TNUoS charges depend on the grid connection, asset size, and duration
Embedded export tariffs
These tariffs only apply to distribution-connected batteries with a capacity below 100MW.
Embedded export tariffs vary from region to region
Depending on the Grid Supply Point (GSP), the amount that distribution-connected batteries are paid for exporting during Triads varies. We model Embedded Export tariffs using NESO’s five-year regional Transmission Network Use of System (TNUoS) charges. We assume that they remain stable from year 6 onwards.
In revenue curves, the benefit of TNUoS revenues from triads is smeared over the 12 month period, where a TNUoS charging year runs from April to March.
We assume no site imports during Triads
We assume sites don’t import during Triads—so you don’t pay import flexible TNUoS (which everyone, distribution or transmission connected, pays if they import). If the site does import during Triads, it can be expensive.
We assume a capture rate for export revenues dependent on battery duration
Analysis of the battery fleet’s success in hitting triad periods is available for 2024/2025 and 2023/2024 on the Modo Energy platform.
Given this historic performance, we assume that 1h systems achieve 33% of the total possible triad revenue, and 2h systems achieve 85%.
For durations between these values, we apply a linear fit, and no system can capture more than 100% of triad revenues.
Wider generation TNUoS forecasts
BESS sites that are transmission connected or of capacity ≥100MW face wider generation TNUoS charges. These are flat rates that a site must pay each year.
Wider Generation TNUoS charges feature in both the Run Library and in Custom Runs.
Transmission-connected batteries pay fixed TNUoS
Export rates for transmission-connected generation have shifted from time-of-use (via the Triad mechanism) to a fixed rate via the Wider Generation tariffs. This is a result of the Targeted Charging Review.
The rate can be positive or negative and varies throughout the country. For a full breakdown of the 2026/27 zone tariffs, see Modo Energy’s TNUoS charges for BESS in 2026/27.
Example: Transmission-connected battery in South Wales
Let’s model a transmission-connected battery site in South Wales for the 2026/27 charging year. Transmission-connected batteries fall into the ‘Conventional Carbon’ generating class for TNUoS calculations.
The calculation for the Wider TNUoS tariff, Conventional Carbon, is:
Taking numbers from the 2026/27 Final TNUoS Tariffs tables, Table 2 for South Wales & Gloucester (zone 21), and assuming the site has no historical data, we use the generic Annual Load Factor (ALF) for storage of 3.89% (from the 2025/26 Final TNUoS Tariffs — the value carried in the April forecast).
This gives the calculation:
2.591993 + (-9.044134 × 3.89%) + (0 × 3.89%) + (-2.476760) £/kW = -0.2366 £/kW (to 4 significant figures), or -£237/MW/year. South Wales sits in the southern half of the country, where the wider generation tariff is negative, so the site receives a small credit rather than paying.
We use NESO Wider Generation TNUoS forecasts
The National Energy System Operator (NESO) publishes Wider Generation TNUoS forecasts each year. We use the latest Five-Year Tariff Report (covering 2026/27 to 2030/31) and push the final value forwards for the rest of the forecast horizon, depending on the Generation Zone of a site.
Wider Generation TNUoS in the Modo Energy Forecast
Tariffs are given per Generation Zone:
In the run library, users can pick the distribution region of their run. DNO regions have a many-to-many relationship with generation zones, so we have used the following mapping for simplicity:
| Distribution Network Region | Assumed Generation Zone |
|---|---|
| East Midlands | South Lincolnshire and North Norfolk |
| Eastern | Mid Wales and The Midlands |
| Merseyside & North Wales | North Midlands and North Wales |
| Midlands | Mid Wales and The Midlands |
| North Western | North Lancashire and The Lakes |
| North of Scotland | North Scotland |
| Northern | North East England |
| South Eastern | Essex and Kent |
| South Wales | South Wales & Gloucester |
| South of Scotland | Lothian and Borders |
| Southern | Somerset and Wessex |
| Yorkshire | South Lancashire, Yorkshire and Humber |
| South Western | West Devon and Cornwall |
| London | Central London |
Specific generation zones are available via custom runs.
Half-hourly demand tariffs
Transmission-connected assets that import during triad periods will also be subject to Half Hourly Demand Tariffs. These vary depending on the region.
Note: In the Modo Energy forecast for GB, we assume that no battery will import during a triad period. Thus we do not factor in the cost of this demand tariff in our TNUoS revenues.
The TNUoS charging regime is slightly complicated for batteries. It depends on if the site is transmission- or distribution-connected, where it is, and what it does during Triad periods.
- Generally, if you import during a Triad, you’ll pay
- If you export during a Triad, you might get some revenue depending on where the site is, according to Embedded Export tariffs
- If the site is larger than 100MW or connected directly to the transmission network, you also face fixed-cost Wider Generation tariffs
Note: All costs (or revenues) we display in our forecast numbers are purely for the battery on a site. Batteries on co-located sites will be subject to different TNUoS revenues.
TNUoS Overview
Batteries connected to the distribution network are exempt from TNUoS fixed import fees (provided they submit a Non-Final Demand declaration to NESO).
All batteries (distribution or transmission) are exposed to flexible TNUoS charges if they import during a Triad, according to import rates (see Modo Energy’s TNUoS charges for BESS in 2026/27). Distribution-connected assets get paid flexible TNUoS rates depending on where they are and their average power over Triad periods, according to Embedded Export Tariffs (shown below).
Transmission-connected assets are subject to fixed-cost TNUoS charges as per the Wider Generation tariffs. They can be positive or negative. Annual load factors are used in the calculation of these charges. For batteries without three years of historical data, the generic Annual Load Factor (ALF) is 3.89% (NESO 2025/26 Final TNUoS Tariffs, Table 27) — the value carried in the April forecast. After three years of operation, the battery’s actual operational ALF is used instead.
Transmission-connected assets that import during triad periods will also be subject to half hourly demand tariffs (see figure above).