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?

DWG reconfirms its preferred TOM following consultation

The DWG thanks everyone who responded to its recent consultation on its preferred TOM.

Overall, the DWG agrees that the responses:

  • Positively affirm its market segment approach to the TOM design
  • Validate that the TOM captures all essential Settlement data and processes (noting that the requirements for ‘behind the meter’ metering are being developed separately under Modification Proposals P375 and P379)
  • Mirror the majority / minority DWG views on the preferred TOM
  • Confirm that, subject to respondents’ views on their preferred TOM and based on current knowledge, the TOM is not a barrier to future market innovation
  • Highlight the importance of a managed transition to the reduced Settlement timetable that minimises Settlement risk, given current uncertainty over the smart rollout penetration, data quality under MHHS and future performance targets
  • Affirm the DWG’s view that a Trading Disputes process / window is still required
  • Confirm that, aside from a minor point of clarification, the DWG’s proposed transition principles are appropriate 
  • Raise a variety of other relevant points and suggestions for consideration when developing the transition approach

The DWG agrees that no fundamental changes are therefore required to the TOM. It notes that some responses comment on areas that fall outside of its control and will be a matter for Ofgem’s policy decisions, Request for Information and Business Case under the wider SCR. It also recognises the challenges for participants in identifying costs and benefits without knowledge of the target architecture, but notes that Ofgem has tasked it with developing an architecture-neutral TOM. 

You can find more information on the DWG’s discussions in the DWG16 Headline Report.

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. The DWG subsequently consulted on this from 18 February 2019 to 15 March 2019. Click here to read the public consultation responses. The DWG discussed the responses at its meeting on 26 March 2019 (see ‘What’s new?’ above).

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. 

Transition approach

The DWG is now developing a high-level transition approach for moving from the current Settlement arrangements to the TOM. The DWG will consult on this and deliver its final Stage 2 report to Ofgem during Summer 2019. Ofgem will then make its Full Business Case decision on when and how to implemement MHHS.

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


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.

In Stage 2, to help it develop the TOM service requirements, the DWG also formed sub-workgroups supplemented with experts in more detailed areas. 

You can find the DWG’s and workgroups’ Terms of Reference and membership on this webpage.


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