Tidal lagoons could be cheaper, generate more electricity, have a lower environmental impact and provide more habitats for wildlife
Industry experts say that the proposed Swansea Bay Tidal Lagoon could be the first step towards a network of coastal lagoons that would significantly contribute to Britain’s expanding energy needs as detailed in the Government’s Energy Bill published today.
Dr Simon Boxall of the University of Southampton, National Oceanography Centre says that UK tidal power is potentially the most reliable and least disruptive of all renewable energy resources:
“Tidal power is considered by many as a new and, as yet, untested source of energy, but it is in fact one that has been used to great effect across Europe since the 7th Century. At their peak there were more than 200 tidal mills in operation along the coast of England and Wales, and each had its own tidal pond which provided important natural habitats for birds and marine life. Many of these ponds are today classified as sites of special scientific interest such is their importance to bio-diversity.”
“The proposed Swansea Bay Tidal Lagoon is a 21st Century tide mill, making use of our vast tidal range in generating sufficient electricity to supply all of the domestic needs of the growing city of Swansea. The tide can be predicted over a million years in advance and the lagoon will generate power for at least 70% of the day. The wonderful thing about the tide is that when it is slack water (not generating power) in one location, just 50 miles down the coast the tide will be in full flood or ebb feeding energy into the National Grid 24 hours a day. The impact of the lagoon is an improved habitat for both wildlife and the local population, all whilst utilizing a free and very traditional source of power. What’s more, we benefit from a big smile, a cleaner planet and cheaper electricity – now that can’t be all bad.”
A tidal lagoon is a man-made sea wall structure impounding an area of water on the rise and fall of each tide, in order to harness hydrokinetic energy and generate power through low-head hydro turbines.
Tidal lagoons are a simple concept involving the adaptation of standard, proven components used in global engineering projects. The Swansea Bay Tidal Lagoon will comprise a UK standard sand-core breakwater or rock bund, similar to many seen in coastal defence schemes and harbour walls. The generating equipment of bulb hydro turbines have been used for many years on run-of-river hydro power schemes as well as some landmark tidal barrages. The hydro turbines are mounted inside concrete turbine housings and are permanently submerged so the resulting view is of a ring-shaped harbour wall with one section of concrete casing.
As the sea outside the breakwater rises and is held back a difference in water levels is created, known as ‘head’, and once a sufficient head height is reached sluice gates are opened and water flows into the lagoon through turbines to generate electricity. This process then occurs in reverse, on the ebb tide, as sea levels start to fall and a tidal head is created by holding water back within the lagoon. This way the tides can flow through turbines four times daily to generate power.
Using established methods, the proposed construction method involves the use of dredged sandy materials from a relatively thin layer of the sea bed within the lagoon, which are then hydraulically filled into long geotextile casings known as Geotubes®. On top of these Geotubes® and compact sand fill are placed small rocks and on top of this the larger rock armour to protect against degradation.
Low-head bulb turbines will generate the electricity when water flows the past turbine blades. These will be permanently submerged below the low water level in Swansea Bay. The flow is then created by gravity through the difference in head (or tidal height) between the inside and outside of the lagoon walls, as you would find in a dam structure. This type of turbine has been used in many hydro power applications including La Rance barrage in Brittany, France, which has been successfully operational for half a century.
Eva Bishop, Development Director of the company behind the Swansea Bay Tidal Lagoon says:
“Tidal lagoons offer the first renewable form of baseload electricity generation which encompass the predictabilty of tides and generation periods. The proposed Swansea development provides a low risk, low cost renewable energy source that is available for deployment by 2020 without significant innovation.”
“They hold the potential to harness significant power from a natural resource widely available from an island nation and in close proximity to population centres for low loss distribution. This renewable energy source is also able to be plugged into the national grid without requirement for additional balancing fossil fuel driven capacity.”
Studies have shown that the marine environment stores enough energy in the form of heat, currents, waves and tides to meet total worldwide demand for power many times over. As water accelerates over the 200 mile continental shelf to the west of the United Kingdom a large body of water enters a relatively shallow pool to bring with it wave energy and tidal range. The UK has the second largest tidal range in the world, much of that range adjacent to major cities like Bristol, Cardiff, Liverpool, London and Swansea.
“We believe that tidal lagoons should form a significant part of our future energy mix and can help us achieve greater security of supply while reducing the cost of electricity to consumers. This project will be the first of its kind, a flagship for the UK and Wales, generating cost effective, predictable and fully renewable power from the tidal range in Welsh waters.”
Geotube® systems are a product of TenCate.