Wind report

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A wind report predicts the average wind speed and the expected energy yield for the location of a wind turbine to be built over the expected future operating life of up to 20 years.

The basis is measured and calculated wind conditions, the power curve of a wind turbine, shading and turbulence effects , restrictions on use due to icing, shadows and noise protection rules . In addition to the pure wind reports, in which the energy production is calculated, there are also separate reports on turbulence, shadows and noise emissions . Independent wind reports form a data basis for the evaluation of future projects in project reviews ( due diligence ).

methodology

In principle, based on the analysis of measured and long-term correlated wind data from the past, it is assumed that there is a certain probability that this will also occur again in the future. Meteorological parameters measured at certain points (mainly wind speed and wind direction) are transferred to a spatial wind field using suitable modeling methods.

At the beginning there is an assessment of the future location. With the help of topographic maps (topographic maps 1: 25000) and a site visit, a digital terrain model is created for micrositing . While the roughness is usually digitized within a radius of 20 to 40 kilometers using the maps and the site inspection, the contour lines can be generated from GIS or SRTM data . The direct environment must be determined in more detail because of possible shading effects. Buildings, roads, trees, bodies of water, hedges and other wind turbines are part of it. It must also be taken into account here that this changes over time and it is therefore recommended that the wind expert and the client agree on possible changes in the development plans.

Various options are used to simulate the air currents. On the one hand, it is common to use the wind data from weather stations ( e.g. the DWD ) or wind measurements. The long-term correlation is important here . Processed data must cover a period of at least 10 years. The longer this period, the more reliable the long-term forecasts are. In addition to this variant, there is also the option of calculating wind speeds by interpolating altitude and latitude and taking topographical conditions into account. An air pressure database from weather stations and satellite data serve as the basis. However, it must be taken into account here that such mesoscale models are associated with very large uncertainties due to their relatively low resolution.

The wind conditions at the reference location are described using the mean wind speed and, on the other hand, the energy density depending on the height above ground. The composition of the proportions of wind speed intervals is described with the Weibull distribution (A & k parameters). Since the wind speed is included in the energy calculation with the third power, it is not only important to know how high the mean wind speed is, but also how the measured wind speeds are distributed.

According to the Renewable Energy Sources Act (EEG), the relationships between freely flowing wind turbines and the reference yield must be determined. With the formation of a wind park , so-called park losses occur due to shadowing. Also of interest are the turbulence effects, which increase with decreasing distance from obstacles or other wind turbines and can shorten the life of the rotor blades .

A more detailed explanation of the approach also includes an uncertainty assessment, in which the individual analysis parts are considered individually and, if necessary, high uncertainties, such as calculated characteristic curves , are pointed out.

Web links

  • [1] - Wind expert advisory board in the BWE
  • [2] - Wind Energy Promotion Agency; Technical guideline for wind reports
  • www.wea-nis.de - WEA emergency information system: Database of wind turbines in Germany (IWET)