The minute-long grid glitch, explained

Every 60 seconds, the frequency on power grids in Europe, Australia, the U.S., and Malaysia dips by a tiny, nearly invisible amount. What made the anomaly so hard to explain wasn't the size of the drop but its timing: the sags landed at the exact same moment on grids separated by continents and oceans. Tennet Germany, the country's largest transmission system operator, brought the puzzle to Dirk Witthaut, a researcher at Forschungszentrum Jülich, and it took years of investigative and modeling work to arrive at an answer.

According to TechCrunch's reporting on the research, that answer turned out to be mundane and entirely fixable: the batteries themselves, checking their state of charge on a synchronized clock.

A puzzle that crossed borders

Grid operators have watched these anomalies for years without a satisfying explanation. The drops are small enough that they don't, on their own, knock anything offline, but the pattern was consistent across national grids and continents alike. Germany's Tennet Germany, the largest transmission system operator in the country, handed the problem to Witthaut's team, and the investigation drew on data from Europe to Australia, the U.S. to Malaysia, where the same signature appeared.

Frequency sags are not, in themselves, unknown territory for grid engineers. But the regularity of this particular disturbance made it stand out. A signal that repeats minute after minute, without fail, doesn't look like the noisy, intermittent behavior that mechanical systems usually produce.

Why frequency has to hold steady

The grid depends on frequency staying inside a defined band. When oscillations grow too large, or when operators don't understand their cause and respond the wrong way, they can lead to blackouts, according to the reporting. Even when no outage follows, unaddressed sags can damage equipment in power plants, with hydropower turbines called out as a particular concern.

Hydropower has historically been a major source of what are known as ultra-low frequency oscillations (UFLOs). Every turbine vibrates, and when those vibrations line up with a system's resonant frequency, they can amplify, sometimes to dangerous levels. The comparison offered in the reporting is a wine glass shattering in front of an opera singer: that is resonance at work.

The hydropower hypothesis falls short

Hydropower was the obvious first suspect, so Witthaut and his team built a computer model of a hydropower plant control system on the Scandinavian grid and tested it. They did find conditions that could produce a resonance peaking once per minute. What the model could not explain was persistence.

Resonances in mechanical systems tend to come and go, and the signal they leave on the electrical grid follows the same pattern. This one didn't. The frequency drop kept occurring minute after minute, on a 60-second cadence that never slipped. That reliability is what pushed the team toward a different idea: anything that operates with that kind of clockwork must be using an actual clock.

Eighty meters on campus

To test the new hypothesis, the researchers looked close to home. They installed more than 80 smart power quality meters around the Jülich campus, a site with medium- and low-voltage distribution lines, transformers, solar panels, and battery energy storage systems acting as uninterruptible power supplies. The campus also runs a high-performance computer system alongside ordinary office computers backed by much smaller UPS units. The meters sampled frequency, voltage, current, and power once every three seconds.

The answer arrived quickly. Measurements taken at the transformer attached to the battery energy storage system peaked every minute, matching the pattern seen on far larger grids. The batteries were checking their state of charge on a one-minute schedule, and because those devices are internet-connected, their clocks run in near-perfect sync with one another. A single battery's check is imperceptible against the wide grid. Thousands of them doing it at the same instant is not.

Ireland's data centers as evidence

To confirm that UPS systems were the main driver at grid scale, the team turned to data supplied by grid operators. Ireland provided the clearest case. Data centers there have grown to consume a large fraction of the country's electricity, and by 2022 they represented 18% of the load on the Irish grid, with each facility served by a fleet of UPSes.

The numbers tracked the theory. Between 2016 and 2021, the minute-by-minute frequency drop on the Irish grid quadrupled, from 3 milli-Hertz (mHz) in 2016 to 12 mHz in 2021. More recently, some drops have exceeded 20 mHz.

• Ireland's data centers accounted for 18% of grid load by 2022.
• The Irish grid's minute-by-minute frequency drop rose from 3 mHz in 2016 to 12 mHz in 2021.
• Some recent drops have exceeded 20 mHz.
• Ireland's 50 Hz grid is built to withstand swings of plus or minus 200 mHz, though the operator would prefer to hold them to 100 mHz.
• Fewer than 3% of IoT devices run the latest firmware, per a recent study cited in the reporting.

Against a tolerance of 200 mHz, a 20 mHz dip is not large on its own. The complication is that data centers are not the only loads drawing on the grid. If other sources also pull frequency down, the extra contribution from every UPS checking its charge at once could move the system toward blackout conditions.

A fix that needs a random number

The problem is preventable, and the remedy is modest. Rather than querying state of charge exactly on the minute, Witthaut and his team recommend that UPS and grid-scale battery manufacturers introduce randomization into the schedule. Spreading the checks out would keep any individual disturbance from stacking on top of the others.

UPS systems are driving the issue today, but the researchers found reason to expect it could outlast them. They also tested IoT devices, and in hardware as varied as a smart oven and Raspberry Pi clusters they detected periodic power fluctuations of the same kind. A software patch can address that too, but many IoT devices never receive updates. A recent study cited in the reporting found that less than 3% of IoT devices are running the latest firmware.

The coordination problem

Regulators may eventually be compelled to require changes, but any single authority can only govern its own corner of the grid. Because the disturbance shows up simultaneously across countries and continents, addressing it fully would require coordination on a global scale. The mystery has been solved; the problem, as the reporting frames it, could remain for years.

Why it matters

For grid operators, the finding suggests that the load growth around data centers carries a synchronization cost that isn't captured by simple demand figures. Each new facility brings another fleet of batteries checking their charge on the same clock as everyone else's, and those contributions accumulate in the same narrow frequency band. The remedy the researchers propose — randomized timing in firmware — is the kind of change that costs little to implement but depends on manufacturers acting before deployment rather than after.

For businesses running their own UPS fleets, the implication is that a device everyone treats as passive backup infrastructure can collectively influence the grid it sits on. And because the researchers found the same periodic signature in consumer-grade IoT hardware, the pattern may extend well beyond the data center floor, into equipment that is rarely patched at all.