GW Wakes

Motivation

The ongoing development in the use of wind energy in Europe implies the installation of large offshore wind farms in the North Sea and the Baltic, with electrical power outputs between several hundred megawatts up to several gigawatts. Due to technical, financial and ecological restrictions most of the currently approved wind farms are located in the western Baltic Sea and the southern North Sea, resulting in a high wind turbine density within these areas. The operational experiences and results from the already operational large wind farms, e.g. »Horns Rev I« and »Nysted«, show high uncertainties regarding the wake induced deficits and mechanical loads resulting from the wind turbines influences on each other. Thus, there is a high economic interest in the further investigation and consideration of these wake losses in the wind farm design with the help of analytical and engineering models.

Measurements performed in »alpha ventus«

The research project “Analysis of wake induced deficits and wake turbulence characteristic of large offshore wind farms, by comparison of »alpha ventus« and »BARD Offshore 1«” (GW Wakes) (FKZ 0325397), funded by the German Federal Ministry for Economic Affairs and Energy (BMWi) started in August 2012 and consists of two sub-projects. Part A comprises a measurement campaign in »alpha ventus« performed by ForWind – Oldenburg in the framework of the research initiative RAVE. Subsequently in part B measurements will be conducted in a larger offshore wind farm.

The main goal of the research project is the reduction of the operational and planning risks of large offshore wind farms by verification of the interaction of the turbulent maritime boundary layer with the flow affected by the wind farm and its wake. By the development of engineering models, these effects could be considered for the planning of large offshore wind farms.

The verification of these models will be performed by the combination of wind flow data, measured by remote sensing technology which is able to capture the wind flow within the offshore wind farm, and data from numeric wind flow simulations, performed by cluster computing.

For this purpose, ForWind – Oldenburg performed Multi-Lidar measurements within the offshore wind farm »alpha ventus« from July 2013 till April 2014. Lidar is a remote sensing technology using infrared laser light to capture the wind flow. With ranges of up to several kilometers, long-range Lidar wind scanners are able to capture the wind flow of the whole offshore wind farm with high resolution. This world-first application of a multi-Lidar system in an offshore wind farm consisted of three long-range Lidar scanners. Two systems were installed on the research platform »FINO1«, while the third system was deployed at the wind farms substation, as shown in Figure 1 and Figure 2

Due to the installation of the Lidars at two different locations, it is possible to perform different scanning trajectories, allowing the capture of the horizontal two-dimensional wind vector in a large area of the wind farm. To obtain information about the atmospheric stability a measurement buoy, developed by the University of Oldenburg, was deployed at a fixed position near FINO1 to measure, among other quantities, the water surface temperature (Figure 3).