What is reserve power?

Reserve power is extra electricity that NESO (National Energy System Operator) can call on when supply and demand fall out of balance. It acts as a backup to keep the system running smoothly when unexpected events occur, such as a sudden increase in demand or a generator outage.NESO secures reserve services so it can quickly add more power to the system when needed.

What is reactive power?

Reactive power helps NESO (National System Operators) maintain voltage at safe and stable levels across the electricity system. Generators and other assets can be instructed to: Absorb reactive power to reduce voltage Produce reactive power to increase voltage This keeps voltage within its required range and supports reliable system operation.

What are pathfinders?

Pathfinders are trial-market projects developed by NESO (National Energy System Operators) to explore new solutions for emerging system challenges. These challenges often relate to stability, voltage management, or the increasing share of renewables. Each Pathfinder tests innovative technologies that can deliver essential services, such as inertia or reactive power support. The findings help shape future commercial markets.

Valuing Ancillary Services: GB and beyond

Energy transition Power insights

Chris Matson Partner

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Gurpal Singh Ruprai Principal

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Lydia Davies Associate Consultant

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Max Albert Energy Modelling Associate Consultant

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01 January 2026

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Navigate the complex and evolving world of ancillary services with confidence.

The Great Britain (GB) power market is undergoing a fundamental transformation, driven by the shift towards net zero. The security and stability of the grid rely heavily on a complex and evolving suite of Ancillary Services. These critical functions, procured by the National Energy System Operator (NESO), represent significant revenue opportunities for generators, battery owners, and flexible assets.

Whether you're a power generator, developer, or investor, this report helps you:

Understand the full range of ancillary services available in GB and six European countries.
Identify historic and emerging revenue streams.
Access 5 years of market value and pricing data across each service.
Stay ahead of the curve with insights into live, legacy and future services.

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Market insights for reserve power

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Market value highlights for reactive power

We break down the financial opportunity behind the services:

£232.6m

Fast Reserve peak market value (2021/22)
1,700MW

STOR requirement from April 2025
£128m

Fast Reserve value in 2024/25 (declining as Quick Reserve phases in)
Super SEL

Service now retired, with just £0.01m spent in 2024/25

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Read previous editions

The April 2025 update of the report including the shifting procurement strategy for Balancing Reserve to target high-value periods. This detailed analysis is essential for any participant looking to understand the future direction of system security and revenue opportunities within the reserve market.

Valuing Ancillary Services: GB and Beyond - Power Insights

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Your questions answered

: Reserve power is extra electricity that NESO (National Energy System Operator) can call on when supply and demand fall out of balance. It acts as a backup to keep the system running smoothly when unexpected events occur, such as a sudden increase in demand or a generator outage.
NESO secures reserve services so it can quickly add more power to the system when needed.

Reactive power helps NESO (National System Operators) maintain voltage at safe and stable levels across the electricity system.

Generators and other assets can be instructed to:

Absorb reactive power to reduce voltage
Produce reactive power to increase voltage

This keeps voltage within its required range and supports reliable system operation.

: Pathfinders are trial-market projects developed by NESO (National Energy System Operators) to explore new solutions for emerging system challenges. These challenges often relate to stability, voltage management, or the increasing share of renewables.

Each Pathfinder tests innovative technologies that can deliver essential services, such as inertia or reactive power support. The findings help shape future commercial markets.