And until recently there were many who believed they would never close.

But reality began to hit home in late 2020 when the plants' owner AGL announced the first of Liddell's four 420 megawatt units will shut down in April 2022. The remaining three units are due to be brought offline in 2023.

The company announced in February that the 2640 megawatt Bayswater generator, initially slated to close in 2035, would now cease operating between 2030 and 2033.

The window could be brought forward further depending on the growth of renewable energy in the national grid.

"We are not stubborn. If the market is showing us and if there is sufficient new capacity coming on, then for us it would be an economic decision not to continue (with Bayswater)," AGL chief operating officer Markus Brokhof told the Newcastle Herald following the stock market update.

Mr Brokhof, who is overseeing AGL's transition to net zero emissions, admitted the company had been surprised by the pace of the energy transition, which has at times rendered coal uncompetitive with other supply sources.

Another driving force was shareholders who were demanding companies adopt an environmental, social and governance bottom line principle.

"Maybe in the past transition was nice to have, but now it is a must have," Mr Brokhof said.

"At the end of the day we recognise that society demands we accelerate the transition away from coal.

Software billionaire Mike Cannon-Brookes is also keen to see the company transition to a clean energy future as soon as possible.

Cannon-Brookes and Canada's Brookfield Asset Management last week launched an extraordinary $8 billion bid for the company with plans to close its remaining coal assets by 2030 and spend $20 billion more to replace them with large-scale renewable energy and batteries.

"This is not crazy futuristic technology, this is taking the technologies we have today and deploying them very pragmatically and sensibly at scale to bring that transition here as quickly as we can to bring down prices for power customers, industrial manufacturing all the way down to residential," Mr Cannon-Brookes said earlier this week.

AGL's board has rejected the initial takeover bid saying it "materially undervalued" the business.

AGL chief executive Graeme Hunt added the plan to close the coal-fired power plants earlier risked disrupting the market and would ultimately punish households and businesses with higher energy bills.

The Australian Energy Market Operator (AEMO) has also said the grid would likely lose two-thirds of its coal capacity by 2030, and this could occur without reducing reliability.

Even if Cannon-Brookes and Brookfield ultimately present an offer that is acceptable to shareholders, the deal will need to get Foreign Investment Review Board approval in addition to Australian Competition and Consumer Commission approval.

Liddell celebrated its 50th year of operation in 2021. While the event was seen by many as the end of an era, for Liddell and Bayswater general manager Len McLachlan it also represented new beginnings.

Mr McLachlan said he had seen a significant shift in attitudes regarding the transition away from coal to renewables during his three years in the Upper Hunter.

"When I first got here, you could see that there were still people that just didn't believe it was going to happen," he said.

"When they looked at the market they just couldn't see how it was possible. They would look at how the supply and demand was and what we needed or didn't need and they just didn't see it. Over the last few years as more and more renewables have come on and people are starting to see that impact.

"You can see a shift in the employees to actually starting to go and say, 'actually, you know what, this is going to happen'. They are now focused on what's coming next."

At the same time work is under way to creating the Hunter Energy Park on the 10 hectare Liddell footprint.

The project includes waste to energy and solar thermal pilot projects with the aim of creating one of the world's most versatile renewable energy hubs.

There are also plans to build a 500 megawatt battery on the site.

AGL signed a memorandum of understanding with Fortescue Future Industries in December to conduct a 12-month feasibility study into the production of green hydrogen as part of the Hunter Energy Park. It is estimated the green hydrogen project has the potential to create about 1000 full-time jobs.

"The future is definitely renewable energy. The change we are going through will be bigger than anything we have ever seen; it will be a greater change than the industrial revolution. And we ladies and gentlemen here in the Hunter are at the heart of it," Fortescue chairman Twiggy Forrest told Liddell workers last December.

"I would like to see the Hunter become one of the great pearls if not the great pearl of the renewable energy product and fuel sector of our planet and of our country."

Dr Forrest said green hydrogen had the potential to "dwarf the size of the coal industry".

"The renewable energy future will not be where the biggest oil deposits are or where the biggest gas deposits are or the biggest coal deposits. It will be where the leadership is strongest because it is not renewable energy that is finite, that is infinite, but it is the market which is finite," he said.

Mr Hunt said early estimates indicated the Liddell site had the capacity to support a gigawatt scale hydrogen facility, however, critical inputs including renewable energy costs, firming requirements, electrolyser capital costs, logistics and utilisation would need to be tested over the next 12 months.

Mr Brokhof said the Hunter Energy Park would play a central role in Hunter's transition to a clean energy economy.

"Our large-scale assets like Liddell power station, Loy Yang power station (Victoria) and Torrens Island power station (South Australia) have a very well-defined infrastructure when it comes to road access, railway access and access to water, giving us a competitive advantage when creating energy hubs," he said.

"What is even more important is the grid connection we have at our locations, about 8 gigawatts, which is a valuable asset for the high penetration of renewables.

"We want to create a very efficient ecosystem at our energy hubs, using all value streams from our industrial processes like heat, cooling, CO2 and biomass to form a circular economy.

"All these value streams are unique selling propositions here in Australia, and we have seen other regions like Asia Pacific and Europe successfully use much more of this integrated approach."

AGL is also investigating the viability of a pumped hydro project at a disused coal mine at Bells Mountain and a wind farm at Bowmans Creek.

Between 50 to 60 per cent of employees presently working at Liddell will transfer to Bayswater while the energy hub is developed.

Others will be involved in the decommissioning of Liddell and other power stations.

Mr McLachlan said he was optimistic that a significant number of workers would be involved in the energy hubs.

"I think that once we start getting into some of those new types of plants, even though the amount of employees per plant is less we'll be able to then shift our employees into those. I would expect and I would hope that we would see 20, 30 per cent of our employees actually be able to go and and run those plants and also participate in any other renewable investment that's taking place in the valley and see that continue to grow over the next, you know, 20 years would be fantastic," he said.

Mr Brokhof said the company's future was riding on the success of the company's investment in renewables.

"I think that the transition is really a must. It's not a trend or something like that. We have to, as a prudent operator and also protecting a shareholder value, we have to move into this direction and we have to make it a success," he said.

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