Renewable Energy in Power Systems

Foreword xv Preface to the First Edition xix Preface to the Second Edition xxi Acknowledgements xxiii About the Companion Website xxv 1 Energy and Electricity 1 1.1 The World Energy Scene 1 1.1.1 History 1 1.1.2 World Energy Consumption 1 1.1.3 Finite Resources 2 1.1.4 Energy Security and Disparity of Use 3 1.2 The Environmental Impact of Energy Use 4 1.2.1 The Problem 4 1.2.2 The Science 5 1.2.3 The Kyoto Protocol 7 1.2.4 Economics of Mitigation 10 1.2.5 Efficient Energy Use 11 1.2.6 The Electricity Sector 14 1.2.7 Possible Solutions and Sustainability 15 1.3 Generating Electricity 16 1.3.1 Conversion from Other Energy Forms – The Importance of Efficiency 16 1.3.2 The Nuclear Path 17 1.3.3 Carbon Capture and Storage (CCS) 17 1.3.4 Renewables 18 1.4 The Electrical Power System 20 1.4.1 Structure of the Electrical Power System 20 1.4.2 Integrating Renewables into Power Systems 23 1.4.3 Distributed Generation 23 1.4.4 Renewable Energy Penetration 24 1.4.5 Network Stability 25 References 25 2 Features of Conventional and Renewable Generation 27 2.1 Introduction 27 2.2 Conventional Sources: Coal, Gas and Nuclear 28 2.3 Hydroelectric Power 29 2.3.1 Large-Scale Hydro 30 2.3.2 Small Hydro 31 2.3.2.1 Turbine Designs 32 2.4 Wind Power 33 2.4.1 The Resource 33 2.4.2 Wind Variability 34 2.4.3 Wind Turbines 37 2.4.4 Power Variability 40 2.4.4.1 Variability from Second to Second 40 2.4.4.2 Variability from Minute to Minute 41 2.4.4.3 Variability from Hour to Hour and from Day-to-Day 41 2.4.4.4 Seasonal Variability 42 2.4.5 Offshore Wind 42 2.5 PV and Solar Thermal Electricity 47 2.5.1 The Resource 47 2.5.2 The Technology 49 2.5.3 Photovoltaic Systems 49 2.5.4 Solar Thermal Electric Systems 52 2.6 Tidal Power 54 2.6.1 The Resource 54 2.6.2 Tidal Enhancement 54 2.6.2.1 Funnelling 54 2.6.2.2 Resonance 55 2.6.2.3 Coriolis Effect 55 2.6.3 Tidal Barrages 55 2.6.4 Operational Strategies 55 2.6.4.1 Power Variability 56 2.6.5 Tidal Current Schemes 57 2.7 Wave Power 59 2.7.1 The Resource 59 2.7.2 The Technology 59 2.7.3 Variability 60 2.8 Biomass 62 2.8.1 The Resource 62 2.8.2 Resource Sustainability 62 2.9 Summary of Power Generation Characteristics 63 2.10 Combining Sources 64 References 65 3 Power Balance/Frequency Control 67 3.1 Introduction 67 3.1.1 The Power Balance Issue 67 3.2 Electricity Demand 68 3.2.1 Demand Curves 68 3.2.2 Load Aggregation 69 3.2.3 Demand-Side Management – Deferrable Loads 70 3.3 Power Governing 71 3.3.1 Power Conversion Chain 71 3.3.2 Governor Steady State Characteristics 72 3.3.3 Parallel Operation of Two Generators 73 3.3.4 A Multi-Generator System 74 3.3.5 The Steady State Power–Frequency Relationship 75 3.4 Dynamic Frequency Control of Large Systems 76 3.4.1 Demand Matching 76 3.4.2 Demand Forecasting 77 3.4.3 Frequency Limits 79 3.4.4 Generation Scheduling and Reserve 79 3.4.5 Frequency Control at Different Timescales 80 3.4.6 Meeting Demand and Ensuring Reliability 82 3.4.7 Capacity Factor and Capacity Credit 83 3.5 Impact of Renewable Generation on Frequency Control and Reliability 84 3.5.1 Introduction 84 3.5.2 Aggregation of Sources 85 3.5.2.1 The Monthly Distribution of Power Availability 85 3.5.2.2 The Daily Distribution of Power Availability 85 3.5.2.3 Short Term Variability 86 3.5.2.4 The Capacity Factor 86 3.5.3 Value of Energy from the Wind 88 3.5.4 Impact on Balancing 88 3.5.5 Impact on Reliability 90 3.5.6 Discarded/Curtailed Energy 91 3.5.7 Overall Penalties Due to Increasing Penetration 92 3.5.8 Combining Different Renewable Sources 92 3.5.9 Differences Between Electricity Systems 93 3.5.10 Limits of Penetration from Non-Dispatchable Sources 94 3.6 Frequency Response Services from Renewables 96 3.6.1.1 Wind Power 96 3.6.1.2 Biofuels 100 3.6.1.3 Waterpower 100 3.6.1.4 Photovoltaics 100 3.7 Frequency Control Modelling 101 3.7.1 Background 101 3.7.1.1 Modelling a Generator 101 3.7.1.2 Modelling Released Demand 102 3.7.1.3 Modelling the Grid’s Inertial Energy Store 102 3.7.2 A Modelling Example 103 3.8 Energy Storage 105 3.8.1 Introduction 105 3.8.2 Storage Devices 106 3.8.3 Dynamic Demand Control 108 References 111 Further Reading 113 4 Electrical Power Generation and Conditioning 115 4.1 The Conversion of Renewable Energy into Electrical Form 115 4.2 The Synchronous Generator 116 4.2.1 Construction and Mode of Operation 116 4.2.2 The Rotating Magnetic Field 119 4.2.3 Synchronous Generator Operation When Grid Connected 120 4.2.4 The Synchronous Generator Equivalent Circuit 122 4.2.5 Power Transfer Equations 123 4.2.6 Three-Phase Equations 124 4.2.7 Four-Quadrant Operation 125 4.2.8 Power–Load Angle Characteristic 125 4.3 The Transformer 126 4.3.1 Transformer Basics 126 4.3.2 The Transformer Equivalent Circuit 128 4.3.3 Further Details on Transformers 129 4.4 The Asynchronous Generator 130 4.4.1 Construction and Properties 130 4.4.2 The Induction Machine Equivalent Circuit 132 4.4.3 The Induction Machine Efficiency 134 4.4.4 The Induction Machine Speed-Torque Characteristic 134 4.4.5 Induction Generator Reactive Power 137 4.4.6 Comparison Between Synchronous and Asynchronous Generators 137 4.5 Power Electronics 139 4.5.1 Introduction 139 4.5.2 Power-Semiconductor Devices 139 4.5.2.1 Diodes 139 4.5.2.2 Thyristors 139 4.5.2.3 Transistors 140 4.5.3 Diode Bridge Rectifier 141 4.5.4 Harmonics 142 4.5.5 The Thyristor Bridge Converter 143 4.5.6 The Transistor Bridge 145 4.5.6.1 Basic Square Wave 146 4.5.6.2 Quasi-Sine Wave (Modified Square Wave) 146 4.5.6.3 Pulse-Width Modulation 146 4.5.6.4 Comparison of Switching Methods 148 4.5.6.5 Output Control in a Grid-Connected Inverter 148 4.5.6.6 The Three-Phase Bridge 149 4.5.7 Converter Internal Control Systems 149 4.5.8 DC–DC Converters 150 4.5.8.1 Step-Down DC–DC Converter 150 4.5.8.2 Step-Up DC–DC Converter 150 4.5.9 Multi-Level Converters 151 4.5.10 Matrix Converters 151 4.5.11 Z-Source Converters 151 4.6 Applications to Renewable Energy Generators 152 4.6.1 Applications to PV Systems 152 4.6.1.1 PV System Characteristics 152 4.6.1.2 Basic Grid-Connected PV Inverter 153 4.6.1.3 Transformerless Grid-Connected PV Inverter 153 4.6.1.4 PV Inverter Using a High-Frequency Transformer 154 4.6.1.5 PV Inverter Using a Steering Bridge 154 4.6.1.6 PV Inverters for Stand-Alone Operation 155 4.6.2 Applications to Wind Power 155 4.6.2.1 Fixed Versus Variable Speed – Energy Capture [4] 155 4.6.2.2 Fixed Versus Variable Speed – Dynamics 156 4.6.3 Synchronous Generator Supplying an Autonomous Network 157 4.6.3.1 Fixed-Speed Wind Turbines 157 4.6.3.2 Variable Slip Wind Turbines 158 4.6.4 The Principle of Slip Energy Recovery 159 4.6.4.1 DFIG Wind Turbines 160 4.6.4.2 Wind Turbines with Full Converters 162 4.6.5 Synchronous Generators in Wind Turbines 162 4.6.6 Gearless Wind Turbines 163 4.6.7 Hybrid Drive Train Designs 164 4.6.8 DC Transmission for Wind 165 4.7 Applications to Small Scale Hydro 166 4.8 Applications to Tidal Stream Turbines 167 References 168 5 Power-System Analysis 171 5.1 Introduction 171 5.2 The Transmission System 171 5.2.1 Single-Phase Representation 173 5.2.2 Transmission and Distribution Systems 173 5.2.3 Example Networks 174 5.3 Voltage Control 176 5.4 Power Flow in an Individual Section of Line 178 5.4.1 Electrical Characteristics of Lines and Cables 178 5.4.2 Single-Phase Equivalent Circuit 178 5.4.3 Voltage Drop Calculation 179 5.4.4 Simplifications and Conclusions 180 5.5 Reactive Power Management 181 5.5.1 Reactive Power Compensation Equipment 182 5.5.1.1 Tap Changers and Voltage Regulators 182 5.5.1.2 AVRs 183 5.5.1.3 Static Compensators 184 5.5.1.4 FACTS 184 5.5.1.5 RE Generator Interfaces 184 5.6 Load-Flow and Power-System Simulation 184 5.6.1 Uses of Load Flow 184 5.6.2 A Particular Case 185 5.6.3 Network Data 186 5.6.4 Load/Generation Data 186 5.6.4.1 Time Dependence 186 5.6.4.2 Types of Nodes (Buses) 187 5.6.5 The Load-Flow Calculations 188 5.6.6 Results 189 5.6.7 Unbalanced Load-Flow 189 5.7 Faults and Protection 190 5.7.1 Short-Circuit Fault Currents 191 5.7.2 Symmetrical Three-Phase Fault Current 191 5.7.3 Fault Currents in General 191 5.7.4 Fault Level (Short-Circuit Level) –Weak Grids 192 5.7.5 Thévenin Equivalent Circuit 193 5.8 Time Varying and Dynamic Simulations 193 5.9 Power-System Stability 194 5.9.1 Equal Area Stability Criterion 195 5.9.2 Power-System Stabilisers 196 5.10 Dynamic Line Rating 196 5.11 Reliability Analysis 197 References 197 6 Renewable Energy Generation in Power Systems 199 6.1 Distributed Generation 199 6.1.1 Introduction 199 6.1.2 Point of Common Coupling (PCC) 200 6.1.3 Connection Voltage 200 6.2 Voltage Effects 201 6.2.1 Steady State Voltage Rise 201 6.2.2 Automatic Voltage Control – Tap Changers 202 6.2.3 Active and Reactive Power from Renewable Energy Generators 203 6.2.4 Example Load Flow 204 6.3 Thermal Limits 207 6.3.1 Overhead Lines and Cables 207 6.3.2 Transformers 208 6.4 Other Embedded Generation Issues 208 6.4.1 Flicker, Voltage Steps and Dips 208 6.4.1.1 Flicker 208 6.4.1.2 Steps and Dips 209 6.4.2 Harmonics/Distortion 209 6.4.3 Phase Voltage Imbalance 210 6.4.4 Network Reinforcement 211 6.4.5 Network Losses 211 6.4.6 Fault Level Increase 211 6.5 Islanding 212 6.5.1 Introduction 212 6.5.2 Loss-of-Mains Protection for Rotating Machines 213 6.5.3 Loss-of-Mains Protection for Inverters 213 6.6 Fault Ride-Through 214 6.7 Generator and Converter Characteristics 215 References 216 7 Power System Economics and the Electricity Market 219 7.1 Introduction 219 7.2 The Costs of Electricity Generation 219 7.2.1 Capital and Running Costs of Renewable and Conventional Generation Plant 219 7.2.2 Total Generation Costs 221 7.3 Economic Optimisation in Power Systems 221 7.3.1 Diversity of Generator Characteristics in a Power System 221 7.3.2 Optimum Economic Dispatch 221 7.3.3 Equal Incremental Cost Dispatch 224 7.3.4 OED with Several Units and Generation Limits 225 7.3.5 Costs on a Level Playing Field 228 7.4 External Costs 229 7.4.1 Introduction 229 7.4.2 Types of External Cost 230 7.4.3 The Kyoto Protocol and Subsequent Agreements 231 7.4.4 Costing Pollution 233 7.5 Effects of Embedded Generation 234 7.5.1 Value of Energy At Various Points of the Network 234 7.5.2 An Example Cash-Flow Analysis 235 7.5.3 Value of Embedded Generation – Regional and Local Issues 237 7.5.4 Capacity Credit 238 7.5.5 Summary 241 7.6 Support Mechanisms for Renewable Energy 241 7.6.1 Introduction 241 7.6.2 Feed-in Law 242 7.6.3 Quota System 242 7.6.3.1 Renewables Obligation (RO) 242 7.6.3.2 Contract for Difference (CFD) 243 7.6.4 Carbon Tax 243 7.6.4.1 Climate Change Levy 243 7.6.4.2 Eco-Tax Reform 243 7.6.4.3 Tax Relief 244 7.7 Electricity Markets 244 7.7.1 Introduction 244 7.7.2 The UK Electricity Supply Industry 244 7.7.2.1 The State-Owned Central Electricity-Generating Board 244 7.7.2.2 The Electricity Pool 244 7.7.2.3 The Operation of the Pool and Pool Rules 245 7.7.2.4 Hedging 246 7.7.2.5 Electricity Market Reform (EMR) 247 7.7.2.6 Ancillary Services 247 7.7.2.7 Marketing Green Electricity 248 References 248 8 The Future – Towards a Sustainable Electricity Supply System 249 8.1 Introduction 249 8.2 The Future of Wind Power 251 8.2.1 Large Wind Turbines 251 8.2.2 Offshore Wind Farm Development 254 8.2.2.1 Electrical Integration 256 8.2.2.2 DC Transmission for Wind 257 8.2.2.3 Innovative Collector Systems 257 8.2.2.4 A Proposed European DC Supergrid 257 8.2.2.5 Smarter Wind Farms 260 8.2.3 Building Integrated Wind Turbines 262 8.3 The Future of Solar Power 264 8.3.1 PV Technology Development 264 8.3.1.1 Different Deployment Options 265 8.3.2 Solar Thermal Electric Systems 267 8.4 The Future of Biofuels 268 8.5 Geothermal Power 271 8.6 The Future of Hydro and Marine Power 271 8.7 The Shape of Future Networks 272 8.7.1 Transmission System Evolution 273 8.7.2 Low Inertia Power Systems 275 8.7.3 Distribution Network Evolution 276 8.7.3.1 Active Networks 277 8.7.4 Problems Associated with Distributed Generation 278 8.7.4.1 Fault Levels 278 8.7.4.2 Voltage Levels 278 8.7.4.3 Network Security 279 8.7.4.4 Network Stability 279 8.7.5 Options to Ameliorate the Technical Difficulties 279 8.7.5.1 Planning Standards 279 8.7.5.2 Using Power Electronics Technology 279 8.7.5.3 Islanding 280 8.7.5.4 Dynamic Loads 280 8.7.5.5 Demand-Side Management of Loads 281 8.7.5.6 Storage 282 8.7.5.7 Microgrids 282 8.7.5.8 Virtual Power Stations 283 8.8 Conclusions 283 References 285 Appendix A Basic Electric Power Engineering Concepts 289 A.1 Introduction 289 A.2 Generators and Consumers of Energy 289 A.3 Why AC? 291 A.4 AC Waveforms 291 A.5 Response of Circuit Components to AC 292 A.5.1 Resistance 292 A.5.2 Inductance 293 A.5.3 Capacitance 295 A.6 Phasors 296 A.7 Phasor Addition 297 A.8 Rectangular Notation 298 A.9 Reactance and Impedance 300 A.9.1 Resistance 300 A.9.2 Inductance 301 A.9.3 Capacitance 301 A.9.4 Impedance 301 A.10 Power in AC Circuits 302 A.11 Reactive Power 304 A.12 Complex Power 305 A.13 Conservation of Active and Reactive Power 306 A.14 Effects of Reactive Power Flow – Power Factor Correction 307 A.15 Three-Phase AC 308 A.16 The Thévenin Equivalent Circuit 310 Reference 311 Index 313