The ESB has had its average price increase of 9% approved, to take effect from October.
The Commission for Energy Regulation (ComReg) said that it was permitting the price hike because of the escalating cost of fossil fuels on world markets.
The Commission said that if world fuel prices fall, it would ensure that the benefit is passed on to ESB customers.
A decision on a further 3.5% increase to take effect from next January will be made at the end of September.