In amongst the complaints that noise might ruin a good night’s sleep, what are the real issues, how big are they in reality, and what can be done about them?

Back to basics

Noise emanating from wind turbines comes from two principal sources, Stefan Oerlemans, an engineer at Siemens, speaking at an EWEA technology workshop on noise held in Oxford in December, said. “There is the mechanical noise from the turbine’s nacelle caused by the gearbox and generator, and there is the aerodynamic noise from the wind turbine’s blade,” he explained.

“The dominant of these two sources is the blade, mainly during the blade’s downwards stroke during a rotation,” he said.

As blade lengths have increased over the years – a wind turbine rotor is now bigger than the wingspan of a Boeing 747 and turbines have grown from 200 kw power ratings up to 7.5 MW – then the potential for greater noise levels goes up too. However, since the earlier days of modern wind power, turbine blades designs have improved drastically.

Designs of earlier modern turbines were inspired by 1930s aircraft designs, Oerlemans said. But today blades are custom made with much thinner trailing edge designs and aerodynamic blade tips designs - both of which make the blade much more slender and less noisy as it cuts the air.

Some designers have also started to explore “add-on” concepts, such as attaching extra features to a blade to further streamline its movement, although this approach is very sensitive to local conditions and can be a success or failure, he said.

“Blades undergo acoustic wind tunnel testing to fi nd the right designs: many noise sources can be supressed by good design,” Oerlemans stated. Noise from the nacelle is easier to reduce, and can be achieved by adding greater nacelle insulation, he added.

Noise, what noise?

While wind turbine noise from the outset might seem like something scientifi c that can be measured categorically it is a highly complex process once ‘in the field’.

“Measuring noise is very frustrating, especially in residential areas where background noise is very similar,” Andy Mckenzie, from Hayes Mckenzie Partnership, said.

Wind turbine noise can be intermingled with the noise of rainfall, geographical water features, the sound of gravel crunching under car tyres, the wind blowing through the trees, farmyard noises and – one of the biggest annoyances to measurement – the noise of passing traffic. “All these and other sources affect the results,” Mckenzie said.

What is more, it is impossible to measure everywhere. Places like people’s back gardens – and if we’re talking about noise affecting public opinion this is surely a key place to measure – are usually off limits. And there is the effect of the wind direction over the noise survey period – are the measurement instruments downwind from the wind farm? – he added. “Simply put, background noise is very similar to turbine noise,” Mckenzie stated.

So, if we know that turbines do produce some noise, particularly as the blades swoop down, but we don’t really know accurately how much noise they create in a given setting, what is the argument against wind turbines when it comes to noise?

Do wind turbines impact human health?

“Sound from wind turbines does not pose a risk of hearing loss or other direct adverse health impacts,” Mark Bastasch, Principal Acoustical Engineer at CH2M HILL, USA, told delegates at the December EWEA noise workshop.

He pointed to 17 different peer-reviewed studies which back-up his statement, available on the CanWEA website. In addition to those studies there are many more: in 2010 the Australian government National Health Medical Research Council concluded that, “there are no direct pathological effects from wind farms and that any potential impact on humans can be minimised by following existing planning guidelines.”

In January 2012 a study for the Massachusetts Department of Public Health said: “there is insuffi cient evidence that noise from wind turbines is directly…causing health problems or disease.” For more studies, search for “health” on www.ewea.org/blog.

As Robert Hornung, President of CanWEA, put it: “wind has been attacked by opponents on the grounds that it is harmful to human health. This is despite the fact that the balance of scientifi c evidence clearly shows that wind turbines do not adversely affect human health, and in fact, wind energy is broadly recognised to be one of the safest forms of electricity generation available today.”

However, it goes without saying that wind turbine-related noise is not an issue that can be swept under the carpet by wind farm developers: objectively noise should not be an issue, but subjectively it is – and it is often a cause of concern for communities surrounding a wind farm even before the farm is up and running.

Involving the community

Numerous opinion polls show that the public in general is in favour of renewable energy technologies like wind, but at a local level that support can wane without community engagement. “Communication with the community is key,” Tom Levy, Manager of Technical and Utility Affairs at CanWEA, explained. “You can have the strictest regulation in the world but you won’t prevent problems if you don’t approach the community, engaging people before and after the project is built.”

CanWEA has developed a set of best practice guidelines aimed at helping wind farm developers involve the local community and listen to their health-related concerns, he added.

Levy’s ideas include engaging local prominent people, such as a town mayor, to show them how wind turbine noise blends in with background noise. Local media are also “critical” Levy said, advising developers to go and meet editors of local papers, local radio show hosts and local TV presenters.

“Change is often controversial and wind farm projects will often meet with local opposition. Education is the most powerful tool, but developers must also show respect by answering questions and listening to fears,” he said. “Wind farm developers want to be good neighbours,” Jeremy Bass, Senior Technical Manager at RES, added.

And so, in short, it seems that yes wind turbines make noise – some of which has been eliminated with modern turbine designs – and, no, this noise does not impact human health. But that noise does exist, even if it is at a very similar level to general background noise even in rural areas, and therefore all those involved in a wind farm project cannot ignore it.

Respecting national regulations on distances from dwellings is one thing – noise regulation varies hugely from country to country the scope of which goes beyond this article – but the most effective solution – community engagement – is something that should be built into every wind farm project sited near a community from the planning and construction phases to the operational phase.

EWEA holds a series of technology workshops throughout the year; for more information visit www.ewea.org/events/workshops.

Read the full February issue of Wind Directions here.