Editing Water turbine (section)

=== Pumped-storage hydroelectricity ===
Some water turbines are designed for pumped-storage hydroelectricity. They can reverse flow and operate as a [[pump]]<ref name="Roman helix-turbine mill" /> to fill a high reservoir during off-peak electrical hours, and then revert to a water turbine for power generation during peak electrical demand. This type of turbine is usually a [[Deriaz turbine|Deriaz]] or [[Francis turbine]] in design.

This type of system is used in El Hierro, one of the Canary Islands: "When wind production exceeds demand, excess energy will pump water from a lower reservoir at the bottom of a volcanic cone to an upper reservoir at the top of the volcano 700 meters above sea level. The lower reservoir stores 150,000 cubic meters of water. The stored water acts as a battery. The maximum storage capacity is 270 MWh. When demand rises and there is not enough wind power, the water will be released to four hydroelectric turbines with a total capacity of 11 MW."<ref>{{cite web|url=https://www.greenbiz.com/blog/2014/03/03/how-small-spanish-island-became-renewable-energy-pioneer-el-hierro|title=How a small Spanish island became a renewable energy pioneer|first=Laurie|last=Guevara-Stone|date=3 March 2014|website=greenbiz.com|access-date=4 May 2017|archive-date=3 October 2017|archive-url=https://web.archive.org/web/20171003032051/https://www.greenbiz.com/blog/2014/03/03/how-small-spanish-island-became-renewable-energy-pioneer-el-hierro|url-status=dead}}</ref><ref>{{cite web|url=http://euanmearns.com/an-independent-evaluation-of-the-el-hierro-wind-pumped-hydro-system/|title=An Independent Evaluation of the El Hierro Wind & Pumped Hydro System|first=Benjamin|last=Jargstorf|date=23 February 2017|website=euanmearns.com/}}</ref>