The electricity system operator (ESO) has launched its first ever tender for inertia as part of its efforts to make the power grid ready for zero-carbon operation by 2025.
The body is seeking to procure up to 25 GVAs (gigavolt-ampere-seconds) of inertia for a six-year period starting in April 2020. This equates to around a third of the ESO’s minimum overall requirement of 70 GVAs.
Inertia refers to the resistance of the electricity system to sudden changes in frequency. It is currently provided by coal and gas-fired power stations – synchronous generators featuring large spinning masses rotating in harmony with the frequency of the power grid.
As old fossil fuel plants are replaced by new asynchronous renewable generation, the inertia of the power grid is falling, leaving it more susceptible to disturbances.
The ESO’s stability pathfinder tender will seek to maintain the requisite level of inertia but without boosting generation from conventional power plants: “This is about buying the spinning element rather than the megawatts,” explained Julian Leslie, head of network capability at National Grid ESO.
He said the ESO has sometimes been forced constrain interconnectors and renewables to make way for conventional generation, adding: “If we can get plants to come on without the megawatts, then we get the inertia but without having to create space”.
Leslie told Utility Week the services are initially expected to be provided by coal and gas plants that are spinning their turbines whilst on standby but not generating any electricity – or least very little.
However, the ESO plans to hold a second pathfinder tender early next year for services beginning in 2023. This will give providers the opportunity to construct purpose-built assets such flywheels and compensators.
Leslie said synthetic inertia – a form of fast-acting frequency response – could also be provided by varying the output from wind turbines:“If we can create a virtual synchronous machine from wind that looks and feels like a conventional power plant obeying the laws of physics, then that would be an amazing step forward.”
He noted that synthetic inertia is currently being tested by Scottish Power Renewables at its Dersalloch onshore windfarm in South Ayrshire.
The ESO launched another pathfinder tender in October for reactive power services in the Merseyside area, offering one-year contracts starting in April 2021.