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Tidal Lagoons

A proposed tidal lagoon in Cardiff has the potential to generate a mammoth 5.6 billion kWh of energy.1 That’s enough energy to power some 300,000 homes.2 However, how much of our energy demand can we supply using tidal lagoons and how much do they cost to build?

What Are Tidal Lagoons?

A tidal lagoon is a gigantic circular structure that encloses a portion of the ocean in order to generate huge amounts of energy.3 Generally several kilometres in size, tidal lagoons generate energy by opening a series of gates when the tide is high to allow the water to rush in and fill up the lagoon.4 When the tide is low, the gates are again opened, allowing the enclosed water to rush back out into the sea.5 In both instances, the onrushing water is channelled through a series of turbines to generate electricity.6 As well as generating energy though, tidal lagoons can also be used to provide much-needed flood protection for low-lying areas.7 They do this, by closing the tidal lagoon’s gates at low tide in order to convert it into a huge water store.8 Any flood water can then be drained or pumped into the tidal lagoon.9 Further to this, if designed well, tidal lagoons can become major tourist attractions that provide a variety of recreational facilities. This includes cycling, running, walking and angling.10 People can also enjoy open water swimming, rowing and sailing within the lagoon itself.11 There are currently plans to construct six lagoons along the UK coast, which would meet 8% of the country’s electricity demand.12 Unfortunately though, much like tidal barrages, there are only a limited number of appropriate sites around the world, and as a result, the global potential of this technology is extremely limited.13

What’s Good About Them?

  • They provide a highly predictable energy source.14
  • They have minimal impact on the environment.15
  • They can offer flood protection in low-lying areas.16

What’s Bad About Them?

  • They have very limited global potential.
  • They can only supply energy for around 14 hours per day.17
  • They are relatively expensive compared to other devices.18

How Much Area Do We Need?

If the United States were a shallow sea flowing at around 1.5 metres per second, some 5% of the country would have to be covered with tidal lagoons in order to meet the country’s energy demand.19 Furthermore, to meet the energy demand for the UK, which has eight times as many people per kilometre,20 the equivalent of 17% of the country’s landmass would have to be covered with tidal lagoons.21

Map showing the equivalent area of the United States of America that would need covered with tidal lagoons in order to meet the country's energy demand.

What Impact Do They Have on the Landscape?

Tidal lagoons are impressive structures that will be visible along the coastline. This is particularly the case at low-tide when the lagoon’s banks can be as much as 12 metres tall.22 However, in the context of coastal landscapes, twelve metres is not very tall. For example, cliffs can rise more than 100 metres out of the water.23 What’s more, with much of a lagoon’s banks located far out at sea, the banks will generally be little more than a thin line on the horizon. As such, if the banks incorporate materials that are sympathetic to the surrounding landscape, the visual impact of tidal lagoons will likely be minimal.

The proposed tidal lagoon for Swansea Bay in Wales includes a beach, rockpools, art installations and an offshore visitor centre.24

Where Are Tidal Lagoons Best Located?

No maps showing optimum placement for Tidal Lagoons appear to have been created, however, due to their similarities with tidal barrages, we assume they would be most effective in similar parts of the world. Specifically, this means they are likely to be effective on the coasts of France, China, Canada, the UK, Australia, India, Pakistan, Argentina and Russia.

How Do They Perform?

Energy PriceLife SpanEnergy per KM²
¢17/KWH25120 Years2639 GWH/YR27

Economic OffsetEnergy OffsetWorld Potential
27 Years284 Years291.5 PWH30

How Do They Rate?

Value for Money|★ ★ ★ ★ ★ ★
Reliability|★ ★ ★ ★ ★ ★
Eco-friendliness|★ ★ ★ ★ ★ ★
Global Potential|★ ★ ★ ★ ★
Overall|★ ★ ★ ★ ★ ★

Tidal Lagoons in a Nutshell

To summarise, tidal lagoons could provide a highly predictable energy source that would have minimal impact on the environment. What’s more, they could also provide flood protection in low-lying areas. However, tidal lagoons have limited global potential as there are only a few viable sites. Furthermore, they can only supply energy for around 14 hours per day. Finally, tidal lagoons are relatively expensive. Despite this, once the initial cost has been paid off, they would provide cheap energy for many years to come. Nevertheless, there may be a better solution for extracting energy from our tides. Why not check out tidal streams by clicking the link below? Alternatively, find out other ways we can stop climate change by returning to the main menu.

Image Credit

Title image created by Tidal Lagoon PLC and reproduced with permission.

United States map created by SUPER RADICAL.

Image of tidal lagoon visitor centre created by Tidal Lagoon PLC and reproduced with permission.

World map based on data sourced from Boyle, Godfrey –’Renewable Energy: Power for a Sustainable Future’ – Oxford University Press – Page 227. World map created by SUPER RADICAL.

General Notes

All figures presented in this section are estimates based on best available data, assume optimum locations, and, wherever possible, are based on comparable studies. That said, many of the studies assume different economic conditions, climatic conditions, time frames and locations. Furthermore, the technologies discussed in this section are in a constant state of development. As a result, the figures presented within this section provide a rough guide only and should not be viewed as a definitive performance level.

For the total world energy demand, a figure of 104.4 million GWh has been used. The figure is based on 2012 data and sourced from International Energy Agency – 'World Balances for 2012' – www.iea.org.

All UK to USA currency conversions have been set at $1.656 USD for each £1 GBP. The figure is based on the conversion rate as of the 1st January 2014 and sourced from XE – 'XECurrency Table: USD - U.S. Dollar' – www.xe.com.

Article Endnotes

  1. Tidal Lagoon Plc – ‘Energy Calculator’ – www.tidallagoonpower.com.
  2. Based on a UK home using an average 18,738 kWh of energy in 2014. Sourced from UK Department of Energy and Climate Change – ‘Energy Consumption in the UK’ – Page 7.
  3. Harrabin, Roger – ‘World’s First Lagoon Power Plants Unveiled in UK’ – www.bbc.com.
  4. Harrabin, Roger – ‘World’s First Lagoon Power Plants Unveiled in UK’ – www.bbc.com.
  5. Harrabin, Roger – ‘World’s First Lagoon Power Plants Unveiled in UK’ – www.bbc.com.
  6. Harrabin, Roger – ‘World’s First Lagoon Power Plants Unveiled in UK’ – www.bbc.com.
  7. Tidal Lagoon Swansea Bay PLC – ‘Coastal & Flood Defences’ – www.tidallagoonswanseabay.com.
  8. Science Media Centre – ‘Expert Reaction to Somerset Flooding’ – www.sciencemediacentre.org.
  9. Science Media Centre – ‘Expert Reaction to Somerset Flooding’ – www.sciencemediacentre.org.
  10. Tidal Lagoon Swansea Bay plc – ‘Project Benefits’ – www.tidallagoonswanseabay.com.
  11. Tidal Lagoon Swansea Bay plc – ‘Project Benefits’ – www.tidallagoonswanseabay.com.
  12. Harrabin, Roger – ‘World’s First Lagoon Power Plants Unveiled in UK’ – www.bbc.com.
  13. Based on a 2012 data that estimates tidal lagoons could theoretically generate 25 TWh per year in the UK, less than 2% of the UK’s energy demand. As the UK has arguably the greatest tidal potential in the world, basic logic allows us to establish that the global potential for tidal lagoons will be extremely limited. Tidal lagoon potential sourced from The Crown Estate – ‘UK Wave and Tidal Key Resource Areas Project’ – Page 7. UK energy demand based on 2012 data sourced from International Energy Agency – ‘United Kingdom: Balances for 2012’ – www.iea.org.
  14. Pöyry Management Consulting – ‘Levelised Costs of Power from Tidal Lagoons’ – Page 27.
  15. Harrabin, Roger – ‘World’s First Lagoon Power Plants Unveiled in UK’ – www.bbc.com.
  16. Science Media Centre – ‘Expert Reaction to Somerset Flooding’ – www.sciencemediacentre.org.
  17. Harrabin, Roger – ‘World’s First Lagoon Power Plants Unveiled in UK’ – www.bbc.com.
  18. Based on onshore turbines, offshore turbines, photovoltaics, solar thermal plants, hydroelectric dams, biomass power plants and geothermal plants all being cheaper than tidal lagoons.
  19. Based on the United States of America having a total land area of 9,147,420 square kilometres, the United States of America demanding 16.8 million GWh of energy per year, tidal lagoons generating 39 GWh per hectare, a 2% loss due to power conditioning and 6.5% loss due to transmission and distribution. Land area sourced from The World Bank – ‘Land Area (SQ. KM)’ – data.worldbank.org. Energy demand based on 2012 data and sourced from International Energy Agency – ‘United States: Balances for 2012’ – www.iea.org. Energy generated by tidal lagoons based on 4.5 Watts of energy being generated per square metre. Sourced from MacKay, David J.C. – ‘Sustainable Energy – Without the Hot Air’ – Page 84. Power conditioning losses based on data sourced from Fuji Electric – ‘Large-scale Photovoltaic Power Generation Systems’ – Page 7. Transmission and distribution losses based on 2007 data for the United States and sourced from U.S. Department of Energy – ‘Frequently Asked Questions – Electricity’ – tonto.eia.doe.gov.
  20. Based on the United States of America having 35 people per square kilometre of land area and the United Kingdom having 267 people per square kilometre of land area. Figures based on 2014 data sourced from The World Bank – ‘Population Density (People Per SQ. KM of Land Area)’ – data.worldbank.org.
  21. Based on the United Kingdom having a total land area of 248,532 square kilometres, the United Kingdom demanding 1.48 million GWh of energy per year, tidal lagoons generating 39 GWh per hectare, a 2% loss due to power conditioning and 6.5% loss due to transmission and distribution. Land area sourced from The World Bank – ‘Land Area (SQ. KM)’ – data.worldbank.org. Energy demand based on 2012 data and sourced from International Energy Agency – ‘United Kingdom: Balances for 2012’ – www.iea.org. Energy generated by tidal lagoons based on 4.5 Watts of energy being generated per square metre. Sourced from MacKay, David J.C. – ‘Sustainable Energy – Without the Hot Air’ – Page 84. Power conditioning losses based on data sourced from Fuji Electric – ‘Large-scale Photovoltaic Power Generation Systems’ – Page 7. Transmission and distribution losses based on 2007 data for the United States and sourced from U.S. Department of Energy – ‘Frequently Asked Questions – Electricity’ – tonto.eia.doe.gov.
  22. White Consultants – ‘Swansea Bay Tidal Lagoon – Review of Environmental Statement: Seascape, Landscape and Visual’ – Page 4.
  23. Based on the White Cliffs of Dover. Sourced from Dover Museum – ‘White Cliffs of Dover’ – www.dovermuseum.co.uk.
  24. Tidal Lagoon Plc – ‘Opportunities & Benefits’ – www.tidallagoonpower.com.
  25. Based on volume-weighted average. Sourced from Pöyry Management Consulting – ‘Levelised Costs of Power from Tidal Lagoons’ – Page 2.
  26. Tidal Lagoon Plc – ‘Tidal Lagoon Power’ – Page 5.
  27. Based on 4.5 Watts of energy being generated per square metre. Sourced from MacKay, David J.C. – ‘Sustainable Energy – Without the Hot Air’ – Page 84.
  28. Calculation undertaken within the ‘Renewable Solution’ section of the ‘ZERO-FIFTY World Energy Database’ and based on a lifespan of 35 years. Lifespan sourced from of Pöyry Management Consulting – ‘Levelised Costs of Power from Tidal Lagoons’ – Page 2.
  29. Tidal Lagoon Swansea Bay plc – ‘Environmental Statement Volume 3, Appendix 5.1 – Sustainability: Carbon Balance’ – Page 16.
  30. Based on the annual global potential of tidal head energy available in shallow waters being 2,500 PWh and tidal lagoons having a capacity factor of circa 60%. Annual global potential sourced from International Institute for Applied Systems Analysis (IIASA) – ‘Global Energy Assessment (GEA)’ – Page 853. Capacity factor sourced from Excell, Jon – ‘Your Questions Answered: Tidal Lagoons’ – www.theengineer.co.uk. Please note, power conditioning, distribution and transmission losses have not been considered.

For further information about any of the above sources, please visit the ZERO EMISSION WORLD Works Cited page.

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