Our new approach to inertia and other stability services

National Grid ESO has just outlined a new approach to managing some key characteristics of the electricity system. Central to this approach will be the way we control one of the most important things keeping the system stable: inertia. Here’s our head of networks, Julian Leslie, to explain what that means – and why it’s key for our zero carbon targets.

First things first – what is inertia? 

If you look in the dictionary, inertia is defined as an object’s tendency to continue in its existing state of rest or motion. In other words, it stays still if it’s still, or keeps it moving if it’s moving. For moving objects, only an external force (like friction) will make it stop. 

This makes inertia incredibly important to the stable operation of the electricity system. Many generators producing electricity for the grid have spinning parts – they rotate at the right frequency to help balance supply and demand, and can spin faster or slower if needed. 

The kinetic energy ‘stored’ in these spinning parts is our system inertia. If there’s a sudden change in system frequency, these parts will carry on spinning – even if the generator itself has lost power – and slow down that change (what we call the rate of change of frequency) while our control room restores balance. 

Inertia behaves a bit like the shock absorbers in your car’s suspension, which dampen the effect of a sudden bump in the road and keep your car stable and moving forward.

Read our announcement in full: ESO outlines new approach to stability services

What’s different about our new approach to inertia? 

Traditionally inertia has been provided by the spinning power of big coal and gas-fired generators. But this means inertia is a by-product of burning coal and gas. Renewables like wind and solar don’t synchronise with the grid in a way that provides inertia, so as the older coal and gas plants come off the system we need to find new ways to provide stability. 

With our new approach, either new assets or existing infrastructure that has been modified, will draw energy from the grid to power their turbines and create inertia – rather than inertia being a by-product of producing electricity. So the same generators can continue providing inertia for the system, but with dramatically reduced need to burn fossil fuels. 

This is a world-first initiative, will save millions for the consumer, and marks another significant step towards us meeting our ambition to be able to operate the electricity system carbon free by 2025. We’re looking forward to moving onto the second phase of our stability pathfinder, and continuing the transformation of our system to ensure reliable, affordable energy for Great Britain.