Tidal Power in the UK Research Report 2 - Tidal technologies overview An evidence-based report by Entec for the Sustainable Development Commission October 2007 Sustainable Development Commission Tidal Technologies Overview Contract 2 Final Report May 2007 Creating the environment for business Copyright and Non-Disclosure Notice The contents and layout of this report are subject to copyright owned by Entec (© Entec UK Limited 2007) save to the extent that copyright has been legally assigned by us to another party or is used by Entec under licence. To the extent that we own the copyright in this report, it may not be copied or used without our prior written agreement for any purpose other than the purpose indicated in this report. The methodology (if any) contained in this report is provided to you in confidence and must not be disclosed or copied to third parties without the prior written agreement of Entec. 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Document Revisions No. Details Date 0 C020i First draft January 2007 1 C042i Second draft, additional March 2007 details added in all sections according to comments on C020i and discussions with SDC. 2 C055i Third draft, incorporating May 2007 reviewer comments and executive summary 3 C055i2 Final report, incorporating June 2007 comments from SDC © Entec UK Limited Page ii Doc Reg No. 19495 C055i2 May 2007 Creating the environment for business Executive Summary Purpose of this Report Entec UK Ltd. were commissioned as independent consultants by the Sustainable Development Commission (SDC) to produce this report, which explores the varied issues surrounding the generation of tidal power in the UK from the perspective of sustainable development. This report has been produced for the purpose of providing the SDC with a high-level overview of the main technological, environmental, economic and social issues relating to the UK’s tidal energy potential. The SDC will use the information in this report (and reports from other consultants working on their tidal power project) as an evidence base for the preparation of a report (provisionally entitled ‘Tidal Power in the UK’) which will provide the basis for the SDC position on tidal power, and will inform its advocacy and advice to the UK Government, the Devolved Administrations and the South West Regional Development Agency (SWRDA) on this issue. The report is an overview of tidal energy in the UK, introducing key concepts and issues to the reader, and referring them to referenced information sources for more detailed analysis. The technological, environmental, economic and social issues surrounding the generation of tidal power are multiple and interlinked. An attempt has been made in this report to unravel the complexities of the subject by presenting information in four clear sections which set out the key points and ideas in a coherent fashion. Following a general introduction to the concept of tidal power, which explores the different technologies available and their methods of action, wider issues surrounding the technologies, the environmental effects and the social and economic issues are set out in separate sections. The key points from each of these sections are summarised below. Sections use available information to differentiate between different tidal energy technologies, and to present the benefits and disbenefits of each technology type. The issues raised in each section are intended to relate to a generic technology type rather than to a specific device or proposed scheme. However, in some cases it has not been possible to avoid reliance on information from certain technologies or specific schemes as a result of a lack of general information. Tidal technologies The waters of the ocean rise and fall twice every 24 hours as a result of gravitational interactions between the sun, moon and earth. The rise and fall of tides can be used to generate electricity, and is a highly predictable source of renewable energy. There are two ways in which electricity can be generated from the tides: • When tides rise and fall, water moves in and out of shallow basins and estuaries, and this causes a change in the height of the water. The tidal range is the difference in height between high and low tides. This difference in height can be used to generate electricity. The tidal range resource is greatest in shallow waters. © Entec UK Limited Page iv Doc Reg No. 19495 C055i2 May 2007 Creating the environment for business • As tides rise and fall, differences in pressure between areas of sea cause water to move from areas of high pressure to areas of low pressure. As the water moves, it can be accelerated around headlands and through channels. This is the tidal stream, and the movement of water can be used to generate electricity. The tidal stream resource is found in both shallow and deep water. Tidal range technologies exploit the difference in height between high and low tides by holding back water at high tide and releasing it through turbines at low tide. Tidal barrages and tidal lagoons are tidal range schemes; barrages span an estuary or embayment, whereas tidal lagoons enclose a discrete area of water in shallow coastal locations. Tidal stream technologies generate electricity using the flow of water created by the tides and accelerated by coastal topography. There are many different types of tidal stream devices, although they all work on the principle of the tidal stream causing a part of the device to move, and this movement being used to generate electricity. The moving part may be a hydrofoil, or a horizontal or vertical rotor. Some devices have a duct around the rotor to increase the flow of water. Some tidal stream devices are fixed to the seabed on monopiles or concrete bases, while others float and are moored to the seabed using chains and anchors. Some devices are completely submerged, while others may have parts above the water. In the majority of cases, the moving part of the tidal stream devices is directly moved by the tidal stream flowing past it; however, in venturi systems the movement of water is used to cause flow through a turbine in a secondary circuit. Currently in the UK there are no functioning commercial tidal energy schemes, although there is a significant tidal range and tidal stream resource in UK waters, and therefore a strong potential for the generation of tidal electricity. There are a number of functioning tidal barrages in the world, but no tidal lagoons. There are a wide range of tidal stream devices currently in development in the UK and elsewhere in the world. Several of these are at the stage of prototype or part-scale model deployment, and are receiving funding from various sources including the Department of Trade and Industry (DTI) and the Scottish Executive. Technological differentiators Tidal energy, in common with other renewable sources of energy, would have the advantage of reducing the UK’s overall carbon emissions from electricity production. By replacing electricity production by fossil fuels, tidal energy schemes such as the Cardiff-Weston barrage could reduce carbon emissions by over 7 million tonnes per year; the Swansea Bay tidal lagoon scheme could reduce emissions by over 53,000 tonnes per year, and a tidal stream farm by up to 1 million tonnes per year (depending on the quality of the tidal stream resource exploited). Such emissions reductions are a significant environmental and political driver for the development of the UK’s various renewable energy industries. There are many different factors which affect the economic and commercial viability of tidal power generation in the UK, and many of these factors differ between different types of tidal energy schemes. The key issues are: • The size and accessibility of the tidal range and tidal stream resource; © Entec UK Limited Page v Doc Reg No. 19495 C055i2 May 2007 Creating the environment for business • The amount of electricity which can be generated by a scheme; • The ability to transmit this electricity to consumers; • The cost of constructing, maintaining and decommissioning the tidal energy scheme; and • The cost (actual and competitive) of the electricity produced. Resource size and accessibility The tidal range resource of the UK is difficult to accurately assess, but has been estimated to be in the region of 19 TWh/y. This has the potential to supply almost 5% of the UK’s electricity demand. Some sources estimate the tidal range resource in the UK to be as high as 50 TWh/y. The majority of the tidal range resource is located along the west coast of England and Wales, with the Severn Estuary alone accounting for 17 TWh/y. Smaller and shallower inlets around the coast have the potential for tidal range schemes, but there are engineering difficulties with exploiting the resource here, and barrage schemes in these areas may not be commercially viable.