Wind turbines and the wake-up effect: limiting production?



While energy transition accelerates with the goal of achieving 40% renewable electricity by 2030 in France, many outdoor wind farm projects are being launched in particular in Dunkirk. Europe’s goal will be to reduce greenhouse gas emissions by more than 80% compared to 1990, by 2050. Therefore, the share of renewable energy sources has increased significantly in recent years, especially for Europe, offshore wind turbines.

These coastal wind turbines (a term that literally means “coastal”) operate in the same way as onshore wind turbines, except that they are located more than 10 km from the coast. Winds at sea, which are stronger and more regular than on land, generate up to 60% more energy per wind turbine. In 2019, 22 GW (gigawatt) were produced in Europe, and three quarters of that capacity was installed in the North Sea. By 2050, that power should be more than multiplied by ten, with a project to reach 300 GW for the old continent. And the North Sea really needs to be emphasized: almost half of this power, or more than 200 GW, will be installed there, at a rate of 8.8 GW per year in the 2020s – the equivalent of eight nuclear power plants.

But with the installation of wind farms come productivity issues. Many construction projects mean that wind farms are getting closer and closer, and to these researchers from‘Helmholtz-Center Hereon Institute in Germany, led by Naveed Akhtar, an expert on regional climate modeling. The results of their study were published in Scientific reports on nature June 3, 2021

.fr / nature-environmentnement / climat / the-energy-transition-challenge-for-the-electricity-network_153419 “> energy transition is accelerating with the aim of achieving 40% renewable electricity by 2030 in France, many outdoor wind farm projects are being launched in particular in Dunkirk. Europe’s goal will be to reduce greenhouse gas emissions by more than 80% compared to 1990, by 2050. Therefore, the share of renewable energy sources has increased significantly in recent years, especially for Europe, offshore wind turbines.

These onshore wind turbines (a term that literally means “coastal”) operate in the same way as onshore wind turbines, except that they are located more than 10 km from the shore. Winds at sea, which are stronger and more regular than on land, generate up to 60% more energy per wind turbine. In 2019, 22 GW (gigawatt) were produced in Europe, and three quarters of that capacity was installed in the North Sea. By 2050, that power should be more than multiplied by ten, with a project to reach 300 GW for the old continent. And the emphasis really needs to be on the North Sea: almost half of this power, or more than 200 GW, will be installed there, at a rate of 8.8 GW per year in 2020 – the equivalent of eight nuclear power plants.

But with the installation of wind farms come productivity issues. Many construction projects mean that wind farms are getting closer and closer, and to these researchers from‘Helmholtz-Center Hereon Institute in Germany, led by Naveed Akhtar, an expert on regional climate modeling. The results of their study were published in Scientific reports on nature June 3, 2021

Wind turbines affect each other

Vigilance is needed in setting up these new “windmills” that allow for decarbonization of energy: the study focuses on what is called the waking effect of wind turbines. What is it about ? During operation, the wind turbine captures the kinetic energy of the wind, allowing it to rotate. Thus, the wind speed decreases when it leaves the propeller, which then implies a reduction in the operation of the windmills located behind. Also called vortex awakening, this drop in wind speed is accompanied by turbulent flow behind the wind turbines: it will impair the production of those who follow or even damage their structure.

When creating a wind farm, ie a large group of wind turbines, this effect becomes essential for the installation of each of them. Because if each wind turbine affects those behind, the vortex will also have an overall effect on the park, changing the dynamics of the winds to several hundred meters around the wind turbines that make it up. In the case of offshore wind turbines, this effect is clearly visible at sea level, where it creates turbulence. Then a water trail is formed behind the wind turbine, the length and amplitude of which depend on the speed.

As part of their study, a team of researchers questioned the effect that an increase in the number of Pula wind farms in the North Sea could have on wind characteristics. To do this, they used a climate model that simulates wind power scenarios in the near future, taking into account those that already exist or are planned in the North Sea. To verify the model data, the team compared the simulations with wind measurements from 2008 to 2017. They then estimated the losses in electricity production and the differences in wind that could result from these wind farms. In their forecast, they used the 2015 North Sea wind farm planning as a basis for determining future wind farm locations.

Up to 20% of reduction by a factor unload

The results of their study show a speed deficit that can average about 40 km downwind, up to 100 km, depending on weather conditions. This deficit is higher during stable weather, mainly in March and April. On the other hand, during stormy weather – especially in November and December – the atmosphere is so mixed that the effects of waking up become relatively weak. In addition, the proximity of large wind farms affects not only the performance of its own wind farms, but also neighboring wind farms. Depending on the size of this park, the calculated speed loss reaches up to 2.5 meters per second per year, or almost 9 km / h (the wind turbine starts working when the speed reaches about 10 km / h)!

According to their calculations, the load factor, which is the ratio between the electricity actually produced over a given period of time and the energy it would have produced had it worked at its rated power during that period, could go through a drop to more than 20%. This pressure drop implies higher production costs and reduces energy and thus economic profitability. Researchers insist on the need to consider proximity effects in future offshore wind projects.

Although the group first looked at how wind farms affect each other, in the near future they plan to study the effect of reduced wind speed, life at sea. Indeed, wind and waves mix water and change its salt and oxygen content, such as its temperature and the amount of nutrients it contains. “Now we would like to know how the mixture affects the marine ecosystem,” said Naveed Akhtar ua communicated.



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