Scotland also has an increasing number of wind farms, due to the large proportion of upland areas.
Scotland has two pumped-storage hydro-electric power stations, which pump water back up to a storage reservoir during periods of off-peak demand.
[17] Cruachan can hold 7 gigawatt-hours (25 TJ) of energy,[18] equivalent to 22 hours of full production.
[41] 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.