Losses on the Transmission System are allocated across BSC Parties through the use of Transmission Loss Multipliers (TLMs). Transmission Loss Factors exist for each TLF Zone (aligning with the existing Grid Supply Point Groups) for each BSC Season in order to allocate transmission losses on a geographical basis.
2024/2025 Estimated Transmission Losses Adjustment values published18 December 2023
Consultation: P350 Draft Reference Network Mapping Statement 2024-2531 August 2023
New 2023/2024 Estimated Transmission Losses Adjustment values published2 February 2023
New TLFA-I014 Data for Summer 2022 on the Elexon Portal13 June 2022
Transmission Loss Factor values for Spring 2022 Part A Season availableSource: BSC Portal 30 March 2022
Latest Prevailing Network Mapping Statement availableSource: BSC Portal 22 March 2022
How it relates to you
As energy is transported from the point of production to the end user, some of it is lost. Under the BSC arrangements there are two ways in which these losses are accounted for:
- Losses on the Transmission System
- Losses on the Distribution Networks
Losses on the Transmission System are allocated across BSC Parties through the use of Transmission Loss Multipliers (TLMs).
Losses on the Distribution Networks are allocated through the use of Line Loss Factors (LLFs)
Changes to TLMs
The CMA has mandated, through secondary legislation and licence changes, the introduction of Transmission Loss Factors for each TLF Zone.
This was initiated by P350 and implemented from 1 April 2018.
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Accessing operational data
The Balancing Mechanism Reporting Service (BMRS) is the primary channel for providing operational data relating to the GB Electricity Balancing and Settlement arrangements.
Accessing the Transmission Loss Factor (TLF) data
Data is available via the Elexon Portal but we have produced a dedicated web page to highlight all the relevant data and implementation guidance.
Historic Transmission Loss Multipliers’ Historic Transmission Loss Multipliers data can be downloaded from the Elexon Portal,
Estimated Transmission Loss Adjustment (ETLMOs)’ Historic Estimated Transmission Loss Adjustment (ETLMOs), are indicative parameters set for the purposes of Balancing Mechanism Reporting Service (BMRS) reporting.
These parameters are the estimated values of the ‘Delivering Transmission Losses Adjustment’ (TLMOj+), and the ‘Off taking Transmission Losses Adjustment’ (TLMOj-). The ISG reviews the ETLMO values annually on behalf of the BSC Panel.
Under the BSC arrangements, TLMs are applied to non-Interconnector Balancing Mechanism (BM) Unit Metered Volumes as a means of scaling to account for losses on the Transmission System.
Interconnector BM Units are assigned a TLM of 1 and are exempt from Transmission Losses.
Transmission Losses on the System is defined in the BSC as the sum of BM Unit Metered Volume over all BM Units (with BM Units that import having a negative value of BM Unit Metered Volume).
The formulas for calculating TLMs are set out in BSC Section T, Paragraph 2.3.1.
There are only two values for TLM per Settlement Period, Zone and BSC Season:
- one for BM Units belonging to Trading Units that are off-taking in the Settlement Period
- one for BM Units belonging to Trading Units that are delivering in the Settlement Period
The TLM adjusted Metered Volume for each BM Unit is described as the BM Unit’s ‘Credited Energy’.
In accordance with BSC Section T, Paragraph 2.2, the Transmission Loss Factor Agent (TLFA) determines every year the Transmission Loss Factors (TLFij) for each Zone and for each BSC Season.
The Offtaking TLM applies to all non-interconnector BM Units that are part of an Offtaking Trading Unit.
The Delivering TLM applies to all non-interconnector BM Units that are part of a Delivering Trading Unit.