What is inertia?
A simple definition of inertia is that it’s an object’s tendency to continue in its existing state of rest or motion.

So things that are not moving need a force – like a gust of wind – to get them moving, while things that are moving will keep moving unless a force, like friction, causes them to 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. 

How is inertia produced? 

Inertia is a by-product of coal and gas-fired generators so sometimes we have to switch on coal when we don’t need to, so we can get more inertia. 

But we’re looking at ways to generate inertia in other ways as part of plans to build a zero carbon grid. 

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.  

A new approach to inertia? 

At the ESO, we’re looking at a new approach – using either new assets or existing infrastructure that has been modified, to 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.  

Hear from our Head of Networks, Julian Leslie, who talks more about how inertia will help us move towards our zero carbon 2025 ambition.