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).

What’s new?

Ofgem and ELEXON held a joint Market wide Half-Hourly Settlment Stakeholder event on 6 February 2019. The aim of the event was to inform interested parties about the settlement design work undertaken to date, as well as introduce the TOM and discuss the development of a transitional approach.

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.

Having considered Ofgem’s ‘least-regrets’ steer, the DWG has chosen its preferred TOM and will report to Ofgem on this in late January 2019. The report will include the requirements for the different TOM services. The DWG will also consult on its preferred TOM in early 2019.

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

About the TOMs

Development of the TOMs for MHHS forms part of Ofgem’s Significant Code Review (SCR) on Electricity Settlement Reform.

The DWG is undertaking this 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 will shortly deliver a single preferred TOM to Ofgem (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 Final 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.


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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