A reversible pumped storage hydroelectric power plant works like an enormous rechargeable battery. Its reversible turbines use cheap electricity during the night to pump water to an upper reservoir, in readiness for charging the turbines to meet peak demand the following day.
There are nearly 300 pumped storage projects in the world, and 40 in the United States.
The first use of pumped-storage in the United States was in 1930 by the Connecticut Electric and Power Company, using the 11 mi (17.7 km) long Candlewood Lake, a large reservoir located near New Milford, Connecticut, pumping water from the Housatonic River to the storage reservoir 230 ft. (70 m) above.
Its Chief Engineer, Paul Heslop described his design “The statement that a hydro-electric plant can pump its own water supply sounds absurd on the face of it, yet this is virtually what happens in the case of our the Rocky River Hydro Plant. ” The technology pioneered at the Rocky River project using reversible pumps that also act as generators was not widely used in other U.S. projects until the 1950s and 1960s.
Another RPSS, the Cruachan Power Station, located in Argyll and Bute, Scotland which takes water between Cruachan Reservoir to Loch Awe, a height difference of 1,299 ft (396 m.) has a capacity of 7.1 GWh. It was the brainchild of Sir Edward McColl, a Dumbarton-born engineer and pioneer of hydro power while the civil engineering design of the scheme was carried out by James Williamson & Partners of Glasgow, and the main project contractors were William Tawse of Aberdeen and Edmund Nuttall of Camberley. Consulting electrical engineers were Merz & McLellan of Newcastle on Tyne.
Construction began in 1959 to coincide with the Hunterston A nuclear power station in Ayrshire. Many working models of the turbines were built and work tests were carried out on completed alternators before being delivered to the site. At the peak of the construction, there were around 4,000 people working on the project. It was opened Queen Elizabeth II on 15 October 1965 and is still in service.
Over in the USA, the Bath County Pumped Storage Station was built for the Virginia Electric and Power Company (VEPCO) between March 1977 and December 1985 The station consists of two reservoirs separated by about 1,260 ft. (380 m) in elevation. It is the largest pumped-storage power station in the world with a maximum generation capacity of 3,003 MW, when all six generators are operating at full power. National Public Radio called the station “The World’s Biggest Battery.”
Pumped hydroelectric storage (PHS) is by far the largest and most cost-effective form of energy storage today. In 2009, world pumped storage generating capacity was 104 GW, while other sources claim 127 GW, which comprises the vast majority of all types of utility grade electric storage. While the facility in Bath County is the largest now, a 4,000 MW project at Lake Revelstoke in British Columbia has been proposed.
In 2017 the largest pumped storage in Europe was the Cortes-La Muela hydroelectric project in Spain, rated at 1,762MW.
The largest in China was the Cuntangkou Pumped Hydro Power Station in Sichuan, rated at 2,000MW. The Snowy Hydro 2.0 pumped storage project in Australia completed a feasibility study in 2017 that proposed to expand the existing network of hydropower dams to provide up to 6,000 MW of generating capacity. It would become the world’s largest hydropower scheme with pumped storage. It has yet to be built.
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