How Wakes Impact Wind Energy Efficiency

The fast-moving wind turbine blades create wakes which can change the amount of wind energy reaching the turbines and plants downwind. Wakes may cost as much as 10 per cent of energy losses to the Wind Farms.

Wake Effect

Wake is a long trail of wind which is quite turbulent and slowed down when compared to the wind arriving in front of the turbine – an expression derived from the wake behind a ship.

In simpler terms, wind turbines create wakes, which are areas of reduced wind speed and increased turbulence downstream of the turbines. When wind turbines are placed close together in a wind farm, these wakes can interact with each other, creating even larger wakes and reducing the overall energy output of the wind farm.

The energy loss due to long wakes at wind farms is known as wake loss or wake effect. Wake loss occurs because the turbines in the downstream Wakes receive less wind energy than the turbines in the upstream Wakes. This results in reduced power output from the downstream turbines, which reduces the overall energy output of the wind farm.

To minimize wake loss, wind farms are typically designed with careful consideration of turbine placement and spacing. Researchers and engineers are also developing new technologies, such as advanced control systems and wind farm optimization algorithms, to improve wind farm efficiency and reduce wake loss. However, the losses may even be larger than predicted. Large-scale wakes can even persist 20 miles or more and reach entirely different wind plants.

Considerable Losses – Studies

A study by ArcVera Renewables at New York Bight offshore development sites found that there is a severe under-prediction of long-range wake losses by engineering wake loss models in common use.

“Velocity deficits, as high as 1 m/s or 10 per cent, 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 notes.

According to another study on the interaction between two identical wind farms with 72 turbines each published by Cambridge University Press, the wake generated by an upstream farm showed a pronounced influence on the flow development inside and around the downstream farm.

Further, the power production of the first row of the downstream wind farm is reduced by 33 per cent when the distance was 5 km and by 13 per cent when the distance was 15 km –  showing an inverse relation of wake effect with distance.

Need of Further Research

While the studies clearly show the loss in energy production due to the wake effect, a consensus on an effective way to counter it is not solid, especially regarding the long-range wake. The engineering models utilized for wake estimation have undergone validation for internal wakes and external wakes in close proximity. However, these models have not undergone regular validation for such long distances and have not been validated at all for wind turbines with large nameplates (>12 MW) and rotor diameters (>200 m). There is a clear need for further research.