Synchronous Condensers: Buying Back Grid Inertia
For 150 years, every spinning coal, gas and nuclear generator gave electricity grids something nobody had to pay for separately: inertia, the resistance of a heavy rotating mass to a sudden change in speed, which buys a grid time to react when supply and demand fall out of balance. This video explains the physics of that free byproduct, and why grid operators on three continents are now spending hundreds of millions of pounds and dollars to buy it back on purpose, from machines that generate no electricity at all.
It traces the synchronous condenser back to 1919, when General Electric shipped the first high-voltage unit to Ontario Hydro to correct voltage on long transmission lines, not to supply inertia. It explains why retiring coal and nuclear plants take their spinning mass out of the grid with them, why wind, solar and batteries connect through electronic inverters rather than a physically spinning rotor, and the real, sourced distinction between what grid-forming batteries can do (match a spinning machine's frequency response for a few seconds) and what they still cannot (push the same surge of fault current into a short circuit).
It covers Britain's Stability Pathfinder programme in detail - the roughly £650 million spent across two contract phases since 2020, and the real machines that money built: Statkraft's Lister Drive site in Liverpool, Uniper's converted and new-built sites at Killingholme and Grain, Conrad Energy's 2024 financing, and RWE's newest machine at Pembroke, Wales, which entered service in August 2026. It covers South Australia's four ElectraNet synchronous condensers, built after a 2017 system-strength shortfall at a regulator-approved cost of about AU$166 million, and what bolting a flywheel onto one of these machines actually buys in extra seconds of inertia.
Every figure carries its date and source. Two figures in the original brief could not be verified and were corrected rather than used as given, and the video does not assert a UK regulatory decision date that could not be confirmed.
Educational documentary. Not financial or investment advice.
In these topics
Chapters
- A grid that must stay at exactly one speed
- What inertia actually is
- 150 years of free inertia
- Born for a different job: 1919
- The problem: plants close, inertia disappears
- Why batteries can't do this job
- The fix: buying inertia back
- Britain's Stability Pathfinder
- Australia's syncon fleet
- What a flywheel buys you
- Steam-era machine, AI-era grid
- Forwards or backwards?
Sources and credits
Photo credits (Wikimedia Commons)
- Early high-voltage synchronous condenser installation, North Substation, 1924: Unknown authorUnknown author, Public domain - https://commons.wikimedia.org/wiki/File%3ANorth_Substation_interior_showing_the_15%2C000_kVA_synchronous_condenser%2C_October_22%2C_1924_%28SPWS_166%29.jpg
- STAL Ljungstrom 50MW steam turbine rotor: Unknown authorUnknown author, Public domain - https://commons.wikimedia.org/wiki/File%3ASTAL_Ljungstr%C3%B6m_steam_turbine_rotor_50MW.jpg
- Alabama Power Company coal-fired power plant: Russell Lee, Public domain - https://commons.wikimedia.org/wiki/File%3APower_plants_of_Alabama_Power_Company%2C_that_are_operated_by_coal_from_this_mine._Plants_use_3300_tons_of_coal_per_day..._-_NARA_-_540647.jpg
- Bulimba B coal-fired power station, Brisbane, c.1954: Contributor(s): Thiel Studio, Public domain - https://commons.wikimedia.org/wiki/File%3AStateLibQld_1_152999_Bulimba_B_Power_Station%2C_Brisbane%2C_ca._1954.jpg
- Shippingport Atomic Power Station, 1956: Nuclear Regulatory Commission from US, Public domain - https://commons.wikimedia.org/wiki/File%3AShippingport_Atomic_Power_Station_-_Oct._10%2C_1956_%2814492222700%29.jpg
- NASA Mod-0 experimental wind turbine: Unknown authorUnknown author, Public domain - https://commons.wikimedia.org/wiki/File%3AMod-0_Wind_turbine.jpg
- NASA Mod-1 experimental wind turbine: Unknown NASA employee, Public domain - https://commons.wikimedia.org/wiki/File%3ANASA_Mod_1_wind_turbine.jpg
- NREL solar panel array: NREL, Public domain - https://commons.wikimedia.org/wiki/File%3ANREL_Array.jpg
- National Grid control room, Central Electricity Board, Britain, 1945: Ministry of Information Photo Division Photographer, Public domain - https://commons.wikimedia.org/wiki/File%3AThe_British_Grid_System-_the_work_of_the_Central_Electricity_Board_in_Wartime%2C_c_March_1945_D24288.jpg
Primary sources
- GE / GE Vernova, 'GE's industry-leading portfolio of synchronous condensers celebrates 100th' anniversary release, and 'In Sync: How a Steam-Era Machine Can Upgrade the 21st Century Electric Grid' - the 1919 Ontario Hydro unit (10 MVAr), the 1920 voltage-correction context, and GE's 1928 hydrogen-cooled milestone.
- ABB, 'Statkraft chooses ABB synchronous condensers...' and 'ABB's synchronous condensers go live in Liverpool to stabilize the UK's power grid' - Lister Drive's two 67 MVAr condensers, 40-tonne flywheels, ~3.5x inertia boost, live March 2023.
- Osborne Clarke, 'Osborne Clarke advises Conrad Energy on financing of two Pathfinder synchronous condenser projects for £200m', and Renewable Energy Magazine, 'Conrad Energy closes UK financing of Pathfinder', 29 March 2024.
- National Grid ESO / NESO, Stability Pathfinder Phase 1 contract announcement (2020, £328m, 12.5 GVA.s) and Phase 2 results (April 2022, £323m); Modern Power Systems, Pathfinder coverage.
- NESO, 'Pembroke project marks latest milestone in clean grid stability programme', and Electrical Review, Pembroke synchronous condenser coverage - live August 2026, NESO's own 17.2/26.9 GVA.s inertia figures.
- Ofgem, 'FRCR 2025 Authority Decision' PDF, dated 28 May 2026 - the nearest confirmed UK regulatory decision on minimum system inertia found.
- EirGrid, 'EirGrid awards four contracts for new renewable integration technologies', 7 November 2024 - four Low Carbon Inertia Services contracts, ~6,963 MVA.s of synchronous inertia.
- Australian Energy Regulator, ElectraNet system-strength spending approval, and ElectraNet, 'System Strength Economic Evaluation Report', 18 February 2018.
- AEMO newsroom, Davenport and Robertstown synchronous condenser commissioning notices, 2021 - all four units commissioned August-October 2021, following AEMO's October 2017 system-strength shortfall declaration.
Not regulated financial advice.