Air traffic controllers often veto preliminary applications for new wind farms because radar screens cannot differentiate between aircraft and the turbines. National Air Traffic Services (NATS) says that a wind turbine’s spinning propellers can be picked up as clutter on screens, leading a controller to believe that there are unidentified light aircraft in the air.

The airport operator, BAA, describes the clutter effect on radar screens as similar to “flying into a snowstorm of planes”.

Wind farms can also obscure low-flying aircraft when they pass out of the line of sight behind a turbine, NATS says.

Richard Wright, the spokesman for NATS, said: “If there is an air traffic tower and on the next hill there is a wind farm and behind that there is an airport, then the wind farm could cause a shadow preventing radar from picking up the signals of aircraft. This is a safety hazard.”

Before a provisional wind farm planning application can be approved, it must be scrutinised by NATS, the Ministry of Defence, the Civil Aviation Authority and the Met Office.

Nearly half of draft plans are rejected each year, according to NATS and the wind energy industry. NATS is looking at more than 1,000 applications for wind farms.

Wind energy specialists believe that the Government’s target of 10 per cent electricity from renewable energy, up from today’s 3 per cent, by 2010 may not be met. A later target of 20 per cent of electricity generated from renewable sources is also in doubt.

Chris Tomlinson, the head of onshore wind at the British Wind Energy Association, says that wind energy will play a crucial role in helping the Government to achieve its objectives.

“Wind energy is expected to provide 7 per cent of renewable energy in six years’ time,” he said. “It is less than 1 per cent at the moment while hydro power makes up about 2 per cent.

“The rejections are certainly hindering the chances of meeting the 2010 target by taking out half of suitable areas for wind farm developments in the UK.

“It is difficult enough to find sites as it is. For 50 per cent of sites to be nullified will threaten not only the 2010 target but certainly the 2020 target.”

There are 90 wind farms across the UK comprising 1,000 turbines, most on land. Another 2,000 must be built to meet the Government’s 2010 target.

NATS insisted that it was not trying to stand in the way of wind energy expansion but had to safeguard air safety.

A Department of Trade and Industry spokesman said: “We anticipate sustained building of wind farms both on and off shore over the coming years, making a major contribution to meeting our targets on renewable energy. To date, very few have been turned down on grounds of air safety.”

Wind energy promoters are funding research on software to help air traffic controllers to differentiate between wind farms and aircraft.

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