Wind turbines are extremely loud. The secrets of owl flight may provide a solution.

• Wind turbines are great for clean energy but they are not perfect. One issue is how tall they can be.

• To address this, designers are using owls as a model to make their turbines quieter.

• One company adds sawn edges like owl feathers to its turbine blades to reduce noise.

One of the biggest problems wind farms face is keeping their turbines quiet. Their constant hum is quieter than your average city traffic, but it can cause headaches and tinnitus in people living nearby.

To help solve this issue, Biome Renewables has created a quieter wind turbine shaped like the wings of an owl. Their FeatherEdge technology saw its first installation in the summer of 2023.

“This seems like one of those perfect marriages where you have a problem, and then there’s an animal analog right in front of you,” said Ryan Church, founder of Biome Renewables.

How owls can help make wind turbines quieter

Owls can fly very quickly because of their trailing edge — a set of feathery blindfolds on the back of their wings. This edge dampens the sound by breaking up the air vortices that flow off the wing. In other words, it lowers the amount of air turbulence behind the wing.

A recent study measured how much noise this fringe can reduce in owls by comparing digital models of owl wings with and without fringes.

​​​​The researchers found that the edged wing was up to 6.5 dB quieter than the bare wing, depending on the angle of flight. It only takes one loud wing flap to signal an owl’s prey, so every decibel counts.

The authors of the study admit, however, that the edges of real owl wings are not uniform. All threads have different thicknesses and curvatures that affect how they redirect air. This is important because owls’ hooves don’t just break up air currents – they angle sound waves in such a way that frequencies within their prey’s hearing range cancel each other out.

And the “it” factor is behind Biome Renewable’s FeatherEdge technology.

The story continues

Many turbine manufacturers have taken inspiration from the edges of owls to add serrated edges (stripes) to their turbine blades. Uniform serrated edges can reduce the noise within the human hearing range by 1 dB to 2 dB compared to a bare blade.

But FeatherEdge takes owl mimicry a step further, being the first to give their edge multiple layers. Their patented technology is called double dipped serration.

“The standard serrated trail edge is a single spike, but we have a kind of tank or double spike at the top,” Church said.

“What that’s actually doing is, it’s starting with a sound wave up at that top bit and another sound wave starts at the bottom. And they’re offset by a certain wavelength, so they knock each other, “Church Church said.

Specifically, the double dipping serration knocks out sound waves that make the turbines’ whirring noise. These sound waves are on the lower end of frequencies within the range of human hearing (below 1000 hertz).

At these frequencies, Church said the FeatherEdge is 3.9 dB quieter than a standard serrated edge blade, and over 5 dB quieter than a fully bare blade. Decibels increase on a logarithmic scale, meaning that if something is 5 dB quieter, people hear it 25% softer. That’s much less than the difference between a whisper and normal speech, but the contrast is significant enough for the human ear to detect.

Save energy and space

This noise reduction doesn’t just help neighbors with sensitive ears. It is also good for the bottom line of a wind farm.

Due to wind farm noise regulations in the US, wind turbines often run in noise reduction mode, which saves a lot of energy.

But if the turbine blades are naturally quiet, you don’t need to spend that energy muffling their noise. “Every dB you can get back, you can get basically 4% to 5% more power in a year,” said Church.

Quieter turbines also help developers use land more efficiently.

“If you have a turbine with a lower noise signature, you can put it closer to receptors, which means if you’ve got a piece of land, you can put more turbines on that piece of land than you could do the opposite,” Church said.

Biome Renewables is currently working with developers to roll out their turbines across North America and Europe in 2024. But thanks to the inspiring silence of an owl’s wings, you might not even hear their turbines running.

Read the original article on Business Insider