Renewables get green light to provide synthetic inertia

Renewable generators have been given the green light to begin providing synthetic inertia to the power grid after a “game-changing” modification to the Grid Code came into effect on Monday (14 February).

National Grid Electricity System Operator (ESO) said they will now be able to participate in its stability pathfinder project – its trial of a new grid stability service incorporating inertia, reactive power and short circuit level.

Inertia refers to the resistance of the electricity system to changes in frequency. This resistance is an inherent characteristic of conventional synchronous generators such as coal and gas plants, with large rotating turbines spinning in harmony with the frequency of the power grid.

Their turbines naturally act as shock absorbers for the electricity system. When there is a loss of load, the kinetic energy stored in the turbines is instantly released onto the grid, preventing a sudden drop in frequency.

The closure of these power stations has led to a decline in inertia, making the power grid more susceptible to disturbances such as plant outages.

The asynchronous generators that have displaced them, such as wind and solar farms, do not inherently provide inertia in the same way. However, their converters can mimic its effects by rapidly changing their output as an automatic response to changes in frequency. This fact-acting frequency response is sometimes referred to as synthetic inertia.

The modification GC0137, which was approved by Ofgem at the end of January, has added a minimum specification to the Grid Code for what the proposal document by the ESO described as “virtual synchronous machine capability”.

The ESO said this “world first” will allow renewable generators as well as interconnectors to compete against synchronous generators to provide inertia as part of its new grid stability service.

Tony Johnson, who led the ESO’s work to introduce the specification, said: “This is a breakthrough moment, a key piece in the energy transition jigsaw, that will ensure we can operate a fully decarbonised grid and deliver on our net zero commitments.

“It’s the culmination of up to 10 years of thinking and working with stakeholders to find the common ground between what equipment is capable of doing and what the system needs.

“It also ensures that as we transition away from conventional fossil fuelled generation, we can operate the grid securely and efficiently, which will ultimately save consumers money.”