Dispatch Balancing and Constraints


Dispatch means the sending of instructions by the Control Centres in EirGrid and SONI to power generators, demand side units, interconnectors or pumped storage plant about their times, fuel, manner of operation or output.

Dispatch Balancing Costs

Dispatch Balancing Costs refers to a number of payments related to how generators are instructed. They include Constraint Payments, Uninstructed Imbalance Payments and Generator Testing Charges. The Transmission System Operators (TSOs) are responsible for forecasting and managing Dispatch Balancing Costs.

The costs are recovered through the Imperfections Charge, which is levied on suppliers in the Single Electricity Market (SEM) by SEMO. The Imperfections Charge also recovers the net cost of energy imbalances and Make Whole Payments.

Constraint Payments

The Transmission Operators work to ensure supply of power and system security to customers across the system in real time. That means they may have to dispatch or call in some power generators differently from the schedule in the wholesale power market. This is because of the technical realities of operating a dynamic and fast-changing power system, such as preventing overloads or maintaining enough generation reserve. It may also arise because of generator testing.

Where power stations are run differently from the market schedule, it is termed “constraint”. Subject to the Trading and Settlement Code and Firm Access, Constraint payments keep generators financially neutral for the difference between the market schedule and what actually happened when generating units were dispatched.

Generators can be constrained ‘on’ or ‘up’, if the market schedule indicated they were to be run at lower levels than actually happened. Or they could be constrained ‘down’ or ‘off’ in they were to be run at a higher level than happened in reality. There is always an overall net cost to the system associated with constraints.

Market Modelling Assumptions

Because of mathematical limitations, approximations and assumptions, the market schedule will not always be technically feasible. This is because it can take longer for power stations to increase output to link up with the power system (synchronise).

Uninstructed Imbalance Payments

All dispatchable generation is required to follow instructions from the control centres within practical limits to ensure the safe and secure operation of the power system. Failure to do so will lead to increased costs or major system problems. This is the reason the Uninstructed Imbalance Payments mechanism, as set out in the Trading and Settlement code, provides economic signals to ensure that dispatchable generation follows its instructions within acceptable practical limits.

Firm Access Quantities

The level of “firm” access to the transmission network relates to financial conditions around a generator’s output. Firm Access means that if the output on to the grid by a particular generator is changed by the Transmission Operator (known as ‘constraint’), then it may be eligible for financial compensation as set out in the Trading & Settlement Code. 

Firm Access is linked to Associated Transmission Reinforcements – this is where upgrades or new infrastructure are planned by the Transmission System Operator. In advance of Firm Access being available, some generators may opt to connect to the system on a “non firm” basis. In this instance, if the output of the generator is changed by the Transmission Operator, the generator will not receive financial compensation as set out in the Trading & Settlement Code.

As the transmission system has developed and new generators have applied to connect, Firm Access studies have been carried out. The following are relevant documents in relation to these studies.

The following document details the results for all Gate 3 wind projects:

Results from EirGrid FAQ Analysis for Gate 3 published October 2013

The following document details the results for all Gate 3 Non-Wind projects:

Results from EirGrid FAQ Analysis for Gate 3 Non-Wind published October 2013

The following document details the results for all eligible Non-Group Processing Approach (Non-GPA) projects:

Results from EirGrid FAQ Analysis for Non-GPA projects published October 2013

Those transmission reinforcements assumed to be completed in the period 2012-2020 and included in the study models used for the 2012-2020 FAQ analysis are detailed in the following document:

Transmission Reinforcements Assumed Complete 2012-2020

The technical assumptions underpinning the Gates 1-3 & Eligible Non-GPA FAQ analysis (commenced in August 2012) are available here:

FAQ Analysis for Gate 3 and eligible Non-GPA Projects -Technical Assumptions

An information note which sets out the basis upon which changes in modelling assumptions may affect the determination of FAQs, and subsequently ATRs, during EirGrid’s ITC Program analysis are catered for can be found here:

Application Of Changes In Modelling Assumptions To The ITC Analysis

The results of the original FAQ analysis for Gate 3 projects, completed in January 2010, are available at the following link:

Gate 3 Firm Access Quantities (published January 2010)

Gate 1 and Gate 2 Firm Access Quantities

Following the CER’s direction in June 2011 (CER/11/102) and the publication of the initial Gate 1 and Gate 2 Firm Access Quantities Results in 2011, EirGrid re-evaluated the Gate 1 and Gate 2 Firm Access Quantities to determine if there is any incremental levels of transmission firm access for generators ahead of the completion of a generator’s full complement of Associated Transmission Reinforcements.

The results from this analysis are available in the documents below:

Results from EirGrid FAQ Analysis for Gate 1 published 21st Dec 12

Results from EirGrid FAQ Analysis for Gate 2 published October 2013

The following documents detail the results of the FAQ analysis for Gate 1 and Gate 2 which was completed in 2011:    

Gate 1 Firm Access Quantities (published December 2011)

Gate 2 Firm Access Quantities (published December 2011)

For further information on how Firm Access Quantities are calculated and some related information, please refer to Section 3 of the Frequently Asked Questions Documents below.

Frequently Asked Questions

An audit of the results of EirGrid’s initial FAQ analysis for Gate 3 was carried out by consultants appointed by EirGrid in accordance with the CER direction CER/08/260.

The audit report can be viewed by clicking on the link below:

ITC Programme Audit - Final Report

Associated Transmission Reinforcements (ATRs)

Associated Transmission Reinforcements are new or upgraded transmission infrastructure projects which have been identified as delivering capacity for new generation projects.

They relate to dates for the connection of generation projects in the group process for connection applications.They are also of assistance to customers looking at Firm Access (financial conditions around a generator’s output and connection).

EirGrid regularly publishes the list of Transmission Reinforcements associated with Gate 1, 2, 3 and Non-GPA projects and the most recent documents are below.

Background documents on this topic include the CER FAQ Calculation Direction issued on the 23 June 2011 (CER/11/102) and the subsequent Firm Access Quantity (FAQ) analysis undertaken by EirGrid as the Transmission System Operator in 2012.

In the ATR documents below, the first column of dates is the assumed completion date for each ATR.

The freeze date for these assumed completion dates was July 2012. The second column of dates shows the latest update on the completion date or scheduled completion date of ATRs. Where the scheduled FAQ date for a project changes as a result of a change to the scheduled completion date of an ATR for that project, or when an ATR is completed, the customer is notified in writing by their System Operator. 

ATR Website Updates:

Q2 2015 ATR Website Update - published 31-Jul-2015

Q1. 2015 ATR Website Update - published 30-Apr-2015 

Updates for previous years can be found in our Library section.

An Information Note on the sequencing of transmission projects is available here.