Electricity from Wave and Tide

Preface ix Acknowledgements xi 1. Introduction 1 1.1 Marine energy and Planet Earth 1 1.2 Marine resources 5 1.2.1 Waves of the world 5 1.2.2 Tides of the world 11 1.3 A piece of history 18 1.3.1 Working with waves 18 1.3.2 Tapping tides 23 1.4 Power, energy and performance 27 1.5 Into the future 34 References 37 2. Capturing marine energy 39 2.1 Ocean waves 39 2.1.1 Linear waves 39 2.1.2 Random waves 43 2.1.3 Wave spectra48 2.1.4 Wave modification 52 2.1.5 Wave measurement 56 2.2 Wave energy conversion 59 2.2.1 Introductory 59 2.2.2 Types of wave energy converter 60 2.2.3 Principles of wave energy capture 62 2.2.3.1 Floating devices 62 2.2.3.2 Tuning and damping 64 2.2.3.3 When waves meet WECs 68 2.3 Tidal streams 71 2.3.1 Hydrodynamics 71 2.3.2 Tidal harmonics 76 2.3.3 Predicting tidal streams 83 2.4 Tidal stream energy conversion 86 2.4.1 Introductory 86 2.4.2 Tidal stream turbines 89 2.4.2.1 Turbine sizes and power ratings 89 2.4.2.2 Extracting energy: the Betz Limit 93 2.4.2.3 Lift and drag 96 2.4.2.4 Rotor speed and power coefficient 102 2.4.3 Turbine siting 105 2.5 Research and development 108 2.5.1 Models and test tanks 108 2.5.2 The European Marine Energy Centre (EMEC) 111 2.5.2.1 Wave and tidal test sites 111 2.5.2.2 Research activities 121 References 124 3. Generating electricity 125 3.1 Introductory 125 3.2 Power take-off 126 3.3 AC electricity 130 3.4 Generators 141 3.4.1 Introductory 141 3.4.2 Synchronous generators 147 3.4.3 Asynchronous generators 151 3.4.3.1 Squirrel-cage and wound-rotor induction machines 151 3.4.3.2 Doubly-fed induction generators 157 3.4.4 Linear motion generators 162 3.5 Connecting to the grid 166 3.5.1 Setting the scene 166 3.5.2 Grid strength and fault levels 169 3.5.3 Electrical quality 173 3.6 Large-scale renewable energy 175 3.6.1 Introductory 175 3.6.2 Intermittency and variability176 3.6.3 Capacity credit and backup generation 179 References 183 4. Case studies: Wave energy converters 185 4.1 Introductory 185 4.2 Case studies 186 4.2.1 Pelamis 186 4.2.2 Oyster 192 4.2.3 Limpet andMutriku 199 4.2.4 Wave Dragon 205 4.2.5 PowerBuoy(r) 211 4.2.6 Penguin 216 References 221 5. Case studies: Tidal stream energy converters 223 5.1 Introductory 223 5.2 Case studies 224 5.2.1 Andritz Hydro Hammerfest 224 5.2.2 Atlantis Resources 229 5.2.3 Marine Current Turbines 234 5.2.4 OpenHydro 240 5.2.5 Pulse Tidal 245 5.2.6 Scotrenewables Tidal Power 251 5.2.7 Tidal Generation 258 References 262 Index 263