . . . . . . . 315
7 Solar Air Cooling Conditioning and Refrigeration . . . . . . 320
7.1 Passive Cooling of Building . . . . . . . . . . . . . . . . 320
7.2 Principles of Active Solar Cooling . . . . . . . . . . . . 322
7.3 TechnicalMaturity of SAC . . . . . . . . . . . . . . . . 326
7.4 Energy Performance of SAC . . . . . . . . . . . . . . . 328
7.5 Economic Viability and Environmental Benefits
of SAC . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
7.6 Market Status of SAC. . . . . . . . . . . . . . . . . . . 332
7.7 Technical Potentials of SAC . . . . . . . . . . . . . . . 333
7.8 SAC Costs and Economics . . . . . . . . . . . . . . . . 334
7.9 Market Opportunities for SAC . . . . . . . . . . . . . . 335
8 Economic and Policy Issues Related to Solar Heating and
Cooling Thermal Applications . . . . . . . . . . . . . . . . . 337
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 338
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
9. Solar Thermochemical Processes 345
Roman Bader and Wojciech Lipi´nski
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
1.1 Overview of Processes . . . . . . . . . . . . . . . . . . . 346
1.2 Thermodynamic Limits . . . . . . . . . . . . . . . . . . 349
2 Thermolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
3 Thermochemical Cycles . . . . . . . . . . . . . . . . . . . . . 354
3.1 Two-Step Redox Cycles . . . . . . . . . . . . . . . . . . 355
3.1.1 Zinc oxide cycle . . . . . . . . . . . . . . . . . . . 357
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3.1.2 Ferrite cycle . . . . . . . . . . . . . . . . . . . . . 366
3.1.3 Ceria cycle . . . . . . . . . . . . . . . . . . . . . 370
3.1.4 Perovskite cycle . . . . . . . . . . . . . . . . . . 377
3.2 Multi-Step Cycles . . . . . . . . . . . . . . . . . . . . . 378
4 Conversion of Carbonaceous Feedstocks . . . . . . . . . . . . 379
4.1 Gasification . . . . . . . . . . . . . . . . . . . . . . . . 379
4.2 Cracking and Reforming . . . . . . . . . . . . . . . . . 382
5 Production of Lime and Cement . . . . . . . . . . . . . . . . 385
6 CO2 Capture . . . . . . . . . . . . . . . . . . . . . . . . . . 386
7 Other Processes . . . . . . . . . . . . . . . . . . . . . . . . . 388
8 Summary and Conclusions . . . . . . . . . . . . . . . . . . . 389
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389
