German grid needs foreign power
At the beginning of December 2011, German grid operator Tennet had to ramp up a mothballed power plant in Austria for the first time to compensate for great power demand in southern Germany. At the time, a lot of wind power was being generated in the North, and a nuclear reactor had to be switched off.
Up to now, the German government's sudden decision to switch off nearly half of its nuclear power production capacity in March has not yet led to any power outages, but the effects are certainly making themselves felt. There were concerns, in particular, that winter – when power demand is at its greatest – might lead to trouble.
Fluctuating wind power production in northern Germany has to be transported to the south via 380-kilovolt power lines. And to maintain grid stability, Germany's four transit grid operators increasingly have to take action, as Renewables International reported.
According to the transit grid operators, December 2011 was a record month for wind power, with nearly 7,940 gigawatt-hours (GWh) generated – more than twice as much as in November (2,900 GWh) or in December 2010 (3,600 GWh). A winter storm on December 8 and 9 caused the wind power to peak at 19 GW, near the maximum wind forecast for northern Germany. As a result, coal and gas plants in northern and central Germany had to be ramped down to make way for wind power on the grid. At the same time, Block C of RWE’s Grundremmingen nuclear plant, which serves consumers and southern Germany, also failed.
The shortage would not have been a problem if wind power from the north could have been transported to the south. Unfortunately, Germany has failed to properly expand its grid for this purpose. The operating reserve in southern Germany was then insufficient because conventional power plants had been ramped down, and grid operator Tennet had not expected a nuclear plant to go offline when two defective fuel rods had to be swapped out. In addition, Tennet apparently attempted to export wind power to southern Europe according to media reports on January 4.
"There was no alternative to the cold reserve," as reserve power plants not in use are called in German, "when Grundremmingen went off-line," Tennet spokesperson Ulrike Hörchens told Renewables International. She called the event "precautionary measure" that turned out to be the right decision. "We initially only ramped up the plant to its minimum capacity, but then we had to use its full capacity of around 1,000 megawatts for both days," she explained. In addition, two gas turbines and an old oil power plant in Austria were reactivated. Tennet says the event is unprecedented, but it also had to intervene on the grid 990 times on 309 days last year – three times more often than in 2010. The regulatory measures include delayed maintenance of power plants and the rescheduling of grid servicing so that power plants and power lines of sufficient capacity are available.
Tennet says the cost of grid stabilization has already crossed the million-euro threshold. And these costs will be passed on to consumers as grid fees. If the winter turns out to be harsh and Germany experiences a long cold spell, Hörchens says the situation could worsen, and the "cold reserve" could become a regular feature on the German grid.
After the German government switched off some 40 percent of its nuclear power capacity in March, Germany's Network Agency signed agreements with owners of disused power plants to ensure emergency operating reserves for the German grid. This "cold reserve" has a capacity of around two gigawatts, one of which is in Austria. Eon’s old high-voltage grid, which Dutch state-owned grid operator Tennet took over, faces the greatest fluctuations thanks to wind turbines in northern Germany. This transit grid is a sort of a corridor between the states of Schleswig-Holstein to the north, Hessen in central Germany, and Bavaria to the south.
Nonetheless, the Network Agency says the reliability of German power grids and gas networks remains high. "But this quality will only remain high over the long term if the grid is expanded in pace with the growth of renewable power," argues Matthias Kurth, head of the Network Agency. (Niels Hendrik Petersen / Craig Morris)