Nicholas Hamilton has listened to the wind for hundreds of hours. “It’s actually rather soothing,” Hamilton, who is a research engineer at National Renewable Energy Laboratory, said (NREL). “It’s easy to lose sight of the fact that you’re listening to data. It reminds me of white noise.” Those sounds, however, are far from white noise: they form the basis of the most extensive dataset on how quiet modern land-centered wind turbines can be.
In the United States, wind energy is among the fastest expanding — and inexpensive — renewable energy sources. The industry must grow five to ten times its current size to fulfill the Biden–Harris administration’s target of net zero emissions by 2050. While this expansion may reduce carbon emissions and the energy prices while also creating jobs, it may also bring wind farms closer to residential areas.
Because current wind farms employ innovative operating tactics to maximize energy output — strategies that may potentially increase noise — potential noise may deter new projects, inhibiting the development of the cost-effective source of renewable energy.
Currently, turbines are placed far enough away from people’s homes that noise is barely audible (an around wind facility is no louder than the refrigerator heard from other room). Owners and manufacturers of wind turbines are now employing new technology to improve the overall performance of wind farms: wake steering. Wakes are areas when the wind speeds down behind a wind turbine, reducing the amount of energy produced by downwind turbines. Wind plant operators can manage wakes by yawing wind turbines — moving them to face wind at substantially different angles — reducing energy production for individual turbines while enhancing production for the overall wind farm. Wind plant makers need to know if yawing adds (or reduces) noise before it becomes the go-to strategy for plants.
“We must comprehend how wake steering could affect acoustic emissions,” Hamilton added, citing public worries over wind turbine noise. Regulators will also require observational data in order to determine noise restrictions.”
Hamilton, as well as his colleagues at NREL’s Flatirons Campus, carefully positioned 11 microphones beneath the 1.5-megawatt General Electric wind turbine owned by the US Department of Energy. The microphones recorded sounds over the whole frequency range that humans can hear. According to Hamilton, they also took “full-field data” to see how noise varies across a vast area. Their findings were unexpected.
Wind turbines featuring yaw offsets were projected to produce more noise, according to acoustic emission models. However, the evidence collected by the team reveals the opposite: Wind turbine noise was minimized by using a yawed operation. Even if the reduction is minor, any noise reduction is a win: “If you can reduce the noise produced by the wind turbine, you can be able to open up new wind turbine design possibilities,” Hamilton said. “Rotors that make less noise, for example, may execute at a higher speed. They may utilize a lighter gearbox to generate the same amount of energy at a greater speed, lowering the cost of the turbine.”