Monday, 22 September 2014
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Engineers head to Swansea for tidal energy lagoon world first

Investigatory work is about to begin in South Wales for what could become the world’s first purpose-built tidal energy lagoon.

UK firm Tidal Lagoon Power (TLP) is planning a four-week study of the seabed conditions and physical characteristics of Swansea Bay that will inform the company’s plans for a 250MW tidal power plant, which would also be the world’s first bi-directional tidal lagoon generator.

Locally based TLP claims the power station would could be connected to the National Grid by 2017, providing predictable, renewable baseload energy for 16 hours a day, saving 200,000 tonnes of CO2 per year for its design life of over 100 years.

‘The Swansea project will hopefully be the first in a network of lagoons around the UK coastline, driving a critical change in our energy mix with low cost, low carbon electricity sources that are sustainable long-term,’ said TLP technical director Ton Fijen in a statement.

If built, the Swansea Bay project would be the first purpose-built tidal lagoon power plant in the world, although plans exist for several other projects around the world and a similar scheme was opened in 2011 at Sihwa Lake in South Korea based on existing tidal reservoir.

Tidal lagoons use tidal range technology that relies on the gravity-driven flow of water from one level to another to power a generator, rather than the currents that driven tidal stream turbines.

The Swansea Bay plant would be the first powered by both incoming and outgoing tides. Water would flow out of the lagoon as the level of the water outside dropped and back in once the tidal level rose again.

‘You can make turbines run efficiently when it flows in a certain way and normally they optimise the turbines on the outgoing tide,’ Fijen told The Engineer. ‘But to make them also run efficiently the other way round has not really been done before.

‘We do that by changing the angle on the turbine propellers so that when the tide runs one way it has one angle and when it runs the other way you change the angle of the blades so that it also runs relatively efficiently – not as efficiently but good enough.’

The development will comprise a sand core seawall and hydro turbines mounted in a concrete turbine housing. This seawall will use sandy materials sourced from the seabed within the lagoon, hydraulically filled into long geotextile casings 5m in diameter, and covered with small rocks and then larger rock armour to protect it from environmental damage.

The investigation work, which will be conducted by contractor Environmental Scientifics Group, will provide information about the seabed surface that will enable TLP to optimise its designs for the 20m by 80m walls needed to create the lagoon.

The company has already selected the preferred shape of the lagoon from 14 proposed designs but estimates the plans will take until 2015 to finalise before construction can begin – providing it can raise the £10m needed through its current public investment round.

Plans to harness tidal energy in the Severn Estuary where Swansea Bay is located have been discussed for years, mainly focused on a barrage across the entire estuary. But Fijen said the much smaller lagoon project would bring the level of commitment and financial resource needed to make such plans a reality.


Readers' comments (6)

  • Promising - a reliable supplementary energy supply that utilises both incoming and outgoing tidal energy. Should be relatively easy to service inland with none of the potential radar interference drawbacks off offshore wind.

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  • What am I missing here- why can't the turbine rotate 180 degrees so it is equal efficiency in both directions? Plenty of time at slack water to do it.

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  • The more we venture into tidal and wave energy the better mainly due to the power being far more predictable than wind and solar energy. However tidal lagoons would have more an environmental inpact. I would hope that a lagoon would have long sloping banks to mimic tidal retreat and therefore a similar enviroment for marine invertibrates and birds.

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  • I have been a supporter of tidal energy for the UK for 40 years. Few other European countries have suitable tides - certainly not around the Baltic or Mediterranean.
    Round Britain, high tide occurs at different times so somewhere on the coast always has enough flow to generate power. Unlike wind of course.

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  • Why the need for changing the blade angle? Or rotating the turbine completely?A very simple lock gate system would enable the flow to be in the same direction, while the lagoon was filling or emptying.

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  • We've had a response to your questions from the project's technical director, Ton Fijen:

    The turbines are so-called Kaplan turbines and the turbine blades are 7 to 8m in diameter. They fit very tightly inside a draft tube that is designed to minimize friction headlosses. These turbines are mounted on a horizontal shaft and they are directly coupled in-line to the generator, which is housed inside a bulb.

    For the main flow direction, water flows from the lagoon to the sea, it flows past the bulb through the turbines and out through the draft tube. For the reverse flow, the efficiency will always be lower, because the bulb is now on the other side of the turbine, and because the outlet draft tube must now become the inlet.

    This arrangement does not allow us to rotate the turbine 180 degrees. All we can do is to change the angle of the blades on the turbine.

    There is actually a patent in place for such a lock system that will allow water to flow in the same direction through the turbines , irrespective of whether the lagoon was filling or emptying. It is called the Gokhman system.

    We had detailed discussions with the inventor of this system to do exactly that. In the end, it proved to be a very expensive lock system and in addition, the extra friction losses (both ways) through this system were higher than the gain in efficiency.

  • Ah, I didnt know that, but then I just effectively drew up the system on the "back of a fag packet" (small piece of paper) Cant find any details of the Gokhman system online.
    :-)

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