Balancing Service Use of System (BSUoS) costs explained
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The information in this video and article was accurate as of 1 April 2025. We update our TPCs Explained hub every Spring to reflect any changes.
What’s BSUoS?
Balancing service use of system, or BSUoS, charges recover the cost of the day-to-day operation of balancing the electricity transmission system. These operational costs also include system security features such as back-up and reserve power for the grid.
What do BSUoS costs cover?
The day-to-day management of the GB transmission system includes automated and manual triggers that are constantly working to keep everything in balance. These triggers might include requests by the National Energy System Operator (NESO) to generators, storage operators, or consumers to increase or decrease generation or demand.
Such requests come as a result of imbalances or physical constraints on the system, or for other reasons. These include the need for:
- Reserve power, to cover any unexpected losses by the biggest generators on the system
- Back-up power for a so-called ‘Black Start’, to get the GB system up and running again after a complete blackout
- Other services, to support certain essential electrical characteristics on the network such as inertia or voltage management
How are BSUoS costs recovered?
BSUoS costs are recovered on a “pounds per megawatt hour” (£/MWh) basis, with the charge set twice a year – one tariff for the summer and another for the winter.
This seasonal approach has only been in place since 2023, when the Electricity System Operator (ESO, now the National ESO, or NESO) started forecasting and setting the charge in advance.
Naturally, the actual costs of balancing the system vary significantly on a half-hourly basis.
How much of your energy bill does BSUoS account for?
BSUoS is expected to make up around 6% of the total bill in 2025, making it the third largest third party cost.
Will you know about BSUoS costs in advance?
Right now, BSUoS is set nine months in advance. The charges are the same for electricity consumers across all regions and voltage levels – although BSUoS is affected by electrical losses in the system.
From April 2026, however, the Summer tariff will be set three months in advance, and the Winter tariff will be set nine months in advance.
What drives the BSUoS charge?
The four main drivers of the BSUoS charge are:
- Inputs to asset flexibility, such as fuel prices
- The availability of energy sources
- System demand
- System constraints
To learn more about the other TPCs in your energy bill, head to our TPCs explained hub using the button below. Or, to understand more about electricity prices, download our latest bi-annual Electricity Prices Explained guide.
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