Publication of ‘Day Ahead’ and ‘After the Day’ Margin Information

1 Background

In line with work taken forward by National Grid in reviewing information released to the market, National Grid is publishing increased levels of information on the level of margin and actions taken to meet margin requirements on a Day ahead and, post-event, on a Day +1 basis.  The overall aim is to increase the transparency of National Grid’s actions. This data complements and dovetails with other revisions to published data, such as Operational Planning Margin Requirements (OPMR) and Demand Forecast data, being undertaken simultaneously by National Grid.

The Day ahead and Day+1 published data relates directly to that used by the Control
Room when making decisions on the procurement of additional Reserve. The aim is that publication should increase awareness and understanding of National Grid’s balancing actions, and therefore imbalance price risk, helping the participants to manage risks and balance their own positions ahead of Gate Closure. 

2 Data to be published: The Daily Reserve Information File

National Grid is undertaking to publish the data below by approximately 1500h each business day. There are two separate data sets for each day in question, one set published Day-ahead and one set published Day+1.

At present National Grid, receives significant operational data from market participants regarding BM Unit Physical Notification [PN], Maximum Export Limit [MEL] and declared availability (under Grid Code OC2). Part of this submitted short-term data, once aggregated, is available through the publication of the MELNGC (Total MEL above demand forecast) figure on the BMRS. However the specific aggregations used by National Grid for its own purposes to manage within-day Reserve have not previously been available to the market ahead of real-time.

Within day, National Grid manages the level of Reserve available above forecast demand in order to meet demand in real time. Reserve is held to cover for the within day loss of generation, demand forecast errors, plant shortfalling, etc. The breakdown of Reserve is shown in Figure 2. The data that National Grid is publishing relates to the specific portion of Short Term Operating Reserve Requirement [STORR] that is secured on the day. STORR is held by National Grid through the final 4 hours before real time. A portion of STORR is met by National Grid-contracted balancing services and the balance is secured on the day by National Grid. Figure 1 illustrates this in more detail.

2.1 Day Ahead Data publication

At the day-ahead stage National Grid will publish two figures. These will be contained within the yearly ‘Daily Reserve Information’ CSV File on the operational information section of National Grid’s electricity homepage. These figure reflect:

• Scheduled Reserve Requirement
• Residual Reserve Requirement

The Scheduled Reserve Requirement [SRR] is that level of Short Term Operating Reserve Requirement not already contracted by National Grid. The Residual Reserve Requirement [RRR] is that portion of the Scheduled Reserve Requirement that is not by met by synchronised generation availability as submitted by market participants.

The published Scheduled Reserve Requirement and the Residual Reserve Requirement are based on day-ahead data as submitted to National Grid by market participants. These two figures are taken directly from the Control Room Operating Plan, based on the maximum forecast demand peak for the day in question. The two figures are described in more detail below and illustrated in Figure 1.

2.1.1 Scheduled Reserve Requirement

The Scheduled Reserve Requirement gives an indication of the level of reserve to be secured by National Grid for the peak of the day. The Scheduled Reserve Requirement is the level of additional Reserve required by National Grid that is not already contracted ex-ante, in order to meet the Short Term Operating Reserve Requirement. The portion of this Requirement that is already contracted is made up from Standing Reserve, other ex-ante Reserve contracts and Contracted Frequency Response. The remaining portion, that must be met ‘on-theday’, (the Scheduled Reserve Requirement) is typically met by Free Headroom (MEL-PN on synchronised plant), Market length and through additional dispatch by National Grid of balancing services, including: Warming Contracts, PGBTs (Pre Gate closure BMU Transactions), synchronising additional plant in the BM etc.

2.1.2 Residual Reserve Requirement

The Residual Reserve Requirement indicates the portion of the Scheduled Reserve Requirement required to be procured by National Grid to meet the overall Short Term Operating Reserve Requirement. It is based on the day-ahead data submitted to National Grid by the market and is calculated as follows:

RRR = Maximum Forecast Output – (Demand + STORR) – National Grid CR

RRR = Residual Reserve Requirement

Demand = Demand Forecast, including Station Load
STORR = Short Term Operating Reserve Requirement
National Grid CR = National Grid Contracted Reserve

Maximum Forecast Output = The maximum anticipated output of synchronised
generation and active demand-side BMUs, capable of delivering Reserve in Realtime
(i.e. sustained delivery of increased export or decreased import), based on PN National Grid Margin Data Information Document and MEL data submitted by market participants. This is also modified to include the notified French Interconnector Flow and to reflect any additional significant technical limitations and non-BMU contributions known to National Grid. However, the total excludes any output that requires National Grid balancing actions in order to make it available for dispatch in real time. 

Therefore by subtracting ‘Demand Forecast + STORR’ and ‘National Grid CR’ from the ‘Maximum Forecast Output’ this gives the expected level of RRR that remains to be secured by National Grid through additional balancing actions. By illustration, if the RRR is positive then no additional Reserve actions are expected to be required. If the RRR is negative, then this represents the level of additional Short Term Operating Reserve Requirement that remains to be secured by National Grid.

Any remaining RRR (i.e. any negative figure) may be met by within-day market response (change in PN and MEL submission by BMUs) or by balancing actions as instructed by National Grid.

2.2 Day+1 Data publication

At the day-after stage National Grid will publish two figures. These will also be published in the daily reserve information file. 

The Day+1 data is based on initial outturn data and data taken from the Final Operating Plan, produced by the Control Room at the Final Planning Stage, approximately four hours ahead of real time. Two items of data will be published:

• Scheduled Reserve Requirement, as above but for the Final Planning Stage
• The level of additional plant warmed by National Grid to meet the Operating Margin Requirement

2.2.1 Scheduled Reserve Requirement

The Scheduled Reserve Requirement is calculated as discussed above, but based on data at the Final Planning Stage. It is at the Final Planning Stage that the Control Room makes final decisions on procurement of additional Reserve to meet the Short Term operating Reserve Requirement. At the Final Planning Stage variances from the day-ahead figure could, for example, be the result of:

i. Changes in the availability of National Grid contracted Reserve or Response

ii. Changes in System conditions resulting in a change in Response or Reserve Requirements for the peak of the day.

Typically variations from Day ahead to Final Planning Stage are not significant but will affect the level of Residual Reserve Requirement to be secured by National Grid.

2.2.2 Level of Warming actions

This figure complements and supplements data already provided on National Grid warming actions at longer timescales. For this data, National Grid will publish the initial indication of the level of plant warmed by National Grid in order to meet the Operating Margin Requirements for the maximum demand peak of the day. This data is already published by National Grid but at daily resolution and much greater timescales. The provision of this data at the Day+1 stage will increase visibility of the trend of National Grid actions day-on-day allowing the market to better respond to balance the system day-National Grid Margin Data Information Document on-day. The figure represents the aggregate indicated MEL of all units warmed by National Grid for the maximum demand peak of the day.

3 Summary

National Grid will publish the following data:

This data will give market participants better visibility of National Grid actions and the drivers behind those actions, allowing better understanding of balancing actions and associated imbalance price risks.