TECH

Mystery of 60-second fluctuations in power grids solved

Why do our grids show a brief spike in electricity demand every minute? A team led by Dirk Witthaut from Forschungszentrum Jülich has now demonstrated that this is due to regular power checks carried out by large-scale battery storage systems. These findings could help to make our electricity supply more robust, as the team reports in an article published in Nature Energy.

Tennet Germany, the largest transmission system operator in Germany, has observed over several years that the frequency in the European power grid dips briefly every 60 seconds. While these deviations were not critical to grid security, they were clearly measurable and unusually regular. The cause of this phenomenon was initially unclear.

A team from Jülich led by Dirk Witthaut, together with researchers from the University of Cologne and the Karlsruhe Institute of Technology, set out to investigate – and found the answer: the cause appears to be the many large-scale battery storage systems that check their state of charge every minute. This leads to measurable fluctuations in electricity consumption, which can contribute to turbine wear and tear, for example. The battery storage systems ensure an uninterrupted power supply, and their numbers have increased significantly worldwide in recent years. The researchers found that this was not a European phenomenon, but a global one.

Many devices, a common rhythm...“It really was years of detective work,” says Witthaut. The grid frequency pattern is shaped by many different factors. For example, it reveals the influence of electricity trading, with power stations being switched on and off abruptly, as well as the fluctuating feed-in from renewable energy sources, and various other disturbances.

“It quickly became clear to us that the cause must be something controlled by the clock,” says Witthaut. There was no other way to explain the precise 60-second cycle. It was also clear that: “The observed effect can only be produced if many devices are consuming electricity at the same time.” A single consumer or generator could therefore be ruled out.

Measurements on campus provide the clue...But how do all these devices synchronize their consumption? The researchers finally found the crucial clues with the help of the Living Lab Energy Campus. This research infrastructure on the Jülich campus is primarily used to develop and test highly integrated energy supply systems. The team installed measuring points on end devices at a total of 80 locations – and sure enough, the same periodic pattern in electricity consumption was observed precisely at the locations where large-scale battery storage systems are designed to ensure an uninterrupted power supply. “We took a closer look at one of them and found a spike in electricity consumption at the start of every minute due to the power check,” explains Witthaut.

As there are no binding standards for such power checks, Witthaut suspects that most battery manufacturers assumed that a 60-second interval would be sensible. The start of every minute was simply chosen as the test time. “It is entirely possible, however, that battery storage systems are only part of the problem here,” says Witthaut. “It cannot be ruled out that other digitally controlled appliances – such as air-conditioning systems, heat pumps, washing machines, and dishwashers – may also exhibit similar patterns.”

Less synchronization, less wear and tear...The periodic fluctuations in electricity demand are already having an impact on hydroelectric power stations. The brief spikes in demand mean that the turbines slow down momentarily before accelerating back to their original rotational speed. This increases wear and tear. With the expansion of storage technologies, such problems could become even more prevalent. In Ireland, for example, where data centres with large-scale battery storage systems currently account for around a fifth of the country’s electricity demand, the amplitude of the 1-minute signal quadrupled between 2016 and 2021. The solution, however, would be simple: “You would simply have to distribute the checks randomly, rather than always starting them at the same time,” says Witthaut.

One fallen power line exposed a growing AI data center problem — here’s how to fix it...A power line went down outside of Washington, DC, this week. Normally, the grid would only need a few seconds to recover from such an event. But this one took more than 10 minutes because data centers stopped drawing over 3 gigawatts’ worth of power nearly simultaneously.

The event caused voltage across the PJM grid to spike from Northern Virginia to Chicago, according to data collected by Ting Labs, a startup that runs an IoT sensor network out of people’s electrical sockets.

The event didn’t cause a blackout, but it did cause lights across the region to flicker. The incident demonstrated the effect that data centers can have on the grid — an outcome that experts believe will become more frequent.

Northern Virginia, which is in PJM’s territory, is home to the highest concentration of data centers in the world.

“It’s the canary in the coal mine,” Ricardo de Azevedo, CTO at ON.Energy, told TechCrunch. These sorts of events involving large loads like data centers are “happening more and more,” he added.

The event echoes one that happened two years ago, also on PJM’s grid, and it could foreshadow larger events if data centers aren’t built to more elegantly handle disruptions to power supplies. The PJM Interconnection manages grids from New Jersey to Illinois and serves 67 million customers, making it the largest grid operator in the United States.

When the power line went down this week, it triggered data centers to switch to backup power, and about 3.1 gigawatts of load vanished in about 30 seconds, according to PJM data. The grid appeared to recover somewhat, but a short time later additional loads dropped off. At its peak, PJM’s grid had an extra 3.49 gigawatts of electricity on it. It took another 11 minutes before it stabilized. The disconnected data centers represented around 3% of total demand on PJM at the time, according to Reuters.

A few percent may not sound like much, but the electrical grid needs to operate in a state of near-perfect balance, with supply and demand closely matched. If they don’t, voltages can sag or spike. The grid and devices connected to it can tolerate small fluctuations, but if those fluctuations grow too large, they’ll trigger fail-safes within the grid or within individual facilities, causing them to disconnect. 

When data centers in Northern Virginia sensed the fluctuation caused by the failed power line, they switched to backup power, which removed their load from the grid. As more data centers made the switch, they removed greater amounts of load from the grid. What started as a relatively small drop in supply became an even larger drop in demand, sending supply surging and causing light bulbs to flicker. 

Large-scale battery energy storage systems are the source of mysterious 60-second fluctuations detected in power grids worldwide. An international study led by researchers at Forschungszentrum Jülich, published in the journal *Nature Energy*, has solved the puzzle that had been baffling transmission system operators across the globe.

European regulators recently published a nearly 500-page report on the outage, attributing it to numerous and interacting factors. The report cited work from researchers in WSU’s School of Electrical Engineering and Computer Science regarding poorly understood frequency oscillations throughout the power grid that were part of the event. The work cited came from PhD students, Arash Nezam Sarmadi, Tianying “Lily” Wu, Yuan Zhi, and Salman Shiuab. All have since graduated.

“We have the best students, and it is really something to be proud of for WSU that this report, originating in Europe, cited publications from four of our students, and that these tools we developed are being used — both in real time and for offline analysis of complex events — for this Iberian blackout,” said Mani Venkatasubramanian, Boeing Distinguished Professor in Electrical Engineering who led the work.

It was a beautiful spring day last year when the European power grid began oscillating in frequency. Venkatasubramanian, director of WSU’s Energy Systems Innovation Center, who holds a joint appointment at Pacific Northwest National Laboratory, has worked with graduate students for decades to develop online monitoring tools to detect these harmful oscillations that cause fluctuations in power outputs in the power grid. The work was funded by the U.S. Department of Energy and by the Power Systems Engineering Research Center. He received a patent and started a company, Phasor Informatics LLC, that has licensed the technology. The software uses a suite of algorithms to assess oscillation problems in transmission systems and to notify operators when they occur.

Two five-minute oscillation events occurred that morning in Spain, and each time, power grid operators in Paris, France, received notifications from the software developed at WSU. The operators in Spain, in coordination with their counterparts in France, took actions to dampen them.

“The phenomenon that a forced oscillation resonated with the system mode was something that we had postulated in our papers, and we showed the theory on how that would affect the large power system,” said Venkatasubramanian. “So those were what caused the big oscillations that were seen between Spain and France and possibly other countries.”

As grid operators reacted, however, voltages on the power lines increased above acceptable limits, and power plants automatically disconnected in a cascading event. In less than two minutes around noon, about 60 million people across Spain and Portugal lost power in an outage that lasted 12 to 16 hours.

A new open-source tool developed at WSU helped Iberian blackout investigators uncover the likely source of the first oscillation that originated in Spain.

Using a new open-source tool developed at WSU that uses measurements with a slower reporting rate to detect faster oscillations, the Iberian blackout investigators helped uncover the likely source of the first oscillation that originated in Spain.

“That was exciting because we developed this tool just two years ago,” Venkatasubramanian said.

Oscillations remain a challenge for the power grid. The researchers have developed controls intended to dampen them, but they don’t fully understand why those actions don’t always work.

The U.S. has strict regulations and a more robust system than many other countries, but there have been oscillation events here, which are warnings for the system. In recent years, power grid operators have been planning for and seeing significant changes in the grid’s management. The cost of renewable energy production has dropped dramatically so that solar and wind power are now the cheapest and often the most attractive ways to produce electricity. Renewables provide variable amounts of energy during the day and are often distributed around a region instead of being centralized. At the same time, climate change, extreme weather events, and the growth of AI and data centers add to power grid challenges. Meanwhile, the system remains hampered by the lack of transmission support.

“Because of economic and societal issues, it’s very difficult to build new transmission lines in the U.S., and that is stressing the system more and more,” said Venkatasubramanian. “It is requiring us to become smart in how we use the existing resources to serve this growing demand.”

Venkatasubramanian’s group is developing open-source planning tools for modeling and analyzing the complexities and uncertainties that come about from the use of renewables and from extreme weather events.

The mechanism behind the phenomenon:

• Involuntary synchronization: Thousands of commercial battery systems around the planet have been programmed by their manufacturers to perform internal state-of-charge tests at the very beginning of every minute.

• Instantaneous consumption spike: While the impact of a single battery is negligible, the simultaneous and precisely coordinated behavior of a vast number of units creates a measurable fluctuation in the frequency of the global power grid.

• Lack of standards: The 60-second pattern emerged spontaneously because manufacturers simply chose an intuitive time interval, with no regulatory standard in place to account for this domino effect.

Practical consequences:

• Infrastructure wear and tear: These brief, cyclical oscillations force hydroelectric turbines to momentarily slow down and then speed back up, increasing the mechanical wear on the equipment.

• Amplification through technological advancement: As the energy transition progresses and more storage systems are connected to the grid, the amplitude of this signal grows. In Ireland, driven by the expansion of data centers equipped with battery backups, the magnitude of this impact on the grid has quadrupled over a five-year period.

The proposed solution... The definitive resolution to the problem is surprisingly simple. The study suggests that the issue can be resolved by decentralizing the tests—specifically, by introducing a randomized time distribution for when the batteries perform their checks. Instead of responding to the clock in an identical manner at the very first second of each minute, the devices would take their measurements at staggered times, completely neutralizing the collective peak load.

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