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?

On 15 February 2019, Ofgem published the DWG’s report on its preferred TOM for MHHS.

The DWG is now consulting on its report. This consultation is your opportunity to comment on the TOM, before Ofgem decides whether to approve it. It closes on 15 March 2019.

Ofgem and ELEXON held a joint MHHS stakeholder event on 6 February 2019 to support the consultation. Click here for the presentation slides.

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’ (high-level) 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 detailed design and evaluation in Stage 2.

Stage 2:

The DWG has developed high-level service requirements for the TOMs, has evaluated the different TOMs and has delivered a single preferred TOM to Ofgem. It is now consulting on this TOM (see ‘What’s new?’ above).

The DWG will next develop a 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, and its more detailed Forward Work Plan, under ‘Related Content’ on the right-hand side of this page.

Ofgem has provided the DWG with a ‘least-regrets’ steer on the outstanding policy decisions that materially affect the TOM design. This does not prejudge Ofgem’s final policy decions but allows the design work to progress with the intention of having the least impact on overall programme timescales, while minimising the risk of doing nugatory work.

The DWG has also written separately to the BSC’s Performance Assurance Board, asking it to oversee identification of any Performance Assurance Framework changes resulting from the TOM.


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 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 under ‘Related Content’.


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