An amber alert that was earlier issued on the electricity market for the second day in a row has now been lifted.

Eirgrid said the alert was lifted at 8.30pm after a number of electricity generators came back on.

"It had been issued due to forced outages at a number of generators, low wind generation and limited electricity imports," it said.

"During the course of the day, just over one third of conventional generation was unavailable out of a total capacity of 6.3 gigawatts."

A similar alert was issued yesterday and lifted later in the evening.

"The outlook for Thursday is positive," Eirgrid added in a statement.

In a message on the website of the Single Electricity Market Operator (SEMO) this morning, the reason given for the amber alert was "a generation shortfall in Ireland".

SEMO is a joint venture between Eirgrid and SONI, the Northern Ireland grid operator.

The alert is issued when there is a threat to the supply of electricity.

In a statement, Eirgrid said: "The alert means that the buffer between the demand for electricity and the available supply is currently smaller than optimum. It does not indicate a loss of electricity supply to customers."

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But an expert has warned of a "perfect storm" hitting electricity supplies.

Professor Brian Ó Gallachóir pointed to higher demands in recent years due to the growth in data centres.

Mr Ó Gallachóir is Professor of Energy Engineering at UCC and Director of MaREI, Science Foundation Ireland's Research Centre for Energy.

He said that high temperatures are also a factor, as they lead to lower wind speeds which reduce electricity generation. Nor can Ireland rely on the East–West Interconnector, as the UK - which is also experiencing unusual heat - has less electricity to export, and has increased its reliance on solar power.

Norway usually exports hydroelectricity to the UK, but low water levels have reduced that flow of power.

"We don't have sufficient fossil fuel powered back-up generation to have a cushion when the wind power is low", Professor Ó Gallachóir said.

He noted that the amber alert indicates a potential threat to supplies.

"We're heading to a point where we might be at risk," he said, adding that we need to "watch this space carefully".

Senator Timmy Dooley, Fianna Fáil Seanad Spokesperson for Climate Action, has cautioned against data centres being "demonised".

Speaking on RTÉ's Drivetime, he insisted that they play a vital role in job creation.

"Data centres are the office blocks of the past, and provide necessary space to store all the data that's created," he said.

However, Paul Murphy, Solidarity-People Before Profit TD, warned that blackouts should be expected this winter, and called for an immediate embargo on the construction of data centres.

Deputy Murphy accused the Government of having "walked the country into a crisis situation", and said that "we are close to blackouts".

Dr Muireann Lynch, Senior Research Officer at the ESRI, said that Ireland is not at a point yet where blackouts are possible, but that she had concerns for the winter ahead when demand increases.

She said it was not unusual to have this type of warning, but usually during the summer electricity demand is low and the type of outages are scheduled ones.

Speaking on RTÉ's Today with Philip Boucher-Hayes, she said that at the moment there is no danger of supply being larger than demand, but usually the grid likes to have a "buffer" and at the moment it is not as high as would be desired.

She said that warning was more about "being ready" due to reserve levels not being as high as would be liked, and she said that the ESRI would call on large energy users doing what they can to reduce demand.

Dr Lynch added that blackouts could happen at an "absolute last resort" or "last-case scenario", but in the winter time, the grid could be relying on wind to help out if there is a shortfall.

"If demand is very high at a time when it happens to be windy, we might get around it, otherwise we will see crunches this winter," she said.

She suggested that households shift their usage at peak hours from 5pm to 7pm, and that the use of a smart meter can help.

Elsewhere, Bloomberg News is reporting that Britain is making plans for organised blackouts for industry and households over winter when cold weather may coincide with gas shortages.