Design Working Group

The DWG supports Ofgem in the ELEXON-led project to design and assess the Target Operating Models (TOMs) for Market-wide Half Hourly Settlement (MHHS).

What’s new?

ELEXON and the DWG thank everyone who responded to the consultation on the skeleton TOMs. You can find a link to the responses below.

The DWG is encouraged that the responses confirm all five TOMs to be viable options and that it has not missed any other TOM or significant aspects of design. The responses show no industry consensus on an overall preferred TOM. As a result, the DWG is taking all of the TOMs forward for further detailed design and evaluation in Stage 2. You can find a more detailed summary of the DWG’s discussion of the responses in its Meeting 8 Headline Report.

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 now complete and 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.

Stage 2:

The DWG is developing high-level service requirements for the TOMs and will deliver a single preferred TOM to Ofgem (taking into account Ofgem’s related policy steers/decisions). Following its decision on the Business Case, Ofgem will then decide if, and when, to implemement MHHS.

You can view the DWG’s latest 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, the DWG has formed sub-workgroups supplemented with experts in more detailed areas. These will aid in the development of designs for specific topics.

You can find the DWG’s and workgroups’ Terms of Reference and membership under ‘Related Content’.


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