Comparative Exercise: Uncertainties and error estimates of lidar measurements in complex terrain

IEA Wind Task 32 Comparative Exercise:

Uncertainties and error estimates of lidar measurements in complex terrain

Wind LIDAR measurements have become an accepted and useful tool for many applications in the wind energy. However, one of the main obstacles to a more widespread application of wind LIDAR systems are the uncertainties involved with LIDAR measurements on sites classified as “complex terrain”.

January 2020 - Mid 2021

Exercise leader: Alexander Stoekl (Energiewerkstatt)

Organization team: Andreas Krenn (Energiewerkstatt), Doron Callies (Fraunhofer IEE), Andy Clifton (U. Stuttgart).

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The exercise

This exercise in the framework of IEA Wind TCP Task 32 aims to increase the utility of LIDAR measurements on such complex terrain sites. Coordinated by Energiewerkstatt, the exercise builds upon the knowledge and experience of partners among Task 32 members to address the following questions:

  • How to quantify the “complexity” of a site in a meaningful way with regard to LIDAR measurements?
  • What are suitable techniques to compute corrections for the effect of the complexity?
  • What is the remaining uncertainty in the LIDAR data after the application of a correction?

The results and conclusions from these investigations will then be published in a Task 32 report on wind LIDAR measurements in complex terrain.

Method and procedure

The investigations are centered around a number of LIDAR datasets from different Austrian wind measurement sites, ranging from sites with moderate complexity to sites in the Austrian Alps at 1500 m elevation. These sample datasets are provided to the contributing partners together with orographic data and surface roughnesses. Each partner is then asked to use their preferred method to compute corrections to the data for the effect of the complexity, as well as a measure for the remaining uncertainty.

While the selection of a suitable method (e.g. CFD simulations or statistical methods) is up to the partner, the overall goal is to have several different methods included in the project.

To assess the suitability of the individual methodologies, the corrected time series are then compared to wind mast data obtained at the same sites. In doing so, two aspects are taken into account:

  1. The deviations between the corrected LIDAR data and the wind mast measurements.
  2. The agreement of the remaining deviations and the predicted uncertainty.

The results of this assessment will form the main part of the intended Task 32 report authored by the project participants. To allow a useful interpretation of the results, it is therefore necessary to provide neutral, impartial, and anonymous descriptions of the deployed methodologies.

Participation and Organization

Due to the international scope of the project, exchange among the partners will primarily be organized in the form of virtual meetings. For a mutual exchange of the results and a joint discussion of the findings, a project workshop will be organized at a later stage (when first results are available) and probably will take place in 2020. Finally, the creation of the Task 32 report on the results and conclusions is scheduled for the second half of 2021.

As an expansion to the provided LIDAR datasets, partners are also invited to contribute additional LIDAR data to this study. The requirements are that parallel LIDAR and wind mast measurements data must be available for a significant period in time (at least several weeks) on a site that can be classified as a “complex terrain” site. The data must be cleared for distribution under the terms of a non-disclosure agreement. The location of the site will not be distributed, but necessary geographical information such as orography and surface roughness in the vicinity must be provided. While no part of the actual data will be released to the public, the conclusions obtained with the data will be part of a public report.

For more information

Please contact Alexander Stoekl at Energiewerkstatt.