Here's our easy-to-understand guide to the Cruachan power plant

1 - When generation is required, the valves are opened to allow a rush of water to drive the turbine

2 - Each of the station's four generator motors receives water from the upper reservoir

3 - After the water passes through the turbines, generating electricity, it flows into a surge chamber then into Loch Awe along a tailrace tunnel that is 22ft in diameter and 3198ft long

4 - Its reversible turbines use cheap electricity during the night to pump water from Loch Awe to its upper reservoir, in readiness for charging the turbines to meet peak demand the following day. This water is essentially stored electricity that can be released at any time

A - Cruachan reservoir 1299ft above Loch Awe storing 26,417 gallons of water

B - One of two concrete lined shafts, known as a Penstock

C - Full pumping speed can be achieved in eight minutes, each generating set absorbing between 110 MW and 120 MW from the grid to pump water from Loch Awe to the reservoir. There are four generators each the size of a football pitch

D - Shaft to generator

E - Water inlet

F - Water flow

G - Downstream outlet into Loch Awe

H - Wind power can be used to provide power for reverse pumping back to the reservoir