For more than half a century, Liddell Power Station in the NSW Hunter Valley has burnt coal to power homes and industries.
Today, AGL is shutting down the first of four turbines, signalling the beginning of the end for the ageing plant.
Today's switch-off has been a long time coming after AGL announced the retirement of Liddell in 2015.
The remaining units will operate for another year until Liddell's full closure in April 2023.
AGL chief operating officer Markus Brokhof says the closure of Unit 3 is a significant moment in AGL's energy transition.
"We announced the retirement of Liddell in 2015," Mr Brokhof said.
"And seven years later, we are pleased to be in a position to begin the orderly and responsible closure and transition of the power station in line with our climate commitments."
AGL says today's unit closure will deliver a reduction in greenhouse gas emissions equivalent to taking about 400,000 cars off the road.
"That is quite a sizeable reduction of emissions," he said.
Liddell opened in 1971 and at one point was the most powerful generating station in Australia.
Beyond April 2023, Liddell is ground zero for the Hunter Energy Hub site that will house a grid-scale battery, solar thermal storage, wind, hydrogen and pumped hydro.
Mr Brokhof said planning was well underway to ensure there would be no power shortage as a result of Liddell's closure.
"We made this announcement early enough and we believe there will be no issue with Liddell's retiring from service," he said.
"It will be a staggered approach."
Green groups have welcomed the first phase of Liddell's shutdown.
Brad Smith of the Nature Conservation Council NSW said retiring the Liddell plant would help improve air quality for residents of the Upper Hunter.
"There is still a long way to go, but this is a good start."
AGL has announced windows for the closure of its remaining coal-fired power stations with Liddell neighbour Bayswater to shut between 2030-33 and Loy Yang A in Victoria between 2040-45.
