Reserve is needed for frequency management when there is an imbalance between supply of energy and demand for energy.

System conditions are changing, and faster-acting services procured closer to real-time are required to meet three distinct criteria: 

  1. To restore frequency to within statutory limits within 60 seconds.
  2. To recover frequency to within operational limits within 15 minutes.
  3. To respond to transient supply demand imbalances that take pre-fault frequency close to operational limits.

A suite of new Reserve products are being designed to replace the existing suite of positive and negative Reserve products: Short Term Operating Reserve (STOR), Fast Reserve (FR) and Optional Downward Flexibility Management (OFDM).

Slow Reserve, separated into Negative Slow Reserve (NSR) and Positive Slow Reserve (PSR), will be the first of our series of new Reserve products. It is designed to operate post-fault, and aims to provide ESO with access to firm, bi-directional energy to displace large losses on the system and recover frequency to ± 0.2Hz within 15 minutes​.

Further enquiries:

Email: [email protected]

Technical requirements

N.B these are draft technical requirements whilst we are engaging with industry on designing the new services. Service design and procurement strategy will be formalised through an EBR consultation.

Product Criteria​ Proposal​
Pre-/ Post-fault Post-fault
Full Activation Time​ Providers must reach full activation within 15 minutes of instruction​
Maximum Activation Time​ (Non-zero time) A minimum of 120 minutes​
Minimum Activation Time​ (Non-zero time) A maximum of 30 minutes​
Maximum Recovery Period​ A maximum of 30 minutes​
Aggregation rules​ Providers can aggregate units within a GSP Group​
Dispatch Solution​ BM – BOAs / Non-BM - ASDP​
Operational Metering​ 1Hz  ​
Performance Metering​ 1Hz​
Ramp rates​ As per envelope restrictions​
Baselining​ 60-minute nomination baseline​


Latest news

19 May 2023

ESO has come to the decision to delay the delivery of the new Reserve reform products, Slow and Quick Reserve – originally planned for October and November 2023.  As a result, we will not be launching our EBR Article 18 consultation to industry as planned at the end of May.

This decision has been taken in light of the significant changes that would have been required in our existing, legacy balancing systems and processes, given the complexity of the new service designs. In the midst of a complex and rapidly evolving systems change environment, we believe it is more prudent to re-evaluate these changes to consider if implementation into our legacy systems is still appropriate, as opposed to direct implementation into our Open Balancing Platform (OBP).

Postponing the rollout of our new Reserve services grants us the opportunity to re-examine our proposed service designs, evaluate our IT options, and collaborate with you more effectively. This will ensure that the best solutions are delivered and that the necessary updates to our balancing systems are apt for enhancing our operational toolkit and are better aligned with the implementation of our future systems.

In the coming weeks we will be looking to understand the extent to which we review the proposed services designs and IT solutions. We will then communicate how and when we intend to engage with you in this process via the Future of Balancing Services distribution list.

20 April 2023

Last month, we held a webinar on 9 March where we updated industry on our delivery plan and provided a refresh of the services (please refer to the Document Library tab for the documentation and recordings). 

This delivery plan indicated launching our EBR consultation towards the end of April with the dependencies being further exploration of system changes and the quantum of change acceptable to market providers as well as the ENCC. We have also noted the feedback on Crossovers from the market and we are still analysing the most optimal solution for the end consumer. 

As we are still working through these dependencies and feedback, the EBR consultation will be moved provisionally to the end of May. 

We intend to update and confirm our delivery plan for Quick Reserve and Slow Reserve in Future of Balancing Services newsletter. 

Woman looking at phone with glowlines

Further enquiries

Get in touch with the right team within Balancing Services, who are on hand to answer any questions you may have.