Transmission Network Use of System (TNUoS) charges recover the cost of installing and maintaining the transmission network in Great Britain. Of assets included on the Leaderboard, only transmission-connected battery energy storage systems (BESS) are liable for these charges.

An asset-specific TNUoS generation tariff (£/kW) is calculated for all transmission-connected assets. This generation tariff is made up of a wider tariff and a local substation tariff. The local substation tariff is collected in our Modo database, and corresponds to an asset's Grid Supply Point (GSP) and the connection type found there. The wider tariff is based on locational zones, detailed by National Grid and calculated using:

  • Annual Load Factor (ALF): currently BESS are classified as a 'Conventional Carbon' generation type.

  • 'Year Round Shared' and 'Year Round Not Shared': these represent the proportion of transmission network costs shared with other zones, specific to each locational zone.

  • Adjustment Element: a flat rate for all generation zones.

These variables are used in the equation (shown below) to calculate the wider tariff which is then added to the substation tariff to calculate each asset's generation tariff.

Conventionally, TNUoS is charged annually. This annual figure is calculated by taking the generation tariff (£/kW) and multiplying it by each asset's Transmission Export Capacity (assumed to be their rated power). This is then shown on the Leaderboard as a monthly average of this estimated annual figure.

Triad revenues (a.k.a. embedded export tariff, or EET) also play a role in BESS revenues for embedded generation. However, this is not accounted for in our TNUoS column on the Leaderboard. You can learn more about how we tackle Triads in our article here.

To learn more about TNUoS, watch our Energy Academy here.

Did this answer your question?