TNUoS Charges 2026: The 60% Rise Explained — and What It Costs Your Business

Update — July 2026: TNUoS Has Just Risen by Around 60%. Here’s What Happened.

From 1 April 2026, TNUoS charges rose by roughly 60% on average — the largest single-year increase in the charge’s history. NESO’s final 2026/27 tariffs, published on 30 January 2026, take average TNUoS costs from around £18.9/MWh to £31/MWh, as the total revenue recovered through the charge jumps from approximately £5.1 billion in 2025/26 to £8.9 billion in 2026/27.

The driver is the scale of transmission investment required to connect new generation — offshore wind above all — under the push to decarbonise the grid. Someone has to fund the pylons, and under the current charging framework, that someone is substantially the demand side: business and domestic consumers.

Three practical consequences for business electricity users:

• You pay it regardless of consumption. Since the Targeted Charging Review reforms, most demand TNUoS is recovered through fixed, banded residual charges — effectively standing charges set by your voltage level and consumption band. The 2026/27 reset increases those residual charges by anywhere from roughly 28% to over 100% depending on banding. Using less electricity does not make this element smaller.
• Expect it to show as a 5–10% rise in total electricity cost for a typical business, larger for low-consumption sites where fixed charges weigh heavier per unit.
• Contract structure now really matters. On an all-inclusive fixed contract signed before the rise, your supplier absorbs the 2026/27 increase for the remainder of your term — one reason well-timed fixed deals agreed in 2025 are looking good today. On pass-through contracts, the increase lands on your bills directly from April 2026. When you next tender, whether non-commodity costs are fixed or passed through deserves a deliberate decision, not a default — and with further network investment planned, 2026/27 is unlikely to be the last step up.

The rest of this guide explains what TNUoS actually is and how the charge works.

TNUoS Charges Fund the High-Voltage Transmission Network That Moves Electricity From Power Stations to Your Local Area. For Larger Businesses They Include a Seasonal Component Worth Thousands of Pounds.

Transmission Network Use of System charges (TNUoS) are the costs recovered from electricity market participants to fund the operation and maintenance of the high-voltage national transmission network owned and operated by National Grid. This is the infrastructure of pylons, underground cables, and substations at 132kV and above that carries electricity from power stations and offshore wind farms to the regional distribution networks that deliver it to your premises.

TNUoS is a significant component of the business electricity bill — typically 8–12% of a total all-inclusive unit rate — and it contains a specific sub-component called Triad charging that deserves particular attention from larger electricity users.

How TNUoS Is Calculated and Charged

National Grid (now NESO for system operation purposes) publishes TNUoS tariffs each year, setting the charges for the forthcoming financial year (April to March). The total revenue requirement for the transmission network is divided between generators (who pay for their connection and use) and demand customers (who pay for their use of the network to receive electricity).

The demand component of TNUoS — which is what affects business electricity consumers — is charged in two ways:

1. Running charges: A continuous per-kWh charge applied to all electricity consumed, regardless of when it is consumed. This element is relatively stable and is reflected in the unit rate on standard electricity contracts.

2. Triad charges: A specific demand-based charge applied to the three half-hours of peak system demand during the winter period (November to February) — the “Triads.” These are the three half-hour settlement periods with the highest aggregate system demand across the entire November to February window, with each Triad separated by at least 10 days.

The Triad charge methodology means that your TNUoS liability for the year is significantly affected by your consumption during these three specific half-hours. Businesses that consume heavily during Triad periods pay a large annual Triad charge. Businesses that successfully reduce their consumption during Triad periods pay proportionally less.

TNUoS Location Variation

TNUoS tariffs vary by location in Great Britain. The charging methodology reflects the actual cost of using the transmission network at different points — specifically, the cost of transmitting electricity from where it is generated (predominantly Scotland and northern England for wind and nuclear) to where it is consumed (predominantly southern England and London).

Demand customers in the south of England pay higher TNUoS demand charges than those in Scotland, because transmission infrastructure must carry electricity further south and the cost of that infrastructure is higher per unit delivered. This means a business in Surrey pays more in TNUoS than an equivalent business in Glasgow, all else being equal.

The location-based TNUoS methodology is one of the reasons that energy costs genuinely vary by location even for otherwise identical businesses — it is not simply a supplier pricing choice but a structural network cost difference.

The Triad Mechanism in Detail

A note on current relevance: since the Targeted Charging Review took effect, the residual (largest) element of demand TNUoS is recovered through fixed banded charges rather than Triad demand — so Triad avoidance no longer reduces TNUoS liability the way it did historically. Triad periods remain relevant to some legacy and pass-through arrangements and to wider peak-price exposure, so the mechanism is explained below, but treat the savings arithmetic as historical context rather than a current strategy without checking how your contract recovers TNUoS.

Triad avoidance is one of the most practically valuable energy management activities available to larger UK electricity consumers. Here is how the mechanism works:

Triad identification: At the end of each winter period (February), National Grid identifies the three half-hours that had the highest aggregate system demand, separated by at least 10 days. These are retrospectively designated as the Triads for that winter.

Triad charge calculation: Your demand during each of the three Triad half-hours is measured from your half-hourly meter. Your average demand across the three Triads (in kW) multiplied by the applicable TNUoS Triad tariff (in £/kW/year) determines your annual Triad charge.

Example: A business with an average demand of 300 kW during the three Triad half-hours, in a TNUoS zone with a tariff of £45/kW/year, pays 300 × £45 = £13,500 in Triad charges for that year. This charge is recovered across the following year’s bills.

Triad avoidance: Because Triad events occur during predictable conditions — peak demand, cold evenings, low wind generation, typically between 4pm and 7pm on weekday evenings in November–February — businesses can receive forecast signals from aggregators or market services and reduce their consumption during those windows. A business that successfully reduces demand from 300 kW to 100 kW during the three Triad half-hours saves (300-100) × £45 = £9,000 per year — from a 30–60 minute demand reduction on three evenings per winter.

Who Should Actively Manage Triad Exposure

Triad management is most financially worthwhile for businesses on mandatory half-hourly metering (demand above 100 kW) in high TNUoS zones (broadly, southern and eastern England) with consumption flexibility during the 4pm–7pm winter evening window.

The minimum scale at which active Triad management is typically worthwhile is approximately £3,000–£5,000 of annual Triad charge — which corresponds to roughly 70–100 kW of Triad-exposed demand in southern England TNUoS zones. Below this level, the management overhead and any demand reduction costs typically exceed the potential saving.

For businesses above this threshold who are not actively managing Triad exposure, raising the question with your energy adviser is worth the 15-minute conversation.

TNUoS on All-Inclusive vs Pass-Through Contracts

On all-inclusive fixed contracts, the supplier embeds an estimate of TNUoS (including expected Triad costs based on your historical demand profile) in the unit rate. If actual TNUoS rises due to regulatory reset or your Triad performance is worse than modelled, the supplier absorbs the impact.

On pass-through contracts, TNUoS is passed through at actual rates — including actual Triad charges based on your actual Triad demand. This means your effective electricity cost under a pass-through contract reflects your Triad management performance directly. Good Triad management reduces your pass-through costs; poor Triad management increases them.

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