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Delegates are invited to meet and discuss with the poster presenters during the poster presentation sessions between 10:30-11:30 and 16:00-17:00 on Thursday, 19 November 2015.

Lead Session Chair:
Stephan Barth, ForWind - Center for Wind Energy Research, Germany
Annette Westerhellweg Ul International GmbH - DEWI, Zweigstelle Oldenburg, Germany
Co-authors:
Annette Westerhellweg (1) F Daniel Fabian (1) Jan Raabe (1)
(1) Ul International GmbH - DEWI Zweigstelle Oldenburg, Oldenburg, Germany

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2015 and are published here unedited

Annette Westerhellweg has been working in the wind industry for 15 years. She is currently working in the field of energy yield assessment at UL International GmbH - DEWI. She studied Physics at the University of Oldenburg. Her main activities at DEWI are energy yield assessments, remote sensing data analysis, production losses due to icing, CFD applications and offshore wakes.


Poster

Poster Download poster (11.70 MB)

Abstract

Short-term wind profile measurements with remote sensing devices and consideration of seasonal effects

Introduction

Hub heights much above 100 m become more and more usual for new planned wind farms. On the other hand wind measurement masts often have a lower measurement height and therefore the estimation of the vertical wind profile has distinct uncertainties. Short term measurements by remote sensing devices (RSD) provide a way to assess and verify the wind profile between the mast measurement height and the planned hub height.

Approach

In this work seasonal effects have been tested by the evaluation of several remote sensing measurements with duration of a whole year for varying input periods. The input periods has been varied in length (of 3 months and 6 months) and season (winter, summer, intermediate).

Main body of abstract

In this contribution the limits and prerequisites of such short term wind profile measurements will be presented. Special focus is given on the variation of the wind profile over the time of the day and over seasons and an analysis of its influence on the results. Furthermore, a directional variation of the wind shear because of differences in orography, roughness and general weather conditions is investigated. The representativeness of the measured wind profile was checked by comparing short term periods with full years periods of several full year RSD measurements
The representativeness of the measured wind profile has to be validated and in case that it is not representative the wind profile has to be corrected. DEWI has developed and uses two different methods for the correction of seasonal effects, the seasonal correction based on a stability parameter (the solar altitude or z/L) and the wind shear correlation.


Conclusion

The application of the measured wind shear during a short-term RSD measurement without any correction for seasonal effects can lead to distinct prediction errors in an energy yield assessment. The consideration of seasonal effects is necessary and leads in most cases to a reduction of the error. The evaluation of 3 months measurements showed improved results if a seasonal correction was applied. Short-term wind profile measurements in pure summer or winter season should be omitted. The assessment shows that uncertainties can be reduced by an extension of the measurement period to 6 months performed in an appropriate period, e.g. Jan-Jun or Jul-Dec. For 3 months campaigns additional tests of the representativeness in respect to wind speed and direction distribution have to be performed to assess the reliability of the seasonal correction


Learning objectives
This evaluation of several full year RSD measurements aims to assess the effectiveness of the seasonal corrections methods, address uncertainties and determine the limits of these procedures.