Mandatory and Commercial Frequency Response (MFR/CFR)
We are starting a major reform of these services and welcome your input. Please see the Future of Frequency Response section for more information.
Frequency Response is an automatic change in active power output in response to a frequency change. This helps us to keep frequency within statutory and operational limits.
Depending on their size and location, a power station may be obliged to have the capability to provide Frequency Response. Provision under this obligation is known as Mandatory Frequency Response, or MFR. This requirement will be set out in their connection agreement and is summarised under Technical Requirements.
Providers able to offer Frequency Response over and above their obligations may enter into a bilateral agreement with NESO, known as a Commercial Services Agreement, or CSA, to give NESO access to this additional capacity. This additional capacity is called Commercial Frequency Response, or CFR. It is also sometimes referred to as Mode B.
The obligation to provide MFR is set out in the Grid Code (CC 8.1/ECC 8.1)
The process for provision of MFR or CFR is set out in the CUSC (Section 4.1.3)
Providers of MFR and CFR submit capabilities as part of pre-qualification, and holding prices on a monthly basis. These are available below.
We are starting a major reform of these services and welcome your input. Please see the Future of Frequency Response section for more information.
Generators submit their own prices for holding payments on a monthly basis via the Frequency Response Price Submission System (FRPS).
FRPS is available between the 5th and 15th working day of each month. Previously submitted prices are published on our website.
Providers of MFR are required to have the following technical capabilities:
They must have a 3 to 5 per cent governor droop characteristic. Droop is defined in the Grid Code CC6.3.7 (C)(ii)) as: "The ratio of the steady state change in speed in the case of a Generating Unit, or in Frequency in the case of a Power Park Module, to the steady state change in power output of the Generating Unit or Power Park Module.”
They must be capable of providing continuous modulation power responses via synchronised generation through their automatic governing systems in order to counter frequency changes.
The requirements for MFR provision are summarised in the table below :
| NESO | Scottish Power | Scottish Hydro Electricity Transmission | |
|---|---|---|---|
| Small | < 50 MW | < 30 MW | < 10 MW |
| Medium | 50 MW =< 100 MW | N/A | N/A |
| Large | => 100 MW | => 30 MW | => 10 MW |
Providers with an obligation to provide MFR (see Technical Requirements) will go through testing and accede to the relevant agreements as part of the connections process. This will result in the creation of a Mandatory Services Agreement (MSA).
Providers interested in providing CFR should contact their Customer Account Manager to begin the process of creating, or enhancing, a CSA.
Providers can offer one or more of the following categories of response. In the case of MFR, the volumes provided must be sufficient to meet the governor droop requirements (see Technical Requirements)
Primary response: Low frequency response provided within 10 seconds of an event, which can be sustained for a further 20 seconds.
Secondary response: Low frequency response provided within 30 seconds of an event, which can be sustained for a further 30 minutes.
High frequency response: High frequency response provided within 10 seconds of an event, which can be sustained indefinitely.
Frequency Response Price Submission Calendar
Submitted prices and capabilities
Frequency response volumes
Settlements Frequency Data
The documents below contain weekly minute by minute frequency data.
| Name | Published Sort ascending |
|---|---|
| 2025-26 Average Frequency | 18 Jun 2025 |
| 2024-25 Average Frequency | 26 Mar 2025 |
| 2023-24 Average Frequency | 3 Apr 2024 |
Frequently Asked Questions
We have put together a bank of frequently asked questions about the mandatory services. This document will be updated as necessary, so please continue to check back on this page. All information is correct as of the publication date and may be subject to future updates and changes.
Download our Mandatory Frequency Response (MFR) document
*Last updated 16 January 2025.
If you can’t find the answers you’re looking for, please submit an enquiry via the following email address: [email protected]
Further enquiries
Get in touch with the right team within Balancing Services, who are on hand to answer any questions you may have.