How we balance the electricity transmission system

When we watch television, turn the lights on or charge our smartphone, we rely on electricity that has passed across the high-voltage electricity transmission network.

We are responsible for managing the flows of electricity to homes and businesses on a real-time basis. Once electricity is generated and enters our network, our job is to ‘balance’ the network, ensuring supply and demand are matched second by second.

Balancing the system to make sure that demand is met by supply is one of the most important things we do, and it is becoming more challenging as intermittent generation – such as wind power – becomes a bigger part of the overall energy mix.

How we do it

As we continually work to balance the system, we can ask generators of all kinds – not just wind farms – to come on or off the grid to help us balance supply and demand, or to manage ‘constraints’ – effectively bottlenecks – in the network.

This is something we do many times every day and have done for many years. It is a normal part of our job, and we have a number of well-proven tools to help us do it, including buying generation onto or off the network one or two days ahead of real time, and bids on the balancing mechanism within one or two hours of when the energy is needed.

Our demand forecasting team is always planning ahead, so we can make sure there is enough backup power available to cover any potential shortfall, whether that’s due to a power station breakdown or an unexpected event.

For instance, in very high winds, many wind farms will shut down their turbines for their own protection, often automatically. When that happens, we can use our backup generation to balance the system. Sometimes it works the other way too.

Balancing up the costs

There is a cost in this balancing activity, but it is very low for consumers - no more than a few pence a year on a typical electricity bill. As part of a ‘balancing mechanism’, each power station makes a ‘bid’ that reflects what they are willing to be paid – or to pay – to be taken off or moved on to the network. Ofgem regulates these balancing costs and gives us incentives to keep them down.

The balancing costs are made up of a number of elements and one of these is constraint costs. Wind constraints reduced because of the investment made in reinforcing the transmission network. The reinforcements increase the capacity to transport more energy, but while doing the work, we need to take parts of the network out of service which reduces the capacity and leads to us needing to constrain some energy in the interim.

Of course, more generation is connecting to the system so there will continue to be outages to aid the investment of new transmission infrastructure, which means we will still be managing wind constraints but not proportionally to the capacity of installed wind.

Adapting for the future

We expect that new technology, from smart meters to innovative forms of electricity storage, could offer new opportunities for large and small consumers to help us balance the system.

We also carry out a number of consultations to give the rest of the industry an opportunity to contribute to the debate.

Frequently asked questions (FAQs) about balancing

What is ‘balancing’?

Unlike gas, electricity can’t be stored in large quantities. As a result, part of National Grid’s role involves making sure that demand and supply match up. We do this on a minute-by-minute basis. It’s a bit like trying to keep a car at 50mph while driving up and down hills. 

Balancing is sometimes used for other reasons, too, such as a sudden surge in demand during a televised sporting event, or if a power station suddenly stops generating because of a technical problem. 

What role do power stations play?

The energy suppliers who provide electricity to consumers and businesses buy energy from the power stations. The power stations then tell us how much electricity they are going to feed into the network. To balance the network we can request more or less generation in the hour leading up to real-time. 

What is a ‘constraint’?

Effectively it’s congestion in the transmission system – like a traffic jam – that prevents surplus power being transmitted to other parts of the country when there isn’t enough demand to use it. This might happen, for instance, if it’s very windy over several days and wind farms are producing much more energy than usual, or if demand is much lower than usual.

Why do you ask generators to come on or off the grid?

We do this to help us manage the constraints of the network when the power being generated is greater than the demand. It’s one of the tools we use to balance the system, and we’ve done this for many years. We do it through the ‘balancing mechanism’ or through direct contracts with power stations. 

What is the ‘balancing mechanism’?

Great Britain has a free energy market that is open to competition in generation and supply. A balancing mechanism was introduced in 2001 as part of a new trading arrangement, agreed by the Government and the regulator. Each power station makes a ‘bid’ that reflects what they are willing to be paid – or to pay – to be taken off or moved on to the network.

What is ‘intermittent generation’?

This phrase describes a power source that doesn’t produce a constant amount of energy. The most obvious of this type is energy generated by a wind farm, which will vary according to how windy it is. Sometimes there will be very little wind, and sometimes the wind will be too strong and the turbines will shut down automatically for their own protection.

How do you forecast wind power?

We have an electricity demand forecasting team, which uses its knowledge and various tools to predict what demand will be. 

What backup reserves does National Grid have?

Backup generation is used day-in, day-out to balance the system, to cover for power station breakdowns, forecasting errors and for unexpected events. In the past, we’ve seen periods when the level of electricity generated from wind within the UK, Ireland, and parts of Northern Europe has been very low. This can coincide with days of peak electricity demand when it’s cold and still. The cost of using backup generation is part of the total cost of balancing the system.