Martin Dörenkämper

Fraunhofer Institute for Wind Energy Systems IWES | IWES · Department of Aerodynamics and Numerical Wind Energy Meteorology

The coastal discontinuity imposes strong signals to the atmospheric conditions over the sea that are important for wind-energy potential. Here, we provide a comprehensive investigation of the influence of the land–sea transition on wind conditions in the Baltic Sea using data from an offshore meteorological tower, data from a wind farm, and mesosca...

Abstract. This is the second of two papers that document the creation of the New European Wind Atlas (NEWA). In Part 1, we described the sensitivity experiments and accompanying evaluation done to arrive at the final mesoscale model setup used to produce the mesoscale wind atlas. In this paper, Part 2, we document how we made the final wind atlas p...

In terms of predicting wind turbine wakes, the stably stratified atmospheric boundary layer (SABL) is taking an exceptional position as wake effects and thus loads on subsequent turbines are stronger. In this study we show the impact of the SABL on power production and wake effects (power deficits) in offshore wind farms by means of measurements as...

Our aim with this paper was the analysis of the influence of offshore cluster wakes on the power of a far-distant wind farm. We measured cluster wakes with long-range Doppler light detection and ranging (lidar) and satellite synthetic aperture radar (SAR) in different atmospheric stabilities and analysed their impact on the 400 MW offshore wind far...

Low-level jets (LLJs) are wind speed maxima in the lower part of the atmospheric boundary layer. Accurately accounting for these mesoscale phenomena in wind resource assessment is increasingly important as the height of wind turbines continues to grow. During LLJ events, wind speeds increase, leading to a general increase in power output. We utiliz...

We propose a modification to the Fitch wind farm parameterization implemented in the Weather Research and Forecasting (WRF) model. This modification, derived from 1D momentum theory, employs a wind-speed-dependent induction factor to correct the local grid wind speed back to freestream before computing the turbine's power and thrust. While the orig...

The planned expansion of wind energy in the German Bight is creating much more densely staggered wind farms and wind farm clusters. This results in a significantly greater influence of the generated wakes on energy production of neighboring wind farms. The Dornier‐128 research aircraft operated by the Technische Universität of Braunschweig was used...

The interaction between wind farms and the surrounding atmosphere is an extremely complex process which brings significant modelling challenges. As offshore wind farms and cluster increase in size and scope, the risk of potential biases and uncertainty on Annual Energy Production (APE) increases thereby requiring greater understanding of this inter...

The interaction between wind farms and the surrounding atmosphere is an extremely complex process which brings significant modelling challenges. As offshore wind farms and cluster increase in size and scope, the risk of potential biases and uncertainty on Annual Energy Production (APE) increases thereby requiring greater understanding of this inter...

With the aim to increase the energy yield of large offshore wind farm clusters, especially during low wind speeds, innovative rotor concepts with low specific ratings are being developed. We use mesoscale simulations, to compare wakes and power production of a wind farm cluster with a rated power of 1.17 GW, equipped with a turbine featuring a low...

This study presents a multi-model approach for wind resource assessment of a wind farm affected by external wakes. The Weather Research and Forecasting model (WRF), a mesoscale model, is employed to simulate external wind farm wakes, while the Farm Optimization and eXtended yield Evaluation Software (FOXES), an engineering model, is used to simulat...

Inter-farm wakes between offshore wind farms can cause a significant production loss at the downstream wind farm. We compare the power production at two wind farms that are separated by approximately 20 km to engineering model results provided by three different wind farm developers. Model inflow conditions were derived from the nacelle anemometry...

The interaction of wind farm clusters with the atmospheric flow is complex. It comes along with phenomena that have still not been fully understood in detail. However, having an understanding of the flow is a prerequisite for the derivation of models that can accurately and with limited computational resources replicate the most prominent features...

With a large number of wind farms already deployed in German waters and aiming to achieve a minimum of 70 GW of offshore wind capacity by 2045, investigating the potential for extended operation of existing assets is an important task. This paper documents the development of a life cycle cost/revenue framework capable of incorporating CAPEX and OPE...

We propose a modification to the Fitch wind farm parameterisation implemented in the Weather Research and Forecasting (WRF) model. This modification, derived from the 1D momentum theory, employs a wind speed dependent induction factor to correct the local grid wind speed back to free stream, before computing the turbine’s power and thrust. While th...

This study investigates the performance of pumping-mode ground-generation airborne wind energy systems (AWESs) by determining cyclical, feasible, power-optimal flight trajectories based on realistic vertical wind velocity profiles. These 10 min profiles, derived from mesoscale weather simulations at an offshore and an onshore site in Europe, are in...

We propose that considering mesoscale wind direction changes in the computation of wind farm cluster wakes could reduce the uncertainty of engineering wake modeling tools. The relevance of mesoscale wind direction changes is investigated using a wind climatology of the German Bight area covering 30 years, derived from the New European Wind Atlas (N...

The OWC Project Consortium has, on behalf of Bundesamt für Seeschifffahrt und Hydrographie (BSH), performed an assessment of the historic long-term representative wind conditions across site N-6.7. The site N-6.7 is in the German Exclusive Economic Zone in the North Sea. The report was published by BSH: https://pinta.bsh.de/N-6.7

The atmospheric boundary layer experiences multiple changes in coastal regions, especially with wind directions from land towards the sea, where the wind speed usually increases due to the smaller roughness of the ocean surface. These effects are of particular relevance for offshore wind energy utilization; they are summarized under the term coasta...

As wind is the basis of all wind energy projects, a precise knowledge about its availability is needed. For an analysis of the site-specific wind conditions, Virtual Meteorological Masts (VMMs) are frequently used. VMMs make use of site calibrated numerical data to provide precise wind estimates during all phases of a wind energy project. Typically...

While some airborne wind energy system (AWES) companies aim at small, temporary or remote off-grid markets, others aim at utility-scale, multi-megawatt integration into the electricity grid. This study investigates the scaling effects of single-wing, ground-generation AWESs from small- to utility-scale systems, subject to realistic 10 min, onshore...

As part of the ongoing X-Wakes research project, a 5-month wake-measurement campaign was conducted using a scanning lidar installed amongst a cluster of offshore wind farms in the German Bight. The main objectives of this study are (1) to demonstrate the performance of such a system and thus quantify cluster wake effects reliably and (2) to obtain...

We propose that considering mesoscale wind direction changes in the computation of wind farm cluster wakes could reduce the uncertainty of engineering wake modelling tools. The relevance of mesoscale wind direction changes is investigated using a wind climatology of the German Bight area covering 30 years, derived from the New European Wind Atlas (...

This document has been produced by OWC (Aqualis) GmbH in cooperation with ProPlanEn GmbH, and Fraunhofer IWES (Consortium referred to as OWC Project Consortium, OWC-C) for the sole use and benefit of, and pursuant to a client relationship exclusively with Bundesamt für Seeschifffahrt und Hydrographie (BSH, "Client"), and may not be relied on by any...

To establish long-term flow measurements for the validation of wake models, a scanning Doppler wind lidar system was installed at the western edge of the wind farm Gode Wind 1 in the German Bight for a period of five months. The main goal was to detect the wakes from clusters for different wind directions and atmospheric stabilities. The lidar data...

Under the term global blockage , the cumulative induction of wind turbines in a wind farm has been recently suspected to be responsible for observed overestimations of the energy yield in large-size wind farms. In this paper, the practice of modeling this effect after linear superposition of single turbine inductions, calculated with three of the m...

The objective of this paper was the experimental investigation of the accumulated induction effect of a large offshore wind farm as a whole, i.e. the global-blockage effect, in relation to atmospheric-stability estimates and wind farm operational states. We measured the inflow of a 400 MW offshore wind farm in the German North Sea with a scanning l...

Like almost all measurement datasets, wind energy siting data are subject to data gaps that can for instance originate from a failure of the measurement devices or data loggers. This is in particular true for offshore wind energy sites where the harsh climate can restrict the accessibility of the measurement platform, which can also lead to much lo...

Power converters in wind turbines exhibit frequent failures, the causes of which have remained unexplained for years. Field-experience based research has revealed that power- and thermal-cycling induced fatigue effects in power electronics do not contribute significantly to the field failures observed. Instead, clear seasonal failure patterns point...

Under the term global blockage, the cumulative induction of wind turbines in a wind farm has been recently suspected to be responsible for observed overestimations of the energy yield in large-size wind farms. In this paper, the practice of modeling this effect after linear superposition of single turbine inductions, calculated with three of the mo...

In wind energy site assessment, one major challenge is to represent both the local characteristics as well as general representation of the wind climate on site. Micro-scale models (e.g., Reynolds-Averaged-Navier-Stokes (RANS)) excel in the former, while meso-scale models (e.g., Weather Research and Forecasting (WRF)) in the latter. This paper pres...

The objective of this paper was the experimental investigation of the accumulated induction effect of a large offshore wind farm as a whole, i.e. the global blockage effect, in relation to atmospheric stability estimates and wind farm operational states. We measured the inflow of a 400 MW offshore wind farm in the German North Sea with a scanning l...

While some Airborne Wind Energy System (AWES) companies aim at small-scale, temporary or remote off-grid markets, others aim to integrate utility-scale, multi-megawatt AWES into the electricity grid. This study investigates the scaling effects of single-wing, ground-generation AWESs from small to large-scale systems, subject to realistic 10-minute,...

Airborne wind energy systems (AWESs) aim to operate at altitudes well above conventional wind turbines (WTs) and harvest energy from stronger winds aloft. While multiple AWES concepts compete for entry into the market, this study focuses on ground-generation AWES. Various companies and researchers proposed power curve characterizations for AWES, bu...

Like almost all measurement datasets, wind energy siting data are subject to data gaps that can for instance originate from a failure of the measurement devices or data loggers. This is in particular true for offshore wind energy sites where the harsh climate can restrict the accessibility of the measurement platform, which can also lead to much lo...

This is the second of two papers that document the creation of the New European Wind Atlas (NEWA). In Part 1, we described the sensitivity experiments and accompanying evaluation done to arrive at the final mesoscale model setup used to produce the mesoscale wind atlas. In this paper, Part 2, we document how we made the final wind atlas product, co...

This is the first of two papers that document the creation of the New European Wind Atlas (NEWA). It describes the sensitivity analysis and evaluation procedures that formed the basis for choosing the final setup of the mesoscale model simulations of the wind atlas. The suitable combination of model setup and parameterizations, bound by practical c...

Abstract. This is the first of two papers that documents the creation of the New European Wind Atlas (NEWA). It describes the sensitivity analysis and evaluation procedures that formed the basis for choosing the final setup of the mesoscale model simulations of the wind atlas. An optimal combination of model setup and parameterisations was found fo...

Airborne wind energy systems (AWESs) aim to operate at altitudes above conventional wind turbines where reliable high-resolution wind data are scarce. Wind light detection and ranging (lidar) measurements and mesoscale models both have their advantages and disadvantages when assessing the wind resource at such heights. This study investigates wheth...

This review article aims to provide an overview and insight into the most relevant aspects of wind energy development and current state-of-the-art. The industry is in a very mature stage, so it seems to be the right time to take stock of the relevant areas of wind energy use for power generation. For this review, the authors considered the essentia...

Our aim with this paper was the analysis of the influence of offshore cluster wakes on the power of a far distant wind farm. We measured cluster wakes with long range Doppler light detection and ranging (lidar) and satellite synthetic aperture radar (SAR) in different atmospheric stabilities and analysed their impact on the 400 MW offshore wind far...

This report describes the sensitivity studies performed with the mesoscale model WRF in preparation of the mesoscale production runs for the New European Wind Atlas (NEWA). The objective of this work was to find a model setup that is not just a best practice setup but well-founded and based on scientific evaluation.

Airborne wind energy systems (AWES) aim to operate at altitudes above conventional wind turbines where reliable high resolution wind data is scarce. Wind LiDAR measurements and mesoscale models both have their advantages and disadvantages when assessing the wind resource at such heights. This article investigates whether assimilating measurements i...

This article presents the Ferry Lidar Experiment, which is one of the NEWA Experiments, a set of unique flow experiments conducted as part of the New European Wind Atlas (NEWA) project. These experiments have been prepared and conducted to create adequate datasets for mesoscale and microscale model validation. For the Ferry Lidar Experiment a Doppl...

As a part of the New European Wind Atlas project, we investigate the estimation of extreme winds from mesoscale simulations. In order to take the smoothing effect of the simulations into account, a spectral correction method is applied to the data. We show that the corrected extreme wind estimates are close to the values obtained from offshore met...

An effective methodology for CFD simulations of stratified atmospheric boundary layer flows is presented, based on the Poiseuille-type zero pressure gradient boundary layer. The concept of precursor inflow generation is applied in the scope of Reynolds Averaging Navier-Stokes (RANS) simulations, and combined with mean temperature control via explic...

High frequency wind data derived from LES simulations which are driven by results from mesoscalic WRF simulations for Pritzwalk in northern Germany. Comparison between WRF simulations with and without implementation of additional LiDAR measurements using observation nudging.

The presentation describes the process of implementing LiDAR measurements into a mesoscale weather model (WRF). These results then drive high resolution large eddy simulations (LES) in PALM. See the full presentation here: http://www.awec2017.com/2-uncategorised/54-markus-sommerfeld-2.html PDF on request.

The annual energy production of an existing wind farm including thermal stratification is calculated with two different methods and compared to the average of three years of SCADA data. The first method is based on steady state computational fluid dynamics simulations and the assumption of Reynolds-similarity at hub height. The second method is a w...

The rapid increase of the wind energy utilization during the last two decades led to an urgent demand for models that are able to give precise estimates of the flow characteristics in wind farms. For several years large-eddy simulation models have now been used to gain a deeper knowledge of the processes of the wind farm flow. The knowledge gained...

For a further development of offshore wind energy exploration a profound understanding of the interaction of the marine atmospheric boundary layer with wind energy systems is needed. This study aims at increasing this understanding by investigating spatial and temporal fluctuations of wind and power in offshore wind farms based on numerical simula...

In this study, high-resolution large-eddy simulations of two German offshore wind farms are performed with the LES model PALM in which the turbines are parameterized with an actuator disk approach. The simulation of a single wind farm is realized by a stationary model domain with a turbulent inflow. Different atmospheric stratifications from slight...

Power curves for offshore wind turbines within the German offshore wind farm alpha ventus were derived based on the IEC standard. Binning in groups of shear and turbulence intensity as measures of atmospheric stability were performed. The derived power curves show a strong dependency on these two parameters. Differences of up to 15% in power output...