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Last Updated: Tuesday, 11 December 2007, 10:02 GMT
Q&A: Offshore wind farms
Burbo Bank wind farm
Britain's newest wind farm - Burbo Bank off the coast of Liverpool

Energy secretary John Hutton has announced plans to build 7,000 offshore wind turbines around Britain's coastline.

How much of a contribution will this ambitious project make to the UK's energy needs?

And what are the pros and cons of offshore wind farming, compared to conventional energy sources?

Where are they built?

Up until now the turbines were built about three or four miles out to sea - but there are now plans to site them further offshore to reduce their visual impact.

Engineers sink a huge pile into the sea bed. They construct a platform, and the turbine is assembled on top of it.

Offshore wind turbines have big advantages over onshore ones. They can be built a lot bigger and there is a lot more wind out at sea rather than on land.

How do they work?

The technology is easily understandable: turbines are basically big windmills that use the energy of moving air to generate electricity.

Sensors on the turbine detect the wind direction and turn the blades into the wind. The blades then power a generator to convert the energy into electricity. Undersea cables then carry the electricity to land where it goes into the national grid.

For: environmentally friendly
For: the wind is free - and not owned by foreign governments
Against: expensive to build and maintain
Against: not 100% reliable - the wind can drop.

To give an idea of how much electricity wind farms generate, the Inner Dowsing /Lynn wind farm in the Great Wash will have 54 turbines generating 194 megawatts. That is enough to supply a city the size of Coventry.

What is the potential of offshore wind power?

With its 7,760 miles of coastline, the UK is ideally placed for offshore wind generation.

Under the current offshore wind farm programme about eight gigawatts (GW) are expected to be generated by 2016.

John Hutton's new proposals allows for that figure to rise to 33GW. The government ultimately wants up to a third of Britain's electricity to be generated from offshore wind power.

But this needs to be seen in the context of current performance. On current trends, it may be that the industry might not produce enough power to help meet the government target of 10% renewable energy by 2010.

The British Wind Energy Association (BWEA) says offshore wind could potentially generate close to 1,000 terawatt hours per year. That is equivalent to several times the UK's current total electricity consumption.

The BWEA predicts that a substantial proportion of the total European offshore wind resource will one day be located in Britain's waters.

Who will build the wind farms?

Most of the major utility companies - like British Gas (Centrica) and NPower - have invested in the industry.
Windmill and power station

About a dozen firms - such as Airtricity, EDF and Eon are currently running or planning offshore wind farms.

There are already five major off-shore wind farms generating power for the national grid: North Hoyle, off the coast of North Wales, operated by NPower; Scroby Sands, off the coast of Great Yarmouth (Eon); Kentish Flats off Whitstable in Kent (Vattenfall), Barrow off the Cumbrian coast (Dong Energy/Centrica) and Burbo bank, in the mouth of the Mersey river (Dong Energy).

How expensive are they?

Offshore wind farms cost significantly more to build and maintain than their onshore equivalent. And because they involve new and untested technology they also suffer from "first of a kind" costs. But the industry is confident that those costs will fall over time.

It is difficult to compare the cost of electricity obtained from a wind farm rather than a conventional energy source like gas. This is because it involves assumptions about future construction costs, the cost of carbon emissions, and the cost of gas.

However, right now offshore wind farms are significantly more expensive than thermal generation and require a government subsidy to make them economic. The industry estimates that electricity from offshore wind farms costs more than 10p per kilowatt hour to produce, compared to natural gas at around 4p per kilowatt hour.

Are wind farms environmentally friendly?

One of the reasons companies have moved into offshore wind generation is because supporters say they are much less visually intrusive than windmills on land.

In other words, unlike a wind farm in the unspoilt Lake District, there is less risk of the neighbours complaining.

And if there are no disputes about planning permission, then there is more chance that the wind farms will be built quickly - which means less cost to the industry.

What about wildlife?

Offshore wind generation is generally wildlife-friendly, according to a Danish report published last year.

Offshore wind power is thought to be environmentally friendly.

Danish energy companies and the Danish government carried out an eight-year study into the environmental impact of world's two largest offshore wind farms, Horns Rev and Nysted.

The study concluded that seabirds rarely collide with the turbine propellers and that fish and other sea life flourished in the artificial "reefs" created by the turbine undersea structures. And although seals and porpoises moved away from the wind farms when they were under construction, they are slowly returning.

Most importantly, supporters of offshore wind power say all forms of energy supply have environmental drawbacks. However, they say that compared to the risks of global warming or nuclear meltdown, wind power is the most environmentally-friendly option we have.

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