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 and Head of Power

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Gurpal Singh Ruprai Principal - Power Asset Modelling

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Lydia Davies Associate Consultant - Energy Storage

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Max Albert Associate Consultant - Power Model Development

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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.

Read the reserve service extract

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Market insights for reserve services

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Market value highlights for reserve services

We break down the financial opportunity behind the services:

1,800MW

Slow Reserve volume requirement
£54.6m

STOR market value in 25/26, now retired
£135.8m

Fast Reserve value in 25/26, now replaced by Quick Reserve
£4.43/MW/h

Average prices for positive Quick Reserve across 25/26
£3.78/MW/h

Average prices for negative Quick Reserve across 25/26

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Read previous editions

The October 2025 update sets out the review of the Obligatory Reactive Power Service to align remuneration with the evolving energy landscape, alongside a detailed analysis of the 2025 Iberian blackout and key learnings for GB's system. This detailed analysis is particularly valuable for market participants and stakeholders seeking to understand current and future approaches to reactive power procurement, system resilience, and emerging opportunities within ancillary services markets.

Read the October 2025 reactive power extract

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.

Read the April 2025 reserve power extract

Valuing Ancillary Services: GB and beyond

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.