Hydroelectric Dams

The Three Gorges Dam in China produced more than 100 billion kWh of energy in 2018.1 That’s enough energy to power some 5.3 million homes.2 However, can hydroelectric dams provide us with enough energy to replace all our existing fossil fuel power plants? What’s more, does hydroelectricity really reduce our greenhouse gas emissions?

What Are Hydroelectric Dams?

Hydroelectric dams are huge human-made structures that can generate substantial amounts of energy from rivers.3 They do this by blocking the natural course of the river in order to create a huge reservoir of water,4 often several hundred metres deep.5 This places the water at the base of the reservoir under huge amounts of pressure which, when released, creates an extremely powerful flow of water.6 This water is directed onto turbines that are connected to generators in order to create an abundance of electricity.7 Unfortunately though, hydroelectric dams can be extremely harmful to the environment. Not only do they deprive agricultural land and fish downstream of essential nutrients and minerals,8 but they also result in a huge amount of greenhouse gas emissions. This is because several thousand kilometres of natural habitat is flooded, including tress, plants and wildlife – all to make space for the new reservoir. The remains from the flood are then left to rot at the bottom of the reservoir, whereby they release enormous amounts of greenhouse gases.9 In fact, the greenhouse gases emitted from building a hydroelectric dam can be more than twice the amount that would have been emitted by an equivalent coal power plant.10 Currently, hydroelectricity is the most widely used form of renewable energy, however, it still produces less than 3% of the world’s energy demand.11 It does have the potential to generate some 14 PWh of energy – around 13% of our planet’s current demand.12

What’s Good About Them?

  • They provide an extremely reliable source of energy.13
  • The energy can be stored until required.14
  • They last a long time and require little maintenance.15
  • The reservoir’s water can be used for irrigation purposes.16

What’s Bad About Them?

  • There is a limited number of viable sites.17
  • They can cause substantial greenhouse gas emissions.18
  • Construction can lead to significant ecological damage.19
  • The reservoirs can take up a huge amount of space.20

How Much Area Do We Need?

To power the United States using hydroelectric dams, a reservoir roughly 29% the size of the country would be required.21 What’s more, to catch all the rainfall, a land area of around ten times the landmass of the country would be needed.22 For the United Kingdom, a reservoir roughly 93% the size of the country would be required.23 On top of this, to catch all the rainfall, a land area of around 38 times the country would be needed.24

Map showing the land area of the United States of America that would have to be flooded with water in order to meet the country's energy demand using hydroelectric dams.

What Impact Do They Have on the Landscape?

Hydroelectric dams are enormous concrete structures that have a significant visual impact. However, when well designed, they can become major tourist attractions. A great example of this Hoover Dam.25 Despite this, the construction of a hydroelectric dam also necessitates flooding huge swathes of the surrounding landscape.26 This includes forests, wildlife habitats, agricultural land, and communities.27 In fact, for the Three Gorges Dam in China, an incredible 630 square kilometres of land was flooded.28 Incredibly, this included two cities, 114 towns and 1,680 villages.29

When full, the water contained within the Three-Gorge reservoir actually increases the length of each year by 22 microseconds.30

Where Are Hydroelectric Dams Best Located?

Hydroelectric dams work best in mountainous regions with high rainfall.31 This means they have the most potential in the United States, South America and much of Asia. However, they have little potential in Russia, Canada, Argentina, Australia, the Middle East and the majority of Africa.

How Do They Perform?

Energy PriceLife SpanEnergy per KM²
¢8/KWH32250 YRS337 GWH/YR34

Economic OffsetEnergy OffsetWorld Potential
16 YRS353614 PWH37
Economic Offset

How Do They Rate?

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

Hydroelectric Dams in a Nutshell

To summarise, hydroelectric dams provide a cheap and reliable source of energy that can be stored until required. Furthermore, hydroelectric dams can operate for more than 100 years with only minimal maintenance. However, the construction of a hydroelectric dam can result in significantly more greenhouse gases than would have been emitted by an equivalent coal power plant. Furthermore, the resulting reservoirs can take up a huge amount of space and construction can lead to immense ecological damage. When this is combined with the fact there are only a few viable sites around the world, hydroelectric dams don’t appear to have a place in our renewable future. Hydroelectric dams are not the only way we can generate energy from water though. Why not find out what tidal barrages 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 taken by Andy and reproduced under license from Adobe Stock.

United States map created by SUPER RADICAL.

Image of Russian hydroelectric dam taken by Evgeny V and reproduced under license from Shutterstock.

World map shows all countries that have a gross theoretical hydraulic energy potential greater than 300 MWh per square kilometre. World map based on 2004 data sourced from Energie-Atlas GmbH – ‘Hydraulic Energy Potential’ and 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. Jie, Zhang – ‘Three Gorges Dam Generates Record Amount of Power’ – www.chinadaily.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. U.S. Geological Survey – ‘Hydroelectric Power: How it Works’ – usgs.gov.
  4. U.S. Geological Survey – ‘Hydroelectric Power: How it Works’ – usgs.gov.
  5. Based on at least twelve dams being taller than 200 metres. Sourced from Encyclopaedia Britannica – ‘Dam’ – www.britannica.com.
  6. U.S. Geological Survey – ‘Hydroelectric Power: How it Works’ – usgs.gov.
  7. U.S. Geological Survey – ‘Hydroelectric Power: How it Works’ – usgs.gov.
  8. International Rivers – ‘Environmental Impacts of Dams’ – www.internationalrivers.org.
  9. Area based on Brazil’s Tucurui Dam and sourced from Fearnside, Philip M. – ‘Environmental Impacts of Brazil’s Tucurui Dam: Unlearned Lessons for Hydroelectric Development in Amazonia’ – Page 382. Methane emissions sourced from International Rivers – ‘Dirty Hydro: Dams and Greenhouse Gas Emissions’ – Page 1.
  10. International Rivers – ‘Dirty Hydro: Dams and Greenhouse Gas Emissions’ – Page 4.
  11. Based on 2012 data sourced from International Energy Agency – ‘World: Balances for 2012’ – www.iea.org.
  12. Hoogwijk, Monique and Graus, Wina – ‘Global Potential of Renewable Energy Sources: A Literature Assessment’ – Page 39. Please note, figure does not include power conditioning, distribution and transmission losses.
  13. U.S. Geological Survey – ‘Advantages of Hydroelectric Power Production and Usage’ – usgs.gov.
  14. U.S. Geological Survey – ‘Advantages of Hydroelectric Power Production and Usage’ – usgs.gov.
  15. Maintenance sourced from U.S. Geological Survey – ‘Advantages of Hydroelectric Power Production and Usage’ – usgs.gov. Long life span based on large scale hydroelectric dams lasting for 200 years and other renewable energy sources lasting as little as 20 years.
  16. U.S. Geological Survey – ‘Advantages of Hydroelectric Power Production and Usage’ – usgs.gov.
  17. Based on a global potential of only 14 PWh.
  18. International Rivers – ‘Dirty Hydro: Dams and Greenhouse Gas Emissions’ – Page 4.
  19. International Rivers – ‘Environmental Impacts of Dams’ – www.internationalrivers.org.
  20. Based on the reservoirs requiring more than twice as much space as onshore turbines and the reservoirs created having extremely limited use.
  21. 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, hydroelectric dams generating 7 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 hydroelectric dams based on 1 TWh being generated each year for every 152 square kilometres of reservoir. Data sourced from Diolettas, Stamatios – ‘Distributed Energy Resources: Prometheus of Renewable Energy’ – Page 153. 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. 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, hydroelectric dams generating 175 MWh per hectare of rainfall, 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 hydroelectric dams based on 0.02 watts of energy being generated per square metre of rainfall. Figure sourced from MacKay, David J.C. – ‘Sustainable Energy – Without the Hot Air’ – Page 55. 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. Please note that figures assume the use of every drop of rainwater for hydroelectric power. Realistically, we would only be able to exploit a fraction of this rainfall because it would not be possible to create a dam for every stream. Furthermore, much of the rainfall would evaporate before it could be used to generate energy.
  23. 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, hydroelectric dams generating 7 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 hydroelectric dams based on 1 TWh being generated each year for every 152 square kilometres of reservoir. Data sourced from Diolettas, Stamatios – ‘Distributed Energy Resources: Prometheus of Renewable Energy’ – Page 153. 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.
  24. 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, hydroelectric dams generating 7 GWh per hectare of rainfall, 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 hydroelectric dams based on 0.02 watts of energy being generated per square metre of rainfall. Figure sourced from MacKay, David J.C. – ‘Sustainable Energy – Without the Hot Air’ – Page 55. 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. Please note that figures assume the use of every drop of rainwater for hydroelectric power. Realistically, we would only be able to exploit a fraction of this rainfall because it would not be possible to create a dam for every stream. Furthermore, much of the rainfall would evaporate before it could be used to generate energy.
  25. Based on 7 million people visiting the Hoover Dam each year. Sourced from National Park Service – ‘Nevada and Arizona: Hoover Dam’ – www.nps.gov.
  26. Union of Concerned Scientists – ‘Environmental Impacts of Hydroelectric Power’ – www.ucsusa.org.
  27. Union of Concerned Scientists – ‘Environmental Impacts of Hydroelectric Power’ – www.ucsusa.org.
  28. European Space Agency – ‘Three Gorges Dam, China’ – earth.esa.int.
  29. Government of the People’s Republic of China – ‘[总体规划]三峡库区的淹没情况’ – www.gov.cn.
  30. NASA Jet Propulsion Laboratory – ‘Details Earthquake Effects on the Earth’ – www.jpl.nasa.gov.
  31. Rheinisch-Westfälisches Elektrizitätswerk (RWE) AG – ‘Fact Sheet – Hydro Power’ – Page 1.
  32. Based on projected costs for 2020 sourced from U.S. Energy Information Administration – ‘Levelized Cost and Levelized Avoided Cost of New Generation Resources in the Annual Energy Outlook 2015’ – Page 6.
  33. Figure based on a standard hydroelectric dam having a typical lifespan of between 50 to 100 years and a large hydroelectric dam having a lifespan of between 200 to 300 years. Sourced from Chiras, Daniel D. – ‘Environmental Science’ – Page 333.
  34. Figure based on 1 TWh being generated each year for every 152 square kilometres of reservoir. Data sourced from Diolettas, Stamatios – ‘Distributed Energy Resources: Prometheus of Renewable Energy’ – Page 153.
  35. Calculation undertaken within the ‘Renewable Solution’ section of the ‘ZERO-FIFTY World Energy Database’ and based on a lifespan of 30 years. Lifespan sourced from U.S. Energy Information Administration – ‘Levelized Cost and Levelized Avoided Cost of New Generation Resources in the Annual Energy Outlook 2015’ – Page 2.
  36. Based on detailed studies undertaken by Ivan Lima and his colleagues from Brazil’s National Institute for Space Research (INPE) that demonstrates registered dams greater than 15 metres tall emit a combined 104 million tonnes of methane annually via reservoir surfaces, turbines, spillways and rivers downstream. Data sourced from International Rivers – ‘Greenhouse Gas Emissions from Dams FAQ’ – www.internationalrivers.org.
  37. Hoogwijk, Monique and Graus, Wina – ‘Global Potential of Renewable Energy Sources: A Literature Assessment’ – Page 39. Please note, power conditioning, distribution and transmission losses have not been considered.

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