Different wind turbines generate different noise levels (sound power emission levels [“SPL”]), with the SPL levels provided by the manufacturer either as the apparent SPL, maximum warranted SPL, a calculated SPL (for new WTG where the noise levels were not previously measured) or measured sound power levels as reported in terms of IEC 61400-11 or IEC 61400-14. It is unique for each make and model and the sound power levels already include the effect of the hub height, rotor diameter, and abatement technologies.
There are smaller WTG (lower generating capacity) with higher SPL, with larger WTG (higher generating capacity) with a lower SPL. Therefore, the generating capacity, hub height, or rotor diameter of the potential WTG should not be used to assume the noise levels.
The wind energy market is fast changing and adapting to new technologies and site-specific constraints. Optimizing the technical specifications can add value through, for example, minimizing environmental impact and maximizing energy yield. As such the wind farm developer will be evaluating several wind turbine models, however, the selection will only be finalized at a later stage once the most optimal wind turbine is identified (considering factors such as meteorological data, price and financing options, guarantees, maintenance costs, etc. must be carefully evaluated).
Even if a potential wind turbine was identified, a wind farm developer may not want to reveal the details of their preferred wind turbine due to various reasons, whether for commercial/economic reasons, possible Non-Disclosure Agreements etc.
EARES has done full Environmental Noise Assessments for more than 150 wind projects, and reviewed a significant number of other projects, each involving at least one noise propagation model (though frequently more). The result is that we have evaluated the potential noise emissions of various wind turbine models in the last decade.
I have notified a number of our clients in a circular in the last few weeks about the use of the worst-case WTG (or the latest available WTG). Wind turbines have been increasing in size in the last couple of years, and the noise emissions have subsequently also increased (for an unmitigated wind turbine). But layout developers however do not know how this would influence noise emissions.
In terms of acoustics/noise, a change from 106 dBA to 109 dBA (or 109 to 112 dBA) effectively doubles the sound energy. Some might mistake the “small” change of only 3 dBA as being insignificant, hover, in terms of acoustics this does have a significant impact. This is illustrated in the image above (using actual and accurate noise modelling), displaying the potential extent of noise from different wind turbines.
This should be something that all the layout developers should take note of. Noise emissions should be considered early in the design of the layout and I generally recommend our clients that we start assisting early in the design phase.
While there are a few other companies providing similar services (each with certain benefits and disadvantages), I will focus on why making use of EARES, there are significant advantages to working with us. These are:
- EARES do not treat the Noise Impact Assessment as just another tick, just another document to be appended to the EIA report, but to assist the client in defining a viable layout without potential issues that may appear in the future (noise).
- EARES normally assist existing clients in a quick evaluation of a potential wind turbine layout (to identify potential fatal flaws) before the client distributes the layout for evaluation by other specialists. Distributing a potential layout with a potential noise issue may result in a change in the layout, resulting in additional costs to re-assess the new layout.
- At the start of 2023 EARES had 11 class 1 sound level measuring equipment/analysers, each fitted inside an all-weather case, each instrument with the imported WS-03 windshield. These windshields are specifically designed to allow the measurement of ambient sound levels during periods with increased winds. Most of these instruments are fitted with spectral analysers, with two instruments being able to measure down to 1 Hz (which I specifically purchased to address any questions can concern about low-frequency noise from wind turbines). Most of the other companies only have one or two instruments.
- EARES on default do 2 – 4 long-term measurement locations per wind project, whereas all my competitors do one long-term location or a few short-term measurements.
- EARES am the only company in South Africa that actually measure and log wind speed alongside sound level measurements (as far as we know), having 5 all-weather wind speed / temperature /humidity weather stations). We do not take just one reading, nor do we exclude that data from the noise report;
- EARES is the only company that analyses the sound/wind data, where the data is split into day- and night-time readings with the data presented in the reports to motivate a higher noise limit for wind farm projects (see Figures below). Other companies only refer to the WHO/IFC night-time noise limit and state that 45 dBA is acceptable, yet, completely ignoring the 35 dBA night-time recommendation for a rural environment as well as the requirements of the Noise Control Regulations (or relevant provincial regulations).
- EARES has measured ambient sound levels over a period longer than 24 hours since 2010, and have amassed a huge database of ambient sound levels (and spectral data, which is always measured) of ambient sound levels all over South Africa. The experienced gained during this cannot be taught or bought.
- Similarly, EARES has done significant work at existing wind farms, where we have measured noise levels from operating wind turbines over periods of a few days to more than a week (Cookhouse, Hopefield, Jeffries Bay, Waainek, Dassiesfontein, Noupoort, De Aar, etc.). With most of these projects, EARES coupled the actual noise level measurements with noise modelling to compare and assess the accuracy of modelling. Again, experience that cannot be taught of bought.
- EARES was fortunate to be the selected acoustic consultant to work on various renewable projects in South Africa for an international company. They decided to select and train a specialist in South Africa on international best practice (modelling, sound and noise level measurements, etc.), and over a period of a few months I closely work with their specialists on their projects. Again, the experience gained cannot be bought.
- At last count, EARES is the only company that include a cumulative noise model of all renewable projects located within 5km from the project being investigated. This is another advantage of having done a significant number of projects, as we most likely would have the layout of an adjacent project. Also note, I do it at no additional cost to the client.
- Unfortunately, having done a significant number of Wind Farms, documents done by us have had various appeals and legal challenges. And, in such cases, the EAP and client benefit from a comprehensive report covering all potential issues that may be raised by regulatory authorities or stakeholders. This is one of the reasons why EARES invested in additional equipment, as well as two that can measure down to 1 Hz (and why some companies only make use of our services).
