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.