Harmful greenhouse gas leaks at the Moneypoint power station in Co Clare were equal to about 6300 tonnes of carbon dioxide released into the atmosphere, a court heard on Thursday.
ESB Networks was fined €1,000 and must pay €20,390 in legal costs over the emission of sulphur hexafluoride (SF6) in 2018 and 2019.
The Environmental Protection Agency (EPA) prosecuted it for failing to comply with emissions laws through undue delays in repairs to equipment after leakages of fluorinated greenhouse gases.
Judge Anthony Halpin heard at Dublin District Court that the potent gas was used as an insulating medium in electricity switchgear in the high voltage substation.
The facility was adjacent to the power generation plant. As a result, it handled large amounts of electricity before transferring it into the network for distribution.
The company faced six charges, but the EPA withdrew five, and it accepted a guilty plea to one count on a full facts basis.
Cyril Tynan of EPA’s enforcement team agreed with prosecuting counsel Brian Gageby that "topping up" records showed one section had leaked 275 kilogrammes of SF6.
The amount topped up equalled the amount released into the atmosphere.
Mr Tynan told the court that one kilogramme of SF6 was the same as 23 tonnes of carbon dioxide. The 1997 Kyoto Protocol, designed to enable industrial nations to address climate change, listed SF6 as a greenhouse gas.
The court heard the gas survived in the atmosphere for 3,000 years.
There were also more minor leaks from other sections of the substation, and records were kept.
Mr Tynan confirmed there had been ongoing engagement between the EPA and ESB network.
He agreed with Brendan Grehan SC, defending, that the 400kV substation, built in the 1970s, has been decommissioned and replaced by a state-of-the-art facility.
The EPA witness agreed with Mr Grehan that the Kyoto Protocol recognised that using SF6 to a certain extent was a "necessary evil".
However, he added that since 2020 the EU has been looking for alternatives.
The court heard that the ESB had two prior convictions, but its subsidiary ESB Networks had none. Mr Grehan submitted that over the past two years, there had been no delays to repairs.
ESB Networks had also carried out checks on 30,000 pieces of equipment using SF6 throughout its network.
Mr Grehan submitted it was somewhat a legacy issue.
The charge was contrary to Regulation 13 of the European Union (Fluorinated Greenhouse Gas) Regulations and carried a maximum €5,000 fine.
Finalising the case, Judge Halpin noted ESB Networks' total cooperation with the EPA, the guilty plea, the defence submissions and the offer to pay legal costs. He also remarked that the ESB was a professional producer and supplier which gave guidance and advice to countries worldwide.