Editing Pumped-storage hydroelectricity (section)

== Potential technologies ==

===Seawater===
Pumped storage plants can operate with seawater, although there are additional challenges compared to using fresh water, such as saltwater corrosion and barnacle growth.<ref>{{cite Q|Q107212803}}</ref> Inaugurated in 1966, the 240&nbsp;MW [[Rance Tidal Power Station|Rance tidal power station]] in France can partially work as a pumped-storage station. When high tides occur at off-peak hours, the turbines can be used to pump more seawater into the reservoir than the high tide would have naturally brought in. It is the only large-scale power plant of its kind.

In 1999, the 30&nbsp;MW [[Okinawa Yanbaru Seawater Pumped Storage Power Station|Yanbaru project]] in Okinawa was the first demonstration of seawater pumped storage. It has since been decommissioned. A 300&nbsp;MW seawater-based Lanai Pumped Storage Project was considered for Lanai, Hawaii, and seawater-based projects have been proposed in Ireland.<ref>{{Cite web |date=18 February 2012 |title=Massive Energy Storage, Courtesy of West Ireland |url=https://www.science.org/content/article/massive-energy-storage-courtesy-west-ireland |url-status=live |archive-url=https://web.archive.org/web/20170908034315/http://www.sciencemag.org/news/2012/02/massive-energy-storage-courtesy-west-ireland |archive-date=8 September 2017 |access-date=21 June 2017 |website=sciencemag.org}}</ref> A pair of proposed projects in the [[Atacama Desert]] in northern Chile would use 600&nbsp;MW of photovoltaic solar (Skies of Tarapacá) together with 300&nbsp;MW of pumped storage (Mirror of Tarapacá) lifting seawater {{convert|600|m}} up a coastal cliff.<ref>{{Cite web |date=11 March 2015 |title=Project Espejo de Tarapacá |url=http://valhalla.cl/espejo-de-tarapaca/ |url-status=live |archive-url=https://web.archive.org/web/20170618160703/http://valhalla.cl/espejo-de-tarapaca/ |archive-date=18 June 2017 |access-date=19 June 2017 |website=Valhalla}}</ref><ref>{{Cite web |date=4 May 2016 |title=The Mirror of Tarapaca: Chilean power project harnesses both sun and sea |url=https://www.power-technology.com/features/featurethe-mirror-of-tarapaca-chilean-power-project-harnesses-both-sun-and-sea-4872272/ |url-status=live |archive-url=https://web.archive.org/web/20190504012539/https://www.power-technology.com/features/featurethe-mirror-of-tarapaca-chilean-power-project-harnesses-both-sun-and-sea-4872272/ |archive-date=4 May 2019 |access-date=4 May 2019}}</ref>

===Freshwater coastal reservoirs===
Freshwater from the river floods is stored in the sea area replacing seawater by constructing [[coastal reservoir]]s. The stored river water is pumped to uplands by constructing a series of embankment canals and pumped storage hydroelectric stations for the purpose of energy storage, irrigation, industrial, municipal, rejuvenation of overexploited rivers, etc. These multipurpose coastal reservoir projects offer massive pumped-storage hydroelectric potential to utilize variable and intermittent solar and wind power that are carbon-neutral, clean, and renewable energy sources.<ref>{{Cite journal |last=Sasidhar |first=Nallapaneni |date=May 2023 |title=Multipurpose Freshwater Coastal Reservoirs and Their Role in Mitigating Climate Change |url=https://www.ijee.latticescipub.com/wp-content/uploads/papers/v3i1/A1842053123.pdf |access-date=2023-05-23 |journal=Indian Journal of Environment Engineering |issn=2582-9289 |volume=3 |issue=1|pages=30–45 |doi=10.54105/ijee.A1842.053123 |s2cid=258753397 }}</ref>

===Underground reservoirs===
The use of underground reservoirs has been investigated.<ref>{{Cite book |last=Pummer |first=Elena |url=http://publications.rwth-aachen.de/record/667419/files/667419.pdf |title=Hybrid Modelling of the Hydrodynamic Processes in Underground Pumped Storage Plants |publisher=RWTH Aachen University |year=2016 |location=Aachen, Germany |access-date=19 May 2020 |archive-url=https://web.archive.org/web/20201104044602/http://publications.rwth-aachen.de/record/667419/files/667419.pdf |archive-date=4 November 2020 |url-status=live}}</ref> Recent examples include the proposed Summit project in [[Norton, Ohio]], the proposed Maysville project in [[Kentucky]] (underground limestone mine), and the Mount Hope project in [[New Jersey]], which was to have used a former iron mine as the lower reservoir. The proposed energy storage at the [[Callio]] site in [[Pyhäjärvi]] ([[Finland]]) would utilize the deepest base metal mine in Europe, with {{Convert|1450|m|ft}} elevation difference.<ref>{{Cite news |title=Energy storage |language=en-US |work=Callio Pyhäjärvi |url=https://callio.info/energy-storage/opportunities/ |url-status=live |access-date=2018-03-14 |archive-url=https://web.archive.org/web/20180315050701/https://callio.info/energy-storage/opportunities/ |archive-date=15 March 2018}}</ref> Several new underground pumped storage projects have been proposed. Cost-per-kilowatt estimates for these projects can be lower than for surface projects if they use existing underground mine space. There are limited opportunities involving suitable underground space, but the number of underground pumped storage opportunities may increase if abandoned coal mines prove suitable.<ref>{{Cite web |date=17 March 2017 |title=German Coal Mine to Be Reborn as Giant Pumped Storage Hydro Facility |url=http://www.renewableenergyworld.com/articles/2017/03/german-coal-mine-to-be-reborn-as-giant-pumped-storage-hydro-facility.html |url-status=live |archive-url=https://web.archive.org/web/20190709081435/https://www.renewableenergyworld.com/articles/2017/03/german-coal-mine-to-be-reborn-as-giant-pumped-storage-hydro-facility.html |archive-date=9 July 2019 |access-date=20 March 2017}}</ref>

In [[Bendigo]], Victoria, Australia, the Bendigo Sustainability Group has proposed the use of the old gold mines under Bendigo for Pumped Hydro Energy Storage.<ref>{{Cite web |last=Smith |first=Trevor |title=Bendigo Mines Pumped Hydro Project |url=https://www.bsg.org.au/bendigo-pumped-hydro-project/ |url-status=live |archive-url=https://web.archive.org/web/20180715235943/https://www.bsg.org.au/bendigo-pumped-hydro-project/ |archive-date=15 July 2018 |access-date=2020-07-13 |website=Bendigo Sustainability Group |language=en-AU}}</ref>  Bendigo has the greatest concentration of deep shaft hard rock mines anywhere in the world with over 5,000 shafts sunk under Bendigo in the second half of the 19th Century.  The deepest shaft extends 1,406 metres vertically underground.  A recent pre-feasibility study has shown the concept to be viable with a generation capacity of 30&nbsp;MW and a run time of 6 hours using a water head of over 750 metres.

US-based start-up Quidnet Energy is exploring using abandoned oil and gas wells for pumped storage. If successful they hope to scale up, utilizing some of the 3 million abandoned wells in the US.<ref>{{Cite news |last=Lo |first=Chris |date=27 November 2016 |title=Could depleted oil wells be the next step in energy storage? |url=https://www.power-technology.com/analysis/featurecould-depleted-oil-wells-be-the-next-step-in-energy-storage-5680002/ |access-date=16 May 2022}}</ref><ref>{{Cite web |title=Press Release: CPS Energy & Quidnet Energy Announce Landmark Agreement to Build Grid-Scale, Long Duration, Geomechanical Pumped Storage Project in Texas |url=https://www.quidnetenergy.com/news/2022/03/cps-energy--quidnet-energy-announce-landmark-agreement-to-build-gridscale-long-duration-geomechanical-pumped-storage-project-in-texas/ |access-date=16 May 2022 |website=quidnetenergy.com}}</ref>

Using [[hydraulic fracturing]] pressure can be stored underground in [[Permeability (Earth sciences)|impermeable]] strata such as shale.<ref>{{cite journal|title= Is Hydraulic Fracturing the Next Big Breakthrough in Battery Tech?|journal= [[Society of Petroleum Engineers#Magazines|Journal of Petroleum Technology]]|publisher= [[Society of Petroleum Engineers]]|volume= 75|number =10|date =October 2023|pages= 36–41|last= Jacobs|first= Trent}}</ref> The shale used contains no hydrocarbons.<ref name="TM91221">{{Cite news |last=Russell Gold |date=September 21, 2021 |title=Fracking Has a Bad Rep, but Its Tech Is Powering a Clean Energy Shift Texas start-ups are harnessing know-how born of the shale boom in pursuit of a greener future. |work=Texas Monthly |url=https://www.texasmonthly.com/news-politics/fracking-clean-energy-geothermal/ |url-status=live |access-date=September 23, 2021 |archive-url=https://web.archive.org/web/20210924171206/https://www.texasmonthly.com/news-politics/fracking-clean-energy-geothermal/ |archive-date=24 September 2021}}</ref>

===Decentralised systems===
Small (or micro) applications for pumped storage could be built on streams and within infrastructures, such as drinking water networks<ref>{{Cite web |title=Senator Wash |url=http://www.iid.com/water/water-transportation-system/colorado-river-facilities/senator-wash |url-status=live |archive-url=https://web.archive.org/web/20160626043856/http://www.iid.com/water/water-transportation-system/colorado-river-facilities/senator-wash |archive-date=26 June 2016 |access-date=6 August 2016 |website=www.iid.com |publisher=Imperial Irrigation District |language=en}}</ref> and artificial snow-making infrastructures. In this regard, a storm-water basin has been concretely implemented as a cost-effective solution for a water reservoir in a micro-pumped hydro energy storage.<ref name=":1a" /> Such plants provide distributed [[energy storage]] and distributed flexible [[electricity production]] and can contribute to the decentralized integration of [[intermittent renewable energy]] technologies, such as [[wind power]] and [[solar power]]. Reservoirs that can be used for small pumped-storage hydropower plants could include<ref name="Thesis">{{Cite thesis |last=Crettenand |first=N. |url=https://infoscience.epfl.ch/record/176337?ln=en |title=The facilitation of mini and small hydropower in Switzerland: shaping the institutional framework. With a particular focus on storage and pumped-storage schemes |publisher=Ecole Polytechnique Fédérale de Lausanne |year=2012 |doi=10.5075/epfl-thesis-5356 |archive-url=https://web.archive.org/web/20180913040049/https://infoscience.epfl.ch/record/176337?ln=en |archive-date=13 September 2018 |type=PhD Thesis N° 5356.}}</ref> natural or artificial lakes, reservoirs within other structures such as irrigation, or unused portions of mines or underground military installations. In [[Switzerland]] one study suggested that the total installed capacity of small pumped-storage hydropower plants in 2011 could be increased by 3 to 9 times by providing adequate [[Market-based environmental policy instruments|policy instruments]].<ref name="Thesis" />

Using a pumped-storage system of [[cistern]]s and small generators, [[pico hydro]] may also be effective for "closed loop" home energy generation systems.<ref name="sciencedaily">{{Cite web |date=2016-10-24 |title=Is energy storage via pumped hydro systems is possible on a very small scale? |url=https://www.sciencedaily.com/releases/2016/10/161024090454.htm |archive-url=https://web.archive.org/web/20170510054924/https://www.sciencedaily.com/releases/2016/10/161024090454.htm |archive-date=2017-05-10 |access-date=6 September 2018 |website=Science Daily}}</ref><ref name="homepower">{{Cite news |last=Root |first=Ben |date=December 2011 – January 2012 |title=Microhydro Myths & Misconceptions |volume=146 |page=77 |publisher=Home Power |url=https://www.homepower.com/articles/microhydro-power/design-installation/microhydro-myths-misconceptions |access-date=6 September 2018 |archive-url=https://web.archive.org/web/20180905214822/https://www.homepower.com/articles/microhydro-power/design-installation/microhydro-myths-misconceptions |archive-date=5 September 2018}}</ref>
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===Underwater reservoirs===
{{Further|Stored Energy at Sea}}
In March 2017, the research project StEnSea (Storing Energy at Sea) announced their successful completion of a four-week test of a pumped storage underwater reservoir. In this configuration, a hollow sphere submerged and anchored at great depth acts as the lower reservoir, while the upper reservoir is the enclosing body of water. Electricity is created when water is let in via a reversible turbine integrated into the sphere. During off-peak hours, the turbine changes direction and pumps the water out again, using "surplus" electricity from the grid.

The quantity of power created when water is let in, grows proportionally to the height of the column of water above the sphere. In other words: the deeper the sphere is located, the more densely it can store energy.
As such, the energy storage capacity of the submerged reservoir is not governed by the [[gravitational energy]] in the traditional sense, but by the [[vertical pressure variation]].

===High-density pumped hydro===
RheEnergise<ref name="RheEnergise">[https://www.rheenergise.com/ RheEnergise company website]</ref> aim to improve the efficiency of pumped storage by using fluid 2.5x denser than water ("a fine-milled suspended solid in water"<ref name="IoME article">[https://www.imeche.org/news/news-article/high-density-pumped-hydro-could-be-installed-on-thousands-of-small-hills] Institution of Mechanical Engineers article</ref>), such that "projects can be 2.5x smaller for the same power."<ref name="RheEnergise_how_it_works">[https://www.rheenergise.com/how-it-works] RheEnergise 'how it works' article</ref>