Plans unveiled for Swansea Bay tidal lagoon

Electricity will be generated by creating a head of water and channelling the flow through turbines Electricity will be generated by creating a head of water and channelling the flow through turbines

Plans have been released for the world’s first, purpose-built, tidal lagoon power plant that will be capable of generating electricity equivalent to the entire domestic consumption of Swansea in South Wales.

The proposed 250MW power plant will produce predictable, base load electricity for 16 hours each day, using both the ebb and flood tides. It will save over 200,000 tonnes of CO2 per year for its design life of over 100 years. The project represents an investment of £650m and according to the development company behind the scheme is a significant opportunity for Wales to take the lead in the tidal industry for the UK. The power plant could be connected to the National Grid and be ‘power ready’ in 2017.

The tidal lagoon will comprise a ‘land attached’ impoundment, located between the dredged channels of the Tawe and Neath rivers. The impounded area will be surrounded by a 10km long wall. Landfall points will be located at or near Swansea Docks, but the lagoon will not obstruct the entrance to any rivers or marinas, nor adversely affect the operation of the port.

The total height of the seawall will be approximately 11m (shore side) and 19m (offshore). The visibility of the wall at low water will be 11.3m, at high water it will measure 2.8m. The site will have a total installed capacity of circa 250MW with a potential annual output of circa 400GWh.

Tidal Lagoon Power plc, the company behind the project, says it will hopefully be the first in a network of lagoons around the UK. Electricity is generated by creating a ‘head’ of water, a difference in water level between the inside and outside of the lagoon, and channelling the resulting flow through turbines. Once there is a sufficient difference in water level, the lagoon gates are opened and the turbines begin to generate. It is proposed to generate on both the incoming (flood) tides and outgoing (ebb) tides, maximising the energy extraction potential from any site.

Detailed plans for the lagoon are now being finalised prior to beginning formal consultation in summer 2013. An application for development consent will be submitted to the Planning Inspectorate in the late autumn of 2013.

Tidal range schemes differ from ‘tidal stream’ technology in their use of head to generate power. Tidal stream technologies generate power using water velocity arising from currents, which is less efficient and requires very large machines to produce relatively small amounts of power. Tidal range, on the other hand, uses exactly the same head principle as normal run-of-river hydro schemes to produce energy and therefore the turbine technology is very similar i.e. robust, efficient and proven. Tidal range lagoons also offer the opportunity to control the direction and velocity of the water flows that are harnessed.

Swansea Bay has been chosen as it offers the necessary conditions for building lagoons – the water must be shallow and the tidal range must be large. The Severn Estuary holds the second highest tidal range in the world and Swansea Bay reaches a range of just over 10m. As well as benefitting from this key characteristic, Swansea has a gently sloping seabed (suitable for this construction method) and proximity to a population centre, such that transmission losses are minimised from the electricity produced.

The development will include a sand core seawall and hydro-turbines mounted in a concrete turbine housing. The seawall will use sandy materials gained from the seabed within the lagoon footprint which are hydraulically filled into long geotextile casings 5m in diameter. On top of these Geotubes and compacted sand fill are placed small rocks and on top of the small rocks, larger rock armour to protect the structure against degradation from the marine environment, sun and weather.

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