Tapping the Tidal Power Potential of the Eastern Irish Sea: Final Report

Abstract:

<p>The geographical location of the United Kingdom and the seas that surround it provide internationally enviable renewable resources. Technologies for wind power extraction are now mature and an increasing role for the opportunistic capture of this intermittent energy source for the electricity grid is firmly established. Marine wave energy offers even greater scope for the future, with somewhat slower temporal variability but with necessary technological advances still outstanding. Even more exclusive, however, is the potential for tidal energy extraction from around the UK coastline. The most attractive locations for harnessing tidal power are estuaries with a high tidal range for barrages, and other areas with strong tidal currents (e.g. straits and headlands) for free-standing tidal stream devices. Barrage schemes, drawing on established low-head hydropower technology, are fully proven. The La Rance plant in France has now passed its 40th year of operation.</p> <p>Of about 500-1000TWh/year of tidal energy potentially available worldwide (Baker, 1991), Hammons (1993) estimated the UK to hold 50TWh/year, representing 48% of the European resource, and few sites worldwide are as close to electricity users and the transmission grid as those in the UK. Following from a series of government-funded studies commissioned by UKAEA in the 1980s, 8 major estuaries were identified where tidal barrages would be capable of procuring over 40TWh/year. In rank order of scale, they were the Severn, Solway Firth, Morecambe Bay, Wash, Humber, Thames, Mersey and Dee (see UKAEA, 1980 and 1984, Baker, 1991). Thus, about half of this energy was located in the North West of England (House of Commons, 2008).</p> <p>Also within the Eastern Irish Sea, exploitable tidal stream resources have been identified to the north of Anglesey and to the north of the Isle of Man, with more localised resources in the approaches to Morecambe Bay and the Solway Firth (DTI, 2004). Note, however, that in estuaries it is unlikely that tidal stream options can come close to the energy yield of barrage alternatives. Recent assessments for the Mersey offer estimates of 40-100GWh/year for tidal stream arrays, contrasting with 1200GWh/year estimated for a barrage at an equivalent location (RSK Environmental Ltd, 2007). In a similar vein, whilst tidal lagoons are often mooted as a viable alternative to estuary barrages, offering a similar operational function, it is highly unlikely that they could be realised at a comparable scale and remain competitive on cost against the major barrage schemes cited above.</p> <p>Barrages on the Solway Firth, Morecambe Bay, Mersey and Dee, operating in ebb-only generation with 1xDoEn turbine provision could meet about 5% of UK demand. With further scheme optimisations and refined representation of pumping efficiencies, a figure close to 6% might be achieved. Based on the scale of the North West's 'economy' at approximately 12% of the UK total, this energy capture should supply about half the North West's present electricity needs.</p> <p>In economic terms, this study has shown that the North West schemes should be no more than 70% more expensive in unit cost of energy produced when compared to that achievable from the Severn with, in each case, lowest costs arising from installations consistent with the Department of Energy's 1980s studies (1xDoEn turbine installations).</p> <p>Increasing turbine provision substantially (to up to 3 times the default provision) would increase energy capture and enable retention of more of the intertidal area in the estuarial basin, so alleviating some of the environmental concerns, but at extra cost of electricity produced.</p> <p>2-D modelling significantly alters the energy predictions from the 0-D modelling, so demonstrating the necessity of the more rigorous approach. As a consequence of this, further investigation is required to determine how much of the substantial energy increases predicted from 0-D modelling of 3xDoEn installations can be realised in the 2-D modelling. Presently, only about a 20% enhancement has been achieved, in part because of the reduction of tidal amplitudes at the barrage locations.</p> <p>Earlier studies (DoEn, 1989) reported the potential for an outer line for the Severn barrage producing an additional 6.80TWh/year and barrages on the Wash, Humber and Thames capable of yielding 3.75, 1.65 and 1.37TWh/year, respectively (UKAEA, 1980). Combining these with the 33TWh/year obtained herein for the North West barrages and the Cardiff-Weston Severn barrage scheme (for similar 1xDoEn ebb-mode operation) would achieve a total of about 46.5TWh/year. This should be capable of uplift to around 50TWh/year by addition of positive head pumping, representing 13% of the UK (2005) electricity consumption of 387TWh/year.</p> This report is divided into the following sections: <ol> <li>Introduction</li> <li>Preliminary Studies</li> <li>Energy from Major Barrage Schemes (0-D Modelling)</li> <li>Conjunctive (Multi-Scheme) Energy Capture (2-D Modelling)</li> <li>Environmental Implications</li> <li>Conclusions and Recommendations</li> <li>References and Bibliography</li> </ol> Appendices <ul> <li>A.1.1 The research team</li> <li>A.1.2 House of Commons evidence</li> <li>A.1.3 Tidal stream energy extraction from estuaries</li> <li>A.2.1 Theoretical background to energy computations (0-D modelling)</li> <li>A.2.2 Implication of entry and exit losses in turbine conduits</li> <li>A.2.3 Validation of Turgency/Generation Matlab computational routines</li> <li>A.2.4 Preliminary studies - potential from barrages on major UK estuaries</li> <li>A.2.5 Constructional aspects</li> <li>A.3.1 Barrage lines, cross sections and bathymetries</li> <li>A.3.2 Energy computation spreadsheets</li> <li>A.3.3 Costing calculations</li> <li>A.4.1 ADCIRC background</li> <li>A.4.2 Barrage operation in ADCIRC</li> <li>A.4.3 Tidal stream farms in ADCIRC</li> <li>A.4.4 Validation of simulation grid</li> </ul>

Author(s):

Burrows, R., Walkington, I., Yates, N., Hedges, T., Chen, D., Li, M., Zhou, J., Wolf, J., Proctor, R., Holt, J. and Prandle, D.