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[[Category:Done 2015-09-06]]  
[[Category:Done 2021-10-29]] [[Category:Translated to French]]
[[category:371 topics]]
[[fr:Hydroélectricité]]
[[File:MicaDam.JPG|360px|thumb|right|Figure 1. The Mica Dam in British Columbia is one example of how hydropower can be harnessed for human use.<ref>Wikimedia Commons. (September 2, 2015). ''Mica Dam'' [Online]. Available: http://en.wikipedia.org/wiki/File:MicaDam.JPG</ref>]]
[[es:Energía hidroeléctrica]]
[[Category:Translated to Spanish]]
[[File:Ingur_Hydroelectric_Power_Station.jpg|360px|thumb|right|Figure 1. A hydroelectric dam where hydroelectricity is generated.<ref>Wikimedia Commons. (August 31, 2015). ''Ingur Hydroelectric Facility'' [Online]. Available: https://commons.wikimedia.org/wiki/File:Ingur_Hydroelectric_Power_Station.jpg</ref>]]
<onlyinclude>'''Hydropower''' extracts [[mechanical energy]] from [[water]], transforming it into [[electrical energy]] to generate  [[electricity]]. Water in the environment often has both gravitational potential energy and kinetic energy, which can generate electricity using a generator.</onlyinclude> Note that traditionally this does '''not''' refer to the energy obtained from flowing water in the form of tides. In the case of obtaining energy from the tides, the term [[tidal power]] is used. The amount of potential energy stored in a body of water at a hydroelectric dam is measured using the height difference between the '''head race''' and [[tail race]], known as the [[hydraulic head|elevation head]] (part of the hydraulic head). Roughly 1/6th of the electricity in the world comes from hydropower facilities, while values in the earlier twentieth century were much higher. In some countries around the world, hydroelectricity is the dominant form of electrical power generation.<ref>dom (May 23, 2020). "Global Use of Hydroelectricity" [Online]. Available: https://www.e-education.psu.edu/earth104/node/1060</ref>


<onlyinclude>'''Hydropower''' is the overall [[power]] that can be harnessed from [[water]] and its flows. It is the overall summation of the [[potential energy]] and [[kinetic energy]] that the water has.</onlyinclude> The potential energy of water is usually referred to as its [[hydraulic head]]. In [[hydroelectricity|hydroelectric]] generation, this hydraulic head represents a height difference between the [[hydroelectric reservoir|reservoir]] and the outflow channel or [[tail race]]. Generally speaking this hydraulic head is any height difference in a water flow. The kinetic energy of the water is related to the [[velocity]] of moving water and the [[volume]] of water being moved, also known as the [[flow rate]].<ref>Engineering Toolbox. (September 2, 2015). ''Hydropower'' [Online]. Available: http://www.engineeringtoolbox.com/hydropower-d_1359.html</ref>
Countries such as China, Canada, and Brazil are the leaders in total hydroelectricity generation with capacities of [[watt|200 GW]], 89 GW, and 70 GW respectively.<ref name="RE1">Abhishek Shah. (September 2, 2015). ''List of World’s Largest Hydroelectricity Plants and Countries – China Leading in building Hydroelectric Stations'' [Online]. Available: http://www.greenworldinvestor.com/2011/03/29/list-of-worlds-largest-hydroelectricity-plants-and-countries-china-leading-in-building-hydroelectric-stations/</ref> Other notable producers include Russia, India, Norway, Japan, and Venezuela (which is almost completely dependent on hydropower).<ref name="RE1"/> See the data visualization below for more statistics on hydroelectricity around the world.


With special [[technology|technologies]], hydropower can be harnessed by humans and used for [[electricity generation]]. The [[electricity]] generated from this process is known as [[hydroelectricity]]. Humans have been harnessing hydropower for millennia. The ancient Greeks used [[water wheel]]s to grind wheat over 2000 years ago.<ref>IEA. (September 2, 2015). ''What is hydropower’s history?'' [Online]. Available: http://www.ieahydro.org/What_is_hydropower’s_history.html</ref> Hydropower continued to be exclusively converted directly into [[mechanical power]] up until the end of the 19th century when electrical dynamos where attached to the shaft to generate electricity.<ref>Water Power Program: History of Hydropower. (n.d.). Retrieved from http://www1.eere.energy.gov/water/hydro_history.html</ref>
[[File:AncientWaterWheel Syria.png|thumb|right|Figure 2. Photograph of a water wheel in Syria in 1916 used here for irrigation purposes.<ref>Wikimedia Commons. (May 30, 2020). ''Popular Science Monthly Vol. 88'' [Online]. Available: https://archive.org/details/popularsciencemo88newyuoft/page/82/mode/2up/search/water+wheel</ref>]]


The energy of  moving water is purely [[mechanical energy]], one of the highest-quality forms of energy. So in theory, since it is such a high-quality energy it can be converted to electrical energy with near 100% [[efficiency]] since there is no [[thermal energy]] involved (and thus [[thermodynamics]] doesn't have to be taken into account). However, there are still minor losses associated with [[friction]] and inefficiencies in the [[electrical transmission|transportation of electricity]] (as a result of factors such as [[resistance]] in [[wire]]s). Overall, this means hydropower can be converted to electricity with efficiencies higher than 90%.<ref>R. Wolfson. ''Energy, Environment and Climate'', 2nd ed. New York, U.S.A.: Norton, 2012</ref>
==Generation==
Humans have been harnessing energy from water for millennia, although not explicitly for electricity generation. The ancient Greeks used [[water wheel]]s to grind wheat over 2000 years ago.<ref>IEA. (September 2, 2015). ''What is hydropower’s history?'' [Online]. Available: http://www.ieahydro.org/What_is_hydropower’s_history.html</ref> Hydropower continued to be exclusively converted directly into [[mechanical power]] up until the end of the 19th century when electrical [[dynamo]]s were attached to the shaft to generate electricity.<ref>Water Power Program: History of Hydropower. (n.d.). Retrieved from http://www1.eere.energy.gov/water/hydro_history.html</ref> Dynamos were the first type of electrical generator.


==Energy in Water==
Hydroelectricity is generated at a [[hydroelectric facility]] which for large-scale generation includes a [[hydroelectric dam]]. At these facilities a dam holds back a large volume of water, creating a [[Hydroelectric reservoir|reservoir]]. This reservoir holds water at a higher elevation than the water on the downstream side of the dam. Compared to the water in the river, the water in the reservoir has a greater amount of [[potential energy]]. When a gate is opened at the top of the dam, the water from the reservoir flows through channels called [[penstock]]s down to the [[hydro turbine|turbines]]. When the water reaches the turbines the potential energy it contains is converted into [[kinetic energy]]. This flowing water is then used to turn the blades of the turbine. As the turbines spin, they move a [[generator]] and generate electricity.  
The potential and kinetic energy of water varies as it moves through some body, such as a river. If some sort of device is used to harness this [[energy]] - such as a [[hydro turbine]] - this kinetic and potential energy can be transformed into a type of energy that can be used.
===Potential Energy of Water===
The potential energy of water is the energy the water obtains as a result of being at some elevation. Put simply, the head difference of water is what results in potential energy. The relationship for the power from the potential energy of water can be expressed as:<ref name="RE2"> Vishul Suresh. (September 2, 2015). ''Physics of Hydropower'' [Online]. Available: http://www.academia.edu/8701598/Physics_of_Hydropower</ref>


<center><m>P=\rho\,Qgh\</m></center>
Although many hydroelectric facilities utilize dams, there are some types of systems that do not use dams and have very little [[water storage]] (meaning there is no large reservoir of stored water). These types of systems are known as [[run-of-the-river systems]], and have been gaining popularity as an alternative to large-scale reservoir dams.<ref name="ror">BC Sustainable Energy Association (May 23rd, 2020) "Small Hydro and Run-Of-River Hydro" [Online]. Available: https://www.bcsea.org/node/4063/bcsea-info</ref>


where:
==Classifications==
* <m>P</m> = power in watts (W)
Conventional hydroelectric generation relies on a [[hydraulic head]] difference created by man-made dams and obstructions. The majority of current hydroelectric generation is conventional and is comprised of hydroelectric dams and [[tidal dam]]s. Unconventional generation techniques generally rely on flow rate or on a small head differential. These unconventional techniques produce less energy than conventional methods, but also have less impact on the surrounding environment.<ref name = "ror"/> Some examples of unconventional hydropower platforms are [[low head hydro]], run-of-the-river systems, [[Instream microhydro power generator|instream hydro]], and [[kinetic tidal]].
* <m>\rho</m> = [[density]] of water in kilograms per [[cubic meter]] (kg/m<sup>3</sup>)
* <m>Q</m> = flow rate of the water in cubic meters per second (m<sup>3</sup>/s)
* <m>g</m> = [[acceleration due to gravity]] in meters per second squared ([[meters per second|m/s]]<sup>2</sup>)
* <m>h</m> = height difference between two points of the water flow in [[meter]]s (m)


This expression is known as the [[hydroelectric power equation]]. The height difference between inlet and outlet in conventional generation is generally created by [[hydroelectric dam|damming]] a river to create a [[reservoir]]. Water from the reservoir is then directed through [[turbine]]s which convert the energy in in [[fluid]] into [[electrical energy]]. The amount of energy that can be converted is related to the efficiency of the turbine and electrical generator.
Each type of hydroelectric generation method has an associated output classification based on its capacity and are outlined in the table below.<ref>IPCC. (September 2, 2015). ''Chapter 5 - Hydropower'' [Online]. Available: www.ipcc.ch/pdf/special-reports/srren/drafts/SRREN-FOD-Ch05.pdf</ref>


===Kinetic Energy of Water===
<center>
The kinetic energy of the water is a result of the [[speed]] of the flow of the water. The relationship for the power from kinetic energy of water is proportional to this velocity and can be expressed as:<ref name="RE2"/>
{| class="wikitable"
|-
! Classification !! Capacity
|-
| Large || > 100 MW
|-
| Medium || 15 - 100 MW
|-
| Small|| 1 - 15 MW
|-
| Mini || 100 kW - 1 MW
|-
| Micro  ||  5 - 100 kW
|-
| Pico || ~ 200 W - 5 kW
|}
</center>


<center><m>P=\frac{1}{2}\rho A v^3</m></center>
==Benefits and Drawbacks==
Hydroelectric power stations produce significantly fewer [[greenhouse gas]] emissions than other electricity generation options, such as the [[combustion]] of [[fossil fuel]]s.<ref name="feshg">International Hydropower Association (May 30,2020).''GHG Measurement Guidelines for Freshwater Reservoirs'' [Online]. Accessible: https://www.hydropower.org/sites/default/files/publications-docs/GHG%20Measurement%20Guidelines%20for%20Freshwater%20Reservoirs.pdf</ref> The cost of operation once the [[hydroelectric dam|dams]] and [[hydroelectric reservoir|reservoirs]] are built is relatively inexpensive and these facilities can operate at very high [[efficiency|efficiencies]].<ref name="RE1"/> However, the construction of these dams and reservoirs can result in habitat loss for aquatic species and an increase in greenhouse gas emissions due to the decomposition of organic matter in the newly flooded reservoirs.<ref name="feshg"/> For more information on the ecological impacts of hydropower facilities, see: [[water quality degradation]] and [[environmental impacts of hydropower]].


where:
The mechanical energy derived from hydropower is considered [[high-quality energy]] and can be converted to electrical energy with near 100% [[efficiency]]. This is because there are minimal amounts of [[thermal energy]] transformation involved, though there are still minor losses associated with [[friction]] and inefficiencies in the [[electrical transmission|transportation of electricity]] (as a result of factors such as [[resistance]] in transmission lines). Overall, this means energy from water can be converted to electricity and delivered to the end user with efficiencies higher than 90%.<ref>R. Wolfson. ''Energy, Environment and Climate'', 2nd ed. New York, U.S.A.: Norton, 2012</ref>
* <m>P</m> = power in watts (W)
* <m>\rho</m> = density of water in kilograms per cubic meter (k/m<sup>3</sup>)
* <m>A</m> = cross-sectional area of the flow in square meters (m<sup>2</sup>)
* <m>v</m> = velocity of the fluid in meters per second (m/s)


The result of the cubic relationship is that a flow with twice the velocity of a reference will have eight times the kinetic energy. This fact has a large influence on the placement of potential hydroelectric [[generator]]s.
==World Electricity Generation: Hydroelectricity==


== References ==
The map below shows the primary energy sources different countries use to generate their electricity. Hydroelectricity is seen in blue. Click on the region to zoom into a group of countries, then click on the country to see where its electricity comes from. Some notable countries include China, Canada, Brazil, Russia, India, Norway,  and Venezuela.
 
<html><iframe class='charts-iframe' id='world-energy'></iframe></html>
 
==For Further Reading==
*[[Dispatchable source of electricity]]
*[[Electricity storage]]
*[[Turbine]]
*[[Solar power]]
*[[Wind power]]
*Or explore a [[Special:Random|random page]]
 
 
==References==
{{reflist}}[[Category:Uploaded]]
{{reflist}}[[Category:Uploaded]]
[[category: Mark edit]]

Latest revision as of 20:21, 20 December 2021

Figure 1. A hydroelectric dam where hydroelectricity is generated.[1]

Hydropower extracts mechanical energy from water, transforming it into electrical energy to generate electricity. Water in the environment often has both gravitational potential energy and kinetic energy, which can generate electricity using a generator. Note that traditionally this does not refer to the energy obtained from flowing water in the form of tides. In the case of obtaining energy from the tides, the term tidal power is used. The amount of potential energy stored in a body of water at a hydroelectric dam is measured using the height difference between the head race and tail race, known as the elevation head (part of the hydraulic head). Roughly 1/6th of the electricity in the world comes from hydropower facilities, while values in the earlier twentieth century were much higher. In some countries around the world, hydroelectricity is the dominant form of electrical power generation.[2]

Countries such as China, Canada, and Brazil are the leaders in total hydroelectricity generation with capacities of 200 GW, 89 GW, and 70 GW respectively.[3] Other notable producers include Russia, India, Norway, Japan, and Venezuela (which is almost completely dependent on hydropower).[3] See the data visualization below for more statistics on hydroelectricity around the world.

Figure 2. Photograph of a water wheel in Syria in 1916 used here for irrigation purposes.[4]

Generation

Humans have been harnessing energy from water for millennia, although not explicitly for electricity generation. The ancient Greeks used water wheels to grind wheat over 2000 years ago.[5] Hydropower continued to be exclusively converted directly into mechanical power up until the end of the 19th century when electrical dynamos were attached to the shaft to generate electricity.[6] Dynamos were the first type of electrical generator.

Hydroelectricity is generated at a hydroelectric facility which for large-scale generation includes a hydroelectric dam. At these facilities a dam holds back a large volume of water, creating a reservoir. This reservoir holds water at a higher elevation than the water on the downstream side of the dam. Compared to the water in the river, the water in the reservoir has a greater amount of potential energy. When a gate is opened at the top of the dam, the water from the reservoir flows through channels called penstocks down to the turbines. When the water reaches the turbines the potential energy it contains is converted into kinetic energy. This flowing water is then used to turn the blades of the turbine. As the turbines spin, they move a generator and generate electricity.

Although many hydroelectric facilities utilize dams, there are some types of systems that do not use dams and have very little water storage (meaning there is no large reservoir of stored water). These types of systems are known as run-of-the-river systems, and have been gaining popularity as an alternative to large-scale reservoir dams.[7]

Classifications

Conventional hydroelectric generation relies on a hydraulic head difference created by man-made dams and obstructions. The majority of current hydroelectric generation is conventional and is comprised of hydroelectric dams and tidal dams. Unconventional generation techniques generally rely on flow rate or on a small head differential. These unconventional techniques produce less energy than conventional methods, but also have less impact on the surrounding environment.[7] Some examples of unconventional hydropower platforms are low head hydro, run-of-the-river systems, instream hydro, and kinetic tidal.

Each type of hydroelectric generation method has an associated output classification based on its capacity and are outlined in the table below.[8]

Classification Capacity
Large > 100 MW
Medium 15 - 100 MW
Small 1 - 15 MW
Mini 100 kW - 1 MW
Micro 5 - 100 kW
Pico ~ 200 W - 5 kW

Benefits and Drawbacks

Hydroelectric power stations produce significantly fewer greenhouse gas emissions than other electricity generation options, such as the combustion of fossil fuels.[9] The cost of operation once the dams and reservoirs are built is relatively inexpensive and these facilities can operate at very high efficiencies.[3] However, the construction of these dams and reservoirs can result in habitat loss for aquatic species and an increase in greenhouse gas emissions due to the decomposition of organic matter in the newly flooded reservoirs.[9] For more information on the ecological impacts of hydropower facilities, see: water quality degradation and environmental impacts of hydropower.

The mechanical energy derived from hydropower is considered high-quality energy and can be converted to electrical energy with near 100% efficiency. This is because there are minimal amounts of thermal energy transformation involved, though there are still minor losses associated with friction and inefficiencies in the transportation of electricity (as a result of factors such as resistance in transmission lines). Overall, this means energy from water can be converted to electricity and delivered to the end user with efficiencies higher than 90%.[10]

World Electricity Generation: Hydroelectricity

The map below shows the primary energy sources different countries use to generate their electricity. Hydroelectricity is seen in blue. Click on the region to zoom into a group of countries, then click on the country to see where its electricity comes from. Some notable countries include China, Canada, Brazil, Russia, India, Norway, and Venezuela.

For Further Reading


References

  1. ↑ Wikimedia Commons. (August 31, 2015). Ingur Hydroelectric Facility [Online]. Available: https://commons.wikimedia.org/wiki/File:Ingur_Hydroelectric_Power_Station.jpg
  2. ↑ dom (May 23, 2020). "Global Use of Hydroelectricity" [Online]. Available: https://www.e-education.psu.edu/earth104/node/1060
  3. ↑ 3.0 3.1 3.2 Abhishek Shah. (September 2, 2015). List of World’s Largest Hydroelectricity Plants and Countries – China Leading in building Hydroelectric Stations [Online]. Available: http://www.greenworldinvestor.com/2011/03/29/list-of-worlds-largest-hydroelectricity-plants-and-countries-china-leading-in-building-hydroelectric-stations/
  4. ↑ Wikimedia Commons. (May 30, 2020). Popular Science Monthly Vol. 88 [Online]. Available: https://archive.org/details/popularsciencemo88newyuoft/page/82/mode/2up/search/water+wheel
  5. ↑ IEA. (September 2, 2015). What is hydropower’s history? [Online]. Available: http://www.ieahydro.org/What_is_hydropower’s_history.html
  6. ↑ Water Power Program: History of Hydropower. (n.d.). Retrieved from http://www1.eere.energy.gov/water/hydro_history.html
  7. ↑ 7.0 7.1 BC Sustainable Energy Association (May 23rd, 2020) "Small Hydro and Run-Of-River Hydro" [Online]. Available: https://www.bcsea.org/node/4063/bcsea-info
  8. ↑ IPCC. (September 2, 2015). Chapter 5 - Hydropower [Online]. Available: www.ipcc.ch/pdf/special-reports/srren/drafts/SRREN-FOD-Ch05.pdf
  9. ↑ 9.0 9.1 International Hydropower Association (May 30,2020).GHG Measurement Guidelines for Freshwater Reservoirs [Online]. Accessible: https://www.hydropower.org/sites/default/files/publications-docs/GHG%20Measurement%20Guidelines%20for%20Freshwater%20Reservoirs.pdf
  10. ↑ R. Wolfson. Energy, Environment and Climate, 2nd ed. New York, U.S.A.: Norton, 2012
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