When the wind doesn't blow

By 2020, more than a third of Britain's electricity will be generated by wind power, according to government plans. One problem - six out of 10 days aren't windy enough to make sufficient power. So what happens then?

On a clear summer's day the Horns Rev wind farm off the coast of Denmark could almost double as a tourist attraction. Watching the rows of 200 foot white steel turbines turning gently in the wind, occasionally catching the afternoon sun is beautiful, almost hypnotic.

To see it properly you need a helicopter, as it's in the middle of the North Sea. I had hitched a ride with Bent Johansen, who manages the operations of Danish turbines for the energy company, Vattenfall. For him the future of wind is off-shore.

"Horns Rev can produce as much power as all our 300 onshore turbines put together," says Mr Johansen.

Horns Rev is currently the biggest off-shore wind farm in the world, covering an area of over 20km. In the next decade Britain will be seeing its own versions of Horns Rev cropping up off the coastline.

The government estimates about 35% of electricity will need to be generated from wind power by 2020, to meet an EU target. This will mean a massive increase in the amount of wind power generated, from 2% at present to 35%.

It's a big leap, admits Maria McCaffery of the British Wind Energy Association, "but we believe it is possible".

Denmark is the poster boy for wind power - 20% of the electricity it generates comes from wind, it claims. Horns Rev can provide enough power for 150,000 homes. On the day I visited it would be lucky to power a village. So what does Denmark do when the wind doesn't blow?

The answer is on the giant screens which dominate the control room of Energinet, the Danish national grid. Peter Jorgensen, the vice president of Energinet, directs me to the map of Scandinavia which fills one vast screen. On it are the unique energy connections Denmark has to its neighbours in Norway, Sweden and Germany.

This allows them to import power when it's not windy or export it when they have too much.

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