Transmission Network Use of System charges (TNUoS) are how the transmission network is paid for in Great Britain


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Transmission Network Use of System (TNUoS) charges are a complex set of charges which collectively pay for the GB transmission network. Broadly, there are three main components to TNUoS charges:

  • Generation charge
  • Demand charge
  • Embedded Export Tariff payment

You can read more about the different TNUoS charge components, and how they're expected to evolve over the coming years here.

TNUoS charges are tracked as part of our Benchmarking product, but are not included in the BESS Indices.

Generation charge

Generation charges are a flat rate applied to all generators connected to the transmission network, and embedded generators (those connected to the distribution network) with a generation capacity equal to or above 100 MW. These charges are a function of the generators location, capacity, asset class, and average annual load factor.

The generation charge is fixed based on the asset's location, so will not (significantly) vary based on a battery's operational profile. Because of this, and the fact that generation charges are generally quite small compared to revenues, we do not include generation charges in the Benchmark.


Demand charges and Embedded Export Tariff (EET) payments are both levied against the energy imported or exported during Triads. The Triads are the three half-hour settlement periods of highest demand on the GB electricity transmission system between November and February (inclusive) each year, separated by at least ten clear days.

Triad periods are not officially announced until March following the winter season. During the winter season, we estimate which periods are likely to be Triads using Elexon's indicative operational Triad peaks dataset, considering only the indicative Triads that exceed a dynamic demand threshold. This threshold will begin the season at a level set by Modo Energy based on demand in the run-up to the winter season and previous years' minimum Triad demand, and will tend towards the minimum demand of Elexon's indicative Triads throughout the season.

TNUoS charges in the Benchmark are liable to shift as the indicative Triad periods are updated by Elexon throughout the Triad season.

These tariffs are billed against an asset's gross imported and exported energy across Triads. As we do not have visibility over the half-hourly import/export schedule of non-Balancing Mechanism units, we do not calculate their demand charges or EET payments.

Demand charge

Demand charges are levied against all assets that import energy during Triads, with tariffs varying by demand region. Any asset which imports during a Triad will pay a demand charge. It is a very expensive period to charge a battery in!

Embedded Export Tariff payment

EET payments are only paid to assets which are embedded (i.e., connect to the distribution, rather than the transmission network), and export during a Triad. EET rates vary by demand region.

We calculate Triad revenues on net, not gross, demand

We calculate the Benchmark at half-hourly resolution in order to increase performance of the live Benchmark. Because of this, we calculate net import/export across Triads, and report a single combined Triad revenue/charge rather than separate demand charges and EET payments.

The table below outlines the errors this introduces into our Triad charges/revenues. We expect most assets to participate in Triad avoidance, and therefore net export across Triads.

Triad positionDistribution connectionTransmission connection
Net exportUnderestimate revenues, error increasing as gross import/export increasesUnderestimate charges. For sites which gross import and should experience a demand charge, we calculate no charge
Net importOverestimate charges, error increasing as gross import/export increases. We do not expect many assets to significantly net import during TriadsUnderestimate charges, error increasing as gross import/export increases. We do not expect many assets to significantly net import during Triads