BSUoS
What is BSUoS?
You will not spot BSUoS as its own line on most business electricity bills, yet it is quietly baked into the rate you pay. It stands for Balancing Services Use of System, and it covers the cost of keeping the grid in perfect balance second by second, something the system operator does on your behalf every minute of the day. For years it was one of the most unpredictable costs in the market. A 2023 reform changed that, and understanding what changed helps you read your contract properly. Here is what BSUoS is and why it matters to you.
On this page
BSUoS is a network-related cost, not a supplier margin. It funds the real-time balancing of the grid, it is set by the system operator, and since April 2023 it has been a fixed, predictable tariff charged only to electricity demand.
What BSUoS is
BSUoS, the Balancing Services Use of System charge, is the cost of keeping electricity supply and demand balanced in real time. Electricity cannot be stored at grid scale in any meaningful quantity, so the amount generated has to match the amount used at every instant. The National Energy System Operator, NESO, does that balancing, and BSUoS is how the cost of doing it is recovered from the market.
It is not a profit line for your supplier and it is not something they invented. It is a genuine industry cost that every electricity user contributes to, passed through to you as part of your rate.
What it pays for
To keep the system balanced, NESO buys and sells a range of balancing services minute to minute. BSUoS recovers the cost of things like:
- Balancing actions in the wholesale market, paying generators to turn up or down at short notice.
- Reserve and response services that stand ready to cover sudden gaps or frequency changes.
- Constraint costs, paying generators to reduce output when part of the network is congested and paying others elsewhere to make up the difference.
These are real operational costs, and they can swing sharply with weather, demand and network conditions, which is what once made BSUoS so hard to predict.
How it is charged
BSUoS is charged in pounds per megawatt hour (£/MWh) of electricity. Your supplier pays it to NESO based on how much electricity its customers use, then recovers it from you through your contract. Because it is levied per unit of consumption, the more electricity your site uses, the more BSUoS it contributes, which is why it matters more to larger users.
The 2023 reform explained
Two code changes came into effect on 1 April 2023 and reshaped BSUoS:
- Charged to demand only. Under the change known as CMP308, BSUoS is now recovered solely from final demand, that is, electricity consumed, rather than being split between generators and demand. Generators no longer pay BSUoS directly.
- A fixed, known-in-advance tariff. Under CMP361, BSUoS became an ex-ante fixed tariff, set in advance for fixed periods (running in roughly six-month blocks, April to September and October to March) with long notice of the rate.
In plain terms, BSUoS went from a volatile figure that could only be known after the event to a fixed rate published ahead of time. That makes it far easier for suppliers to price and for you to plan around.
A worked example
Say the fixed BSUoS tariff for a period is around £5/MWh, and your business uses 200,000 kWh a year, which is 200 MWh. Your annual BSUoS contribution would be roughly:
200 MWh × £5/MWh = £1,000 a year.
Example only. The BSUoS tariff changes each period and your usage will differ, so treat this as illustrative rather than a quote.
On a fixed contract you would not see that £1,000 broken out, it is folded into your unit rate. On a pass-through contract it could appear as its own line.
BSUoS on fixed vs flexible contracts
How you experience BSUoS depends on your contract type:
| Contract type | How BSUoS is handled |
|---|---|
| Fixed / fully bundled | BSUoS is included in your unit rate. You pay one all-in price and the supplier absorbs the tariff changes within the fixed term. |
| Pass-through / flexible | BSUoS is passed to you as a separate line at the actual tariff, so it moves when the published rate changes at each period. |
Neither is automatically cheaper; a fixed contract buys certainty, a pass-through contract exposes you to the rate but removes the supplier’s risk premium. The reform narrowed the gap by making the underlying tariff predictable.
Why it used to be so volatile
Before the reform, BSUoS was calculated after each settlement period from the actual balancing costs, and those costs spike when the system is tight, on still, cold evenings, during network faults, or when demand is unexpectedly high. That meant suppliers had to guess the figure in advance and build in a risk buffer. Businesses on pass-through deals sometimes saw sharp swings from month to month. Fixing the tariff removed that guesswork, which is the main practical benefit of the change.
How it shows up on your bill
On most fixed business electricity contracts, BSUoS is invisible, it sits inside the unit rate alongside wholesale, network and policy costs. On a pass-through or half-hourly contract it may be itemised, often grouped with other non-commodity charges. If you want to see it, a bill validation can separate out the balancing element so you understand what share of your rate it represents.
Can you reduce your BSUoS?
BSUoS is a per-unit charge, so the honest answer is that the main lever is using less electricity overall, there is no special exemption to claim. Because it is now a fixed published tariff, you also cannot time your usage to dodge a high-cost half hour the way some large users once tried to. What you can do is make sure the BSUoS built into a fixed quote is fair, and that a pass-through contract is applying the correct published rate rather than an inflated estimate. That is where comparing suppliers and validating bills earns its keep.
What it means for your business
For most businesses, BSUoS is a cost to understand rather than fight. Know that it funds real-time grid balancing, that since 2023 it is a fixed and predictable tariff on your consumption, and that it is bundled into your rate on a fixed contract or itemised on a pass-through one. When you review your business electricity contract, the useful question is not how to remove BSUoS but whether the whole non-commodity element of your rate is priced fairly. A periodic bill check confirms you are being charged the correct published tariff and nothing more.
Frequently asked questions
What is BSUoS?
BSUoS, the Balancing Services Use of System charge, is the cost of keeping electricity supply and demand balanced in real time. The system operator, NESO, does that balancing, and BSUoS recovers the cost from electricity users through their supplier.
What does BSUoS pay for?
It funds real-time balancing of the grid: balancing actions paying generators to turn up or down, reserve and frequency response services, and constraint costs when part of the network is congested. These are genuine operational costs, not supplier margin.
How is BSUoS charged?
In pounds per megawatt hour of electricity used. Your supplier pays it to NESO based on its customers’ consumption, then recovers it from you through your contract. The more electricity you use, the more BSUoS you contribute.
How did the 2023 BSUoS reform change things?
From 1 April 2023, BSUoS became a fixed tariff set in advance for roughly six-month periods, and is now charged only to demand rather than to generators. It went from an unpredictable after-the-event cost to a known, published rate.
Who pays BSUoS now?
Since the 2023 reform, BSUoS is recovered solely from final demand, meaning electricity consumed by users. Generators no longer pay it directly, so it now falls entirely on the demand side and reaches you through your supplier.
Is BSUoS fixed or variable?
Since April 2023 it is a fixed, ex-ante tariff, published ahead of each period rather than calculated after the event. This removed most of the volatility that used to make it hard to forecast.
Do I see BSUoS on my bill?
Usually not on a fixed contract, where it is bundled into your unit rate. On a pass-through or half-hourly contract it may be itemised, often grouped with other non-commodity charges. A bill validation can separate it out.
How much is BSUoS?
It is set as a fixed tariff in pounds per megawatt hour, which changes each period. As an illustration only, at around £5/MWh a business using 200 MWh a year would contribute roughly £1,000. The actual tariff and your usage will differ.
Can I reduce my BSUoS charges?
There is no exemption to claim, so the main lever is using less electricity overall. Because it is now a fixed published tariff, you also cannot time usage to avoid a high-cost period. You can make sure a quote or bill applies the correct rate.
Is BSUoS the same as TNUoS?
No. BSUoS covers the real-time cost of balancing the system. TNUoS is a separate charge that recovers the cost of building and maintaining the high-voltage transmission network. Both are network-related costs inside your rate.
Why was BSUoS so volatile before?
It used to be calculated after each settlement period from the actual balancing costs, which spike when the system is tight. Suppliers had to guess it in advance and add a risk buffer, so pass-through customers saw sharp swings. Fixing the tariff removed that.
Does BSUoS apply to small businesses?
Yes, indirectly. Every electricity user contributes to BSUoS through their rate, though on a small fixed contract it is invisible inside the unit price. It matters more to larger users because it is charged per unit of consumption.
What is the difference between fixed and pass-through BSUoS?
On a fixed contract the supplier includes BSUoS in your unit rate and absorbs tariff changes during the term. On a pass-through contract you pay the actual published tariff as a separate line, so it moves at each period.
Who sets the BSUoS tariff?
NESO, the National Energy System Operator, sets the fixed BSUoS tariff under the industry charging arrangements, publishing rates in advance for each period. The reform was implemented following an Ofgem decision.
Is BSUoS a policy cost or a network cost?
It is best thought of as a network-related operational cost. It sits in the non-commodity part of your bill alongside transmission and distribution charges, separate from wholesale energy and from environmental policy levies.
Network operator charging statements (neso.energy) · Ofgem network charging guidance (ofgem.gov.uk)