The tidal range energy potential of the West Coast of the United Kingdom
Introduction
Since the late 1980s, a number of barrage schemes for power production have been suggested for various estuarial sites around the coast of the UK, in a range of studies for the then UK Department of Energy (DoEn), now the Department of Energy and Climate Change (DECC). These schemes vary from small scale sites such as the Dovey, which might produce about 50 GWh per year [1], to very large power generation schemes, such as the proposed outer line in the Severn Estuary, which could potentially produce up to 19.7 TWh per year [2], [3]. The detailed operation of a tidal barrage has only been considered in a small number of cases, most notably the Severn and Mersey estuaries. Arising largely from the former, empirical methods have been employed to estimate power output for a large number of potential schemes of varying scale [2], [3]. Most notable amongst these have been the opportunities from the West Coast of England in the Dee Estuary, Morecambe Bay and the Solway Firth, supplementing the Severn and Mersey schemes (see Fig. 1).
The basis for previous UK studies has generally been to achieve optimal economic power generation and, to this end, ebb-mode turbine energy generation has been the preferred mode of operation. However, no consideration has been given to the interactive aspects of the conjunctive operation of the schemes.
The major benefit of multiple schemes is the possibility of a longer generation window than the single pulse per tidal cycle produced from an individual scheme operating in one-way generation. In recent preliminary investigations within the Joule Centre study discussed here [4], [5], the joint operation of 8 major barrage schemes, including barrages on the East Coast of the UK (Thames, Wash and Humber), has demonstrated the potential for about 15% of the UK electricity need to be met from tidal range energy, with a further 5% likely to be achievable from tidal stream turbine arrays [6].
In operation, a barrage for power production utilising banks of turbines and sluices merely delays the flux of water as the tidal level changes: holding back the release of water as the tide level subsides under one-way ebb-mode generation so that the ‘head’ (water level) difference is sufficient for turbine operation; or deferring the entry of rising tidal flow to the inner estuary basin for flood-mode generation (see Fig. 2). In two-way (dual-mode) operation, there is a combination of both. Each mode has some restricting effect as energy is extracted from the tide, so reducing the range of tidal variation within the basin: ebb generation generally uplifts low water levels; flood generation generally reduces high water levels; and dual mode results in smaller changes but to both high and low water levels.
Section snippets
0-D modelling
Zero-dimensional modelling was used to study the local behaviour of a barrage with turbine and sluicing systems, assuming flat water surface levels either side (sometimes referred to as a ‘flat-estuary/basin’ or ‘two-tank’ model). This representation can rigorously treat the hydraulics and energy generation from the double-regulated bulb turbine systems considered here, but it makes no allowance for the hydrodynamics of flows arriving at, or flowing from, the barrage.
Conjunctive (multi-scheme) energy capture (2-D modelling)
The operation, power production and impacts of barrages, when operated conjunctively in the Irish Sea and the Severn Estuary, were examined through the use of the computational ocean model ADCIRC. This is a 2-D, depth-integrated, shallow-water finite element model. It is run using an unstructured grid for the discretisation of the mass and momentum equations. The model was developed in the USA [9], [10] for use in modelling tides and surges on shelf seas. It has been modified so that barrages
Wider context
The renewable energy capture estimated herein could reliably meet about half of the North West of England’s present electricity need. A similar scale of benefit to the UK would be contributed by the Severn scheme. The broader potential contribution, including schemes on the UK’s East Coast, has been discussed by Burrows et al. [4], [13]. For the present schemes considered here [5], these inputs could be achievable at unit electricity costs which are comparable to alternative sources, assuming
Conclusions
- 1.
Prandle’s parametric 0-D modelling provides a valuable first estimate of the energy potential of any tidal impoundment scheme (barrage or lagoon). In ebb mode, approximately half of the ebb-phase change in potential energy is captured and the basin water level drops only marginally below the mean sea level.
- 2.
The more rigorous 0-D modelling adopted by the UK Department of Energy in the 1980s yielded practicable schemes, at similar levels of energy capture to Prandle’s approach, focusing almost
Acknowledgements
The work reported herein has been undertaken in the UK as part of project JIRP 106/03 funded over the period 2006–2008 by the Northwest Regional Development Agency through the Joule Centre. The views expressed are those of the authors and do not necessarily reflect those of the sponsors or the host institutions in which the work was conducted.
References (15)
- United Kingdom Atomic Energy Authority (UKAEA). Preliminary survey of small scale tidal energy. Severn tidal power...
- Department of Energy (DoEn). The potential for tidal energy from small estuaries. ETSU TID 4048-P1;...
- House of Commons (HoC). Renewable electricity-generation technologies. Innovation, universities, science and skills...
- Burrows R. et al. Tapping the tidal potential of the Eastern Irish Sea. Final Report, Joule Project JIRP106/03....
- Sustainable Development Commission (SDC). Turning the tide: Tidal power in the UK. London: SDC; 2007....
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