Tidal Streams

A typical onshore turbine can generate as much as 6 million kWh per year.1 That’s enough energy to power some 1,500 homes.2 The question is, could onshore turbines provide us with enough energy to replace our existing fossil fuel power plants?

What Are Onshore Turbines?

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 stream turbine can generate as much electricity 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 energy source.12
  • They cause comparatively minimal disruption to marine life.13
  • They generally have minimal visual impact.14

What’s Bad About Them?

  • They are currently prohibitively expensive.15
  • They can cause disruption to shipping.16
  • There is limited global potential.17

How Much Area Do We Need?

If we pretend that the UK is a shallow sea flowing at around 1.5 metres per second, some 12% of the area of the country would have to be covered with tidal streams to meet the country’s energy demand.18

What Do They Look Like?

To be completed.

Where Are Onshore Turbines Best Located?

Tidal streams are best located in areas of strong tidal movement.19 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?

¢18/KWH20Based on a predicted 2035 price inclusive of accelerated cost reduction. Sourced from The Carbon Trust – ‘Accelerating Marine Energy’ – Page 36.2120 Years22Douglas et al. – ‘Life Cycle Assessment of the Seagen Marine Current Turbine’ – Page 3.2353 GWH24Based on six Watts of energy being generated per square metre. Sourced from MacKay, David J.C. – ‘Sustainable Energy – Without the Hot Air’ – Page 84.25
Energy PriceLife Spanper KM² per Year
20 Years26Calculation 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 14.278 Months28Douglas et al. – ‘Life Cycle Assessment of the Seagen Marine Current Turbine’ – Page 11.290.8 PWH30Ocean Energy Systems – ‘2013 Annual Report’ – Page 36.31
Economic OffsetEnergy OffsetWorld Potential

How Do They Rate?

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

Onshore Turbines in a Nutshell

To be completed.

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.

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.

Article Endnotes

  1. European Wind Energy Association – 'Wind Energy's Frequently Asked Questions' – www.ewea.org.
  2. European Wind Energy Association – 'Wind Energy's Frequently Asked Questions' – www.ewea.org.
  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. Calculated using data sourced from 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. Evans, Jayne – ‘Energy Generation in the Marine Environment’ – Page 5.
  14. CleanTech Investor – ‘Tidal Generation: UK Potential’ – www.cleantechinvestor.com.
  15. Based on electricity generated from tidal streams appearing to cost around three times as much as electricity generated from natural gas.
  16. TidalStream – ‘Triton – Halving the Cost of Tidal Energy: Environment’ – www.tidalstream.co.uk.
  17. Based on a global potential of less than 1% of world energy demand.
  18. Based on a calculated area of 30,550 square kilometres required to meet the UK’s energy demand. Figure includes losses of 2% due to power conditioning and 6.5% due to transmission and distribution. 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.
  19. CleanTech Investor – ‘Tidal Generation: UK Potential’ – www.cleantechinvestor.com.

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