Tidal Power in the UK Research Report 5 - UK case studies An evidence-based report by AEA Energy & Environment for the Sustainable Development Commission October 2007 Tidal energy case studies Review of seven UK tidal energy case studies Report to the Sustainable Development Commission ED Number ED02701100 Issue Number 1 Date October 2007 Seven UK tidal energy case studies AEA/ED02701/ Issue 1 \\LER330FS\COMMON\GB536DF\SDC\WORK PROGRAMME\ENERGY\TIDAL PROJECT\RESEARCH REPORTS\CONTRACT 5 - AEA\FINAL DRAFT - OCTOBER\20071011AEACONTRACT5FINAL.DOC Seven UK tidal energy case studies AEA/ED02701/ Issue 1 Title Review of seven UK tidal energy case studies Customer Sustainable Development Commission Customer reference Tidal power project research contracts contract no. 5. ITT dated 13th October 2006 Confidentiality, This report is the Copyright of the Sustainable Development copyright and Commission and has been prepared by AEA Technology plc under reproduction contract to Sustainable Development Commission dated 14 November 2006. The contents of this report may not be reproduced in whole or in part, nor passed to any organisation or person without the specific prior written permission of Sustainable Development Commission AEA Technology plc accepts no liability whatsoever to any third party for any loss or damage arising from any interpretation or use of the information contained in this report, or reliance on any views expressed therein File reference Reference number ED ED02701 - Issue 1 AEA Energy & Environment The Gemini Building Fermi Avenue Harwell Didcot OX11 0QR t: 0870 190 6083 f: 0870 190 6336 AEA Energy & Environment is a business name of AEA Technology plc AEA Energy & Environment is certificated to ISO9001 and ISO14001 Author Name James Craig, Howard Rudd, Philip Michael (AEA Energy & Environment). Scott Couch (University of Edinburgh), John Hartley (Hartley Anderson) Approved by Name Philip Michael Signature Date AEA Energy & Environment iii Seven UK tidal energy case studies AEA/ED02701/ Issue 1 iv AEA Energy & Environment Seven UK tidal energy case studies AEA/ED02701/ Issue 1 Executive summary As part of a wide ranging review of the UK’s tidal energy potential, the Sustainable Development Commission (SDC) has commissioned a series of five reports to evaluate various aspects of tidal power in the UK. This report consists of a series of seven case studies of different tidal energy technologies around the UK. These case studies were selected to illustrate different tidal energy technology concepts from a range of different locations throughout the UK (Figure 1.1). It should be emphasised that these case studies are not based on any proposed commercial projects. In each example the background to the scheme is outlined including the rationale for the location, the capital cost, energy output and estimated carbon savings. Each case study also includes a section on regional benefits including employment, related benefits from tourism, leisure pursuits or where appropriate transport infrastructure might also be developed. The potential environmental impacts that each scheme might cause are also outlined including the preliminary conclusions from previous studies. Table 1 Summary of key data from tidal energy case studies Technology Region mean Spring Annual tidal range (m) Installed CO2 Average Case study or peak Spring Capacity saved/year Energy Output current velocity (MW) (tonnes) (GWh/year) (m/sec)* Strangford Lough Tidal Current Northern 3.0* 30 137.14 58,910 Tidal Current Array Ireland Pentland Firth Tidal Current Northern 4.15* 195.75 636.74 273,798 Tidal Current Array Scotland Liverpool Bay Tidal lagoon North Wales 6.7 340 938.0 403,424 lagoon Tidal energy North West Mersey Barrage 8.0 700 1,450.0 623,500 barrage England Tidal energy South Wales Loughor Barrage 3.9 5 15.1 6,622 barrage Tidal energy North West Duddon Barrage 5.8 100 212.0 91,160 barrage England Tidal energy North West Wyre Barrage 6.6 63.6 133.0 57,190 barrage England Strangford Narrows tidal current array This case study is based on a hypothetical array of tidal current devices deployed in Strangford Narrows, which connects the Strangford Lough with the open sea. The exchange of water between the lough and the sea creates strong currents with peak velocities typically over 3m/s. As there are no commercial tidal current devices we have chosen for our case studies a pile mounted, twin rotor concept similar to MCT’s SeaGen concept. This concept is one of the best known and most advanced tidal current devices. It must be emphasised that MCT have no plans for commercial development of this technology at this site. This case study was selected to illustrate the full range of potential environmental impacts from tidal AEA Energy & Environment v Seven UK tidal energy case studies AEA/ED02701/ Issue 1 current technology and because we were required to include at least one case study from Northern Ireland. This tidal stream concept is a pile-mounted device and is best suited to sites where the water is up to 40m deep. The machine has two, 16m diameter, two-bladed rotors attached to the ends of a horizontal cross beam that is supported on a vertical pile. The pile is a steel tube 3m in diameter, 55m long and weighs 270 tonnes. It is cemented into a 21m deep socket that is drilled into the seabed. The rotors always point in the same direction but can be operated on both the ebb and flood tides by changing pitch of the blades through 180°. In this example the distance between the centres of the two rotors is 27m. This means that there is an 11m gap between the edges of the disks swept out by the two rotors. This will prevent the wake of the pile impinging on the rotors when they are downstream of the pile. The clearance between the rotor disk and the seabed is 5m and at low tide the rotors occupy two thirds of the depth of the water column. The powertrains (rotors, gearboxes and generators) are mounted on the cross beam, which is attached to a collar that can slide up and down the pile. Hydraulic rams lift the crossbeam and rotors out of the water for inspection and maintenance. The control systems are in a pod on the top of the pile and the transformer is in the top of the pile just below the pod. It must be stressed that tidal current technology is still at an early stage of development and capital and operating costs and performance have yet to be determined and are highly uncertain. We have therefore assessed the cost of energy for a range of possible future capital costs, between £6,000/kW installed and £1,000/kW installed.. The highest figure we used was derived from the published information on the Government grant to SeaGen, together with assumptions about how much of that is for the machine itself; this gives an estimated capital cost of the project of £183 million, which is equivalent to ~£6,000/kW. However, some caution needs to be applied to this estimate because it is based on a technology at a very early stage of development. Experience from other technologies has shown that through economies of scale, experience and innovation, technologies that can be deployed in modular units should be able to achieve cost reductions. However, the extent of future cost reduction that may be achieved is not known. A machine at this location could be designed to produce up to 1MW of electricity when the water velocity is 2.8m/s. At lower water speeds it would produce correspondingly less electricity, roughly in proportion to the cube of the current speed. An array of these devices could generate an estimated 137.14 GWh/year at the following unit costs of generation. Capacity Energy Capital cost Unit Cost of generation (p/kWh) Output (£/kW (% discount rate assuming a 20 year installed) technical life) (MW) (GWh/year) 3.5% 8% 10% 15% 30 137.14 6,000 12.45 15.30 16.63 20.02 30 137.14 1,000 2.07 2.55 2.77 3.34 Although there are no plans that we are aware of, a hypothetical array in the Strangford Narrows could benefit the local economy by about £9.2 million. The Belfast shipyard, Harland and Wolfe, could provide a reliable regional base for assembly of the device components prior to shipment and installation in the Strangford Narrows. There would be a limited demand for possibly 5 permanent staff on site to operate the array. vi AEA Energy & Environment Seven UK tidal energy case studies AEA/ED02701/ Issue 1 Strangford Lough is a popular area for recreational activities including water sports, boating, sailing, walking, bird watching are tourism. The array would be confined to the Narrows and would not necessarily affect these activities elsewhere although the presence of prominent monopile structures in this stretch of water would present a collision risk for vessels moving within the Narrows. Strangford Lough and the Narrows have important nature conservation status and are protected by five different designations. Strangford Narrows is a Special Protection Area, a Marine Nature Reserve and an Area of Special Scientific Interest. These designations would be important to any development activity considered or proposed for Strangford Lough. There are specific concerns that submerged turbines might present a collision risk to marine mammals and possibly to sea birds above the water. During construction there is potential for contamination of the sea-bed and temporary increases in turbidity. Tidal current turbines could cause localised changes to tidal flows and sediment transport, although the extent of these changes has not been quantified by research. The monopile structures would be clearly visible from each shore of the Narrows as slim linear features.