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


Memorandum submitted by R V Power Company Ltd


  RVco is a company which has been specifically set up to exploit the opportunities for electrical power generation offered by global offshore and estuarine tides and current. It employs novel RV technology which suffers from none of the disadvantages inherent in traditional tidal barrage schemes. In the RV system, there are no moving electrical or mechanical components under water, there is little environmental impact, and the output is in the form of compressed air which can be piped, underground, to the generating station without significant power loss. Turbines driven by compressed air are more compact and efficient than those driven by relatively slow moving water, so the capital cost of the generators is much less than in a comparable barrage scheme.

  The founders of RVco Ltd were the author, Dr Geoff Rochester, and Dr John Hassard. Our present team includes Professor Sir Eric Ash (director), Dr Keith Pullen (turbine expert), Nigel Stokes MBA (director), Niall McGlashan (engineer), Dr Joseph Neil (US Co-ordinator), Dr Colleen Lee (UK Co-ordinator), Professor Dennis Anderson (business adviser).


  It has been estimated (1), that if all the opportunities for generating power from water currents around the UK were exploited, it might ultimately be possible to win 200 TWh per annum, which is equivalent to the continuous operation of a 23 GW power station, or about half the nation's electrical energy needs. These water currents themselves represent, however, only a fraction of the total tidal potential energy around the UK, as much of this energy is lost to turbulence.

  Because the energy resource in the tides is so vast, the possibility of turning it into useful power has long attracted interest. The extraction of this power is difficult, though, because the energy density is so low; large scale installations are needed to harness it. This is particularly difficult in a hostile marine environment.

  Mostly, the schemes proposed in the past have involved setting up a tidal barrage, such as that currently operating at La Rance. Similar barrages across the Severn and the Mersey have been considered. However, even La Rance, although technically successful, has proved uneconomic. The Severn and Mersey schemes have been shelved on the grounds of cost and environmental impact.

  While the Inquiry to which this Memorandum is addressed does not include the consideration of tidal barrages, they will provide a useful benchmark against which other proposals may be measured.

  Conventional tidal barrier schemes work by trapping the water at high tide and then letting it out at low tide, while the head falls from the high tide level to some minimum below which the turbines cannot work efficiently. As the biggest output is obtained at exactly low tide, this means that, ideally, to take full advantage of the available potential energy, there has to be a huge generating capacity which is used for only a very short time.

  In the similar situation, an RV, which does not attempt to trap the tide and only partially obstructs the flow, will develop a smaller head of water than that which is contained by a barrage. This small head, which arises as long as the tide flows, is amplified, by the unique design of the RV to something comparable with the height of high tide. The amplified head is then used to drive a relatively small quantity of water around a secondary water circuit. The secondary flow can be maintained for a good fraction of the tidal cycle, so the output is much less sharply peaked than it is from a barrage. This means that, for an equivalent electrical energy output, the generating capacity can be less and the duty cycle greater, thereby increasing the economic viability of the project. Tests on a scale model have shown that it should be possible, even on a conservative estimate, to convert 20 per cent of the total water power dissipated in the RV into electricity.


  It has been requested in the press notice that this Memorandum addresses the following issues.

3.1  Technological Viability

  It is undoubtedly the case that RV technology is feasible. This has been proved in laboratory tests. The laboratory tests also showed that a high conversion efficiency, from tidal power to electrical output, can be expected.

3.2  Commercial Viability

  Currently, large scale tests of RV's are being prepared. These will confirm commercial viability. It is clear that, ultimately, commercial viability will depend upon the site of the installation. Some sites will be much more tractable than others. In order to carry the project forward, once commercial viability has been proved in principle, the easiest sites, namely those with favourable tides and geology, and fewest conflicting interests, will be tackled first. The experience thereby gained will be used to assess the profitability of building similar structures in more difficult locations. As we accumulate knowledge and experience, it is possible that the return on investment will increase, despite the sites becoming more challenging.

  Our present estimates suggest we can produce electrical power at between two and ten pence per kWh, with the most viable sites clustering around two pence or three pence per kWh. The greatest uncertainties in our costings come from site-specific issues, marine civil engineering estimates and planning permission.

3.3  Current Projects and Earlier Failures

  As far as we know there are only two other current tidal energy projects in the UK. One is that run by IT Power (, funded with 1M Euro by the EU, which involves placing a 300 kW submarine propeller driven turbine under the sea off Cornwall. Clearly, this will suffer all the drawbacks of having mechanical components (turbine and gearbox) and electrical components (generator and wiring) in a hostile and corrosive marine environment. However, we believe that IT Power's cost estimates, which predict power production at six pence per kWh or better, are well founded. Their group has great expertise in the necessary technologies. Their work will assuredly lead to a far greater understanding of the economics of such installations, and is to be highly commended. The other proposal, from the Southampton Oceanic Institute, is to put a similar device in the Solent.

  We believe that RV technology suffers from none of the drawbacks inherent in the technology being applied by these two teams.

  In 1994 ETSU carried out a survey of tidal stream technology for the Department of Trade and Industry (2). This survey concluded that the extraction of such energy would be uneconomic. It suggested, for instance, that the unit cost for a tidal scheme in the Pentland Firth or off the Channel Islands, where the currents are especially strong, would be 10 pence per kWh at 8 per cent discount, or 16 pence per kWh at 15 per cent discount. Their summary stated "Tidal streams do not therefore appear at present to offer an economically viable energy source". However, ETSU's costings have been widely discredited as being far too conservative and its assumptions biased against tidal energy. Moreover, RV technology was not considered in ETSU's survey, which points out that "the costs partly reflect the hostile environment where the resource is located. The strong currents and large waves would represent major hazards to support vessels and particularly to divers; moreover, shipping channels pass through or near five of the 33 sites considered. Machinery would be subject to potentially severe corrosion damage, encrustation by marine organisms and fluctuating forces, which would increase fatigue and shorten plant life". The RV approach sidesteps these issues.


  A Renewables Strategy should be at the heart of a coherent, consistent, comprehensive, long-term Energy Policy. This should take account of the following:—

  1.  The rate at which oil reserves are being discovered is slowing down. When rising demand meets falling supply, the price will skyrocket. The same logic applies to gas. Gas prices have already doubled in the past year. This increase is unambiguously associated, at least in part, with a new realism about total reserves.

  Hence, in the long term, the relative cost of renewable energy supplies can only improve. Global demand is due to increase enormously as countries such as China and India strive to reach consumption levels taken for granted in the West. Hence, investment in renewables now is certain to bear fruit later. The UK is in the enviable position of being in the lead in many of the areas required for tidal energy extraction, and could capitalise on investment commitments made now, in the same way that Danish and German companies are reaping the benefits of early investment in wind energy technology and expertise.

  2.  The per capita demand for electricity is rising in the West as citizens buy more electrically powered items, transport relies increasingly on electrification, and new power sinks such as computer server farms and air conditioning become more common. The ongoing crisis in California illustrates how vulnerable advance economies have become, and while the UK and EU do not face such brown-outs in the immediate future, a convergence of factors—the phasing out of nuclear power, the Kyoto Accords, and the increasing cost of fossil fuels—makes renewable energy more attractive.

  3.  Exceptional demand for electricity due to climate change are also possible, either for air-conditioning, or, if the Gulf Stream fails, for additional winter heating.

  4.  Even if global warming, for which there is now abundant evidence, is not a consequence of human activity, it still needs to be brought under control. Ideally, all electricity should be derived from renewable sources. This means reducing demand as well as securing an environmentally friendly source of supply. Pressure to reduce demand will also develop as the price of fossil fuels rises. Options here are improvements in efficiency, subsidisation of insulation, and a carbon tax.

  5.  If the Greenland ice sheet melts and turns off the Gulf Stream, northern Europe is likely to be plunged into a Siberian climate. This could put overhead transmission lines at risk from ice storms. It could therefore be prudent to abandon the policy of having a few huge generating stations in favour of a much more widely distributed network of smaller local installations. This change of attitude would favour renewable technology.

  6.  Further to the above, the increase in transport costs which will follow rising oil prices will tend to enhance the significance of local communities and their products at the expense of global trade. Local, renewable, power schemes would harmonise with this philosophy. RV's are particularly suitable here, as they promise to be as effective on a small, as on a large, scale.

  Hence, a firm Renewables Strategy would anticipate future trends and give the UK a lead in what is likely to be an expanding global market. One way to put this Strategy on a sound footing would be to impose a carbon tax, as this would transform the economics of wave and tidal power overnight. To tax users of electrical irrespective of its origins, as in the incoming Climate Change Levy, is perverse.

3.5  Research and Development

  Getting ideas to the market place has always been difficult in the UK. Once a technical principle has been proved, the next question invariably concerns the economic viability or the cost effectiveness. Finding an answer to this question can involve considerable financial risk. At this level, nine ideas may fail, before the 10th produces big returns. Generally, UK funding agencies are unwilling to take this risk. It is at this stage that the idea goes abroad.

3.6  Environmental Aspects

  Traditional tidal barrages have a significant detrimental environmental effect. Water heights are permanently altered, marine life is segregated from the area of trapped water, shipping is obstructed and hardware tends to be visually obtrusive.

  The proposed RV installations would restrict the flow of water but not bring it completely to a halt. Indeed, in environmentally sensitive locations, the fraction of energy extracted can be reduced until the environmental impact is brought down to an acceptable level. Our studies show that, in many locations, a fraction of the energy, even within natural variations, can, when extracted, still produce a viable return on investment.

  In an RV

    (a)  Water heights are not permanently altered. The times at which high and low tides occur are slightly delayed.

    (b)  Marine and bird life will be unperturbed. Marine life may even be enhanced, because the submerged RV can be designed to be an attractive habitat for fish and crustaceans.

    (c)  Most of the RV will be underwater, and therefore visually unobtrusive, but in some locations it may emerge at low tide, like a jetty or breakwater.

    (d)  The RV can be incorporated into existing or planned constructions, such as coastal defences, off-shore windmills or oil-rigs, bridges, causeways and tunnels.

    (e)  Energy, in the form of compressed air, can be piped underground some distance from the offshore RV to the generator, sited near existing electricity grid lines. The eyesore of pylons in scenic locations should therefore be avoided.

    (f)  The impact on shipping is more uncertain. Initially, sites for RVs will be chosen where shipping is not an issue. However, there would be difficulties on busy routes. If an RV were installed in the Thames, for instance, shipping movements would have to be restricted to about one quarter of the tidal cycle, necessitating compensation payments to shipowners. Elsewhere, the RVs would come near enough to the surface to have to be lit and marked with buoys. The partial obstruction of channels by RVs would also result in increased currents in the shipping lanes.

  The RV strategy is to cherry pick the best sites, those at which no conflicts of interest occur, moving on to the more difficult ones as expertise builds. Fortunately, there are hundreds of sites round the UK which are suitable, thousands round the EU and tens of thousands around the world, including those in the open ocean. As the benefits of tidal energy become apparent, we believe remaining difficulties can and should be solved.

    (g)  In contrast to the traditional tidal barrage, the RV electricity generating plant will be running for at least half the tidal cycle. This means that, to generate the same amount of power, the capital costs of the generators and their capacity is correspondingly less. Furthermore, the turbines will be driven by compressed air, allowing the use of small compact units. The power generating plant is therefore expected to be easily accommodated within existing planning regimes.

3.7  International Comparisons

  All the other being done in this area, in the UK or abroad, involves placing turbines under the surface of the sea, either in a fast natural current or in one which has been artificially accelerated.


  We have high hopes that the generation of electricity using RV technology will prove environmentally benign as well as profitable. It is based upon entirely new ideas and therefore offers an opportunity for the UK to take a lead in contributing to a solution to the problem of global warming. The RVs are scalable, making them adaptable to different circumstances, and modular, allowing many units to be connected to the same generator, thereby achieving economies of size. A subsidiary advantage is that they can be used to aereate and thereby purify the water at the same time as providing electrical power. The potential global market is huge, and could provide both employment within the UK and income from abroad. If we can seize the initiative by installing a wide range of different types of generator and proving their various abilities in different circumstances, as well as using them to make a significant positive contribution to the electricity budget of the UK, so that Britain acquires the reputation of being a world leader in this technology, then, when the price of oil and gas starts to rise, the UK will be in a superb position to dominate the market. However, the lead time for these developments is measured in years, so it would be as well to make an early start.


  2.  ETSU T/f05/00155/REP

8 January 2001

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