National Grid Electricity System Operator (ESO) has awarded contracts worth £328 million to five companies as part of the pilot tender for a new stability service incorporating inertia, voltage control and short circuit level contribution.
The ESO said it expects the contracts to save consumers between £52 million and £128 million in reduced balancing costs.
Inertia refers to the resistance of the electricity system to sudden changes in frequency. It is provided by synchronous generators – those with large rotating masses spinning in harmony with the frequency of the power grid.
However, the closure of conventional fossil fuel plants and the proliferation of asynchronous renewable generation means inertia is declining and the electricity system is becoming more susceptible to disturbances.
The tender held for the initial phase of the ESO’s Stability Pathfinder project marks the first time it has been procured separately as a service. Speaking to Utility Week in November, ESO head of network capability Julian Leslie said: “This is about buying the spinning element rather than the megawatts.”
He said the ESO had previously been forced to constrain interconnectors and renewables to make way for conventional generators and raise inertia: “If we can get plants to come on without the megawatts, then we get the inertia but without having to create space”.
The ESO sought to procure up to 25GVAs of inertia. It received offers for 22.5GVAs and awarded contracts for 12.5GVAs.
They cover seven sites owned by five companies – Drax, Welsh Power, Triton Power, Uniper and Statkraft. The sites include the Cruachan pumped hydro power station and the Deeside, Killingholme and Grain combined-cycle gas turbine plants.
The contracts all run until March 2026. Most begin in April 2021, although several will start later this year.
Commenting on the latest announcement, Leslie said: “This approach is the first of its kind anywhere in the world and is a huge step forward in our ambition to be able to operate the GB electricity system carbon free by 2025.
“Our system is one of the most advanced in the world, both in terms of reliability and the levels of renewable power, and we’re really excited to be adding to that with this new approach to managing stability.
“These contracts are finding new ways to help balance the grid which are cheaper and greener, reducing emissions and saving consumers over £100 million.”
The ESO plans to hold a second pilot tender for services beginning in 2023, allowing developers more time to construct purpose-built assets such flywheels and compensators.
In December, the ESO proposed an amendment to the Grid Code adding minimum specifications for the provision of synthetic inertia – a type of fast-acting frequency response – by asynchronous sources of power such as wind, solar and interconnectors.