Germany Wind Integration: Wires below the surface speed up grid build

A new German law is speeding much-needed expansion of transmission capacity by allowing new wires to be built underground in a fast-track permitting process.

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Four pilot project expansions of Germany's high-voltage grid network are now on a fast-track permitting process initiated by a new law that took effect in June. The projects are deemed critical for the future of both offshore and onshore wind in Germany, says the national energy agency, Deutsche Energie-Agentur (DENA). The four projects are paving the way for a series of underground high-voltage cables that will facilitate the passage of large volumes of wind generation in the north of the country to centres of population in the south.

Some 43 GW of offshore wind is planned off Germany's northern coastlines fronting the Baltic Sea and North Sea, and more than half the country's 23.9 GW of onshore wind power is already concentrated in the windy rural north, with more to come. With all the offshore wind power by necessity feeding into the northern grid, a serious bottleneck on the wires threatens, warn Germany's transmission system operators (TSOs).

Each of the pilot projects involves laying 380 kV cables underground, an option three to ten times more expensive than stringing overhead cables on pylons. Public opposition to land lines is the reason for pursuing the underground route, to speed up the permitting process. But the much greater cost of the underground option has set alarm bells ringing at the Bundesverband der Energie und Wasserwirtschaft, the national federation of energy and water utilities. It warns that household and industrial electricity customers are likely to face higher bills as network charges rise.

The 380 kV cables follow four routes: Wahle-Mecklar in central Germany; Ganderkesee-St Hulfe and Diele-Niederrhein in the north-west; and Altenfeld-Redwitz in the south-east (map). The law initiating them, Energieleitungsausbaugesetz, or Enlag, simplifies the approval process for new wires. A streamlined procedure - until now reserved for motorways, airports and railways - is being applied to construction of cables with voltages of 110 kV, 220 kV and 380 kV. It bundles into one process a tangle of permits until now required from multiple authorities.

Congestion tales

Germany's high-voltage transmission network was originally built to carry power in bulk from large power stations across the country along a high-voltage 380 kV network, then to 110 kV wires crossing rural regions and finally across local networks at lower voltages to households. That configuration is far from suited to Germany's large scale introduction of wind power over the past 20 years, with its current concentration of turbines in the more windy north, far from centres of demand.

Congestion on the wires is a problem, the TSOs claim. They say it can become particularly acute at night, during public holidays and in other periods when winds might be high and electricity demand low. In the east of Germany, regional network company Enviam Netz points out that it has 2.8 GW of wind feeding into its system along with 412 MW of other renewables and just 1060 MW of non-renewables. It says that on 30 occasions between 2008 and mid-June 2009 it had to curtail renewables generation, mainly wind, over periods ranging from 32 minutes to more than ten hours. The curtailments of capacity varied from 0.2 MW to 473 MW.

These curtailments were necessary because some stretches of the existing high-voltage transmission wires have insufficient capacity to transfer the wind power to urban centres in central and south-west Germany. A study by DENA published in 2005 identified where new transmission is needed and by when. The authors of Enlag drew from the study in specifying the routes of the 380 kV underground cable pilot projects. Under the new law, fast-track permitting for 110 kV underground cables is only facilitated where overhead cable project planning has not begun and where the cost is no more than 1.6 times that of a technically comparable overhead cable.

Federal wind energy association Bundesverband Windenergie (BWE) says it is generally pleased with the law. It points out, however, that the insistence on overhead cable projects being continued, instead of allowing them to switch to the underground option, will slow network upgrades by many years as public opposition kicks in. BWE estimates that while construction of 110 kV underground cables is up to three times more expensive than building the overhead variety, when the costs of a protracted permitting battle are taken into account along with the lower maintenance costs of underground wires, overhead cables could end up being more expensive.

Unlike 220 kV and 380 kV transmission lines, 110 kV cables are already widely used underground, especially in urban areas, adds BWE. As recently as November last year, Danish network company resolved to draw up a plan on how and when its regional transmission grid, made up of 132 kV and 150 kV lines, can all be put underground over the next few years.

Norway-Germany link

One of the first transmission projects to benefit from the streamlined procedure could be NorGer's 570 kilometre, 1400 MW direct current, high-voltage link from the German North Sea coast near Wilhelmshaven to Kristiansand on the Norwegian coast. The cable link could help deal with power surpluses generated by steadily growing onshore and offshore wind capacity in northern Germany by allowing its temporary storage in Norwegian pumped-storage hydro stations (box).

More such cross-border cable link projects may be needed in the longer-term future. By around 2025, Germany could have as much as 45 GW of wind capacity in operation on land and offshore. Experts project that, on occasion, the volume of wind power generation could exceed the country's total electricity demand in any specific period. Demand is expected to vary from 40 GW to 70 GW by 2025. Periods of wind power generation in excess of demand could add up to several hundred hours a year. Exporting the power is one option for dealing with surpluses when they occur.

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