Transmission Loss Adjustment Factors (TLAFs)

When electricity is being transported through networks, there are losses, which mean that not all of the power is transferred.  This can occurred either in Transmission or Distribution networks, although higher voltages generally reduce losses.

To ensure that the wholesale market is settled correctly, the transmission losses are allocated to generators (including generators embedded in the distribution system), using Transmission Loss Adjustment Factors (TLAFs). These are calculations of the losses and are calculated jointly by EirGrid and SONI and approved by the Regulatory Authorities (RAs) on an annual basis

Some generators are responsible for proportionally more transmission losses than others, depending on their point of connection to the grid. For this reason, TLAFs are site specific.

At present the following parties that participate in the SEM (market participants) are subject to TLAFs: Generators connected to the transmission network; Generators connected to the distribution network;  Interconnectors, and Suppliers (the Trading and Settlement Code (TSC) specifies that TLAFs for Supplier Units will be set equal to 1.0).

Further information on the TLAFs and their calculation can be found in the TLAF Methodology Explanatory Paper v1.0  published on 27 September 2012.

See SEMO website for details of the CLAFs currently applied in the market.

Below, you will find proposed EirGrid TLAFs for the 2018/19 tariff year amended for I-SEM deferral, and approved EirGrid TLAFs for the 2017/18 tariff year.

2018/19 Proposed TLAFs Accompanying Note

2018/19 Proposed TLAFs Excel Version

2018/19 Proposed TLAFs PDF Version

2017/18 Approved TLAFs Accompanying Note

2017/18 Approved TLAFs Excel Version

2017/18 Approved TLAFs PDF Version

2016/17 Approved TLAFs Accompanying Note

2016/17 Approved TLAFs Excel Version

2016/17 Approved TLAFs PDF Version

2015/16, 2014/15 and 2013/14 TLAFs can be found in our Library section.