Transmission Use of System Charges (TUoS)

Suppliers and Generators seeking to use the Transmission System will be required, prior to using the Transmission System, to enter into a Transmission Use of System Agreement (TUoSA) with SONI setting out the ‎‎obligations of both parties.

Also before a Supplier or Generator can participate in the Single Electricity Market (SEM) the TUoSA must be signed by both the TSO and Supplier/Generator.

For more information on registering in the SEM please visit the SEM registration page.

The Transmission Statement of Charges which is published annually (see documents section) describes the charges for use of the All-Island Transmission Networks in respect of generation and supply in Northern Ireland and also sets out Other System Charges in respect of centrally dispatched generators in Northern Ireland.

Transmission Use of System charges are designed to recover the NIE Networks' Transmission Revenue Entitlement as approved by The Utility Regulator. The Transmission Revenue Entitlement is calculated as a percentage of NIE Networks' Transmission and Distribution Entitlement which includes costs such as return on assets, depreciation of assets and operating expenditure.

Currently 75% of the Transmission Revenue Entitlement is recovered from Suppliers via the charges set out in Schedule A of this Charging Statement. The remaining 25% of the Transmission Revenue Entitlement is recovered from Generators through the Generator export charge.

Transmission Use of System (TUoS) charges comprises of three parts:

  1. Network Charges
  2. System Support Services
  3. Collection Agency Income Requirement


SONI Transmission Use of System Charging Statement 2020/21

TUoS Statement of Charges 2019-20

To view previous tariff years please visit the publications centre.

Contact Us

For TUoS related queries please email