Britain's energy operator is betting on an age-old technology to future-proof its grid, as the power plants that traditionally helped stabilise it are closed and replaced by renewable energy systems.

Spinning metal devices known as flywheels have for centuries been used to provide inertia -- resistance to sudden changes in motion -- to various machines, from a potter's wheel to the steam engine.

Grid operators are now looking to the technology to add inertia to renewable-heavy electricity systems to prevent blackouts like the one that hit Spain and Portugal this year.

In an electricity grid, inertia is generally provided by large spinning generators found in coal-fired and gas power plants, helping maintain a steady frequency by smoothing fluctuations in supply and demand.

But renewable energy sources like solar and wind power don't add inertia to the grid, and usually cannot help with other issues, such as voltage control.

Flywheels can mimic the rotational inertia of power plant generators, spinning quicker or slower to respond to fluctuations.

Without rotating turbines, "the system is more prone to fluctuations than it would be otherwise", explained David Brayshaw,........

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