Wind turbines are annoyingly loud. The secrets of owl flight could provide a solution.

• Wind turbines are great for clean energy but they aren't perfect. One issue is how loud they can be.
• To address this, designers are using owls as a model for making their turbines quieter.
• One company adds saw-like edges akin to owl feathers to its turbine blades to reduce noise.

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

To help solve this issue, Biome Renewables has crafted a quieter wind turbine modeled after owl wings. Their FeatherEdge technology debuted in its first installation in the summer of 2023.

"This seems to be one of those perfect marriages where you have a problem, and then you have an animal analog right in front of you," said Ryan Church, founder of Biome Renewables.

How owls can help make quieter wind turbines

Owls can fly in near silence thanks to their trailing edge fringe — a layer of feathery fuzz on the back edge of their wing. This fringe dampens sound by breaking up the swirls of air flowing off the wing. In other words, it lowers the amount of noisy air turbulence in the wing's wake.

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

The researchers found that the fringed 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 alert an owl's prey, so every decibel counts.

However, the study authors admit fringe on real owl wings isn't uniform. The strands all have different thicknesses and curvatures that affect how they redirect air. This is important because owl fringe doesn't simply break up air streams — it also angles sound waves in such a way that frequencies within their prey's hearing range cancel each other out.

And there lies the "it" factor behind Biome Renewable's FeatherEdge technology.

Many turbine manufacturers have taken inspiration from owl fringe to put saw-like edges (serrations) on their turbine blades. Uniform serrated edges can reduce noise within 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 fringe multiple layers. Their patented technology is called double-dip serration.

"The standard serrated trailing edge is one spike, but we have a kind of a trough or a double spike at the top," Church said.

"What that's actually doing is, it is starting off a sound wave up at that top piece and another sound wave is started off at the bottom. And they're offset by a certain wavelength, so that they knock each other out," Church said.

More specifically, the double-dip serration knocks out sound waves that make the turbines' whooshing noise. These sound waves are on the lower end of frequencies within human hearing range (under 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 completely bare blade. Decibels increase on a logarithmic scale, meaning that if something is 5 dB quieter, humans hear it as 25% softer. That's significantly less than the difference between a whisper and normal talking, but the contrast is noticeable enough for the human ear to detect.

Saving energy and space

This noise reduction doesn't just help neighbors with sensitive ears. It's also good for a wind farm's bottom line.

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

But if the turbine blades are naturally quiet, you no longer 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," Church said.

Quieter turbines also help developers use land more efficiently.

"If you have a turbine that has a lower noise signature, you can place it closer to receptors, meaning if you have a given plot of land, you can put more turbines on that plot of land than you could otherwise," 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 owl wings, you might not even hear their turbines running.