An exciting renewable technology

Tidal Generator

Regular readers of this column will know that I am not impressed by the theory of anthropogenic global warming.  But I am very concerned about energy security, so I am in favour of renewables if they meet basic tests of environmental and economic sustainability.  Clearly wind turbines do not meet these criteria.  But under-sea tidal turbines just might.
A current of water has a much greater energy density than a current of air, so you can generate more power from a much smaller device.  Tidal power, like wind power, is intermittent, but critically, unlike wind power, it is totally and entirely predictable, which is a huge advantage.  The managers of the grid will know exactly how much power they can expect, and when.  And tidal turbines, which work both ways (on the flow and on the ebb) can produce power perhaps sixteen hours out of twenty-four.  Under-sea tidal turbines also avoid the huge environmental damage that on-shore wind farms do, despoiling landscapes, and blighting communities, and homes, and lives.  Moreover while wind turbines have to shut down for safety reasons in very high winds, it seems that there is no limit to the current speed in which a tidal turbine can generate power.
Of course the sea-bed presents a very corrosive and challenging environment, together with problems of cabling, and accessing the grid, but these problems are arguably no greater than those being addressed for off-shore wind.  After decades of North Sea drilling, British engineers are well experienced in creating durable structures for under-sea environments.  The turbines will be sufficiently deep to allow ships to pass over them, although of course trawlers and submarines will need to keep clear.
So I was delighted to be able to visit Rolls-Royce in Derby on Nov 20th to learn about their tidal turbine project.  Of course Rolls-Royce have unrivalled experience with turbines, and indeed with propeller systems, and are well-placed to take a leading role in this endeavour.  They have a pilot project, with a trial turbine due to be located in the Orkneys next year.  I saw the plans.  They start with a large tripod structure which can be anchored to the sea-bed using a ship and a remote-control submersible.  Then the turbine, looking for all the world like a torpedo with an out-size propeller, is attached at the top.  This can rotate around a vertical axis through 180 degrees to face the tidal current either way.  The blades can be feathered to present the most efficient angle of attack for the rate of flow at the time.
Britain has one of the best tidal environments for tidal power of any country in Europe — and a world-class engineering company capable of developing and exploiting the technology.  Rolls-Royce estimate that up to 5% of Britain’s electricity needs could be generated in this way — and the technology could be exported around the world.  I wish them every success, and I hope to be able to visit the Orkney site in due course.

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6 Responses to An exciting renewable technology

  1. Ivan.G.Blood says:

    I have worked in power plants since 1962 including construction of 500mw station. Ratcliffe Power Station is a 2000mw station and I believe that the largest wind turbine is 3mw, to replace this with wind turbines you would need 666 turbines and they only work with the right wind conditions.
    Fossil fired stations are now all installing/or have already installed FGD systems to reduce the gas emissions.
    No one seems to mention this fact, why not.

  2. Roger Helmer says:

    You’re missing the point, Ivan. According to our new religion, fossil fuels are BAD, and only wind is GOOD. That’s why the lights will go out around 2015.

  3. Grant Perkins says:


    Somewhat more than 666 turbines I believe.

    According to a source I stumbled upon recently the maximum possible efficiency of a wind turbine is about 60 something percent. So rating at 3 (which sounds high but in the future probably doable reliably) and taking 60% you get 1.8 .

    This kind of level is more achievable off-shore – but current experiences, apparently, indicate about a 15% downtime for maintenance. So the effective potential is about 1/2 of rated capacity – 1.5 . Therefore you need to double the number of turbines to 1332 to get the same output as Radcliffe (assuming Radcliffe can output at the max rating when required.)

    As far as I can tell by looking at the ROC claims (and assuming that the generators always make as big a claim as they are allowed to) the actual average output achieved against rating is little more than 30% at best, often closer to 20%.

    Given current government policy I really hope I have the figures wrong.

  4. Philip Burrows says:

    I agree with you Grant, by Prof David Mackaye puts forward an independent analysis of our energy needs that supports your >666 turbines. He puts several scenarios forward: with or without nuclear, with or without coal, with or without wind etc.
    In terms of energy security and renewables, I find a really exciting opportunity.
    What do you guys think?

  5. Philip Burrows says:

    P.S. Does anybody know whether this article is relevant to the UK?

    I don’t how our aging coal fired power station compare to the US. Are there still significant (non-CO2) risks from new coal fired power stations too?

  6. Grant, You’re absolutely right, I’m afraid. I don’t know where this figure of 60% came from — typically on-shore wind-farms deliver only around 25% of rated capacity. 30% is good. Some poor sites get below 20%. Yet the developers base their claims on “meeting the needs of X,000 homes” on rated capacity — not estimated output.

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