But neither the German transmission system operator (TSO) E.ON Netz, the federal energy regulator, nor Europe's organisation of European Electricity Transmission Operators (ETSO) made the same conclusion. All three cautioned against hasty blame-laying prior to the facts being known -- in hindsight a wise move.
The blackout occurred after both circuits of a 380 kV line crossing the river Ems in northern Germany were taken out of action on the evening of November 4 to ensure safe passage of a new passenger cruiser, the Norwegian Pearl, from the Meyer shipyard at Papenburg to the North Sea. According to the Union for the Co-ordination of Electricity Transmission (UCTE) for west and central Europe, the line was taken out at 21:38 and power flows redirected south. At 22:00, wind power was supplying 3300 MW of the 13,500 MW load on the E.ON Netz system, a situation described as "normal." But a surge in load on a specific transmission route shortly afterwards, unconnected with wind power, coupled with staff errors at an E.ON Netz control centre, started a cascade of trips which split the UCTE network into three isolated islands with different frequencies (map).
The north-east island, covering eastern Germany, Poland the Czech and Slovak republics, Hungary and the east of Austria had a generation surplus of 6 GW. The western island, which included the Netherlands, Belgium, France, Spain, Portugal, Switzerland, Italy and the western parts of Austria and Slovenia, lacked power as did the south-eastern island stretching as far as Spain.
To re-establish the balance between generation and consumption, customers were cut off in a load shedding exercise. "This wasn't a blackout, but rather a controlled handling of the situation. We had to purposely reduce demand to avoid an uncontrolled blackout," explains ETSO's Danial Dobbeni. The UCTE network was reconnected after 38 minutes and customers progressively supplied again.
According to E.ON Netz board member Urban Keussen, wind energy was not to blame. "There wasn't a single trigger from wind turbines to cascade the overhead lines, but wind plays a role in the general allocation. We don't blame wind energy for the incident, but it didn't ease the situation. It must be taken into account for grid stability," he says.
In Spain, the incident caused 2.8 GW of a total of 4 GW of wind in operation at the time to trip off line, along with 400 MW of other power plant. The losses meant that 1.5 GW of customer load had to be shed, according to Jose Luis Fernandez speaking for Red Eléctrica de España (REE), Spain's TSO. He points to a long outdated 1985 ministerial order requiring wind plant to automatically disconnect from the grid if frequency drops from 50 Hertz to 49 Hz as a probable cause for the massive loss of wind power. Regulations today require wind plant to provide grid support like other generation.
"If a ship passing by in Emden can cause lights to turn off and elevators to stop in Paris, we need a European energy regulator to coordinate developments," says Christian Kjaer of the European Wind Energy Association.