The power station was sold to the Electricity Supply Commission (Escom) in January 1927. It used coal that was brought in by rail from the coalfields of North Natal and water from the Tugela. It continued to be the provider of electrical power for the railways which by 1937 consisted of the whole of the Natal section of the Durban – Johannesburg line (516 route km) and the spur to Bethlehem in the Orange Free State. Between 1944 and 1959 a series of new generators were commissioned resulting in the power station's capacity being increased to 160 MW. However, in the 1960s, changes in technology led to a change in the economics of power production. New power stations such as Ingagane were built at the coal fields themselves and the use of 400 kV power lines from 1972 onwards reduced the cost of transporting electricity. In the early 1980s Eskom initiated a massive development program: in 1980 new large power stations at Kriel (3,000 MW), Hendrina (2,000 MW) and Camden (1,600 MW) had been commissioned and in the next few years a number of other new power stations gave South Africa a surplus of generating capacity and many of the 1960s vintage power stations (including Colenso's refurbishment) had become uneconomic. This meant that the continued use of the Colenso power station was no longer economically viable. The original part of the power station was decommissioned in 1970 and the 1944-1959 extensions in 1985.