Delta Electricity could extend the closure of Vales Point Power Station from 2029 to 2033, amid concerns about delays with renewable energy projects and the "early closure" of other coal-fired plants.
The company said it had advised the Australian Energy Market Operator (AEMO) of "a 2033 technical life assessment" for the power plant on the southern shore of Lake Macquarie.
Delta's interim chief executive David Morris said Vales Point "continues to provide high levels of availability to the system and is expected to continue to do so through to 2033".
Nature Conservation Council of NSW CEO Jacqui Mumford said a 2033 closure for Vales Point would "make it almost impossible for NSW to reach its emission reduction targets".
"If this extension goes ahead, Vales Point would therefore account for 70 per cent of NSW's electricity emissions," Ms Mumford said.
Greens MP and spokesperson for climate change Sue Higginson said extending Vales Point would be "reckless, dangerous and foul play".
"Have we forgotten the climate induced fires and floods? We are in a climate emergency, young people are suffering from climate anxiety and many across the country are doing all that they can to ensure we have a liveable planet in the years ahead," she said.
Delta said the purpose of the plant's assessment was to examine the condition of "the existing generation equipment, ash dam capacity and general condition of the facility".
The previous closure date had been set for 2029, based on "a nominal 50-year asset life".
A Delta statement noted the "delays being experienced by new generation and transmission projects, along with earlier closure dates being announced by owners of other coal-fired generators".
"Given the uncertainties surrounding the capacity of electricity resources over the next 10 years and the urgent need to maintain system security throughout this period, Delta considers it a responsible step to advise AEMO of the availability of Vales Point Power Station's capacity."
Ms Mumford said it was "incredibly disappointing that the community hasn't even been asked if they want such an extension".
Billionaires Trevor St Baker and Brian Flannery sold the Vales Point plant in December last year to Sev.en Energy, a company owned by Czech billionaire Pavel Tykac.
"We know that Sev.en has been lobbying the government to extend the life of this plant since they acquired it earlier this year," Ms Mumford said.
"And why wouldn't they - the exemptions granted to this power plant are a bonanza for a company willing to profit from causing serious harm to our climate and human health."
Ms Mumford urged the NSW government to "rule out any support to keep Vales Point operating longer than 2029".
"In an era of increasing climate catastrophe, we cannot allow such reckless disregard for our future."
Delta's statement said its announcement "does not denote a commercial commitment to operate the facility".
"The energy system is in transformation, and this brings higher levels of uncertainty when forecasting market conditions for the longer term," Mr Morris said.
Delta said the Vales Point plant "continues to be a key asset in the transitioning energy market".
It provided "essential firming capacity" to support the "growing integration of renewable energy" and ensured "a reliable and secure source of electricity".
"Currently the Vales Point Power Station generates approximately 10 per cent of NSW electricity needs," the company said.
Ms Higginson said there was also speculation about Eraring Power Station remaining open beyond 2025.
"If we let Eraring and Vales Point coal fired power stations continue beyond their planned closures, we lose hope of reducing our emissions and meeting our net zero targets. We need to make big, bold changes and we need to make them now," she said.
The Newcastle Herald reported on Wednesday that the federal government had declared the nation's second offshore wind zone off the Hunter coast.
Power-generating wind turbines will cover 1800 square kilometres from Port Stephens to Swansea, 1000 square kilometres smaller than the zone proposed in February.
The declared area will start 20 kilometres from the coast at Port Stephens, about 9km further offshore than first proposed, and more than 35km from the coast at Swansea.
The Hunter Community Environment Centre released a report in May, titled Delta's Dirty Deeds Done Dirt Cheap.
The report said Vales Point was responsible for the loss and degradation of vast areas of seagrass and marine life, but Delta dismissed it as misleading.
