91色情片

WIND power enthusiasts have been a little flustered this week. An energy analyst has claimed that the UK government鈥檚 plans to derive a fifth of the nation鈥檚 energy from renewable sources by 2020 are not feasible.

The majority of this power, some 20 gigawatts, is to come from wind energy, but Hugh Sharman, principal of the energy consulting and brokering company Incoteco in Hals, Denmark, argues that the UK鈥檚 energy grid will not be able to handle more than 10 gigawatts (Proceedings of the Institute of Civil Engineering, vol 158, p 161).

The report comes at a time when environmentalists are already more than usually worried. 91色情片s from UK prime minister Tony Blair on 1 November suggested that he was drawing back from emissions targets as the way to tackle climate change. And a report on 10 November on the looming 鈥渆nergy gap鈥� caused by the shutdown of nuclear power stations recommended building more nuclear plants.

Now Sharman says we can鈥檛 rely on wind power. The problem, he says, is that the wind doesn鈥檛 blow when we most need electricity. Typically turbines start generating energy at wind speeds of 4 metres per second and reach full capacity at 14 metres per second. They shut down again at around 25 metres per second (above gale force 9) to protect the drivetrain and gearbox.

West Denmark, a region one-seventh the size of the UK, has 2.4 gigawatts of wind capacity delivering over 60 per cent of the region鈥檚 power. This is only possible because of well-established connections with Sweden and Norway that allow the country to import or export electricity to balance supply with demand. The UK does not have equivalent links and so would not be able to do this.

What is more, Sharman says that Germany鈥檚 turbines, which have a capacity of 17 gigawatts or 14 per cent of the total energy demand, shut down so frequently that averaged over a year they only generate around 15 per cent of their notional capacity.

Should the UK be concerned by the experiences of Denmark and Germany? Not really, says Robert Gross of the UK Energy Research Centre in London, a publicly funded research organisation. The clustering of both countries鈥� wind farms makes it difficult to extrapolate to the British situation, he says. Denmark鈥檚 farms are concentrated in the west, and Germany鈥檚 in the north-west. The wind speed and direction are also more variable in Germany because of its continental climate.

鈥淚t means the potential swings that the system needs to cope with can be much greater than they would be in the UK,鈥� says Gross. If turbines are dotted more evenly around the UK as is planned, there will be a 鈥渟moothing鈥� effect on the energy from wind. When wind farms at one end of the country are not generating electricity, the chances are turbines elsewhere will be running.

Even so, Sharman thinks that dealing with the variable supply from wind will mean building excess capacity into the system in the form of gas-fired power stations, for example, reducing the climate gains. But arguably this is not a problem unique to wind. All forms of generation need to be backed up to cater for unexpected power outages caused by faults. And although wind speeds do vary, they can been predicted pretty accurately over the timescale of a few hours.

In short, it is not valid to extrapolate from the Danish or German experience, says Graham Sinden of the Environmental Change Institute at the University of Oxford. 鈥淚t presents a more negative view than UK data would suggest.鈥�