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Measurement of the Stöttener Berg site with a view to the east using various meteorological measuring techniques, (from left) such as a radio acoustic sounding system (RASS), met mast and LiDAR measuring devices.
© Universität Stuttgart - SWE
Wind conditions in low mountain ranges
17.01.2017

The layout shows the side view of the test field.
© Technische Universität München / Lareg

The simulation shows the test field at Stöttener Berg from a WindFors video.
© 2Dmedia

New wind energy test field in southern Germany

Because of the pronounced terrain structures, wind farms in low mountain ranges have to cope with more turbulent wind conditions than in lowland areas. These meteorological conditions mean that development and maintenance costs have been higher up to now in landlocked mountainous areas, while precise profit forecasts are more difficult. A new wind energy test field belonging to the southern German research group WindForS now aims to close the gaps in meteorological knowledge and optimise the wind turbine engineering.

In Germany, the largest electricity demand is in the west and south. If more wind power were generated in future near the main areas of demand, this would relieve the electricity grid. However, because of the mountainous, complex terrain there, wind farm sites in these low mountain ranges are subject to more turbulent wind conditions than on low-lying coastal plains. These meteorological conditions in southern Germany are causing uncertainties and errors when forecasting the electricity production of the wind turbines. The calculations are needed when planning wind farms in order to assess their profitability. In addition, the wind conditions create higher loads on the turbine components than at sites in lowland areas, which also results in higher maintenance and repair costs.

At Stöttener Berg, which is a hill near Geislingen an der Steige, a new wind energy test field is being established for the researchers from Baden-Wuerttemberg and Bavaria in order to optimise the wind turbine engineering for such wind conditions.

Four 100-metre-high meteorological masts and two 750-kilowatt research wind turbines will be erected on the site. The aim is that the test field will create a versatile platform for future scientific and industrial research. Project manager Andreas Rettenmeier from the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW), which is leading the project, explains the advantages of the site: "The prevailing west wind is accelerated over the edge of the upstream terrain level, forming irregular currents and turbulence. In addition, the area has a high average annual wind speed."

Measuring turbulence and currents

Measurements at the site have shown that the wind accelerates up to 1.8 times the wind speeds measured further along the Alb plateau. In addition, wind turbulence and vortices occur due to the air flowing over the terrain. These conditions are typical of mountainous, complex terrain. The met masts will be located in the main wind direction in front of and behind the two wind turbines. In addition, further remote sensing measurements will be carried out, including from the ground and the wind turbines, using laser-assisted devices such as LiDAR and with unmanned measurement aircraft on a model scale. The wind speed and direction, the air humidity and pressure as well as the inflow and wake currents will be recorded at a high temporal resolution. The main research areas are concerned with investigating the wind turbine performance as well as the micro-climatic and topographical influences on the wind. For this purpose, the exchange of energy, water and trace gases will be measured on and behind the test field. The data will be used to develop improved programs for performance and load simulations. These programs are aimed at depicting the flow conditions from the mesoscale to the flow around the rotor blades.

Checking out the mechanical loads

The two research wind turbines with a hub height of 75 metres and a rotor diameter of 50 metres will already be equipped with sensors right from the bottom of the foundations up to the rotor blades during their construction. These will enable the mechanical loads acting on the individual components to be determined. The researchers have chosen two 750-kilowatt turbines because components of this size are relatively easy to change, for example in order to test new rotor blades. In addition, the knowledge gained from this turbine class can be transferred to the market-standard multi-megawatt turbines, whereby for the first time the entire design and structural data as well as the control algorithms for the two research wind turbines will be available to the researchers. These will enable the loads on the individual components caused by changing wind conditions to be estimated more precisely – and thus the effects on their service life.

The two wind turbines will also be used to test not only new material and construction principles but also optimised operating management strategies in order to be able to respond more intelligently to the changing wind conditions. The researchers are also working on models to improve the storage of surplus wind power. One focus is on the interactions of the wind turbines with the ground through vibrations and oscillations. This is concerned on the one hand with the influence of the wind force on the ground emissions of the wind turbines and, on the other, with seasonal changes in the ground conditions such as frost. Accompanying ecological research will investigate changes to the fauna and flora as a result of constructing and operating the test field. The researchers want to use their results to help encourage manufacturers to improve the wind turbine technology.

From KonTest to WINSENT

The construction and commissioning of the test field and the scientific research programme form part of the Wind Science and Engineering in Complex Terrain (WINSENT) research project, which was launched in December 2016. The construction of the test field is scheduled to start in late summer 2017. The work is based on the results of the previous project, KonTest, in which the conception and requirements for the test field were developed. These formed the basis in the search for a windy site at an elevated altitude. More than 3,500 municipalities and local authorities received mail from WindForS. The selected site on Stöttener Berg fulfils these criteria best of all. The German Federal Ministry for Economic Affairs and Energy and the state government of Baden-Württemberg are supporting the WINSENT project with a total of 11.6 million euros.

The Centre for Solar Energy and Hydrogen Research Baden-Württemberg is coordinating the project. It is being partnered by Stuttgart University, Eberhard Karls Universität Tübingen, the Technische Universität München, Karlsruhe Institute of Technology and Esslingen University of Applied Sciences.

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ZSW Baden-Württemberg

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Film about the test field
The WindForS research group has released a short film on the planned test field (in German).

WindForS network
Stuttgart and Tübingen universities, the Technische Universität München, Karlsruhe Institute of Technology, Aalen and Esslingen Universities of Applied Sciences and the Centre for Solar Energy and Hydrogen Research in Baden-Württemberg are bundling their wind energy research expertise in the "WindForS" network.

Info tip

Measuring wind potential in low mountain ranges
BINE-Projektinfo 12/2016