As coal and gas plants retire, the energy transition conversation focuses on replacing their generation capacity. What gets far less attention is the loss of the physical properties those machines provided for free: inertia that stabilises frequency, fault current that supports voltage during disturbances, and reactive power that regulates voltage across the network. These services come from the physics of enormous spinning rotors synchronised to the grid, responding instantaneously, without sensors, software or control loops. As inverter-based resources replace them, that mechanical immune system disappears, and a new, extreme stress test is arriving at the same time in the form of AI data centres whose loads can swing by hundreds of megawatts in a fraction of a second.

Host Bridget van Dorsten is joined by Kristina Carlquist, General Manager of Synchronous Condensers at ABB, and Christian Payerl, Sales Manager of Synchronous Condensers at ABB, to unpack why a technology that has existed for as long as the grid itself is now experiencing a revival.

Christian explains the three ancillary services the grid is losing, inertia, short-circuit current and reactive power, and why inverter-based generation does not replace them. Grid-forming batteries can be programmed to simulate inertia, but each charge-discharge cycle degrades lifetime, overload capacity is limited to microseconds, and the models needed for accurate grid simulation are often tied up in manufacturer IP. Synchronous condensers respond on physics alone, in both directions, with no degradation and no modelling uncertainty. The recent blackout in Spain illustrates what happens when that gap is left unfilled.

Kristina walks through the commercial traction. ABB's partnership with VoltaGrid on isolated data center microgrids has grown from an unexpected inbound enquiry in late 2024 to dozens of synchronous condensers delivered. On the grid-connected side, the Faroe Islands have deployed four units with a fifth on the way as part of their push toward 100% renewables, already achieving multi-day periods of fully renewable operation. ABB is also working with Korea's Jeju Island on its first flywheel-equipped deployment. The demand pattern is widening: islands integrating renewables, TSOs managing weak grid regions, mines electrifying operations, and now data centre developers who had never considered grid stability equipment before.

The episode closes on regulation and standards. Christian, who participates in international standards work through CIGRE, notes that there is still no international standard for flywheel safety and that the treatment of inertia as a paid service varies dramatically by country. While inertia is compensated as a paid service in the UK, in Sweden it is treated as free – rotating machines providing it receive no income stream for doing so. As data center load grows faster than regulation can respond, both guests argue that the answer is not one technology but a combination, provided the industry, utilities and policymakers can align on what the grid actually needs to remain stable.

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