WIND ENERGY

Rotors take to the high seas

Having exploited the North Sea’s oil and gas resources since the 1960s, Europe has already acquired extensive experience with platforms at sea. It is currently enriching this experience with the DOWNVInD (Distant Offshore Windfarms with No Visual Impact in Deepwater) project, which focuses on an inexhaustible resource: powerful and steady offshore wind. The wind generators measure 126 metres in diameter… yet are almost invisible.

© EWEA/WINTER © EWEA/WINTER

According to the latest estimates from the European Wind Energy Association (EWEA), by the end of 2007, one-quarter of the European Union’s energy requirements could be met by installing wind generators across 5% of the North Sea’s total surface area (1). However, we are currently a long way from this proportion.

Only five countries use offshore wind energy at present: Denmark, Ireland, the Netherlands, the United Kingdom and Sweden. At the end of 2006, their cumulative 900 MW represented only 3.3% of the European Union’s wind-energy production. Today, their 25 offshore wind farms produce 1 100 megawatts. The conclusion is plain. Only a small portion of Europe’s offshore wind energy resources are being exploited.

However, on 10 December 2007, amid a blaze of publicity the British government announced the launch of a national plan designed to supply 33 GW of electricity (or 33 000 MW – one-fifth of national requirements) to the country using offshore wind energy between now and 2020.

Based on the use of current technology, this would require no less than 7 000 turbines to be built. The project’s critics, complaining of the resulting disfigurement of the landscape, have made the somewhat misleading but hard-hitting calculation that this would mean seeing a wind generator every 800 metres all along Britain’s coastline … Obviously nobody seriously envisages distributing wind turbines all along the coast. On the contrary, the DOWNVInD project is seeking to make them as unobtrusive as possible.

The aim of this €65 million project, of which €6 million is funded by the European Commission, is to set up and test offshore wind generators far out at sea in places where they are barely, if at all, visible from the shore.

Inspired civil engineering

The chosen site is 25 km out to sea in the Moray Firth off north-east Scotland. The new wind farm was given the quaint name of Beatrice Wind Farm, after the Beatrice oil rig only a few hundred metres away, which it has been supplying with one-third of the rig’s electricity requirements since July 2007. The two wind generators that make up the wind farm, each with a capacity of 5 MW, are the first ever to be erected in waters around 50 metres deep. Up to now, such structures have been built only at depths of around 20 metres. “Our chief problem has been to erect such a large infrastructure at sea so far from the coast”, explains Allan MacAskill, Director of the DOWNVInD project. “Many parts were assembled onshore and transported out to sea to be set up at the correct site. In fact ‘only’ two trips were required: the first to transport the substructure jacket for anchoring the wind generator to the seabed and the second to transport the tower, turbine and blades previously assembled onshore.” This is quite a civil engineering feat, since the two wind turbine generators are immense. The 70-metre-tall substructure jacket, 20 metres of which will be submerged, weighs 750 tonnes.

Although the tower-turbine-blade unit weighs less than 1 000 tonnes, it is rather bulky: with its 88-metre-high tower and 63-metre-long blades, the total diameter is 126 metres… After anchoring the substructure jacket, the engineers transported the wind generators in a vertical position, before setting them down on the substructure using giant floating cranes.

And the environment?

In parallel with the many studies conducted for the erection of these two turbines, the University of Aberdeen in Scotland has piloted a number of research programmes to assess the potential environmental impact of such wind generators both on the shores of the Moray Firth and out at sea. A maximum number of scenarios was considered in all project phases, ranging from onshore assembly to the operation of the turbines, including transporting, fixing, installing and maintaining the structures, dismantling them at the end of their life and even possible accidents and emergencies.

DOWNVinD has obviously left nothing to chance. It has made a census of the various animal and plant species living in the surrounding area, introduced measures to assess air and water quality, together with the visual, noise and electromagnetic impact, conducted surveys of the people living on the shores of the Moray Firth, and so on. A special radar system has even been set up to monitor bird movements through the wind-generator blades.

The public tends to think of the sea as an area to be left wild and untouched. It is not risk-free for a company to set up major infrastructure that could harm nature, including in terms of image. To convince industry of the benefits of exploiting the potential of offshore wind energy, DOWNVinD therefore had to lay all its cards on the table.

According to Allan MacAskill, “The greatest challenge for DOWNVinD is to create the technical conditions for developing largescale, commercially viable projects. In other words, to set up wind farms with 200 wind generators, not just two like the Beatrice Wind Farm.”

Matthieu Lethé

  1. Delivering Offshore Wind Power in Europe, www.ewea.org.

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Very small wind generators

While offshore wind generators can be viewed as the extra-large version, there is also an extra-small version: urban wind generators. Specially designed for built-up areas where winds behave highly randomly, these small wind generators are usually positioned on or near building roofs. Their design, tailored to suit these special conditions, differs significantly from that of conventional wind generators. The main difference is that the axis of rotation of urban wind generators is vertical rather than horizontal.

They have a fairly small capacity of between 1 kW and 20 kW (that is, between 0.001 MW and 0.02 MW), which does not allow them to supply all the requirements of an ordinary building. “This is probably their main drawback”, admits Patrick Clément, coordinator of WINDEUR – a project to raise awareness and provide information on small wind turbines in an urban environment, which is 50% funded by the European Commission (to the tune of €450 000). “As the output is quite low, manufacturers are not interested in them, and so costs remain high. Wind generators are in the same situation today as photovoltaic systems were 15 or so years ago: they were expensive because production was only on a small scale.” However, the technology is already highly developed and, while a few elements could still be improved, such as the profiles and the electronic starting and shut-down systems, several groups have launched projects of varying sizes. “The Netherlands and UK are particularly proactive in this area”, says Patrick Clément. “For instance, The Hague is developing a project for 50 or so small wind generators in the city. And France’s electricity generation and distribution giant, Electricité de France (EDF), has applied to the European Commission for technological research funding. This is a sign of its potential.”



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