A THREE-dimensional radar system may finally have solved a problem hindering the roll-out of wind farms across the UK.
Wind turbines reflect radar signals because their carbon-fibre blades are shot through with metal lightning conductors. That means they are picked up by the radar used for controlling air traffic 鈥� but current systems can鈥檛 distinguish between flying planes and whirling turbines, creating serious safety concerns.
Air traffic control radar is designed to screen out stationary objects, identifying moving objects from the Doppler shift in their reflected signals. But the resolution of current systems is not fine enough to distinguish between the Doppler shift from an aircraft and one from a moving turbine blade. Since the radar beam scans the horizon, hitting targets for only a few microseconds in every 4-second sweep, objects are not sampled for long enough to tell them apart.
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鈥淭he turbines look like twinkling blobs and an aircraft looks just like one of those blobs, so you can鈥檛 tell which is which,鈥� says Chris New, a radar engineer with Qinetiq in Portsmouth, UK.
The upshot of this is that until now wind farms have only been built where there is no aviation radar nearby. That鈥檚 not too much of a problem in the wide open spaces of the US and continental Europe, but is more limiting for a small island like Britain. Forty wind farm projects that would have generated up to 6 gigawatts of power 鈥� representing 拢12 billion of investment in renewable energy 鈥� have been refused planning permission for this reason.
Not for much longer, perhaps. Cambridge Consultants, an engineering firm in the UK, has developed a radar that can make the distinction. CCL鈥檚 answer is to replace the troublesome scanning process with one that produces a low-power radar beam that 鈥渋lluminates鈥� the whole sky above a wind farm 10 times per second, rather than once every 4 seconds. This produces a 3D picture of the airspace which CCL calls 鈥渉olographic鈥� radar. This increased sampling rate provides the Doppler resolution needed to distinguish between aircraft and wind turbines.
Software takes care of the rest. 鈥淭urbine blades have a spread of different velocities along them that generate little glints 鈥� and a computer can recognise those as very different from a plane,鈥� says Craig Webster, an engineer at CCL. The company is planning tests of the system at a wind farm in Swaffham, Norfolk.
Qinetiq is also filing patents for a radar system that will not confuse aircraft with turbines, says Samantha Dearman, who assesses the impact of wind farms on aviation radar for the company.
New adds that work is beginning on the inclusion of military stealth technology into wind turbine blades. If exotic coatings can make blades transparent to radar, future wind farms may not require special systems at all.
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