Elexon's Beginners Guide

  • Created by: ellieedf
  • Created on: 02-03-20 12:26

Settlement Periods

Electricity is traded in half hour 'chunks' - referred to as Settlement Periods.

There is 48 Settlement Periods in one day - with Period 1 starting at 00:00.

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Gate Closure

PN Gate Closure is one hour prior to the start of a Settlement Period. This is the point at which BSC Parties must submit information regarding their planned production or consumption (PN's).

Trading Gate Closure is 15 minutes before the start of a Settlement Period.

Submission Deadline

At a certain point, all contracts are frozen and trading ceases. This is currently at the start of the Settlement Period. E.g. a contract for Settlement Period 1 must be notified before 00:00. 

Our trading gate closure is 15 minutes before delivery in order to give Epex time to notify.

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All trades are notified to Elexon who act as the Energy Contract Volume Aggregation Agent (ECVAA). Once a trade has been struck between two counterparties, one of the parties is responsible fo notifying Elexon and acts as the Energy Contract Volume Notification Agent (ECVNA).

Notifications are sent through the net (overwrite) method.

There is the following reports to assist in checking notifications:

  • Acceptance Feedback Reports (AFR's) - tells us that a notification has been processed.
  • Rejection Feedback Reports - tells us that a notification has been rejected and why.
  • Daily Notification Report - recieved at the end of the day and shows all of your notifications for that day.
  • Forward Contract Report (7-day report) - provided at specified times (09:00, 14:00, 18:30, 22:00) and shows you the notifications that you have in place for the next 7 days.
  • The ECVAA Web Service - allows you to view your notifications in a user-friendly format. It can also be used to amend existing, or submit new contracts.
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Why do we get Imbalance?


  • Electricity can't be stored so must be generated and consumed instantaneously.
  • Delivery of electricity can be impacted by system contraints
  • Electricity isnt delivered directly from the generator to the contracted demand. There is no direct feed from suppliers to customers. Generators puts electricity on to the Grid and customers take it off
  • Electricity isnt metered in real-time, so delivery and demand via metered volumes must be indentified after the event.
  • Demand is not fixed ahead of time. It is hard to forecast demand.
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How is the system balanced?

National Grid have a range of services to assist balancing the system. Options include:

  • Bid-Offer Acceptances - instructions from Grid to a BM unit to increase (offer) or reduce generation (bid). They are only made after PN Gate Closure for a Settlement Period. This system is called the Balancing Mechanism.
  • Balancing Services - Reactive Power, Short Term Operating Reserve (STOR), Frequency Response, Black Start and Reserve Services.
  • Contract Notifications Ahead of Submission Deadline - Grid can buy and sell electricity ahead of the Submission Deadline. Pre-Gate Closure BM Unit Transactions (PGBT) is a special type of contract which provides electricity in a profiled way across the settlement period. (i.e specifies the volumes it wants on a minute-by-minute basis across the Settlement Period. This is BSAD.
  • Trans-European Replacement Reserves (TERRE) - enables Balancing Services Providers to submit bidson an hourly basis to fulfill 15 minute delivery periods. These are processed by a central European platform.
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Bids and Offers

When Grid wants to make a Bid/Offer Acceptance on your Primary BM Unit, it will contact you directy. The Acceptance information is a set of 'spot points', which represent the change in output away from the FPN. 

The Offer price is what Grid must pay (per MWh) to increase generation within this band. The associated bid price can be seen as an 'undo' option. If the offer has already been accepted, this is price Grid will be payed to undo the acceptance. A difference between the two ensures you still have a profit.

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