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Wednesday, 12 March 2014
16:30 - 18:00 Wakes: Do we need different models for onshore and offshore wind farms?
Resource Assessment  


Room: Ponent
Session description

The accurate prediction of the wake effects within and between wind farms is vital to wind farm design and to provide a prediction of the energy output. To date, the vast majority of wind farms have been designed using engineering models which have been tuned and validated using experimental data. As wind farms become larger, empirical correction upon empirical correction are being developed upon the basis of scarce and perhaps erroneous experimental data. Perhaps this is the appropriate time to question if this is the right and only approach.

In the session advanced models and observations will be described and discussed.

Learning objectives:

  • Describe what wakes are, how they can be seen in observations and how they are modelled
  • Identify different models, state-of-the-art and more classical ones
  • See wakes in observations and understand the related issues
Lead Session Chair:
Lars Landberg, DNV GL – Energy (Garrad Hassan), Denmark
RJ Barthelmie Indiana University, United States
Co-authors:
RJ Barthelmie (1) F P
(1) Indiana University, Bloomington, United States

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Rebecca Barthelmie is Professor of Atmospheric Science and Sustainability at Indiana University. Her research in wind energy focuses on resources and wind turbine wakes. She is author of 109 journal papers and over 250 conference papers and reports. She is co-chief editor of the journal Wind Energy, and on the scientific and technical committees of many wind energy conferences. She received the 2009 scientific award from the European Wind Energy Academy for ‘her extraordinary efforts and achievements in the field of wind energy research’. She currently leads research projects funded by the Department of Energy and National Science Foundation.

Abstract

Measuring full scale wind turbine wakes

Introduction

Measurements of wind turbine wakes are relatively rare. There have been many studies on the few data sets from
large offshore wind farms that have been made available by a few developers but more data sets are needed.
Measurements from the 3D Wind Experiments will be presented focused on the experiment in Indiana in 2012.

Approach

A series of experiments have been conducted to characterize wind and turbulence in 3D on wind farm scales.
These are focused on integrating models and measurements to quantify wind speed gradients,wind speed and
turbulence profiles, to characterize atmospheric stability and to measure wind turbine wakes of individual
wind turbines and of whole wind farms.

Main body of abstract

Indiana has approximately 1.4 GW of installed wind capacity which is placed in several very large wind farms
in the northwest of the state. The wind farm site has several hundred turbines in a semi-regular array, with
moderate in-row spacing and large between row spacing. The measurement suite employed at the northern
Indiana wind farm included three vertically pointing lidar, a scanning lidar, anemometers on two 80 m
meteorological masts on opposite sides of the wind farm, a sonic anemometer mounted on an Unmanned
Aerial Vehicle and two anemometers on a tethersonde to quantify atmospheric stability through the lowest
400 m of the atmosphere. The intensive experiment was conducted over a three week period in May 2012
and the results have been integrated with simulations from the WRF and WAsP models. Main findings of the
analysis to date include (I) the excellent agreement between wind speeds measured by all instruments
and the models during convective conditions when the spatial gradients over the area of the wind farm
are small (ii) the methods required to process data to quantify wakes and (iii) an assessment of the downwind
impact of the whole wind farm.

Conclusion

Successful strategies for measuring wind turbine wakes rely on (I) precise characterization
of the inflow conditions and (ii) integrating a range of measurements with models to provide
accurate vertical profiles of wind speed and turbulence and to depict spatial and downwind
variability in the wind field. Our results illustrate the magnitude and behavior of individual wind
turbine wakes in addition to the behavior of the whole wind farm.


Learning objectives
The presentation will highlight advantages and limitations of different instruments,
strategies and processing procedures will be described focused on how full-scale wakes can be quantified