Electricity from Wave and Tide An Introduction to Marine Energy

A concise yet technically authoritative overview of modern marine energy devices with the goal of sustainable electricity generation

With 165 full-colour illustrations and photographs of devices at an advanced stage, the book provides inspiring case studies of today’s most promising marine energy devices and developments, including full-scale grid-connected prototypes tested in sea conditions. It also covers the European Marine Energy Centre (EMEC) in Orkney, Scotland, where many of the devices are assessed.

Topics discussed:

• global resources – drawing energy from the World’s waves and tides
• history of wave and tidal stream systems
• theoretical background to modern developments
• conversion of marine energy into grid electricity
• modern wave energy converters and tidal stream energy converters

This book is aimed at a wide readership including professionals, policy makers and employees in the energy sector needing an introduction to marine energy. Its descriptive style and technical level will also appeal to students of renewable energy, and the growing number of people who wish to understand how marine devices can contribute to carbon-free electricity generation in the 21^st century.

Dr Paul A. Lynn, Consultant, UK

Paul Lynn was Founding Managing Editor of the successful and highly prestigious Wiley journal, Progress in Photovoltaics,from 1993 until 2006. He was formally Assistant Lecturer at Imperial College London and Lecturer and Reader in Electrical and Electronic Engineering at the University of Bristol from 1969 until 1984.

As a retired academic, Paul Lynn’s continued interest in renewable energy includes designing and building solar-powered boats. He designed and constructed the catamaran that completed the first ever solar-powered voyage along the non-Tidal Thames in 2003. He was awarded 1^st and 2^nd prizes in the Sustainable Transport section at the Royal Bath & West show in 2008 for two more recent solar catamarans.

Paul Lynn has written six technical books to date and is author of over 50 technical papers and articles.

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®   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

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