I have written several times about the challenges facing system operators as the energy transition sees increasing amounts of intermittent generation increasing frequency variation. However, between mid-January and early March, there was a persistent frequency deviation that caused clocks to lose time across the 25 countries connected to central Europe’s synchronous electricity system that had nothing to do with managing intermittency from renewables.

“Since the European system is interconnected … when there is an imbalance somewhere the frequency slightly drops,”
– Claire Camus, spokeswoman for ENTSO-E, the European Network of
Transmission System Operators for Electricity

The deviation was small, with the system averaging 49.996 Hz instead of 50 Hz (the system can operate down to 46.7 Hz), however even such small deviations can have real effects. Clocks that take their time from the grid frequency, rather than oscillating quartz crystals, lost around six minutes over the period.

frequency deviationMore importantly, the system also delivered around 113 GWh less energy than it should, raising the issue over who will provide compensation. (Apparently this is equivalent to the power consumption of Greenland for six months.)

The root cause of the problem was a political dispute between Serbia and Kosovo over their power grid, where Kosovo had been using more electricity than it generated after a power plant went offline for maintenance. Serbia, which is responsible for balancing Kosovo’s grid, refused to make up the difference, despite an agreement to do so.

The political dispute centres mainly on regulatory issues and a row between Serbia and Kosovo over grid operation. The two countries signed an agreement on operating their power grid in 2015, however, it has never been implemented since there are conflicting claims about ownership of the grid that was built when both states were part of Yugoslavia.

Kosovo seceded from Serbia in 2008, but Belgrade still does not recognise Kosovo, making a political solution more difficult. Under the 2015 agreement, Belgrade created companies to supply ethnic Serbs in northern Kosovo who wanted to pay their bills to a Serb utility, and were refusing to pay for electricity supplied by the Kosovan utility even though it was generated in Kosovo, costing the company tens of millions of dollars per year. However the registration of the Serb utilities in Kosovo has been prevented as the documents do not recognise Kosovo as an independent country.

According to Kosovan officials quoted in the New York Times, since Serbia’s state-owned utility owns and profits from much of Kosovo’s grid, it has no incentive to resolve the problem, while Kosovo’s power company is running out of money.

ENTSO-E has urged European governments and policymakers to take swift action and exert pressure on Kosovo and Serbia to resolve the issue, which is also hampering integration of the western Balkans energy market required by the European Union.

The New York Times summed up the situation quite poetically:

“Physicists tell us that time expands and contracts because of relativity. Poets and philosophers tell us that time alters with love and age. And, across Europe, microwave ovens tell us that time changes with tussles between Balkan nations.”

However, the real problem is not with clocks – applications that require reliable accuracy don’t depend on grid frequency for setting the time anyway – it is how to resolve the political situation in the Balkans as it relates to electricity so that there is no repeat of the situation. In the short term, Kosovo was able to restore its supply/demand balance, but it cannot continue to provide free electricity to large segments of its consumers, nor can it ignore generation issues and maintain consumption levels regardless.

For anyone that would like to read more about synchronous clocks and time error correction services provided by some system operators to correct for frequency deviations, these papers (one and two) are interesting.


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