TNUoS Charges Explained: Why Transmission Costs Are Rising

How Transmission Network Use of System charges work, why they jumped in April 2026, and which parts of the bill your business can still do something about.

TNUoS Charges Explained – Two charges on a business electricity bill cover the wires. DUoS pays for the local network. TNUoS pays for the motorway, the high-voltage grid that carries power across the country from where it is generated to your region. For years it sat quietly in the background. Not any more.

TNUoS rose sharply in April 2026 and is forecast to keep climbing through the rest of the decade. For a large site the increase runs into tens of thousands of pounds a year. So it is worth understanding where the charge comes from, why it is going up, and which parts of it you can actually do something about.

What TNUoS Pays For

TNUoS stands for Transmission Network Use of System. It recovers the cost of building, running and reinforcing the high-voltage transmission network, the pylons and overhead lines that move electricity at 275kV and 400kV, along with the interconnectors that link Britain to neighbouring markets.

The network is run under a price control agreed with Ofgem, and the tariffs are set by the National Energy System Operator. Your supplier collects the money and passes it through, so the rate is the same whichever supplier you buy from.

Unlike the wholesale price, which moves with the market day to day, TNUoS is a regulated cost. It reflects what the grid is allowed to spend, not what gas happens to be trading at.

TNUoS Charges Explained – Why the 2026 Jump Happened

April 2026 brought a new five-year price control for transmission, known as RIIO-ET3, with the final figures confirmed in December 2025. The headline is steep. The volume weighted average TNUoS for power consumers rose by roughly 64% year on year, and for some sites the fixed element climbed by anywhere from 28% to well over 100%.

In practice the all-in TNUoS figure goes from around 10.77 pounds per MWh in 2025-26 to about 18.74 pounds in 2026-27, and keeps rising toward 26 pounds by 2028-29.

The reason is investment. The grid is being rebuilt to connect offshore wind and meet net zero targets, with roughly 80 major transmission projects now in the pipeline. Someone has to pay for that build, and a large share of it lands on TNUoS.

The Residual and the Locational Parts

TNUoS comes in two parts, and they behave very differently.

The residual is a fixed charge. It is set by a banding system based on your site’s agreed capacity and voltage, and you pay it as a flat amount per day regardless of when you draw power. After the Targeted Charging Review shifted most of the cost onto this fixed basis, the residual now makes up more than 90% of total TNUoS. You cannot dodge it by moving load, but the band you sit in matters, and a site close to a threshold can sometimes be re-banded.

The locational part is the older mechanism, usually called the triad charge. It is based on your demand during the three half-hour periods of highest national demand between November and February. The further your site is from where power is generated, the higher the per-kW rate. This is the part you can influence.

Triad Avoidance and Where It Still Pays

For years, triad avoidance was the headline TNUoS-saving tactic. Predict the three winter peak half-hours, cut your demand to near zero during them, and shave a useful sum off the locational charge.

It still works, but the prize has shrunk. The locational element is now a small slice of a charge dominated by the fixed residual, and the rates vary hugely by region. Across the north of England and Scotland the locational tariff is effectively zero, so there is nothing to avoid. In the South Western zone it is the highest in the country and still rising, so a site in Devon or Cornwall has far more to gain than one in Yorkshire.

Whether triad response is worth the operational effort now comes down almost entirely to where you are. It also pairs naturally with demand side response, so the same actions can earn flexibility payments at the same time.

TNUoS Charges Explained – What You Can Actually Do

Because most of TNUoS is fixed, the levers are narrower than they are with DUoS. That does not mean nothing can be done.

Start with your banding.

The residual is driven by your agreed capacity and voltage band, so a site carrying more capacity than it genuinely needs may be sitting in a higher band than it has to. This ties into the same capacity review that affects DUoS and supplier capacity charges, so it is worth checking once and getting right.

For sites in a high locational zone, triad response still earns its keep, and it works well with on-site storage. A battery discharging through the forecast triad windows cuts locational TNUoS while doing the same job for your capacity market and DUoS exposure, so one asset works across several charges at once.

Beyond that, the main defence is making sure TNUoS is correctly forecast and priced into your contract in the first place, which is part of any sensible energy procurement exercise.

TNUoS Charges Explained – Getting Ahead of a Rising Charge

TNUoS is going up, and the published price control means the broad direction is known several years out. That is genuinely useful, because it lets you budget rather than be caught out.

The first step is to see what TNUoS is really costing your sites today and how the 2026 increase has landed. From there we can check your capacity bands, work out whether locational savings are available in your region, and make sure the charge is properly reflected in your forward energy budget.

Catalyst breaks the network and policy charges out of your bills, shows you what each one is doing, and finds the parts worth acting on. If your transmission costs have jumped this year and you want to know why, ask our team for a review.

Related service: Non-Commodity Costs, how Catalyst helps businesses understand and reduce the network and policy charges hidden in their energy bills.

Further reading: Capacity Market Charges Explained covers the other big winter peak charge, the Capacity Market levy, which roughly doubled in 2026 and is recovered across weekday winter evenings.