Czech billionaire Pavel Tykac poised to buy Delta Electricity, Vales point power station, Chain Valley coalmine from Trevor St Baker, Brian Flannery

Delta announced on Sunday that the international investment arm of Mr Tykac's Sev.en Energy would buy a 100 per cent stake in the firm from shareholders Trevor St Baker and Brian Flannery.

The sale is subject to government approvals.

"It is expected that, subject to these approvals, the transaction will complete in the coming weeks," Delta said.

Sev.en already has a 50 per cent stake in United Kingdom-based InterGen, which owns the Callide and Millmerran coal-fired power stations in Queensland and four gas-fired plants in the UK.

Sev.en owns four coal-fired plants and two brown coal mines in the Czech Republic and a 100 per cent stake in US coalmining firm Blackhawk.

Mr St Baker flagged at the start of the year that Vales Point, which supplies about 11 per cent of the state's electricity, could stay open up to 20 years beyond its scheduled closure in 2029.

He and Mr Flannery bought Vales Point from the NSW government in 2015 for $1 million.

They did not reveal on Sunday the price of the sale to Sev.en, but late last year they downgraded the plant's value to $156 million, after pricing it at $732 million four years earlier.

Community and green groups have criticised plans to keep Vales Point open beyond 2029, arguing it contributes to air and water pollution and climate change.

The NSW Environment Protection Authority is investigating whether the plant contributed to the deaths of an estimated 15,000 fish in the lake in two incidents in the past six weeks.

Under the terms of the controversial 2015 sale, taxpayers are liable for the cost of remediating any pollution at Vales Point, including an estimated 60 million tonnes of coal ash, that occurred before Delta took over.

Sev.en chief executive Alan Svoboda said the firm made "strategic investments with long-term commitment".

"We always look for ways to make our business more sustainable, support local communities and take care of the employees," he said.

Lake Macquarie and Central Coast Coal-Ash Community Alliance spokesperson Kim Grierson said Sev.en appeared be expanding its footprint in fossil fuels.

"All their interests seem to be very much focused on gas and coal around the world, which is alarming to me as a local resident because I don't see them as someone who's thinking on planning a transition," she said.

She said any change in ownership of Delta must be subject to the "most stringent requirements".

"The indemnities that were given to Delta by the state government, do they flow then to the new shareholder, and what securities do we get from the new owner?

"The community is very clear in its demand that all ash dams need to be emptied. Plans to this effect need to be developed as a matter of utmost urgency between power station owners and the state government as the former owner and operator, and the necessary funding needs to be made available."

The alliance promotes using the power station ash to manufacture products.

"The old practice of just covering up ash dams with some earth fill and vegetation is no longer an acceptable option for the community," Ms Grierson said.

"Any power station owner, no matter how far away they may live, needs to be made aware of this community demand."

Mr St Baker said Delta "continues to have a firm view that around the clock dispatchable generation will be necessary for the National Energy Market well into the future".

"[We] recognise that there are opportunities to grow the business and that this can be better accomplished in a portfolio with Sev.en's other base-load capable generation interests," he said.

Swansea MP and Shadow Minister for the Hunter Yasmin Catley said she had asked Energy Minister Matt Kean to detail how the government would scrutinise Delta's proposed new owner.

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