Wider generation TNUOS forecasts

BESS sites that are transmission connected or of capacity >=100MW face wider generation TNUoS charges.

These are flat rates that a site must pay each year.

Wider Generation TNUoS charges feature in both the Run Library and in Custom Runs.

Transmission-connected batteries pay fixed TNUoS

Export rates for transmission-connected generation have shifted from time-of-use (via the Triad mechanism) to a fixed rate via the Wider Generation tariffs. This is a result of the Targeted Charging Review.

The rate can be positive or negative and varies throughout the country. See Figure 4 here.

For example, let's model a transmission-connected battery site in South Wales, due to come online during 2028

Transmission-connected batteries fall into the 'Convention Carbon' generating class for TNUoS calculations.

The calculation for the Wider TNUoS tariff, Conventional Carbon, is:

Taking numbers from the 5-year view of TNUoS tariffs, in the year 2028/2029 (p.14) and assuming the site has no historical data, we use an Annual Load Factor (ALF) generic for storage of 1.6301% (p.71).

This gives the calculation:

6.711930 + (- 7.300407 x 1.6301%) + (0 x 1.6301%)+ - 2.997585 £/kW = 3.5953 £/kW (to 4 significant figures), or £3595/MW/year.

We use the ESO Wider Generation TNUoS forecasts to inform our projections

The Electricity System Operator has produced Wider Generation TNUoS forecasts for 2025-2029.

We use these and push the final value forwards for the rest of the forecast horizon, depending on the Generation Zone of a site.

Wider Generation TNUoS in the Modo Forecast

Tariffs are given per Generation Zone:

In the run library, users can pick the distribution region of their run. DNO regions have a many-to-many relationship with generation zones, so we have used the following mapping for simplicity:

Specific generation zones are available via custom runs.