A new milestone on the nation’s decarbonisation journey was reached on March 21st this year when for the first time ever the lowest daytime electricity demand level fell below the night-time valley. The key factor at play was almost certainly the very significant increase in the amount of rooftop solar panels installed on homes around the country.
According to Diarmaid Gillespie, director of system operations with electricity transmission system operator EirGrid, peak electricity demand for the Republic is about 6GW, with the record of 6,024MW having been set on January 8th, 2025.
The impact of rooftop – or embedded – solar can be seen in the March 2026 demand statistics. Demand in the early afternoon of Thursday March 19th was almost 1GW less than the previous Thursday. “This can largely be explained by the amount of embedded solar available in addition to the better weather on that day,” says Gillespie.
This isn’t the only recent good news for the energy transition. A combination of spring sunshine and a growth in utility-scale solar power connected to the grid helped contribute to new records being set. On April 25th, a new peak for grid-scale solar of 1GW (1,133MW) was reached.
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“Utility-scale solar has tripled over the past three years and now exceeds 1GW, which is enough to power almost 500,000 customers,” Gillespie says.
Solar isn’t the only renewable power source making records. A new high for wind generation of 3,898MW was reached on Saturday February 14th at 5.50pm.
“We’ve had a great story with wind as part of the energy mix over the past two decades,” Gillespie points out. “There is now over 5GW of wind installed on the system. A huge proportion of the energy mix can be provided by wind. As we add more and more renewables, we will become less reliant on fossil fuels.”
This progress is very welcome, but it does present certain challenges to EirGrid as the transmission system operator. EirGrid’s job is to develop, manage and operate the transmission grid and to balance supply and demand every minute of the day. As part of its remit, EirGrid is developing the necessary infrastructure and operational requirements to facilitate the energy transition and to increase the proportion of renewable electricity generation to supply 80 per cent of demand in line with the Government’s climate action targets.
The key challenge is intermittency. “Wind is quite predictable,” he notes. “For the most part the forecasts can be quite accurate. Solar is less predictable. It can drop off very quickly because of a passing cloud. That’s a new challenge for us.”
Embedded solar is a different challenge. Because it is not connected directly to the grid, EirGrid has no control over it. That means demand can increase quite suddenly because of cloud rolling in.
“We match supply with demand second by second. If an imbalance occurs, we must rectify it immediately.”
When there is an excess of supply, the solution can be to take less power from providers, but when a deficit occurs due to wind or solar suddenly dropping off, that usually means calling on other sources. Typically, this has meant open-cycle gas turbine generation which can get up and running in minutes.
“Our preference is not to reach out to fossil-fuel generation,” says Gillespie. “We are looking at battery energy storage which can provide an immediate injection of power to the system. There is between 700 and 800MW now connected to the system and more on the way. We have had storage for many years in Turlough Hill. We are also seeing a lot of people installing battery storage along with solar. That is very encouraging.”
It’s not all about megawatts and gigawatts though. The frequency of the power on the system is critically important. That’s where inertia comes into play. Traditional large centralised generating stations have large rotating masses in the form of turbines spinning at 50 times a second – the 50hz frequency of the grid.
“Because they are heavy, they don’t slow down that quickly, that’s inertia,” Gillespie notes. “Renewables don’t have a big rotating mass. But we can compensate for that with synchronous condensers which provide the inertia and slow down the rate of frequency change on the system.”
There are now two synchronous condensers installed, one at Moneypoint and the other at Shannonbridge, which are reducing dependence on fossil fuel generation for grid stability.
“Thanks to these and other measures employed by EirGrid, the electricity grid can now accommodate up to 75 per cent of electricity from renewable sources at any one time. This is known as the system non-synchronous penetration (SNSP) limit. This will need to increase to 95 per cent to meet a target of 80 per cent of electricity being met by renewables sources.”
