Select Committee on Science and Technology Appendices to the Minutes of Evidence


Memorandum submitted by Professor S Forbes Pearson


  My practical expertise is in the field of Industrial Refrigeration and I am a professional engineer, holding the degrees of BSc, PhD, ARCST. I am a Member of the Institution of Mechanical Engineers and a Fellow and past-President of the Institute of Refrigeration. I am, at present, Chairman of the Technical Committee of the Institute of Refrigeration. I am a Visiting Professor of Mechanical Engineering at the University of Strathclyde.


  1.  The United Kingdom is one of the best areas in the world for the exploitation of tidal stream power.

  2.  The tidal stream resource is very large, much greater than wind resource.

  3.  The principle of extracting power from tidal streams has already been demonstrated by small-scale trials in Scotland, Japan and Australia.

  4.  Economic use of tidal stream power depends on using the largest possible turbines in the fastest available tidal streams.

  5.  Industry will not develop tidal stream turbines while the cost of fossil fuel is so low.

  6.  Governments cannot afford to increase the cost of fossil fuel.

  7.  The fundamental technology of tidal stream turbines is well understood.

  8.  It is not more research which is needed but finding for design and construction of large tidal stream turbines.

  9.  Funding is also needed for a careful examination of the tidal stream resource, which has not been accurately measured.

  10.  Allocation of all possible sites for tidal stream turbines should be discussed and agreed with all interested parties as soon as possible. The restrictions to be imposed when the sites are brought into use should be agreed in advance.

  1.  My interest in the potential of tidal stream power is strictly as an informed amateur. However I was involved in the development of freezing fish at sea (probably one of the sources of our current fisheries crisis) and I have sailed in trawlers to the Hebrides, Orkneys, Shetlands, Faroes, North Norway Coast and Bear Island. I have therefore some experience of the power of the sea as manifested in winds, waves and tides. I have also lived for most of my life on the West Coast of Scotland. I am also interested in sailing.

  2.  I should perhaps also mention that I am a founder Director of Star Refrigeration Ltd. Which is the leading industrial refrigeration firm in the UK and notable for innovation and sound engineering. I am the President of that company and a major shareholder in it.

  3.  My interest in tidal stream power dates back for a few years to the time when I was handing over responsibilities at Star Refrigeration Ltd. to the younger generation and looking for something interesting and useful to do. It was obvious that there is a huge potential for energy extraction from the tides around the UK coasts. The puzzle was why it was not being done.

  4.  Some preliminary calculations were done which seemed to indicate that over 20 per cent of the UK electrical requirement could be provided from tidal stream power. It was a great surprise to me when the Twenty-Second Report of the Royal Commission on Environmental Pollution "Energy—The Changing Climate" seemed to contradict that view. The report stated (7.96) "The amounts (sic) of energy it is practicable to obtain from tidal streams and shoreline wave energy seems likely to be quite modest". It seemed obvious to me from practical experience that this conclusion was wrong. I then began to seek out the facts on which the Royal Commission conclusion had been based.

  5.  I found that DTI had commissioned reports on tidal stream power in 1989, 1993 and 1999. It was from the 1999 report that the Royal Commission Report formed its conclusion. The 1999 Report, ETSU R-122 pp 137-145 concludes "The prospects for conventional tidal stream technology in the UK appear limited". On examining the 1999 Report and the 1993 Report (which was a more impressive document), I found that they had significantly underestimated the power available and had consistently overestimated the likely cost.

  6.  It is obviously not possible for a private individual to calculate the power available from many individual sites so I decided to study one well-known site, the Gulf of Corryvreckan. Figures of mean spring and reap tidal stream velocities were available from Admiralty charts as were the depth contours and dimensions of the gulf. Corryvreckan is about a mile wide and over 100 m deep for about half its width. Tides are quoted as running at up to 10 kn. In my initial calculations, which were done from first principles because I had not then obtained much in the way of literature specific to tidal streams, I proposed that an underwater barrier should be placed across the gulf at its narrowest point to increase the velocity by reducing the depth to 50 m.

  7.  The 1993 ETSU report, ETSU T/05/00155/REP also quotes an average power output for Corryvreckan. In 1996 the European Commission published a report through DGXIII on "The exploitation of marine currents", Report EUR 16683 EN. This is a much more practical report than the 1993 ETSU report and it also gives figures for possible power production from Corryvreckan. Both the ETSU and the EU reports produce the power generation by employing a "farm" of turbines covering the area of high stream velocity. This is different from my method which intensifies the velocity and uses a single row of turbines which I think would be much cheaper.

  For purposes of comparison I calculated the power available at Corryvreckan using a farm of turbines and assuming the same efficiency as had been assumed in the EU Report. There are therefore four figures for power production at Corryvreckan.

Rotor Dia
No. of Rotors
Installed Capacity
Average Power
ETSU (Table 6.3)
EUR (Summary Table/1)
Pearson (Intensified)
Pearson (Farm)

  8.  I have applied for a patent on some novel methods of power generation from tidal streams and it includes the method of intensification. I have had the calculations for the intensified systems checked by several competent engineers who confirm that my figures are broadly correct. I have no idea why my figures differ so much from the "official" figures but I do not believe that my figures can be wrong by several orders of magnitude.

  9.  It is probable that official figures for other sites are not wrong to the same extent as the figures for Corryvreckan. For example, the rated power at Kyle Rhea and the Dorus Mor are given as 32MW and 194MW in EUR 16693 EN both have much less potential than Corryvreckan. The figures for Corryvreckan are just wrong!

  10.  I shall try to answer the specific issues which you have been charged to cover. I do not wish to discuss wave power in detail beyond saying that there is awesome power in storm waves but I very much doubt that it can safely be harnessed.

11.  Technological viability

  Equipment is not at present available for efficient large scale-generation of power from tidal streams. This is because it has not been designed and tested. The principle of tidal stream generation is sound and has been proved. There is nothing highly technical in the design but, to be efficient and effective, the equipment must be designed on as large a scale as possible. The cost of design will be high so individuals cannot undertake it. It must be done by partnership between government and industry. I shall return to what requires to be done after I have dealt with all the other issues.

12.  Commercial viability

  Judging by the example of wind power, tidal stream energy will become commercially viable after large scale designs have been proved. Tidal stream power is theoretically much more attractive than wind power. Much more power can be generated from the same size of machine. The tidal stream generator will be submerged and therefore not an eyesore. The submerged tidal stream generator will not be subject to storm or wind damage and will not have to be designed to withstand the severe overload conditions to which wind turbines are subjected.

  Sub-sea technology has advanced in recent years but neither the oil companies, who are the main experts, nor the electricity companies, who have excess hydro and nuclear capacity in Scotland, have any present motive to develop tidal stream power.

13.  Current Projects

  The only project that I am aware of is one funded by an EU grant for a 300kW post-mounted turbine to be sited off the North Devon coast. The turbine will be designed and provided by Marine Current Turbines Ltd. This is a worthy project but it is too small. Marine Current Turbines, for sound commercial reasons, plan to increase the size of their installations step by step. This will take a long time and will tend to restrict the diameter of turbines which will be designed. I am not aware of any past projects which failed. They were all very small because of limited resources and they were all taken out of service after they had proved the soundness of the principle. A case in point is the Corran Narrows turbine which produced its design power of 15kW without turbine problems. Most of the work was funded by Scottish Nuclear, who have never published a report, and who have a surplus of pollution-free power and other problems. As far as I know the Canadian, Japanese and Australian projects all produced power as they were intended to do but they were very small. What is needed is financial support for a full-scale project with a turbine as large as can be designed and accommodated.

14.  Renewable Strategy

  We need all the renewable power which can be obtained at reasonable cost. I am agnostic about the viability of wave power because of the extreme conditions for which the devices will have to be designed.

  Tidal stream energy is a huge resource which could be exploited over the course of a few years if design and prototype costs could be funded. There are many design challenges but they do not take us into any really new technology. In my opinion tidal stream energy should be given top priority by government.

15.  Research and Development

  Very little research and development is being undertaken at present which is not surprising given the conclusions of the Royal Commission of June 2000 and the ETSU Report of 1999. Most people would take these at face value.

  I do not think there is a great need for fundamental research. Even assuming turbine efficiencies lower than those being achieved by wind turbines, there is still a vast amount of power available. The urgent priority is to get large turbines working. A certain amount of development would go hand in hand with the design and testing but wind turbine experience can be used to design tidal stream turbines which, of course, have to be much stronger. In my opinion we should start designing and building a large turbine now, making use of existing knowledge. We should not look for perfection but for a big, robust machine which works.

  The only peer review which is of any importance is the examination and testing which the ocean will provide.

16.  Environmental aspects

  I do not think that either wave or tidal stream generators would have any significant effect on marine life. Large tidal stream generators would rotate at only three or four revolutions per minute and would be static. High-speed pleasure boats are potentially much more damaging.

  Marine life in the form of weed and barnacles would have a significant effect on tidal stream turbines. Anti-fouling measures would have to be taken as they are on every ship.

  Tidal stream turbines and merchant shipping cannot co-exist in a restricted area. Small pleasure craft would not be a problem because the turbines would be submerged by several metres. The area of turbines would have to be buoyed and entry of merchant ships, fishing and naval vessels restricted. This should not be a great inconvenience because the sea is very large and alternative shipping routes could be specified. Many of the best locations for tidal stream power are at present designated "Submarine exercise areas" but, no doubt, matters could be arranged.

17.  International comparisons

  Britain is at present a world leader thanks to the enterprise of private companies like Marine Current Turbines. I am not aware of ongoing research by other nations. Obviously the EU has given a lot more support than UK government but even the EU support is marginal.

  UK is one of the best placed countries to exploit tidal stream power because of the shape of our coastline and our proximity to the continental shelf. Other countries with strong tidal streams include France, Norway, Japan, Canada, USA and Chile/Argentina.

  I would be surprised if the Japanese were not carrying out some useful research bearing in mind their lack of indigenous energy sources. A literature search produced many Japanese papers but no evidence of current large-scale projects. I would expect any large-scale Japanese project to be kept confidential for as long as possible in order to allow them to build up a technological lead.

18.  Costs and Benefits

  The cost of the actions proposed in the following paragraphs runs into many millions of pounds but these costs are very small compared to the costs which can be attributed to environmental damage.

19.  Actions Needed

Survey of the resource

  It is fairly obvious that the tidal stream resource is very large—much larger than the wind power resource even allowing for the siting of wind farms at sea. Unfortunately the size of the resource and the details of its position are not known. Recent work, such as EUR 166683 EN "The exploitation of tidal marine currents" 1996 and ETSU T/05/00155/REP "Tidal Stream Energy Review" 1993, differ widely in the size of resource allocated to the same sites. This is partly because of different methodologies but more because of differing estimates of the gross power in the tidal streams.

  The main source of information on tidal stream velocities is the Admiralty Chart and the Admiralty Tidal Stream Atlas. Unfortunately these were prepared for navigation and often do not show tidal stream velocities at the positions which would most be suitable for the generation of power. The tidal stream atlases are also difficult to quantify because the velocity of the tidal streams is indicated by the size of the arrow rather than by figures in many cases.

  It is probable that the Admiralty has raw data from which the tidal stream atlases were prepared. If so it should be possible to get reliable figures for tidal stream velocities. This should be investigated as a matter of urgency.

  The Admiralty data, some of which goes back to the days of sailing ships, should be supplemented by a modern detailed survey making use of satellite positioning and echo sounding of the sea bed. The nature of the sea bed is important whether the turbine is to be post mounted or anchored in position. The modern survey could occupy a large survey vessel and crew for several years. This work should be carried out while prototype large turbines are being designed and constructed, not after.

Negotiation of locations

  Locations for the siting of UK tidal stream generators will all be within the territorial waters of Great Britain and on the continental shelf. The conflicting interests of commercial shipping, fishing and Naval forces (mostly submarines) will have to be resolved. It will almost certainly be necessary to close certain areas to shipping and to restrict access to narrow lanes in others. This should not be a major problem provided the Government is prepared to adjudicate firmly.

  Preliminary work for preferred tidal stream sites should start as soon as possible, involving all the interested parties from the first.

Topography modification

  Tidal stream velocities are strongly affected by the shape of the sea bed and the shape of adjacent land masses. The strongest tidal streams occur round headlands where the tide is flowing from one part of the ocean to another, in straits and gulfs through which the tide flows and especially where a shelving bottom causes velocity to increase to conserve the momentum of the stream. Examples include the Bay of Fundy, Corrievreckan and the Bristol Channel. In some cases the natural frequency of the water in the region is tuned to the forcing frequency, giving rise to remarkably high velocities. The Bay of Fundy and the narrows at Kyle Rea are examples of this phenomenon.

  Power available from a turbine varies as the cube of the velocity. If the velocity can be doubled the available power increases by a factor of eight. It is therefore vital to make use of velocities which are as high as possible.

  It has been proposed that the shape of the sea bed should be modified in regions where tidal stream velocities are already high, to increase the velocity still further. A way of doing this is by the creation of artificial underwater reefs. These can be used either to decrease the cross-sectional area of the flow or to deflect flows into preferred areas. This is a much cheaper and less environmentally damaging method than the construction of tidal barrages. The reefs would be underwater all the time. "Barrier" reefs to decrease flow area would be submerged significantly more than the turbine diameter. "Deflector" reefs to deflect tidal stream flow would approach the surface more closely but could be kept below keel depth of small boats. The reefs, probably formed from quarried rock, could simply be dropped into place. The reefs would, in addition to their function of increasing tidal stream velocity, would serve as a shelter and breeding ground for fish. However, prediction of the effect of reefs on tidal stream flow is not simple. There would appear to be a need for computational fluid dynamical studies of a novel kind. I would like to suggest that these studies should be funded at the same time as the resource is being studied.

  The importance of increasing tidal stream velocities, if possible, can hardly be exaggerated. The number of turbines required is reduced by a significant factor (eight, if the velocity could be doubled) and this would have a marked effect on capital cost.

20.  Suggested Government Support

  The potential of tidal stream energy has existed since the end of the ice age. It is only in the last few years that the need to make use of it has been understood as the costs of excessive use of fossil fuel begin to dawn. Fossil fuel is much too cheap; however, it is politically inexpedient to cause sharp rises in fuel prices.

  While fossil fuel is cheap, industry has no incentive to invest in tidal stream turbines. A way out of this impasse would be for government to fund design, construction, siting and setting to work of the largest practicable tidal stream turbine. The costs of the enterprise should be underwritten but the profit, which should be generous, should be released when turbine and generator have met their specifications. It might be advantageous to make such contracts with several design and construction teams. Competition concentrates the mind.

  Developing non-polluting sources of power is at least as important as national defence. If even one-tenth of defence funding were allocated, and rigorously supervised, the problem would be solved within a few years.

  When power and fuel from renewable sources are available in quantity it will be possible to raise the price of fossil fuels to levels more commensurate with the cost of using them. This will not only improve the environment but will conserve valuable resources which are, at present, being consumed in a prodigal manner.

2 February 2001

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