Round Robin Numerical Flow Simulation in Wind Energy - DEWI

173 Pages·2015·15.43 MB·English

Round Robin
Numerical Flow Simulation in Wind Energy
Final Report
Francesco Durante, Volker Riedel
Ulrike Bunse, Peter Busche, Harald Mellinghoff, Dr. Kai Mönnich, Till Schorer
DEWI GmbH - Deutsches Windenergie-Institut
Wilhelmshaven, Germany
2008-03-08
This project was sponsored by the German Federal Ministry for the Environment, Nature Conservation
and Nuclear Safety, FKZ 0329965.
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Disclaimer
The following results refer to one single site with three met masts installed, they refer to the model in
the version and configuration used in the test and they refer to a specific model operator/team. Under
no circumstances can these results be considered as a general statement about the quality of the
service provided by each company, nor can these results be considered as a general quality assessment
of the computer model used. In particular, if a third party flow model is used by the participant, the
results cannot be considered as a statement of quality of the third party model. The reasons are as
follows:
1. Flow models in general have many parameters to set and simulation design decisions have to be
made, depending on the site under consideration and depending on the experience of the model
operator. It is not clear if the model operator during the Round Robin Test will be the same than
during normal business model operation.
2. Wind farm sites are very different, especially regarding orographic complexity. The results that
refer to this site are not transferable to any other site and are valid only for this specific site.
3. Measurement uncertainties specified below refer to the standard uncertainty, assuming a normal
distributed error. Although less likely, the actual deviation between measurement value and real
value can be higher than the standard error.
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Round Robin Numerical Flow Simulation in Wind Energy
Table of Content
1 Preface...........................................................................................................................................9
2 Sponsors.......................................................................................................................................10
3 Setup of the Round Robin test.......................................................................................................11
3.1 The aim...................................................................................................................................11
3.2 The choice of the test site.......................................................................................................11
3.3 The dummy Run......................................................................................................................12
4 Description of the Participating Models.........................................................................................13
5 Description of the Main Test.........................................................................................................20
5.1 Input Data-set.........................................................................................................................20
5.1.1 Elevation..........................................................................................................................21
5.1.2 Land Cover.......................................................................................................................23
5.1.3 Meteorological data.........................................................................................................25
5.1.4 Coordinates.....................................................................................................................28
5.2 Output Data-set......................................................................................................................28
5.2.1 Mean Horizontal Wind Speed for terrain-following surfaces............................................28
5.2.2 Mean Wind Speed for the target locations.......................................................................29
5.2.3 Wind Statistics for target locations in 80 m above Ground Level......................................29
6 Assessment of the Results.............................................................................................................30
6.1 Weibull A- and k-Parameter....................................................................................................30
6.2 Mean Horizontal Wind Speed for a terrain-following surface at different heights...................33
6.3 General Remarks on the Evaluations Regarding Wind Speed...................................................43
6.3.1 Technical details on the assessment of the statistics........................................................43
6.4 Important Remarks regarding the Results of the Participant ANM...........................................46
6.5 Incomplete Data Submitted by Participant UNJ.......................................................................49
6.6 Incomplete Data Submitted by Participant REP.......................................................................49
6.7 Evaluations Regarding Mean Wind Speed...............................................................................50
6.7.1 Quantitative Evaluations with Respect to the Sector-wise Speed-Up Factors....................51
6.7.2 Deviations from all Participants Mean Values...................................................................54
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6.7.3 Mean Absolute Values of Sector-wise Errors....................................................................55
6.7.4 Overall Direction Independent Wind Speed Prediction Error............................................56
6.8 Evaluations Regarding Mean Squared Wind Speed..................................................................67
6.9 Evaluations Regarding Mean Cubed Wind Speed....................................................................77
6.10 Evaluations Regarding Wind Direction....................................................................................86
6.10.1 Qualitative Evaluation Regarding Veer Angles..................................................................86
6.10.2 Qualitative Evaluation Regarding Veer Angles: Target Mast 1...........................................86
6.10.3 Qualitative Evaluation Regarding Veer Angles: Target Mast 2...........................................87
6.10.4 Evaluations Regarding the Overall Wind Direction Distributions.......................................88
6.10.5 Assessment of Average Sector-Wise Wind Direction Errors..............................................90
6.10.6 Assessment of the Directional Dispersion of the Single Sector Wind Direction Results.....90
6.11 Single Turbine AEP................................................................................................................104
6.12 Energy Yield Results: Single Turbine AEP...............................................................................105
6.13 Wind Farm Energy Yield Results............................................................................................113
7 Conclusions.................................................................................................................................121
8 Appendix....................................................................................................................................125
8.1 Overview of the properties of the on-site measurements.....................................................125
8.1.1 Wind Direction Effects...................................................................................................129
8.1.2 Speed-up Factors...........................................................................................................132
8.1.3 Turbulence Intensity......................................................................................................135
8.1.4 Sector-wise Wind Speed Correlation Properties.............................................................142
8.1.5 Filling of a Gap in Target Mast 1 Data.............................................................................148
8.1.6 Filling of a Gap in Target Mast 2 Data.............................................................................152
8.2 Issues related to the site selection process............................................................................156
8.2.1 General Considerations..................................................................................................156
8.2.2 Wind Speed Measurement............................................................................................157
8.2.3 Spatial Arrangement......................................................................................................158
8.2.4 Wind Direction Measurements......................................................................................158
8.2.5 Exemplary illustrations of some problematic effects found during site search................161
8.2.6 Maps.............................................................................................................................166
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8.2.7 Forest............................................................................................................................166
8.2.8 Coordinates...................................................................................................................167
8.2.9 Data from Numerical Site Calibrations...........................................................................168
8.3 Output data Format..............................................................................................................170
8.3.1 Mean Horizontal Wind Speed for terrain following surfaces - Data Format.....................170
8.3.2 Mean Wind Speed for target locations - Data Format.....................................................170
8.3.3 Wind Statistics for target locations - Data Format..........................................................171
9 References..................................................................................................................................173
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1 Preface
Wind energy has successfully developed world wide during the last years. Along with this good
development, there have been continuous improvements of the tools used for the simulation of the
wind flow conditions. Future installations are foreseen to concentrate over off-shore areas and to
develop more and more over internal complex terrain sites. With the exploitation of wind energy over
internal areas, the complexity of the surface and flow conditions makes the requirements for a proper
wind resource assessment and for a correct definition of the financing risks even higher. Despite a
general improvement of several aspects of resource assessment methods (such as the analysis of the
anemometers effects, the long term correlation techniques etc. ), the methods for extrapolation of
wind conditions from a measurement mast to a wind turbine site has remained more or less unchanged
since the early nineties: The European Wind Atlas is a „de facto“ standard method for most of the
energy yield calculations. Limitations and weaknesses of this methodology are well known and under
complex terrain conditions (or other non-standard situations) large systematic errors are to be
expected. An alternative solution to improve the reliability of resource assessment over complex
orography is represented by the use of fluid dynamical numerical models. Presently, different
typologies of numerical models and methodologies are adopted for wind resource evaluation. Most of
them have been initially developed for purposes marginally related to wind energy applications such as
automotive industry or weather forecasting. While in other sectors of research and engineering the
numerical solution of the fluid dynamic equations has become a standard approach for the derivation
of the flow properties, in wind energy the adoption of numerical flow models as an accepted standard
method still lacks the necessary experience and still requires a systematic classification and a scientific
evaluation of errors and of the related uncertainties. Such an evaluation would support decisions for a
wide range of wind energy actors like banks, financing companies, developers, etc. It is believed that
the presence of a scientific classification and an independent assessment of the myriad of different
wind simulation methods will eventually improve the acceptability of the concept of numerical
simulation on the whole. This project aims, as much as possible, to fill the aforementioned gaps.
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2 Sponsors
This research was sponsored by the following parties:
- German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety
- Bremer Landesbank
- Commerzbank
- Deutsche Immobilien Leasing GmbH
- GE Energy
- HSH Nordbank AG
- Nord/LB
- Ostwind Verw.ges.
- WPD Beteiligungs GmbH
- DEWI GmbH
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