Site assessment wind and sea

The development of new locations for inland and offshore wind energy utilization requires a detailed characterization of environmental conditions. Knowledge of this is indispensable for wind energy turbine design and the success of wind farm projects, focusing on land, on the planning of wind farms with large hub heights in hilly or wooded areas. Questions arising in this field of potential assessment, resource definition and load assumptions are processed, among others, using a 200 m high measuring mast and several LiDAR-Systems (laser supported wind speed measuring).

Fraunhofer IWES has developed innovative and adapted measuring and analysis methods, for offshore wind energy utilization, for the on-site conditions of wind, waves, current and the sea floor, as well as methods for recording the ecological effects of offshore wind farms. New systems for measuring wind up to great heights are based on LiDAR systems operated from ships or buoys. A modern measuring method for geophysical construction-ground exploration has also been developed which specifically meets offshore wind industry requirements.

Fraunhofer IWES North-West conducts Lidar measurement campaigns for wind resource assessments. Lidar systems allow ground based remote sensing of wind speed and direction in several heights up to 200 m without need for a measurement mast - this saves money and time in project development.

The service range comprises planning, execution and analysis of Lidar wind measurement campaigns with a Leosphere Windcube v2 Lidar system. For specific applications the Galion G-4000 Scanning Lidar with up to 4000 m measurement range is available.

Highest data quality is ensured by verification according to IEC 61400-12-1 from accredited measurement institutes. An autonomous power supply allows measurements at sites without grid connection.  

  • Ground-based wind measurements in multiple heights up to 200 m without mast
  • Suitable for resource assessment, e.g. according to the German TR6 guideline
  • Full service contract offered: from campaign planning to data analysis

 

 

 

LiDAR buoy

Infographic LiDAR Buoy
© Photo Fraunhofer IWES Nordwest

LiDAR systems send pulsed laser beams into the atmosphere, which reflect off of aerosol particles in the air. From the frequency shift of the backscattered signal, the wind speed and direction are calculated at the corresponding measurement heights

Measurement campaigns for an offshore wind resource assessment with the in-house developed Fraunhofer IWES Wind Lidar buoy include the complete yield assessment for the development of an offshore wind project. The floating system integrates a Wind-cube® v2 Lidar device in an adapted marine buoy. Its compact design, an autonomous power system and an efficient data processing and communication system ensure reliable and flexible offshore wind measurement campaigns at minimal costs. The motion correction algorithm guarantees high data accuracy and measurement uncertainties similar to those for offshore mast measurements. in all project phases including planning, installation and operation.

SERVICES
• Wind velocity measurements up to 200 m
• Additional measurements available: waves, currents, temperature etc.
• Full service contract including permission, deployment, service, data transfer, quality control
• Wind resource assessment based on these data
• Measurement campaigns from one week to one year possible.

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Ship-based LiDAR system


For flexible wind measurements under offshore conditions, the "ship-based Lidar system" facilitates the application of standard wind lidar technology on ships. Whereas measurements from fixed platforms or anchored buoys are a recommendable solution for long-term applications, a ship-based solution is best when a ship is in use at the location of interest anyway or when a measurement is needed for a rather short period only.

A prerequisite for a precise measurement from a moving ship is the correction of the measured data with respect to the concurrent motions. Hence, an integrated motion-measurement system is an essential part of the developed Ship-Lidar System. Data for the up to six degrees of freedom of the system placed on the ship are recorded with high resolution, processed and applied for a correction of the concurrently recorded lidar data.

Aquadopp units measure the direction and speed of the current

© Photo Jan Meier

Detailed characterization of the current and wave conditions is vital for designing offshore wind turbines. Site assessment with accurate prediction of the expected energy output lowers the technical and financial risks for project planners and investors. The current conditions around the foundations of offshore wind turbines determine not only the loads on the structure but also cause sediment transport close to the structure which can lead to pitting.

Detailed analysis of current data has highlighted the complex spatial and time variability of sea currents. The cause of current variations are the effects of turbulence, waves and wind on the avarage current. As a consequence, the electrical output of the turbine varies considerabely and high dynamic loads on the rotor and structure can occur. Accurate analysis of the current field is limited by the low spatial and time resolution of the ADCP (Acoustic Doppler Current Profiler) method that is currently used - but can be improved significantly by using acoustic measuring units. In the direct vicinity of the foundation of an offshore wind turbine they allow detailed investigation of the interaction between the structure and current and the resulting sediment transport.