Grid Frequency Dips Every Minute Traced to Battery Backups

From hydropower to a hidden clock

Grid operation depends on keeping frequency within a set range. Large oscillations, or a wrong response by operators who don't know the cause, can lead to blackouts. Unchecked sags can also damage power plant equipment, especially hydropower turbines.

Hydropower was the obvious first suspect, since turbine resonance has historically driven ultra-low frequency oscillations. Using a computer model of a hydropower control system on the Scandinavian grid, the team found conditions that produced a once-per-minute resonance. But it could not explain why the signal persisted minute after minute. That regularity suggested a clock.

The team installed more than 80 smart power quality meters across the Jülich campus, which has solar panels, battery storage and UPS devices. Measurements at the transformer connected to the battery system peaked every minute. Because the devices are internet-connected, their clocks are nearly synchronized, so individually negligible disturbances add up.

Ireland shows the effect

Grid operator data pointed to Ireland, where data centers made up 18% of grid load by 2022. From 2016 to 2021, the minute-by-minute dip quadrupled from 3 mHz to 12 mHz, and some drops have since exceeded 20 mHz. Ireland's 50 Hz grid is built to tolerate swings of plus or minus 200 mHz, and the operator prefers to stay within 100 mHz. So 20 mHz is small, but combined with other loads it could push the grid toward blackout conditions.

The researchers recommend that UPS and grid-scale battery makers randomize the timing of the checks. IoT devices, including a smart oven and Raspberry Pi clusters, also showed periodic power fluctuations. The fix is a simple software patch, yet a recent study found fewer than 3% of IoT devices run the latest firmware. Regulators may need to step in, but because the problem is global, lasting relief will require international coordination.