Fraunhofer Institute for Wind Energy Systems
The lidar buoy provides quick, reliable, and cost-effective measurement data for offshore wind farm planning.
Wind measurement and wind modeling: Assessment of wind turbine sites – from the measurement of wind at specific points up to the modeling of large-scale wind fields
Wind turbines are exposed to complex conditions both onshore and offshore. The challenges for the numerical simulation and assessment of potential sites are correspondingly different, making precise modeling of wind fields indispensable. IWES is active in the optimization of numerical methods and data sets on all relevant scales in order to meet the industry’s requirements. For example, during the construction of offshore wind farms, the wind parameters influence the design and layout of the turbines as well as their components, including the foundations and towers. IWES conducts offshore lidar surveys in order to customize the numerical models for the sites. To this end, it has developed lidar measuring buoys, which record meteorological and oceanographic measurement data on the high seas. IWES employs innovative measurement concepts – using a variety of remote sensing technologies – to document the wind conditions.
Our areas of expertise
Aerodynamics
Wind field modeling: Multiscale simulation of wind and wake effects
The expansion of wind energy is taking place under different environmental conditions all around the world. Whereas wind farms are increasingly being planned and constructed in very complex terrain on land (onshore), large “power plants” with hundreds of wind turbines are being installed at sea (offshore), where they interact with the marine atmospheric boundary layer (MABL). The challenges in the numerical simulation and assessment of the sites are correspondingly different.
The modeling of wind fields is primarily required to supplement wind measurement and yield data in space and time as well as for the simulation of future planning conditions. Fraunhofer IWES has been active in the further development, improvement, and application of numerical methods and data sets on all relevant scales for more than a decade, employing open source models and methods in particular.
The numerical simulation of wind energy sites requires the application of different methods in order to satisfy the industry’s requirements on precision and speed as well as to adapt precisely to the various associated scales. To this end, Fraunhofer IWES has developed a range of different numerical site assessment tools for the calculation of wind fields and wind farm yields in complex terrain geometries and the calculation of wind turbines and wind farm wakes in recent years.
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Modeling of wind energy sites in complex terrain
The modeling of complex sites with computational fluid dynamics (CFD) methods first requires the generation of suitable meshes, as the quality of the results depends highly on them. For this purpose, IWES has been developing the terrainMesher mesh generator, which is capable of projecting high-quality grids onto even large sites in very complex terrain automatically, since 2012. On the basis of the open source tool OpenFOAM, a number of parametrizations and flow solvers for the simulation of wind turbines, forest effects, and the atmospheric stability have been developed and validated in a variety of projects, and methods for the calculation of uncertainties have been implemented.
Together, terrainMesher, OpenFOAM, and Fraunhofer IWES’ own developments in OpenFOAM form the FIWind tool: FIWind is a fully automatic software solution which can be run on high-performance computers (HPCs) or on the cloud and controlled via a web frontend. It is an industry-suitable modeling tool for the efficient and precise calculation of wind fields, wind time series, and yields of turbines in complex terrain.
Multiscale modeling of wakes
With the advancing expansion of wind energy in large wind farms and wind farm clusters (predominantly offshore in Europe), the consequences of wind turbine wake effects on each other are playing an ever-greater role. Various studies – including some with Fraunhofer IWES’ involvement – have shown that wake effects can extend up to and beyond 100 km offshore. The wake effects on these scales can be visualized via mesoscale simulations in which the wind farm effects are parametrized. Fraunhofer IWES has been cooperating with partners to drive forward the development and validation of these parametrizations for a number of years already.
IWES has employed this modeling approach to calculate expansion scenarios and large-scale wake effects for a range of clients.
The open source industry model FOXES (Farm Optimization and eXtended yield Evaluation Software), with which wind farms have already been planned in different offshore regions, has been developed for the detailed planning of wind farm areas and their optimization since 2012. Coupled with mesoscale modeling, it is possible to map coastal effects and long-range wake effects extending over different scales.
Certification I Accreditation
Wind measurement
Wind measurements at specific points
Offshore wind farms are increasingly being constructed at sites mostly far away from the coast, where the wind conditions are not known with sufficient accuracy. Even at locations surveyed in the past, subsequently constructed wind farms with their wake effects can lead to a change in the prevalent wind resource. The different wind parameters are required not only for determination of the wind potential, and thus for calculating the profitability of a wind farm, but also for the design/layout of the wind turbine and its components, including the foundations and towers. Accurate measurement data, low measurement uncertainties, and, additionally, high availability are generally indispensable. To this end, Fraunhofer IWES has developed its own measurement buoy, which records meteorological and oceanographic measurement data relevant for the wind industry on the high seas. IWES also creates innovative measurement concepts utilizing a wide range of different remote sensing technologies.
Offshore wind surveys with floating lidar systems
Fraunhofer IWES has been working on the development of floating lidar systems (FLS) and methods for the correction of measurement data corrupted by the movements of the lidar buoy itself since 2009. The first prototype of the Fraunhofer IWES wind lidar buoy was tested for the first time offshore in 2013 and has also been in use in commercial measurement campaigns to determine offshore wind potential since 2017.
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In addition to the data analysis, IWES also takes care of the planning of the measurement campaigns as well as the installation, operation, and maintenance of the lidar buoy.
The lidar buoys are made of a robust steel body for measurements far out at sea. The core element of the buoy – the WindCube V2.1 or ZX300 lidar device – is also additionally protected by an aluminum casing. The buoy’s superstructures allow the installation of further meteorological and oceanographic measuring sensor technologies; customized buoy structures are also possible.
IWES has performed numerous comparative measurements on measuring masts in the North Sea to guarantee the accuracy of the measurements and reduce measurement uncertainties, developing a wide variety of type classifications and methods for correcting turbulence intensity (TI) when doing so.
In addition to the development and application of the FLS technology, IWES also plays a leading role in the standardization of the FLS application – including OWA roadmaps and the PT 61400-50-4 standard – and also offers its expertise independently of its own lidar buoy.
Innovative measurement concepts for the characterization of wind fields
Reliable and meaningful wind measurements are required in different phases of the life cycle of a wind project and in many areas of wind energy research. IWES predominantly employs wind lidar technology – be that as a vertical profiler on buoys (as described above) and vessels, foreseeably on wind turbine nacelles, or scanning lidars with flexible scan geometries and large ranges – to generate extensive measurement data. These data are used to plan wind farms, in operation, and to validate wind farm models or for the calibration of mesoscale simulations. For example, IWES is implementing innovative measurement concepts in the projects FLOW and NEMO . IWES is testing and evaluating the dual Doppler radar technology as a possible next generation of optical wind remote sensing systems in the Windpark RADAR project. In addition, IWES has taken on a leading role in recent years in the normative and pre-normative standardization of wind measurements using remote sensing. Among other things, IWES is an operating agent of IEA Wind Task 52 on wind lidars.
Certification I Accreditation
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