National Grid ESO – Electricity National Control Centre Hi Res
What are system notices?
Everything you need to know about the different types of system notices and why we issue them.

As Great Britain’s electricity system operator, it’s our job to keep the lights on. We don’t create or sell electricity – there’s an electricity market where that happens.

Our role is to move it around the country from where it’s generated to where it’s needed.

To do this, we make sure the supply of electricity from the market always matches demand. It’s what we call ‘balancing’ the system, and it’s all managed in our national control room.

Our control room experts have a set of tools at their disposal to help make this happen – the main one being the balancing mechanism – but it requires continuous communication with the electricity market, where the electricity is being created.

System notices can sound serious, but they're a routine way that we operate the system and they don't mean electricity supply is at risk

This might mean asking generators to turn power up or down. Or we might ask them to increase or decrease demand.

Because our analysts are constantly forecasting how much electricity will be needed at a given time – and providing this forecast to the market – normally only small adjustments will need to be made to match supply with demand.

If demand or generation don’t happen as we forecast, we may have too much power or not enough power on the system at a given time.

Occasionally, if we’re not able to match supply and demand through the normal mechanisms, we’ll send a more formal message to the electricity market to let them know.

These messages are sometimes referred to as system warnings or notifications.

While that sounds quite serious, these notices are a routine way that we communicate to the market and operate the system, and they don’t mean that electricity supply is at risk.

We’re simply telling the market what we need.

What are the main notices we might issue, and why?

National Grid ESO - Electricity Control Centre

Electricity demand in Great Britain has been impacted by COVID-19 – and in particular by the lockdown measures put in place. We saw around a 20% drop in demand over spring and summer 2020, an unprecedented change.

It’s just as important for us to manage the lower demands for electricity seen over summer as it is to manage winter's peak demands. It's a different set of challenges that we plan for, and are used to dealing with.

At times of low demand, or in periods where less controllable generation connected directly to distribution networks makes up more of the supply, we might identify that we need some additional flexibility on the system.

We may issue what we call a Negative Reserve Active Power Margin (NRAPM) notice. It’s a way to tell power stations that we might need them to turn down output to retain our safety margin, and we’d expect them to respond. NRAPM notices are rare – a small number of local NRAPMs have been issued, and none at a national level.

Likewise, there may be times when we’d like providers to be able to increase output.

If we can see that our normal safety margin for operating the system is not as big as we’d like, and we can’t address it through the normal mechanisms, then we would consider issuing an Electricity Margin Notice (EMN).

This doesn’t mean we don’t have enough electricity to meet demand; it just means we’d like a larger cushion of spare capacity, and we want the market to provide it.

EMNs are issued by our control room using operational and engineering judgements based on our experts’ experience, skill and knowledge of managing the electricity system.

If our safety margins for operating the system are reduced, a Capacity Market Notices (CMN) might also be issued.

Unlike EMNs (which are issued manually) CMNs are based on specific industry data and are triggered automatically four hours in advance when our safety margin falls below a certain point.

The CMN is a reminder to providers in the capacity market to pay closer attention to any notices or instructions that may appear from us.

In extremely rare and unusual circumstances where demand for electricity is greater than the levels of supply available, the margin notices above might be followed by a High Risk of Demand Control (HRDR) or Demand Control Imminent (DCI) notification.

In the unlikely event of us instructing Distribution Network Operators (DNOs) to begin demand control, they might reduce voltage to manage demand without affecting supply, or – in more severe situations – they might temporarily disconnect some consumers for a short period of time to reduce electricity demand on the system.

This is a controlled process managed by the DNOs, and consumers are reconnected at the earliest opportunity.

We have considerable experience and expertise operating the system safely and responsibly in these scenarios. Moving energy industry participants to make sure we can balance supply and demand is our day job, and something we’re accustomed to doing.

Whatever the time of year, you can rest assured that our expert team of control engineers are working 24/7 to keep electricity flowing to where you need it.