 Water is pumped from Loch Awe to the upper reservoir , 396 metres ( 1 @,@ 299 ft ) above , during periods of low energy use ( such as at night ) , and then released during the day . The upper reservoir also receives rainwater , supplemented by a network of 19 kilometres ( 12 mi ) of tunnels . Around 10 % of the energy from the station is generated from rainwater ; the rest is from the water pumped up from Loch Awe . 
