Emergency Assistance: what it is, and why we used it over the last week

Keeping Great Britain's electricity system secure is a core responsibility at NESO. Every day, we balance electricity supply and demand in real time, ensuring homes and businesses continue to receive the power they need.

This week, NESO issued two requests for Emergency Assistance. While the term can sound alarming, it is an established tool used by our control room and other system operators.

What is Emergency Assistance? 

Emergency Assistance is a precautionary measure used when additional support is needed to maintain system security. It provides extra flexibility when conditions are tighter than expected; it does not mean supplies have been lost or customers face immediate disruption.

Generation, demand and network availability change throughout the day, sometimes at short notice. NESO does not own power stations, transmission infrastructure or interconnectors; our role is to operate the system using the generation and network capacity available. When conditions change, Emergency Assistance is one of the tools we can use to keep the system secure.

What happened on Friday? 

We expected net imports to fall by around 700MW, with exports reducing power in the south by 1,200MW while imports in the north increased by around 500MW.

This left us needing around 400MW of additional power in the south. Ordinarily, excess generation elsewhere on the system could help meet that need, but constraints on the transmission network meant we could not move enough of the electricity already being produced in the north to where it was needed in the south.

We responded by instructing all the generation the market could make available in the affected area. This included around 400MW of generation and batteries running at full output – the amount we required. However, during this period we saw wind generation reduce quickly, falling by around 20MW every minute. This sudden drop in wind caused system frequency to fall, lower than we would have liked, but it remained above the statutory limit.

Our control room temporarily increased flows across parts of the network above normal constraint limits while reassessing them in real time—something we can do safely when conditions allow. We also requested Emergency Assistance from France, increasing electricity available in the south, helping to restore frequency and reducing flows across the constrained network. Given the conditions and generation available, this was the most effective option.

What happened on Monday? 

Monday was a different event, with the challenge driven by network constraints.

Transmission infrastructure in the South East that had been expected to return to service did not and remained unavailable. This was outside NESO's control and reduced the amount of electricity that could be transferred into the South East, creating a constraint similar to the one we experienced on Friday.

Great Britain had not run out of electricity: generation was available elsewhere, but network constraints prevented enough power reaching London and the surrounding region.

To maintain the balance between supply and demand and keep the system secure, we requested Emergency Assistance on an interconnector. We initially instructed 700MW. As demand increased throughout the day and the network constraint continued, a further 500MW was required to ensure transmission assets remained within their normal operating limits, bringing the total volume of Emergency Assistance to 1,200MW.

Why does this matter? 

In both cases, changing market conditions and network availability created operational challenges. We identified them and used the Emergency Assistance tool, alongside other measures, to maintain a secure and reliable system.

These requests are relatively uncommon but that is why the capability is valuable in a dynamic electricity system.

NESO's role is to operate the system as it exists on the day, using the tools available to keep electricity flowing securely across Great Britain.