Short term operating reserve (STOR)

NESO’s objective is to operate the transmission system economically, and the assessment is made consistent with that.

STOR is procured on a daily basis in an auction for contracts lasting one day. Providers submit their availability prices and MW offering prior to the day ahead auction, which is then cleared to secure firm capacity for STOR for lowest availability cost.

We consider the alternative costs for securing short term operating reserve closer to real time, and will compare all STOR bids against the economic costs of procuring the same volume of reserve from alternative sources.

A STOR bid will only be accepted where we consider that the total costs of securing and operating the system are lower with the bid, than without it.

For further details and examples of how the auction works, you can find the STOR assessment principles in the documents library.

There are three types of payment for the STOR service:

Availability payment

This payment is for being available to provide the service within the committed availability window.

Utilisation payment

This payment is for delivering the service when instructed by us. This includes the energy delivered in ramping up to and down from the contracted volume.

Proof of delivery from metered data, which is taken automatically from the unit or sent to National Energy System Operator via Excel.

Providers submit their prices for the committed availability window and utilisation during the auction.

Optional utilisation payment

Non-BM providers are able to offer STOR outside the defined availability windows. For these optional periods, they can offer optional utilisation prices should we wish to use the service. No availability payments are made for optional periods.

What providers can expect to be paid

Providers submit their own prices for availability and utilisation during the auction. These prices will inform the economic assessment to determine which parties are accepted.

STOR is procured through a daily pay-as-clear auction process for contracts lasting one day. The auction closes at 05:00 for delivery the following service day (05:00-05:00) covering the Firm or ‘Committed Windows’. Providers submit their availability prices and MW offering prior to the auction.  

Committed Windows 

Typically, the service is used over two pre-defined windows: 

• morning window; and 
• evening peak window. 

Providers successful in the daily auction are required to be available to operate at their contracted volume during both these Committed Windows. 

STOR may be required outside of these Committed Windows and providers are able to offer this as an Optional STOR service (only open to non-BM providers). 

There are three types of payment for the STOR service: 

• Availability payment - for being available to provide the service in Committed Windows. 
• Utilisation payment - for delivering the service when instructed by us, covering the energy delivered in ramping up to and down from the contracted volume. 
• Optional utilisation payment - for delivering the Optional STOR service when instructed by us. No availability payments are made for optional periods. 

STOR dispatch 

BM providers will be dispatched through the Balancing Mechanism, while non-BM providers will be instructed and metered through the Platform for Ancillary Services (PAS). 

Daily auction results and the buy curve are published on the Data Portal.

View market information on the Data Portal

STOR daily procurement requirement

STOR daily procurement requirement - January 2023 update

STOR daily procurement requirement - April 2023 update

STOR daily procurement requirement - April 2024 update

STOR daily procurement requirement - July 2024 update

STOR daily procurement requirement - November 2024 update

Both Balancing Mechanism (BM) and non-BM participants with a connection to either the electricity transmission or distribution network are able to provide STOR.

The service is open to any technology with the ability to increase generation or reduce demand by at least 3 MW.

There are particular times of the day when the STOR service is more likely to be required. These are known as ‘committed windows’.

Providers are required to be available to operate at their contracted volume during these windows.

Committed windows

Providers are required to be available to operate at their contracted volume during these windows.

Availability windows

Typically, the service is used over two pre-defined windows:

• morning window; and
• evening peak window.

Optional STOR may be required outside of these times.

STOR dispatch

BM providers will be dispatched through the Balancing Mechanism, while non-BM participants will be instructed and metered through the Platform for Ancillary Services (PAS).