The coal-fired Moneypoint power plant has not produced electricity for the past seven weeks - five years ahead of its scheduled phase-out.
ources say it is unlikely the plant will be used again in its current form although the official date for ending coal-fired electricity remains 2025.
Coal was last used on January 3 and even then just one of the three turbines was in use.
It produced only 3pc of total electricity, a dramatic turnaround from just five years earlier, when coal fuelled 20pc of total output.
The country has coped without coal before due to technical issues at Moneypoint but this is the longest period for which it has been dropped by choice in favour of wind and gas.
There is a reluctance in official circles to formally declare an end to coal, however.
Keeping Moneypoint online is considered necessary in case of disruption in the supply or rise in price of alternative sources.
ESB acknowledged Moneypoint's output had "declined dramatically" but said only that coal-burning would end "no later than 2025".
"Running at Moneypoint between now and then is likely to be quite low depending on market conditions," the company said.
The side-lining of coal comes as a report from Christian Aid documents human rights and environmental abuses at the Cerrejon mine in Colombia where ESB sourced millions of tons of coal up to 2018.
Christian Aid said the case showed the need for legislation in Ireland to compel companies to rights-proof their supply chain whether sourcing goods at home or abroad.