German boffins use "anti noise" to silence wind turbines

The dull hum that emanates from many wind turbines could soon become a thing of the past thanks to a group of German researchers who claim to have developed a new sound muffling technology capable of cutting noise levels by an estimated 50 per cent.

Engineers at the at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Dresden claim to have developed an automated noise absorber designed to stop vibrations from a wind turbine's gear box reaching the surrounding tower and being amplified. They are now looking to talk to turbine manufacturers about undertaking field tests for the technology.

Speaking to BusinessGreen.com, Holger Kunze, one of the researchers working on the project, said that many turbines already use some form of sound dampener, but these typically only prove effective at muffling one frequency of sound.

In contrast, the device the IWU team has developed measures the vibrations in the gear box and then feeds electricity into piezo actuators, small devices that convert an electric current into mechanical vibrations. The vibrations feed into a "mesh" around the bear box and are set at a level to cancel out the sound vibrations emanating from the gear box, creating what Kunze refers to as "anti noise".

"The tricky bit was getting the control algorithm right so that the mesh vibrates at the right frequency and can work at variable speeds," he said. "But we've undertaken lab tests where we've managed to cut noise levels by 10 decibels and we'd hope to be able to cut the noise from a turbine by half."

Kunze added that the IWU was now looking for wind turbine operators to help undertake field tests of the technology and was confident the technology could be commercialised. "What is so attractive about the system is that it can be retrofitted to existing turbines," he added.

Noise levels remain a major issue for many onshore wind farm operators with large numbers of proposed projects having been rejected as a result of concerns over the effect of noise on local residents. Energy firm E.ON, for example, recently ditched plans for a 10MW wind farm after concerns over noise forced it to scale down the original the project proposal to just 5MW.

Moreover, many existing turbines are unable to operate at full capacity as a result of noise legislation that can require them to operate at lower speeds in high winds.