Usually, we don't expect too much from renewables during the summer months (defined, for this report, as May to August, inclusive) since winds are significantly weaker compared to the winter months. The winds during summer 2024 were, if anything, a little lower than usual. However, the recent growth in solar made up the difference and helped 2024 (3876GWh) just edge out 2023 (3873GWh) as the summer with record renewable generation, demonstrating the complementary nature of these two resources.

Seven notable records we've witnessed during the summer:

1. Highest monthly utility-scale solar generation: 126.5GWh (July 2024)
2. Highest peak utility-scale solar output: 719MW (August 31, 2024 @ 1pm)
3. Highest peak rooftop solar output (Republic of Ireland): 399MW (August 31, 2024 @ 1pm)
4. Most wind energy during an August month: 1068.7GWh (August 2024)
5. Lowest fossil fuel generation to demand ratio for a summer month: 46.5% (August 2024)
6. Lowest monthly average grid carbon intensity for a summer month: 245gCO2/kWh (August 2024)
7. Highest discharging storage (pumped hydro plus batteries) to demand ratio: 9.2% (August 18 @ 9:30pm)

Solar farms delivered 50% more electricity in summer 2024 than 2023

When we say it was the best summer yet for renewables, it was really the best for solar power. Solar farm capacity grew from 360MW in May 2023 to 827MW in August 2024. Having more than doubled the capacity, even with dull conditions at times throughout the summer (particularly in May), we saw at least one new solar record in each summer month.

In June, the south-west and the south-east had the most sunshine; in July, it was sunniest in the east and the south-west. Since 40% of the island's solar farm capacity is in Meath, July had the highest monthly generation of 126.5GWh, meeting 3.9% of total demand.

The end of August also sneaked in a last-minute peak solar output record. On August 31 at 1pm, all solar farms' output reached 719MW, meeting 17.2% of demand at that time.

The map below shows each solar power plant's contribution at the time. Note: since we only have access to plant-level data for solar farms registered with SEMO (Single Electricity Market Operator), the map below shows approximately 90% of the 719MW record.

Wind was on the weaker side but performed as expected during the past summer

With the exception of a short period in August during which a wind output record was achieved, wind speed wasn't particularly high this past summer. This is not uncommon for this time of year: the chart below compares wind capacity with generation since 2019 and how despite wind capacity having climbed slowly, wind generation during the summer hasn't changed much over the last few years.

Lowest summer grid carbon intensity

On average, the grid carbon intensity from May-August 2024 was 282gCO2/kWh. As shown on the chart below, all four months - with the exception of July - had record low grid carbon intensity. It's worth noting that July 2023 was particularly windy and that July 2024 still had one of the lowest ever monthly average grid carbon intensities.

A continued reliance on imports since early 2023 further decreased domestic fossil fuel generation. Fossil fuel generation equalled 74% of demand from May to August in 2022 and 56% in 2023, while that share lowered to 53% in 2024. This metric has generally been lower in 2024 than previous years due to a few factors.

In addition to more solar and imports, another main reason behind low grid carbon intensity is the end of peat-fired power in Ireland, as Edenderry fully converted from peat to biomass at the beginning of 2024. We estimate peat generation is approximately 4x more carbon-intensive than gas generation.

Rooftop solar is estimated to have generated 249GWh this summer in the Republic of Ireland; output from solar farms and microgenerators at one point reached 1.1GW, meeting at least 24% of all-island demand then

There still isn't great data transparency on distributed energy resources like rooftop solar or behind-the-meter batteries. However, since 1/3 of all solar capacity in Ireland now consists of microgenerators, we thought it was time to revise our methodology in estimating rooftop solar capacity, distribution, and generation profiles, in order to fairly assess solar's performance this summer.

Based on data from ESB Networks, Met Éireann, and the 2022 Census, we estimate there was about 450MW of rooftop solar in the Republic of Ireland (ROI) by the end of the summer (unfortunately, we couldn't find good data as basis for a similar estimate for Northern Ireland - if you have a source, please let us know!).

The chart below shows how rooftop solar in ROI performed on average in each month, along with one day each month with the highest peak output: May 10, June 23, July 31, and August 31.

When utility-scale solar reached a record output of 719MW during the early afternoon on August 31, rooftop solar is also estimated to have reached a record high output of 399MW.

During the last few days of August, when the record utility-scale solar output was set, we can see a dip in demand, as rooftop solar was also producing electricity to satisfy demand. As the chart below shows, rooftop solar used for self-consumption helps lower grid demand throughout the day and in turn decreases peak demand, which usually occurs during early mornings and evenings. It's unclear how much microgeneration feeds back to the grid, although ESB Networks and suppliers surely have access to such data through smart meter readings.

Assuming all microgeneration goes to self-consumption, around 1pm on August 31, all solar output, grid-scale and distributed together, reached more than 1.1GW, equalling at least 24% of all-island demand then.

Looking ahead

As the end of year approaches, we're paying special attention to a few things:

1. Firstly, the Greenlink Interconnector is expected to start operating soon. This will allow more exchange with the GB market which recently experienced the momentous occasion of closing down its last coal-fired power plant.
2. Speaking of bidding farewell to coal, Ireland is not far behind. The remaining coal units at Moneypoint will convert to last-resort oil capacity at the beginning of 2025. We will definitely make some noise when the last coal-fired electricity generation in Ireland occurs! One thing we can be certain of is this was the last summer with coal-fired generation.
3. Last but not least, you might have noticed we haven't talked much about batteries. Peak battery discharge during the summer months was 143MW on August 18 (shown on the chart below) - far from the current all-time high of 175MW and much lower than the current all-island capacity of 956.5MW/1,062MWh. Batteries are, of course, busy. The market currently encourages batteries to rely on revenues from the DS3 programme, a suite of ancillary services that helps stabilise the grid and increase instant injections of intermittent resources such as wind and solar. Going forward, as grid operators continue to lower revenue potential from ancillary services, we expect to see more and more batteries participate in energy trading to supplement revenues, if they are able, leading to higher peak battery discharges.