Tir John Power Station, near Swansea, was a 'super' coal-fired power station built 1931-5. It produced electricity for the newly-created National Grid, a system of transmission cables developed by the Central Electricity Board to distribute electricity nationally from privately-run power stations. Built by Swansea Corporation as part of an unemployment relief scheme, Tir John was the largest engineering project in Wales at the time and the largest power station in Britain. It was in operation from 1936 to 1976, originally burning low-cost anthracite duff (waste from the washing of mined coal at the colliery), and had a potential output of 155 megawatts. Around 6 million gallons of sea water per hour were drawn from the nearby King's Dock (nprn 419502) for cooling and returned to the larger Queen's Dock (nprn 410503). The water was carried in two large concrete-lined tunnels, each about 3m in across and about 1km long, cut through solid rock at depths of up to 90m. Tir John became part of the British Electricity Authority, later Central Electricity Generating Board, when the electricity industry was nationalised in 1948. Taking advantage of the huge Llandarcy oil refinery (nprn 91695) nearby, the power station was converted to run on oil in 1967 but rising oil prices in the 1970s led to its closure just nine years later.
Sources include: 'Early digital data processing from 1953', Noel Cox, May 2008.

RCAHMW, 25 October 2013.