Transmission Network Use of System (TNUoS) costs explained
Welcome to our Third Party Costs explained video series. Before enjoying this content we recommend you refer to our disclaimer and associated material.
The information in this video and article was accurate as of 1 April 2025. We update our TPCs Explained hub every Spring to reflect any changes.
Third Party Costs Explained: Transmission Network Use of System (TNUoS)
The TNUoS charge recovers the cost of maintaining and upgrading Great Britain’s onshore and offshore transmission system. It also includes any support for cap-and-floor supported subsea interconnectors with other markets.
How does TNUoS work?
The transmission system operates at very high voltages. It’s responsible for flowing bulk flows of power from the transmission system to local distribution networks, where most end customers are located. It’s also responsible for flowing power to and from interconnectors with other countries.
How much of your energy bill does TNUoS account for?
In 2025, the charge is expected to account for around 5% of the electricity bill for a typical low-voltage, site specific customer. This figure makes it the fourth largest third-party cost. However, TNUoS will vary by location and customer type.
How are TNUoS costs recovered?
This charge covers the maintenance and upgrading of infrastructure, including power lines, substations, and transformers that operate at high voltages. These high-voltage lines are the ‘motorways’ of the energy system. A few very large power consumers are connected at this level.
The transmission network across England, Wales, and Scotland includes extremely high-voltage lines carrying either 400kV or 275kV. In Scotland, the 132kV network is also classed as transmission.
How is the TNUoS fee structured?
The charge is set by the transmission network operators and depends on the users’ location and energy consumption over peak periods. For example, areas farther away from the bulk of power stations may have higher charges due to the cost of transporting electricity over long distances.
Looking at TNUoS as a proportion of all network costs, it accounts for a significant 18%. This covers the high-voltage power lines and other infrastructure, including the wind farm connectors and undersea bootstrap cables.
How do the TNUoS usage fees work?
TNUoS includes a substantial fixed element, and a pence-per-day charge that varies according to customer size and connection voltage. There’s also a much smaller usage-based charge that varies from zero in Scotland and the north of England to the highest charge in London and the south-west.
This variation occurs because the north generates the most electricity, but the south uses more, so the Grid tends to flow power southwards. Currently, the East Midlands region doesn’t pay, but National Grid forecasts this will change in 2027.
For half-hourly customers, the charge is multiplied by their usage over the so-called ‘triad periods’. For non-half-hourly customers, the charge is based on a forecast of their weekday usage between 4pm and 7pm over the winter period.
Will you know about TNUoS costs in advance?
Yes - the National Energy System Operator (NESO) publishes the TNUoS tariffs annually by 31 January, which then take effect from 1 April. It also publishes forecasts of the upcoming charge throughout the year.
While we know the charge, each customer’s consumption is only forecast. Therefore, depending on your tariff, there may be a period of reconciliation between the forecasts and actual usage once the winter period is over.
What drives the TNUoS charge?
The main drivers of this charge are:
- The low carbon transition and construction of power stations in remote locations
- Regulatory changes, either through regulatory intervention or code governance changes, can lead to changes to the Connection and Use of System Code (CUSC). CUSC outlines how the charges are recovered
- Changes to applicable demand and meter numbers
To learn more about the other TPCs in your energy bill, head to our TPCs explained hub using the button below. Or, to understand more about electricity prices, download our latest bi-annual Electricity Prices Explained guide.
Go to the TPCs explained hubLegal disclosure
Cautionary Statement
This content may contain certain statements, statistics, projections, expectations (including expectations related to targets, goals or objectives such as emissions targets) and other information that are, or may be, “forward-looking statements”. Forward-looking statements often do not solely relate to historical or current facts, and may contain words such as ‘aims’, ‘believes’, ‘expects’, ‘intends’, ‘likely’, ‘plans’, ‘seeks’, and words of similar meaning.
By their nature, forward-looking statements involve risk and uncertainty because they relate to events and depend on circumstances that may occur in the future. Therefore, the accuracy and completeness of all such statements are not warranted or guaranteed. Although Drax believes that the statements, expectations, statistics, targets, projections and other information reflected in such statements are reasonable, they reflect Drax’s current view and no assurance can be given that they will prove to be correct or achievable. Information contained in this content, including commitments, goals, targets and objectives, and their related frameworks, methodologies or approaches, are subject to change without notice.
Actual results and outcomes may differ materially from those expressed, implied or projected by the forward-looking statements in this document. There are a number of factors, many of which are beyond the control of Drax, which could cause actual results and developments to differ materially from those expressed or implied by such forward-looking statements.
Disclaimer
Whilst every effort is made to ensure the accuracy of any information or material contained in or associated with this content, none of Drax Energy Solutions Limited, their affiliates and employees, either individually or collectively accept any responsibility for any loss, damage, cost or expense of whatever kind arising directly or indirectly from or in connection with the use by any person whomsoever of any such information or material; neither do they make any express or implied representation or warranty as to the accuracy or completeness of the data, information or statements contained herein and such data, information or statements are not to be relied-upon by any party accessing such data, information or statements.