Pumped-storage hydro-electric

Hydroelectricity relies on gravity to propel water through power-generating turbines. The difference in height between the turbine and the water source is known as the "head". Scotland has two pumped-storage hydro-electric power stations, which pump water back up to a storage reservoir during periods of off-peak demand. Although claimed to be the first such station in the world when it opened in 1965 by the Visit Cruachan website, Drax Group PLC's Cruachan Power Station^[15] was preceded by the Ffestiniog Power Station in North Wales, which opened in 1963,^[16] and on a smaller scale by the North of Scotland Hydro-Electric Board's Sron Mor power station opened in 1957, part of the Shira Hydro-Electric Scheme.^[17] Cruachan can hold 7 gigawatt-hours (25 TJ) of energy,^[18] equivalent to 22 hours of full production. 12 hours is reserved for black start.^[19]

There are several proposals for new pumped storage hydro-electric schemes in Scotland, mostly in the Great Glen;

• A 300–600 MW scheme was proposed by SSE at Balmacaan north of Invermoriston using Loch Ness as the lower reservoir.^[24] Progress on this scheme seems to have stalled, in January 2024 it is no longer listed on the SSE website.
• The 600 MW Coire Glas scheme is being developed by SSE above the northwestern shores of Loch Lochy.^{[25][26][27][28]} The scheme was given planning permission in October 2020 and exploratory geotechnical work had started by December 2022.^[29]
• The 450 MW Red John Pumped Storage Hydro Scheme to the southeast of Dores.^[30][31] It would involve a new upper reservoir constructed near Loch Duntelchaig. The scheme was developed by Intelligent Land Investments Group and acquired by Statkraft at the end of 2023.^[32]
• An up-to 600 MW Loch Kemp Storage scheme, southwest of Loch Ness near Whitebridge.^[33] A planing application was submitted in November 2023. If built, the water level in Loch Kemp could fluctuate by up to 28 m. The Ness District Salmon Fisheries Board have raised concerns about the cumulative impact of these schemes on water levels in Loch Ness, and the effect this might have on Salmon.^[34]
• The 900–1800 MW Earba Storage is being developed by Gilkes Energy in the Ardverikie Estate to the southwest of Loch Laggan.^[35][36] It would use Lochan na h-Earba and Loch a’ Bhealaich Leamhain as the lower and upper reservoirs, both with new dams required. An application for consent under Section 36 of the Electricity Act was submitted in March 2024, supported by an environmental impact assessment.^[37]

Scotland has a potential for around 500 GWh of pumped storage.^[38]

Conventional hydro-electric

Several of Scotland's hydro-electric plants were built to power the aluminium smelting industry, but many more were built in the mid-20th century by the North of Scotland Hydro-Electric Board to supply the communities of the Highlands. These were built in several "schemes" of linked stations, each covering a catchment area, whereby the same water may generate power several times as it descends.

Onshore

Offshore