Eirgrid has confirmed that the Huntstown power station in Dublin is back in operation this weekend feeding electricity into the national grid.
The move comes in the wake of warnings from the Commission for the Regulation of Utilities that there were challenges to the security of energy supply.
The gas-fired power plant has been out of commission for some time, along with Whitegate in Cork.
Huntstown has a capacity of 400 megawatts (MW).
Peak national demand is 5,000MW, so the Huntstown station is a major contributor to the grid at 7.5%.
Eirgid also said work is ongoing to ensure Whitegate is back in action shortly, but supply remains tight.
It said: "The unit, which is owned by Energia, returned on Thursday having been unavailable since last winter.
"Its return reduces the risk to the security of energy supply over the coming months.
"A second generator, Whitegate in Cork, is making very good progress in fixing a technical problem and will return very soon.
"The plant, which is owned by Bord Gáis Energy, has a capacity of 444MW and has been unavailable since last winter."
Eirgrid had previously said that even with Huntstown and Whitegate back, the system would remain "tight" this Winter. https://t.co/VLFBP4gHc7— Sandra Hurley (@sandra_hurley) October 24, 2021
Junior Minster Pippa Hackett said the reopening of Huntstown power station would amount to a "serious improvement" to energy supply.
Speaking on RTÉ's The Week in Politics, she said Eirgrid's CEO Mark Foley had promised that people could sleep safely in their beds this winter without blackouts.
Sinn Féin's Matt Carthy said the issue underlined the need to fast-track the move to renewable energy sources.
Meanwhile, the Sunday Independent newspaper reported that ministers have been told that power cuts cannot be ruled out over the winter in the face of energy supply issues.
Government sources say that cutting electricity to domestic homes would be a last resort.
If there are supply shortages, the first step would be cutting back the usage of large business users, such as data centres. There would also be a switch to generators.
For domestic supply to be restricted, several issues would have to occur at the same time, including no wind, generator failure and issues with the interconnector to the UK.