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Windtech International May June 2024 issue

 

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A recent study by ArcVera Renewables confirms the severe under-prediction of long-range wake losses by engineering wake loss models in common use and investigates long-range wake loss potential at the New York Bight offshore development sites.
 
Velocity deficits, as high as 1 m/s or 10%, persist up to or greater than 100 km downwind of large offshore arrays, leading to long-range energy deficits much greater than expected by most subject matter experts in the industry.
 
ArcVera’s methodology of utilising the Weather Research and Forecasting (WRF) model, a high-fidelity numerical weather prediction model, is the company's core expertise.  The Wind Farm Parameterization (WFP) was added to the model to account for the effects of the wind turbines in the domain. WRF-WFP’s results here show that engineering wake or WFAI models currently under-predict long-range wake losses by a significant margin. Unexpected losses are likely to accrue from wind farms once thought to be too far away to be material to project performance.
 
Engineering models commonly used to estimate wakes have been validated for internal wakes and nearby external wakes but have not been validated regularly at such long distances and have not been validated at all for large nameplate (> 12 MW) and rotor diameter (> 200 m) wind turbines. 
 
On the other hand, The WFP in WRF has been validated against SCADA recorded production for an onshore case by ArcVera, and it was accurate with respect to long-distance wakes within 16% at a 5-km (50 rotor diameter) range.
 
In the onshore validation study that the company conducted in Iowa, USA, wakes were found to travel over 40 km overland, in stable atmospheric conditions. Over the ocean, it is common for atmospheric stability to be enhanced, especially when warm air flow passes over colder underlying water. They also surmise that the very large turbines used in the study produce unusually strong wakes that cannot easily recover their lost momentum, especially under enhanced atmospheric stability conditions.
 
ArcVera calls for further critical research into long-distance wake losses of offshore wind plants.
 
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