Wind turbines are often billed as one of the world’s best solutions to climate change.
And why not?
They are a mature and effective means of generating large amounts of electricity with next to zero carbon emissions. In fact, they are so effective that many more wind farms are planned to be installed over the next 10-30 years.
But the wind energy story is not all rosy. As more wind farms have been installed, there have been an increasing number of complaints from those who live nearby.
Sleeplessness, headaches and high blood pressure are just a few of the symptoms, collectively known as “Wind Turbine Syndrome”, reported by residents who live within a few kilometres of the turbines.
Given the level of financial and political investment in wind energy, “Wind Turbine Syndrome” is a controversial and emotional issue.
It is fiercely denied by wind farm operators and wind energy industry groups. Those who claim their health has been compromised by wind turbines are equally passionate.
Regardless of this intense debate, we know that wind turbines do produce noise and this is limiting our ability to produce green energy. The challenge is to be clever enough to do something about it.
So what causes wind turbine noise?
Most wind turbine noise is generated via aerodynamic means and the dominant form of noise is what is technically known as “airfoil self noise” or the noise created by the rotor blades as they slice through the air.
Most of this type of noise is generated by a quirk of nature that makes the turbulent flow in the region close to the trailing edge (known as the boundary layer) radiate sound much more efficiently, thus making it loud enough to be heard considerable distances from the turbine.
By itself, airfoil noise is “broadband” or contains many frequencies and sounds similar to a hiss. But this type of noise is also very directional, so as the blade rotates, a listener on the ground will hear this hiss-like noise increase and decrease with time.
This is known as blade swish and is one of the reasons why wind turbine noise has been found to be so annoying.
Wind turbines can be made quieter but in order to do so we need to first understand the complicated physics behind the noise.
We need to study turbine aerodynamics and acoustics in more detail so we can create new computer models of wind turbine noise, and how it propagates in the atmosphere.
Such models can then be used to design new quiet wind turbine blades and possibly, whole wind farms.
It will allow engineers and scientists to model the noise created by wind farms and study how they interact, thus providing more detailed planning and operational guidelines than are presently used.
Currently, there are different planning guidelines in each state, with some governments requiring wind farms to be placed more two kilometres away from the nearest human residence.
In many cases, this makes a wind farm economically unviable, due to a lack of electrical transmission infrastructure in remote regions.
If we want to use wind power to reduce greenhouse gas emissions, we need to understand and control the noise from wind turbines better.
Relying on existing technology appears to be creating expensive health and litigation problems that will only get worse as the number of wind farms increase.
There is an incredible opportunity to invest in research and development in this area now, solve these important problems and create a new industry that provides quiet wind power solutions for the 21st century.