The ESB is to return Lough Ree power plant in Co. Longford to service.
The plant closed in July after concerns were raised by the Environmental Protection Agency over hot water discharge into the River Shannon.
It resulted in staff being let go from nearby Bord na Mona.
The ESB says its made the decision to re-fire the plant based on the current conditions on the river Shannon.
It says over the next week the plant will gradually re-commence generation at prudent levels to ensure compliance with their environmental licence obligations.