Wider Access and TERRE Implementation Guidance


This page sets out the implementation guidance related to Wider Access and TERRE. It provides an overview of the two-stage implementation approach and includes drafts of the New Electricity Trading Arrangements (NETA) Interface Definition Documents (IDD) documents that you may need in order to develop your systems for TERRE go-live and wider market access to the GB Balancing Mechanism (BM).


Wider Access and TERRE

BSC Modification P344 ‘Project TERRE implementation into GB market arrangements’ not only implements the TERRE product functionality, but also implements the functionality (both systems and legal text) to enable wider market access. The implementation date for Modification P344 was 28 February 2019 (as approved by Ofgem) and normally BSC Parties would be required to comply with a modification proposal from its implementation date. However, there is a special provision in the P344 changes to BSC Section H ‘General’ paragraph 2.5, which states that certain P344 requirements would not come into effect on the Relevant P344 Implementation Date. Instead, these provisions will come into effect on the date specified by National Grid in its role as the Electricity System Operator (ESO) in “the P344 Final Implementation Date Notice” (a letter to Elexon as the Balancing and Settlement Code Company (BSCCo).

Change Proposal (CP) 1517

As the BSC Central Systems will not go live until the date specified in the P344 Final Implementation Date Notice, it would not be appropriate for the BSC system documentation to be misaligned to the current operational state. Therefore, we raised CP1517 ‘Changes to BSC Configurable Items for the TERRE Final Implementation Date’ to facilitate the development, review and approval of the BSC Configurable Items, reflecting the Central Systems documentation, which should become effective on the P344 Final Implementation Date. At the same time, we identified opportunities to clarify and update other BSC Configurable Items, to better support Wider Access and TERRE to be delivered through Modification P344.

Implementation approach

We are delivering Wider Access and TERRE in two stages. Stage 1 implemented changes to the BSC Systems and Configurable items that would allow Virtual Lead Parties (VLPs) to accede to the BSC in time for Stage 2, which is the implementation of the full TERRE and Wider Access software solution. The table below summaries the stages


February 2019 Release


Wider Access and TERRE Standalone Release

(P344 Final Implementation Date, CP1517)

Impacted BSC Systems

Balancing Mechanism Reporting Agent  (BMRA), Central Registration Agent (CRA) and Energy Contract Volume Allocation Agent (ECVAA)

BMRA, ECVAA, Funds Administration Agent (FAA), Settlement Administration Agent (SAA) and Supplier Volume Allocation Agent (SVAA)

Key Data Flows

No data flows to BSC Parties were changed, but:

·        ‘VP’ for Virtual Lead Party was added to the Valid Set for BSC Party Type 

·        ‘V’ for Secondary BM Unit was added to the Valid Set for BM Unit Type

The effect of these changes Parties will be seen in the relevant CRA and SAA data flows once a Virtual Lead Party has completed Qualification.

SAA-I014, sub-flows 1 & 2  are being amended to include elements of the TERRE calculation

SAA-I014, sub-flow 4: a new variant is being developed for Virtual Lead Parties

BMRA-I036: a new data flow is being developed for the TERRE data to be sent by NGESO to BMRS & SAA

BMRA-I002 from NGESO to BMRS & SAA is being amended to include a RR Instruction Flag, where:

·        “True” denotes a RR Instruction; and

·        “False” denotes a Balancing Mechanism BOA

NG ESO TERRE Derogation Request

Alongside the GB market, the TERRE product is due to go-live across eight other European countries later in 2019. We were made aware on 21 June that National Grid ESO has raised a derogation request with the GB regulator (Ofgem) to delay its participation in the TERRE balancing product to no later than December 2020. The request has been made because French electricity Transmission System Operator (TSO) RTE has announced that it has also requested a derogation. Subject to RTE not participating in the TERRE product, National Grid ESO suggests there would be no consumer benefits for the GB market in going live with the TERRE platform.

Elexon is committed to supporting Wider Market Access to the GB BM and GB market participation in TERRE. We still intend to make wider BM access available this year, regardless of whether GB participation in TERRE is deferred. This is to ensure that independent aggregators have access to the GB BM (as part of, and set out in Modification P344 ‘Project TERRE implementation into GB market arrangements). Elexon is continuing to work closely with National Grid ESO to ensure that we play our part in enabling GB’s participation in Project TERRE on the date approved by Ofgem.

We will communicate the potential impact of the delay to TERRE go-live on BSC Central System documentation, which includes the NETA IDD documents, through our Release Circular communication channel.

Stage 1

The first stage was the implementation of Modification P344 ‘Project TERRE implementation into GB market arrangements’ on 28 February 2019 as part of the February 2019 BSC Release. All BSC System changes and all BSC Configurable Items amended for P344, other than those specified in Section H2.5 or being developed under CP1517, became effective on 28 February 2019.

A summary of changes implemented are:

  • Market Participants, that could not previously become BSC Parties, can now accede to the BSC as VLPs
  • VLPs must register Secondary BM Units
  • VLPs must allocate MSID Pairs to Secondary BM Units
  • BSC Charges introduced for VLPs are lower than for other BSC Parties
  • Existing Suppliers can register Additional BM Units comprised of MSID Pairs for use
  • SVAA must submit a request to each HHDA responsible for a Metering System included in a Secondary BM Unit to provide HH Metering System Metered Data for that Metering System

These changes were implemented to allow VLPs to accede to the BSC and to register Secondary BM Units & related MSID pairs. This is to ensure that they are ready to participate in TERRE when it goes live.

Further information on the changes that were implemented as part of this release can be found under P344 on the February 2019 BSC Release web page.

Information on how to accede to the BSC as a VLP can be found on the Market Entry webpage.

Stage 2

The final stage includes further changes to BSC Configurable items and to BSC Central Systems to enable market participants to participate in TERRE and Wider Market Access. These changes will be implemented as part of the ‘Wider Access and TERRE Standalone Release’, the date of which is the P344 Final Implementation Date, as notified to Elexon by National Grid ESO in the ‘P344 Final Implementation Date Notice’, which we expect to be served closer to the time of go-live.

A summary of changes to be implemented when the aforementioned Notice is received are:

  • VLPs may submit RR Bids and / or BM Bid Offer Data to NGESO
  • [Out of scope: NGESO to accept or restrict RR Bids, and forward them to the Libra Platform; the Libra Platform to send auction Results to NGESO]
  • NGESO to provide FPN, Dynamic Data, and / or BM Bid Offer Data, RR Bids, BM Acceptance data and Auction Results to BMRA/SAA 
  • HHDAs to provide HH Metering System metered data to SVAA for the Metering Systems notified to them by the SVAA
  • VLPs must submit MSID Pair Delivered Volumes to SVAA for each accepted RR Bid or BM Bid / Offer
  • BMRS must publish the Settlement Exchange Rate each day
  • BMRS must publish RR Bids, RR Auction Results in addition to existing BM related data received from NGESO               
  • BMRS carry out and publish indicative TERRE calculations in addition to existing BM indicative calculations
  • BSC Parties should amend their systems in accordance with the revised version of the Interface Definition and Design (IDD) spreadsheet developed under CP1517 and other BSC Configurable Items relating to the Stage 2 software changes 
  • VLPs must submit MSID Pair Delivered Volumes to SVAA for each accepted RR Bid (duplication)
  • Settlement Calculations amended to include TERRE and Wider Access Bids
  • Settlement Calculations amended to calculate Supplier imbalance adjustments for VLP activity on their sites
  • Invoicing of Trading Charges amended to include TERRE and Wider Access Bids

Further information on the specific document, system changes and implementation is available on the Wider Access and TERRE Standalone Release webpage

What else do I need to know?


Wider Access and TERRE Interface Design Documents

Elexon made available early drafts of the NETA Interface Design Document (IDD) spreadsheets in order to support market participants with their preparation for Wider Access and TERRE Implementation. We shared these early drafts of the NETA IDDs so that VLP and other BSC Parties could develop or amend their systems.

However, a Change Proposal is required to formally amend any existing BSC Configurable Items (including the NETA IDD Part 1 and part 2 spreadsheets) that are needed to become effective when the full Wider Access and TERRE solution is implemented. Elexon raised CP1517 for this purpose.

CP1517 was issued for a second CP Consultation on 8 July 2019 with a revision to the NETA IDD spreadsheets.. The consultation ended on 2 August 2019 and further amendments to the NETA IDD spreadsheets were made as a result of comments received.

The final draft versions of the NETA IDD Part 1 and 2 spreadsheets (“Draft G”) are available below (published on 16 August 2019):

The NETA IDD Part 1 and Part 2 word documents (published on 16 August 2019) are:

These drafts remain subject to change until approved. We will request approval of the BSC Configurable Items amended for CP1517 from the Imbalance Settlement Group (ISG) on 20 August 2019 and the Supplier Volume Allocation Group (SVG) on 3 September 2019, as required by the BSC Baseline Statement.

Please note that the earlier drafts of the IDD Spreadsheets, Draft D (29 April 2019), Draft E (17 May 2019) and Draft F (11 July 2019) are no longer in use.

If you have any suggestions to improve readability, questions, comments or other feedback, please contact [email protected].

Industry testing of Wider Access and TERRE

Elexon has published its Industry Testing Strategy for Wider Access and TERRE. Testing will run from late August to October 2019, starting with the provision of sample files for the most important settlement interfaces. Elexon will work closely with National Grid ESO to support its testing of GB participation in TERRE.

Overall GB market testing for TERRE, including interactions with the central platform, was due to commence this autumn, followed by go-live by the end of the year. National Grid ESO has raised a derogation request with energy regulator Ofgem to delay its participation to no later than December 2020. Depending on Ofgem’s decision on whether to grant the derogation request, there may be an impact on industry testing timescales.

We will continue to work closely with National Grid ESO to ensure that we play our part in enabling GB’s participation in the TERRE balancing product on the date approved by Ofgem, which we will communicate to market participants once received.


Click on the X next to any of the icons to replace them with a short-cut link to the page you are currently on or search for a specific page.