Cruachan Reservoir, Argyll

The Cruachan dam holds back the Cruachan Reservoir.

Water is released down to Loch Awe through turbines to generate hydro electricity at times of peak demand.
When surplus electricity is available at night, the surplus is used to force water uphill from Loch Awe to the Cruachan reservoir.
Cruachan can generate up to 440 megawatts for up to 22 hours.

See video of Cruachan Power Station: