Wind Curtailment Down in 2016 Despite Increase in Installed Capacity

What is wind dispatch down?

Due to its current status in the SEM as a price taker with priority dispatch, wind generation is typically dispatched to its availability provided it is possible to do so without compromising the secure operation of the system. However, at certain times it will be necessary to reduce the level of wind generation (dispatch down) to continue to operate the system securely. There are many reasons which could lead to wind generation being dispatched down, these reasons can broadly be divided into either constraints or curtailment events.

• Constraints – Constraints refer to events where generation is dispatched down due to localised network reasons and where only a subset of wind generators can contribute to alleviating the issue.
• Curtailment – Curtailment refers to events where generation is dispatched down due to system-wide issues and dispatching down the generation of any or all wind generators can alleviate the issue.

It is important to distinguish between constraint and curtailment events since a wind generator’s compensation for being dispatched down could vary depending on the type of event. While wind generators with firm access currently receive the market price for volumes dispatched down due to both constraint and curtailment events, from 2018 volumes dispatched down due to curtailment will no longer receive market compensation. Additionally, a wind generator supported through either the REFIT or NIROC schemes will receive these support payments based on its metered generation, i.e generation after curtailment. Curtailment therefore represents a volume risk impacting a wind generator’s revenue.

Dispatch down in recent years

Dispatch down has increased in recent years driven primarily by increases in curtailment as wind capacity continues to increase and with it the level of wind penetration. However, despite record levels of wind installation in 2016 and outages on both interconnectors throughout the year (interconnectors generally facilitate greater levels of wind generation without the need for curtailment), there was still a decrease in dispatch down levels.      

What caused the lower dispatch down levels in 2016?

There are several factors which influence dispatch down of wind but one of the most important factors is the level of available wind output across the year, in other words how much does the wind blow. The average wind load factor in 2016 was 27%, much lower than in previous years (the average of the past six years is approximately 30%). With less wind generation across the year there will generally be less times when wind needs to be curtailed for system security reasons (for example to ensure the SNSP limit isn’t breached) and consequently less dispatch down of wind.    

Future Outlook

Undoubtedly, the continually increasing levels of installed wind capacity on the system will exert upwards pressure on the levels of wind dispatch down in the coming years, potentially counteracted by further increases in the SNSP limit as EirGrid and SONI continues to move towards the targeted SNSP limit of 75% through the DS3 programme. The introduction of I-SEM next year should also help reduce wind dispatch down as implicit market coupling replaces current interconnector scheduling arrangements between the SEM and GB. Today in the SEM, interconnector flows are scheduled by interconnector users in restrictive morning trading gates, which can sometimes result in inefficient power flow and power being imported while wind is being dispatched down. In I-SEM, interconnector flows will be scheduled by market coupling algorithms which will ensure that power always flows to the more expensive market. This should result in greater exports to GB during times of high wind generation, thereby reducing the need for dispatch down of wind generation.