From KlimaNachrichten

By KlimaNachrichten Editor

A quasi wake-up call for the spoiled wind power industry.
Two companies are sounding the alarm, because they are in danger of losing a lot of money.
Although they don’t lose it, they take it less.
It’s about the shading of wind farms by other wind farms.

Windmesse.de  

The expansion of offshore wind energy in the North Sea is a central component of the European energy transition. But now two of the largest players in the industry are warning of negative effects: Ørsted and Equinor have jointly calculated that the planned 1.5-gigawatt “Outer Dowsing” wind farm could cause significant so-called wake losses. These are yield losses that occur when the wind is weakened or swirled by upstream wind farms, causing downstream turbines to produce less electricity.

The estimate of the two companies: Up to 361 million pounds – the equivalent of around 422 million euros – could be lost to their existing wind farm projects in the British part of the North Sea in the long term due to the new wind farm. In particular, the wind farms already in operation, which depend on constant wind conditions to deliver their planned output and ensure economic viability, are affected.

The phenomenon is called the wake effect and is by no means new, as you can see in the Sciencemediacenter, because the corresponding article is from 2012.

“The existence of wind turbine wakes has been known for decades. For a long time, it was not given much importance for smaller wind turbines and onshore wind farms. With the increasing size of individual wind turbines (multi-MW turbines) and larger wind farms in recent years, the size and length of wakes is increasing and becoming more and more relevant. I pointed this out as early as 2010 and developed a simple model that can be used to estimate the length of wind farm wakes. This model shows the dependence of the length of wakes on substrate roughness and thermal stratification of the air. Wake of several tens of kilometers in length is thus predicted for offshore wind farms with stable stratification. Ms. Lundquist’s research group presented simulation results with the WRF flow model as early as 2012, some of which show even longer casters.”

The topic is also dealt with at basicthinking, although the losses could be significantly higher than science thought in 2012.

Based on the results of their study, the researchers estimate that offshore turbines take the wind away from each other. As a result, wind farms in the Atlantic lose more than 30 percent of their capacity. The scientists call this the “wake effect”.

It occurs when the wind passes through the turbines and the front or upstream turbines extract energy from it. As a result, the wind speed behind the turbines slows down. The result: lower electricity generation.

The wake effect is particularly pronounced in offshore wind turbines, as there are no houses or trees swirling the air. Because that would help to disperse the wakes. Under certain weather conditions, they can also reach up to 55 kilometres and also affect other wind farms.

Especially on hot summer days, when the air above the cool surface of the sea remains stable, wakes can last longer and spread further.

Last year, the mdr had a very interesting article on this.
It is interesting that this problem was not thought of when the energy transition was planned.
However, it is not surprising.

Axel Kleidon sees a particular challenge in offshore turbines, i.e. those at sea. These are often only just being built, and many wind turbines are planned in a relatively small space. And this in an environment in which, according to Martin Dörenkämper, losses are generally more pronounced. “Above the sea, the flatter surface leads to a more constant wind speed distribution with altitude and thus a considerably less turbulent wind resource than at onshore locations.” In other words, the almost unchecked wind power hits the rotor blades, provides more electricity there, but subsequently finds its way back to its old power less quickly due to a lack of ambient turbulence and a corresponding mixing: As a result, the wake effects are more durable and still noticeable over longer distances.

According to Axel Kleidon, this may lead to a legal problem, because the further the distances, the sooner wind farms from different operators can “dig up” the wind. This makes it all the more important to coordinate, especially at national borders such as in the North Sea between Germany, Denmark and the Netherlands: “The snippet of the North Sea that is administered by Germany is relatively small. The area of the Netherlands and Denmark is much larger. It would make sense to coordinate this instead of somehow focusing on it at the national level. That you say, if you want to expand 70 gigawatts in the North Sea, that it doesn’t all have to be in the German sector, but it can also be in the exclusive economic zone of Denmark or the Netherlands.”