Long-term correction of short-term wind measurements: Comparative test by the University of Kassel delivers surprisingly good results

In the course of wind farm planning, the wind conditions at the planned site are measured and evaluated. These wind measurement campaigns typically last one year and the measurement results have to be compared with long-term wind data for the yield forecast of the planned wind farm. This process, known as long-term correction, averages long-term values of wind potential (and thus energy yields) and in this way accounts for seasonal and interannual variations in wind supply.

In their comparative test, the researchers at the University of Kassel, supported by Ramboll CUBE GmbH and Fraunhofer IEE, now investigated, among other things, whether the wind measurement campaign could possibly be significantly shortened in the planning phase. Shortening the measurement period could speed up the realization of wind farm projects and save costs. Until now, it was assumed that the uncertainties of the prediction of the long-term wind potential increased massively if the measurement campaign was shortened, i.e. the results of the long-term correction would be significantly less reliable.

However, it is precisely this reliability that is enormously important for the economic viability of a wind farm project. However, the technological advancements of the last years in the field of wind measurements as well as in the field of long-term correction are remarkable, which is why it is discussed whether shorter measurement durations could be sufficient under certain conditions.

Reason enough for the researchers to investigate this aspect in more detail as part of the LiMeS research project funded by the German Federal Ministry for Economic Affairs and Energy (BMWi), using a comparative test in which a measurement campaign shortened to three months was simulated. For this purpose, wind experts experienced in the field of wind potential determination, project planners and wind turbine manufacturers received measurement data of three-month periods of different seasons and used them to perform a long-term correction.

These data were sections of two years of wind measurements at two measurement sites. In this way, the researchers were able to address the differences between different locations and also to verify and analyze the results using the measurement data in the remaining period. The results are remarkable: The average deviations and the scatter of the participants' results were in the lower single-digit percentage range, which is a surprisingly high accuracy for such short measurement periods. Especially for measurement periods in autumn, the participants succeeded extremely well in reproducing the wind conditions.

The fact that such high accuracies were already achieved with such short measurement periods of three months makes the researchers optimistic about a possible shortening of wind measurement campaigns. However, further extensive research is still needed for this, especially with regard to a larger number of different measurement sites. Furthermore, a detailed understanding of the influence of different meteorological boundary conditions on the results of the long-term correction is important. Building on the results of the Round Robin test, the researchers will therefore now conduct further analyses. New results are expected later this year.

Further information on the Round Robin Test is presented in the final report, which can be found on the university's homepage: http://www.uni-kassel.de/eecs/fachgebiete/integrierte-energiesysteme/aktuelles/nachrichten/article/langzeitkorrektur-von-kurzzeitwindmessungen.html.

Information on the LiMeS project, which is funded by the BMWi, can be found at: http://www.uni-kassel.de/eecs/fachgebiete/integrierte-energiesysteme/forschung/limes.html

Contact:
Alexander Basse
University of Kassel
Department of Integrated Energy Systems
Tel.: +49 561 804-6169
E-mail: alexander.basse[at]uni-kassel[dot]de