CMP315: TNUoS: Review of the expansion constant and the elements of the transmission system charged for
What is being proposed
The expansion constant is a key input in setting the value of the locational element of transmission network use of system charges. This modification proposal would review how the expansion constant is determined such that it best reflects the costs involved.
Current status
The Panel met on 26 April 2019 and agreed that it goes to a Workgroup. Workgroup meetings commenced on 5 September 2019.This was de-prioritised by Panel whilst the Modifications to address Ofgem's Targeted Charging Review decision were being progressed. November 2020 Panel agreed to move CMP315 from “Low to Medium” to “High” in light of recent developments re: the Expansion Constant. ESO's modification re: the wider solution on the Expansion Constant (CMP375) was presented to the June 2021 Panel. Panel agreed that CMP315 will be progressed in parallel with CMP375 (rather than be formally amalgamated) with Workgroups on the same day. Panel noted that CMP375 is a complex change and agreed that it is better to commence this as soon as possible and provide clarity for stakeholders on the future of the Expansion Constant and placed this “High” in the prioritisation stack. Given the interaction with CMP315, CMP315 will remain high in the prioritisation stack. Workgroups recommenced on 10 August 2021. Workgroup Report will be presented to July 2022 Panel. Workgroup Consultation issued 14 April 2022 and closed 5pm on 17 May 2022 with 28 non-confidential responses (and 1 confidential response) received. CMP315/CMP375 Workgroup Report was going to be presented to May 2023 CUSC Panel. However, although 2 of the solutions are fully developed, there is one new solution that became a WACM at the Workgroup meeting on 2 May 2023 and this needs further development - timescales (given the requirement for further data from the Transmission Owners). The CMP315/CMP375 Workgroup Report was intended to be issued to the July 2023 CUSC Panel, however a new timeline was approved at the July 2023 CUSC Panel to allow for additional solution refinement. The CMP315/CMP375 Workgroup completed their Workgroup Vote on 16 August 2023, the Workgroup Report was issued to the October 2023 CUSC Panel. The October 2023 CUSC Panel agreed that the Workgroup had met its Terms of Reference and that it could proceed to Code Administrator Consultation. To ensure that industry have sufficient time to consider the Consultation it will be issued on 10 November 2023 until 5pm on 15 December 2023. The Code Administrator Consultation was issued on 10 November 2023 until 5pm on 15 December 2023 and received 17 Non confidential responses and 0 Confidential responses. At the January 2024 CUSC Panel, the Panel recommended by majority that the CMP315 Original solution better facilitate the CUSC Applicable Objectives to complete their recommendation vote. The Final Modification Report was sent to Ofgem on 07 February 2024. CMP315 had an expected decision date of 30 September 2024 as per Ofgem's published update on 2 May 2024. CMP315 had an expected decision date of 30 September 2024 which has now changed to 29 November 2024 as per EDD update from Ofgem on 02 September 2024. CMP315 expected decision date of 07 February 2025 (previously 29 November 2024) as per Ofgem's update at the December 2024 CUSC Panel. (06/03/2025) CMP315 expected decision date is to be confirmed
Details
Timeline
Analysis
CMP315 proposes to review how the transmission network expansion constant is determined, which directly affects locational TNUoS charges paid by generators and large users. The modification has been in development since 2019, with the final decision now expected by February 2025. The Panel recommended the original solution by majority vote in January 2024.
Why it matters
This modification could fundamentally alter how transmission network costs are allocated geographically, affecting the economics of where generation gets built. As such, it represents a structural review of cost allocation rather than mere parameter tweaking — the outcome will determine whether locational signals accurately reflect network reinforcement costs or continue to distort investment decisions.
Key facts
- •Modification in development since April 2019
- •Panel recommended original solution by majority vote January 2024
- •Final decision expected February 2025
- •High impact on all TNUoS charge payers
- •Being progressed in parallel with related modification CMP375