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Exploring Deep Wake Effects in Multi-Gigawatt Wind Farms 

We kick off our blog series by confronting a pivotal challenge in wind farm development — the phenomenon of wake effects. Drawing insights from research published in the Wind Energy Science journal, “Investigating energy production and wake losses of multi-gigawatt offshore wind farms with atmospheric large-eddy simulation (LES), this first article focuses on understanding how wake effects traverse through multi-gigawatt wind farms, influencing energy production and losses.

 In their research paper, Peter Baas and his colleagues highlight the impact of wake effects by harnessing Large Eddy Simulation wind modelling techniques. Before diving into the details, here are a few words on terminology: Wake losses are usually understood to refer to lower production of turbines that are behind other turbines. However, since a few years, it is more widely known that even the first-row turbines are producing less due to the combined (or global) blockage effect of the entire wind farm. Baas et al. sometimes use the term total aerodynamic losses for the sum of these two effects, but whenever the context is clear, the shorter-term wake losses is used and should be understood to represent the total aerodynamic losses. In our third blog post, we will dive further into the subject of global blockage. 

Analyzing Aerodynamic Losses: Turbine Efficiency Under Scrutiny 

Left: free stream and actual energy production for the studied year 2015. Right: relative production losses compared to free stream conditions. Results for 6 different scenarios are presented.

Baas et al.’s study undertakes a thorough exploration, analyzing annual energy production and wake losses over a full year of real weather conditions. For a simulated year, it gives us some insight into aerodynamic losses within a 4 GW offshore wind farm. These losses vary significantly, ranging from 12% for 21 MW turbines to 18% for 10 MW turbines. This highlights a striking efficiency disparity — larger and more powerful turbines prove more efficient compared to the alternative strategy of deploying twice as much, but half as powerful turbines that collectively provide the same capacity. Evidently, these findings hold critical implications for assessing wake losses. The choice of turbines within a 4 GW wind farm exerts a discernible impact on the projected wake losses, thereby underscoring their crucial role in shaping the overall energy yield.  

Turbine Engineering’s Ripple Effect on Wind Farm Energy 

Furthermore, the study emphasizes that even among turbine types boasting similar rated capacities, subtle differences in power and thrust curves can lead to a significant (order 5 – 10%) variation in energy production. This difference depends on turbine design factors like rotor diameter and technical specifications, with power curves taking center stage. This underlines the immense impact of turbine engineering on the overall energy output of wind farms.

The Wind Speed-Aerodynamics Connection 

Added energy production (left) and losses with respect to free-stream conditions (right) for the year 2015 for 1 m/s intervals. Results for 6 scenarios are shown. 

Across all considered scenarios, a significant 80% of aerodynamic losses occur within a relatively narrow wind speed range of 8 m/s to 12 m/s. Conversely, 50% of energy production materializes without encountering any aerodynamic losses when all turbines are operating at their rated capacity. However, it is essential to contextualize these specific numbers within the framework of the wind speed distribution of the simulated year (2015) and the choices made in wind turbine design, particularly concerning power curves for optimization of energy production and mitigation of losses. 

Optimization for your site’s climate

Considering these findings, it becomes evident that a thorough understanding of the wind climate and its interactions with the atmosphere is essential. This study is anchored in a specific year and geographical site and accentuates the importance of tailoring turbine selection to your unique climate conditions. However, optimizing turbine design goes beyond mere efficiency — it extends to a careful balance of efficiency and cost. While prioritizing enhanced energy production holds value, it’s imperative to factor in the associated costs. In other words, the pursuit of optimal energy production doesn’t always align with the most economically viable solution. 

Keen on leveraging this breakthrough technology for your wind resource assessments?

Baas et al.’s research harnesses a wind modelling technique rooted in Large Eddy Simulation (LES). If you’re eager to leverage this breakthrough technology for your wind energy projects, get in touch with us today.

Next up…

In our upcoming blog, we’ll shift our focus to the complex interplay between atmospheric stability and energy production estimates. Join us as we delve deeper into the atmospheric conditions that influence the IJmuiden Ver wind farm and uncover their impact on energy yield assessments. 

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