To generate electricity, wind turbines extract kinetic energy from the wind and convert it into electrical energy. This creates a wake flow. This effect can also be seen in sailing: the leading boat interacts directly with the undisturbed wind field, while the following boat sails in an area of reduced flow velocity.
The greater the distance between the wind turbines, the more the wind can “recover”. This means that the wake effect decreases and the output of the rear wind turbine is comparatively higher. When planning wind farms, the layout is therefore designed according to the prevailing wind direction and the distances between the turbines in this direction are maximized.
Our colleagues Dr. Lukas Vollmer and Dr. Martin Dörenkämper calculate the wind conditions in offshore wind farms and further develop numerical models for these applications. In this interview, they talk about their research, why current models are probably not sufficient for future wind farms, and how fundamental European cooperation is on this topic.
Editorial team: What impact do wake effects have on electricity production and the lifetime of wind turbines?
Lukas: If there were no wake effects, electricity production would be higher – but that is, of course, a purely hypothetical scenario, as wind turbines in wind farms always interact with each other. When calculated over the lifetime, different effects come into play: turbines located in the middle of wind farms are exposed to lower average wind speeds. On the other hand, the turbulence caused by the rotating rotor is higher there.
It depends on the components of the wind turbines whether their expected lifetime is reduced by the higher turbulence or slightly increased by the lower average wind speed. There are therefore opposing effects; on average, however, it is assumed that the operating life of a turbine located in the center of a wind farm is shorter than that of a stand-alone turbine.
Editorial team: Are there any differences between onshore and offshore wind farms?
Lukas: The main difference is that – especially in Europe, but particularly in Germany – due to land use, there are simply no wind farms as large as those offshore, where wind farms and wind farm clusters with more than 100 turbines are built. In addition, there is orography onshore, such as hills and mountains, as well as various land uses such as trees and houses. This makes the wind much more turbulent. This causes faster mixing between the wake of relatively lower energy and the undisturbed flow, resulting in a faster recovery of the wind turbine wakes. Martin: Meteorologically, there is another effect: while atmospheric conditions in offshore wind farms change throughout the year because the sea follows the annual cycle of solar radiation at a very slow pace, this cycle can actually be seen in onshore wind farms within a single day. On land, the land surface is cooler than the air above it at night, and vice versa during the day. Over water, especially in spring, the air is already warm, but the water surface is still relatively cold. The cycle here is therefore characterized by an annual cycle, whereas onshore it is characterized by a daily cycle. Accordingly, wind conditions or the duration of wake effects also change to some extent. When the ground is cold and the air above it is rather warm, we tend to see longer wake effects offshore – for example, in spring.
© Fraunhofer IWES
Editorial team: How can wake effects be minimized?
Lukas: One possible solution is to adjust the positioning of the wind turbines and not build so many wind turbines in a large group and in a confined area. These are basically the main ways to adjust it. There are approaches to minimize wake effects between individual turbines through targeted turbine control. However, this has played a rather minor role so far.
Editorial team: You calculate forecasts of how wind conditions will change with further expansion of offshore wind energy. The results have been incorporated, for example, into the Site Development Plan for the North Sea and Baltic Sea of the German Federal Maritime and Hydrographic Agency (BSH). What methods or models do you use for this?
Martin: We work with a weather model that is particularly frequently used in research: the Weather Research and Forecasting model (abbreviated: WRF), for which there is a wind farm parameterization, i.e., a simplified approach to account for the impact of the wind farm on the flow. This allows us to show how large weather systems move across offshore areas and how this affects the wake effects. We use this in particular for large-scale expansion scenarios, for example for the German Bight or even for the entire North Sea. However, we have also developed our own fast models, such as the open-source model FOXES. It is particularly suitable for quick assessments of wake effects, which also provide sufficient accuracy. In addition, coupling the models can enable detailed planning of wind farms within the large wake simulation. The large-scale wake effects are then calculated using the weather model. Small wind farms may be calculated using the FOXES model and then integrated into the larger-scale flow to achieve optimization.
Editorial team: The forecasts for the German Bight are relatively clear. What about the resulting wake effects of large offshore wind farm clusters?
Martin: Exactly, there is a plan for the German Bight. However, this plan also envisages that we will have wind farms that are very close together – among the densest in the world. In some other countries, there are plans that are not yet as far advanced. This means that in some cases it is not yet clear precisely where the respective expansion targets are to be realized. Furthermore, it is still unclear when which wind farms are to be built. European coordination is needed here, and we are providing scientific support for this with the EuroWindWakes research project, which we are conducting together with partners from the Netherlands and Denmark.
Decisions on expansion targets are, of course, political in nature and must be coordinated between the individual ministries and planning authorities. We are developing methods that can be used as a basis for making well-informed decisions on how to improve European coordination.
Editorial team: In the tender for offshore wind turbines in August 2025, there were no bids for the centrally surveyed areas N-10.1 and N-10.2 in the German Bight. What role do wake effects play in this?
Martin: The wake effects on these two areas, N-10.1 and N-10.2, are among the largest in the German Bight and thus also the largest that are likely to occur in the entire North Sea. However, these are not the areas with the absolute greatest effects. These are expected to occur in areas of a neighboring cluster that were successfully awarded in 2024. So, the wake effects are not the decisive factor; other aspects also come into play here – for example, the current conditions for marketing the electricity in the future. But it’s also a question of the supply situation for wind turbines and components, as there are strict deadlines for the realization of the areas. These are all issues that influence whether operators and developers submit a bid or not.
Editorial team: Where do you see further research needs?
Lukas: We now have wind farms with a capacity of 1 to 2 gigawatts – future offshore wind farm clusters will have an installed capacity of more than 10 gigawatts. The main research question is whether the models for current wind farms can also be validly applied to future larger wind farms. We are currently addressing this question in several research projects – C²-Wakes, EuroWindWakes, Reallabor 70GW.
Martin: As wind turbines are getting bigger and bigger, the installed gigawatts per wind farm are also increasing, and data on such large farms is not yet available, it is important to accompany this development over the next 10 years with data analysis. We have made many assumptions in the models that we will only be able to validate once these future turbines and wind farms are in operation. Ideally, this should also be done in collaboration with European partners.
Editorial team: What misconceptions about wakes and energy losses at wind farms do you often encounter in public debate?
Martin: There was recently a big discussion in Great Britian about “wind theft”. The issue was that the wake effects were particularly large, and then people falsely claimed that the models were unable to predict them. In these cases, it was actually often a lack of spatial planning. An operator had a new neighboring wind farm that was supposed to be placed upstream in the main wind direction, and this wind farm had not been taken into account in any planning beforehand. Then, of course, it is completely irrelevant how accurately the model can calculate the wake effects. The wind farm simply did not play a role before.
Lukas: There is currently a recurring discussion that 55 gigawatts of capacity in the North Sea could generate as much energy as 70 gigawatts of capacity. However, this is incorrect; it would be impossible to generate the same amount of energy with less installed capacity in the same area. Instead, the available area would have to be significantly increased.
Martin: There is often talk of great optimization potential for smaller wind farms. Significant optimization potential can arise in specific situations where two or a few turbines are located in a row in the main wind direction. In such cases, there are already opportunities to achieve a ten percent increase in yield with individual configurations – simply by placing the turbines in a different location. However, this is not possible in large, developed wind farm clusters, as a large number of wind turbines are already spread out over a large area.
© Fraunhofer IWES
Editorial team: What challenges do you see in achieving the 70 GW target?
Martin: The keys to success are an existing supply chain and available ports – the entire coastal economic infrastructure requires ultimately a significant transformation. Added to this is the challenge of grid connection.
Editorial team: What are further areas of application for your calculations?
Martin: Questions of economic efficiency are becoming increasingly important: How can areas be operated economically and sustainably in the long term, even when it comes to extending operating life and dismantling? Or how can installation and operation be optimized? We are working very intensively on linking our models with other models at Fraunhofer IWES (e.g., those for Offshore Logistics) in order to be able to make statements about economic efficiency. We then calculate not only gigawatt hours and terawatt hours, but also cost indices, which enables us to make statements about the economic impact of the scenarios.
Our models determine yield time series and can thus relatively accurately map which amounts of electricity are generated, when and in which expansion scenario. Here, we were able to support grid development planning with an accompanying study, which is then carried out by the German Federal Network Agency together with the transmission system operators.
Editorial team: Thank you for your time.
Further information
The BDEW recently published a report on the operation, continued operation, installation, uninstallation, and decommissioning of wind farms, with a view to consolidating smaller wind farm areas into larger ones in the future: BDEW-Studie: Offshore-Windparks bis 35 Jahre effizient weiterbetreiben | BDEW (German only, executive summary in English on p. 4)
The reports on wake effects mentioned in the text are publicly available and can be viewed here:
Endbericht – Weiterentwicklung der Rahmenbedingungen zur Planung von Windenergieanlagen auf See und Netzanbindungssystemen (German only)
https://iopscience.iop.org/article/10.1088/1742-6596/2767/9/092024