The Future of Marine Technologies.pdf

E N E R G Y The Future of Marine Technologies Technology developments, key costs and the future outlook By Paul Breeze ii Paul Breeze Dr Paul Breeze has specialized in the electricity sector for the past 25 years. He is contributing editor for the monthly international magazine for the power industry, Modern Power Systems, and as freelance writer he has contributed to The Financial Times, The Guardian, The Daily Telegraph, The Observer and The Economist. In addition to the power sector, Paul Breezes interests include science and the computer industry. Copyright © 2010 Business Insights Ltd This Management Report is published by Business Insights Ltd. All rights reserved. Reproduction or redistribution of this Management Report in any form for any purpose is expressly prohibited without the prior consent of Business Insights Ltd. The views expressed in this Management Report are those of the publisher, not of Business Insights. Business Insights Ltd accepts no liability for the accuracy or completeness of the information, advice or comment contained in this Management Report nor for any actions taken in reliance thereon. While information, advice or comment is believed to be correct at the time of publication, no responsibility can be accepted by Business Insights Ltd for its completeness or accuracy iii Table of Contents The Future of Marine Technologies Executive summary 10 Introduction 10 Ocean energy resources 10 Ocean thermal energy conversion 11 Wave power generation 11 Tidal stream technologies 12 Tidal barrage power plants 12 Salinity gradient power generation 13 The economics of marine power generation 13 The prospects for marine power generation technologies 13 Chapter 1 Introduction 16 Summary 16 Marine energy resources 17 Energy capture technologies 18 The structure of the report 20 Chapter 2 Ocean energy resources 22 Introduction 22 Global resource levels 23 Wave energy 27 Tidal power 30 Thermal gradient 32 Salinity gradient 33 Mapping marine resources 33 iv Chapter 3 Ocean thermal energy conversion 36 Introduction 36 Background 37 Heat engine efficiency 39 OTEC configurations 41 Open cycle OTEC 43 OTEC projects 44 Major challenges and developments 46 Environmental considerations 47 Economics 49 Chapter 4 Wave power generation 54 Introduction 54 History of wave energy capture 56 Types of wave energy capture device 57 Shore line and near shore devices 58 Oscillating water columns 58 Tapered channels and overtopping devices 59 Oscillating flaps 60 Offshore wave energy converters 61 Floats, wave pumps and swings 61 Snakes, ducks and pontoons 62 Piezo-electric converters 63 Intermittency and wave energy 63 Wave energy pilot projects 64 Environmental impact 67 Economics 68 Chapter 5 Tidal stream technologies 74 Introduction 74 Tidal stream energy 75 Tidal stream technology 78 Horizontal axis tidal stream turbines 80 Vertical axis tidal stream turbines 83 Cross flow turbines 84 v Hydrofoils 84 Other tidal current systems 85 Tidal stream pilot projects 86 Environmental considerations 88 The economics of tidal stream power generation 89 Chapter 6 Tidal barrage power plants 94 Introduction 94 Tidal barrage principles 98 Bunded reservoirs and tidal lagoons 100 Tidal turbines 101 Tidal barrages 102 Seawater pumped storage 103 Tidal barrage projects 104 Environmental considerations 105 The economics of tidal barrages 107 Chapter 7 Salinity gradient power generation 110 Introduction 110 Extracting power from a salinity gradient 111 Osmotic power 111 Vapor compression 112 Hydrocratic generation 113 Reversed electrodialysis 113 Environmental considerations 114 Costs 115 Chapter 8 The economics of marine power generation 118 Introduction 118 Comparisons with wind energy 119 Installed cost of marine technologies 121 Cost of electricity from marine power generation technologies 122 vi Chapter 9 The prospects for marine power generation technologies 128 Introduction 128 Comparative costs of power generation 129 Wave and tidal stream power 136 Tidal barrage power plants 139 Ocean thermal energy technology 140 Salinity gradient power generation 143 Conclusions 143 Index 145 vii List of Figures Figure 2.1: Ocean energy resources, (TWh/y) 24 Figure 2.2: Ocean energy potential generating capacity, (GW) 26 Figure 2.3: US wave energy potential, (TWh/y) 29 Figure 2.4: US tidal current potential, (TWh/y) 31 Figure 3.5: Theoretical OTEC efficiencies 40 Figure 3.6: Life cycle carbon dioxide emissions from OTEC plants 48 Figure 3.7: Costs for a 100MW floating OTEC plant 51 Figure 4.8: Annual wave energy content for different regions, (kW/m) 55 Figure 4.9: Estimated installation costs for wave energy converters 69 Figure 4.10: Estimated cost of electricity from wave energy plants 70 Figure 5.11: Tidal current turbine size required to sweep out a power density of 1MW at different current speeds 76 Figure 5.12: Water current power swept out by a 10m diameter turbine at different current speeds 78 Figure 5.13: Estimated installed cost ($/kW) of tidal stream generation in North America 92 Figure 6.14: Tidal reach at best global sites, (m) 95 Figure 6.15: Global tidal sites with largest energy potential 97 Figure 8.16: Cost estimates for generation in the UK (£/kW) 124 Figure 9.17: Comparative installed cost of generating technologies (£/kW), UK 131 Figure 9.18: Cost of electricity from competing technologies (£/MWh), UK 132 Figure 9.19: Levelized cost of electricity from competing technologies ($/MWh), California 134 Figure 9.20: Island states with potential OTEC 142 viii List of Tables Table 2.1: Ocean energy resources, (TWh/y) 23 Table 2.2: Ocean energy potential generating capacity, (GW) 25 Table 2.3: US wave energy potential, (TWh/y) 28 Table 2.4: US tidal current potential, (TWh/y) 31 Table 3.5: Theoretical OTEC efficiencies 40 Table 3.6: OTEC plant configurations 42 Table 3.7: Life cycle carbon dioxide emissions from OTEC plants 48 Table 3.8: Costs for a 100MW floating OTEC plant 50 Table 4.9: Annual wave energy content for different regions, (kW/m) 55 Table 4.10: Types of wave energy converter 57 Table 4.11: Estimated installation costs for wave energy converters 68 Table 4.12: Estimated cost of electricity from wave energy plants 70 Table 5.13: Tidal current turbine size required to sweep out a power density of 1MW at different current speeds 76 Table 5.14: Water current power swept out by a 10m diameter turbine at different current speeds 77 Table 5.15: Types of tidal stream power generation devices 81 Table 5.16: Cost estimates for tidal stream power generation 90 Table 5.17: Economics of tidal stream generation in North America 91 Table 6.18: Tidal reach at best global sites, (m) 95 Table 6.19: Global tidal sites with largest energy potential 96 Table 6.20: Major tidal barrage power plants 104 Table 7.21: Types of salinity gradient power generation 113 Table 8.22: Marine power generation costs 121 Table 8.23: Cost estimates for generation in the UK 123 Table 9.24: Comparative installed cost of generating technologies (£/kW), UK 130 Table 9.25: Cost of electricity from competing technologies (£/MWh), UK 132 Table 9.26: Levelized cost of electricity from competing technologies ($/MWh), California 134 Table 9.27: European growth prospects for wave and tidal stream technologies 137 Table 9.28: Island states with potential OTEC 141 9 Executive summary 10 Executive summary Introduction Many of the world's potential renewable energy resources are being exploited today to generate electricity. The main exception is marine energy, the energy contained in various forms in the world's seas and oceans. Although the history of marine energy capture stretches back a millennium, modern attempts at turning the energy into electricity, which began in the late nineteenth century, have generally proved unsuccessful. This situation looks set to change as the challenge of combating global warming inspires a renewed search for methods to extract marine energy from our seas. Wave power and systems that can exploit the movement of water generated by the tides are attracting the most attention but methods for using the warm seas in the tropics to produce electricity and even the attempts to extract energy released when salt and fresh water mix are now coming under the gaze of scientists and technicians too. Some of the resulting technologies remain far from commercial implementation but several are now close to commercialization. Ocean energy resources The energy contained within the oceans is generated in a variety of different ways. Tidal energy results from the gravitational interaction of the moon and the sun on the water which lies upon the surface of the Earth. This causes diurnal movements in water levels, resulting in the movement of massive volumes of water. Waves are generated when a wind blows across the surface of a sea or ocean. As such it is a type of solar energy since the winds are generated by atmospheric temperature differences created by solar warming. Warm tropical seas are the result of direct heating of the surface of an ocean and the salinity gradient that is created between fresh water on land and sea water is also a solar phenomenon too since fresh water, from rain, is generated by evaporation of water by the sun. The total amount of energy contained in all these 11 resources could be as much as five times annual global electricity production in 2010. Even if only a part of this can be exploited, its potential contribution to global electricity supply is enormous. Ocean thermal energy conversion Ocean thermal energy conversion (OTEC) is the technology used to exploit the heat absorbed from the sun by tropical oceans and seas. The technology uses a conventional heat engine based on a turbine cycle to extract energy and for this both a hot and a cold water source are required. In the case of OTEC, both can be supplied by the seas. The warm surface water provides the hot water source and deep ocean water, which never mixes with the warmer surface water, provides the cold water source. To achieve a temperature difference that is sufficiently large to make energy extraction economically viable, water must be drawn up from one kilometer or more below the surface and this presents OTEC development with perhaps its biggest challenge. The technology is versatile, however, because it is capable of producing desalinated water from the sea as well as electricity. This has made it attractive for use by small island communities where both drinking water and electricity are expensive. Wave power generation Waves form when winds blow across water and the best wind regimes are found where the wind can blow continuously for thousands of miles across the great oceans. The western coastlines of Europe, Africa and the Americas offer some of the best opportunities. Wave fronts can carry up to 100kW for each meter of length. Wave energy is contained in the oscillatory motion of water at the surface of the sea so capturing it involves harnessing this movement in one way or another. Several different techniques have evolved for extracting this energy but all rely on using the oscillating motion to drive an energy capture device. Today there are probably one hundred or more different devices being tested around the world as scientists and technologists seek to perfect wave power generation. The wave energy resource is unpredictable, much like wind power. Good forecasting techniques are helpful in rendering the energy 12 production more reliable but energy storage is the ideal means of getting the best from the waves. Tidal stream technologies Tidal stream technologies are designed to extract energy from a moving current of water. In most cases this will be a current caused by tidal movements but it may also be flowing water in a river. The devices are in many cases the aquatic equivalent of wind turbines and are designed to operate as free standing devices in a waterway or at a coastal site. Others use more novel approaches to extracting energy. Water is much denser than wind and the energy content of flowing water is much higher than for moving air. As a result, turbines for extracting energy from water can be much smaller than similarly-rated wind turbines. Tidal stream devices can be placed on the sea or river bed, they can be designed to be buoyant and then tethered at the required height in the stream or they can be lowered into the water from a barge. All these approaches are being tested in the large number of devices currently under development and several demonstration projects are underway or planned. Tidal barrage power plants The tidal barrage power plant is the only type of marine power plant that has seen commercial service. A 240MW plant has been operating in France since 1966. A tidal barrage plant is the tidal equivalent of a hydropower plant, employing a large dam or barrage placed across an estuary or tidal basin and fitted with turbines that can extract energy from the head of water which is developed as the tide moves in and out. Tidal barrages have a significant environmental impact since they change the tidal conditions either side of the plant. They generally tend to be large and therefore expensive plants to build. However tidal power, though intermittent since is relies on the tides, is extremely predictable. Like large hydropower, tidal developments are restricted to suitable sites where the tidal movement is large. There are a significant number of such sites around the globe. 13 Salinity gradient power generation The diluting of seawater with fresh water releases energy that can potentially be exploited to generate electrical power. This energy potential is widely dispersed since it can be found wherever rivers flow into the sea. The availability of this source of energy has only recently been recognized but there now are a number of methods that have been devised to capture it. The most advanced relies on the use of osmosis, the process that occurs when fresh and salt water is separated by a membrane that will only allow water to pass. This can be used to generate hydrostatic pressure and drive a turbine. The economics of marine power generation With all but tidal barrage power plants still in an early stage of development and no commercial plants of any other type in operation, assessing the economics of marine power generation technologies today depends on projections based on early prototypes of early demonstration units. Today these are generally more costly than alternative forms of power generation, both conventional and renewable. However the example of the wind power market shows that costs can fall dramatically as both technology improves and economies of scale are realized. Some early predictions suggest that some marine technologies might be cheaper than wind power but the level of uncertainty in such predictions is high. It is certain, however, that marine power will require additional support in the form o