National Grid Electricity System Operator (ESO) has awarded £323 million to grid stability projects in Scotland, including to what is thought to be the first use of grid forming converters across a large scale.
With the imminent closure of nuclear power stations in Scotland and northern England, and the rising number of onshore and offshore windfarms in Scotland, there will be a loss of inertia which poses a potential risk to system stability.
Inertia refers to the resistance of the electricity system to changes in frequency, an inherent characteristic of conventional synchronous generators such as coal and gas plants whose turbines naturally act as shock absorbers for the 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.
Asynchronous generators, 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 fast-acting frequency response is sometimes referred to as synthetic inertia.
ESO’s stability pathfinder project is trialling a new grid stability service incorporating inertia, reactive power and short circuit levels (SCL) – the amount of current that flows on the system during a fault.
The project’s phase 2 tender attracted 225 proposals from 21 separate companies. Of these, 10 bids submitted by four companies were chosen which delivered 11.55 GVA (giga volt ampere) of SCL and 6.75 GVA seconds of inertia.
The winning 10-year contracts will begin in April 2024. Five of the solutions will comprise what is thought to be a world-first use of new grid forming converters at multiple locations across a region to improve inertia and SCL when disturbances occur.
Five of the other successful solutions are synchronous condensers. These are ‘green’ motors with free-spinning flywheels which boost inertia and SCL.
Winning tenders
| Company | Location | Technology type |
| Statkraft | Coylton | Grid forming battery storage |
| Statkraft | Neilston | Grid forming battery storage |
| TINZ Programme 1 ProjectCo 3 Ltd | Beatrice | Synchronous condenser |
| Zenobe Energy Limited | Blackhillock | Grid forming battery storage |
| Zenobe Energy Limited | Kilmarnock South | Grid forming battery storage |
| Zenobe Energy Limited | Eccles | Grid forming battery storage |
| WP Grid Services 3 Ltd | Gretna | Synchronous condenser |
| WP Grid Services 8 Ltd | Rothienorman | Synchronous condenser |
| WP Grid Services 1 Ltd | Thurso South | Synchronous condenser |
| WP Grid Services 9 Ltd | Neilston | Synchronous condenser |
The ESO said these green solutions will provide the equivalent combined SCL and inertia of almost four coal-fired power stations.
Julian Leslie, head of networks at National Grid ESO, said: “We believe this is the first time in the world where grid forming inverters have been used in multiple locations across a region to provide a system-wide solution to short circuit levels and inertia.
“These zero-carbon stability-improving devices will enable more green electricity to run, are cheaper for consumers, and will allow the market to deliver as much wind generation as possible.
“This technology will help to future-proof Scotland’s wind generation success story, help us continue to operate the fastest decarbonising electricity network in the world and achieve our plans to be able to operate a zero-carbon grid by 2025.”