The UK's Ministry of Defence (MoD) is blocking five of the country's 18 proposed offshore wind farms, claiming that they will interfere with military aviation radar.

In a classic demonstration of how not to do "joined-up government", the MoD's objections will almost certainly prevent the government from meeting its target of generating 10 per cent of electricity from renewable sources by 2010. Chris Shears of the British Wind Energy Association (BWEA) told New Scientist that MoD opposition is the most important obstacle facing offshore wind development.

Four of the threatened wind farms are in the Irish Sea off the coast of Lancashire. The fifth is in the North Sea, off Cromer in Norfolk. All five are close to RAF bases, and the MoD is concerned that they might interfere with air traffic control, and possibly provide cover for enemy aircraft.

The main problem is that wind turbine blades can show up on the radar used to track planes. "You get this sort of twinkling effect," says Malcolm Spaven, a consultant to BWEA. He says that this makes it difficult to pick out planes flying close to the turbines.

But Spaven points out that air traffic controllers routinely cope with interference from other sources such as trees and moving vehicles. He thinks that the MoD should talk to RAF operatives to find out whether the wind farms would really constitute an unacceptable distraction. "It all depends how much clutter controllers are prepared to deal with," he says.


Invisible planes


Turbines may also create a radar shadow behind them, where planes would be invisible, but this idea is controversial and in any case would only affect a tiny volume of airspace about 100 metres high, extending just 500 to 700 metres behind the turbines.

Germany and Denmark have found simple technical fixes for the interference problem. The Middelgrunden offshore wind farm, for example, is just eight kilometres from Copenhagen airport, but according to Christian Soerensen of Spok Consult, all they needed was a small software package fitted to the radar system, which filters out the signal from the turbines.

Other potential solutions lie in using radar-absorbent materials to build the turbines, carefully choosing the spacing between them, and turning them off under certain conditions.

A spokesperson at the MoD denied that the organisation is generally hostile to turbines. "Each case is judged on its merits," he says. He adds that the MoD is commissioning studies, along with the Department of Trade and Industry, that will look into mitigating the effects of interference. He did not give any details.

Spaven says he has become frustrated by MoD opposition. "It is rather difficult to get the MoD into a practical dialogue," he says.


James Randerson



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