Researchers at Forschungszentrum Jülich in Germany have solved a years-long mystery that has troubled grid managers worldwide: unexplained frequency drops occurring every 60 seconds simultaneously on power grids across continents. The culprit is battery backup systems, including those in data centers, that check their charge status at precisely the same time every minute due to internet-synchronized clocks.
Director Dirk Witthaut led the investigation after Germany's largest transmission system operator, Tennet Germany, brought the puzzle to his team. The researchers initially suspected hydropower plants, which can cause ultra-low frequency oscillations, but could not explain why the pattern persisted without interruption. They realized that such precise timing required a clock mechanism and began installing more than 80 smart power quality meters around the Jülich campus, which houses battery energy storage systems and data center equipment.
The measurements revealed that transformers attached to battery systems peaked every minute, matching the pattern seen on larger grids. Many stationary batteries, from data center uninterruptible power supplies to grid-scale batteries, check their state of charge every 60 seconds. Because these devices synchronize their clocks via internet connection, they perform this check simultaneously, creating a collective disturbance on the grid. Data from Ireland provided confirmation: as data centers grew to consume 18 percent of the country's electricity by 2022, the minute-by-minute frequency drop on the Irish grid quadrupled from 3 millihertz in 2016 to 12 millihertz in 2021, with some recent drops exceeding 20 millihertz.
The researchers recommend that manufacturers add randomization to battery charging schedules rather than checking state of charge exactly on the minute. While Ireland's 50 hertz grid can withstand swings of 200 millihertz, the added disruption from synchronized battery checks could push grids toward blackout conditions when combined with other loads. The team also detected similar periodic power fluctuations in internet-connected devices ranging from smart ovens to computer clusters, though a recent study found that less than 3 percent of such devices run the latest firmware, complicating efforts to deploy software fixes.