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UNKNOWN MALE:'Many of the things that we work on are mission critical. They save lives, they protect our troops.

ROB:QinetiQ work on classified government projects. So everybody is security cleared. At least as far as Restricted, often up to as far as Secret.

NARRATOR:'QinetiQ is an international company that specialises in top secret government defence projects.

NARRATOR:'But one of their current projects, involving smart materials as used in stealth technology by the military, is now being used in the production of wind turbines.

NARRATOR:'By 2020, the UK must increase its green energy production from two to 15%. And as we're Europe's windiest country, harnessing this resource could be the key to helping us meet this target.

NARRATOR:'A single on-shore wind turbine can meet the energy needs of 1,100 households a year.

NARRATOR:'But there is a serious problem with them.

NARRATOR:'Across the country, the construction of thousands of turbines, enough to provide power for 3.4 million homes, are on hold, because of the unique effect they have on aviation radar.

NARRATOR:'Air traffic controllers use bounced radar pulses to locate moving objects.

NARRATOR:'Because of their spinning blades, turbines reflect these pulses in the same way as an aeroplane. So air traffic control can't distinguish between a wind farm and a rogue moving aircraft.

NARRATOR:'But now engineers believe they may have found the solution.

NARRATOR:'Stealth technology.

NARRATOR:'For over six decades, they've been working on ways to make boats and planes disappear from enemy radar. And now the team are applying these techniques to the wind turbine problem.'

GREG FIXTER:Ready?

UNKNOWN MALE #2:Yeah.

GREG FIXTER:Clear, yep.

UNKNOWN MALE #2:Looking good?

GREG FIXTER:Round about 30db.

GREG FIXTER:'Stealth is the shape of the vehicle' and it's the materials that it's made of.

GREG FIXTER:So you either reflect the signal

GREG FIXTER:away from the radar that's looking for it in a different direction, you do that by shaping the aircraft or ship, or you make it out of something that absorbs the energy that's been sent out by the radar.

NARRATOR:'QinetiQ don't build wind turbines, so they're working with one of the world's biggest turbine manufacturers, Danish company Vestas, to solve the problem.

NARRATOR:'It's been a hugely complex challenge.'

NARRATOR:'because every inch of a turbine blade has been precisely engineered for maximum performance, the shape, weight or manufacturing process can't be changed.

NARRATOR:'Engineers here are working on a special solution to add stealth material layers into the composite skins of the blades.

STEVE APPLETON:These guys are just measuring and marking the position of the various materials, so that we get them in the right place.

STEVE APPLETON:It's important that we put these materials in exactly to within a few millimetres, otherwise we could upset the later joining of the two parts of the mould.

STEVE APPLETON:It's nice to get away from computer models of what we're doing and actually work with these guys and see it coming together as a component.

NARRATOR:'The composition of these layers is a closely guarded secret, but they work by absorbing most of the radar pulses, so only a very small amount is reflected.

NARRATOR:'With the weakened returned pulse, the turbines become distinguishable from aircraft to radar operators.

NARRATOR:'Initial tests are positive, and the teams are now building what will become the world's first stealth turbine.

NARRATOR:'It is a breakthrough for QinetiQ, and a brilliant example of how a smart material developed for the military, is being utilised to enable the development of renewable energy sites.'