National Grid ESO’s inertia initiative: an update

Above: Cruachan (Drax)

The NOA (Network Options Assessment) Stability Pathfinder – an initiative of National Grid ESO (the GB electricity system operator) – aims to find the most cost-effective ways to address stability issues in the electricity system created, in particular, by reduced inertia due to the decline in transmission-connected synchronous generation.

It consists of three phases:

• Phase 1. Following the award of 12 contracts to five organisations in January 2020 covering a range of new-build synchronous condenser systems and repurposed generators, several of these units have now started to support the electricity system. Over the coming months, the remaining facilities will enter operation.
• Phase 2. The next phase of the Stability Pathfinder is looking for sources of additional inertia, short circuit level and dynamic voltage across Scotland. NG ESO reports good progress, with explorations of how possible solutions could work and consultations. The commercial submission window was open until 14 January 2022 for proposals that had already successfully completed the feasibility study stage.

In early March, successful tenderers will be awarded contracts, or in the case of transmission operators, they’ll be asked to deliver the proposed solutions from September 2022 onwards.

There has been interest from providers of a range of technologies, including synchronous condensers, grid forming converters (an emerging technology that allows solar and other inverter-based energy sources to restart the grid independently) and hybrid solutions.

• Phase 3. On 20 December, the invitation to tender for phase 3 was launched, again looking for additional inertia, short circuit level and dynamic voltage, but across specific locations in England and Wales. This is a one stage tender, where both technical and commercial proposals will be submitted by the deadline of 16 May, with the expectation that technologies will be similar to those seen in Phase 2. Phase 3 contracts will be awarded later in 2022, with provision of services starting from as early as April 2025.

Phase 1 project updates

Phase 1 saw the awarding of contracts to Drax, Rassau Grid Services (Welsh Power), Statkraft, Triton and Uniper. The contracts, amounting to procurement of about 12 GVA.s of inertia (equivalent to that provided by five large coal fired power plants), were worth a total of about £328 million for delivery of services over a six-year period.

Inertia will be provided without having to provide electricity – allowing more renewable generation to operate and ensuring system stability at lower costs.

The Phase 1 projects can be summarised as follows:

• Drax, Cruachan (533.3 MVA.s). One of the four turbines at the 440 MW Cruachan hydro pumped storage facility has ceased generation and since mid 2020 has been providing inertia and other services to the grid.
• Uniper, Killingholme (2 x 1430 MVA.s). Two redundant Siemens turbine generators at Killingholme, Lincolnshire, UK, repurposed and flywheels installed to deliver inertia services and voltage control to the grid. Siemens Energy is providing the new equipment and control systems. Expected to be operational during Q1 2022.
• Uniper, Grain (2 x 1729 MVA.s). Siemens Energy has supplied and installed two new custom designed synchronous condenser units at the Grain power plant site, Kent, UK. They employ Siemens Energy rotating machines, flywheels and control systems. Expected to be operational during Q1 2022.
• Welsh Power, Rassau (750 MVA.s). This is a new build project, consisting of Siemens Energy synchronous condenser and flywheel to be installed at Welsh Power’s Rassau site, in Ebbw Vale. Expected to be operational early 2022. Partnering with Quinbrook Infrastructure Partners, Welsh Power is managing the construction.
• Triton, Deeside (2 x 1553 MVA.s). Two Alstom 13E2 gas turbines at the Deeside combined cycle plant have been repurposed to provide inertia and stability services, without generating power, believed to be the first conversion of gas turbine rotors to provide such services on a standalone basis anywhere in the world. Deeside power station began providing these stability services on 18 June 2021. The combined cycle plant, consisting of the two gas turbines, plus two CMI heat recovery steam generators and an Alstom steam turbine, had been shut down and in preservation mode since March 2018.
• Statkraft, Lister Drive (2 x 450 MVA.s). ABB was awarded a turnkey contract in February 2021 by Statkraft to design, manufacture and install two high-inertia synchronous condenser systems for the Lister Drive Greener Grid project, Liverpool, northwest England. It is also the first project anywhere in the world to feature ABB’s “high-inertia” configuration. This couples a 67 MVAr synchronous condenser with a 40 tonne flywheel, which increases the instantaneously available inertia by 3.5 times. The Lister Drive facility is scheduled to go on line in 2022.
• Statkraft, Keith (2 x 450 MVA.s). GE was awarded a contract by Statkraft in mid 2020 to install its Rotating Stabiliser technology at Statkraft’s Keith Greener Grid Park, Moray, northeast Scotland, close to SSEN’s Keith substation. The Rotating Stabiliser was manufactured in GE Power Conversion’s factory in Rugby, UK, with a key component provided by Sheffield Forgemasters. The facility was declared operational on 23 December 2021, providing inertia to the grid, as well as short circuit level and frequency support.

Measuring inertia

As well as projects to introduce increased inertia to the grid NG ESO has also taken steps to improve its measurement.

It has, for example, deployed GE Digital’s inertia measurement and forecasting technology and is in the process of introducing Reactive Technologies’ GridMetrix grid stability measurement system. As part of this, in October 2021, UK/Finnish start-up Reactive Technologies announced completion of what it describes as “the world’s largest continuously operating grid-scale ultracapacitor.”

GridMetrix aims to provide instantaneous inertia data instead of relying on estimates to manage system stability.

Constructed by Spanish technology group Ingeteam, the ultracapacitor (located in Teesside) sends pulses of power through the grid “like the underwater sound waves used in sonar”, says Reactive, and once live, “the system operator will have an enhanced real time view of inertia.”

Reactive says 2021 has been a transformational year for the company, in which it also closed a record fundraising round from a group of global investors including the Bill Gates-backed clean energy fund Breakthrough Energy Ventures, BGP and Eaton. “As an independent clean technology company specialised in inertia”, Reactive says it is “well-poised to export its technology globally and support grids around the world in unlocking renewables growth and accelerating their transition to zero carbon energy systems.”

Marc Borrett, CEO, Reactive Technologies, commented: “The commercial adoption of GridMetrix by National Grid is a significant milestone in the journey of our technology from a conceptual innovation to a proven and fundamental grid management solution.”

The challenges facing Britain on its net zero journey are familiar to grids across the world and with the support of our strategic investors and partners, we are extremely excited to help unlock as many 100% renewable grids around the world as possible, accelerating the global transition to a clean energy system.”

Fintan Slye, executive director of National Grid ESO, added: “Our ambition to be able to operate an electricity system that can deliver periods of 100% zero carbon power by 2025 is a stretching target, but thanks to cutting-edge technologies such as this we’re on track to achieve a significant milestone on that zero carbon journey.”