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Low-noise serrations: Less noise, more yield

Serrations are sawtooth-shaped structures on rotor blades that reduce the noise level of a wind turbine. As a result, nearby residential areas are protected from excessive noise pollution, the construction of new, larger wind farms is more likely to be approved and the limited space can be used more efficiently. Even wind turbines that have already been built can be retrofitted with serrations.

The start-up company WTS - Wind-Tuning-Systems has developed and patented special low-noise serrations. Together with Deutsche Windtechnik, the company installed a pilot system on an Enercon E-82 for testing purposes, and initial noise measurements have already been completed by DNV-GL. We spoke about the project with Stefan Brassel, the project manager at Deutsche Windtechnik, Klaus Röhm, CEO at Wind-Tuning-Systems and Jens Dreessen, the wind farm operator and Managing Director of C&D Ölservice GmbH.

The installation is carried out independently of the weather and within a short time on the hanging rotor blade with the help of the company's own platform technology. (Photo: Deutsche Windtechnik)

Installed serrations on an Enercon E-82. (Photo: Deutsche Windtechnik)

Mr Röhm, how exactly do low-noise serrations workand how does the wind farm operator benefit from installing them?
Our serrations replace the straight trailing edge of the rotor blade with small, spiral-shaped structures that change the flow behaviour and the end edge vortices. This reduces the size of the vortices that generate sound. Changing the trailing edge sound in this manner currently allows us to reduce the noise by up to 3.3 dB (A). During the day, the retrofit reduces the volume of the sound by about half, ensuring higher acceptance with people who live nearby. At night, it makes it possible to operate the turbines at higher power levels while still complying with the noise limits. The additional yield makes installing them very attractive: Depending on the installation location and the remuneration situation, payback periods can be as short as 1-2 years. 

What makes your product stand out from other products? 
Our serrations are spiral-shaped, three-dimensional and small, and this gives them a completely new design. This new solution approach enables us to achieve a noise reduction that is about 1/3 greater than the serrations offered by wind turbine manufacturers, which are only available for certain newer wind turbines. It also makes the sound much less unpleasant. For example, when the rotor blade passes by the tower, the 'boom' noise is almost no longer audible. 

Further technical improvements for even higher noise reduction on existing turbines are planned and patent pending.
We are also breaking new ground when it comes to materials: The high-performance plastic that we use is very durable, and the adhesive technology makes it easy and quick to install.  

Mr Dreessen, what led to your decision to use serrations?
We had already installed serrations on an Enercon wind turbine at a wind farm in 2015. In 2020, we decided to find a better, easier-to-install solution. This led to the contact with Mr Röhm and the offer to test WTS's innovation in a pilot project. The new solution approach and the differences to previous solutions convinced me to test the product on an Enercon E-82 at the Büttler-Balje 1 Betriebs KG wind farm in Schleswig-Holstein.   

Mr Brassel, what do you expect from this new development? 
We are always looking for new solutions for our customers to further optimise the operation of wind turbines. WTS's serrations have this potential for improvement. We expect to offer this solution to other customers as well. Currently, we are focusing on retrofitting existing turbines. The second step will be to equip new turbines. Installing the system is also very interesting for wind farms that will continue to operate past the usual service life of 20 years, particularly due to the increased yields. We are already seeing high demand from our contract clients, who are very interested in the solution.  

Mr Röhm, can the technology be installed on any rotor blade or turbine type? 
As a serration manufacturer, independent from the system manufacturer, we are currently in the process of getting the component certification for the Enercon E-82 E2 turbine type. Our next step will be to certify the product for the Enercon E-70 turbine type. In the foreseeable future, we are also planning to offer our product for a number of other commonly used turbine types (1.5 - 3.4 MW) from various manufacturers. 

Mr Brassel, how complex is the installation of the upgrade? 
Installation can be carried out rapidly on the attached rotor blade using our own platform technology, which makes us independent from the weather. We currently expect the work to take three days, including set-up time.  

Mr Dreessen, is success already measurable? 
We had the system measured by DNV-GL one week after it was put back into operation. Compared to the previous measurements, we achieved an average noise reduction of 3.3 dB(A). This means that installing the serrations reduces the noise volume by half. At night, the 2.3 MW system can run three to five levels higher than before. The higher power level, from previously 1,000 kW to between 1,600 and 2,000 kW, leads to an increased yield. Forecast for the year, we expect the installation to increase the yield by 400,000 kWh. This is a very positive result, especially considering the current electricity market prices. 

Thank you for the interview! 

Your contact person - we look forward to hearing from you!
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