Wind power usage is growing at a steady rate. In the U.S., Texas plans to unleash a massive amount of capacity by connecting remote areas with turbines to their main power grid. In China, wind power is growing so fast the targets have to be constantly be revised upwards.
However, for all its potential, wind power has some key criticisms. One major problem is the noise. When wind turbines are placed in populated areas the noise they make when displacing air can be unpleasant. It can range from a whistle to a clatter. As a result, turbines in populated areas are forced to artificially limit their speeds to lower noise. This however results in lower power output.
Now researchers at the Fraunhofer-Gesellschaft Institute have developed technology to effectively cancel this noise, allowing full-speed operation. To accomplish this, they first identified the significant sources of noise -- the rotor blades and the cogwheels in the gear box. They then examined how these sources transmit vibrations into the central tower, causing it to produce a whining pitch that is considered very unpleasant.
André Illgen, a research associate at the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Dresden, explains, "People find these monotone sounds particularly unpleasant, rather like the whining of a mosquito."
As the wind speed varies, the pitch of the noise varies as well. This makes cheaper passive dampening systems ineffective. Current active dampening solutions work better, but they are typically expensive and require rebuilding of the gearbox, as well.
Researchers with IWU worked with a number of other teams -- including researchers from Schirmer GmbH, ESM Energie- and Schwingungstechnik Mitsch GmbH and the Dr. Ziegler engineering office -- to develop a better active dampening solution. The researchers first attached sensors to the gearbox which measured vibrations from the gears and rotors. This information is passed to a control system.
After processing the control system sends a signal to piezoelectrics on the gearbox's bearings that connect it to the pylon. The piezoelectrics transform electric control signals into precise mechanical vibration. The control unit uses this vibration to counteract the resonance in the system, by "pushing" in the exact opposite direction. The researchers describe this as creating an "anti-sound".
While this kind of sound dampening technology is common in other fields, the key aspect of the research was the adaptation of it to the windmill form factor. The new tech is mountable and should be relatively inexpensive.
Researchers already have tested a working scale model. They plan to soon begin full field tests. Assuming they continue in their early success, one of the major complaints about wind power may soon be on its way to being removed. The speed may still need to be limited to protect the turbines in heavier winds, but overall this will raise their operational speed and output.