Sweden joins Denmark and Holland at sea

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Final permission for an offshore wind farm in Swedish waters off Gotland was granted by the government's water board on August 20. Test drilling to analyse the sea bed will start this month and the 2.5 MW wind farm will be installed in August next year.

The first off shore wind farm in Sweden, Bockudden-Valar will consist of five slightly modified but otherwise standard 500 kW Wind World turbines from Denmark. It is to be jointly developed by Swedish wind developer Vindkompaniet of Gotland, British company Seacore and WindWorld. Seacore specialises in offshore drilling and construction.

The wind plant, four kilometres off Näsudden, is intended as a pilot project to develop a new method for installation of wind turbines offshore. It will also test new electronic equipment for connecting wind turbines to a weak grid. Early last month the developers learned that their application for inclusion in this year's round of European Commission funding under its Thermie programme had been approved. Thermie will pay 32% of the total costs.

Originally, construction of the wind farm was scheduled for this year, but fears for the local seal population off Näsudden slowed the permitting process. Now an important part of the project will be a comprehensive report on seals and wind power to build a fund of knowledge for future use in other projects. The seal population will be closely monitored -- also by video camera.

When complete, Bockudden-Valar will be the fourth offshore wind farm on line, joining Vindeby (11 x Bonus 450 kW units) and Tunø Knob (10 x Vestas 500 kW) in Denmark and the four Nedwind 500 kW turbines in the Ijsselmeer in Holland. But unlike any of these projects, the turbines will be stepped on solid cylindrical piles for which holes were drilled into the rocky sea bed. In Denmark the turbines are mounted on heavy concrete foundations resting on the sea floor, while the Dutch turbines sit on 25 metre pillars poled into to the soft sea bed of sand.

Through eight metres of rock.

The piles for the Gotland plant will be placed in seven to eight metre holes drilled into rock by Seacore in six metres of water. Seacore is experienced in laying pillars for bridge-building. This work will be carried out from a work platform and the turbines will be hoisted from the platform too. According to the developers, the cost of these foundations is comparable with the concrete foundations used in Denmark. However, the use of a work platform, with the turbines and piles on a barge, rules out the need for a floating crane and other heavy vessels. This will become a significant economic advantage in the larger offshore projects envisaged for the future, says Göte Niklasson of Vindkompaniet.

The five Wind World turbines will be sited in a V-shaped formation 350 metres apart, with the tip of the V pointing towards the prevailing southwesterly winds. An underwater cable will link the plant into a 10 kV grid four kilometres distant. Innovative electronics developed by Wind World, for which the Thermie support was granted, allow the connection of 2.5 MW to such a weak grid. Without the 32% Thermie support the project would have been in doubt. The drawn-out permitting process meant that Vindkompaniet missed the chance of gaining a 35% government wind subsidy for the project. Government wind subsidies in Sweden have now run dry. However, if the subsidy pot is replenished, the offshore project could still win a subsidy.

The project's economic disadvantage compared with those onshore does not concern the developers. According to Vindkompaniet's Andreas Wickman, the economic profit from the project will be minimal, but in terms of know-how quite considerable. Although construction at sea adds 30% to the cost, this will be compensated for by an expected 30% increase in output. Several Wind World 500 kW units are already turning at Näsudden, allowing for a direct comparison of the advantages of harnessing offshore winds. The experience gained by Vindkompaniet will be used in future projects offshore in Sweden as well as in Britain, says the company, where it intends to use megawatt class wind turbines. Vindkompaniet already has rights to offshore areas near Gotland for three 56 MW wind farms and identified suitable offshore sites in the southern half of Sweden for a total production from wind energy of 10 TWh a year.

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