TNUos Charges: An explainer.

Why are TNUoS charges rising, and what does it mean for EV charging?

Electricity costs for public charging networks are rising once again. This time, the key driver is an increase in Transmission Network Use of System (TNUoS) charges, which for some users will rise by as much as 64% in the 2026/27 financial year. For a 1MW charging hub, that amounts to approximately £12,000 per year extra. Across a large rapid charging network, the cumulative impact could exceed £4 to 5 million annually.

Understanding why these charges are rising matters. It is not simply a case of energy companies passing on higher costs. The causes run deeper, into the regulatory frameworks that govern how the UK funds its transmission network, and the unintended consequences for industries investing ahead of demand.

What are TNUoS charges?

TNUoS charges recover the cost of installing and maintaining the UK's high-voltage electricity transmission network. Everyone who uses the electricity network contributes towards these costs, but the way they are calculated differs depending on the type of user.

There are four main categories:

Half Hourly (HH) — used by commercial sites charged according to their demand during the three peak periods of the year, known as the Triads.
Non-Half Hourly (NHH) — covering domestic and smaller non-domestic premises, charged based on annual usage between 16:00 and 19:00.
Transmission Demand Residual (TDR) — recovers the remaining revenue required, with sites placed into bands that each carry a set proportion of the cost.
TNUoS Generation Tariffs — applicable to generation of 100MW or above. For the vast majority of business users, including EV charging operators, this is not directly relevant.

How are TNUoS costs calculated?

The process is set by Ofgem and administered by the National Energy System Operator (NESO). Ahead of each five-year regulatory period, known as a RIIO period, Transmission Owners (TOs) submit business plans to Ofgem. Ofgem then assesses those plans and publishes price controls that set each TO's allowed annual revenue. The current period, running from 2026/27, is governed by the RIIO-3 price controls.

Once the total revenue requirement is established, NESO calculates how much each category of user should pay. For Half Hourly users, charges are based on demand during the Triad periods, with location-based rates set a year in advance. For Non-Half Hourly users, charges vary by location and are calculated after the HH revenue has been subtracted. TDR charges are apportioned across bands based on actual consumption data from the preceding year.

Why are TNUoS charges rising so sharply?

There are three principal reasons for the significant increase in FY2026/27.

First, an increase in pass-through charges. Additional revenue is required to recover shortfalls from previous years, including licence fees and business rates that were not fully recouped at the time.

Second, a decrease in Half Hourly Triad demand. Triad demand has fallen by 230,000kW. When the total revenue requirement is divided across a lower volume of demand, the result is a higher tariff per kilowatt. The maths is straightforward, but the impact is significant.

Third, and most substantially, an increase in Transmission Owner revenue requirements. Ofgem approved a Baseline expenditure allowance of £10.7bn for the RIIO-3 period. This covers capital expenditure such as substation reinforcement and network strengthening, operational expenditure on maintenance and fault response, indirect costs including project management and legal functions, and significant new funding for innovation and digitalisation.

It is this last category that has been a particularly notable driver of cost in this period. Ofgem approved over £163 million in Network Innovation Allowance (NIA) funding and over £574 million in data and digitalisation across the TOs. National Grid Electricity Transmission's NIA alone has increased by 130% compared to the previous price control period.

NIA-funded activities include delivering new onshore and offshore network infrastructure, improving construction methods to reduce emissions, and developing new approaches to system operability as the energy mix changes. Digitalisation funding covers areas such as AI-supported connection offers, intelligent asset management systems, and building data-driven cultures within the transmission owners themselves.

These are not abstract line items. They represent the genuine, long-term cost of modernising and decarbonising a national infrastructure network. But they are costs that fall disproportionately on industries such as EV charging that are building out capacity ahead of the demand curve.

What does this mean for EV charging?

Public rapid charging networks are particularly exposed to TNUoS increases. A 1MW charging hub will face an additional cost of approximately £12,000 in FY2026/27 as a direct result of the TNUoS tariff change. For a large network, that aggregates to millions of pounds in additional annual operating costs.

This increase sits on top of the substantial rises in standing and capacity charges that have already impacted the industry over the past two years.

EV charging infrastructure is built at scale today to serve the mass-market demand of tomorrow. A 3MW charging hub installed now operates at a fraction of its capacity while fewer than 4% of vehicles on UK roads are electric. Yet that hub is charged as though it is fully utilised, because the tariff structures do not distinguish between current and future use.

These are the unintended consequences of regulatory frameworks designed for a different energy landscape. The RIIO-3 settlement and the cost mechanisms that govern transmission charging were not designed with EV charging specifically in mind. But their effect is to make the economics of public rapid charging harder at precisely the moment when investment in that infrastructure is most critical.

What needs to happen?

Osprey is working with Ofgem, the Department for Energy Security and Net Zero, and other charge point operators through ChargeUK to ensure these issues are properly understood at a regulatory and policy level. The goal is not to avoid the legitimate costs of network investment, but to ensure that the way those costs are allocated does not undermine the industries that are most actively driving the energy transition.

Temporary relief from, or discount on, TNUoS and related grid charges whilst EV charging throughput grows would help ensure the investment case for public rapid charging remains viable. So would a more thorough review of how costs are spread across different user types, including those that are building ahead of demand in the national interest.

The UK's public charging network has been built largely through private investment, without the benefit of the grid subsidies and direct public funding that comparable infrastructure has received in other sectors. Getting the regulatory framework right is essential to keeping that investment flowing.