Electric Ireland are to refund €12.97 million to customers after they discovered that they'd been overcharging for five years.
The electricity provider miscalculated how much they needed to charge as a levy on their bills, and are now repaying the affected customers, of which there are two million.
The overcharging, which occurred between 2008 and 2013, was flagged to the energy regulator earlier this year. They have ruled that the repayments must occur in the next 12 months, and that interest must be applied to the original figure, which will push the total cost up over €13 million.
The refunds will be paid out in the form of a PSO(Public Service Obligation) Levy reduction in future bills.
Electric Ireland will cover the costs my taking money from a fund established to provide gauranteed prices for renewable energy from windfarms.