Design Working Group

The DWG supports Ofgem in the ELEXON-led project to design and assess the Target Operating Model (TOM) for Market-wide Half Hourly Settlement (MHHS). The TOM is a key output of Ofgem’s Significant Code Review (SCR) on Electricity Settlement Reform.

What’s new?

Your opportunity to comment on the DWG’s transition approach

The DWG is consulting on its approach for transitioning from the current Settlement arrangements to the TOM:

This is your chance to comment on the transition approach, as developed by the DWG, before Ofgem decides whether to approve it.

The deadline for responses is 08:00 (8am) on 8 July 2019. We will also give an overview of the transition approach, and answer any questions, at our Half Hourly Settlement Workshop on 12 June 2019.

About the DWG’s work

The DWG has developed the TOM in two stages:

Stage 1:

This stage is complete. It involved the DWG’s development and asessment of a set of ‘skeleton’ TOMs. The output was a report to Ofgem on 4 April 2018, setting out the five skeleton TOMs to be taken forward for industry consultation. The consultation was issued on 30 April 2018 and closed on 29 May 2018. Click here to read the collated consultation responses.

The responses showed all five TOMs to be viable options and that the DWG had not missed any other TOM or significant aspects of design. They showed no consensus on an overall preferred TOM. The DWG therefore took all of the TOMs forward for further design and evaluation in Stage 2.

Stage 2:

This stage comprises development of both the final high-level TOM design and a high-level transition approach.

TOM design

Between April 2018 and January 2019, the DWG developed high-level service requirements for the TOMs, evaluated the different TOMs and delivered a single preferred TOM to Ofgem. On 15 February 2019, Ofgem published the DWG’s report on its preferred TOM for MHHS.

You can also find supporting information to the DWG’s TOM report here. This contains the contents of the report’s Attachment A, but separated out by the individual services within the TOM. 

The DWG consulted on its report from 18 February 2019 to 15 March 2019. Click here to read the public consultation responses. The responses validated the overall approach and coverage of the TOM design, and resulted in no fundamental changes to the TOM.

Transition approach

The DWG is now consulting on its high-level approach for transitioning to the TOM (see ‘What’s new?’ above). It will consider the responses and submit its final Stage 2 report to Ofgem during Summer 2019.

You can view the DWG’s latest Gantt chart plan under ‘Related Content’ on the right-hand side of this page.

How the DWG fits into Ofgem’s SCR process

The DWG’s outputs form one of several work streams in Ofgem’s wider SCR. The DWG makes recommendations for Ofgem’s approval. Ofgem will make the final decision on the TOM and transition approach.

Ofgem’s other parallel SCR work streams include:

Ofgem will bring the outputs of all the SCR work streams together in its Final Business Case decision on how and when to proceed with MHHS.

ELEXON chairs the DWG and Ofgem appoints its members. Ofgem is not a member but attends as an observor and provides strategic input where necessary.


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.

List of ELEXON insights

ELEXON Circulars

Training services delivered by ELEXON

Market Entry

Charge Codes and Switch Regimes

Add New