night-time nuclear generated electrical energy. The power station was originally operated by the North of Scotland Hydro-Electric Board, before being transferred to the South of Scotland Electricity Board. It was owned by Scottish Power from the privatisation of Britain's electricity industry in 1990 until Drax Group purchased it along with other Scottish Power assets on 1 January 2019. Maintenance of the penstocks, which formerly required them to be drained, is now done using a remotely operated underwater vehicle. To commemorate the 50th anniversary of the station's opening, a 2015 BBC radio documentary "Inside the Rock" covered the history of construction. In June 2021, Drax applied to build a further 600 MW pumped storage capacity using the same reservoir, to a combined 1 GW for 7 hours of storage. Several financing modes are possible. Design The Cruachan station temporarily stores energy at times of low demand, and releases it at times of high demand, when electricity prices are higher, reducing the maximum power that must be provided by power stations. It is also used to cope with sudden surges in the demand for electricity, such as at the end of television programmes. Despite the use of some rainwater, Cruachan is not a net generator of electricity: it uses more energy for pumping water and spinning its turbines than it generates. Water is pumped from Loch Awe to the upper reservoir, 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 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. The station is capable of generating of electricity from four turbines, two of and two of capacity, after two units were upgraded in 2005. It can go from standby to full production in two minutes, or thirty seconds if compressed air is used to start the turbines spinning. When the top reservoir is full, Cruachan can operate for 22 hours before the supply of water is exhausted. At full power, the turbines can pump at per second and generate at per second. The power station is required to keep a 12-hour emergency water supply in order to provide a black start capability to the National Grid, to enable utilities to be restarted without access to external power. It