Coordinated disturbances haunt grids worldwide. Here’s how researchers solved the mystery.

A team at Germany’s Forschungszentrum Jülich has identified the cause of regular, one‑minute disturbances that appear on electricity networks across Europe, Australia, the United States and Malaysia. The researchers, led by scientist Dirk Witthaut, were approached by TenneT Germany, the country’s largest transmission system operator, after the phenomenon – described in headlines as a “grid twitch” and a “hidden one‑minute heartbeat” – drew attention from industry and media.\n\nThe team first considered hydroelectric turbine vibrations, which can produce resonant oscillations once per minute. Modelling showed that such resonance was theoretically possible, but it could not explain why the signal repeated with such clockwork regularity in disparate grids. To investigate further, the scientists deployed more than 80 smart power‑quality monitors on the Jülich campus, recording frequency, voltage, current and power every three seconds. At a transformer linked to an energy‑storage system they observed minute‑by‑minute peaks that matched those reported on the larger networks.\n\nAnalysis revealed that many stationary batteries – from uninterruptible power‑supply (UPS) units in data centres to large grid‑scale storage installations – perform a state‑of‑charge check every 60 seconds. Because these devices are internet‑connected, their timing is almost synchronized worldwide. Each individual check is too small to be noticed, but when thousands occur simultaneously they generate a measurable dip in grid frequency. The researchers also detected similar periodic fluctuations in some Internet of Things devices, such as a smart oven and Raspberry Pi clusters.\n\nData from Ireland provided additional confirmation. In 2022, data centres accounted for 18 % of the country’s electricity load. The amplitude of the minute‑by‑minute frequency drop in the Irish grid rose from 3 millihertz in 2016 to 12 millihertz in 2021, and recent individual dips have exceeded 20 millihertz. Ireland’s 50 Hz grid tolerates deviations of plus or minus 200 millihertz, though the operator aims to keep them within 100 millihertz.\n\nTo mitigate the effect, the team recommends that manufacturers of UPS systems and grid‑scale batteries introduce random offsets into the schedule for charge‑level checks, breaking the global synchrony that creates the disturbance.