The former Stormont environment minister Edwin Poots was legally entitled to approve a plan to construct gas caverns under Larne Lough, the Court of Appeal has been told.
Campaigners opposed to the plans are continuing their legal challenge against the project.
They claim the plans are so significant and controversial they should have been referred to the Stormont Executive.
Mr Poots, now Stormont Speaker, gave consent for the plans in 2021.
On Tuesday, a barrister for the group told the court few projects "come close to this in terms of strategic significance in terms of energy supply and security".
The proposal would see seven large storage caverns hollowed out underneath the lough by carving out salt layers.
The space will be able to store about half a billion cubic metres of natural gas, creating a 14-day buffer during periods of peak demand.
Groups including Friends of the Earth and No Gas Caverns argue the project should have been referred to the Executive because of its cross-cutting nature.
They add a community fund, which was taken into account as a mitigating measure in approving the decision, was an irrelevant consideration.
The groups previously sought a judicial review of the decision at Belfast's High Court on the same grounds which was later dismissed.
Islandmagee Energy, the firm behind the project, has previously said there will be no long-term damage to wildlife and that any impact created by the discharge of brine - very salty water - would be confined to a small area at an approved distance offshore, away from Larne Lough.
On day two of the case, the Court of Appeal heard from the counsel for the Department of Agriculture, Environment and Rural Affairs (DAERA), Tony McGleenan KC.
He insisted "the significant and controversial issue is a matter of political judgment" and the decision was being wrongly depicted as a question of law.
"If the appellants' analysis is right, you strip context and political judgment entirely out of the exercise, and you bring all of these matters to a court as hard-edged questions for public law determination," he said.
The court was also told that policy on gas storage caverns has been settled at a UK level since 2011.
Mr McGleenan also told the court that no Executive ministers had voiced concerns about the planning decision.
"You would expect the alarm to be raised by the other ministers if they identified something that was fundamentally problematic," he said.
The appeal continues.