Solar gets on the map despite a wet and windy summer in Ireland: grid constraints a glaring issue in the face of renewable growth

The renewables story in Ireland has largely been about wind energy. However, since the first utility-scale solar farm was connected in April 2022, there has been impressive growths in solar capacity and generation. At the end of Q2 2023, there is 634.5MW of utility-scale solar in Ireland. The first 6 months of 2023 alone saw more than 400MW of solar capacity connected to the grid.

The now substantial solar capacity certainly performed during summer months. Peak solar output reached 415.6MW on 28 July at 11:15am, meeting 8.9% of demand then. This is impressive, considering July was wet and windy, which is unusual for the month even in Ireland. The 3 charts below show the range of solar generation throughout the day for each summer month: June, July, and August.

In addition to aggregated generation data, we have also been able to track down plant-level output of 11 plants that make up 83% of total solar capacity. To gain a holistic view of electricity generation in Ireland, plant-level wind and fossil fuels generation has also been plotted below, alongside solar. Each bubble on the 4 maps below represents the size of generation for that date, and data points shown on the maps are in GWh. Scroll down and you will see, from 26 to 29 July, when wind and solar generation increase, grey bubbles, representing mostly gas, either shrink in size or disappear all together.

Now we have organized plant-level generation data for analysis, I was curious about how often renewable electricity generators receive signals from the grid operator to either produce less than they can or shut down altogether. This is called curtailment in many markets, but it's called "dispatch down" in Ireland and the grid operators make the distinction between 2 dispatch down instructions:

1) Constraints: When local networks are congested and hit capacity limits, wind and solar generators receive instructions to reduce output.

2) Curtailment: When the broad power system has limitations, such as hitting the System Non-Synchronous Penetration (SNSP) of 75% (up to 75% of generation at a time can come from inverter-based resources such as wind and solar), wind and solar generators also receive instructions to reduce output.

I am particularly interested in constraints, since seeing the locations of those dispatch instructions would be enlightening for identifying where networks should be upgraded and reinforced, where batteries should be deployed, and which transmission lines should be prioritized to deploy grid enhancing technologies.

While I had a difficult time finding forecast availability or dispatch limit of wind and solar generators, I created a proxy metric to illustrate network congestion. The Single Electricity Market Operator (SEMO), essentially grid operators in Ireland and Northern Ireland, publishes timely records of plant-level dispatch down instructions and they distinguish between constraints and curtailment. The number of hours within a day during which a generator receives dispatch down instructions due to constraints can serve as an indicator of network congestion.

Looking at dispatch instruction data from August, here is a breakdown of the metric by province. Ulster, consisting largely of the Northern Ireland network, has the highest frequency of such dispatch down instructions. However, that doesn't mean the scale of reduced renewable generation in MWh is larger in Northern Ireland, since we do not currently have the visibility into how much each renewable generator is capable of generating when they are told to reduce output.

To zoom into plant-level conditions, I picked a windy day, 21 August, when wind generation met 71% of all-island demand. It is abundantly clear where network congestion is most severe during days of high renewable generation. We will have to keep monitoring the numbers a bit longer to be more certain, but it's safe to assume for now Northern Ireland and southwestern Ireland should be prioritized.

At the moment, SONI, the transmission system operator in Northern Ireland, has an open consultation on strengthening the transmission grid in the Mid Antrim area. That is great, and the networks throughout the island also need more.

In addition to building and upgrading transmission and distribution networks, precisely sited battery energy storage can help avoid reduced renewable generation due to constraints. Additionally, grid enhancing technologies such as dynamic line rating should be more widely deployed to make the most out of existing infrastructure.