IN A blaze of publicity last month, the UK government announced the world鈥檚 biggest ever expansion in wind energy. But on past form, over a third of the proposed developments will fall at the first hurdle because of objections from the Ministry of Defence that the turbines will interfere with radar. 鈥淪tealth turbines鈥� may be the answer.
Radar problems remain one of the key barriers facing the industry, says Chris Tomlinson of the British Wind Energy Association. The MoD opposes 34 per cent of all proposals for new wind farms at the pre-application stage 鈥� before a formal planning application. Other radar operators such as civil aviation, marine navigation and weather stations also raise objections that are often enough to scare off developers.
Because of their size 鈥� turbines can be up to 180 metres high 鈥� and the way they rotate, wind turbines are a headache for radar operators. The magnitude of the radar 鈥渞eturn鈥� signals reflected from a turbine can be a thousand times that from a small plane. And unlike the returns from a building, they can be difficult to filter out, because the radar can pick up different blades with successive scans, says Andy Beck, a radar expert at military research company Qinetiq in Malvern. This creates a twinkling effect that interferes with the returns from an aircraft flying over the wind farm (快猫短视频, 27 April 2002, p 8).
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To get around the problem, Qinetiq is developing turbine blades that are nearly invisible to radar. The technology is already out there, says Stephen Appleton, who heads the project. The trick will be applying it to wind turbine blades without adding to their cost or compromising their strength. The idea is to reduce the strength of the radar return to a level at which it can be filtered out. 鈥淲e鈥檙e not trying to make a stealth bomber,鈥� he says.
The new turbine material will combine radar-absorbing materials with thin layers of radar-reflecting materials, each of which will return a separate radar signal. These separate returns will interfere with each other to produce a weakened overall signal. If the peaks from one signal exactly coincide with the troughs from another, the two will cancel each other out, while near matches will reduce the overall trace.
Beck expects to have designed a suitable material within a year. But even if the new designs show promise, they will come too late for developers bidding for the current offshore wind developments. They must submit their proposals to the government by October.