Transmission Network Use of System (TNUoS) charges are becoming one of the biggest talking points in the UK energy market – and for good reason. With network investment accelerating, demand residuals going up by two thirds, and final tariffs for 2026/27 due for publication at the end of January, many businesses want to know what this means for their energy invoices.
Here, we’ll break down what TNUoS is, how it’s calculated, why it’s increasing, and how the recent announcements could affect your energy costs.
What is TNUoS?
TNUoS stands for Transmission Network Use of System, and TNUoS charges fund the operation and maintenance of the UK’s high-voltage electricity transmission network, covering the backbone infrastructure that moves power from generators to local distribution networks.
TNUoS charges are set by the National Energy System Operator (NESO) and typically account for 5-10% of total energy costs, appearing on electricity invoices as part of the non-commodity element.
How is TNUoS calculated?
TNUoS charges are mainly driven by two components. The first is the residual charge, which functions as a fixed standing charge and mainly recovers the fixed costs of maintaining and reinforcing the transmission network. This is applied as £/site/day, and is set to rise significantly from April 2026, with NESO forecasting an increase in TNUoS costs collected from £4.3 billion in 2025/26 to £7 billion in 2026/27.
The second component is the locational demand charge, which reflects regional differences in network use. This charge varies depending on where electricity is consumed, with areas that place greater strain on the network paying higher costs. This means businesses in certain regions may see larger increases than others.
Beyond these two elements, several other factors influence the final TNUoS calculation. These include the voltage level a site is connected at (Low Voltage (LV), High Voltage (HV), or Extra High Voltage (EHV)), the business’s agreed kilovolt ampere (kVA) capacity/banding, and for generators, their Transmission Entry Capacity (TEC).
All these components combine to determine the TNUoS charges applied to a business for the year.
What’s driving the large increase in TNUoS from April 2026?
The large rise in TNUoS charges from April 2026 is primarily driven by the incorporation of Clean Power 2030 into Ofgem’s RIIO-3 (Revenue = Incentives + Innovation + Outputs) for the 2026-2031 price control. This requires major transmission reinforcements to connect remote renewable generation – especially offshore wind – and move this power across the network.
These grid upgrades, essential to delivering the UK’s decarbonisation and clean power objectives, significantly increase the allowed revenues that transmission operators recover through TNUoS.
Finally, updated Targeted Charging Review (TCR) banding thresholds coming into effect in April 2026 will shift many sites into higher charging bands, raising fixed standing charges as a result.
How much are TNUoS costs expected to rise by?
Businesses in the UK could face record increases in non-commodity costs from April – around £26/MWh. However, the exact impact will depend on your region, meter type, voltage level, banding assignment, and whether you’re on a fixed or pass‑through contract. We recently held a webinar where we discussed this in further detail. You can find it here.
You can calculate your estimated TNUoS costs using our industry-first Energy Cost Calculator.
