A new study by ArcVera Renewables has found that commonly used engineering wake models vastly underpredict energy losses at wind farm arrays due to external wakes.
The research confirms the severe under-prediction of long-range wake losses by engineering wake loss models in common use and Velocity deficits, as high as 1 m/s or 10%, persist up to or greater than 100km downwind of large offshore arrays.
This can lead to long-range energy deficits much greater than expected by most subject matter experts in the industry.
The study by the Indian offshore tech service provider investigated the long-range wake loss potential at the New York Bight offshore development sites in the US using validated, high-fidelity long-range wake loss modelling,
ArcVera utilized the he Weather Research and Forecasting (WRF) model, a firmly established high-fidelity numerical weather prediction model, while adding Wind Farm Parameterization (WFP) to account for the effects of the wind turbines in the domain.
The tech service provider also consulted with Professor Julie Lundquist’s research group at the University of Colorado to consider the uncertainty in these model predictions of large, long-range wakes.
Several tests of sensitivity to model configuration parameters show that the above results produce the weakest wakes of all the configurations tested.
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 (>12MW) and rotor diameter (>200 metre) wind turbines, ArcVera said.
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, the tech service provider added.
ArcVera said it is open to opportunities to work with the owners and operators of large offshore wind facilities to move the research forward and elevate the success of global offshore wind development.
ArcVera Renewables chief executive officer Greg Poulos said: “This new study provides an important cautionary lesson as the wind industry proceeds to ever-larger wind turbine models with greater farm density across the globe.
“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.”
ArcVera atmospheric science innovation lead Mark Stoelinga said: “In the onshore validation study that we 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.
“We 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.”