Fifty years ago, Ben Cru­achan in Argyll and Bute was the equiv­a­lent of London’s Sil­i­con round­about – a place of tech­no­log­i­cal inno­va­tion on which an entire nation was pin­ning its hopes for the future. The mad­cap idea was to turn a rugged peak in the Scot­tish high­lands into a geo­log­i­cal bat­tery: using excess ener­gy in the nation­al grid, water would be pumped from Loch Awe at the bot­tom of the moun­tain into a reser­voir at the top.