Pipes leading to a hydroelectric power station at the Alcan aluminium works, Fort William, Scotland. These pipes take water from Loch Laggan and Loch Treig, some 20km distant. The electricity demand of the aluminium plant is extremely high, as aluminium is obtained by an electrolytic process. It is thus cheaper to use mostly in-house" electricity, taking power from the national grid only at very cheap off-peak times."