Transmission Use of System charges (TUoS)

As part of their Transmission Use of System Agreement, generators and suppliers agree to certain charges. The Transmission Statement of Charges describes these charges. It includes TUoS charges, along with other system charges for centrally dispatched generators.

TUoS charges are made up of three parts: network charges, system support services and collection agency income requirement.

Network charges are set for using the transmission system to transport electricity. They are levied on both generators and suppliers through monthly invoices. There are two types of network charges in Northern Ireland, GTUoS and STUoS.

Generator transmission use of system (GTUoS)

This charge is calculated based on the Network Capacity Charge Rate (£/MW/month) and the Maximum Export Capacity of the generating unit. All-island GTUoS charges have been in effect since 2011, approved by the Utility Regulator and the CER.

Supplier transmission use of system (STUoS)

STUoS is a charge for each unit delivered through the transmission system at the trading point. It is charged per kWh. The charges are calculated at jurisdictional level. 

STUoS is designed to reflect costs of the Transmission System that are not recovered through the connection charge, the costs of operating, maintaining and reinforcing the Transmission System where connection charges are not applicable, and associated on-costs. They are higher at peak times as demand on the transmission system is also higher.

A charge per kWh for each unit delivered through the Transmission System at the trading point. It is designed to recover the costs of operating the Transmission System, including the costs of ancillary services. This is a flat rate tariff levied only on suppliers. 

This charge relates to the Moyle interconnector. Moyle’s transmission licence allows them to raise revenues from sales of capacity on the Moyle interconnector. It also permits Moyle to recover the balance of its revenue requirements from payments received from SONI.

We collect the CAIRt from suppliers and pay it to Moyle Interconnector Limited. It is allocated across the predicted units transmitted. The amount allocated per trading point depends on the kWh used in each charging period.

Suppliers receive an invoice with the amount charged for CAIRt.

OSCs are intended to incentivise the optimum performance of generators connected to ensure efficient use of the power system. This is detailed on our System Services page.

If you have a question about TUoS charges, please get in touch.