Brexit means that Ireland is "no longer compliant" with the EU's requirements for energy security, an Oireachtas committee has heard.
The Commission for the Regulation of Utilities (CRU) said that Ireland's energy security has usually been guaranteed by access to gas supplies from the UK, but Brexit has put an end to that.
Aoife MacEvilly, Chairperson of the CRU, said that she will be emphasising the importance of "resilience within our gas infrastructure" when contributing to the Government's review of the security of energy supply.
She was appearing before the Committee on the Environment and Climate Action, which is is examining progress made on delivering renewable energy in Ireland.
The CRU is Ireland's independent energy and water regulator.
It challenged assertions by environmental campaigners that Ireland does not need gas or coal to ensure energy security.
Jerry McEvilly of Friends of the Earth called on Government to cut Ireland's reliance on all fossil fuels, including gas.
"Energy security and sustainability go hand in hand", he said, adding that "more gas" does not mean "more security".
He called for "the current moratorium" on liquefied natural gas (LNG) "be made permanent", and he insisted that it was not good enough to have gas on hand for when "the wind doesn't blow".
However, Aoife MacEvilly said LNG should be considered to ensure security of supply.
She added that any LNG facilities must be adaptable to green hydrogen in the future.
And while she noted that Ireland can generate up to 5,000 megawatts by wind, she said that on "quiet days" only a fraction of that is delivered.
This morning, Ms MacEvilly said, wind energy provided only 19 megawatts of electricity.
Quiet days can last weeks in Winter, she said, and "ensuring the lights stay on" means using coal- and gas-generated electricity.
Tara Connolly, Senior Gas Campaigner at Global Witness, cautioned against a "dash for gas", pointing to a commitment by the US to provide the EU with more LNG.
Global Witness and Friends of the Earth both said that building more LNG terminals to tackle the energy crisis will simply push up prices, in part due to construction and running costs.
Speaking from Brussels, Ms Connolly appealed to the Government to phase out fossil fuels, and hit net zero carbon emissions, by 2050.
CRU's Director of Security of Supply and Wholesale, John Melvin, said that energy policy is all driving towards fulfilling that commitment.
The committee also heard that the CRU is accelerating the deployment of green energy in light of the "shocking" Russian invasion of Ukraine.
Ms McEvilly pushed for "an acceleration" of the review of the planning process, which has a direct bearing on the delivery of new energy projects.
She also revealed that 745,000 smart meters have been installed in Irish homes to date.
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