Tidal Streams

A single tidal stream turbine can generate some 6.1 million kWh of energy.1 That is enough to power some 330 homes.2 However, can we build enough tidal stream turbines to power all our needs? Furthermore, what impact do tidal turbines have on marine life?

What Are Tidal Streams?

Tidal streams are underwater turbines that take advantage of the fast-moving sea currents that occur when the tides rise and fall.3 The energy generated by the turbines is then transferred back to the land via underwater cables. Available in a variety of forms, the most common is a multi-blade turbine, not too dissimilar to an onshore wind turbine.4 However, because water is some 800 times denser than air,5 a 15-metre-diameter tidal turbine can generate as much energy as a 60-metre-diameter wind turbine.6 Furthermore, if the tidal stream turbines are able to swivel, they can capture energy both as the tide comes in, and as it goes out.7 To allow for safe maintenance, both the turbine and the generator can be mechanically lifted above the water.8 To date, no large-scale tidal stream arrays have been constructed, but a number of schemes are under construction including one in Scotland that, when finished, will have 269 tidal stream turbines.9 Together, they are expected to generate enough energy to power 175,000 homes.10 Unfortunately though, it is estimated that tidal streams can only supply 1% of the world’s energy demand.11 As such, although they have some relevance, they cannot be considered a global solution.

What’s Good About Them?

  • They provide a highly predictable source of energy.12
  • They can provide energy for twenty hours each day.13
  • They cause minimal disruption to marine life.14
  • They generally have minimal visual impact.15

What’s Bad About Them?

  • They are currently prohibitively expensive.16
  • They can cause disruption to shipping.17
  • They are difficult to maintain.18
  • There is limited global potential.19

How Much Area Do We Need?

If we pretend that the United States is a shallow sea flowing at around 1.5 metres per second, some 4% of the area of the country would have to be covered with tidal streams to meet the country’s energy demand.20 For the UK, the equivalent of some 12% of the country’s landmass would have to be covered with tidal streams to meet the nation’s energy demand.21

Map showing the equivalent area of the United States of America that would need to be a body of water in order for tidal streams to meet the country's energy demand.

What Impact Do They Have on the Landscape?

Tens or even hundreds of tidal streams could be used together so that we can maximise the amount of energy we generate from our tides.

Tidal streams are large structures, but, as they can be submerged entirely beneath the water, visual impact will be minimal. Despite this, some form of way-finding will be required for waterborne transport to avoid collisions with the submerged tidal streams. Furthermore, the tidal streams will be visible when they are raised for maintenance. However, raising the tidal streams for maintenance is more likely to be considered a spectacle than as something that damages the appearance of the landscape.

Where Are Tidal Streams Best Located?

Tidal streams are best located in areas of strong tidal movement.22 This can be found along small streches of the world’s coastlines and particularly in areas that funnel or capture large expanses of the ocean.

How Do They Perform?

Energy PriceLife SpanEnergy per KM²
¢18/KWH2320 YRS2453 GWH/YR25

Economic OffsetEnergy OffsetWorld Potential
20 YRS268 MTHS270.8 PWH28

How Do They Rate?

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

Tidal Streams in a Nutshell

To summarise, tidal streams provide a highly predictable energy source that causes minimal disruption to marine life. Tidal streams can also be submerged so they have minimal visual impact. Despite this, there is limited global potential and they are currently prohibitively expensive. However, it is likely the cost will significantly reduce once the technology becomes more developed. We are not limited to using the tides to generate our energy from the sea though. Why not see what waves have to offer 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 and copyrighted to Siemens.

United States map created by SUPER RADICAL.

Image of underwater turbines created by and copyrighted to Siemens. Minor modifications undertaken by SUPER RADICAL LTD.

World map created by SUPER RADICAL. World map based loosely on all coastlines not covered by ice that benefit from a tidal range greater than four metres. Tidal range sourced from Commonwealth of Australia, Bureau of Meteorology – ‘Tidal Range’ – Map. Areas of ice cover sourced from Koistinen, Ville – ‘The Main Biomes in the World’ – commons.wikimedia.org.

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. Based on the four tidal stream turbines that form the first phase of the MeyGen project in Scotland generating 24.7 GWh of energy in 2019. Sourced from Edmond, Charlotte – ‘A New Tidal Energy Project Just Hit a Major Milestone in Scotland’ – www.weforum.org.
  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. The European Marine Energy Centre (EMEC) Ltd – ‘Tidal Devices’ – www.emec.org.uk.
  4. Lynn, Paul A. – ‘Electricity from Wave and Tide’ – John Wiley & Sons – Page 86.
  5. National Aeronautics and Space Administration (NASA) – ‘Welcome to Rocket Research 101: Good That Takes Us to Momentum’ – nasa.gov.
  6. Araquistain, Tatiana Montllonch – ‘Tidal Power: Economic and Technological Assessment’ – Page 31.
  7. Boyle, Godfrey – ‘Renewable Energy: Power for a Sustainable Future’ – Oxford University Press – Page 232.
  8. Green Rhino Energy – ‘Tidal Stream Energy’ – www.greenrhinoenergy.com.
  9. BBC News – ‘Tidal Energy Project to be Constructed in the Pentland Firth’ – www.bbc.com.
  10. BBC News – ‘Tidal Energy Project to be Constructed in the Pentland Firth’ – www.bbc.com.
  11. Ocean Energy Systems – ‘2013 Annual Report’ – Page 36. Please note, figure does not include power conditioning, distribution and transmission losses.
  12. Green Rhino Energy – ‘Tidal Stream Energy’ – www.greenrhinoenergy.com.
  13. Power Engineering International – ‘Turning the Tide on Marine Power Generation’ – www.powerengineeringint.com.
  14. Evans, Jayne – ‘Energy Generation in the Marine Environment’ – Page 5.
  15. CleanTech Investor – ‘Tidal Generation: UK Potential’ – www.cleantechinvestor.com.
  16. Based on electricity generated from tidal streams appearing to cost around three times as much as electricity generated from natural gas.
  17. TidalStream – ‘Triton – Halving the Cost of Tidal Energy: Environment’ – www.tidalstream.co.uk.
  18. Roberts et al. – ‘Current Tidal Power Technologies and Their Suitability for Applications in Coastal and Marine Areas’ – Page 241.
  19. Based on a global potential of less than 1% of world energy demand.
  20. 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 streams generating 53 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. Power conditioning losses based on data sourced from Fuji Electric – ‘Large-scale Photovoltaic Power Generation Systems’ – Page 7. Energy generated by tidal streams based on six Watts of energy being generated per square metre. Sourced from MacKay, David J.C. – ‘Sustainable Energy – Without the Hot Air’ – Page 84. 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.
  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 streams generating 53 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 streams based on six 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. CleanTech Investor – ‘Tidal Generation: UK Potential’ – www.cleantechinvestor.com.
  23. Based on a predicted 2035 price inclusive of accelerated cost reduction. Sourced from The Carbon Trust – ‘Accelerating Marine Energy’ – Page 36.
  24. Douglas et al. – ‘Life Cycle Assessment of the Seagen Marine Current Turbine’ – Page 3.
  25. Based on six Watts of energy being generated per square metre. Sourced from MacKay, David J.C. – ‘Sustainable Energy – Without the Hot Air’ – Page 84.
  26. Calculation undertaken within the ‘Renewable Solution’ section of the ‘ZERO-FIFTY World Energy Database’ and based on a lifespan of 20 years. Lifespan sourced from The Carbon Trust – ‘Accelerating Marine Energy’ – Page 14.
  27. Douglas et al. – ‘Life Cycle Assessment of the Seagen Marine Current Turbine’ – Page 11.
  28. Ocean Energy Systems – ‘2013 Annual Report’ – Page 36. 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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