Transmission Network Use of System (TNUoS) charges pay for the operation of the transmission network in Great Britain. The National Energy System Operator (NESO) collects them. TNUoS charges totalled £7.6bn in 2026/27, up 50% from 2025/26. The driver is RIIO-ET3, the new transmission price control that started in April 2026.

Demand customers absorb the bulk of the £2.5bn YoY increase. Limiting Regulation, a retained EU rule, caps the average generation charge at €2.50/MWh of metered output. The average generation tariff therefore fell from £12.73/kW in 2025/26 to £12.12/kW in 2026/27.

For BESS, location decides whether TNUoS is a cost or a credit. TNUoS charges generation where the network is congested and credits it where the network needs more. In 2026/27, the worst zone costs a transmission-connected BESS £6.75/kW per year, and the best zone earns it £7.88/kW.

For questions on this research, contact shaniyaa@modoenergy.com.

Key takeaways