Renewable Energy in Power Systems

Transcription

1 Renewable Energy in Power Systems Leon Freris Centre for Renewable Energy Systems Technology (CREST), Loughborough University, UK David Infield Institute of Energy and Environment, University of Strathclyde, UK WILEY A John Wiley & Sons, Ltd, Publication

2 Foreword Preface Acknowledgements jd xiii xv 1 Energy and Electricity The World Energy Scene History World energy consumption Finite resources Energy security and disparity of use The Environmental Impact of Energy Use The problem The science The Kyoto protocol The Stern Report Efficient energy use The electricity sector Possible Solutions and sustainability Generating Electricity Conversion from other energy forms - the importance ofefficiency The nuclear path Carbon capture and storage Renewables The Electrical Power System Structure of the electrical power System Integrating renewables into power Systems Distributed generation RE penetration 19 References 20 2 Features of Conventional and Renewable Generation Introduction Conventional Sources: Coal, Gas and Nuclear Hydroelectric Power Large hydro Small hydro 25

3 vi Wind Power The resource Wind variability Wind turbines Power variability PV and Solar Thermal Electricity The resource The technology Photovoltaic Systems Solar thermal electric Systems Tidal Power The resource Tidal enhancement Tidal barrages Operational strategies Tidal current schemes Wave Power The resource The technology Variability Biomass The resource Resource sustainability Summary of Power Generation Characteristics Combining Sources References Power Balance/ Frequency Control lntroduction The power balance issue Electricity Demand Demand curves Aggregation Demand-side management - deferrable loads Power Governing Power conversion chain The governor Parallel Operation of two generators Multigenerator System The steady State power-frequency relationship Dynamic Frequency Control of Large Systems Demand matching Demand forecasting Frequency limits Generation scheduling and reserve Frequency control at different timescales Meeting demand and ensuring reliability Capacity factor and capacity credit Impact of Renewable Generation on Frequency Control and Reliability lntroduction Aggregation of sources

4 vii Value of energy from the wind Impact on balancing Impact on reliability Discarded/curtailed energy Overallpenalties due to increasingpenetration Combining different renewable sources Differences between electricity Systems Limits of penetration from nondispatchable sources Frequency Response Services from Renewables Wind power Biofuels Water power Photovoltaics Frequency Control Modelling Background A modelling example Energy Storage Introduction Storage devices Dynamic demand control 93 References 94 Other Useful Reading 95 4 Electrical Power Generation and Conditioning The Conversion of Renewable Energy into Electrical Form The Synchronous Generator Construction and mode of Operation The rotating magnetic field Synchronous generator Operation when grid-connected The synchronous generator equivalent circuit Power transfer equations Three-phase equations Four-quadrant Operation Power-load angle characteristic: stability The Transformer Transformer basics The transformer equivalent circuit Further details on transformers The Asynchronous Generator Construction and properties The induction machine equivalent circuit The induction machine efficiency The induction machine speed-torque characteristic Induction generator reactive power Comparison between synchronous and asynchronous generators Power Electronics Introduction Power semiconductor devices Diode bridge rectifier Harmonics The thyristor bridge Converter 126

5 viii The transistor bridge Converter internal control Systems DC-DC Converters 4.6 Applications to Renewable Energy Generators Applications to PV Systems Applications to wind power References 5 Power System Analysis 5.1 Introduction 5.2 The Transmission System Single-phase representation Transmission and distribution Systems Example networks 5.3 Voltage Control 5.4 Power Flow in an Individual Section of Line Electrical characteristics oflines and cables Single-phase equivalent circuit Voltage drop calculation Simplifications and conclusions 5.5 Reactive Power Management Reactive power compensation equipment 5.6 Load Flow and Power System Simulation Uses of load flow A particular case Network data Load/generation data The load flow calculations Results Unbalanced load flow 5.7 Faults and Protection Short-circuit fault currents Symmetrica! three-phase fault current Fault currents in general Fault level (short-circuit level) - weak grids Thevenin equivalent circuit 5.8 Time Varying and Dynamic Simulations 5.9 Reliability Analysis References 6 Renewable Energy Generation in Power Systems 6.1 Distributed Generation Introduction Point of common coupling (PCC) Connection voltage 6.2 Voltage Effects Steady State voltage rise Automatic voltage control - tap changers Active and reactive power from renewable energy generators Example load flow

6 ix 6.3 Thermal Limits Overhead lines and cables Transformers Other Embedded Generation Issues Flicker, voltage steps and dips Harmonics/distortion Phase voltage imbalance Power quality Network reinforcement Network losses Fault level increase Islanding Introduction Loss-of-mains protection for rotating machines Loss-of-mains protection for inverters Fault Ride-through Generator and Converter Characteristics 192 References Power System Economics and the Electricity Market Introduction The Costs of Electricity Generation Capital and running costs of renewable and conventional generation plant Total generation costs Economic Optimization in Power Systems Variety of generators in a power System Optimum economic dispatch Equal incremental cost dispatch OED with several units and generation limits Costs on a level playing field External Costs Introduction Types of external cost The Kyoto Agreements Costing pollution Pricing pollution Effects of Embedded Generation Value ofenergy at various points ofthe network A cash-flow analysis Value of embedded generation - regional and local issues Capacity credit Summary Support Mechanisms for Renewable Energy Introduction Feed-in law Quota System Carbon tax Electricity Trading Introduction The UK electricity supply industry (ESI) 218

7 X Competitive wholesale markets in other countries The value ofrenewable energy in a competitive wholesale market 226 References The Future - Towards a Sustainable Electricity Supply System Introduction The Future of Wind Power Large wind turbines Offshore wind farm development Building integrated wind turbines The Future of Solar Power PV technology development Solar thermal electric Systems The Future of Biofuels The Future of Hydro and Marine Power Distributed Generation and the Shape of Future Networks Distribution network evolution Active networks Problems associated with distributed generation Options to resolve technical difficulties Conclusions 249 References 250 Appendix: Basic Electric Power Engineering Concepts 253 A.l Introduction 253 A.2 Generators and Consumers of Energy 253 A.3 Why AC? 255 A.4 AC Waveforms 255 A.5 Response of Circuit Components to AC 256 A.5.1 Resistance 257 A.5.2 lnductance 258 A.5.3 Capacitance 259 A.6 Phasors 260 A.7 Phasor Addition 261 A.8 Rectangular Notation 263 A.9 Reactance and Impedance 265 A.9.1 Resistance 265 A.9.2 lnductance 265 A.9.3 Capacitance 266 A.9.4 Impedance 266 A.10 Power in AC Circuits 267 A.ll Reactive Power 269 A.l2 Complex Power 269 A.l3 Conservation of Active and Reactive Power 271 A.14 Effects of Reactive Power Flow - Power Factor Correction 272 A.l5 Three-phase AC 273 A.16 The Thevenin Equivalent Circuit 275 Reference 276 Index 277