Insights

A potential revolution in acoustic performance for wind turbine technology.

In the previous months, we have been closely examining the FeatherEdge serration technology developed by Biome Renewables with great interest. Our comprehensive analysis of this blade addition indicates significant noise reduction capabilities, surpassing current state-of-the-art technology. This innovation has the potential to transform the wind industry by reducing noise impact of wind energy projects on neighbouring populations, in turn leading to increased flexibility in design and the potential for maximising energy generating capacity.

Noise and power: The Delicate Balance.

The influence of different noise assessments on the viability, risk and generating capacity of wind farm developments is frequently underestimated. Minor adjustments in environmental noise limits or assessment methodologies can lead to significant variations in renewable energy generation and development opportunities. A mere 2 to 3 dB change can alter a project’s scale by as much as 40%, due to the need for increased separation distances as a primary noise mitigation strategy.

The advent of variable speed, pitch-regulated wind turbine technology has led to an efficient design in terms of noise emissions from modern turbines, leading to low noise emissions at low wind speeds and then increasing to a noise emission peak at or close to the turbine rated power, with noise emissions then either staying constant or decreasing at the highest wind speeds. Noise emissions are now dominated by the trailing edge of the turbine blade.

The next technological step was the creation of Serrated Trailing Edge (STE) technology, typically providing an extra 2 dB(A) reduction at source at no energy cost, and these are now available as standard on most commercial turbine models. This noise reduction has compensated for the potential increases in noise which may have been the consequence of the increasing size of modern turbines with rotor diameter in excess of 100 m. Our previous understanding was that STE blades represented the state-of-the art, and that further reduction could only be obtained in practice through the use of noise-reduced operational modes, which slow the turbine rotation and therefore reduce energy generation.

FeatherEdge technology: A New Benchmark.

Initial tests, conducted by Deutsche WindGuard on a 3 MW capacity turbine, compared standard STE-equipped blades with FeatherEdge blades. Measurements adhered to the IEC 61400-11 (ed. 3) standard. Key findings include:

• At a medium/moderate wind speed, where turbines would normally reach their maximum noise emission level:
  • the relative reduction of FeatherEdge at source on the overall, A-weighted levels was around 4 dB(A).
  • In addition, the effect of FeatherEdge was to provide a frequency shift, with an increase of noise at higher frequencies (2 kHz and above) but with a stronger decrease of lower frequencies below 1 kHz.
  • In particular, an apparent reduction of between 6 and 8 dB for key frequencies of 200 to 800 Hz was observed, which is very large and unprecedented in our experience.
• At lower wind speeds, where turbine noise emissions tend to be lower:
  • The effect on overall levels at source was reduced (less than 1 dB(A)).
  • However, a shift towards high frequencies and a reduction at lower frequencies, although less pronounced, was still clearly apparent, with reductions below 200 Hz circa 4 to 6 dB.

Propagation Effects and Practical Implications.

The observed frequency shift is crucial, given the effects of noise propagation over distance. Higher frequency sounds dissipate more rapidly than lower frequencies, meaning FeatherEdge’s benefits become more pronounced over greater distances. Our modeling, based on ISO 9613-2 standards, indicated:

• At medium/moderate wind speeds:
  • The sound level reduction (relative to a standard STE) improved from 3 dB(A) to 5 to 6 dB(A) at distances of 500m and above, which represents a large and clearly noticeable noise reduction.
  • Depending on the turbine layout configuration and location, this level of noise reduction would mean equivalent levels would be obtained with a separation distance from turbine to receiver reduced by 400 to 800 m. This is comparable to the typical minimum separation distances between turbines of >100m rotor diameter (to minimise wake effects). This could therefore allow, subject to other constraints and design considerations, a substantial increase in generation capacity, potentially allowing for example an extra row of turbines in a wind farm.
  • To obtain a similar level of noise reduction with noise-optimised operational modes would be possible but with estimated peak power generation losses of more than 50 %.

• At lower wind speeds:
  • The effective sound level reduction relative to a standard STE was also improved, with a 1 to 2 dB(A) at distances of 500m and above.
  • This would still be equivalent to a reduced separation distance from turbine to receiver of
    150 to 350 m.
  • Noise-reduced operational modes with similar noise reduction could be associated with power losses of the order of 2 to 5%.

Looking Forward.

Based on the observations from Deutsche WindGuard that the introduction of FeatherEdge did not have an effect on the power generation of the turbine tested, the above initial results, if confirmed, would equate to an unprecedented level of noise reduction relative at no cost to the generated power.

In the UK, the installed onshore wind capacity recently reached 15 GW. The possibility of retro-fitting this technology to existing windfarms which are constrained in their operation due to noise could therefore be potentially be very large. This is in addition to the potential for newly designed and developed sites.

We would welcome further confirmed data showing tested results over the whole wind speed range using the FeatherEdge technology, with a range of modern wind turbine models. This would enable us to recommend this technology to provide additional effective noise mitigation where required and design future noise-optimised wind farms. In conclusion, FeatherEdge represents a pivotal advancement in wind turbine technology, offering unprecedented noise reduction without sacrificing energy output. This innovation promises to enhance the feasibility and sustainability of wind energy projects, reinforcing our commitment to a cleaner, quieter, and more energy-efficient future and could become the standard STE technology in time.

Read more about FeatherEdge here.