Select Committee on Innovation, Universities, Science and Skills Written Evidence

Memorandum 4

Submission from the University of Liverpool


  This submission aims to bring back to full attention the substantial potential role of tidal barrage solutions for renewable energy generation in the UK. It is demonstrated here that installations on as few as eight major estuaries should be capable of meeting 10-12% of present electricity demand (possibly over 15% with a more ambitious scheme on the Severn) this employing fully proven technology. This far exceeds the potential of tidal "stream" turbine or practicable "lagoon systems much vaunted by funding agencies over recent times. It also brings attention to an ongoing study investigating the tidal power potential in the North West of England.


  1.  The medium to long-term procurement of energy and the related issue of climate change is set to remain at the top of government and public agendas, both nationally and internationally, for some time to come. No clear vision has yet emerged for a sustainable global energy future and the combination of rapid growth in both economies and populations in the developing world are set to place extreme pressure on fossil fuel reserves. It seems inevitable, therefore, that as the 21st century evolves, ever greater utilisation of renewable energy resources must be made if the means for modern living are to be preserved. From the perspective of the global community, it is argued that it will ultimately become an obligation for all societies to properly and fully exploit the natural energy resources at their disposal for the common good.

  2.  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 a somewhat lower degree of unpredictability but with necessary technological advances still outstanding at present. 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 large tidal currents (eg straits and headlands) for free-standing tidal stream turbines. Pertinent here is the fact that tidal barrage solutions, drawing on established low-head hydropower technology, are fully proven. The La Rance scheme in France is now in its 39th year of operation (Cottillon, 1978; Pierre, 1993).

  3.  Of about 500-1,000TWh/year of 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, Rufford (1986) identified 16 UK estuaries where tidal barrages would be capable of procuring 44TWh/year and Baker (1986) identified further sites suitable for small-scale installations. In fact the bulk of this energy yield would accrue from eight major estuaries, in rank order of scale, the Severn, Solway Firth, Morecambe Bay, Wash, Humber, Thames, Mersey and Dee (see also Baker, 1991).

  4.  In the context of the future UK energy mix, it is worth noting that the earlier estimates of UK tidal barrage potential amounted to approximately 20% of UK electricity need in the late 1980s and today could offer in the region of 15% (DTI, 2005), with the added benefit (over wind and wave based renewables) of predictable availability. In addition to barrage solutions to tidal energy capture, there is also more modest scope for tidal-stream energy generation using submerged rotors, either free standing or as part of a "tidal fence", these extracting from the kinetic energy of the tidal flows. With attention inevitably to be placed upon reduced energy consumption and demand management, a future tidal power contribution at 20%+ of UK electricity demand would appear realistic.

  5.  Although all tidal energy generation is intermittent locally, covering about 10-11 hours per day, normally in two pulses synchronised with the approximately 12 hour tidal cycle, tidal phase lag around the coastline provides an opportunity for the grid input window to be extended to closer to 24 hours. With its complete predictability, and operating in a mix with thermal, hydropower and nuclear production as well as thermal renewables, an effective base-load role should be attainable.

  6.  The case for a tidal barrage in the Severn estuary, with the highest tidal range in Europe, has and is being actively promoted by the Severn Tidal Power Group with increasing influential support. This scheme alone, (the smaller "inner" of two earlier options [Baker, 1991]), would be capable of meeting about 5-6% of current UK electricity need (Watson & Shaw, 2007).

  7.  The estuaries of the North West of England offer fully complementary potential to the Severn by virtue of the tidal phase lag, as will be illustrated below. The Dee, Mersey, Ribble and Wyre estuaries, Morecambe Bay and the Solway Firth all have a macro-tidal range. Based on the earlier studies (Baker, 1991) a total installed capacity of 12GW was estimated (Ribble excluded), with a potential energy yield of at least 17.5TWh/year, approximately 6% of UK national need and by inference a sizeable proportion of the North West's electricity demand. Of all potential UK sites, the Mersey with a very narrow mouth, and therefore needing a relatively short barrage length (MBC 1992), could offer power production at the lowest unit cost of all UK sites (Baker 1991).

  8.  In this region of the Eastern Irish Sea, exploitable tidal stream resources have also 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). In the estuarial situation, however, 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 40-100 GWh for tidal stream arrays, contrasting with 1200 GWh estimated for a barrage, at an equivalent location. 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.

  9.  It should be noted that a barrage solution attempts merely to delay the natural motion of the tidal flux as sea level changes: holding back the release of water as tide level subsides under "ebb generation" so that "head" (water level) difference is sufficient for turbine operation; deferring the entry of rising tidal flow into the inner estuary basin for "flood generation"; or "dual mode", a combination of both. Each mode has some restricting effect, so reducing the range of tidal variation within the basin, ebb generation solutions generally uplifting mean water levels, "flood" reducing mean levels and dual mode resulting in little change. A degree of environmental modification is, therefore, inevitable, but this does not necessarily imply serious degradation from a physical or ecological perspective, though issues related to protection of habitats would inevitably need to be confronted.

  10.  Barrage schemes are unique amongst power installations, being inherently multi-functional infrastructure, offering flood protection, road and rail crossings and significant amenity/leisure opportunities, amongst other features. Thus, a fully holistic treatment of overall cost-benefit is imperative for robust decision-making. It is suggested that, to date, this position has been inadequately addressed in the formulation of energy strategy, especially in respect of barrages' potential strategic roles in flood defence and transportation planning. It follows, therefore, that apart from the direct appraisal of energy capture, other complementary investigations must be sufficiently advanced to enable proper input in decision-making in respect of these "secondary" functions, as well as the various adverse issues, such as sediment regime change, impact on navigation and environmental modification.

  11.  It is important that robust estimates of the realisable UK tidal energy reserves be established so that they can properly be assimilated into future energy planning (accepting the 10-15 year time horizons necessary). Thereby, rational implementation might be initiated as and when concerns over energy price, security, or carbon emissions dictate. Furthermore, it is considered paramount that this energy potential be fully appreciated when planning application is received for alternative schemes, which might compromise maximum exploitation of the renewable resource. Such instances might arise, for example, should a tidal stream array or tidal fence installation be promoted where the barrage option remains viable and for which a substantially increased energy capture might be expected.

  12.  Following this line of argument, there now remains a need to re-appraise the earlier study estimates of potential barrage energy yield and to further this detailed technical scrutiny with assessment of the various operational mode options (ebb, flood or dual) and in conjunctive action, to firmly establish the scope for an extended (near 24 hour) generation window and a potential base-load role within the electricity grid.

  13.  This submission offers some new insight in this respect, and aims also to bring attention to an ongoing study "Tapping the tidal power potential of the Eastern Irish Sea" being conducted jointly by the University of Liverpool and Proudman Oceanographic Laboratory. Project aims are summarised in the Appendix.

  14. At this early phase of the project, it is possible to offer only preliminary findings on the potential for large scale energy procurement from estuary barrages. This draws on energy generation routines developed for the project (figure 1) and applied to the base data on the estuary bathymetries, barrage lines and tidal regimes taken from the 1980s' literature (later phases will use more precise and updated inputs).

Figure 1


  15.  Figure 2, over the page, illustrates potential outcomes from the introduction of the eight major barrage schemes considered earlier (Baker, 1991). These show the combined power outputs, from the favoured ebb-generation using double regulated axial flow turbines (after Baker, 1991), at each of the barrages. It is immediately apparent that they form essentially two distinct "co-phase" focused groups, the Severn/Wash/Humber and the Solway/Morecambe/Mersey/Dee, with the Thames lying somewhere in between.

  16.  As far as possible an attempt has been made to consider equivalent barrage power schemes to those adopted in the earlier studies (ie similar number and size of turbines and sluices and generator capacities), though limitations in detail available in the literature led to the need for assumptions and compromises, the technical details of which are not given here, but which will be fully explained in future publications.

  17.  The operation strategy depicted in figure 2 is that configured to provide the widest generation window on each barrage. The simulation has been undertaken for 28 tides representing a spring-neap-spring series, shown in part (a), whilst (b) and (c) show the power produced over two-day periods from the neap and spring phases respectively.

  18.  Observations arising and implications:

    —  The North West group of estuary barrages would operate in a complementary fashion to the Severn (and "phase-aligned" Wash and Humber). It should be noted that only approximate estimates of tidal phase have been used herein, based mostly on records from nearest ports and so slight adjustments to the synchronisation might be expected from a more refined analysis.

    —  By judicious use of pumping to enhance water capture around high tide (essentially short-term "pumped storage") and optimal conjunctive operation of the individual schemes, it would seem possible that the power dip between the Severn group outputs and the following NW Group peaks might be smoothed out.

    —  It appears less likely that such action could eliminate the major daily trough, during which only the Thames makes a significant contribution. Other potential estuary barrage or "lagoon" locations, for example around the East coast of Scotland, may be worthy of future consideration, or else different modes of operation may need consideration. "Flood generation" or "dual-mode" operation, whilst generally less efficient in energy conversion than "ebb generation", may provide the added flexibility necessary to provide a significant 24-hr (continuous) output to the grid. The ongoing "Tapping the tidal power potential of the Eastern Irish Sea" study should go some way towards appraisal of these possibilities.

    —  Whilst, therefore, the ability to offer a balanced daily supply remains unproven at this point, it is clear that substantial contributions to daily electricity demands could be made. From this preliminary analysis, it appears that for much of the day, tidal power contributions of close to 6GW could be provided during "springs", falling to around 2GW during "neaps". These figures should be set against typical power demands in summer ranging, approximately, from 25-40GW and in winter from 30-50GW.

    —  The annual energy output from this "maximum generation window" operation simulation is 29.4 TWh, an alternative "maximum power" operation yields 36.1 TWh, these figures representing about 10% and 12 % of UK annual demand, respectively. The more ambitious outer Severn option (Baker, 1991) would be required to lift output above 15%.

    —  The practicability of rapid introduction of such large power inputs to the grid will need careful attention, though this has recently been broached by the proponents of the Severn barrage (Watson & Shaw, 2007)

    —  It is clear that a phased introduction of the schemes in pairs could enable an incremental increase in capacity whilst preserving a reasonable power balance across the generation window, ie pairing the Severn and Solway, Morecambe Bay and Wash, and Humber with Mersey/Dee.

    —  Whilst it is appreciated that the economics are likely to play a major part in any progression of these major tidal power proposals, it is reassuring to note that the unit cost estimates made in the 1980s varied by little more than a factor of 2, with the Severn and Mersey lowest and the Thames highest (Baker, 1991).

Figure 2


  a)  28 tide spring-neap-spring series

  b)  2-day segment from "neaps"

  c)  2-day segment from "springs"


  Baker A C, 1986 The development of functions relating cost and performance of tidal power schemes and their application to small-scale sites, in Tidal Power, Thomas Telford, London.

  Baker A C, 1991, Tidal Power, Energy Policy, 19(8), 792-797.

  Cottillon J, 1978 La Rance tidal power station-review and comments. Proc Colston Symp on Tidal Energy, Bristol, Scientechnia, 46-66.

  DTI, 2004 Atlas of Marine Renewable Energy Resources: Technical Report. Report no. R1106, ABP Marine Environmental Research Ltd.

  Hammons J H, 1993 Tidal Power, Proc IEEE, 81(3), 419-433.

  Mersey Barrage Company, 1992 Tidal power from the River Mersey: A feasibility study Stage III, MBC, 401

  Pierre J, 1993 Tidal energy: promising projects—La Rance—a successful industrial scale experiment, Proc IEEE

Trans Energy Conversion, 8(3), 552-558.

  Rufford N, 1986 Tidal power still in the running, New Civil Engineer, 22 May 1986, 12.

  Shaw, T L, 1980 An environmental appraisal of tidal power stations: with particular reference to the Severn barrage.

  Shaw (ed), London: Pitman Advanced Publishing Program, 220pp.

  Watson M J & Shaw T L, 2007 Energy generation from a Severn barrage prior to full commissioning, Proc ICE Engineering Sustainability, 160, March, ES1, 35-39.

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