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:
- Constraints: When local networks are congested and hit capacity limits, wind and solar generators receive instructions to reduce output.
- 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.
Daily average number of hours of renewables receiving constraints dispatch down instructions in August 2023.
Source: Green Collective; SEMO
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.
Number of hours each wind and solar plant received constraints dispatch down instructions on 21 August.
Source: Green Collective; SEMO
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.