title: "BSUoS Charging Methodology" type: wiki updated: 2026-04-10 tags: [neso, bsuos, balancing-costs, system-operation, cusc] canonical: ~/knowledge/sources/neso/bsuos-charging-methodology.md

BSUoS Charging Methodology

What BSUoS Is

Balancing Services Use of System (BSUoS) is the charge through which NESO (National Energy System Operator) recovers the day-to-day costs of balancing the GB electricity transmission system. Every time NESO adjusts generation up or down to keep supply and demand in balance, or pays for standby services to manage the network within physical limits, those costs flow through to BSUoS and ultimately to consumers via their electricity bills.

Legal basis: CUSC Section 14 (paragraph 14.31), underpinned by the Transmission Licence and Electricity Act 1989.

What BSUoS Recovers

BSUoS is a catch-all cost pool. Main components:

• Constraint costs: paying Scottish wind to reduce output when the B6 boundary (Scotland-England interconnect) is congested, and compensating English thermal plant to run instead. The dominant and fastest-growing component.
• Balancing Mechanism actions: bids and offers accepted after gate closure to resolve residual imbalance
• Frequency response and reserve: contracted services (dynamic frequency response, fast reserve, STOR) to cover unexpected generation or demand deviations
• Black start: standby contracts with generators able to restart the grid from a complete blackout
• Other ancillary services: reactive power, inertia, voltage management
• NESO operating costs: control room, scheduling, and forecasting

The April 2023 Reform

Two CUSC modifications took effect simultaneously on 1 April 2023, fundamentally restructuring BSUoS.

CMP308 - demand-only charging: Before April 2023, both generators and demand paid BSUoS on a half-hourly volumetric basis (roughly 50:50). CMP308 removed generators entirely. All recovery now falls on Final Demand (suppliers passing costs to customers, and directly-connected transmission demand sites). The demand-side unit rate approximately doubled in size, but the overall cost to consumers was expected to be broadly neutral: generators, no longer bearing the charge, reduced their wholesale offer prices proportionally.

CMP361 - fixed ex-ante tariff: Before April 2023, the charge was settled post-delivery with high volatility. CMP361 replaced this with a fixed six-monthly tariff published nine months in advance (summer tariff April-September, winter tariff October-March). Suppliers know the charge before entering forward energy contracts, removing the risk premium they previously had to build in. If outturn costs differ from forecast, the difference is smoothed across future periods rather than passed through immediately.

Constraint Costs as the Dominant Driver

Constraint costs at the B6 boundary have become the central BSUoS cost story:

• 2022/23: approximately 44% of total balancing costs
• 2024/25: approximately 71% of total balancing costs, reaching approximately £1.9bn
• Wind curtailment payments in 2023: approximately £920m
• Business-as-usual projections suggest costs of approximately £2.2bn at the B6 alone by 2030

This reflects the structural mismatch between where wind generation is built (Scotland) and where demand sits (England), with transmission capacity lagging behind generation growth. NESO's Constraint Management Pathfinder targets approximately £200m in annual savings through smarter use of existing network capacity.

Approximate Annual Costs

Total BSUoS recovery (all balancing costs, demand-side only post-2023):

The 2022/23 spike reflects elevated wholesale energy prices inflating BM offer prices, not only constraint costs.

How BSUoS Interacts with CfDs

Under pre-reform CfD standard terms, generators held a BSUoS uplift in their strike prices, compensating them for the charge they paid. When CMP308 removed the generator obligation, the CfD mechanism required adjustment:

• AR4 contracts and earlier had strike prices adjusted downward at the annual strike price adjustment, using a reference period (October 2020 to September 2021) to calculate the uplift to remove
• AR5 and later contracts were written without a BSUoS uplift, as generator exemption was already in place

Under the pre-reform half-hourly regime, CfD generators faced a basis risk: their BSUoS exposure peaked at the same times as their output (high wind = high generation = high constraints = high BSUoS). Removing generator BSUoS eliminated this correlation, simplifying CfD economics.

Quarterly and Six-Monthly Fixed Tariff Mechanism

The CMP361 tariff is set twice yearly. NESO:

1. Publishes an initial forecast each June
2. Publishes draft tariffs each September
3. Publishes final tariffs each December, effective from the following April and October

The tariff is set by forecasting total expected balancing costs (using forward commodity prices and constraint projections), then dividing by expected demand volume (estimated via linear regression on NESO's national demand forecast). The result is a flat £/MWh rate applied to all metered demand.

Representative published tariffs: - April-September 2024: approximately £7.63/MWh - October 2026-March 2027 (draft): approximately £11.93/MWh

BSUoS currently represents approximately 6% of a typical business energy bill.

Relationship to REMA

Constraint costs are the fastest-growing BSUoS component, and their reduction would be the primary transmission benefit of locational electricity pricing. Zonal pricing would have placed a lower price on electricity in areas with excess generation (Scotland), signalling generators and demand to locate where the grid is less stressed - reducing the volume of constraint actions NESO takes and therefore reducing BSUoS.

In July 2025, the government rejected zonal pricing, opting for Reformed National Pricing with supplementary measures including long-term contracts to incentivise demand to locate behind constraints (including data centre demand) and transmission investment to expand B6 capacity. Whether these measures reduce constraint costs materially will show up directly in future BSUoS tariffs.

Key Documents

• CUSC Section 14: https://www.neso.energy/document/301931/download
• NESO BSUoS charges page: https://www.neso.energy/industry-information/charging/balancing-services-use-system-bsuos-charges
• BSUoS fixed tariff model methodology: https://www.neso.energy/document/262041/download
• CMP308 modification: https://www.neso.energy/document/204451/download
• CMP361 modification: https://www.neso.energy/industry-information/codes/cusc/modifications/cmp361-cmp362-bsuos-reform-introduction-ex-ante-fixed-bsuos-tariff-consequential-definition-updates
• NESO Annual Balancing Costs Report (2025): https://www.neso.energy/document/362561/download
• BSUoS tariff data portal: https://www.neso.energy/data-portal/bsuos-fixed-tariffs/_balancing_services_use_of_system_charges_bsuos_tariffs