Australia's largest individual consumer of electricity says it needs 24/7 guaranteed power to keep its aluminum smelter running amid fears early shutdowns of coal-fired plants could exacerbate the impact of a renewable energy shortage/.

Tomago Aluminum CEO Matt Howell is asking Origin and AGL for more details on their plans to> address power shortages caused by the upcoming closures of the Eraring and Liddell coal-fired power plants.

After AGL turned down an initial $8 billion takeover bid by Canada's Brookfield and billionaire Mike Cannon-Brooks this week, and Origin announced the early closure of the country's largest coal-fired power plant, Mr Howell said Tomago commits to "translate our electricity needs to a portfolio of sustainable renewable sources no later than the end of 2028".

"We recognize the significant changes already taking place in the national electricity market and will continue to play our part in keeping the system safe with our extensive and fast intermittent load," he said.

"As the largest consumer of electricity in Australia, it is critical that adequate electricity generation and storage is available continuously and especially during long periods of renewable energy downtime (low or no wind at night)."