Towards a Cleaner Marine Environment
10. Marine wind turbines - a new source of energy
Fresh winds blow over Danish waters. This makes it tempting to erect wind turbines at sea. There is plenty of space and the noise of the generators is apparently not a disturbance at sea. Five wind power farms are planned for completion in Danish coastal waters by 2030, so that our wind turbines will supply 35 percent of Denmark's energy consumption, the major part by the above five farms. The goal is to reduce coal and oil consumption, thus reducing our contribution of CO2 to the atmosphere and, therefore, enabling Denmark to contribute to reducing the greenhouse effect and global warming.
A decision has therefore been made to construct five test installations, each with about 80 giant wind turbines. Each installation will be able to produce about 500 mill. kilowatt hours, or the equivalent of the annual electricity consumption of 125,000 households. The first two installations at Horns Rev and Rødsand are expected to be finished within a few years. The test installations must manage their own engineering and economic conditions, which will be included in the assessment of the environmental impact of wind turbines in general.
Focus on effects
The main environmental benefit of marine wind turbine farms derives from their permanence as a source of energy. But such large installations can have negative effects on the environment during the construction and operating phases.
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Demonstration projects - Siting of wind turbine farms in Denmark |
The environmental effects are highly dependent on the location of the wind turbine farms. The first step is to perform an Environmental Impact Assessment (EIA). The EIAs for Horns Rev and Rødsand indicated limited environmental effects. The Rødsand area, where the sea-bed is particularly abundant and where many migratory birds and seals gather, is most exposed.
In fact, the foundations of the marine wind turbines will act as artificial reefs and will attract a wide variety of the animals and plants normally found on reefs - especially mussels which, in turn, attract fish and birds. In other words, we must decide whether or not we wish to attract flora and fauna that do not have their true habitats in these areas.
Birds and marine mammals
Marine wind turbines can possibly constitute a threat to migratory birds. The extent to which these birds would fly into the turbines - especially in poor visibility - is not known. Birds are therefore closely observed at Rødsand. All bird migrations are recorded and modelled under the conditions estimated to prevail when the turbines have been erected.
Such marine mammals as seals and porpoises will hardly be disturbed by the finished wind turbines, provided that the turbines are not sited at their breeding grounds. The underwater disturbance from the turbines is limited, and the magnetic field that surrounds the undersea transmission cable does not appear to disturb the animals significantly. Thus, there is much to indicate that marine wind turbines have only a limited effect on the marine environment. The continual nature and environmental monitoring of the first test installations will broaden our knowledge base in a few years' time.